DEPARTMENT OF ECE IV YEAR / VII SEMESTER EC 8071 – COGNITIVE RADIO 04.01.2021 KNCET 1 EC 8071- COGNITIVE RADIO UNIT I: INTRODUCTION TO SOFTWAREDEFINED RADIO AND COGNITIVE RADIO Evolution of Software Defined Radio and Cognitive radio: goals, benefits, definitions, architectures, relations with other radios, issues, enabling technologies, radio frequency spectrum and regulations. 04.01.2021 KNCET 2 INTRODUCTION • Data communication plays a vital role in society. • With the exponential growth in the ways and means by which people need to communicate – ➢ Data communications ➢ voice communications ➢ video communications ➢ broadcast messaging ➢ command and control Communications ➢ Emergency response communications • Modifying radio devices easily and cost-effectively has become business. 04.01.2021 KNCET 3 SOFTWARE DEFINED RADIO BASIC CONCEPT • Radio can be totally configured or defined by the software so that a common platform can be used across a number of areas. • There is also the possibility that it can then be re-configured as upgrades to standards. 04.01.2021 KNCET 4 RADIO WAVES • The range of the radio spectrum is considered to be 3 kilohertz(KHz) up to 300 gigahertz(GHz). 04.01.2021 KNCET 5 RADIO WAVES ▪ Like waves on a pond, a radio wave is a series of repeating peaks and valleys. ▪ The entire pattern of a wave. ▪ A radio wave is generated by a transmitter and then detected by a receiver. ▪ An antenna allows a radio transmitter to send energy into space and a receiver to pick up energy from space. ▪ Transmitters and receivers are typically designed to operate over a limited range of frequencies. 04.01.2021 KNCET 6 SOFTWARE DEFINED RADIO(SDR) DEFINITION: • Radio in which some or all of the Physical Layer Functions are software-defined • Software-defined refers to the use of software processing within the radio system or device to implement operating (but not control) functions • Software for this definition refers to modifiable instructions executed by a programmable processing device 04.01.2021 KNCET 7 SOFTWARE DEFINED RADIO • SDR refers to technologies wherein the functionalities are performed by software modules. • The characteristics of radio such as coding, modulation type, frequency band can be changed at will simply by loading a new software. • Multiple radio devices using different modulations can be replaced by a single radio device. • SDR, currently used to build radios that support multiple interface technologies(CDMA, GSM, WiFi) with a single modem by reconfiguring it in software. 04.01.2021 KNCET 8 SDR-EVOLUTION IN THE UNITED STATES • SDR concept started in the late 1970s with the introduction of multimode radios operating in VHF band • U.S. Air Force Avionics Laboratory initiated the Integrated Communication, Navigation, Identification and Avionics (ICNIA) program in the late 1970s • Developed an architecture to support multifunctional, multiband airborne radios in the 30 MHz -1600 MHz band • Successful flight test and final report delivery in 1992 • ICNIA radio was the first programmable radio 04.01.2021 KNCET 9 SDR-EVOLUTION IN THE UNITED STATES • In the late 1980s, the Air Force Research Laboratory initiated the Tactical Anti-Jam Programmable Signal processor (TAJPSP) • Developed a processor capable of simultaneous waveform operations using modular approach – TAJPSP later evolved into the SPEAK easy program • SPEAK easy was a joint U.S. Government program to develop the architecture and technology to meet future military requirements for multimedia networking operations • The first significant military investment to integrate various existing radio families into one family • SPEAK easy evolved into the Joint Tactical Radio System (JTRS) 04.01.2021 KNCET 10 SDR-EVOLUTION IN THE UNITED STATES • JTRS Joint Program Office was established in 1999 • Envisioned to be the next generation tactical radio for future advanced military operations • Mission is to “acquire a family of affordable, high-capacity tactical radios to • provide interoperable LOS/BLOS C4I capabilities to the war fighters” • The SDR Forum provides expertise in software radio technology for the JTRS program 04.01.2021 KNCET 11 SDR-EVOLUTION IN EUROPE • R&D in Advanced Communications in Europe (RACE) and Advanced Communications Technology and Services (ACTS) programs. • ACTS projects, FIRST and FRAMES, used software radios to investigate next-generation air-interfaces • FIRST: Flexible Integrated Radio System and Technology • FRAMES: Future Radio Wideband Multiple Access System • RACE and ACTS focus on incorporating 3G and potentially 4G standards into its Global System for Mobile (GSM) Communications network – Pave the way for more capable and more powerful products and flexible services • – Key research areas include receiver architecture, baseband DSP architecture, enabling technologies 04.01.2021 KNCET 12 SDR-EVOLUTION IN ASIA • In 1999, Japanese Institute of Electronics, Information and Communication Engineers (IEICE) software radio group was formed • Held technical conferences, workshops, panel discussions and symposia, in conjunction with SDR Forum Radio. • In 2000, Korea Electromagnetic Engineering Society (KEES) sponsored a workshop to monitor software radio activities in Korea, Japan and Taiwan 04.01.2021 KNCET 13 SDR-EVOLUTION IN ASIA • IEICE and KEES mission: – Promote R&D in SDR – Allow protocol, software, hardware to be easily integrated for future radio system – Foster cross-organization and collaboration among academia, industries and governments – Organize symposia and workshops on SDR 04.01.2021 KNCET 14 COGNITIVE RADIO COGNITION: • The mental action or process of acquiring knowledge and understanding through thought, experience, and the senses 04.01.2021 KNCET 15 COGNITIVE RADIO 04.01.2021 KNCET 16 COGNITIVE RADIO • A cognitive radio may be defined as a radio that is aware of its environment and the internal state and with knowledge of these elements and any stored predefined objectives can make and implement decisions about its behavior. • Utilizes Software Defined Radio, Adaptive Radio, and other technologies to automatically adjust its behavior or operations to achieve desired objectives. 04.01.2021 KNCET 17 COGNITIVE RADIO • Hykin defined cognitive radio as a radio capable of being aware of its surroundings, learning and adaptively changing its operating parameters in real time with the objective of providing reliable anytime, anywhere and spectrally efficient communication. • U.S Federal Communications commission(FCC) defines that cognitive radio that can change its transmitter parameters based on interaction with the environment in which it operates. 04.01.2021 KNCET 18 COGNITIVE RADIO Two Main Characteristics: • Reconfigurability • Intelligent adaptive behavior Cognitive radio functionality requires following capabilities: • Flexibility and agility- Ability to change the waveform and other radio operational parameters. - Reconfigurable - Agility- ability to think quickly • Sensing – Observe and measure the state of the environment including spectral occupancy. • Learning and adaptability - Analyse sensory input, recognize patterns, modify internal operational behaviour 04.01.2021 KNCET 19 EVOLUTION OF COGNITIVE RADIO • Main research work was carried out by Mitola and Maguire in 1999 and early spectrum measurement studies conducted in 1995 to quantify the use of spectrum. IN UNITED STATES: • Focused on dynamic spectrum access(DSA) and secondary use of spectrum • The main goal of spectrum management and policy research project is to study policy servers and secondary use technologies particularly for military purposes. 04.01.2021 KNCET 20 EVOLUTION OF COGNITIVE RADIO 04.01.2021 KNCET 21 EVOLUTION OF COGNITIVE RADIO 04.01.2021 KNCET 22 EVOLUTION OF COGNITIVE RADIO IN UK 04.01.2021 KNCET 23 IN UK 04.01.2021 KNCET 24 Relationship between SDR and CR 04.01.2021 KNCET 25 Relationship between SDR and CR • Main characteristic of CR is adaptability of radio parmeters (frequency, power, modulation bandwidth) and can be changed depending on radio environment, user situation , network condition, geo location. • SDR provide flexible radio functionality by avoiding the use of application specific fixed analog circuits and components. • SDR – core enabling technology for CR • CR is wrapped around SDR • Combination of cognitive engine, SDR and other supporting functionalities results in CR. • Cognitive engine is responsible for optimizing and controlling the SDR and aware of radio hardware resources and capabilities. 04.01.2021 KNCET 26 Relationship between SDR and CR • SDR is built around software based digital signal processing along with software tunable radio frequency components. • SDR is capable of operating with different bandwidth over wide range of frequencies. • SDR supports multiple standards(GSM,EDGE, CDMA2000, Wi-Fi, WiMAX) and multiple access technologies(TDMA, CDMA, OFDM, SDMA) • Sensing devices are required to sense the spectrum, which can be either embedded into SDR internally or incorporated to SDR externally. 04.01.2021 KNCET 27 Relationship between SDR and CR • For Example- Antenna can considered as internal sensor and video camera can be considered as external sensor. • SDR provides spectrum information to cognitive engine. • The captured spectrum is digitized by Analog to digital converter and then the samples are sent to digital signal processor for post processing. 04.01.2021 KNCET 28 Benefits of SDR • Accommodate multiple standards. • Allow multiple services and incentives • Capable for insertions of future technologies and allow easy upgrades. • Implement open architecture to allow multiple vendors to supply, offer declining prices and reduce product development time. • Enable other advanced commercial technologies to offer user services and benefits. 04.01.2021 KNCET 29 Benefits of SDR • • • • • • SDR offers the greatest flexibility Develop software to perform signal processing Developing and debugging software is much easier. Offers service upgrades and bug fixes. This capability saves time and cost of design and deployment Reusability of software 04.01.2021 KNCET 30 Benefits of SDR • Written with the concept of modular code, software can be ported between processors with minimal rewriting required. • Instead of FPGA – based SDR systems where very high speed integrated circuit hardware description language (VHDL) is used GPP(General purpose processor)- based SDR system is used where code portability is advantageous. • Easy to test individual signal processing blocks, simulate performance and test behavior in a closed system and then reuse the same software for a real, over the air system. 04.01.2021 KNCET 31 Benefits of CR IMPROVED COMMUNICATION STRUCTURE: Communication with other networks: • Exists multiple public safety standards. • For eg. When a large disaster occurs at country borders, if countries use different technologies, it will be a challenge • Cognitive radio will support for military standards and other public safety standards would solve this problem. Backwards compatibility: • Large investments and small market are replaced slowly and coexist with new communication networks for a long time. • CR allows an upgrade of the existing equipment 04.01.2021 KNCET 32 Benefits of CR Introduction of new services: • New services could be enabled more easily as it can adjust its parameters according to the requirements of the new service. Improved reliability: • CR tries to minimize interference to other networks by changing its frequency if other signals are present. Enabling Broadband: • CR is used to sense empty frequency bands(white space) and use it as secondary user to set up an auxiliary communication network. • Large bandwidth requirement could be provided by secondary spectrum usage. 04.01.2021 KNCET 33 Architecture of SDR • Architecture is the framework of different types of components utilized to attain specific functions with certain limits and rules. • SDR is a collection of hardware and software technologies where operating functions are implemented through modifiable software or firmware operating on programmable processing technologies. • These devices include FPGA, DSP, GPP, programmable System on Chip(SoC) • These technologies allows new wireless features and capabilities without requiring new hardware. 04.01.2021 KNCET 34 Architecture of SDR • Functions of the software Radio Technology: 04.01.2021 KNCET 35 Architecture of SDR 04.01.2021 KNCET 36 Architecture of SDR • Evolution support is necessary to define waveform personalities and to assure that each new personality is safe. • Multiband technology accesses more than one RF band of communications channel at once. 04.01.2021 KNCET 37 Architecture of SDR Functional model of software radio 04.01.2021 KNCET 38 Architecture of SDR Channel Set: Have RF channels • Radio nodes like PCS-personal communications system base stations and portable military radios interconnect to fiber and cable. Channel encoder: RF/channel access, IF processing and modem • Antennas and RF conversion span multiple RF bands comprise the RF/Channel access function 04.01.2021 KNCET 39 Architecture of SDR 04.01.2021 KNCET 40 Architecture of SDR Joint control function • Implemented using multithreaded multiprocessor software ensures system stability, error recovery, timely data flow, and isochronous streaming of voice and video. 04.01.2021 KNCET 41 Architecture of SDR Analog Stream • Used to interface the external audio, video and facsimile devices with the SDR. • These interfaces may carry continuous streams Source Bit Stream • This interface carries the coded bit streams and packets. • It also carries the signals from ADC, Vocoders, and compressed Text. • Sampling theorem is used for ADC and finite arithmetic precision for coded sequences. 04.01.2021 KNCET 42 Architecture of SDR Clear Bit Streams • These streams are framed, multiplexed and FEC performed packets Protected Bit stream • They carry the authentication responses, public key and private key. • It also carries the enciphered bit streams. • IF Wave form • It carries digitally pre emphasized waveform ready for up conversion 04.01.2021 KNCET 43 Architecture of SDR RF Waveform • This interface deals with the control of power level, adjacent channel interference etc., Network interface • These interface are used to carry the information form the remotely located sources. • This interface uses asynchronous Transfer Mode (ATM) and its associated protocols. • ATM is a telecommunication concept to transfer the user traffic including Voice, data and video signals. • They are widely used for the integrated services digital networks 04.01.2021 KNCET 44 Architecture of SDR Joint Control • This controls all the interfaces between the hardware and software. • This interface is also used for initialization and fault recovery Standardizing an Interface • This way, vendors can develop their waveforms independent of the knowledge of the underlying hardware. • Similarly, hardware developers can develop a radio with standardized interfaces, which can subsequently be expected to run a wide variety of waveforms from standardized libraries. 04.01.2021 KNCET 45 Functional components of Software Radio • Software radio defines all feature of the air interface including RF channel access and waveform fusion in software. • ADC and DAC transform is possible and each RF service among digital and analog forms at IF. • Resulting digitized stream of bandwidth,Ws, accommodates all subscriber channels with bandwidth Wc • Where Ws >> Wc 04.01.2021 KNCET 46 Fig. Key Software Radio Functions and Components 04.01.2021 KNCET 47 Functional components of Software Radio • IF processing may include filtering to isolate subscriber channels. • Acquire high quality waveform • There are multiple IF frequencies • For direct conversion receiver- IF processing is null(minimize interference) • Digital down conversion is the process of converting frequency domain samples to baseband waveform • Pre-selection filters with the required performance are reduced in size to get better performance. 04.01.2021 KNCET 48 Functional components of Software Radio • In a software radio transmitter, baseband signals are transformed into sampled channel waveform via modems functions • Implemented in software using high performance DAC and dynamically reconfigurable FPGA. • Output signals are pre-emphasized or non-linearly pre-coded by IF processor • In some implementation, modem functions, IF processing and RF channel access is integrated into a single component as in direct conversion receiver 04.01.2021 KNCET 49 ARCHITECTURE OF CR • Architecture is a comprehensive, consistent set of design rules by which a specified set of components achieves a specified set of functions in products and services that evolve through multiple design points over time • Some additional functions are added to the SDR so that the architecture can sense the information autonomously and tailor the information according the needs of the user. • Cognitive – a radio must be self aware • Using that knowledge, it should know a minimum set of basic facts about radio and it should be able to communicate with other entities. • For example, it should know that an equalizer time domain taps reflect the channel impulse response. • Cognitive radio contain a computational model of itself including the equalizer’s structure and function. 04.01.2021 KNCET 50 Ideal Architecture of cognitive radio 04.01.2021 KNCET 51 Cognitive Radio Components-Modules • Radio that uses RKRL(Radio knowledge Representation Language) could be organized as shown. • System hardware consists of a set of modules: Antenna, RF section, modem, INFOSEC module, baseband/protocol processor and user interface. • The baseband processor hosts the protocol and control software. • Modem software includes the modem with equalizer. • The architecture are defined in UML(Unified Modeling Language) object models, CORBA(Common Object Request Broker Architecture) Interface design language. 04.01.2021 KNCET 52 ARCHITECTURE OF CR • A cognitive radio contains an internal model of its own hardware and software structure. • Variable bindings between the equalizer model and the software equalizer establish the interface between the reasoning capability and the operational software. • Cognition defines SDR in RXML(Radio eXtensible Markup Language) which includes RF knowledge, structured reasoning and Ad-Hoc reasoning. 04.01.2021 KNCET 53 ARCHITECTURE OF CR • The model-based reasoning capability that applies these RKRL frames to solve radio control problems gives the radio its cognitive ability. • This approach is used to represent radio knowledge in RKRL and to construct reasoning algorithms to use that knowledge for the control of software radios. • CR’s model should contain a representation of its functions such as transmission, reception, coding and mechanisms involved in antenna, RF conversion, DSP. • CORBA IDL initiates a starting point. • CR is an SDR with flexible, formal and semantic based entity to entity messaging through RXML and integrated machine learning. 04.01.2021 KNCET 54 ARCHITECTURE OF CR The Three computational Intelligence aspects of CR are as follows: • Radio Knowledge • User Knowledge • The Capacity to Learn 04.01.2021 KNCET 55 Radio Knowledge • Radio knowledge has to be translated into a body of computationally accessible, structured technical knowledge about radio. RXML : RF– Radio Extensible Markup Language • RXML is the primary enabler and product which helps the formalization of radio knowledge. • RXML will enable the structuring of sufficient RF and user world knowledge to build advanced wireless-enabled or enhanced information services. • These information should meet the levels of accuracy defined by the international bodies like ITU(International Telecommunication Union). 04.01.2021 KNCET 56 User Knowledge • User knowledge is formalized at the level of abstraction and degree of detail necessary to give CR the ability to acquire, from its owner and other designated users relevant to information services. • This gives introduction to machine learning. • Machine recognizes the opportunities for learning. 04.01.2021 KNCET 57 ARCHITECTURE OF CR • CRA1(defines functions, components and design rules) is a rapid prototype which tightly integrates RKRL(Radio knowledge Representation Language) frames into the modelbased reasoning architecture. • CR’s model of its internal structure should then sustain systems-level interactions with the network. • If the radio is to be context aware, it must interact with the outside world. • This is done by cognition cycle. 04.01.2021 KNCET 58 Relations with other radios List of radio technology proposed by GSC(Global Standards Collaboration) group • Two new radio classes • Specific implementations of cognitive radio Two Radio classes: • Policy based Radios - Emphasis on how cognitive radio technology can impact the development and implementation of communications policy. • DFS(Dynamic Frequency Selection) Radios - advanced radio technologies are enabling a multitude of new radio concepts. 04.01.2021 KNCET 59 Relations with other radios Policy based Radios : • Governed by a predetermined set of rules for behavior • Rules define operating limits Rules can be defined and implemented: • During manufacture • During configuration of a device by the user • During over the air provisioning • Over the air control 04.01.2021 KNCET 60 Software reconfigurable radio • Incorporates software controlled antenna filters to dynamically select receivable frequencies • Capable of downloading and installing updated software for controlling operational characteristics and antenna filters without manual intervention. 04.01.2021 KNCET 61 DFS(Dynamic Frequency Selection) 04.01.2021 KNCET 62 DFS(Dynamic Frequency Selection) 04.01.2021 KNCET 63 DFS(Dynamic Frequency Selection) • DFS is used for spectrum management of 5GHz channels by OFDM radio devices. • The European Radiocommunications committee(ERC) and FCC mandate that radio cards operating in the 5 GHz band implement mechanism to avoid interference with radar system. • DFS is essentially radar detection and radar interference avoidance technology. • DFS service is used to meet these regulatory requirements. 04.01.2021 KNCET 64 Issues • Public safety radio lies in the ability of software defined radios to reconfigure the operating characteristics rapidly simply by changing the inherent software and instantiating a different software package to provide the desired operating requirements in terms of over the air characteristics as well as information/networking requirements such as coding. • The ability to do Over-the-Air-Programming (OTAP) becomes an extremely valuable capability for software defined radios in a public safety scenario. • The National Institute of Justice (NIJ) recognized the potential of SDRs and suggested several Key Points for Public Safety Communications. 