Supporting Fast Rendezvous Guarantee by Randomized Quorum and Latin Square for Cognitive Radio Networks

Cognitive radio networks (CRNs) have been widely studied because they significantly enhance spectrum access efficiency. An essential issue for CRN communications is providing rendezvous between two nodes. An easy but impractical way to achieve rendezvous is to use a dedicated channel to exchange control messages. A better way to provide rendezvous is to exploit channel hopping. Most existing channel hopping solutions suffer from poor system performance. In this paper, we propose a novel distributed channel hopping protocol, i.e., randomized quorum and Latin square channel hopping (RQL). Utilizing the concepts of quorum systems, Latin squares, and a pseudorandom number generator, i.e., linear congruential generator (LCG), RQL efficiently provides rendezvous guarantee and balanced channel utilization. The concept of quorum systems is utilized to guarantee balanced rendezvous among nodes, whereas the concept of Latin squares and LCG is used to share the rendezvous among channels and to increase channel utilization, respectively. RQL is considered to be a flexible and robust solution that provides rendezvous guarantee for any pair of nodes in a CRN. Analytical and simulation results verify that RQL performs better in terms of time to rendezvous (TTR) and network throughput when comparing to existing rendezvous protocols, i.e., L-QCH, ACH, and QLCH.

I. Introduction

The rapid development of wireless applications makes the wireless spectrum a precious resource. However, a large portion of the licensed spectrum is underutilized. Cognitive radio (CR) has received a lot of attention recently since it enables more efficient spectrum allocation and utilization. In CR networks (CRNs), an unlicensed user (secondary user, SU)

The terms SU and node may be used interchangeably to represent an SU in this paper.

is allowed to access the licensed spectrum that is not being used by any licensed user (primary user, PU). Exploiting CR technology, SUs are capable of recognizing spectrum holes and are able to hop between them without causing operation interruption of PUs. That is, SUs are capable of detecting the existence of PUs through spectrum sensing techniques [1] and adapting their radio parameters to exploit spectrum opportunities without interfering with PUs [2]. The sensing task is executed across a wide range of spectrum to identify the spectrum holes. SUs are capable of opportunistic utilization of the spectrum hole. Due to the dynamic nature of PUs' activities, spectrum sensing is usually performed periodically to keep the occupancy information up to date. CRs have been proposed as a possible solution to improve spectrum utilization via opportunistic spectrum sharing. In the literature, two cognitive spectrum access models have received a lot of attention: spectrum overlay and spectrum underlay. In an overlay radio CR system, SUs opportunistically utilize licensed spectrum holes without interfering with any PU. In an underlay CR system, an SU can coexist with an active PU in a licensed band if the interference caused to the PU is under a given threshold [3]. In this paper, we consider an overlay CR system. That is, when PUs appear, the SUs must immediately vacate the spectra being used.