On the Outage Probability Optimization in MISO Rician Channels

We address the optimization issue of the outage probability in Rician block fading channels with N transmit antennas and 1 receive antenna. It is already known that the eigenvectors of the covariance matrix of the transmit signal that minimizes the outage probability are the normalized mean vector of the Rician channel and N-1 orthonormal vectors belonging to the space orthogonal to the range of the mean vector. Our contribution is to optimize the eigenvalues. At high SNR, we show that the part of the power allocated to the orthogonal space of the range of the mean vector should be uniformly distributed amongst its N-1 eigenvectors. In addition, thanks to an original approximation of the outage probability, we characterize the part of power associated with the mean vector. We numerically observe improvement achieved by the proposed allocation scheme compared to uniform power allocation.