Sum capacity maximization for MIMO–OFDMA based cognitive radio networks

In the opportunistic Cognitive Radio (CR) networks, the secondary users’ (SU) capacity is limited due to the need to avoid the primary users’ (PUs) bands. The combination of the Multiple-Input Multiple-Output (MIMO) structure with the orthogonal frequency division multiplexing (OFDM) structure is a very promising candidate which can compensate for such a shortage of capacity increasing the spectral efficiency. In this paper, a MIMO–OFDMA structure is proposed for the multiple access in multi-user CR networks. Furthermore, in order to achieve the maximum capacity in this structure, the resource allocation problem including proper allocation of sub-carriers to users and proper power allocation is investigated. To this aim, an efficient algorithm for the resource allocation is introduced. Furthermore, an alternative sub-optimal algorithm is obtained with lower complexity and very good performance. The performance of the suggested algorithms is investigated in a realistic scenario using LTE (Long Term Evolution) parameters with Spatial Channel Propagation Model (3GPP SCM). Simulation results verify the enhancement and efficiency of the proposed algorithms compared to the conventional ones applied in CR networks.