Dar es Salaam institute of Technology (DIT) ETCT 06204 Digital Cellular Network Ally, J jumannea@gmail.com DIT Course Material ◼ Text: Wireless Communications: Principles and Practice by T. Rappaport ◼ References ❑ From GSM to LTE by Martin Sauter ❑ Wireless Communications by Andrea Goldsmith ❑ Wireless Communications by Roy Blake ❑ Wireless & Mobile Networks Architecture by Yi Bing and Imrich Chlamtac ❑ Wireless Communications and Networks by W. Stallings DIT Course Syllabus ◼ Introduction to Cellular Mobile Communication ◼ The Cellular Concept-System Design Fundamentals ◼ Multiple Access Techniques for Wireless Communication ◼ GSM/GPRS/EDGE Networks ◼ UMTS/HSPA/HSPA+ Networks ◼ LTE/LTE Advanced Networks ◼ 5G Network DIT Introduction to Cellular Mobile Communications DIT Wired Vs. Wireless Communication Wired Wireless Each cable is a different channel One media (cable) shared by all Signal attenuation is low High signal attenuation No interference High interference noise; co-channel interference; adjacent channel interference DIT Why go Wireless? Advantages ◼ Sometimes it is impractical to lay cables ◼ User mobility ◼ Cost Limitations ◼ Restricted frequency range ◼ Standards are often restricted ◼ Security DIT Objectives of Wireless Systems ◼ Large Capacity ◼ Efficient use of Resources (Spectrum) ◼ Adaptability to traffic density ◼ Quality of Service ◼ Affordability DIT Mobile Radio Communication Systems ◼ Garage door openers ◼ Remote controllers ◼ Cordless phones ◼ Hand held walkie-talkie ◼ Pagers ◼ Cell telephones These systems differ in cost, complexity, performance and application. DIT What is wireless communication? ◼ Any form of communication that does not require the transmitter and receiver to be in physical contact ◼ Electromagnetic wave propagated through freespace ◼ Radar, RF, Microwave, Optical (infrared, Laser). DIT Classification of Mobile Radio Communication Systems ◼ ◼ ◼ ◼ Simplex Systems: Only one way communication possible. Messages can be received but not acknowledged. (paging systems) Half-Duplex Systems: 2 way communication possible but the same radio channel used for both transmission and reception. At any given time a user can only transmit or only receive information; “Push to talk” and “release to listen” systems. Full-Duplex Systems: Allow simultaneous transmission and reception b/w subscriber and Base Station Simultaneous transmission and reception are achieved by: ❑ ❑ Frequency Division Duplex (FDD) Time Division Duplex (TDD) DIT Frequency Division Duplex (FDD) ◼ It provides simultaneous radio transmission channels for the subscriber and the base station, so that they both may constantly transmit while simultaneously receiving signals from one another. ◼ Uses a pair of frequency bands – one for Downlink (Forward) Channel and another for Uplink (Reverse) Channel. ◼ Downlink Channel (Forward Channel): used for transmission of information from Base Station to Mobile. ◼ Uplink Channel (Reverse Channel): used for transmission of information from Mobile to Base Station. DIT Time Division Duplex (TDD) ◼ Shares a single radio channel in time ➢ a portion of the time is used to transmit from Base station to mobile ➢ the remaining time is used to transmit from mobile to Base Station ◼ TDD is only possible with digital transmission format and digital modulation, and is very sensitive to timing. ◼ Used only for indoor or small area wireless application where the physical coverage distance are much smaller than the many kilometers used in conventional cellular telephone systems. DIT Paging Systems ◼ Broad coverage for short messaging Message broadcast from all base stations ◼ Simple terminals ◼ Optimized for 1-way transmission ◼ Answer-back hard ◼ Overtaken by cellular ◼ DIT Cordless Telephone Systems ◼ ◼ ◼ It is full duplex communication systems that use radio to connect a portable handset and a dedicated Base Station, which is then connected to a dedicated telephone line with a specific telephone number on a Public Switched Telephone Network (PSTN). First generation base station