04.01.2021 KNCET 65 Issues • The first key issue is simply the ability to convert from analog to digital (A-D) signals. • From the host user’s perspective, this is common practice now over any number of devices. • If A-D conversion can take place immediately at the antenna, then all functions within the radio can be done digitally (i.e. in software). • Using Sampling Theorem the signals must be sampled at a rate at least twice the highest frequency in order to be able to accurately and faithfully reproduce the original signal from its sampled values. • Each sample value must be converted to a digital representation 04.01.2021 KNCET 66 Issues • The second issue is the timing and synchronization required within the radio. • Maintains the integrity of information throughout the radio. • It is also critical in establishing the timing relationships between the general purpose processors that are handling part of the software functions and operating at an independent clock speed. • A third major design consideration is the interface to the RF transmission domain. • Antennas propagate signals differently based on the frequency of the signal being transmitted and optimizing RF signal propagation is therefore frequency dependent. 04.01.2021 KNCET 67 Issues • As it is difficult to design antennas over a wide range of frequencies. • The electronic circuits leading to the antennas must be matched to the antenna’s electrical characteristics for maximum power transfer. • The result of this “real world” problem is that multiple antennas – matched to particular frequency bands – must be used. • This complicates the radio design as well as the antenna design – particularly if multiple input/multiple output antennas are used for part of the transmission process. 04.01.2021 KNCET 68 SDR Issues 04.01.2021 KNCET 69 SDR Enabling Technologies NCO- Numerically controlled oscillator; RSP- Receive signal processor TSP- Transmit signal processor 04.01.2021 KNCET 70 SDR Enabling Technologies Antennas: • Receive antennas are easier to achieve wide band performance than transmit ones Waveforms: • Management and selection of multiple waveforms • Cancellation carriers and pulse shaping are relatively new techniques. 04.01.2021 KNCET 71 SDR Enabling Technologies 04.01.2021 KNCET 72 SDR Enabling Technologies 04.01.2021 KNCET 73 SDR Enabling Technologies • Design tools 04.01.2021 KNCET 74 SDR Advantages 04.01.2021 KNCET 75 SDR Advantages • SDR provide software control of a variety of modulation techniques, wideband and narrowband operation, transmission security functions and waveform requirements. • Single system can operate under multiple configurations, providing interoperability, bridging and tailoring of the waveforms to meet localized requirements. • SDR technology and systems have been developed for military applications. 04.01.2021 KNCET 76 Cognitive Radio-Enabling Technologies • Cognitive radio is a concept for the realization of smart and advanced wireless systems. • CR supports context awareness such as spectrum, location, environment, waveform, power and infrastructure awareness. • CR studies focuses on spectrum awareness capability. • Location information has been traditionally used for positioning systems and location based services (LBS). • LBS can be utilized for different applications and solving some issues in wireless networks. • The applications based on utilization of location information can be folded under four categories 04.01.2021 KNCET 77 Cognitive Radio-Enabling Technologies • The applications based on utilization of location information can be folded under four categories - LBS - Network optimization - Transceiver optimization - Environment identification 04.01.2021 KNCET 78 04.01.2021 KNCET 79 Cognitive Radio-Enabling Technologies • Location and environment awareness engines consist of sensing, awareness core and adaption systems respectively similar to the location and environment awareness cycle of creatures in the nature. • Location and environment awareness engines receive tasks from cognitive engine and they report back the results to the cognitive engine for achieving goal driven and autonomous location and environment aware application. • Both engines can utilize various sensors and adaptive waveform generator and processor capabilities of cognitive radio to interact with and learn the surrounding environments. 04.01.2021 KNCET 80 Cognitive Radio-Enabling Technologies • Environment awareness engine senses the environmental parameters and provides the values to the location awareness engine. • Spectrum awareness engine senses the spectrum and provides the spectrum information (available bandwidth) to the location awareness engine. SENSING INTERFACE: • Composed of two main components: • Sensors • Associated data post processing methods 04.01.2021 KNCET 81 Cognitive Radio-Enabling Technologies • Sensors are utilized to convert the signals acquired from environment to electrical signals so that cognitive radios can interpret. • Acquired signals can be in different forms: electromagnetic, optic and sound • Sensors can be categorized in 3 types: • Electromagnetic sensors • Image sensors • Acoustic sensors • Corresponding data post processing algorithm for each sensing technique is different. 04.01.2021 KNCET 82 Cognitive Radio-Enabling Technologies Classification of sensing mechanism in cognitive radio: • 3 main categories based on type of sensors • Radiosensing – sensing technique utilizes electromagnetic sensors and the associated post processing scheme. • Radiovision – sensing approach using image sensors and the corresponding post processing scheme. • Radiohearing – Employs acoustic sensors and the associated post processing scheme 04.01.2021 KNCET 83 Cognitive Radio-Enabling Technologies LOCATION AWARENESS ENGINE: 04.01.2021 KNCET 84 Cognitive Radio-Enabling Technologies • The model consists of the following main subsystems • Location sensing • Location awareness core • Adaptation of location aware systems Location sensing: • Estimate the location information of the target object in a given format. • The format of location information that needs to be sensed can have significant effects on the complexity of location aware algorithms. 04.01.2021 KNCET 85 Cognitive Radio-Enabling Technologies • CR can retrieve physical position of the remote computer from the virtual position along with additional information. • Mapping virtual position to the corresponding physical position already exists. • Extracting physical position of a remote device from its virtual position information can be useful for cognitive radio. • This information can be used to develop efficient location assisted routing protocol • Physical position of an object can be either absolute or relative • Absolute position: Refers to complete coordinate knowledge of an object • Relative position: Position of an object relative to another or neighbor objects that do or do not know their absolute positions 04.01.2021 KNCET 86 Cognitive Radio-Enabling Technologies • CR device can estimate its absolute position using its relative position along with absolute position of the reference device that is used during relative positioning. • Absolute position estimation techniques are more mature and widely used compared to relative position estimation methods. • Depending on accuracy requirements CR can switch between absolute and relative position estimation methods. • The absolute and relative position of the cognitive radio can be quantified using coordinate systems 04.01.2021 KNCET 87 Cognitive Radio-Enabling Technologies 04.01.2021 KNCET 88 Cognitive Radio-Enabling Technologies • There are numerous global, continental and country specific reference coordinate system for absolute position of an object such as NAD(North American Datum), ED50(European Datum), TD(Tokyo Datum), ECF(Earth Centered Fixed), WGS(World Geodetic systems). • Relative position information can be classified under three groups of reference coordinate systems: • 1-Dimentional: provides the location of a cognitive radio in a single axis. Eg. Distance between transmitter and receiver or distance between two cognitive radio • 2-dimentional: Provides the information of a cognitive radio in a plane(x,y) 04.01.2021 KNCET 89 Cognitive Radio-Enabling Technologies • 3-dimentional: Provides the location of cognitive radio in three dimentions(x,y,z) • Eg. Cognitve wireless networks have the capability to estimate 3-D location of a cognitive radio node. Time parameter can be included. RADIO SENSING METHODS: • Antenna based position sensing algorithms are extensively used for wireless positioning systems. • They are categorized under three groups: • Range based schemes • Range-free schemes • Pattern matching-based schemes 04.01.2021 KNCET 90 Cognitive Radio-Enabling Technologies • Antenna based position estimation methods do not have cognition capabilities that cognition radio requires. • Realization of antenna-based position sensing technique with cognition capabilities are done with the help of cognition positioning systems. RADIO VISION METHODS: • Image sensors are used for visual position sensing methods. • The position of the observer is estimated based on the images acquired from the image sensors. • Relationship between video camera mounted to the user and cognition engine in cognitive radios resembles the relationship between eye and brain in the human body. 04.01.2021 KNCET 91 Cognitive Radio-Enabling Technologies • The acquired images can be processed using advanced digital image and signal processing techniques.(Eg. Pattern analysis and machine intelligence algorithms. • Scene state are in desired formats: text, image, video and voice. • A well known visual position sensing techniques is scene analysis. • Scene analysis is a pattern matching based position sensing technique similar to RF pattern matching based methods(eg.RF fingerprinting) • Acquired images are used as patterns in scene analysis whereas channel statistics are used as patterns in the RF pattern matching based methods. 04.01.2021 KNCET 92 Cognitive Radio-Enabling Technologies • Main objective of Radio vision method: • Requirement of image database • Extensive image processing power • Compared to robotics and computer systems, implementing radio vision techniques such as cognitive vision systems is a challenging tasks due to low power, cost and size constraints. RADIO HEARING METHODS: • Radio hearing based position sensing methods utilize acoustic sensors for interaction with environments • Implemented using 3 group of schemes: • Range based • Range-free • Pattern matching based technique. 04.01.2021 KNCET 93 Cognitive Radio-Enabling Technologies • Cognitive radio realizes advanced radio hearing based position sensing techniques functioning similar to Bat echo position systems. • Cognitive radio can acquire sound signal and use it as a pattern. • In addition, it can even calculate the spectrum of the captured sound pattern and compare it with the sound pattern stored in the database to infer its position. • Different radio hearing based position sensing methods using these three approaches are developed. 04.01.2021 KNCET 94 Cognitive Radio-Enabling Technologies LOCATION AWARENESS CORE: • Main objective is to perform critical tasks related to location information such as learning, reasoning and making decisions. The core has the following functionalities: • Seemless positioning and interoperability • Security and privacy • Statistical learning and tracking • Mobility Management • Location aware applications 04.01.2021 KNCET 95 Cognitive Radio-Enabling Technologies SEEMLESS POSITIONING AND INTEROPERABILITY: • It is defined as a system that can keep the position accuracy at a predefined level regardless of the changes in channel environment. Two Approaches: • Waveform based methods • Environment sensing based methods Waveform based methods: • Based on utilization of appropriate waveform or technology depending on the user requirements and environment. • Support all predefined waveforms of the existing and future positioning systems and waveform switching mechanisms 04.01.2021 KNCET 96 Cognitive Radio-Enabling Technologies • Eg. European space project • The SPACE prototype consists of the existing positioning waveforms, algorithms and sensors such as GPS, UWB, WLAN, Bluetooth… • Depending on the user requirements and environments, most appropriate positioning system is selected. Environment sensing based methods • Does not require multiple waveforms • It is based on sensing channel environment parameters(eg.path loss coefficient) and adapt the positioning algorithm in real time. • RSSI(Received signal strength Indication) based location estimation algorithm for unknown channel environment is a good example. 04.01.2021 KNCET 97 Cognitive Radio-Enabling Technologies • IEEE defines interoperability as the ability of two or more systems or components to exchange information and to use the information. Interoperability issues in CR is grouped under two categories: • Cognitive radio - Cognitive radio interoperability Both cognitive radios can have same or different waveforms They can exchange the information directly • Cognitive radio – legacy radio interoperability • Both needs to agree on one of the waveforms in order to communicate • Cognitive radio can switch its waveform to the waveform of legacy radio, since legacy radio does not have reconfigurability features. 04.01.2021 KNCET 98 Cognitive Radio-Enabling Technologies Security and Privacy: • Extensive utilization of location information in cognitive radio and networks has these two issues. • Of many potential threats, tracking the position of a cognitive radio user without authorization and adversarial attacks are the two main ones. • Without authorization can violate the user privacy • Adversarial attacks can result in catastrophic scenarios since LBS highly depend on the location information • It is crucial to develop effective solutions to address these issues. • For instance, local or global geolocation privacy protection methods can be developed to address privacy issues. 04.01.2021 KNCET 99 Cognitive Radio-Enabling Technologies Statistical learning and tracking : • Location awareness engine have the capability to track mobile CR users and it can be trained by the tracking data using statistical learning tools such as neural networks and Markov models to form user location profiles • These profiles are used to predict the trajectory of CR users and improve the positioning accuracy, especially in pattern matching based positioning methods. 04.01.2021 KNCET 100 Cognitive Radio-Enabling Technologies Mobility Management: • Utilization of location information in cognitive radios and networks for different applications will have major impact on system complexity. • System capacity and implementation cost can be affected by introduction of additional services and applications into cognitive wireless networks. • It is desirable to develop an accurate mobility model during the network planning phase. 04.01.2021 KNCET 101 Cognitive Radio-Enabling Technologies Adaptation of location aware system: • Main objective of adaptation block is to support location awareness engine in terms of adaptation of algorithms and parameters for the satisfaction of the user. • The reported performance parameter or requirement of location aware applications is accuracy, integrity, continuity and availability. • Range accuracy is one of the most important performance parameters • Indoor positioning systems demand higher precision accuracy compared to outdoor positioning systems. • In industrial areas which is a local positioning application, typically 0.05 – 30m accuracy is obtained. 04.01.2021 KNCET 102 Cognitive Radio-Enabling Technologies ENVIRONMENT AWARENESS ENGINE: • Environment awareness is one of the most substantial and complicated task in cognitive radios. • Creatures with environment awareness capabilities such as human being and bats can be considered as models for the realization of environment awareness in CR. • Human being has different senses such as observing and learning the surrounding environment and bats utilize their echo position systems for object and environment identification, target detection and tracking. • Similar environment awareness techniques can be developed for CR’s 04.01.2021 KNCET 103 Cognitive Radio-Enabling Technologies ENVIRONMENT AWARENESS ENGINE: 04.01.2021 KNCET 104 Cognitive Radio-Enabling Technologies ENVIRONMENT AWARENESS ENGINE: • The model consists of environment awareness core, topographical information , object recognition and tracking, propagation characteristics, meterorological information, environment sensing and environment adaptation. • For wireless systems, an environment mainly consists of the following entities: topographical information, objects, propagation characteristics and meteorological information. TOPOGRAPHICAL INFORMATION: • Topography is defined as the science or practice of describing a particular place, city, town, parish or tract of land or accurate and detailed delineation and description of any locality. 04.01.2021 KNCET 105 Cognitive Radio-Enabling Technologies • Topology of a local region provides information about not only the relief but also vegetation , human made structures, history and culture of that particular area. • Numerous advanced LBS can be developed. • Eg. Google Map TM • Here a mobile user (tourists) points the embedded camera towards the point of interest and captures the image. • The captured image is transmitted to the server to extract the information related to the image and then send this information to the mobile user. 04.01.2021 KNCET 106 Cognitive Radio-Enabling Technologies OBJECT RECOGNITION AND TRACKING: • Objects are defined as human made entities present in the target local environment temporarily or permanently. • Large and permanent human made structures such as buildings and bridges are considered as part of topography of environment. • Such structures are included in topographical information. • Relatively small and movable human made entities such as vehicles, home and office appliances are considered as objects. • Object detection, identification and tracking are important features of environment awareness engine. 04.01.2021 KNCET 107 Cognitive Radio-Enabling Technologies • Cognitive radar is introduced with the capability of target detection and tracking. • It has the capability of encompassing the transmitter, environment and receiver. PROPAGATION CHARACTERISTICS: • Provides information on the characteristics of signal progression through a medium(Channel environment) • Propagation characteristics of channel environment shows , how the channel affects the transmitted signal. • Statistical characteristics of wireless channel are categorized in two groups: • Large scale • Small scale 04.01.2021 KNCET 108 Cognitive Radio-Enabling Technologies • Large scale statistics provide information on path loss behavior of channel environment. • Small scale statistics determine the drastic variations of received signal in time and frequency due to short displacements. METEOROLOGICAL INFORMATION: • It provides information on the weather of target local region, which can affect the signal propagation. • The current and future weather parameters such as rain , snow, temperature, humidity and pressure can be acquired by either using radio auxiliary sensors or from central cognitive base station. • By having current and forecasted meteorological information, cognitive radio can adapt itself. 04.01.2021 KNCET 109 Cognitive Radio-Enabling Technologies • One of the performance parameters that can be affected from rain is the carrier-to-interference ratio(C/I) and the performance metric depends on the rain intensity of the position of desired signal path and interferer signal path. • If cognitive radio or network has a capability to acquire rain intensity of local regions from a central meteorological server or internet, then C/I adaptation can be performed. • The main task of environment awareness engine in CR can be summarized as acquiring the information on topography, objects, propagation channel and meteorology of the target local region and provides these information to other components of CR used for other applications. • For Eg. Object and environment identification, seamless positioning and LOS-NLOS identification are three potential 04.01.2021 KNCETthat can be developed. 110 environment aware applications RADIO FREQUENCY SPECTRUM AND REGULATION • Electromagnetic spectrum is our planet’s most valuable natural resources • SPECTRUM: Nature’s Communication highway: • Radio frequency spectrum is an abundant natural resource that uniformly covers the planet and is available for a wide variety of useful purposes. • Beyond the voice communications and increasingly dominant multimedia and data networking, this spectrum is regularly used for a diverse array of applications, including radar for finding large and small objects(airplanes in sky, obstacles in the vicinity, to studs in the walls of home), excitation for illuminating spaces, monitoring and sensing applications. 04.01.2021 KNCET 111 Physical Characteristics of spectrum • Frequency is given by, f=c/λ • Time varying signal at a point in space is given by S(t) = A(t) cos (2лft) • S – signal strength • t – time, A- Amplitude of the signal • Like all elements of the electromagnetic spectrum, radio frequency component of this spectrum has the wave like characteristics of reflection, refraction, diffusion, absorption and scattering. 04.01.2021 KNCET 112 Implications for communication Applications • Utility of the spectrum is derived from its ability to be modulated in a variety of ways to transport useful information. • This includes applying or removing power from a specific frequency or spectral range such as pulse modulation or amplitude shift keying(ASK), increasing or decreasing the power level applied to a frequency, such as Amplitude modulation(AM). • Switching the transmitted power from one frequency to another such as frequency modulation or frequency shift keying(FSK) • Altering the phase of the signal, phase shift keying(PSK) • Combining these techniques variety of complex signal encoding structures are created. 04.01.2021 KNCET 113 Regulatory history and successes • History of spectrum regulation closely followed the early development and deployment of wireless communication systems. • First international wireless standards meeting, the international Radiotelegraph conference was organized by International Telegraph union(ITU), the governing body for wired telegraph operation, held in Berlin in1906. Objectives and Philosophy: • ITU mission enables growth and sustained development of telecommunications and information networks and to facilitate universal access so that people everywhere can participate and get benefit from emerging information society and global economy. 