Presentation on theme: "Spectrum Sensing and Identification"— Presentation transcript:
1Spectrum Sensing and Identification Chapter 4Spectrum Sensing and Identification“Cognitive Radio Communications and Networks: Principles and Practice”By A. M. Wyglinski, M. Nekovee, Y. T. Hou (Elsevier, December 2009)
2Outline Introduction Primary Signal Detection Spectrum Opportunities DetectionPerformance vs. ConstraintSensing Accuracy vs. Sensing Overhead
6Spectrum Opportunities in Space, Time, & Frequency (Credit: DARPA XG)(Credit: ACSP Cornell)
7Primary Signal Detection Choice of detectorsCriteria:BayesianNeyman-PearsonParameter settings?Energy detectionPros: easily implemented; minimal assumptionsCons: poor performance with noise uncertainty and with multiple secondary usersPerformance ∼ 1/SNR2 at low SNR
8Choice of Detectors - Cyclic Detectors (2) Exploit guard bands in frequency, known carriers, data rates, modulation typePros:fc, Ts easy to detect via square-law devices, or cyclic approachesCyclic approaches useful when σ2n is unknown (avoid SNR wall)Easily implemented via FFTsCons:Timing and frequency jitter can be detrimentalRequires long integration timesRF non-linearities; Spectral leakage (ACI).
9Choice of Detectors: Matched Filter (3) Exploit pilots or sync (PN) sequences in primary (WRAN )Pros:Correlation detection is usually better than energy detection.Performance ∼ 1/SNR at low SNRCons:fading may null pilot; need to cope with time and freq sync
11Spectrum Opportunities Detection A channel is an opportunity for A − B ifthe transmission from A to B can succeedthe interference power to primary is below a prescribed level
12Spectrum Opportunity: Definition A channel is an opportunity for A − B ifthe transmission from A to B can succeedthe interference power to primary is below a prescribed level
13Spectrum Opportunity: Definition A channel is an opportunity for A − B ifthe transmission from A to B can succeedthe interference power to primary is below a prescribed level
14Spectrum Opportunity: Properties Determined by both transmitting and receiving activities of primary users.Asymmetric (an opportunity for A−B may not be one for B−A).
15Detection of Primary Receivers rI: interference range, Rp: primary tx range, rD: detection rangeDetecting primary Rx within rI by detecting primary Tx within rD
16Detecting Primary Signals (LBT) rD: detection range.H0: no primary Tx within rD, H1: alternative.False alarms and miss detections occur due to noise and fading.
17From Detecting Signal to Detecting Opportunity 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.
18When Is Detecting Signal = Detecting Opportunity? 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)
19Miss Detection May not Lead to Collision There is no primary receiver around AThere are primary transmitters around B
20Miss Detection May Lead to Success There are primary receivers around AThere is no primary transmitter around B
21Correctly Identified Opportunity May Not Lead to Success Successful data transmission and failed ACK
22Performance vs. Constraint 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.
23Performance vs. Constraint Two ModelsGlobal Interference ModelLocal Interference Model
24Performance vs. Constraint Throughput comparison.
25Sensing Accuracy vs. Sensing Overhead Optimal sensing time: efficiency η versus sensing window length n for various SNRs and PMD.
26Sensing Accuracy vs. Sensing Overhead Optimal sensing time: efficiency η and optimal window length n∗/N versus slot length N.
27Chapter 4 Summary The following topics have been covered: Different types of detectors for primary signal detectionDetection 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.