Approximately optimal transmit precoding for MIMO systems with imperfect feedback using directional derivative

An approximately optimal transmit precoding for MIMO systems with imperfect feedback, subject to sum power constraint, is proposed in this paper by using directional derivative. The proposed method is easily carried out, and can be applied to more general channel which follows a nonwhite covariance and nonzero mean complex Gaussian distribution. Additionally, a closed-form solution for power allocation is given, which has not been addressed before. Simulation results demonstrate the effectiveness of the sub-optimal algorithm.