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1 Chapter 4 Spectrum Sensing and Identification Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y.

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Presentation on theme: "1 Chapter 4 Spectrum Sensing and Identification Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y."— Presentation transcript:

1 1 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)

2 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) 2 Outline Introduction Primary Signal Detection Spectrum Opportunities Detection Performance vs. Constraint Sensing Accuracy vs. Sensing Overhead

3 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) 3 Introduction Limited supply

4 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) 4 Introduction Growing demand

5 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Current Policy & Spectrum Scarcity 5

6 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Spectrum Opportunities in Space, Time, & Frequency 6 (Credit: DARPA XG) (Credit: ACSP Cornell)

7 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 7

8 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). 8

9 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 9

10 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, Dyspan05 Signal correlation Zeng et al, PIMRC07 Fast fading Larson-Regnoli, CommLett07 Multiple antennas Pandhripande-Linnartz, ICC07 HMM classifier Kyouwoong et al, Dyspan07 Wavelet-based Tian-Giannakis, CrownCom06 Multi-resolution sensing Neihart-Roy-Allstot, ISCAS07 Compressed sensing Tian-Giannakis, ICASSP07 10

11 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Spectrum Opportunities Detection 11 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

12 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Spectrum Opportunity: Definition 12 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

13 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Spectrum Opportunity: Definition 13 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

14 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Spectrum Opportunity: Properties 14 Determined by both transmitting and receiving activities of primary users. Asymmetric (an opportunity for AB may not be one for BA).

15 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Detection of Primary Receivers 15 rI: interference range, Rp: primary tx range, rD: detection range Detecting primary Rx within rI by detecting primary Tx within rD

16 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Detecting Primary Signals (LBT) 16 rD: detection range. H0: no primary Tx within rD, H1: alternative. False alarms and miss detections occur due to noise and fading.

17 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 17 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.

18 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? 18 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)

19 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 19 There is no primary receiver around A There are primary transmitters around B

20 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 20 There are primary receivers around A There is no primary transmitter around B

21 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 21 Successful data transmission and failed ACK

22 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Performance vs. Constraint 22 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.

23 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Performance vs. Constraint 23 Two Models Global Interference Model Local Interference Model

24 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) Performance vs. Constraint 24 Throughput comparison.

25 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 25 Optimal sensing time: efficiency η versus sensing window length n for various SNRs and PMD.

26 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 26 Optimal sensing time: efficiency η and optimal window length n /N versus slot length N.

27 Cognitive Radio Communications and Networks: Principles and Practice By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009) 27 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.


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