Power Allocation in Nonselfish Symbiotic Cognitive Relaying with Partial Channel State Information

We first address the problem of power allocation at cognitive users (CUs) to maximize the throughput of a nonselfish symbiotic cognitive radio scheme, in which the CUs may assist the data transmission of primary users (PUs) via nonorthogonal amplify-and-forward (AF) cognitive relaying and obtain an incentive time for their own data transmission in a nonselfish manner. Then, an optimal power allocation algorithm is proposed based on the full channel state information (CSI) among PUs, CUs, and base station (BS). In order to reduce the feedback overhead, another power allocation algorithm is devised based only on the partial CSI, that is, the CSI of BS-PU and the CSI of BS-CUs. Simulation results demonstrate that, compared with the optimal power allocation algorithm, the power allocation algorithm with only the partial CSI can achieve a similar performance with a smaller channel feedback overhead. 1. Introduction With underutilized time or frequency resources, the Federal Communications Commission (FCC) has recommended that more efficient spectrum utilization could be realized by implementing devices that can coexist with licensed users or PUs [1]. In consequence, cognitive radio (CR) has been considered as an essential candidate for exploiting spectrum at a higher efficiency [2, 3]. Based on the original CR concept [2], the data transmission of a conventional cognitive radio scheme (CCR) [1] is performed as a passive approach. The CUs need to sense the spectrum and wait for spectrum holes for their data transmission without any interaction between primary and cognitive networks. In this case, there is no need for any modification in the primary network, but, instead, the achievable performance, for example, spectrum efficiency, is quite limited. The relay systems have been actively studied to increase the throughput as well as to increase the service coverage in wireless networks [4–6]. In order to further enhance the performance of the cognitive network, the relay function is actively enabled at the CUs to assist the primary transmission, which may bring the benefits to the CUs, for example, creating more spectrum holes for the cognitive network. As the CUs with relay function come into play, the optimal power allocation at CUs to increase the spectrum efficiency becomes a critical issue for coexisting primary and cognitive networks [7–13]. However, to efficiently utilize the spectrum holes created by cognitive relaying, some interaction between primary and cognitive networks is inevitable, despite that it may break the rule of original CR concept.