provides coverage to a few tens of meters. Second generation base station provides coverage to a few hundred meters. Wireless Link PSTN Fixed Port (Base Station) Cordless Handset DIT Cellular Telephone Systems ◼ A cellular telephone system provides a wireless connection to the PSTN for any user location within the radio range of the system. ◼ Accommodate large number of users over a large geographical area, within limited frequency spectrum. ◼ Provide high quality service comparable to landline telephone systems DIT Examples of Mobile Radio Systems DIT Mobile Communications Systems Definitions ◼ ◼ ◼ ◼ ◼ ◼ ◼ ◼ ◼ Base Station: a fixed station in a radio mobile system used for radio communication with mobile stations. Mobile Station: a station in the cellular radio service intended for use while in motion at unspecified location. Mobile Switching Centre (MSC): it connects the cellular base stations and the mobiles to the (Public Switching Telephone Network (PSTN). Control Channel: radio channels used for transmission of call setup, call request, call initiation, and other beacons or control purposes. Handover (Handoff): the process of transferring a mobile station from one channel or base station to another. Page: a brief message which is broadcast over the entire service area, usually in simulcast fashion by many base stations at the same time. Roamer: a mobile station which operates in a service area (market) other than that which service has been subscribed. Subscriber: a user who pays subscription charges for using a mobile communication system. Transceiver: a device capable of simultaneously transmitting and receiving radio signals. DIT Important First Generation Analog Systems Type AMPS ETACS NTT Region America Europe Japan Multiple access FDMA FDMA FDMA Duplexing FDD FDD FDD Forward band 869 - 894 MHz 935 – 960 MHz 870 – 885 MHz Reverse band 824 – 849 MHz 890 – 915 MHz 925 – 940 MHz Channel spacing 30 KHz 25 KHz 25 KHz No. of channels 831 1000 600 DIT Second Generation (2G) Cellular Networks ◼ ◼ ◼ ◼ Most of today’s ubiquitous cellular networks in use 2G technologies which conform to the second generation cellular standards It uses TDMA/FDD and CDMA/FDD multiple access techniques Most popular 2G standard are: ❑ ❑ ❑ ❑ Global System Mobile (GSM) – TDMA (Europe) Interim Standard 136 (IS-136) – TDMA (North America) Pacific Digital Cellular (PDC) – TDMA (Japan) Interim Standard 95 Code Division Multiple Access (IS95 CDMA) – CDMA (North America) DIT Important Second Generation Digital Systems Type IS-136 IS-95 GSM PDC Region America America Europe Japan Multiple access /Duplexing TDMA/FDD CDMA/FDD TDMA/FDD TDMA/FDD Modulation /4 DQPSK QPSK/OQPSK GMSK /4 DQPSK Forward Band 869 - 894 MHz 869 - 894 MHz 935 – 960 MHz 810 – 826 MHz Reverse Band 824 – 849 MHz 824 – 849 MHz 890 – 915 MHz 940 – 956 MHz Channel Spacing 30 KHz 1.25 MHz 200 KHz 25 KHz Data/chip Rate 48.6 Kbps 1.2288 Mcps 270.833 Kbps 42 Kbps Codec Rate Kbps 7.95 1.2/2.4/4.8/9.6 13.4 6.7 Users/channel 3 Up to 64 8 3 DIT 3G Cellular Design: Voice and Data ◼ Data is bursty, whereas voice is continuous ❑ ◼ Typically require different access and routing strategies 3G “widens the data pipe”: ❑ ❑ ❑ ❑ 384 Kbps (802.11n has 600 Mbps) Standard based on wideband CDMA Packet-based switching for both voice and data 3G cellular popular in Asia and Europe DIT 4G/LTE/IMT Advanced ◼ Much higher peak data rates (100-1000 Mbps) ◼ Greater spectral efficiency (bits/s/Hz) ◼ Flexible use of up to 100 MHz of spectrum ◼ Low packet latency (<5ms). ◼ Increased system capacity ◼ Reduced cost-per-bit ◼ Support for multimedia DIT Cellular Phones Everything Wireless in One Device DIT Challenges ◼ Network Challenges ❑ ❑ ❑ ❑ ❑ ◼ Scarce spectrum Demanding/diverse applications Reliability Ubiquitous coverage Seamless indoor/outdoor operation Device Challenges ❑ ❑ ❑ ❑ Size, Power, Cost Multiple Antennas in Silicon Multiradio Integration Coexistance DIT Simplified picture of most important evolution paths from 2G technologies (e.g., GSM) to 4G technologies (e.g., LTE-Advanced) DIT DIT
