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 through 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 for each branch is investigated. To this aim, an efficient algorithm for the resource allocation is introduced. The performance of this algorithm is investigated and its superior efficiency is verified for CR networks via simulation
Due to their spectrum shaping capability and high adaptability, the multi-carrier systems are considered as prime candidates for use in the Cognitive Radio (CR) networks. In these structures, the deactivation of the primary users’ (PUs) bands makes the secondary users (SUs) use a limited number of sub-carriers, so the total capacity of CR networks is reduced. However, multiple transmit antennas can be applied to OFDM- based CR to compensate for such a low capacity. The present study investigates the problem of power allo-cation in MIMO-OFDM based CR Networks. The objective is maximizing the total capacity of CR systems in the downlink path under both interference on the PUs’ bands and maximum power of the CR transmitter constraints. It is shown that the optimal solution has high computational complexity, and therefore, an effi-cient sub-optimal algorithm is suggested for this application. As simulation results show, the suggested algo-rithm in the present paper is more enhanced and efficient than the previous algorithms
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