Cooperative Spectrum Sensing in Cognitive Radio Networks with Rayleigh Fadings

Spectral sensing in "white space frequencies is important feature for cognitive radio networks. Performances of detection of licensed users by individual secondary users (SU) degraded under the influence of the fading in radio channel, both in the sensing channel and in the reporting channels. Reliable detection of licensed primary users (PU) is implemented on the basis of cooperation of SU (CSS). Two solutions to improve the performances of the CSS are introduced in this paper. First, in the sensing channel, instead of single-threshold detectors scheme, a four-threshold scheme with an "erasure" zone is applied. Only "significant" local decisions from SU that do not fall within "erasure" zone are sent to the central station of CSS,while reducing the average number of messages sent via the reporting channel using QPSK-HM twobit symbols. The highest bit in the hierarchy of the symbol shows the local decision of the VP, and the lowest bit shows the likelyhood level of this decision. This solution does not lead to an increase in traffic over the reporting channel while improve the performances CSS.