A MAC Protocol for Concurrent Channel Access in Cognitive Radio Ad Hoc Networks

Abstract

Cognitive radio ad hoc networks (CRAHNs) consist of autonomous devices that operate in ad hoc mode and aims to perform efficient utilization of spectrum resources. In cognitive radio (CR) networks, unlicensed users sense the licensed spectrum bands and opportunistically access them without interfering operations of licensed users. This requires serious attention on MAC layer design for spectrum access. Especially, in ad hoc networks with no central coordinator, the MAC layer plays an important role in coordinating unlicensed users’ access to the licensed spectrum. Recently, a number of works on designing MAC protocols for this purpose have been published. Most of them, however, are restricted with numerous limitations and assumptions. In this thesis, we examine MAC protocols in CRAHNs and propose a new MAC protocol called CA-MAC (Concurrent Access MAC) in this category. First, we categorize the protocols on the basis of common control channel (CCC) requirements and further review major implementations for each category. Then, we make a qualitative comparison of the protocols in terms of inherent characteristics and performance. Usually, cognitive devices exploit a vast number of available channels. In general, all or some channels are not common to the nodes in a CRAHN. Such a network environment poses the problem of establishing a common control channel (CCC), as there might be no channel common to all the network members at all. Then, we propose a MAC protocol named CA-MAC which operates on this kind of channel environment without requiring any CCC. The two devices in a communicating pair can communicate with each other even if they have only one common channel available. Therefore, the problems with CCC (such as channel saturation and denial of service attacks) can be also resolved. CA-MAC distributes the channel access between communicating pairs and, thus, it increases network connectivity. In addition, CA-MAC allows the concurrent access to multiple channels concurrently. According to our performance study, CA-MAC provides the higher network connectivity with shorter network-wide channel access delay compared to SYN-MAC (which is the conventional key MAC protocol for similar “uncommon” channel architecture in CRAHNs), resulting in better network throughput.