‫دانشگاه صنعتي اصفهان‬
‫دانشكده برق و كامپيوتر‬
‫‪Cognitive Radio‬‬
‫ارائه کننده ‪:‬‬
‫محسن نادرطهرانی‬
‫ارائه مقاله تحقيقي در درس‬
‫” رادیو نرم افزاری “‬
‫مدرس‪ :‬دکتر محمد جواد اميدی‬
‫نيمسال بهار ‪1385-1386‬‬
‫‪1‬‬
Agenda

Introduction
Cognitive radio
 cognitive capabilities
 reconfigurability
Spectrum sensing
Spectrum management
Spectrum mobility
Spectrum sharing
Physical Layer
 TESTBED ARCHITECTURE AND IMPLEMENTATION
Collaborative Spectrum Sensing for Opportunistic Access in Fading Environments

passive primary receiver detection
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Cognitive radio


Today’s wireless networks are characterized by a fixed
spectrum assignment policy.
The limited available spectrum and the inefficiency in the
spectrum usage necessitate a new communication paradigm to
exploit the existing wireless spectrum opportunistically
3
Cognitive radio definition

Cognitive radio systems offer the opportunity to improve
spectrum utilization by detecting unoccupied spectrum bands
and adapting the transmission to those bands while avoiding
the interference to primary users.

A Cognitive Radio (CR) is an SDR that additionally senses its
environment, tracks changes and reacts upon its findings.
4
Introduction : cognitive radio

Cooperative functionalities
 Spectrum sensing & spectrum sharing
 Spectrum management & spectrum
mobility with all layers
5
Cognitive radio

Cognitive capabilities
 Capture information from radio environment
 Temporal & spatial variations in radio environment
 Interference avoidance

Reconfigurability
 Dynamically programmed according to radio environment
 Different transmission access technique
6
Cognitive radio: cognitive
capabilities
Cognitive capabilities :
 Real time interaction with its environment
 Determine appropriate communication parameters
 Adopt to dynamic radio environment
7
Cognitive radio: cognitive
capabilities
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Spectrum sensing


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Spectrum analysis

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Estimating the characteristics of spectrum holes
Spectrum decision
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Monitoring available spectrum bands
Capture their information
Detects the spectrum holes
Determining the data rate
Transmission mode
Bandwidth of transmission
Choosing spectrum band


Spectrum characteristics
User requirement
8
Cognitive radio : reconfigurability

reconfigurability : Capability of adjusting operating parameters
for transmission
 Operating frequency
 Modulation
 User requirements
 Channel condition
 Transmission power
 Communication technology
9
Spectrum sensing

Adopt to its environment by detecting spectrum holes
Detect the primary users receiving data
Hard to have a direct measurements of a channel between
primary receiver & transmitter
Primary transmitter detection
 Matched filter detection
 Energy detection
 Cyclostationary feature detection
Cooperative detection

Interference-based detection
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Spectrum management


Spectrum sensing
Spectrum analysis

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Operating frequency
Bandwidth
Interference level
Path loss
Wireless link error
 Modulation scheme
 Interference level
 Link layer delay
 Different protocols at different spectrum bands, different
packet transmission delay
 Holding time

Spectrum decision
 QoS requirements
 Spectrum characteristics
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Spectrum mobility: spectrum handoff



Spectrum mobility
 Channel condition becomes worse
 Primary user appears
Protocols of different layer of the network
 Adopt to the channel parameters of operating frequency
 Transparent to spectrum handoff and its associated latency
Shifting from one mode of operation to another
 Smoothly
 As soon as possible
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Spectrum sharing
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Spectrum sharing process
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Spectrum sensing
Spectrum allocation
Spectrum access
Transmitter-receiver handshake
Spectrum mobility
Spectrum sharing techniques
 Architecture assumption
 Centralized
 Distributed
 Spectrum allocation behavior
 Cooperative
 Non-cooperative
 Spectrum access technique
 Overlay
 The FCC has legalized this type of sharing in the 5GHz band and is
considering whether to allow it in theTV broadcast bands
 underlay
13
Physical Architecture of the Cognitive Radio
14
Dynamic Range Reduction for ADC


Notch filter
Phase array antenna
15
Modulation
•
Physical Layer: OFDM
Transmitter structure and spectrum
bit
sequence
1
m
Cod
d(l)
N
parallel-to-serial conversion
Cod
...
...
dr(l)
IDFT(FFT)
Cod
1
m
f
d1(l)
...
...
m
...
serial-to-parallel conversion
1
D/A
RFMod.
xRF (t)


x MT(t)
f
f 3
f 2
f 1
f0
f1
f2
f3
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OFDM challenges

co-channel and adjacent channel interferers

There are several spectrum shaping techniques that could be
used to improve OFDM spectral leakage:
 Introducing guard bands
 Windowing
 Power control per sub-carrier
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TESTBED ARCHITECTURE AND
IMPLEMENTATION

Berkeley Emulation Engine 2 (BEE2), which is a generic,multi-purpose, FPGA
based, emulation platform for computationally intensive applications.

