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

Cognitive radio (CR) is a promising solution to improve the spectrum utilization by enabling unlicensed users to exploit the spectrum in an opportunistic manner. However, because unlicensed users are considered as temporary visitors to the licensed spectrum, they are required to vacate the spectrum when a licensed user reuses the current spectrum. Due to the randomness of the reappearance of licensed users, disruptions to both licensed and unlicensed communications are difficult to prevent, which leads to high spectrum switching overhead. In this work, a proactive spectrum handoff framework in a CR ad hoc network scenario is proposed. Based on channel usage statistics, proactive spectrum handoff criteria and policies are devised. CR users proactively predict the future spectrum availability status and perform spectrum switching before a licensed user reuses the spectrum. In addition, a channel coordination scheme is investigated and incorporated into the spectrum handoff protocol design. To eliminate collisions among CR users, a novel distributed channel selection scheme in a multi-user scenario is proposed. Simulation results show that the proposed proactive spectrum handoff protocol outperforms the conventional sensing-based 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 outperforms the purely random channel selection scheme in terms of shorter average service time and higher packet delivery rate.