1 chapter 4 spectrum sensing and identification cognitive radio communications and networks:...
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Chapter 4
Spectrum Sensing and Identification
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
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Outline
Introduction Primary Signal Detection Spectrum Opportunities Detection Performance vs. Constraint Sensing Accuracy vs. Sensing
Overhead
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
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Introduction
Limited supply
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
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Introduction
Growing demand
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Current Policy & Spectrum Scarcity
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“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Spectrum Opportunitiesin Space, Time, & Frequency
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(Credit: DARPA XG) (Credit: ACSP Cornell)
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Primary Signal Detection
Choice of detectors Criteria:
Bayesian Neyman-Pearson Parameter settings?
Energy detection Pros: easily implemented; minimal assumptions Cons: poor performance with noise uncertainty and with
multiple secondary users Performance ∼ 1/SNR2 at low SNR
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“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Choice of Detectors - Cyclic Detectors (2) Exploit guard bands in frequency, known carriers, data
rates, modulation type Pros:
fc, Ts easy to detect via square-law devices, or cyclic approaches
Cyclic approaches useful when σ2n is unknown (avoid SNR wall)
Easily implemented via FFTs Cons:
Timing and frequency jitter can be detrimental Requires long integration times RF non-linearities; Spectral leakage (ACI).
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“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Choice of Detectors: Matched Filter (3)
Exploit pilots or sync (PN) sequences in primary (WRAN 802.22)
Pros: Correlation detection is usually better than energy
detection. Performance ∼ 1/SNR at low SNR
Cons: fading may null pilot; need to cope with time and freq
sync
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“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Other Detectors Receiver leakage Wild-Ramachandran, Dyspan’05 Signal correlation Zeng et al, PIMRC’07 Fast fading Larson-Regnoli, CommLett’07 Multiple antennas Pandhripande-Linnartz, ICC’07 HMM classifier Kyouwoong et al, Dyspan’07 Wavelet-based Tian-Giannakis, CrownCom’06 Multi-resolution sensing Neihart-Roy-Allstot, ISCAS’07 Compressed sensing Tian-Giannakis, ICASSP’07
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“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Spectrum Opportunities Detection
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A channel is an opportunity for A − B if
• the transmission from A to B can succeed
• the interference power to primary is below a prescribed level
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Spectrum Opportunity: Definition
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A channel is an opportunity for A − B if
• the transmission from A to B can succeed
• the interference power to primary is below a prescribed level
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Spectrum Opportunity: Definition
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A channel is an opportunity for A − B if
• the transmission from A to B can succeed
• the interference power to primary is below a prescribed level
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Spectrum Opportunity: Properties
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• Determined by both transmitting and receiving activities of primary users.
• Asymmetric (an opportunity for A−B may not be one for B−A).
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Detection of Primary Receivers
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• rI: interference range, Rp: primary tx range, rD: detection range
• Detecting primary Rx within rI by detecting primary Tx within rD
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Detecting Primary Signals (LBT)
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• rD: detection range.• H0: no primary Tx within rD, H1: alternative.• False alarms and miss detections occur due to noise and fading.
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
From Detecting Signal to Detecting Opportunity
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• H0: opportunity, H1: alternative.• Even with perfect ears, exposed Tx(X) ⇒ FA, hidden Rx(Y) ⇒ MD.• Adjusting detection range rD leads to different operating points.
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
When Is Detecting Signal = Detecting Opportunity?
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A Necessary and Sufficient Condition:
• NS condition: ∀X ∈ Ptx(A) ∩ Pctx(B), its receivers are in Prx(A)
• Perfect detection achieved when detecting Ptx(A) ∪ Ptx(B)
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Miss Detection May not Lead to Collision
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• There is no primary receiver around A
• There are primary transmitters around B
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Miss Detection May Lead to Success
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• There are primary receivers around A
• There is no primary transmitter around B
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Correctly Identified Opportunity May Not Lead to Success
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• Successful data transmission and failed ACK
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Performance vs. Constraint
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Performance Optimal under relaxed constraint on the
average number of active arms. Asymptotically optimal (N →∞ w. M/N
fixed) under certain conditions. Near optimal performance observed from
extensive numerical examples.
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Performance vs. Constraint
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Two Models Global Interference Model Local Interference Model
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Performance vs. Constraint
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Throughput comparison.
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Sensing Accuracy vs. Sensing Overhead
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Optimal sensing time: efficiency η versus sensing window length n for various SNRs and PMD.
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
Sensing Accuracy vs. Sensing Overhead
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Optimal sensing time: efficiency η and optimal window length n∗/N versus slot length N.
“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
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Chapter 4 Summary
The following topics have been covered: Different types of detectors for primary signal
detection Detection of spectrum opportunities based on
the detection of primary signals. The trade-off between performance and
interference constraint. The trade-off between sensing accuracy and
sensing overhead.