Message passing based rendezvous protocols in cognitive radio networks

Recently dynamic spectrum access systems have been proposed to alleviate the spectrum scarcity issue, for which cognitive radio is one of the key enabling technologies. In cognitive radio networks accessing spectrum dynamically, secondary users need to first discover neighbours and form communication links, which is referred to as the rendezvous process. Rendezvous between any two secondary users can only be achieved on the same channel. However, spectrum heterogeneity in terms of both temporal and spatial variance complicates the rendezvous process. In this paper, we study network discovery problems for cognitive radio networks using channel hopping based access protocols. Different from existing works, we propose a message passing based rendezvous protocol, which spreads rendezvous information within the network so that new secondary users can accelerate their rendezvous process and reduce the time to join the network. The protocol is flexible to incorporate existing channel hopping sequence generation algorithms. In a single-hop network, we formulate an individual minimum time rendezvous problem for a single secondary user. We further propose greedy algorithms with different time complexities to solve the problem. We also discuss the situation for multi-hop networks. Simulations demonstrate that the rendezvous time is greatly improved compared with the existing approaches.