04.01.2021 KNCET 114 Regulatory history and successes Early history and success: • ITU became a united nations specialized agency. • International Frequency Registration Board(IFRB) established within the ITU to coordinate the increasingly complicated task of managing the radio frequency spectrum. • Frequency allocations, introduced in 1912 became mandatory to assist, guide and tabulate spectrum use in various countries. • In Unites States, primary regulatory body is Federal Communications Commission(FCC). • FCC develops and enforces regulations in support of the laws governing the commercial use of the spectrum. 04.01.2021 KNCET 115 Regulatory history and successes • National Telecommunications and Information Administration (NTIA) is a organization which reports its responsibility to the department of Commerce in the executive branch of the government. • These bodies determine, maintain and regulate the comprehensive allocation of US spectrum. 04.01.2021 KNCET 116 Emerging Regulatory Challenges and Actions Era of increasing Regulatory challenges • To understand the dynamics behind market based direction, supply of spectrum should be clearly finite, but demand for the spectrum is fundamentally unbounded. • This ever-increasing demand of spectrum is based on “Quadruple whammy”. • It is composed of four elements (i) Applications: • The number and variety of different radio applications are virtually unbounded and rapidly evolving. • For eg. Broadcast communications (Television, radio), commercial communications(emergency services radio) 04.01.2021 KNCET 117 Emerging Regulatory Challenges and Actions • Industrial communications, aeronautical communications, military communications, personal communications(cell phone, two-way radios), wireless networks (personal, local area, metropolitan), satellite communications. (ii) Coverage: • Need to offer the applications to an ever broader audience and eliminate spatial constraints. (iii) Duty Cycle: • Most popular of these applications will be used for ever increasing percentage of the time, following “always on always connected”. 04.01.2021 KNCET 118 Emerging Regulatory Challenges and Actions (iv) Performance: • These applications are used broadly and used all the time. • The demands for ever-increasing levels of performance require increasing allocation of spectral bandwidth, since there is direct correlation between allocated bandwidth and the sustained data rate that a channel can support. • The simplest form is described by Nyquist bandwidth formula, • C = 2B( binary signals) • C = 2Blog2(M) for multilevel signals • Where C – capacity, B – Bandwidth, • M – number of signal levels 04.01.2021 KNCET 119 Emerging Regulatory Challenges and Actions • Market based spectrum management is leading to the establishment of quasi-autonomous entities to manage national communications resource with organizations as the office of communications in the United Kingdom . • The principal duty of Ofcom, in carrying out their functions: • To further the interests of citizens in relation to communications. • To further the interests of consumers in relevant market, by promoting competitions.(This organization is responsible for regulating television, radio, telecommunications and various wireless services) 04.01.2021 KNCET 120 Emerging Regulatory Challenges and Actions Regulatory Actions: • This trend is to enable temporal as well as spatial spectrum sharing in US in 1985. • US FCC modifies its rule for the industrial, scientific and medical band to enable its use for wireless communication. • This was the first major initiatives to begin to address this critical issue. • Other one is the allowance of ultra-wideband(UWB). 04.01.2021 KNCET 121 Emerging Regulatory Challenges and Actions Spectrum task forces and Commissions: • The years of variety of task forces have focused on spectrum usage. • In US these have been commissioned by organizations like, • The Federal communications commission(FCC) • The national Telecommunication and Information administration(NTIA) • The national research council for the national academies • The national science foundation and congress 04.01.2021 KNCET 122 Regulatory Issues of Cognitive Access • The regulator could adopt a variety of approaches to cognitive access, 04.01.2021 KNCET 123 Regulatory Issues of Cognitive Access • The geographic areas between towers where the spectrum has not been licensed to anyone is called white space. • This unowned spectrum can be treated differently because there is no owner. • Different regulatory decision might be expected for such a spectrum compared to a spectrum that has been regionally or nationally licensed. Regulatory Implications of different Methods of Cognition: • Three broad techniques whether bands are free from use, they are, • Sensing • Beacons • Geolocation 04.01.2021 KNCET 124 Regulatory Issues of Cognitive Access • These can be used discretely or in combination to effect the desired level in the attainment of a low-interference environment. Geographical Databases: • Used in alternative for sensing in cognitive device to precisely know its location and have access to a database listing the frequencies allowed to use in each location. Beacon Reception: • Requires the transmission of a signal from appropriate infrastructure providing information on which frequencies are available for cognitive use in vicinity. • Cognitive devices tune to this channel and use the information provided to select their preferred frequency. 04.01.2021 KNCET 125 Regulatory Issues of Cognitive Access • Regulatory developments to date: • FCC concluded that at present sensing alone would result in an unacceptable risk of interference. • It further concluded that geographical databases were also required. • Specific details such as locational accuracy and the frequency of consulting the database were also stipulated in the report. 04.01.2021 KNCET 126 Spectrum measurements and usage Early spectrum occupancy studies: • Spectrum occupancy studies of various kinds have taken for many years. • These resolve into the following three categories: • Short term “Snapshot studies” • Long term “Spectrum Observatory” studies • Sensor array studies Snapshot studies: • These studies demonstrated that there is abundance of unused or lightly used spectrum, which could be exploited through use of dynamic spectrum access networks or even static networks with carefully defined geographic boundaries. 04.01.2021 KNCET 127 Spectrum measurements and usage Spectrum Observatory: • Spectrum observatory is a relatively new idea in the spectrum world. • Snapshot studies focused on relatively narrow spectral band. • These are very effective in gaining general spectral information about location. • First true spectrum observatory is the wireless Network and Communications research Centre (WiNCom) observatory funded by NSF, located at IIT Chicago • One of its fundamental purpose is to detect and characterize spectral holes in time and space that can be exploited by cognitive radio systems. 04.01.2021 KNCET 128 Spectrum measurements and usage Spectral Sensor Arrays: • Sensor arrays should become a very valuable measurement tool. • Major program focused in this area is the European Union’s Seventh Framework collaborative projects. • This sensor array system would be particularly valuable in high network traffic areas and even greater values in areas that have dynamic usage pattern(eg. Mobile, automobile based wireless systems. 04.01.2021 KNCET 129 EC 8071- COGNITIVE RADIO UNIT II: COGNITIVE RADIO ARCHITECTURE Cognition cycle – orient, plan, decide and act phases, Organization, SDR as a platform for Cognitive Radio – Hardware and Software Architectures, Overview of IEEE 802.22 standard for broadband wireless access in TV bands. 04.01.2021 KNCET 1 INTRODUCTION • Structural design for cognitive radio consists of the functions, components and design rules to support the evolution of cognitive radio. • The architecture integrates the contribution of researches on specific disciplines of software radio, network engineering, natural language processing and machine learning. • The architecture minimizes the dependence on knowledge engineering through the integration of machine learning. • This minimizes the burden on the user through the integration of natural language processing 04.01.2021 KNCET 2 COGNITION CYCLE • The architecture comprises of a set of design rules by which cognition level of information services is achieved by a set of components which supports cost-effective evolution of increasingly capable implementations over time. • Cognition subsystem includes • an inference hierarchy • temporal organization • flow of inferences • control states 04.01.2021 KNCET 3 OOPDA Loop COGNITION CYCLE Fig. Simplified Cognition cycle 04.01.2021 KNCET 4 COGNITION CYCLE • This cycle implements the capabilities in a reactive sequence. • Stimuli enter the CR as sensory interrupts, dispatched to the cognition cycle for a response. • Such cognitive radio continually observes (senses and perceives) the environment, orient itself, creates plan, decides and then acts. 04.01.2021 KNCET 5 Epochs • Wake epoch • Primary reasoning activities- reactive to the environment • Receipt of a new stimulus – new primary cognition cycle • Machine learning – computationally intensive • Cognitive radio – sleep and prayer epoch – support machine learning • Sleep epochs • Power down conditions • Long time period – not in use – sufficient electrical power for processing. • CR-ML algorithms without detracking from its ability. 04.01.2021 KNCET 6 Epochs • Dream epoch • Computationally intensive pattern recognition and learning. • Prayer epoch • Interacting with a higher authority – network infrastructure • Learning opportunities – not resolved in sleep epoch – brought to prayer epoch. 04.01.2021 KNCET 7 Observe(Sense and perceive) • Cognitive observes environment • By parsing incoming information streams • Monitoring and speech-to-text conversion of radio broadcasts • Any RF LAN or other short range wireless broadcasts. Observation phase: • Reads Location , temperature and light level sensors • Infer user’s communications context • Senses and perceives the environment • Multiple stimuli + binding – generate plans for action • Cognitive radio aggregates experience – compares prior aggregates to the current situation. 04.01.2021 KNCET 8 Observe(Sense and perceive) • Novelty detector – new stimuli • Partially familiar stimuli- identify incremental learning primitives. • Observe phase – User Sensory perception + environment sensor subsystems 04.01.2021 KNCET 9 Orient Orient phase: • Determines the Significance of observation by binding the observation – previously known set of stimuli. • Orient phase contains, • Internal data structures • Short term memory(STM) • Long-term memory (LTM) • Natural environment – information redundancy –STM to LTM • Cognitive radio transfer from STM to LTM – sleep cycle – analyzed both internally and with respect to existing LTM. 04.01.2021 KNCET 10 Orient • Orient phase is the collection of activity in the cognition component. • Matching – Stimulus recognition and binding Stimulus recognition • Occurs when there is exact match – current stimulus and prior experience • The prototype is continually recognizing the exact matches and recording the exact matches that occurred along with time measured in the number of cognition cycles between the last exact match. • By default, the response to a given stimulus is to repeat the stimulus to the next layer up the inference hierarchy for aggregation of the raw stimuli. •04.01.2021 Nonrecoverable loss of signal on network – “Urgent” path 11 KNCET Orient Binding: • Occurs when there is nearly exact match - current stimulus and prior experience • Criteria for applying prior experience to the current situationmet • Binding is the first step in generating a plan for behaving in the given state similar to the last occurrence of the stimuli. • Determines – priority associated with the stimuli • Better binding – higher priority for autonomous learning • Less effective binding – lower priority for the incipient plan 04.01.2021 KNCET 12 Plan • Stimuli are dealt- deliberatively rather than reactively • An incoming network message – generate a plan(“Normal Path”) Planning includes, • Plan generation • Formal models of causality – embedded into planning tools • Include reasoning about time • Reactive responses – preprogrammed – other behaviors planned • Stimulus associated – simple plan – as a function of planning parameters + planning system 04.01.2021 KNCET 13 Plan Open source planning tools: • Embedding of planning subsystems into the CRA • Enhance the plan component • Enable synthesis of RF and information access behaviors in a goal oriented way based on perceptions(visual, audio, text) and rules and previously learned user preferences. DECIDE: • Selects – candidate plan • CR- have choice • Alert user to an incoming message(behave like a pager) • Defer interruption until later(screening calls during an important meeting) 04.01.2021 KNCET 14 Act Phase Acting Phase • Initiates- selected processing using effector modules • Effectors may access– external world / CR’s internal states Externally oriented Actions: • Access to the external world consists of composing messages to be spoken into local environment or expressed in text form locally or to another CR or CN using, • Knowledge Query and Manipulation language(KQML) • Radio knowledge Representation language(RKRL) • Web Ontology Language(OWL) • Radio eXtensible Markup Language(RXML) • Appropriate knowledge interchange standard 04.01.2021 KNCET 15 Act Phase Internally Oriented Actions: • Actions on internal states include – machine controllable resources • CR can affect the contents of -Internal models – adding a model of stimulus-experience-response(serModel) to the existing internal model structure. • Multiple independent sources of the same concept in a scene reinforce that concept for that scene. • Experience – reactively integrated into RXML knowledge structures. 04.01.2021 KNCET 16 Learning • Function – perception, observation, decisions and actions • Initial Learning: • Observe phase perception hierarchy – which is continuously matched against all prior stimuli to continually count occurrences and to remember time since last occurrences of the stimuli from primitives to aggregates. • Introduction of new internal models • Existing models and case based reasoning(CBR) bindings • Many opportunities to Integrate – ML into CRA • Learning mechanism • New type serModel • Internally generated serModel 04.01.2021 KNCET 17 Self monitoring timing • CR is inherently self-referential and self modifying • Such tools will emerge, assisted by the needs of CR and the architecture framework of cognitive cycle. • Prior phases – computational structures – execution time advance • Each phase – restrict its computations – pre-computed upper bound • Architecture – prohibitions + data set requirements – degree of stability • Unnatural act – next generation compilers + CASE tools 04.01.2021 KNCET 18 Self monitoring timing Cognition cycle • No internal loops • Each iteration – defined amount of time • Amount of computational work done within the cycle will increase but no conditions should explicit or implicit loops be introduced into the cognition cycle that would extend it beyond a given cycle time. 04.01.2021 KNCET 19 Retrospection & Reaching Out Retrospection • Assimilation of knowledge by ML can be computationally intensive. • CR has - Sleep and prayer epoch – support ML • Sleep epoch – long period of time, CR will not be in use, has sufficient electrical power for processing. • Run ML algorithm – without detracting from its ability to support its user needs. • ML algorithm – integrate experience by aggregating statistical parameters. • Sleep cycle – may re-run Stimulus – response sequence + with new learning parameters 04.01.2021 KNCET 20 Retrospection & Reaching Out • fitness landscape- improves decision parameters from recent experience. Reaching Out • Learning opportunities not resolved in sleep epoch • Attention of the user, host network or designer – prayer epochs • Prayer epoch – complex problems to an infrastructure support. 04.01.2021 KNCET 21 Architecture of cognitive radio implemented via cognition cycle • Cognition functions implemented via cognition components 04.01.2021 KNCET 22 Architecture of cognitive radio implemented via cognition cycle • Data structures include the reinforced hierarchical sequences words, phrases, dialogs and scenes of the observe phase. • Novel sequence represent the current stimulus-response cases of the cognitive behavior model. • Known sequence consists of RKRL statements embedded in PDA • Nearest sequence is the known sequence. • World model, S consists primarily of bindings between a prior data structure and current scene. • These structures are associated with the observe phase. 04.01.2021 KNCET 23 Functions of cognitive radio 04.01.2021 KNCET 24 Functions of cognitive radio • Functional component is a black box to which functions are allocated • User interface functions include optimized hardware. • Functional components are, • User sensory perception(SP), includes acoustic, video sensing and perception functions. • Local environment sensors (location, temperature, accelerometer,…) • System applications – media independent services such as network game • SDR functions – RF sensing , SDR applications 04.01.2021 KNCET 25 Functions of cognitive radio • Cognition functions – system control, planning, learning • Local effector functions – speech synthesis, text, graphics and multimedia displays • Primary radio cognition functions consists of: • Recognize user communication context: • Cognition function should rely on processing streams of user interaction with applications as its primary means. • Mediate wireless information services as a function of context: • Continuously track the parameters of wireless networks present in the environment. • Parameters include spectrum occupancy, receive signal strength as a function of time and space, available QoS, related costs. 04.01.2021 KNCET 26 SDR as a platform for cognitive radio • This explores both the hardware and software domains. • Hardware is analyzed in terms of its capabilities. • Radio frequency font end(RFFE) can transmit up to a certain frequency • Software is generally treated as an enabler. • Cognitive radio assumes that system hardware and software infrastructure is capable of supporting the flexibility demanded by cognitive algorithms. • It provides significant flexibility with a series of tunable hardware components that are in direct control of cognitive software. 04.01.2021 KNCET 27 SDR as a platform for cognitive radio • Cognitive system can support large number of protocols and air interfaces. • It is desirable to have a generic hardware structure. • Series of generalized computing structures implies that the cognitive engine must contain hardware specific knowledge. • Cognitive engine can navigate different optimization strategies. • So change in the underlying hardware would require a change in the cognitive engine knowledge base. • This problem increases when we consider porting the engine to other radio platforms. • For eg. There could be a research and development platform used in testing a variety of cognitive algorithms. 04.01.2021 KNCET 28 SDR as a platform for cognitive radio • These algorithms are deployed in systems. • Cognitive engine is used in the deployed system’s management structure. • Cognitive engine could be modified to support new hardware platform. • SDR is a methodology for the development of applications in a consistent and modular fashion in both hardware and software components and can be reused from implementation to implementation. • It also provides the management structure for the description, creation and waveforms. • SDR supports RF and intermediate frequency hardware that is necessary to interface the computing hardware with radio signals. 04.01.2021 KNCET 29 Hardware Architecture • Goal: Explore hardware for SDR from a radio standpoint. • The figure shows the basic radio receiver. • The generic architecture traces from the antenna through the radio and up the protocol stack to the application. 04.01.2021 KNCET 30 Hardware Architecture RF Externals: • Many radios achieve satisfactory performance with an antenna to yield a beam pattern. • Antenna used over a wide frequency range requires antenna tuner to optimize VSWR, radio efficiency. • Each time transceiver change frequency, antenna tuner will be informed. • Many of these antennas update their steering angle as rapidly as once every millisecond. • Sophisticated antenna is MIMO antenna. • The interface boundary between the radio and the antenna is blurred by the wide bandwidth and complex interfaces between the beam steering signal processing , large number of parallel RF front end receivers and final modem signal processing is used. 04.01.2021 KNCET 31 Hardware Architecture • Another external component is RF power amplifier(PA). • Power amplifiers transmit when the transceiver is in the transmit mode and stop transmitting when the transceiver is in the receive mode. • Low noise amplifier (LNA) normally have a tunable filter with it. RF FRONT END • It consists of the receiver and the transmitter analog functions, frequency up converters and down converters, filters and amplifiers. • The front end design will maximize the dynamic range of signals that the receiver can process, through automatic gain control(AGC). 04.01.2021 KNCET 32 Hardware Architecture 04.01.2021 KNCET 33 Hardware Architecture Analog to digital converters: • The digital receiver industry is looking for wider bandwidth and greater dynamic range. • Successive approximation ADC were replaced by flash converters and now replaced with sigma-delta ADC. • ADC can provide 105Msps at 14 bit resolution. • Special purpose ADC provide sample rates over 5G samples per second at 8 bit resolution. MODEM: • After down conversion, filtering and equalization, the symbols are converted to bits by a symbol detector/demodulator combination which may include matched filter. 04.01.2021 KNCET 34 Hardware Architecture • A symbol is selected that most closely matches the received signal. • The bits that are represented by the symbol are then passed to forward error correcting function to correct bit errors. • The received and error corrected bits are parsed into various fields of message, header, address, traffic… • The message fields are then examined by the protocol layers eventually delivering messages to an application.