CogMAC+: A decentralized MAC protocol for opportunistic spectrum access in cognitive wireless networks

The rapidly increasing number of wireless applications are making the wireless spectrum scarcity a serious problem. Cognitive MAC protocols have emerged as a promising solution to address this issue by opportunistically allowing secondary users to utilize unused licensed bands, and enabling spectrum co-existence of multiple secondary networks. In this paper, we present CogMAC+, a decentralized multichannel MAC protocol, which is based on multichannel preamble reservation scheme and CSMA principle. It achieves parallel transmissions for multiple secondary users by enabling them to estimate the duration of channel occupancy of each other. In order to achieve the optimal sensing schedule, it allows secondary users to dynamically access channels according to the channel occupancy of primary users and other secondary networks. Moreover, CogMAC+ uses an adaptive energy detection scheme to dynamically set the energy detection threshold according to the carrier sensing status, the false positive detection ratio and the estimated noise level. CogMAC+ has been verified and evaluated empirically in a software defined radio testbed with realistic spectrum occupancies of licensed users. Our experimental performance evaluation indicates that CogMAC+ is able to carry out reliable parallel communication in multiple channels even in a severely interfered environment.