Spectrum sensing with cooperation of multi antenna based adaptive decode-and-forward relay

In this paper, we have studied an adaptive decode-and-forward (ADF) relay based cooperative spectrum sensing scheme in cognitive radio (CR) network in presence of Rayleigh fading channel. In this proposed model, the primary user (PU) is monitored by the cognitive coordinator (CC) with the help of ADF based cognitive relays. The cognitive relay employs multiple receiving antennas and single transmitting antenna. The relays forward the sensing information regarding the activity of PU to CC. In this adaptive forwarding scheme, a relay transmits the soft sensing information only if it is able to decode successfully, otherwise it remains silent. The CC combines the two signals, i.e., one directly received from PU and the other relayed by relays to make a final decision regarding PU using maximal ratio combining (MRC) or selection combining (SC) schemes. A closed form expression for the probability of detection is derived. The effects of number of antennas at each relay and number of relays on the system performance have also been studied. The impact of the number of relays, number of antennas at the relay, SNR of sensing channel on detection performance is addressed. We have also studied tradeoff between number of antennas at relay and number of relays in the network. The analytical results are verified by MATLAB simulation.