Power Loading for Multicarrier Cognitive Radio with MIMO Antennas

We propose a power loading scheme for multi- carrier cognitive radio (CR) network employing multiple-input multiple-output (MIMO) antennas. We allocate power to different transmitting antennas within different subcarriers maximizing the total system capacity while maintaining the interference to primary user within a prescribed limit. We formulate this as a convex optimization problem and use numerical methods to solve for optimal power allocation. We also compare the performance of power loading scheme proposed in this paper to conventional uniform power loading scheme with and without interference constraint. Simulation results show that the capacity of MIMO CR using our proposed power loading scheme increases significantly with increase in interference temperature limit and the number of transmit antennas. However, we also confirm that if we include interference constraint in the conventional uniform power loading schemes, the capacity does not increase proportionally with increase in number of transmit antennas as those schemes do not take the instantaneous channel condition between cognitive user transmitter and primary user receiver into account.