Spectrum for wireless communications is traditionally assigned by inefficient spectrum access schemes. Portions of the spectrum are exclusively used by specific wireless systems. In recent studies, measurements indicated that allocated spectrum bands are not efficiently used in a certain geographic area, and the utilization of licensed spectrum is highly dependent on location and time. In cognitive radio ad hoc networks (CRAHNs), Secondary Users (SUs) can opportunistically utilize spectrum that is available from Primary Users (PUs). SUs must hop from one spectrum band to another to obtain the spectrum opportunities. In this paper, we propose a distributed medium access control (DMAC) protocol based on power control for CRAHNs, to mitigate the hidden and exposed terminal problems of multichannel PUs and SUs by building an appropriate number of monitor nodes in suitable positions. We develop the Markov chain model to characterize the performance of our proposed DMAC protocol for the saturation network. In this study, transmitter power control is based on the estimated distance between SU communication pairs; this increases channel spatial reuse and throughput, and reduces PU outage probability. In addition, DMAC uses the neighbors of PUs to inform SU communication pairs in the one-hop range; this also reduces PU outage probability. We also compare our proposed scheme to existing MAC protocols for CRAHNs. We show that DMAC will improve channel spatial reuse and normalized throughput, and reduce PU outage probability.
['Chien-Min Wu', 'Chih Pin Lo']
Distributed MAC protocol for multichannel cognitive radio ad hoc networks based on power control