Performance Analysis of the Cognitive Cooperative Scheme Based on Cognitive Relays

We propose a cognitive cooperative scheme based on cognitive relays in the downlink of a time division multiple access (TDMA) system. Cognitive relays utilize the spectrum holes detected via the spectrum detection to relay information, which can share the downlink slots through the frequency-division orthogonal transmission. Therefore, no extra system resources (slots or channels) are allocated for cooperation and the system encounters no bandwidth loss. Compared with the conventional cooperative scheme, the system throughput of our scheme can be significantly improved due to slot savings; however, our scheme suffers from outage performance degradation because the cognitive relays may not acquire spectrum holes or introduce interference from the licensed users of the spectrum as a result of acquiring spectrum "holes" by mistake. The analysis and simulation results suggest our scheme to achieve the system throughput gain at the price of the diversity performance loss.