On Achievable Performance of Cognitive Radio Systems

In this contribution1, we investigate the idea of using cognitive radio to reuse locally unused spectrum to increase the total system capacity. We consider a multiband/wideband system in which the primary and cognitive users wish to communicate to different receivers, subject to mutual interference and assume that each user knows only his channel and the unused spectrum through adequate sensing. Under this scheme, a cognitive radio will listen to the channel and, if sensed idle, will transmit during the voids. Within this setting, we provide two simple methods for sensing the idle sub-bands over the total bandwidth. We impose the constraint that users successively transmit over available bands through proper water filling. We derive the total spectral efficiency as well as the maximum number of possible pairwise communications of such a cognitive radio system and show that we can improve the overall system spectral efficiency by considering cognitive communications in the system. Index Terms Cognitive radio, sensing, power detection, radar detection, capacity, spectral efficiency, band factor gain, water filling.