(eg. Web browser, voice coder) thus delivering the function expected by the user. 04.01.2021 KNCET 35 Hardware Architecture • Forward error correction: • The demodulated bits are passed on to FEC stage for reducing the bit errors. • Medium Access Control: • It generally includes framing information with frame synchronization structures, MAC addressing , error detection, link management structures with possible fragmentation / defragmentation structures. • Network layer is designed for end to end connectivity support. • Network layer is passed to application layer which performs user functions and interface(speaker/microphone, graphical user interface, human-computer interface) 04.01.2021 KNCET 36 Hardware Architecture • User Application: • User application may range from voice telephony, to data networking, to text messaging, to graphic display, to live video. • For voice telephony, dominant mode is to code the voice to a moderate data rate. • Data rates from 4800bps to 13000bps which provides excellent voice quality and low distortion. • Voice coding applications are implemented on DSP 04.01.2021 KNCET 37 Hardware Architecture • • • • • Baseband processor engines: Four basic classes of programmable processors are available: GPP, DSP, FPGA and CCM GPP: Usually pipeline the arithmetic functions and decision logic functions. • Execute many instructions in parallel with arithmetic computation, logic evaluations and branch decisions. • GPP type processors is used for protocol stack processing. 04.01.2021 KNCET 38 Hardware Architecture • • • • • • • • DSP: Signal processes can be performed at high speed. DSP internal architecture is optimized to perform very fast. They have one or more multipliers and one or more accumulators in hardware. DSP is much more efficient in signal processing but less capable to accommodate the software associated with the network protocols. FPGA: Capable of providing multiple accumulate operations on a single chip More than 100 accumulators are arranged to perform accumulate processes at frequencies of more than 200MHz. 04.01.2021 KNCET 39 Hardware Architecture • FPGA provides timing logic to synthesize clocks, baud rate, chip rate, time slot and frame timing leading to compact waveform implementation. • Uses VHDL for defining hardware architecture and functionality. • Baseband Processing deployment: • Once a set of devices and algorithm performance for each of the devices has been established, there is a finite set of possibilities that can be optimized. • Several algorithms exists for optimizing specific values such as minimum mean square error(MMSE), maximum likelihood estimation(MLE), genetic algorithms, neural nets or large set of algorithms. 04.01.2021 KNCET 40 Hardware Architecture • Proposed methodology is partitioned into platform specific and waveform specific analysis • Platform specific analysis is partitioned into two types: DSP/GPP and FPGA. • Platform specific analysis is as follows: • 1. Create an operations audit of the target algorithms (number and type of operations) • 2. For DSP • (a) create a set of target devices. • (b) Establish cycle saving capabilities of each target device. • 3. For FPGA • (a) Create a set of devices 04.01.2021 KNCET 41 Hardware Architecture • (b) Establish mapping between different FPGA families. • (c) Find local device count for each target algorithm • (d) Use mapping between devices to find appropriate target on devices when benchmark is not available. • It is also possible to create performance estimates for different waveforms • (a) Create block based breakdown of the target waveform using target algorithms. • (b) Breakdown target waveform into clock domains. • (c) Estimate the time necessary to complete each algorithm. • (d) Compute the number of operations per second(OPS) needed for each algorithm. 04.01.2021 KNCET 42 Hardware Architecture • (e) Create a set of devices or combination of devices that meet some broad criteria. • (f) Attempt to map algorithm onto the given devices in set. • For DSP, • (a) Compute the number of operations per second(OPS) needed for each algorithm. • (b) The result of algorithm map is a MIPS(million instructions per second) count for each device. • FPGA, • (a) Mapping of the algorithm of the number of occupied logical devices. • (b) Make sure that the clock domains needed for algorithm can be supported by FPGA 04.01.2021 KNCET 43 Hardware Architecture • (c) Apply appropriate optimization algorithm which includes power budgets and performance metrics. • Multicore systems and System-on-chip: • As technology reaches transistors under 100nm, the key problems become the inability to continue as the power dissipation is very high. • Power consumption of an active circuit is given as, • P = α C f V2 • α = switching activity, C = capacitance, f= clock speed, V = operating voltage • By reducing interface capacitance and voltage swing, system efficiency increases. 04.01.2021 KNCET 44 Software Architecture • Software is designed to support baseband signal processing 04.01.2021 KNCET 45 Software Architecture • The stack starts with the hardware and one or more data buses that move information among various processors. • On top of the hardware, several standardized layers of software are installed which includes(boot loader, operating system, board support package and Hardware abstraction layer. • Hardware abstraction layer(HAL) provides a method for GPP to communicate with DSP and FPGA processors. • US government has defined standardized software architecture known as the software Communication Architecture(SCA) • SCA is a core framework to provide a standardized process for identifying the available computational resources of the radio, matching those resources to the required resources for an application. 04.01.2021 KNCET 46 Software Architecture • SCA is built upon a standard set of OS features. Which has standardized APIs to perform OS functions such as file management and computational task scheduling. • SCA specifies a Common Object Request Broker Architecture(CORBA), which provides a standardized method for software objects to communicate with each other • SCA provides a standardized method of defining the requirements for each application, performed in extensible markup language(XML). 04.01.2021 KNCET 47 Software Architecture • Design philosophies and patterns for software architecture: • Software design is formalized into a variety of design philosophies such as object oriented programming(OOP), component based programming(CBP), aspect-oriented programming(ASP) • Linear programming(LP): • It is a methodology in which the developer follows a linear thought process for the development of the code • The process follows a logical flow 04.01.2021 KNCET 48 Software Architecture • • • • • • • • • Execution of a function involves: Swapping of the stack Changing the context of operation Performing the function’s work Returning result to the calling function Object oriented programming: Extends the data structure concept to describe the whole object. An object is a collection of member variables and functions A class is an object type and an object is a specific instance of a particular class. • Several languages are OOP languages eg. Java, C 04.01.2021 KNCET 49 Software Architecture • Component based programming: • It is an extension of OOP concept. • An object is basic unit which comprises of one or more classes and is completely defined by its interfaces and functionalities. • A component could be a computer, where the computer component is defined as the collection of keyboard, mouse, display and actual computer case. • The nature of the computer is irrelevant to the user as long as interfaces and functionality remains the same. • The primary goal of CBP is to create stand-alone components that can be easily interchanged between implementations. 04.01.2021 KNCET 50 Software Architecture • Aspect oriented programming: • Allows for the creation of relationship between different classes. • AOP requires creation of new language constructs that can associate an aspect to a particular class. • There are several languages(AspectJ, AspectC, Aspect#) • Design Philosophy and SDR: • Dominant philosophy in SDR design is CBP, use of separate components for the different functional blocks of a radio system such as link control or network stack • SDR is relatively new discipline with few open implementation examples. 04.01.2021 KNCET 51 Software Architecture • • • • • • Design patterns: These are programming methodologies that a developer uses. Patterns provide two principal benefits: They help in code reuse They create a common terminology Where common terminology is important when working on teams because it simplifies communications between team members. 04.01.2021 KNCET 52 OVERVIEW OF IEEE 802.22 STANDARD • The Wireless regional network is expected to operate in lower population density areas and provide broadband access to data networks in VHF and UHF bands in the range of frequencies between 54MHz and 862MHz. • In 802.22 functional requirement, the capacity at the user terminal is expected to be of 1.5Mbps in the downstream and 384Kbps in the upstream • Prominent target application of 802.22 WRAN(Wireless regional area network) is a wireless broadband access in rural and remote areas with performance comparable to those of existing fixed broadband access technologies(DSL and cable modems) serving urbans and suburban areas. 04.01.2021 KNCET 53 Reference Architecture • 802.22 system specifies a fixed point to multipoint(PMP) wireless air interface whereby a base station(BS) manages its own cell and all associated consumer premise equipment(CPE) 04.01.2021 KNCET 54 Reference Architecture • The base station(BS) controls the medium access in its cell and transmits in the downstream direction to various CPE which respond back to the BS in the upstream direction. • 802.22 system follows a strict master/slave relationship , wherein BS performs the role of the master and CPE are the slaves. • No CPE is allowed to transmit before receiving proper authorization from a BS • 802.22 BS manages a unique feature of distributed sensing. 04.01.2021 KNCET 55 IEEE 802.22 physical layer • 802.22 PHY layer is specifically designed to support a system that uses vacant TV channels to provide wireless communication access over distance of 100km. • The PHY specification is based on orthogonal frequency division multiple access(OFDMA) for both upstream(US) and downstream(DS) access. • Preamble, Control Header and MAP definition: • In 802.22 allocation of resources in OFDMA frame can be made in terms of sub-channels and symbols. • Sub-channel is defined as a set of 28 contiguous OFDM subcarriers and there are 60 sub-channels per symbol. 04.01.2021 KNCET 56 IEEE 802.22 physical layer • In the first frame of the super frame, the first symbol is the super frame preamble followed by a frame preamble symbol. • The third symbol is the super frame control header(SCH) • Fourth symbol contains the frame control header(FCH) • Frame length is 10ms. • Preamble definition: • Two types of frequency domain sequences are defined to facilitate burst detection, synchronization and channel estimation at 802.22 receiver. • 1. Short training Sequence(STS): • This sequence is formed by inserting a nonzero binary value on every fourth subcarrier. 04.01.2021 KNCET 57 IEEE 802.22 physical layer • In time domain, this results in four repetitions of 512 sample sequence in each OFDM symbol. • 2.Long training sequence(LTS): • The sequence is formed by inserting a non zero binary value on every second subcarrier. • In the time domain, this results in two repetitions of a 1024 sample sequence in each OFDM symbol. • STS is used to form the super frame and CBP preambles, while LTS is used to form frame preamble. • The super frame preamble is used by the receiver for frequency and time synchronization. 04.01.2021 KNCET 58 Control header and MAP definition • Here we define the structure of two control headers (SCH and FCH) and the MAPs. • SCH is transmitted using PHY mode 1 and TCP(transmission control protocol) = 1/2TFFT • Transmitted over all data subcarriers, encoded by a rate-1/2 convolutional coder and after interleaving is mapped using QPSK constellation resulting in 336 QPSK symbols. • The FSH is transmitted as part of the DS protocol data unit(PDU) in the DS subframe and uses the basic data rate mode. 04.01.2021 KNCET 59 CBP packet format • He first symbol is the preamble, followed by data payload1 and an optional data payload 2. • The length field of the first symbol enables a receiver to determine the presence and absence of the second data symbol. • The data symbols consists of the data and the pilot subcarriers. • The payload is divided into blocks of 418 bits before encoding and mapping. • The encoded bits are then mapped using QPSK constellation • QPSK symbols is transmitted on 3 sub-carriers to provide additional frequency diversity. 04.01.2021 KNCET 60 Channel coding and modulation schemes • Channel coding includes data scrambling, convolutional coding or advanced coding, puncturing , bit interleaving and constellation mapping. • The frame payload data are first processed by the data scrambler using pseudorandom binary sequence generator with the generator polynomial. • FEC follows the data scrambler. • Coding scheme in 802.22 is convolutional coding. • Data burst is encoded using a rate-1/2 binary convolutional encoder. • The input data to the mapper are first divided into groups of two for QPSK, four for 16-QAM and six for 64-QAM • Mapping is performed using gray coding constellation mapping. 04.01.2021 KNCET 61 Channel coding and modulation schemes • Transmit power control: • TPC is an important feature in 802.22, since it requires only minimum transmit power in maintaining link quality, which further enhances incumbent protection in addition to spectrum sensing, databases and geolocation • IEEE 802.22 MEDIUM ACCESS CONTROL LAYER • Super frame and Frame structures: • 802.22 MAC uses a synchronous timing structure, where frames are grouped into a super frame structure. • Super frame preamble is used for time synchronization, while frame preamble is used for channel estimation. • SCH carries the BS MAC address along with the schedule of period of sensing and other information about the cell. • After SCH , BS transmits the frame control header(FCH) followed by the messages within the first frame. 04.01.2021 KNCET 62 IEEE 802.22 MEDIUM ACCESS CONTROL LAYER • Remaining 15 frames within the superframe start with the frame preamble. followed by the FCH and subsequent data message 04.01.2021 KNCET 63 MAC frame structure 04.01.2021 KNCET 64 IEEE 802.22 MEDIUM ACCESS CONTROL LAYER • The frame is divided into DS and US subframes and the self coexistence window(SCW), which is scheduled by BS at the end of the frame. • The first downstream burst after the FCH is used to transmit DS/US MAPs. The DS/US channel descriptor messages(DCD and UCD) and other MAC protocol messages. • DS/US MAPs are broadcast messages that specify the resource allocation in the DS and US sub-frames. • The DCD and UCD are usually transmitted by the BS at periodic intervals to define the characteristics of the DS and US physical channels. • After control signaling, BS can schedule the DS burst for data transmission using different modulation/coding schemes for each burst. • In the US subframe, BS can allocate resources for contention based access before the data bursts which can be used for ranging, bandwidth requests and urgent co-existence situation(UCS) notification. 04.01.2021 KNCET 65 IEEE 802.22 MEDIUM ACCESS CONTROL LAYER • UCS window is a new feature used by CPE to transmit an indication that an incumbent signal is detected on the channel. • BS may also reserve five symbols at the end of the frame for self coexistence window(SCW). • SCW is used for execution of coexistence beacon protocol(CBP), which involves transmission of coexistence beacons carrying information about the cell and specific coexistence mechanisms. • INCUMBENT DETECTION: • Two important capabilities were introduced in the MAC layer to support incumbent detection. • Network quiet period: • BS can schedule network wide quite periods (QP) during which all transmissions are suspended and sensing can be performed more reliably. • BS can schedule QP by using QP scheduling fields in SCH. 04.01.2021 KNCET 66 IEEE 802.22 MEDIUM ACCESS CONTROL LAYER • Channel measurement management: • In case incumbent is detected by BS, BS takes appropriate steps to avoid interference • But when CPE detects an incumbent, it has to report to the BS. • For that MAC layer includes channel measurement request and reports messages which allows the BS to take full control of the incumbent detection and notification. • Synchronization: • It is needed not only for communication purpose between and CPE but also for incumbent protection. • BS and CPE in a cell must be synchronized to ensure no transmissions occur during the QP for sensing. 04.01.2021 KNCET 67 IEEE 802.22 MEDIUM ACCESS CONTROL LAYER • Self-coexistence: • Unlicensed spectrum access model adopted for 802.22 systems ensures efficient and fair spectrum utilization. • Key elements: • Neighboring network discovery and coordination • Coexistence beacon protocol • Resource sharing mechanisms • Quality of service support: • Several mechanism support QoS for upstream and downstream traffic • Service flow QoS scheduling: • Primary purpose of QoS supports at the MAC layer is to define the transmission ordering and scheduling on the air-interface. 04.01.2021 KNCET 68 IEEE 802.22 MEDIUM ACCESS CONTROL LAYER • Activation model: • Service flow can be classified as provisioned , admitted or active. • To activate a service flow, BS maps the service flow to a CID(connection identifier) which identifies the connection between CPE and BS across which data is delivered. • Service flow can also be in transient admitted state, where the resources are not yet completely activated. • Dynamic service establishment: • MAC layer provides a series of management messages and procedures to create, change or delete service flows. • The DSA messages create a new service flow • The DSC messages change an existing service flow • The DSD messages delete an existing service flow 04.01.2021 KNCET 69 EC 8071- COGNITIVE RADIO UNIT III SPECTRUM SENSING AND DYNAMIC SPECTRUM ACCESS Introduction – Primary user detection techniques – energy detection, feature detection, matched filtering, cooperative detection and other approaches, Fundamental Tradeoffs in spectrum sensing, Spectrum Sharing Models of Dynamic Spectrum Access Unlicensed and Licensed Spectrum Sharing, Fundamental Limits of Cognitive Radio. 04.01.2021 KNCET 1 INTRODUCTION • Due to the rapid advance of wireless communication, digital communication exists in licensed and unlicensed bands suitable for different demands and applications such as GSM/GPRS, IEEE 802.11, Bluetooth, UWB, Zigbee, 3G LTE, IEEE 802.16 • Radio propagation favors the use of spectrum under 3GHz due to non-line of sight propagation. • In the past, spectrum allocation was based on the specific band assignments designed for a particular service. • There is a dramatic increase in the access to limited spectrum for mobile services and applications. 04.01.2021 KNCET 2 INTRODUCTION • Dynamic spectrum access is proposed as a solution to these problems of current inefficient spectrum usage. • The inefficient usage of the existing spectrum can be improved through opportunistic access to the licensed bands by the existing users(primary users). • Cognitive radio technology provides the capacity to share the wireless channel with the licensed users in an opportunistic way. • CR are envisioned to be able to provide high bandwidth to mobile users via heterogeneous wireless architectures and dynamic spectrum access techniques. 04.01.2021 KNCET 3 INTRODUCTION • In order to share the spectrum with licensed users and to meet the diverse quality of service requirement of applications, each CR user in the network must: • Determine the portion of spectrum that is available known as spectrum sensing. • Select the best available channel, called spectrum decision. • Coordinate access to the channel with other users known as spectrum sharing. • Vacate the channel when a licensed user is detected, referred to as spectrum mobility. 04.01.2021 KNCET 4 INTRODUCTION • CR has the capability of being cognitive, reconfigurable and self organized to fulfill the functions of spectrum sensing, spectrum decision, spectrum sharing and spectrum mobility • CAPABILITIES OF COGNITIVE RADIOS: • Cognitive radio enables the improvement of the spectrum use in a dynamic manner. • It is an intelligent wireless communication system that is aware of its surrounding environment and uses the methodology of understanding by building to learn from the environment and adapt its internal states to statistical variations in the incoming RF stimuli by making changes in operating parameters in real time. 04.01.2021 KNCET 5 INTRODUCTION Cognitive radio shall • Sense the environment (cognitive capability) • Analyze and learn sensed information(Self-organized capability) • Adapt to the environment(reconfigurable capabilities) • We summarize cognitive capability • Spectrum sensing: • CR can sense spectrum and detect spectrum holes , those frequency bands not used by licensed users. • CR could incorporate sharing of the spectrum under the agreement between a licensee and a third party. 04.01.2021 KNCET 6 INTRODUCTION • Location identification: • It is the ability to determine its location and the location of other transmitters and select appropriate operating parameters like power and frequency. • Network/system discovery: • It shall discover available networks around it. • The networks are reachable either via directed one hop communication or multi-hop relay nodes. • Service discovery: • It accompanies network/system discovery. • Network/system operators provide their services through their access networks. 04.01.2021 KNCET 7 Reconfigurable Capability of CR • Frequency Agility: • Ability of a radio to change its operating frequency. • This method usually combines with a method to select operating frequency based on the sensing of signals from other transmitters. • Dynamic frequency selection: • Dynamically detects signals from other radio frequency systems and avoids co-channel operation with those system. • Adaptive modulation/coding(AMC): • It is developed to approach channel capacity in fading channels. • It can modify transmission characteristics and waveforms to provide improved spectrum access 04.01.2021 KNCET 8 Reconfigurable Capability of CR • Transmit power control(TPC): • Enables the device to switch dynamically between several transmission power levels. • It allows transmission at the allowable limits and reduces the transmitter power to a lower level to allow greater sharing of spectrum. • Dynamic system/network access: • For cognitive radio terminal to access multiple communication systems/networks that run different protocols, the ability to reconfigure itself to these systems is necessary. 04.01.2021 KNCET 9 Self organized capability: • CR should be able to self-organize their communication based on sensing and reconfigurable functions. • Spectrum/radio resource management: • A good spectrum management scheme is necessary to manage and organize effectively spectrum holes . • Mobility and connection management: • It helps in neighborhood discovery, detect available internet access and support handoffs which helps CR to select route and networks. • Trust/Security Management: • Trust is a prerequisite for security operations to support security functions in dynamic environments. 