Rate enhancement for cognitive radios using the relationship between transmission rate and signal-to-interference ratio statistics

A cognitive radio (CR) tries to intelligently utilise the idle periods of the primary system (PS) for opportunistic transmission and can improve the overall spectral utilisation. When a signal is transmitted, the authors usually consider the spectral occupancy from all propagation directions and assume circular signal coverage. In this study, they derive the relationship between transmission rate and signal-to-interference ratio statistics in a CR network (CRN) while protecting the rate of the PS to a specified level. Applying this relationship to a CR, they show that the regions for a CR receiver to keep an outage probability and bit error rate, defined as permissible areas, are no longer concentric in shape even in a pure path loss channel. Through detecting which permissible area a CR receiver is located, a new cognitive cycle is developed for rate enhancement. Simulation results show that as compared with a distance-dependent rate-adaptation approach, the system sumrate increases significantly. These results suggest a new version of CRN with enhanced system capacity.