Cooperative Cognitive Radio Beamforming in the Presence of Location Errors

Various facets of cognitive radio technology have been studied in recent years. However, one possibility that is only thus-far marginally investigated is the ability to perform secondary access at the same time, band and location as ongoing primary transmissions through beamforming to secondary users. Clearly one reason why this has not been at the forefront of research is that it could imply a significant interference to primary users. This paper, however, demonstrates that such an approach is not only feasible, but derives an optimisation problem to constrain interference to primary users while keeping the received signal-to- interference-plus-noise ratio at the secondary users to above a threshold to maintain an acceptable level of quality of service, even taking into account positioning errors. It analyses the described concept and shows good performance against effective beam width increases in secondary transmissions, enacted to improve coverage to account for angular positioning error.