Power control method for MIMO-based cognitive radio with imperfect channel state information

Cognitive radio (CR) systems aim for more efficient spectrum utilization by having so called secondary user (SU) terminals transmit on a frequency band reserved for licensed primary user (PU) systems. The secondary transmissions are allowed provided that no harmful interference will be caused to the PUs. Equipping the SU terminals with multiple antennas enables them to use transmit precoding combined with power control in order to control the interference levels. In most of the previous works, perfect interference channel state information (CSI) has been assumed. With imperfect CSI, however, the SU is no longer able to guarantee that the interference constraint can be satisfied. In this paper, we investigate the problem of spectrum sharing with estimated CSI in CR systems using multiantenna terminals. Due to the randomness of the estimation error, we set a probabilistic interference constraint and, in order to satisfy it, analyze the interference power statistics. In addition, we provide a framework for transmit power control for satisfying this constraint. Moreover, we briefly cover the estimation-throughput tradeoff and numerically confirm that an optimal value for the estimation period can be obtained.