A hybrid cooperative spectrum sensing for cognitive radio networks in presence of fading

In this paper, we study a hybrid fusion scheme for cooperative spectrum sensing (CSS) where we combine the hard decisions and soft decisions from cognitive radio (CR) users based on quality of their reporting channel (R-channel). The CR users transmit their hard decisions if the estimated R-channel between them and the fusion centre (FC) exceeds censoring threshold else they send soft decision, i.e. the energy values. Based on the received hard decisions, the FC derives an intermediate hard decision using majority rules while an intermediate soft decision is obtained by combining the received soft decisions following MRC or EGC. Finally the FC combines the intermediate decisions via an OR rule to obtain the final decision regarding the primary user (PU). Analytical expressions have been developed as well as simulation has been carried out to evaluate the performance of the proposed scheme in presence of Rayleigh fading in both the sensing channel (S-channel) and R-channel, in terms of detection probability and total error probability. The performance of the proposed scheme is studied and compared for two cases of soft combining such as MRC with majority logic and EGC with majority logic. Furthermore, the scheme is compared with CSS using hard decision fusion based on censoring and CSS using soft decision fusion only. Impact of several parameters such as number of CRs, S-channel and R-channel SNR, censoring threshold, sensing threshold on the performance of the proposed scheme is shown. Our scheme outperforms the hard decision fusion with censoring of CRs in faded R-channel.