04.01.2021 KNCET 10 04.01.2021 KNCET 11 Primary user signal detection techniques • Spectrum sensor performs a binary hypothesis test, whether or not there are primary signals in a particular channel. • The channel is idle under null hypothesis and busy under the alternate • Under idle scenario, the received signal is essentially the ambient noise in RF environment. • Under busy scenario, received signal consists of primary user signal and the ambient noise • W(k) – represents ambient noise , s(k) - primary user signal • k = 1,2,3…n, where n is number of received samples 04.01.2021 KNCET 12 Primary user signal detection techniques • The received signal will have more energy when the channel is busy than when it is idle. • False alarms (Type I errors) occur if an idle channel is detected as busy and missed detections occur when a busy channel is detected as idle. • A missed detection (Type II error) could potentially lead to a collision with primary user leading to wasted transmissions for both primary user and secondary user. • The performance of a detector is characterized by two parameters, probability of missed detection(PMD) and probability of false alarm(PFA) using classical formulation of binary Neyman-Pearson test, defined as, 04.01.2021 KNCET 13 Primary user signal detection techniques • A typical receiver operating characteristic (ROC) • Choosing different sensors, detection algorithms or sensing parameters leads to different ROCs 04.01.2021 KNCET 14 Energy Detector • The signal is passed through bandpass filter in order to limit the noise of bandwidth,W and is integrated over time interval. • The output from integrator is compared to a predefined threshold. • The comparison is used to discover the absence of the primary user. • Threshold value can be fixed or variable based on the channel conditions. 04.01.2021 KNCET 15 Energy Detector • Here w(k) and s(k) are zero mean complex Gaussian random variables with variances • Let denote vector of n observed samples. • We denote standard deviation • Neyman – Pearson is a threshold detector on log-likelihood ratio(LLR) • Where is a suitably chosen threshold • The detector is equivalent to H1 if • Statistic z is a scaled version of a standard with 2n degrees of freedom. 04.01.2021 KNCET random variable, 16 Energy Detector • If are independent real Gaussian variables with zero means and unit variances. • Probability density function is given by, • For probability 04.01.2021 , KNCET 17 Energy Detector • Hence PFA and PMD for the energy detector can be obtained as, • One disadvantage of energy detector is that at low SNR, the number of samples required to achieve specified performance metrics is proportional to 04.01.2021 KNCET 18 Energy Detector • Non-zero mean case: • In 802.22 standard, the primary signal contains known synchronization sequence. • These sequence are repeated to facilitate detection. • The known sync sequence are used in matched filter • Under H1, Statistic z is a non-central distributed with 2n degrees of freedom. • Non-centrality parameter, 04.01.2021 KNCET 19 Energy Detector • Probability of distribution, • • • • • • is the generalized Marcum Q function. In - is the modified Bessel function of order n. Energy detection Under fading: Consider a block fading environment, Under H1, Received signal is expressed as h- random variable, assumed fixed over n samples, represents fading. 04.01.2021 KNCET 20 Energy Detector • PFA remains unchanged, since there is no fading under H0 • Under H1, average probability of detection is computed from, • Where , is the pdf of SNR • In case of weak signal detection, it is performed by higher order detectors. • Another weakness is at low SNR, the number of samples increases as 04.01.2021 KNCET 21 Cyclo stationary Feature Detector • Often PU(primary user) signal structure is known. • Such as data rates, modulation type, carrier frequency, location of guard bands are known. • Digitally modulated signals have periodic features. • The carrier frequency and symbol rate can be estimated via square law devices. • Block diagram of Cyclo-stationary feature detector block diagram 04.01.2021 KNCET 22 Cyclo stationary Feature Detector • Cyclo-stationary feature detector exploits the periodicity in the received primary user signal to identify the presence or absence of the primary licensed users in the frequency band spectrum. • Primary user network uses pilot tone frequency • The use of cyclic prefix leads to periodic signal structures. • The mean and correlation sequences of such signals exhibit periodicity and hence called Cyclo-stationary signals. • The test statistic of a cyclic detector, 04.01.2021 KNCET 23 Cyclo stationary Feature Detector • The received signal y(n) is written as • Where are mutually independent zero-mean wide stationary processes, then for large N, • Where • This detector is implemented via Fast Fourier transform • Knowledge of noise variance is not required to set the detection threshold. • The performance of the detector degrades in the presence of timing and frequency jitters and RF nonlinearities. 04.01.2021 KNCET 24 Matched Filter • Often the pilot or sync sequences used in the primary network are known to secondary users. • Let s(n) denote the pilot sequence, n=1,2,3….N • Assuming perfect synchronization, the received signal at the secondary user is • Where w(n) is additive white Gaussian noise and h- represents unknown channel gain. • The optimal detector is the matched filter. • Matched filter detection is performed by projecting the received signal in the direction of the pilot, s(n) 04.01.2021 KNCET 25 Matched Filter • The test statistic is 04.01.2021 KNCET 26 Matched Filter • The performance of the detector is given by • SNR is defined by • At low SNR, the number of required samples is of the order of in contrast with samples required by the energy detector • This is a significant advantage. • The performance is degraded in the presence of frequency and timing offsets as well as fading and delay spread. 04.01.2021 KNCET 27 Cooperative sensing • Earlier we noted that the performance of a single detector can be severely degraded due to fading, shadowing or faulty sensor. • This is a motivation for cooperative sensing, where observations from multiple secondary users are combined to improve detector performance. • Received signal at the kth secondary user is given by, • Noise sequence are assumed to be independent and identically distributed in time n and mutually independent across the sensors. 04.01.2021 KNCET 28 Cooperative sensing • Channel gain coefficient, is assumed to be independent across the sensors. • Considerable overhead is required to transmit all • Performs local detection and passes only binary decision variables to a fusion center (FC). • LLR is quantized and sent to FC. • Depending on the level of complexity, FC has many choices for its fusion rule, • The cooperative scheme requires a control channel and a trusted spectrum broker. • Latency is an important issue. 04.01.2021 KNCET 29 Cooperative sensing 04.01.2021 KNCET 30 Cooperative sensing • The time required to sense the channel, report the measurements to FC and for the FC to detect white space and allocate spectrum to the user must be considerably less than the channel free time. • Let denote the local performance indices of the kth sensor • If the sensor observations and thus local decisions are conditionally independent, then 04.01.2021 KNCET 31 Cooperative sensing • FC has access to the individual sensor statistics and it can combine in many classical ways • Equal gain combining(EGC) • Selection combining • Consider the case where the K sensor statistics are independent. • Effective SNR is the sum of the individual SNR and adding K non-central random variables each with 2N degrees of freedom and has a non-centrality parameter • Cooperative sensing can be used to localize the active transmitters. 04.01.2021 KNCET 32 Other Approaches • The frequency nonselective flat fading assumes a narrowband channel model. • When the spectrum to be sensed is wideband, there are multiple challenges. • First, one may consider partially overlapping sub-channels for each of flat fading channels. • If the primary traffic is heavy, secondary user(SU) would seek to monitor multiple bands which entails increased sampling rates, receiver complexity and energy consumption. • Multi-resolution and wavelet based methods are proposed for wideband problem 04.01.2021 KNCET 33 Other Approaches • Power spectral density is smooth within each sub-channel but discontinuous across sub-channel boundaries. • By using wavelet transform, the discontinuous can be identified and thus spectrum activity is detected. • Sub-Nyquist sampling schemes, in conjunction with wavelet based edge detection are used to provide coarse estimates of spectrum occupancy and transmitter location. 04.01.2021 KNCET 34 Fundamental Trade-offs in spectrum sensing • Performance versus constraint: • Fundamental question in designing the spectrum opportunity detector is how to choose the detector operating point • It achieves optimal tradeoff between false alarms and missed detection. • Such trade-off should be addressed in terms of MAC layer performance: • The throughput of the secondary user. • Probability of colliding with primary users. • At MAC Layer: • Performance is measured by the throughput of the secondary user and the interference to the primary users. 04.01.2021 KNCET 35 Fundamental Trade-offs in spectrum sensing • The objective is to maximize the throughput under a constraint on the maximum outage probability , that the interference at an active primary receiver exceeds the noise floor , such events are referred to as Collisions with primary users. • The figure of merit at the MAC layer are given by probability, PS of successful data transmission and probability PC of colliding with primary users. • The objective and constraint at the MAC layer is given by, • For a complete data transmission, acknowledgement signal is required. 04.01.2021 KNCET 36 Fundamental Trade-offs in spectrum sensing • For successful data transmission, following three events occur in sequence: • Thus we have • Where 04.01.2021 KNCET 37 Fundamental Trade-offs in spectrum sensing • For best effort, delivery applications, acknowledgement are not required to confirm the completion of data transmission. • In this case • Probability of collision • Clearly, • Global Interference Model: • Consider this model, where the transmission from every primary user of interest affects the reception at B and the transmission from A affects the reception at every primary user 04.01.2021 KNCET 38 Fundamental Trade-offs in spectrum sensing • PHY-MAC translation under the global interference model: • Successful transmission from A and B results only from opportunities • Every correctly identified opportunities leads to successful transmission. • Every missed detection results in collision with primary users. • These properties leads to simple relationship between • {PFA and PMD} and {PS, PC} • PS = (1- PFA) Pr[H0], PC = PMD • To maximize PS under the constraint of , we obtain optimal operating point for the spectrum sensor. 04.01.2021 KNCET 39 Fundamental Trade-offs in spectrum sensing • Local Interference model: • The relationship between PHY and MAC has complex dependency on the applications. • PHY-MAC translation under the Local Interference Model • Used in applications, PC ≠ PMD • For applications with guaranteed delivery, correctly detected opportunities may lead to failed data transmission and miss detections may lead to successful data transmission. • For best-effort delivery, correctly detected opportunities always result in successful data transmission and miss detections may also lead to successful data transmission 04.01.2021 KNCET 40 Fundamental Trade-offs in spectrum sensing • Impact of MAC handshaking: • The fundamental deficiency of detecting spectrum opportunities from detecting primary signals resembles the hidden and exposed terminal problem in conventional ad hoc networks of peer users. • It is necessary to consider the use of RTS(Request to send)/CTS(Clear to send)handshaking to enhance the detection performance. • Although RTS/CTS signaling can improve the performance of opportunity detection at the physical layer, it leads to decreased throughput at the MAC layer for best-effort delivery applications. • For enhanced LBT, transmitter A first detects a chosen set of primary transmitters. 04.01.2021 KNCET 41 Fundamental Trade-offs in spectrum sensing • If there are no signals from this set, it transmits an RTS to B. • Upon receiving the RTS(automatically indicates the absence of interfering primary transmitters). • A successful exchange, A starts to transmit data to B. • PHY/MAC translation with RTS/CTS signaling • Correctly detected opportunities always result in successful data transmission as well as missed detections. 04.01.2021 KNCET 42 Fundamental Trade-offs in spectrum sensing • Sensing Accuracy versus Sensing overhead: • Increasing the sensing time improves the fidelity of the sensing outcomes thus reducing the overlooked spectrum opportunities. • Increasing the sensing time results in less transmission time. • Tradeoff between sensing accuracy and sensing overhead depends on the SNR level, duration of spectrum opportunities and the interference constraint, • Let N represents the slot length, n denotes the duration of sensing window. • PFA(n) and PMD(N) denote the performance metrics based on sensing window of length, n 04.01.2021 KNCET 43 Fundamental Trade-offs in spectrum sensing • Assuming the channel is free, fractional time that the channel will be accessed is 1-PFA(n) and fractional slot available for transmission is (N-n)/N • Spectral efficiency metric is defined as, • • • • • For a specified PD(Interference constraint), PFA is given by, Which decreases monotonically with n. Should select the value of n that maximizes As SNR increases, the required sensing window length decreases and efficiency increases. 04.01.2021 KNCET 44 Spectrum Sharing Models of DSA • Spectrum sharing is the simultaneous usage of a specific radio frequency band in a specific geographical area by a number of independent entities through mechanisms other than traditional multiple and random access techniques. • Key factors of spectrum sharing: • First, independent assumption of coexisting system means legacy MAC mechanisms, which are used to share resources among users in a cellular system • Second, emphasis is on scenario where mechanisms to facilitate spectrum sharing exists. • Dynamic spectrum sharing has broad suggestion that encompass various approaches to spectrum reform. 04.01.2021 KNCET 45 Spectrum Sharing Models of DSA • Dynamic spectrum access strategies categorized under three models. 04.01.2021 KNCET can be broadly 46 Dynamic exclusive use model • This model maintains the basic structure of the current spectrum regulation policy. • Spectrum bands are licensed to services for exclusive use. • The main objective is to introduce flexibility and improve spectrum efficiency. • Two approaches have been proposed for this model: • Spectrum property rights • Dynamic spectrum allocation • Spectrum property rights: • It allows licensees to sell and trade spectrum and to freely choose technology • Economy and market play an important role in driving towards the most profitable use of limited resource. 04.01.2021 KNCET 47 Dynamic exclusive use model • Dynamic spectrum allocation: • The second approach was brought by European DRIVE project. • It aims at improving spectrum efficiency through dynamic spectrum assignment by exploiting spatial and temporal traffic statistics of different services. • In a given region and at a given time, spectrum is allocated to services for exclusive use. • This allocation varies at a faster scale. • These approaches cannot eliminate white space in the spectrum. 04.01.2021 KNCET 48 Opening Sharing model • Also referred to as spectrum commons. • Employs open sharing among peer users as the basis for managing a spectral region. • Wireless services operating in the unlicensed industrial, scientific and medical(ISM) radio band (eg. Wi-Fi) have been analyzed. • Centralized and distributed spectrum sharing strategies have been initially investigated to address technological challenges under this spectrum management model. 04.01.2021 KNCET 49 Hierarchical Access model • This model has hierarchical access structure with primary and secondary users. • The basic idea is to open licensed spectrum to secondary users while limiting the interference perceived by primary users(licensees). • Three approaches to spectrum sharing have been considered: • Spectrum underlay • Spectrum overlay • Spectrum interweave 04.01.2021 KNCET 50 Spectrum Underlay 04.01.2021 KNCET 51 Underlay Spectrum Sharing 04.01.2021 KNCET 52 Spectrum Underlay • Underlay approach imposes severe constraints on the transmission power of secondary users so that they operate below the noise floor of primary users. • By spreading transmitted signals over a wide frequency band(UWB) secondary users can achieve a short range high data rate with extremely low transmission power. • To avoid any interference to the primary users, the underlay system can use interference techniques such as notching and waveform adaptation. 04.01.2021 KNCET 53 Spectrum Overlay 04.01.2021 KNCET 54 Overlay Spectrum Sharing 04.01.2021 KNCET 55 Spectrum Overlay • Spectrum overlay was first envisioned by Mitola under the term spectrum pooling and then investigated by DARPA(Defence Advanced Research project academy) next generation programme under the term opportunistic spectrum access. • This approach does not impose severe restrictions on the transmission power of secondary users, but rather on when and where they may transmit. • It directly targets at spatial and temporal spectrum white space by allowing secondary users to identify and exploit local and instantaneous spectrum availability. • Compared to dynamic exclusive use and open sharing models, this hierarchical model is perhaps the most compatible with current spectrum management policies and wireless systems. 04.01.2021 KNCET 56 Spectrum Overlay • This results in two main design goals, • Minimum interference to licensed transmissions • Maximum exploitation of the gaps in the time-frequency domain. Spectrum Interweave: • The interweave approach is based on opportunistic communication. • There exists temporary frequency voids in a frequency band, which are referred to as spectrum holes not used by the licensed/primary users. • Spectrum holes pop up according to changes in time and geographical locations. 04.01.2021 KNCET 57 • CR must constantly monitor the spectrum typically via physical layer spectrum sensing and to adopt certain medium access strategies to use spectrum holes as transmission opportunities for secondary transmissions with minimum interference to users/nodes Opportunistic Spectrum Access: Basic components • The term Opportunistic Spectrum Access(OSA) will be adopted throughout. • Basic components of OSA include spectrum opportunity identification, spectrum opportunity exploitation and regulatory policy. • The opportunity identification module is responsible for accurately identifying and intelligently tracking idle frequency bands that are dynamic in both time and space. 04.01.2021 KNCET 58 Opportunistic Spectrum Access: Basic components • The opportunity exploitation module takes input from the opportunity identification module and decides whether and how a transmission should take place. • The regulatory policy define basic etiquette for secondary users to ensure compatibility with legacy systems. • The design objective of OSA is to provide sufficient benefit to secondary users while protecting spectrum licensees from interference. • The tension between the secondary users desire for performance and the primary users need for protection dictates the interaction across opportunity identification, opportunity exploitation and regulatory policy. • Thus OSA calls for cross layer approach that integrates signal processing and networking. 04.01.2021 KNCET 59 Unlicensed and Licensed Spectrum Sharing • Components of CRN(cognitive Radio Network): 04.01.2021 KNCET 60 Unlicensed and Licensed Spectrum Sharing • Components of CRN: 04.01.2021 KNCET 61 Unlicensed and Licensed Spectrum Sharing • Basic elements of the primary and CR network: • Primary Network: • An existing network infrastructure is generally referred to as primary network. • It has exclusive right to a certain spectrum band. • Eg. Common cellular and TV broadcast network • • • • Primary User or licensed user: Has the license to operate in a certain spectrum band. This access can only be controlled by primary base station. Primary users do not need any modifications or additional functions for coexistence with CR base stations and CR users. 04.01.2021 KNCET 62 Unlicensed and Licensed Spectrum Sharing • Primary Base station or licensed Base station: • It is a fixed infrastructure network component which has a spectrum license such as base-station transceiver system(BTS) in a cellular system. • Primary base-station does not have any CR capability for sharing spectrum with CR users. • CR Network: • CR network, Dynamic spectrum access network, secondary network and unlicensed network does not have license to operate in a desired band. • The spectrum access is allowed only in an opportunistic manner. 04.01.2021 KNCET 63 CR Network: • Components of an CR network: • CR users: • CR user(unlicensed user, CR user, secondary user) has no spectrum license. • Additional functionalities are required to share the licensed spectrum band. • CR base station: • CR base-station (unlicensed base-station, CR base-station, secondary base-station) is a fixed infrastructure component with CR capabilities • It provides single hop connection to CR users without spectrum access license • CR users can access other networks. 04.01.2021 KNCET 64 CR Network: • Spectrum Broker or scheduling server: • It is a central network entity that plays a role in sharing the spectrum resources among different CR networks. • It can be connected to each network and can serve as a spectrum information manager to enable coexistence of multiple CR networks. • CR networks are operated under the mixed spectrum environment that consists of both licensed and unlicensed bands. • CR users can either communicate with multi-hop manner or access the base-station 04.01.2021 KNCET 65 CR Network: • In CR networks, there are three different access types : • CR Network Access: • CR users can access their own CR base-station both on licensed and unlicensed spectrum bands. • CR Ad-Hoc Access: • CR access can communicate with other CR users through ad-hoc connection on both licensed and unlicensed spectrum bands. • Primary Network Access: • CR users can also access the primary base-station through licensed band. 04.01.2021 KNCET 66 Unlicensed Spectrum Sharing • Unlicensed frequency bands are portion of spectrum used by devices that operate in a way that is not constricted by licenses and are prone to interference. • Commonly used unlicensed bands are 2.4GHz ISM(Industrial, scientific and medical) band used by IEEE 802.11 and Bluetooth devices and 5GHz UNII(Unlicensed National Information Infrastructure) band used by IEEE 802.11a and European HyperLAN standards. • Open spectrum policy caused an impressive variety of technologies and innovative uses. • The capacity of open spectrum access and the quality of service they can offer depends on the degree to which a radio can be designed to allocate the spectrum efficiently. • CR networks can be designed for operation on unlicensed bands such that the efficiency is improved. KNCET 67 Unlicensed Spectrum Sharing • CR network on unlicensed band architecture. 