Each BEE2 can connect to 18 front-end boards via multi-gigabit interfaces.

The BEE2 consists of 5 Vertex-2 Pro 70 FPGAs.
Each FPGA can be connected to 4GB of memory with a raw memory
throughput of 12.8Gps
All computation FPGAs are connected to the control FPGA via 20 Gbps
links.


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Modular front-end system

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The analog/baseband board contains the filters, ADC/DAC chips and a
Xilinx Vertex-II Pro FPGA
Digital-to-analog conversion is performed by a 14-bit DAC running up to
128MHz while analog-to-digital conversion is performed by a 12-bit ADC
running up to 64MHz.

The FPGA performs data processing and control, and supports 4 optical
1.25 Gbs links for transmitting and receiving data to/from BEE2

A separate RF modem module connects to the baseband board.

The RF frequency is fully programmable in the entire 80MHz ISM band.
19
Collaborative Spectrum Sensing for Opportunistic
Access in Fading Environments
20
Fading environment


Log-normal Shadowing
Rayleigh Fading
21
Collaborative Spectrum Sensing



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In order to improve performance of spectrum sensing, we allow different secondary
users to collaborate by sharing their information.
In order to minimize the communication overhead, users only share their final 1-bit
decisions (H0 or H1) rather than their decision statistics
Let n denote the number of users collaborating. For simplicity we assume that all n
users experience independent and identically distributed (iid) fading/shadowing
with same average SNR
A secondary user receives decisions from n−1 other users and decides H1
if any of the total n individual decisions is H1. This fusion rule is known as
the OR-rule or 1-out-of-nrule
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Probabilities of detection and false-alarm
Probabilities of detection and false-alarm for the collaborative scheme
(denoted by Qd and Qf respectively) may be written as follows :
where Pd and Pf are the individual probabilities of detection and false-alarm
This collaborative scheme increases probability of detection as well as
probability of false-alarm
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Probabilities of detection and false-alarm
24
COLLABORATIVE SPECTRUM SENSING UNDER
SPATIALLY-CORRELATED SHADOWING

shadowing correlation would degrade performance of collaborative sensing
when collaborating users are close
25
Question ?
 How
valid is the passive primary
receiver assumption?
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LO Leakage

We explore the possibility of detecting primary receivers by
exploiting the local oscillator (LO) leakage power emitted by
the RF front end of primary receivers

Modern day radio receivers are based to a large extent on the
superheterodyne receiver architecture invented by Edwin
Armstrong in 1918
27
LO Leakage Table

Over the years, improvements have been made to receiver
architectures, resulting in reduced LO leakage power.
28
Detection of LO Leakage

Detecting this leakage power directly with a CR would be
impractical for two reasons.

Firstly, it would be difficult for the receive circuitry of the CR
to detect the LO leakage over larger distances.

The second reason that it would be impractical to detect the
LO leakage directly is that the LO leakage power is very
variable, depending on the receiver model and year
29
Sensor Node

We propose to build tiny, low cost sensor nodes that would be
mounted close to the primary receivers

The node would first detect the LO leakage to determine
which channel the receiver was tuned to.

It would then relay this information to the CR through a
separate control channel using a fixed power level.
30
Sensor Architectire

Several detection schemes exist to detect low energy signals.

Regardless of the detection scheme, the front-end
architecture of the node will be the same
31
Integration time vs. probability of error
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PERFORMANCE IMPROVEMENTS

There is no guarantee that a channel will be available

Assumption
 Density of the primary receivers: D/km2
 Number of channels: M
 Interference Radius of CR: R
 All of the channels are equally likely to be used at any instance of time
and the receivers are uniformly distributed
33
At a receiver density of 10,000/km2 and an interference
radius of 250m the probability is 0.99 that at least one
channel is available
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EXPERIMENTAL RESULTS
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Refrence

[1]Software Define Radio Course Dr. Omidi.M.J.

[2]Detecting primary receivers for cognitive radio applications Wild, B.; Ramchandran,
[3] Physical layer design issues unique to cognitive radio systems Cabric, D. Brodersen, R
[4] Some physical layer issues of wide-band cognitive radio systems Haiyun Tang
[5] Collaborative spectrum sensing for opportunistic access in fading environments



Ghasemi, A.; Sousa, E.S.



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[6] Device-centric spectrum management Haitao Zheng Lili Cao
[7] Cognitive radio for flexible mobile multimedia communications Mitola, J.,
[8]Cognitive radio: brain-empowered wireless communications Haykin, S.
[9] Cognitive Radio An Integrated Agent Architecture for Software Defined Radio
Dissertation Doctor of Technology Joseph Mitola III
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