Optimal resource allocation for opportunistic spectrum access in multiple-input multiple-output-orthogonal frequency division multiplexing based cooperative cognitive radio networks

In this study, the problem of resource allocation in multiple-input multiple-output-orthogonal frequency division multiplexing-based cooperative cognitive radio networks is considered. The cooperation strategies between the secondary users is the decode-and-forward (DF) strategies. In order to obtain an optimal subcarrier pairing, relay assignment and power allocation in the system, the dual decomposition technique is recruited. The optimal resource allocation is realised under the individual power constraints in source and relays, so that the sum rate is maximised, whereas the interference induced to the primary system is kept below a pre-specified interference temperature limit. Moreover, because of the high computational complexity of the optimal approach, a suboptimal algorithm is further proposed. The joint allocation of the resources in suboptimal algorithm is carried out taking into account the channel qualities, the DF cooperation strategy, the interference induced to the primary system and the individual power budgets. The performance of the different approaches and the impact of the constraint values and deploying multiple antennas at users are discussed through the numerical simulation results.