04.01.2021 KNCET 68 Unlicensed Spectrum Sharing • Since there are no license holders, all network entities have the same right to access the spectrum bands. • Multiple CR networks coexists in the same area and communicate using the same portion of the spectrum. • Intelligent spectrum sharing algorithms can improve the efficiency of spectrum usage and support high QoS. • In this architecture, CR users focus on detecting the transmissions of other CR users. • Unlike the licensed band operations, the spectrum handoff is not triggered by the appearance of other primary users. • All CR users have the same right to access to access the spectrum. • Sophisticated spectrum sharing methods among CR users are required. 04.01.2021 KNCET 69 Unlicensed Spectrum Sharing • First, it is easy to develop innovative technologies to operate in unlicensed bands since the approval process is similar to licensed technologies. • Second, there is no cost to the customer of using such bands. • Certain transmission power caps are used described by ITU-R 5.138, 5.150 • These may result in localization of interference by which numerous unlicensed devices operating in those bands are spatially/temporally distributed. • Successful deployment and rapid growth of WLAN technologies such as IEEE 802.11 is one of the creation of unlicensed bands. 04.01.2021 KNCET 70 Licensed Spectrum Sharing • Licensed bands are frequency bands assigned exclusively to a licensee, for instance a specific mobile operator. • Such license also stipulates a specific technology to be used in a band . Eg. GSM(Global system for Mobile communication) or UMTS(Universal Mobile Telecommunications System) • Regulators such as Ofcom in United Kingdom have shown interest in assigning spectrum bands as “technology neutral”. • Depending on the technology used in the licensed band of a specific service provider, various MAC techniques are used to allow end users to share the medium. • Sometimes there exists temporally unused spectrum holes in the licensed spectrum. • CR networks can be deployed to exploit these spectrum holes through cognitive communication techniques. 04.01.2021 KNCET 71 Licensed Spectrum Sharing 04.01.2021 KNCET 72 Licensed Spectrum Sharing • CR network coexists with primary network at the same location and on the same spectrum band. 04.01.2021 KNCET 73 Licensed Spectrum Sharing • There are various challenges for CR networks on licensed band due to the existence of the primary users. • The main purpose of CR network is to determine the best available spectrum and at the detection of the presence of primary users. • The channel capacity of the spectrum holes depends on the interference at the nearby primary users. • The interference avoidance with primary users is the important issue in this architecture. • If primary users appear in the spectrum band occupied by CR users, CR users should vacate the current spectrum band and move to the new available spectrum immediately called spectrum handoff. 04.01.2021 KNCET 74 Licensed Spectrum Sharing • If the cellular system uses a frequency reuse plan, it is not possible to share channels a, b or c with the broadcasting system due to interference. 04.01.2021 KNCET 75 Licensed Spectrum Sharing • In case of spectrum sharing with similar coverage area, misplacement of the broadcast signals of the two systems can have negative impact in terms of Co-Channel Interference. • This is because resource management is not properly coordinated. 04.01.2021 KNCET 76 Fundamental Limits of Cognitive Radio • Mitola envisioned a radio that could make decisions as to the network, modulation and coding parameters based on its surroundings called a “smart radio” a cognitive radio. • Such radios could make decisions by their current location and spectral conditions. • It removes unnecessary regulatory barriers to new secondary market-oriented policies such as: • Spectrum Leasing: Allowing unlicensed users to lease any part or all of the spectrum of a licensed user. • Dynamic Spectrum leasing: Temporary and opportunistic usage of spectrum rather than a longer term sublease. 04.01.2021 KNCET 77 Fundamental Limits of Cognitive Radio • Private Commons: • A licensee could allow unlicensed users access to the spectrum without contract, optionally with an access fee. • Interruptible Spectrum leasing: • Suitable for a leaser that wants a high level of assurance that any spectrum temporarily in use or leased to an incumbent cognitive radio could be efficiently reclaimed if needed. • Cognitive radios have the ability to listen to the surrounding wireless channel, make decisions on the fly and encode using a variety of schemes. • In order to exploit these abilities fully , consider an example. 04.01.2021 KNCET 78 Fundamental Limits of Cognitive Radio 04.01.2021 KNCET 79 Fundamental Limits of Cognitive Radio • As shown in the left, suppose sender X1 is transmitting over the wireless channel to receiver Y1 and a second incumbent user, X2 wishes to transmit to a second receiver, Y2 • In the current secondary spectrum licensing, incumbent user X2, a cognitive radio that is able to sense the presence of other transmitting users, would either wait until X1 has finished transmitting before proceeding or possibly transmit over a different frequency band. • Rather than forcing X2 to wait, it allows X2 to transmit simultaneously with user X1 at the same time in the same band of frequencies. • The wireless nature of the channel will make interference between simultaneously transmitting users unavoidable. 04.01.2021 KNCET 80 Fundamental Limits of Cognitive Radio • My making use of the capabilities of cognitive radio, it is able to potentially mitigate the interference. • Cognitive radio channel is defined as a two sender(X1, X2), two receiver (Y1, Y2) interference channel in which the cognitive radio transmitter X2 is non-causally given by a genie the message X1 plans to transmit. X2 can either mitigate the interference , help X1 in transmitting its message or smooth mixture of both. • A simple cognitive radio channel is considered as a two transmitter, two receiver information theoretic interference channel in which sender 2(cognitive radio) obtains, or is given by a genie, the message sender 1 plans to transmit. 04.01.2021 KNCET 81 Fundamental Limits of Cognitive Radio • Cognitive radio may then simultaneously transmit over the same channel as opposed to waiting for an idle channel as in a traditional cognitive radio channel protocol. 04.01.2021 KNCET 82 Fundamental Limits of Cognitive Radio • An intuitively achievable region for the rates (R1 and R2) at which X1 can transmit to Y1, and X2 to Y2, simultaneously been constructed. • When X2 has a prior knowledge of what X1 will transmit or interference it will encounter, we have two possible course of action. • a) It can try and mitigate the interference. X2 is layering on its own independent information to be transmitted to Y2. This strategy yields points of higher R2 and lower R1 in the cognitive channel region. • b) It selflessly act as a relay to reinforce the signal of user X1. That is, since X2 violate on X1 spectrum, only X1 should somehow benefit. This strategy yields points of high R1 and low R2 in the cognitive channel region. 04.01.2021 KNCET 83 Fundamental Limits of Cognitive Radio • From the figure, region(1) is the time sharing region of two independent senders. • Region(2) is the best known achievable region for the interference channel. • Region(3) is the achievable region described for the cognitive radio channel. • Region(4) is an outer bound on the cognitive radio channel capacity. • The resulting achievable region in the presence of additive white Gaussian noise is plotted as the cognitive channel region. 04.01.2021 KNCET 84 Fundamental Limits of Cognitive Radio • Here we can see four regions: • The time sharing region (1) displays the result of pure time sharing of the wireless channel between users X1 and X2. Points in this region are obtained by letting X1 transmit for a fraction of the time, during which X2 refrains. • The interference channel region(2) corresponds to the best known achievable region of the classical information theoretic interference channel. Both the senders encode independently and there is no message knowledge by either transmitter. 04.01.2021 KNCET 85 Fundamental Limits of Cognitive Radio • The cognitive channel region (3) is an achievable region. In this case X2 received the message of X1 non-causally from a genie and X2 uses a coding scheme that combines interference mitigation with relaying the message of X1. Both users get benefit from this scheme. • The modified MIMO bound region(4) is an outer bound on the capacity of this channel. The 2x2 MIMO Gaussian broadcast channel capacity region, where we have restricted the transmit covariance matrix to more closely resemble our constraints, intersected with the capacity bound on R2 for the channel in the absence of interference from X1. 04.01.2021 KNCET 86 EC 8071- COGNITIVE RADIO UNIT IV MAC AND NETWORK LAYER DESIGN FOR COGNITIVE RADIO MAC for cognitive radios – Polling, ALOHA, slotted ALOHA, CSMA, CSMA / CA, Network layer design – routing in cognitive radios, flow control and error control techniques. 04.01.2021 KNCET 1 INTRODUCTION-MULTIPLE ACCESS • The simplest way of interconnecting two computer host is using a point to point link with a host on each end. • As the number of hosts increases, this approach may be inadequate, since large number of links are needed. • In this case we use broadcast network, where all hosts share a common transmission media. • To share a common media (eg. Cable or wireless channel) efficiently, all hosts must follow a set of rules to access the media. • Host should be able to check the availability of the media and resolve collisions. 04.01.2021 KNCET 2 INTRODUCTION-MULTIPLE ACCESS • Since the bandwidth of the media is limited, it is desirable to share it efficiently. • The sharing rules are defined as media access control protocols which are implemented in the link layer. 04.01.2021 KNCET 3 MAC for Cognitive Radios • Consider a set of frequency bands, • M = { 1,2, …, M} • At time tn, Cognitive radio network operation allows an update of spectrum utilization. • The nth observation or allocation time interval is • Due to the opportunistic nature of each link modelled as morkov chain, the ith frequency band is available with the probability and is invariant to time. • We define indicator function: 04.01.2021 KNCET 4 MAC for Cognitive Radios • The probability mass function of Bernoulli random variable at the ith frequency band is • Where, • For reliable CR operation, spectrum sensing is necessary, so that CR – Tx can have information about the availability of each frequency band. • For network operations, the strategy would be related to • Case 1: is known , Case 2: is unknown • Case 3: can be detected or estimated via some CRN sensing 04.01.2021 KNCET 5 MAC for Cognitive Radios • Traditional CR functions: • When is known, the spectrum sensing strategy for a CR is simply to select the channel. 04.01.2021 KNCET 6 Multi-channel MAC (McMAC) • • • • Allows a number of nodes in the same neighborhood to transmit concurrently on different channels without interfering with one another. Carrier sensing can be coupled with an efficient channel selection mechanism to pick the clearest channel for transmission. A wireless device or node can only use one radio due to its half duplex nature. With the development of SDR and CR, multi-channel MAC plays a critical role in CRN MAC. Advantages of multi-channel MAC protocols in CRN: • Reduce collisions • Enable more concurrent transmissions • Better bandwidth usage even with the same aggregate capacity. 04.01.2021 KNCET 7 Multi-channel MAC (McMAC) 04.01.2021 KNCET 8 Multi-channel MAC (McMAC) • Cognitive multi-channel MAC appears as an enhanced version of McMAC • Every protocol operating frame is divided into three phases: • Spectrum sensing phase • CSMA(carrier sense Multiple Access) contention phase • Data transmission phase • In cognitive multichannel MAC, devices are able to sense the outer environment , information of the network and the information of other interference resources(i.e primary systems). 04.01.2021 KNCET 9 Multiple Access Scheme • In wireless network, mobile users share the wireless channel. • An important network control function is medium access control(i.e) how to share the channel among the users efficiently. eg. With high spectrum efficiency i.e, users should have equal chance of accessing the channel. • In classification of multiple access schemes, Channelization is widely adopted in traditional wireless networks • In this, the wireless channel is partitioned into a number of subchannels, eg. Frequency band, time slot, or spreading code • Then sub-channels are assigned to users. • The processing of sub-channels are done using several access schemes. 04.01.2021 KNCET 10 Classification of MAC schemes 04.01.2021 KNCET 11 Polling • A polling system is a special type of queuing system with one server and m stations (users), where one station is served at a time. 04.01.2021 KNCET 12 Polling • Each station is represented by a queue temporarily storing arriving customers, while customers at each station follows a random process. • Each customer requests service from the server and departs the system when its service is completed. • Stations in a polling system may have, 04.01.2021 KNCET 13 Polling • When the server finishes serving a station, it may decide which station to serve next by following a fixed order (eg.,cyclic) or a random selection. • The time between the end of a service and the beginning of the next service is the switchover time. • There are three kinds of service policies in a polling system: • Limited service polling system: • The server continuously serves a station until either the station is empty or a predetermined number of customers have been served. • Special case-limited system where atmost one customer is served whenever the server visits a station. 04.01.2021 KNCET 14 Polling Gated service system: • The server continuously serves a station until either the station is empty or all customers that arrived before the station is polled are served. 04.01.2021 KNCET 15 Polling Exhaustive service system: • The server serves all customers in a station continuously and leaves the station only when the station buffer is empty. • The fig. shows a gated service system with m=1, where the blocks with different shades represent the service times of customers. • Assume arrival process is poisson with rate λ • Let X denote the service time of a customer with mean • System utilization 04.01.2021 KNCET 16 Polling • Let denote the duration of jth switchover time • Consider ith customer arriving at the system • Before it is served, it has to wait in the queue until all customers that arrived earlier are served. • The waiting time in the queue includes the residual time, Ri, the service time and the next switchover time • The expected waiting time for customer ‘i’ is given by, • Expected waiting time in queue for the single user gated service system as , 04.01.2021 KNCET 17 ALOHA • Original ALOHA also called pure ALOHA was the earliest MAC scheme developed for packet radio networks. • With pure ALOHA, a station transmit a packet whenever it wants to. • After the transmission, the station listens for an amount of time. • If no acknowledgment is received by the sender, which indicates a collision, the frame is sent again. • Pure ALOHA is a very simple multiple access protocol, but its throughput is low. • Assume all packets have same length and the transmission time of a packet is τ seconds. 04.01.2021 KNCET 18 ALOHA • After a round-trip time R > τ , a collision may be detected. • After a random scheduling delay D, a retransmission is tried, T • All transmitted packets including retransmissions follow a poisson process with rate g packets/s. • If a node sends a packet at time t and there is no other transmission during [t- τ, t+ τ], the packet will be successfully received. • Since arrival process is poisson, the number of transmissions has a poisson distribution with parameter 2gτ. • Therefore, successful rate is given as 04.01.2021 KNCET 19 ALOHA • Let G = gτ be the normalized load, the throughput of pure ALOHA is • By differentiating S with respect to G and setting the derivative to zero. The maximum throughput of pure ALOHA is given as, • 2τ can be interpreted as vulnerable time of pure ALOHA • If on average there is only one packet transmission during vulnerable time, pure ALOHA achieves its maximum throughput. • Otherwise channel is either under loaded(channel bandwidth not fully exploited) or overloaded (waste of channel bandwidth due to collision) 04.01.2021 KNCET 20 SLOTTED ALOHA • It is an extension of pure ALOHA for improving throughput. • The time is divided into slots and the length of one time slot is equal to the packet transmission time τ. • Assume all nodes are synchronized • When a node has a packet to send, it starts to send it at the beginning of the next time slot. • If no other transmissions are in the same time slot, the transmission succeeds. • Otherwise, a collision occurs and the packet will be retransmitted after a random delay. 04.01.2021 KNCET 21 SLOTTED ALOHA • Similar to pure ALOHA analysis, assume that all transmitted packets, including retransmission form a poisson stream with rate g packets/s • If a node sends a packet in time slot t and there is no other transmission during the same time slot, the packet will be successfully received. • Assume the number of packets transmitted in a time slot has a poisson distribution with parameter G = g τ • Throughput of the slotted aloha is 04.01.2021 KNCET 22 SLOTTED ALOHA • Differentiating S with respect to G and setting the derivative to zero, maximum throughput of the slotted aloha is • By adopting a time-slot system(with synchronization), the throughput is doubled. • The length of one time slot (τ ) can be interpreted as vulnerable time (when G=1), slotted aloha achieves maximum throughput. 04.01.2021 KNCET 23 CSMA • One major cause of ALOHA‘s low throughput problem is that users do not try to avoid collisions. • Users start transmission whenever they want even when the channel is busy and collision is predestined. • Efficient enhancement is to let each user sense the medium before starting transmission. • If the channel is sensed busy, the user holds its packets until the medium is free. Such an idea is incorporated in carrier sense multiple access(CSMA) • Following three strategies can be used to sense the channel: • I-persistent CSMA • Non-Persistent CSMA • P-Persistent CSMA 04.01.2021 KNCET 24 I-persistent CSMA • A user with data frame waiting senses the medium and sends the frame immediately if the medium is free. • If the medium is busy, the user continuously senses the medium and starts transmitting as soon as it finds the medium free, avoids the idle stage of medium. • When more than one user is sensing the medium(when it is busy), they will start transmitting simultaneously when the channel becomes idle, leading to collision. • NON-Persistent CSMA: • The node waits a random amount of time before sensing again, when it senses a busy medium. • Backlogged users will come back to sense the medium at a different time and the collision rate can be reduced. 04.01.2021 KNCET 25 P-persistent CSMA • • • • • • Demerits: The medium utilization is reduced Increases waiting time for backlogged users. P-Persistent CSMA: It is used when time is divided into slots. A backlogged user senses the medium and starts the transmission with probability P if the medium is found free. • Otherwise it senses the medium at the beginning of the next time slot. • P-Persistent CSMA combines the advantages of the preceding two schemes and can reduce the collision rate and improves the medium efficiency. 04.01.2021 KNCET 26 P-persistent CSMA • Although CSMA can effectively reduce the chance of collision, it cannot completely eliminate collision. • An example of collision in CSMA 04.01.2021 KNCET 27 P-persistent CSMA • At T0, Node A senses an idle channel and starts transmitting. • It takes ‘a’ seconds (propagation delay) for the first bit of the packet to reach node B. • Before T0 + a, Node B still senses an idle channel. • If Node B starts transmitting during (T0, T0 + a ), there is a collision. • Therefore the vulnerable time of CSMA is the maximum propagation delay ‘a’. • For unslotted non-persistent CSMA, assume that there are an infinite number of stations and fixed length packets with transmission time τ seconds. • Also assume that the propagation delay for all other stations to hear a packet is ‘a’ seconds. 04.01.2021 KNCET 28 P-persistent CSMA • Then ‘a’ seconds after a packet is transmitted, all other stations know that the channel is busy and do not attempt to access the channel. • Assume that arriving packets follow poisson distribution with the rate s packets/s. • When a transmission attempt fails, the packet is rescheduled for retransmission. • To simplify the analysis, we assume the overall packets to be transmitted follow a poisson process with rate g seconds/s, including both arriving packet and rescheduled packets. • To have successful transmission, the channel has to be idle when the sender starts sensing, and there is no other transmissions within the next ‘a’ seconds period. 04.01.2021 KNCET 29 P-persistent CSMA • Therefore we have • 04.01.2021 KNCET 30 P-persistent CSMA • Each cycle starts with the period of idle time and then transmission occurs when a station with packets waiting finds the channel idle. • Interfering transmissions are possible during the a seconds after the first transmission starts.(i.e vulnerable time of CSMA) • Z is defined as the time between the beginning of the first transmission and that of the last interfering transmission. • After the end of the last interfering transmission, another a seconds pass before a new cycle starts, so that all stations are aware that the current transmission is over. • The length of the cycle: 04.01.2021 KNCET 31 P-persistent CSMA • From Renewal Theory, • Pr{channel idle} = • Since the arrival process is poisson with exponentially distributed interarrival times, we have • The probability of the channel being idle is therefore, • Successful packet rate is 04.01.2021 KNCET 32 P-persistent CSMA • Normalized rates are • We have • CSMA/CA • Collision is more costly in wireless networks than in wire line networks. • When a collision occurs, bandwidth which is limited in many wireless networks is wasted and energy is also wasted on failed transmissions. • In wired networks, the carrier sense multiple access with collision detection(CSMA/CD) can be adopted to detect collision and the sender can immediately stop the transmission, thus avoid wasting bandwidth and energy on transmitting the remaining part of the corrupted frames. 