Evaluation and Enhancement of MAC Protocols for Efficient Spectrum Management and Sharing in Cognitive Radio Networks

Evaluation and Enhancement of MAC Protocols for Efficient Spectrum Management and Sharing in Cognitive Radio Networks Cognitive radio networks (CRNs) have gained a tremendous interest in the research community, as they tend to solve the existing and future issues of frequency spectrum scarcity by exploiting the spectrum holes in underutilized licensed and unlicensed frequency bands, thereby, improving the spectrum utilization. The number of channels in a Cognitive Radio Network (CRN) always varies with time and location as compared to legacy wireless networks with fixed number of radio channels. This variability of available channels in cognitive radio networks has brought new design challenges in Medium Access Control (MAC) protocols and has led to the need for most efficient and reliable MAC protocols in a CRN that can sustain under variable network conditions. The sharing of discovered spectrum holes among the contending secondary users (SUs) increases the overall spectrum utilization; however, the utilization of these discovered spectrum holes within the CRN depends on the access mechanism of SUs. In random access, waste of these spectrum holes would occur due to collisions and un-attempted slots by SUs. Therefore, optimal use of these discovered holes with minimum or no waste is desirable in an efficient CRN. A selforganizing collision-free MAC protocol is proposed for the distributed CRN that is more efficient in spectrum sharing by avoiding collisions and maximally utilizing un-attempted slots during access phase, thus increasing the spectrum utilization and throughput. This is achieved by organizing and queuing the active SUs through a timer value and directing them in an orderly fashion to use the discovered holes. Finding holes from the underutilized portion of spectrum at varying times and locations is the most important function in CRNs. This requires efficient sensing policy at the MAC layer that can discover more idle channels in minimal time. Spectrum sensing policies for searching idle channels from the underutilized primary band can significantly affect the performance of SUs in terms of throughput, reliability and energy efficiency. The sensing policy depends on the channel sensing order that decides how SUs sense the primary user band in minimal period of time. A cooperative parallel sensing scheme with sequential channel selection order is proposed as part of the MAC protocol, which can discover all the free channels in the primary user band in minimal time. The proposed scheme has been analyzed for the number of channels sensed and the number of idle channels discovered. Furthermore, energy efficiency and throughput of the proposed scheme have also been evaluated. The results show considerable improvement for the proposed scheme as compared to the random channel spectrum sensing schemes prevalent in adhoc CRNs. The work in this thesis has aimed to improve spectrum management by adopting new spectrum sensing policies and improving spectrum sharing by self-organizing the cognitive users for collision free access in adhoc CRN MAC protocols.