Common Hopping Based Proactive Spectrum Handoff in Cognitive Radio Ad Hoc Networks

Cognitive radio (CR) technology is a promising solution to enhance the spectrum utilization by enabling unlicensed users to exploit the spectrum in an opportunistic manner. Since unlicensed users are considered as temporary visitors to the licensed spectrum, they are required to vacate the spectrum when a licensed user appears. Due to the randomness of the appearance of licensed users, disruptions to both licensed and unlicensed communications are difficult to prevent, which lead to low throughput and high spectrum switching overhead. In this paper, a proactive spectrum handoff framework in a CR ad hoc network is proposed to address these concerns. In the proposed framework, channel switching policies and a proactive spectrum handoff protocol are proposed to let unlicensed users perform spectrum switching before a licensed user uses the spectrum to avoid interference. A network coordination scheme for unlicensed users is also incorporated into the spectrum handoff protocol design to realize network rendezvous. Moreover, a distributed channel selection scheme to eliminate collisions among unlicensed users in a multi-user spectrum handoff scenario is proposed. Simulation results reveal that the proposed proactive spectrum handoff protocol outperforms the conventional reactive spectrum handoff approach in terms of higher throughput and fewer collisions to licensed users. It is also shown that the proposed channel selection scheme results in higher packet delivery rate compared with existing channel selection schemes.