A geometric approach to improve spectrum efficiency for cognitive relay networks

Cognitive radio (CR) enables dynamic spectrum access (DSA). In CR networks (CRNs), unlicensed cognitive users (CUs) can share the radio spectrum with the licensed primary users (PUs) if the incurred signal-to-noise-and-interference ratio (SNIR) to the PUs is above a predetermined threshold. In this paper, we investigate the use of relaying to enhance the spectrum utilization of an idealized two-dimensional geometric network in Rayleigh fading channels. To do so, the CUs should be made transparent to the PUs while achieving acceptable reliability themselves. Based on these conditions, we first derive the geometric condition under which CUs could transmit over a single hop with the PUs being active. If the destination is beyond the reach of the source in a single hop, multihop relaying will be used for shorter-distance less-power transmission. Then, we propose and analyze two multihop routing strategies, termed nearest-neighbor routing (NNR) and farthest-neighbor routing (FNR). In multihop relaying, we also study the benefits of concurrency, in which more than one CUs are allowed to transmit at the same time to improve the end-to-end (e2e) channel utilization. Finally, we compare the e2e performance of CRNs with and without relaying.