Performance Analysis of Energy Detector in Relay Based Cognitive Radio Networks

1. Performance Analysis of Energy Detector in Relay Based Cognitive Radio Networks Saman Atapattu Chintha Tellambura Hai Jiang

2. Outline • Introduction • System model • Detection analysis • Upper bound • ROC curves • Conclusions

3. Heavy Use Heavy Use Less than 6-10% Occupancy Sparse Use Medium Use Radio Spectrum • Primary user / license holder • Occupancy of spectrum (below 1 GHz) is around 6~10%. • Spectrum holes • Spectrum under utilization

4. Cognitive Radio • “A radio that can change its transmitter parameters based on the environment in which it operates”. • Cognitive radio • Secondary network • Unlicensed users • Spectrum Sensing…?

5. Spectrum Sensing • PU should not be effected by secondary activities. • Reliability • Decision based on the received signal • Multipath fading & shadowing. • Hidden terminal problem. Ho = Primary user is absent (idle) H0: Y [n] = W [n] H1 = Primary user is in operation (busy) H1: Y [n]= h X [n] + W [n]

6. Shadowing Shadowed node Cooperative nodes Cooperative Spectrum Sensing (CCS) • Improve reliability and detection capability. • Mitigate multipath fading & shadowing by spatial diversity. • Avoid hidden terminal problem.

7. Sensing Techniques • Matched filter: SU has a prior knowledge of the PU, coherent detection. • Cyclostationary detection: PU exhibits strong cyclostationary properties. • Covariance detection: the statistical covariance matrices of the signal and noise. • Energy detection: the received signal strength.

8. Sensing Techniques • Matched filter: SU has a prior knowledge of the PU, coherent detection. • Cyclostationary detection: PU exhibits strong cyclostationary properties. • Covariance detection: the statistical covariance matrices of the signal and noise. • Energy detection: the received signal strength. • Non-coherent • Low complexity

9. Relay-based CCS • Data fusion AF relaying in cooperative communications • Relay Fixed gain (blind/semi blind) Variable gain • Combining MRC/ SLC • Filtering • Energy detector • Multipath fading Rayleigh/ Nakagami-m • Ri to CC (i=1, …, n) channel Orthogonal (TDMA) • Relay links • Relay links + Direct link System Model

10. Binary hypothesis Energy Detector • Output is compared to the predefined threshold. • Non-coherent, optimal, low signal processing.

11. Performance Metrics • Test statistic • False alarm probability: • Detection probability:

12. Detection Analysis • Detection: • Average detection probability:

13. Detection Analysis • Detection: • Average detection probability: • Contour integration: Residue theorem Moment generating function (MGF)

14. MGF • Variable gain • Fixed gain

15. Upper Bound for Pd • Case 1: Multiple-relay Case 2: Multiple-relay + Direct link • SNR: • MGF: • Upper bound: • Case 1

16. n = 1 ROC curves for different number of cognitive relays (n)u=2, average SNR = 5 dB and fixed gain C=1.7

17. n = 1 ROC curves for different number of cognitive relays (n)u=2, average SNR = 5 dB and fixed gain C=1.7

18. n = 1, 2 ROC curves for different number of cognitive relays (n)u=2, average SNR = 5 dB and fixed gain C=1.7

19. n = 1, 2 ROC curves for different number of cognitive relays (n)u=2, average SNR = 5 dB and fixed gain C=1.7

20. n = 1, 2, 3, 4, 5 ROC curves for different number of cognitive relays (n)u=2, average SNR = 5 dB and fixed gain C=1.7

21. n = 1, 2, 3, 4, 5 ROC curves for different number of cognitive relays (n)u=2, average SNR = 5 dB and fixed gain C=1.7

22. ROC curves for relay links + direct linku=2, average SNR = 5 dB and fixed gain C=1.7 Direct link SNR = -5 dB

23. ROC curves for relay links + direct link u=2, average SNR = 5 dB and fixed gain C=1.7 Direct link SNR = -5, -3 dB

24. ROC curves for relay links + direct linku=2, average SNR = 5 dB and fixed gain C=1.7 Direct link SNR = -5, -3, 0 dB

25. ROC curves for relay links + direct linku=2, average SNR = 5 dB and fixed gain C=1.7 Direct link SNR = -5, -3, 0, 3 dB

26. ROC curves for relay links + direct linku=2, average SNR = 5 dB and fixed gain C=1.7 n =3 n =1 Direct link SNR = -5, -3, 0, 3 dB

27. Conclusions • The MGF of received SNR of the primary user’s signal is utilized to analyze the average detection probability. • Tighter upper bound is derived. • Sensing capability is increased with spatial diversity. • Direct link has major impact of the detection capability. • Analysis can be extended to multihop relaying.

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29. Thank you

30. Questions