Rendezvous Protocols Based on Message Passing in Cognitive Radio Networks

In cognitive radio networks, secondary users need to first discover neighbours and form communication links, referred to as the rendezvous process. Rendezvous between any two secondary users can only be achieved on the same channel. However, spectrum heterogeneity in cognitive radio networks complicates the rendezvous process. While most of the existing works study pair-wise rendezvous and design channel hopping sequence, in this paper we focus on the general rendezvous problem for multiple users where each user needs to discover all of its neighbours. We propose to maintain and exchange rendezvous information among encountered users, and leverage rendezvous information spread within the network to accelerate the rendezvous process. With such an idea, we propose a general message passing based framework for rendezvous protocol design, which is flexible to incorporate the existing sequence generation algorithms. For the framework, we formulate rendezvous problems from the perspective of individual user, prove the NP-completeness, and propose an efficient greedy channel switching algorithm. Based on the framework, we design several rendezvous protocols for single-hop and multi-hop networks. When channel hopping sequence generation algorithms with guaranteed rendezvous between any two users are used, the rendezvous with the proposed protocols can still be guaranteed. Simulations demonstrate that the rendezvous performance is greatly improved.