Asynchronous cooperative spectrum sensing in cognitive radio

In cognitive radio networks, the cognitive radio users can be collaborated to perform spectrum sensing so as to detect the primary user more accurately. However, when the sensing nodes suffer from fading, shadowing, and time-varying nature of wireless channels, it needs to set a long observation time for all of the nodes to make decisions and forward the results to fusion center, which induce the severe degradation of the sensing performance. In this paper, we propose an asynchronous cooperative spectrum sensing method, in which the cognitive radio user with high SNR finishes the detection earlier than the one with low SNR, and the fusion center makes the final decision depending on the earliest local decision. The proposed method can exploit the userpsilas SNR diversity so that the sensing performance can be enhanced. Simulation results show that the detection time is reduced significantly at the expense of a little sensing performance degradation compared to the conventional cooperative spectrum sensing.