Coalition Graph Game for joint relay selection and resource allocation in cooperative cognitive radio networks

Cooperative relaying technology among secondary users (SUs) in cognitive radio networks (CRN) is shown to yield a significant performance improvement, such as improving spectrum utilization as well as system fairness in CRN. This paper investigates the problem of the relay selection and resource allocation in a downlink OFDMA cognitive relay network. The objective of this optimization problem is to maximize both system throughput and system fairness, which is achieved through our proposed non-transferable utility coalition graph game algorithm (NTU-CGGA). In this algorithm, the SUs with more available channels can help SUs with less available channels to improve their utility in terms of the throughput and fairness by forming a directed tree graph. The coalition graph is formatted according to spectrum availability and traffic demands of SUs by using merge-split rule. So it can effectively exploit both space and frequency diversity of the system. Simulation results show that, NTU-CGGA significantly improves system throughput while not reducing the fairness level, which has a better performance comparing with other existing algorithms.