A Tutorial on Multichannel Rendezvous in Cognitive Radio Networks

Rendezvous search that asks two persons to find each other among a set of possible locations has regained tremendous research interest lately in the research community of cognitive radio networks (CRNs). In a CRN, there are two types of users: primary spectrum users (PUs) and secondary spectrum users (SUs). SUs are only allowed to share spectrum with PUs provided that they do not cause any severe interference to the PUs. To do this, SUs first sense a number of frequency channels. If a channel is not blocked by a PU, then that channel may be used for SUs to establish a communication link. One of the fundamental problems in a CRN is then for two SUs to find a common unblocked channel. To find a common unblocked channel, channel hopping (CH) schemes are commonly used in the literature. In a CH scheme, time is divided into consecutive time slots and each SU hops to a channel in every time slot according to a specific CH sequence. Eventually, two SUs rendezvous when they both hop to a common unblocked channel. Such a rendezvous search problem in a CRN is known as the multichannel rendezvous problem. The objective of this book chapter is to provide a tutorial on the multichannel rendezvous problem under various categories and assumptions, including asymmetric/symmetric roles, synchronous/asynchronous clocks, homogeneous/heterogeneous available channel sets, and oblivious/nonoblivious rendezvous. Instead of giving rigorous mathematical proofs of the results in the multichannel rendezvous problem, we will provide the needed insights/intuitions to understand these results. Though there are many mathematical theories associated with the multichannel rendezvous problem, including Galois fields, finite projective planes, orthogonal Latin squares, quorum systems, and difference sets, in our view the fundamental theorem for the multichannel rendezvous problem is the Chinese Remainder Theorem and the development of this tutorial will be focused on the Chinese Remainder Theorem.