Joint Random Spectrum Sensing and Access Scheme for Decentralized Cognitive Radio Networks

In this paper we consider a cognitive radio network with access to N licensed primary frequency bands and their usage statistics, where the decentralized secondary users are subject to certain inter-network interference constraint. In particular, to limit the interference to the primary network, secondary users are equipped with spectrum sensors and are capable of sensing and accessing a limited number of channels at the same time due to hardware limitations. We consider both the error-free and erroneous spectrum sensing scenarios, and establish the jointly optimal random sensing and access scheme, which maximizes the secondary network expected sum throughput while honoring the primary interference constraint. We show that under certain conditions the optimal sensing and access scheme is independent of the primary frequency bandwidths and usage statistics; otherwise, they follow water-filling-like strategies. Moreover, we show that the performance of the secondary network depends on the ratio between the "opportunity-detection" probability and the "mis-detection" probability if the former is larger; otherwise, it depends on the ratio between the "false-alarm" probability and the "detection" probability. Finally, we demonstrate a binary behavior for the optimal access scheme at each channel, depending on whether the opportunity-detection probability or mis-detection probability is larger in that channel.