04.01.2021 KNCET 33 • CSMA/CA • In CSMA with collision avoidance(CSMA/CA),two mechanisms are incorporated to avoid collision: • A set of delays , termed Interframe Spaces(IFS), that amounts to a priority system • A contention window and binary exponential back-off • When a station has a frame to transmit, it first senses the channel. • Channel is found to be idle, it waits for an interval of IFS to see if the channel is still idle. If so, the station starts transmission. • Channel is found busy, the backlogged station defers its transmission and keeps on sensing the channel until the current transmission is over. Then the station waits for IFS 04.01.2021 KNCET 34 CSMA/CA • If the channel is still idle, the station backs off further for a random period of time. It starts transmitting only when the channel remains idle after the random back-off time. • The back-off timer is decreased only when the channel is idle. 04.01.2021 KNCET 35 CSMA/CA • The hidden terminal and exposed terminal problems in wireless LANs are inherent from the use of wireless transmissions. • Consider a scenario shown, • Nodes B and C are outside of each other’s transmission range and Node A is inbetween and can hear both Nodes B and C’s transmissions • So, Node B and C are hidden from each other with respect to Node A. 04.01.2021 KNCET 36 CSMA/CA • If CSMA/CA is used, Node C senses an idle channel because it cannot hear Node B’s ongoing transmission. • Node C therefore starts transmitting data to node A and a collision occurs at Node A. This is called hidden terminal problem. • Now consider a different scenario, 04.01.2021 KNCET 37 CSMA/CA • There are four nodes in the system, • If CSMA/CA is used, Node C detects a busy channel and waits until Node A’s transmission is over, resulting in a waste of bandwidth. • The hidden terminal problem can be solved by incorporating a request-to-send (RTS) and clear-to-send(CTS) handshake before data frame transmission. 04.01.2021 KNCET 38 CSMA/CA • When a node has a frame to send, it first broadcasts an RTS message carrying the time needed to transmit the frame. • The target node, if it is free, responds with CTS broadcast. • All other nodes that hear RTS or the CTS, mark the channel as busy for the duration of the requested transmission. • Thus collision due to hidden terminals can be avoided. • CSMA/CA is adopted in IEEE802.11 MAC , which has become the most popular protocol for single or multihop wireless networks. • The achievable maximum throughput(MT) under the best scenario when, • Channel is error free • Exactly one station is active during any transmission cycle 04.01.2021 KNCET 39 CSMA/CA • Where is the minimum back-off window size • - is the slot time 04.01.2021 KNCET 40 CSMA/CA • The data transmission delay and the ACK transmission delay is given by, IEEE 802. • The control overhead of IEEE 802.11 MAC is the main cause of the reduced throughput. By simply increasing the data rate of wireless links without reducing overhead, achievable throughput gain will be limited. 04.01.2021 KNCET 41 Network Layer Design • As cognitive radios have successfully established the links for opportunistic transmissions, the core function of a cognitive radio network lies in network layer design, especially routing, while other design issues such as flow control, network radio resource management and network mobility management are based around that routing. • A CRN node can be considered to be a node with a dynamic spectrum access capability and programmable multi-radio capability. • A CR node seeks and used the spectrum hole in multi-radio systems to forward packets in a self-organized way. • Prior to the routing of any CRN packets/traffic, the very first function of CRN network layer is association, which means cognitive radio node successfully accesses the CRN including PS(primary system). 04.01.2021 KNCET 42 Network Layer Design • After sensing possible transmission opportunities (i.e spectrum holes), a CR must complete association, and then execute dynamic spectrum access(DSA) through physical layer transmission and medium access control to send packets from CR transmitter to CR receiver. • The CR receiver can be a CR or a node in PS. ROUTING AND FORWARDING: • Routing and forwarding are the main functions of the network layer. • The IP modules in the hosts and the Internet routers are responsible for delivering packets from their sources to their destinations. 04.01.2021 KNCET 43 Network Layer Design • • • • It consists of two closely related parts: Maintaining network topology information Forwarding packets Hosts and routers must learn the network topology to know where the destinations are, by exchanging information on connectivity and the quality of network links. • Routing information is derived from network topology information and stored in a data structure called routing tables in hosts and router. • Routing tables are created and maintained either manually or by dynamic routing protocols. • When there is a packet to deliver, a hosts or router consults the routing table to find out where to forward the packet. 04.01.2021 KNCET 44 Network Layer Design • Each router relays a packet to the next hop that brings it closer to its destination. • FEATURES OF ROUTING IN CRN: • Link Availability: • CRN links are available under idle duration of the primary system so that DSA can effectively fetch such opportunities after successful spectrum sensing. • Links in CRN’s, involving CR as transmitters and receivers, allows the CRN topology to be random. • The link available period is in the range of milliseconds, as in wireless networking. • Unidirectional links: Typical wireless networks have bidirectional links because radio communication is half duplex. 04.01.2021 KNCET 45 Network Layer Design • CR node just have an opportunity for transmission from the other direction. • A link involving CR node is likely to be unidirectional • This distinguishes CRN from other wireless networks especially regarding the network layer functions. • Heterogeneous Wireless Networks: • CRN are generally formed by heterogeneous wireless networks(Co-existing primary systems and CR nodes to form ad-hoc networks). • Inter system handover is usually required for routing. • CR links might be available for an extremely short duration and the successful networking lies in cooperative relaying among heterogeneous wireless networks. 04.01.2021 KNCET 46 Network Layer Design • To ensure a CRN link is available for network layer functioning, we go back to hardware operation. • Assume that a genie observes CRN operation for both the PS and CR, the CR must use the spectrum hole window to complete transmission of packets. • A spectrum window period is denoted by , 04.01.2021 KNCET 47 Network Layer Design • Since the link is either available for opportunistic transmission or not available, considering the timings for the change of link availability we can adopt an embedded continuous time Markov chain and the rates specifying this continuous time can be obtained from the statistics of spectrum measurement. 04.01.2021 KNCET 48 Network Layer Design • Illustrates 2-state Markov chain with fixed timing, where A stands for “Link available” and N stands for “Link not available”. 04.01.2021 KNCET 49 Routing in cognitive radio networks • Trusted Cognitive Radio Networking: • We can introduce a trust mechanism in addition to typical network security schemes. • The security in CRN lies on the ground of end-to-end nodes and intermediate nodes in CRN can simply forward the CR traffic packets. • Such a cooperative relay of packets can be facilitated as amplify-and–forward (AF) and decode-and-forward(DF) • Compress-and-forward(CF) cooperative networking facilitate the security of the intermediate nodes due to mixing relay packets and own traffic together. • We can classify a node in CRN and traffic/control packets from such a node into three categories: 04.01.2021 KNCET 50 Routing in cognitive radio networks • Secure: The node has executed a security check that is good throughout the entire heterogeneous wireless networks, such as through a public key infrastructure(PKI) check. • A node classified as secure can be a CR • Trusted: • The level of security for trusted is not as effective as secure. • CR is generally not able to complete a security check of several rounds of the handshaking protocol within the timing window of an available link. • CR source code generates packets for opportunistic transmission and the CR receiver node recognizes a CR source node as trusted and can relay packets towards a CR sink node via appropriate routing mechanism. 04.01.2021 KNCET 51 Routing in cognitive radio networks • Lure: • CR node is neither secure nor trusted by its target receiving node and is classifies as lure. • The purpose of trust mechanism is to create a homogeneous networking functioning environment for heterogeneous wireless networks, and thus allow cooperative relay of packets in spite of the opportunistic and extremely dynamic link availability of CRN. • Some critical issues of the CRN network layer operation: • The CRN consists of CR and nodes from various co-existing primary systems operate using different communication parameters in different frequency bands in different geographical locations. SDR inside CR is capable of reconfigurable realization at multiple frequency bands. 04.01.2021 KNCET 52 Routing in cognitive radio networks • CR source code and CR destination node should conduct their own end-to-end security beyond trust level by employing CRN nodes to complete bidirectional verification. • CRN nodes are assumed to conduct only AF or DF cooperative relaying under the trust domain of CRN. • Nodes in the secure domain may reject relays from trusted nodes, which suggests that such links are not available in trusted network routing. Similarly nodes in trusted domain may reject connection requests from lure nodes. • Any packet from a CR source node, once getting into a primary system or infrastructure, follows the operation of the primary system to get benefits from existing systems and networks. 04.01.2021 KNCET 53 Routing in cognitive radio networks • For example, CR source code wishes to relay its packet through nearby wi-fi to access a website of the internet. • As long as the packets from the CR source node are allowed to the access point of the wi-fi, these packets transport as wi-fi packets. • A CR terminal device is capable of reconfiguring multiple physical layer transmissions and multiple medium access control schemes. • General CRN operation can be summarized as shown. • We have an infrastructure network as the core that might be the Internet, several radio access networks(RAN) that provide various ways to access the core infrastructure network. • Mobile stations(MS) are associated with certain RAN technology. 04.01.2021 KNCET 54 Routing in cognitive radio networks 04.01.2021 KNCET 55 Routing in cognitive radio networks • A CR may also be a MS of a PS. • Bidirectional links have double arrows , and all links in primary systems will be bidirectional. • Opportunistic links owing to CR dynamic spectrum access and certain ad-hoc links have single arrows • From CR source node, there are three different cooperative paths to transport the packets. • There are three cooperative paths to the CR sink as the final destination. 04.01.2021 KNCET 56 Routing of dynamic and unidirectional CR links in CRN • To conduct CRN routing over unidirectional CR links and usually bidirectional links in the primary system, we can extend on-demand routing protocols of MANET for CRN routing by the following: • Each CR link is modelled by a 2-state Markov chain, independent of other CR links. • Without knowing the specific PS, all the links are assumed bidirectional and can support our routing protocol. • Typical MANET routing algorithms are trying to isolate unidirectional links. • CR link might be unidirectional but reverse its direction on network situations 04.01.2021 KNCET 57 Routing of dynamic and unidirectional CR links in CRN • For routing in the CRN, we value one major purpose: • To reduce the latency of traffic due to more cooperative paths • CR sources are not able to transport packets to the CR destination node without CRN technology. • To forward the packet over an effective opportunistic CR link, towards the appropriate direction. • This matches the philosophy of reactive(on-demand) routing in ad-Hoc networks. • Each CR node executes routing only when there is a need (ondemand). 04.01.2021 KNCET 58 CRN On-demand Routing • The routing messages includes the following routing overhead information: • CR destination node IP • CR source node IP • Message ID 04.01.2021 KNCET 59 CRN On-demand Routing • When a new CR node or a new mobile station of the PS comes into scenario, we may not be able immediately to acquire the IP address, and so we can use an ID to serve . • CRNO routing consists of three phases in operation: • Sensing Phase • Path discovery phase • Table update phase 04.01.2021 KNCET 60 CRN On-demand Routing 04.01.2021 KNCET 61 Sensing Phase • The CR node listens to the radio environment, spectrum sensing of multiple co-existing systems(different frequency bands) to update its forward path table. • Forward path table records information regarding each potential CR receiver , estimate of its trust on the CR code and communication parameters to adjust the SDR. • Each potential CR receiver is identified by an IP address acquired from its past transmissions or by an ID designated by the CR node. • Communication system parameters can be obtained from spectrum sensing to adjust the SDR. 04.01.2021 KNCET 62 Path Discovery Phase • Once the CR node originates a packet/frame to the destination or receives a packet/frame for relay, it checks the backward path table for any violation. • In the case of no violation, CR node selects another CR node from the forward path table to relay the packet/frame. • The selection is based on the availability of CR links and the forward path table. • Links to the PS have the highest priority. • When a violation happens, CR relay node seeks an opportunity to “negative-acknowledge” the CR transmitter based on the backward path table. 04.01.2021 KNCET 63 Table Update Phase • In addition to link selection to complete the routing, a backward path route associated with this relay has to update as a part of the backward path table. • Each backward path route consists of parameters • Such as • Both are to specify the operation of co-existing multi-radio systems in CRN. • The violation is defined as the detection of either loop existence or dead-end existence. • plays its role in determining the existence of a loop. 04.01.2021 KNCET 64 Table Update Phase • Time-out to indicate that it is not possible to relay a packet is issued to avoid dead-end which is useful information to update the backward path-table • When negative acknowledge cannot trace back the way to CR source code, it is likely to be due to some permanent unidirectional links. • End-to-end timeout can terminate the routing and re-start a new round of routing, avoids the permanent unidirectional link. 04.01.2021 KNCET 65 Control of CRN • Flow control of CRN: • Flow control can happen in two types in CRN • End-to-end flow control between the CR source code and CR destination node is possible. • For successful operation of CRN on-demand routing protocols, we need flow control in the CRN network layer. • Flow control is primarily for damage control purposes. • Since it is not possible for us to ensure that neither dead-end or loop happens in AODV(Ad-Hoc On-Demand distance vector) • We have to detect these two cases and stop the CR link relaying packets under these scenarios, so that network bandwidth is not wasted. 04.01.2021 KNCET 66 Control of CRN • To achieve such a goal, loop detection and dead end detection are needed and associated with routing. • We can observe several segments and the packets are routed from the CR source node to the CR destination node through the following segments: • Uplink CRN • Co-existing multi-radio primary systems with infrastructure or core network(such as internet) may be considered to transport the packets quickly. • Downlink CRN • Cognitive Radio Relay Network(CRRN) can be considered as a special kind of CRN consisting of pure CRs with the only purpose of relaying packets. 04.01.2021 KNCET 67 Control of CRN 04.01.2021 KNCET 68 Control of CRN • The traffic flow can be categorized as follows: • ROUTING IN CRN BASED ON SEGMENTATION AND DECOMPOSITION: • For the uplink CRN, the routing will try to reach PS via opportunistic CR links. • When the CR relay node is in the process of selecting a forward path, it has a tendency to select the node closer to the PS, which is the node in RAN 1. • The routing will leave the PS via opportunistic CR links for the downlink CRN. 04.01.2021 KNCET 69 Control of CRN • CRN routing favours a way of forwarding packets that is effective for co-existing multi-radio systems. • A longer range primary system is to be favored in relaying packets for a CR relay node enhancing CRN routing efficiency. • END-TO-END ERROR CONTROL IN CRN: • The conventional concept of packet error control lies in the physical layer and data link layer • Error control will be useful in supporting CRN functions. • CRN routing tries to forward the packets and the CR sink receive multiple copies of one transmitted packet, and these copies of one packet might not be correct because no error protection other than forward error control(FEC) is available. 04.01.2021 KNCET 70 Control of CRN • The conventional network layer requires an extremely low packet error rate, which is warrented by physical layer FEC, CRC check and data link control. • For the CRN, data link control may or may not exist, and error control between the CR source code and sink node is needed, while re-transmissions will be minimized due to a much higher price than wireless networks. • We can borrow the idea from hybrid automatic request(HARQ) to conduct the CRN network layer error control, to significantly reduce the error control traffic significantly between the CR source node and CR destination node. • The challenge for HARQ in the CRN lies in the uncertain number of copies of a packet to be received at the CR destination node and in uncertain arrival times. 04.01.2021 KNCET 71 EC 8071- COGNITIVE RADIO UNIT-V ADVANCED TOPICS IN COGNITIVE RADIO Overview of security issues in cognitive radios, auction based spectrum markets in cognitive radio networks, public safety and cognitive radio, cognitive radio for Internet of Things 04.01.2021 KNCET 1 COGNITIVE RADIO NETWORK SECURITY-INTRODUCTION • CR is a revolutionary technology to alleviate the spectrum shortage problem and brings improvements in the efficiency of spectrum utilization. • Successful deployment of CR networks and realization of benefits depends on the placement of essential security mechanisms. • The emergence of the opportunistic spectrum sharing (OSS) paradigm and cognitive radio technology raises new security implications. 04.01.2021 KNCET 2 TAXONOMY OF SECURITY THREATS 04.01.2021 KNCET 3 OVERVIEW OF SECURITY THREADS TO INCUMBENT COEXISTENCE • Spectrum sharing or coexistence is an important attribute to CR networks. • CR networks support two types of coexistence: • Incumbent coexistence(coexistence between primary and secondary networks) • Self- coexistence (coexistence between secondary networks) • CR needs spectrum sensing to identify fallow spectrum bands, i.e) white spaces • Secondary users are permitted to operate in licensed bands only on a noninterference basis to the incumbent user. Secondary user that detect the presence of incumbent signal immediately switch to another band 04.01.2021 KNCET 4 OVERVIEW OF SECURITY THREADS TO INCUMBENT COEXISTENCE • On the other hand, if the secondary user detects the presence of a secondary user, it invokes a self-coexistence mechanism to share spectrum resources. • There are two types of security threads to incumbent coexistence: • Primary user Emulation(PUE) Attack: • A rogue secondary user attempts to gain priority over other secondary users by transmitting signals that emulate the characteristics of the incumbent’s signals. • Due to the programmability of CR, it is possible to modify the radio software of a CR to change its emission characteristics so that they resemble those of incumbent transmitter. 04.01.2021 KNCET 5 OVERVIEW OF SECURITY THREADS TO INCUMBENT COEXISTENCE • The potential impact of PUE attack depends on the legitimate secondary users ability to distinguish the attackers signals and actual incumbent signals while conducting spectrum sensing. • Another security issue threatens the reliability of the distributed spectrum sensing(DSS) process in CR networks. • In DSS, individual nodes send their local sensing data to a fusion center, which processes the data to determine a sensing decision. Byzantine Failures in DSS: • May be caused by either malfunctioning sensing nodes launching spectrum sensing data falsification(SSDF) attacks. 04.01.2021 KNCET 6 OVERVIEW OF SECURITY THREADS TO INCUMBENT COEXISTENCE • The incorrect spectrum sensing data are reported to the fusion center, which affects the accuracy of the sensing decision. • The goal of DSS is to make an accurate sensing decision after carrying out data fusion of local sensing results in the presence of failures. • Investigation of DSS Byzantine failures involves not only the study of data fusion techniques, but also interplay between the data fusion techniques and the spectrum sensing techniques. 04.01.2021 KNCET 7 OVERVIEW OF SECURITY THREADS TO SELF-COEXISTENCE • Self-coexistence mechanisms of CR network are defined as part of the network’s air interface. • Here we focus on self-coexistence mechanisms of IEEE 802.22 • IEEE 802.22 is the first standard for wireless access networks based on CR technology. • It specifies the air interface for a wireless regional area network that uses fallow segments of the UHF/VHF TV bands between 54 and 862MHz. • It is possible for a number of 802.22 cells to have overlapping coverage areas. 04.01.2021 KNCET 8 OVERVIEW OF SECURITY THREADS TO SELF-COEXISTENCE • If non-exclusive sharing is not feasible, then 802.22 WRAN needs to acquire spectrum resources through exclusive spectrum sharing via, the On-demand spectrum contention(ODSC) protocol. ODSC protocol: • ODSC process enables a cell to acquire better or more channels to support the quality of service of the admitted workloads. • Base station collects neighboring cells spectrum utilization information by receiving inter-cell control messages. • The control messages called inter-cell Beacon, are used by BS to exchange spectrum utilization information. • Inter-cell Beacon, are vulnerable to unauthorized modification, as they are not protected by 802.22’s security sub-layer. 