Medium Access Control Protocol for the Distributed Cognitive Radio Network

Abstract

A key challenge in a cognitive radio network is to have an efficient sensing and non-interfering spectrum access decision protocol that enables cognitive users to reserve chunks of the spectrum for certain periods of time. However, the modeling of variable bandwidths for communication in cognitive radio is very complicated, and channel accessing policies must be defined for the cognitive radio users. In this chapter, we compare various medium access control (MAC) protocols for distributed cognitive radio networks and propose a novel multichannel cooperative MAC protocol for distributed cognitive radio networks which has a backoff algorithm for contention solving among the competing cognitive users. The proposed MAC protocol consists of a control channel on which the cognitive users cooperate with each other. The control channel cooperation among the cognitive users is performed by presenting the sensing results of all cognitive users on the control channel, then the idle channels from the pool of total available idle channels, whose information is available on the control channel, are selected by the cognitive users. Each channel is divided into cycle time, which is further divided into four intervals: idle interval, sensing–sharing interval, contention interval, and data transmission interval. The backoff algorithm for solving collisions among the competing users allows the collided cognitive users to succeed by selecting another contention slot from the expanded contention window. The increased number of successful users enhances the throughput of the cognitive radio network by transmitting their data over the detected idle licensed channels. An optimal number of contention slots is identified that maximizes the number of successful cognitive users as well as throughput. The proposed MAC protocol optimizes the number of contention slots depending on the number of cognitive users in comparison to the fixed number of slots in the self-scheduled multichannel-MAC (SMC-MAC) protocol.