A MAC protocol for cognitive radio networks to coexist with CSMA-based primary users

The motivation for Cognitive Radio(CR) networks comes from the apparent scarcity of spectrum as indicated by the multiple allocation of most bands by the Federal Communications Commission (FCC). On the other hand, studies by the FCC show that 70% of the allocated spectrum is not utilized. This discrepancy between allocation and use provides the motivation for opportunistic use of the spectrum. Opportunistic access would enable better utilization of spectrum that is sparsely used (temporally and spatially) otherwise. A cognitive radio would monitor the primary user activity on the channel identifying white spaces and utilize the spectral opportunities for transmission, without affecting the performance of the primary users. Additional challenges exist when primary users are reactive. An example of a reactive system is a CSMA-based primary system where PUs react to SU activities. Besides collision and throughput, additional impact metrics are needed to capture the impact of SU activity on PU. In this thesis, we present new impact metrics. We present a 2-state SU MAC scheme for a CSMA- based primary system that takes into account the reactive nature of the PU access mechanism. Both simulation and experimental results show that the SU can utilize the available spectrum opportunities while generating negligible interference on the PU.