Sub-Optimal Power Allocation in MIMO-OFDM Based Cognitive Radio Networks

Multi-carrier systems are one of the best candidates for applying in Cognitive Radio (CR) networks because of the spectrum shaping and high adaptive capabilities. Since secondary users (SUs) in this structure use a limited number of sub-carriers due to deactivation of the primary users´ (PUs) band, the total capacity of CR networks is limited. On the other hand, multiple transmit antennas can be applied to OFDM-based CR in order to compensate this capacity leakage. This paper aims to investigate MIMO-OFDM as one of the best hybrid Multi-carrier systems, as a physical layer of CR networks. Considering different conditions to obtain maximum total capacity of CR networks, a new proper power allocation algorithm is scrutinized. Theoretically, it is shown that this proposed algorithm can maximize the total capacity and at the same time, keep the caused interference in primary users´ bands in a tolerable range. The simulation results of this new algorithm are compared with previous methods, which present the enhancement and efficiency of the proposed algorithm. Furthermore, the simulation results show that our proposed scheme can load more power into the CR user´s band in order to achieve higher transmission capacity for a given interference threshold.