04.01.2021 KNCET 9 RADIO SOFTWARE SECURITY THREADS • The flexibility and adaptability brought by modern software, low cost microprocessors and smart antennas have made software defined and cognitive radios a reality. • The emergence of software defined radio and software based CR have brought new security threads. • Without proper software protection mechanisms, CR are vulnerable to a host of attacks targeting the radio software. • The attacks in CR may include execution of malicious code, removal of software based authentication or access control functions, Intellectual property(IP) theft.etc… 04.01.2021 KNCET 10 PRIMARY USER EMULATION ATTACK (PUEA) • In dynamic spectrum access environment, the PU always uses the authorized frequency band and SU can utilize this spectrum band when PU is not using it. • In PUEA, the attacker generates fully similar type of signal as PU to make an error in frequency band and to confuse SU. • As an error, the SU, identifies the attacker as PU and vacate the spectrum band immediately. • This kind of attack is referred as PUEA. • In a multi-hop channel environment, if PUEA is launched and there is no idle channel for SU, then the call is dropped or delayed. 04.01.2021 KNCET 11 PRIMARY USER EMULATION ATTACK (PUEA) 04.01.2021 KNCET 12 PRIMARY USER EMULATION ATTACK (PUEA) • A dropped call results in unreliable communication and the delayed call degrades the quality of service. • Almost all the channels are affected by both malicious users and greedy users. • One of the major technical challenges in spectrum sensing, is the problem of sensing primary user signals from secondary user signals. • To distinguish the two signals, existing spectrum sensing schemes based on energy detectors, assume a naïve transmitter verification scheme. • Under such verification scheme, a malicious secondary user(an attacker) can exploit the spectrum sensing process. 04.01.2021 KNCET 13 PRIMARY USER EMULATION ATTACK (PUEA) • For instance, a PUE attacker may be as a primary user by transmitting unrecognized signals in one of the licensed bands thus preventing other secondary users from accessing that band. • There are alternative techniques for spectrum sensing, such as matched filter and cyclo-stationary feature detection. • Devices capable of such detection techniques are able to recognize the intrinsic characteristics of primary user signals, enabling them to distinguish signals from those of secondary users. 04.01.2021 KNCET 14 CLASSIFICATION OF PUE ATTACKS • Depending on the motivation behind the attack, PUE attack can be classified as selfish PUE attack or a malicious PUE attack. SELFISH PUE ATTACK: • An attackers objective is to maximize its own spectrum usage. • When selfish PUE attackers detects a fallow spectrum band, they prevent other secondary users from competing for that band by transmitting signals that emulate the signal characteristics of primary user signals. 04.01.2021 KNCET 15 CLASSIFICATION OF PUE ATTACKS MALICIOUS PUE ATTACK: • The objective of this attack is to obstruct the DSA process of legitimate secondary users. • Prevent legitimate secondary users from detecting and using fallow licensed spectrum bands causing denial of service. • Unlike a selfish attacker, a malicious attacker does not necessarily use fallow spectrum bands for its own communication purpose. 04.01.2021 KNCET 16 ROBUST DISTRIBUTED SPECTRUM SENSING • The Byzantine failure problem can be caused by spectrum sensing devices that are malfunctioning or carrying out spectrum sensing data falsification attacks. • A malfunctioning sensing terminal, is unable to conduct reliable spectrum sensing and may send incorrect sensing reports to the data collector. • In an SSDF attack, a malicious secondary user, intentionally sends falsified local spectrum sensing reports to the data collector to make incorrect spectrum sensing decisions. • Either case could cause interference to incumbent and result in underutilization of fallow licensed spectrum. 04.01.2021 KNCET 17 DISTRIBUTED SPECTRUM SENSING • Carrying out reliable spectrum sensing is a challenging task for CR. • In a wireless channel, signal fading result in “hidden node problem”. • The hidden node problem, in the context of CR networks is described as an instance in which secondary user in a CR network is within the protection region of an operating incumbent but fails to detect the existence of the incumbent. • Besides the hidden node problem, it is also possible for a secondary user to falsely detect an incumbent because of noise or interference in the wireless environment. • In DSS, each secondary acts as a sensing terminal that conducts local spectrum sensing. 04.01.2021 KNCET 18 DISTRIBUTED SPECTRUM SENSING • The results are reported to a data collector(or fusion center) that executes data fusion and determines the final spectrum sensing Byzantine Failure in Data fusion: • The DSS is vulnerable to a number of security threads. • In particular Byzantine failure is a major threat to data fusion process. • The Byzantine failure could be caused by either malfunctioning sensing terminals or an SSDF attack. • Both cases result in one or more sensing terminals sending false local spectrum sensing reports to a data collector, causing the data collector to make a wrong spectrum sensing decision. 04.01.2021 KNCET 19 AUCTION BASED SPECTRUM MARKETS IN COGNITIVE RADIO NETWORKS • Access to the radio spectrum is a key requirement for continuous wireless growth and deployment of new mobile services. • Fast growing demand for radio spectrum, regulators are implementing in a much more flexible and liberal forms of spectrum management, referred as dynamic spectrum management. • Spectrum trading is a market based approach for spectrum redistribution that enables a spectrum license holder to sell or lease all or a portion of its spectrum to a third party. 04.01.2021 KNCET 20 DYNAMIC SPECTRUM MICRO-AUCTIONS • Micro-auction mechanisms allow for the trading of spectrum rights at the network level • These auction mechanism could be highly attractive to network operators: They provide a flexible and cost-effective means for dynamic expansion of spectrum resources • The spectrum obtained through micro-auctions can be used for congestion relief during peak loads in traffic or enhance existing services and provide new services without the need for acquiring additional spectrum • Generally users will be able to dynamically and locally vary their operating frequencies and access the best available spectrum on a time basis. 04.01.2021 KNCET 21 DYNAMIC SPECTRUM MICRO-AUCTIONS THE ROLE OF COGNITIVE RADIOS: • Cognitive functionality is essential in the realization of microauctions because wireless devices can understand the regulatory, technical and economic context within which they perform the required negotiation and decision making tasks. • Access technologies such as OFDMA will play important role in enabling micro auction mechanisms. • These technologies support dynamic bandwidth availability and permit grouping, subdividing and pooling of pieces of the spectrum into neatly packaged spectrum channels. 04.01.2021 KNCET 22 DYNAMIC SPECTRUM MICRO-AUCTIONS MULTIPARTY TRADING WITH SPECTRUM USE: • Multiple providers can selectively offer their idle spectrum pieces and each spectrum piece can be sold to multiple small buyers. • The new market place can exploit spectrum reusability in spatial and temporal domains to improve spectrum usage efficiency. ON-DEMAND SPECTRUM TRADING: • Instead of forcing buyers to purchase predefined spectrum licenses, the new marketplace enables buyers to specify their own demands. • Such flexibility not only attracts a large number of participants but also enables the system to effectively improve spectrum utilization. 04.01.2021 KNCET 23 DYNAMIC SPECTRUM MICRO-AUCTIONS ECONOMIC ROBUSTNESS WITH SPECTRUM REUSE: • Without good economic design, spectrum auctions can be easily manipulated by bidders suffering huge efficiency loss. • Only by preventing market manipulation, auction can attract new entrants and efficiently distribute spectrum to make the best use of resources. ON-DEMAND SPECTRUM AUCTIONS: • On demand spectrum auction must distribute spectrum on the fly to large number of bidders • Spectrum auctions are multiunit auctions, where the spectrum is divided into number of identical channels for sale • An efficient allocation algorithm is also needed to distribute spectrum in real-time subject to the complex interference among bidders. 04.01.2021 KNCET 24 DYNAMIC SPECTRUM MICRO-AUCTIONS BIDDING FORMAT: PIECEWISE LINEAR PRICEDEMAND (PLPD) BIDS • Assume that there are totally k channels • is the set of channels assigned to bidder i • Normalized spectrum • • With the PLPD, bidder i expresses the desired quantity of spectrum at each per unit price Pi, using a continuous concave piecewise linear demand curve. • A simple example is a linear demand curve: 04.01.2021 KNCET 25 DYNAMIC SPECTRUM MICRO-AUCTIONS PRICING MODELS: • Without considering economic robustness, the auction pricing follows directly from each bidder’s bid. • Revenue produced by each bidder is a piecewise quadratic function • • • • Pricing model is divided into two types, Uniform pricing Discriminatory pricing Uniform pricing: The auctioneer chooses a single clearing price p for all the winners. • Discriminatory pricing: The auctioneer sets non-uniform clearing prices across bidders. 04.01.2021 KNCET 26 DYNAMIC SPECTRUM MICRO-AUCTIONS LINEARIZING THE INTERFERENCE CONSTRAINTS : • Consider two nodes i and j located at coordinates • Node i is to the left of node j, if • If , then the node with the smaller index is considered to be to the node to the left. ECONOMICALLY ROBUST SPECTRUM AUCTIONS: • By encouraging bidders to reveal their true valuations, a truthful auction can help the auctioneer increase its revenue by assigning the spectrum to the bidders who value it the most. • An efficient and truthful spectrum auction is one that is truthful and maximizes the efficiency of spectrum usage subject to the interference. 04.01.2021 KNCET 27 DYNAMIC SPECTRUM MICRO-AUCTIONS DOUBLE SPECTRUM AUCTIONS FOR MULTIPARTY TRADING: • In addition to truthfulness and spectrum reuse, a double spectrum auction must achieve two additional properties: individual rationality and budget balance. • A double auction is ex-post budget balanced if the auctioneers profit is • The profit is defined as the difference between the revenue collected from buyers and expense paid to sellers. • A double spectrum auction framework achieves the four required properties: • Spectrum reuse - Truthfulness • Individual rationality - Budget balance 04.01.2021 KNCET 28 DYNAMIC SPECTRUM MICRO-AUCTIONS • • • • • • Trust consists of three components: Grouping buyers Determining winners Pricing Grouping Buyers: TRUST groups multiple non-conflicting buyers into groups so that buyers in each group do not conflict and reuse the same channel. • Determining Winners: • For any group Gl with buyers, the group bid is, • TRUST sorts the seller bids in non-decreasing order and the buyer group bids in non-decreasing order 04.01.2021 KNCET 29 DYNAMIC SPECTRUM MICRO-AUCTIONS • Pricing: • To ensure truthfulness, TRUST pays each winning seller m by the kth seller’s bid and charges each winning buyer group l by the kth buyer group’s bid • This group price is evenly shared among the buyers in the group l: • With such pricing mechanism, auctioneers profit becomes • TRUST achieves 70-80% spectrum utilization of conventional spectrum allocation and TRUST sacrifices 50% of spectrum utilization in exchange for economic robustness. 04.01.2021 KNCET 30 PUBLIC SAFETY AND COGNITIVE RADIO • The communication system of rescue workers should always work even under extreme conditions. • Current day communication system used for public safety lack support for multimedia applications as it comes with low budget mass market cell phones. • Cognitive radio, is able to acquire this spectrum on the fly only when it is needed. • Many incompatible standards and new broadband services are main drivers for investigating how cognitive radio can be applied in this field. 04.01.2021 KNCET 31 PUBLIC SAFETY AND COGNITIVE RADIO • REQUIREMENTS: • Next generation communication system for public safety will have very extensive requirements. • These requirements are studied and specified by commissions such as SAFECOM in the united states and project MESA in Europe. • Communication Structure: • Public safety wireless network consists of a backbone network, base stations and handsets. • The backbone network is used for inter-base station communication • Each type of node has different physical layer requirements. 04.01.2021 KNCET 32 PUBLIC SAFETY AND COGNITIVE RADIO • For instance, emergency workers carry battery powered handsets that are energy limited. • For each communication software to be efficient and perfect for energy conditions, it should be reliable at all times. • RELIABILITY: • For emergency networks, reliability is an important issue. • There are two kinds of reliability: robustness and security • Robustness: • It is the ability of a system to avoid total failure despite unforeseen conditions or partial damage. • A public safety communication system should always be available, especially during large disasters. 04.01.2021 KNCET 33 PUBLIC SAFETY AND COGNITIVE RADIO • The network should have wide coverage in the whole service area including special coverage locations like tunnels. • The backbone of the network, should be very robust against failure. • Robustness can be obtained by having at least two independent backbone connections to each base station. • Security: • It is the ability of a system to withstand malicious attacks. • The communication should be secure against eavesdropping, spoofing and jamming. • In addition, handsets should not contain information that can help unauthorized users access the network. 04.01.2021 KNCET 34 PUBLIC SAFETY AND COGNITIVE RADIO • BROADBAND: • In an emergency situation a picture could say more than a thousand words. • Video is even more powerful in providing a clear impression of a complicated situation. • In next generation public safety communication equipment will provide advanced features like sensors for biomedical and environmental signals. • PAGING: • In paging communication, short, predetermined text messages are sent to mobile devices that are very important for public safety applications. 04.01.2021 KNCET 35 PUBLIC SAFETY AND COGNITIVE RADIO • Paging is even more important than voice communication, used for instance to alarm firefighters. • The advantage of such predefined messages is that they convey a lot of meaning in very few data bits. • Disadvantages of commercial wireless communication networks: • The network gets overloaded as a result the communication network may collapse. • When a disaster occurs, a part of the infrastructure may be damaged. • Commercial networks have no backup for the power supply. • Commercial networks lack coverage in rural areas, tunnels and metro stations. 04.01.2021 KNCET 36 BENEFITS OF COGNITIVE RADIO RELATED TO EMERGENCY CONDITION • Cognitive radio is a smart device that does all kinds of useful things for its owner, based on sensory input and machine learning. • It is a radio that can opportunistically use white space in licensed bands without causing interference. • There are several benefits of cognitive radio technology. • Communication with other networks: • Currently there exists multiple public safety standards. • When a large disaster occurs at the border of countries, these countries face huge challenge if they use different technologies. • Cognitive radio will support for military standards and other public safety standards. 04.01.2021 KNCET 37 BENEFITS OF COGNITIVE RADIO RELATED TO EMERGENCY CONDITION • Backwards compatibility: • Because of large investments and relatively small market, legacy systems are replaced slowly and coexists with new communication networks for a long time. • Cognitive radio allows an upgrade of the existing equipment to this new release without replacing the hardware. • Introduction of New Services: • New services could be enabled more easily by cognitive radio. • As it can adjust its parameters according to the requirements of the new service without any limitations. 04.01.2021 KNCET 38 BENEFITS OF COGNITIVE RADIO RELATED TO EMERGENCY CONDITION • Improved Reliability: • A Cognitive radio always tries to minimize interference to other networks by changing its frequency if other signals are present. • Adaptability feature automatically makes a cognitive radio more resilient to jamming. • Enabling Broadband: • In case of emergency, public safety networks are heavily used and there is demand for more capacity. • Implementing the whole network would be very costly. • A different approach to sense empty frequency bands(white space) and use it as a secondary user is to set up an auxiliary communication network. 04.01.2021 KNCET 39 PUBLIC SAFETY COMMUNICATIONSTANDARDS • Several communication standards have been developed for public safety applications. • P25(APCO Project 25), TETRAPOL and TETRA. • APCO Project 25 systems are used by the federal, state and local public safety agencies in North America. • TETRAPOL is one of the first digital public safety standards developed in France, used by French Gendarmerie Nationale • Terrestrial trunked mobile radio (TETRA) communication network was developed and is used in European countries. • TETRA: • It is known as trans-European trunked radio. TETRA was specifically designed for use by government agencies, emergency services(police forces, fire dept.and ambulance) 04.01.2021 KNCET 40 PUBLIC SAFETY COMMUNICATIONSTANDARDS • • • • • • • TETRA system supports several types of data communication: Status messages Short data services Packet data Circuit switched data communication Uses TDMA with four user channels on one radio carrier Both point-to-point and point-to-multipoint transfer can be used. • All voice and data traffic is protected by encryption C2000: • The public safety communication network in Netherlands is called C2000. 04.01.2021 KNCET 41 PUBLIC SAFETY COMMUNICATIONSTANDARDS • T2000: • A TETRA based network for voice and low rate data communication uses the frequency band 380-385 MHz for uplink and 390-395 MHz for downlink communication. • Uses both direct mode and trucked radio mode. • For special coverage locations like tunnels and stadiums, the system has additional low power base stations. • To facilitate helicopters and airplanes, TETRA AGA(airground-air services) was constructed. • P2000: • Paging is a very important communication application in public safety, where short predetermined text are transmitted and displayed on pager devices.eg. Used as alarm for firefighters 04.01.2021 KNCET 42 PUBLIC SAFETY COMMUNICATIONSTANDARDS • M2000: • It is a software system used in public safety answering point(PSAP). • It is a call center responsible for answering calls to an emergency phone number for police, firefighting and ambulance services. • It helps to identify which resources should be allocated to emergency. • It acts as an help desk in talk groups and also monitors it to use in network management and network planning. • C2000 network fulfills all important public safety but lacks support for multimedia/broadband internet communication. 04.01.2021 KNCET 43 APPLICATION OF COGNITIVE RADIO • The requirements for the next generation system include features that require broadband communication. • Cognitive radio provide a means to find the required bandwidth. • Public safety agencies have desperately needed additional spectrum allocation to ease frequency congestion and enhance interoperability. • These problems can be mitigated through the use of cognitive radio technology. • For emergency and public service providers, major part is spectrum sharing which helps in maintaining call priority and response time. • CR improves interoperability between different frequencies and modulation formats. 04.01.2021 KNCET 44 APPLICATION OF COGNITIVE RADIO • Cognitive radio technology caught the attention of the US department of justice which employed the national public safety telecommunications council(NPSTC) to aid with public safety communication issues. • NPSTC effort focuses to expand spectrum allocation and reuse • CR can prove to be more effective by utilizing some of the existing spectrum that is not widely used. • PROPAGATION CONDITIONS: • Determine how far a radio wave propagates. • A high path loss allows more spectrum reuse.i.e spectrum usage increases. • For CR, a high path loss is better, because it reduces the area in which interference can be caused. 04.01.2021 KNCET 45 APPLICATION OF COGNITIVE RADIO • SYSTEM SPECTRAL EFFICIENCY: • A wireless communication system should use the spectrum in an efficient manner. • System spectral efficiency can be defined as, • • • • R – Bit rate B – Bandwidth K – Cluster size R/B can be considered as the link spectral efficiency 04.01.2021 KNCET 46 APPLICATION OF COGNITIVE RADIO 04.01.2021 KNCET 47 APPLICATION OF COGNITIVE RADIO 04.01.2021 KNCET 48 APPLICATION OF COGNITIVE RADIO 04.01.2021 KNCET 49 APPLICATION OF COGNITIVE RADIO 04.01.2021 KNCET 50 IOT • IOT integrates the interconnectedness of human culture – out things with the interconnectedness of our digital information system – the internet • Four stages of IOT: • Stage 1: Networked things(wireless sensors and actuators) • IOT should be equipped with sensors and actuators thus giving the ability to emit, accept and process signals. • Stage 2 (Sensor data aggregation systems and analog to digital data conversion) • Data from the sensors starts in analog from which needs to be aggregated and converted into digital streams. • Process the enormous amount of information collected on the previous stage and optimize it. 04.01.2021 KNCET 51 IoT • Stage 3 (Edge Analytics) • Once IoT data has been digitized and aggregated, it requires further processing before it enters data fusion. • For example: machine learning and visualization technologies. • Stage 4(Analysis, Management, and storage of data at cloud Analytics) • Data that need more in-depth processing get forwarded to physical data centers or cloud-based systems. 04.01.2021 KNCET 52 Cognitive radio for IoT 04.01.2021 KNCET 53 Cognitive radio for IoT 04.01.2021 KNCET 54 Cognitive radio for IoT 04.01.2021 KNCET 55 COGNITIVE IOT FRAMEWORKS 04.01.2021 KNCET 56 COGNITIVE IOT FRAMEWORKS 04.01.2021 KNCET 57 COGNITIVE IOT FRAMEWORKS 04.01.2021 KNCET 58 STANDARDIZATION EFFORTS IN CR BASED IOT 04.01.2021 KNCET 59 SECURITY AND PRIVACY RELATED TO CR-IOT 04.01.2021 KNCET 60 SECURITY AND PRIVACY RELATED TO CR-IOT 04.01.2021 KNCET 61