In this paper, an optimal power control for minimizing bit error rate (BER) subject to a power constraint for space-time block coded MIMO systems with beamforming over Rayleigh fading channels under imperfect channel state information (CSI) is presented. The optimal power control procedure is developed. It is shown that the Lagrange multiplier for the constrained optimization does exist and is unique. To simplify the power control procedure, a closed-form suboptimal power control scheme is drived based on the asymptotic performance analysis of the optimal power control and Taylor's series expansion. The calculation of the suboptimal power control is straightforward with low computational complexity. Moreover, the suboptimal scheme can provide the BER performance close to that of the optimal power control and is lower than that of the existing suboptimal scheme. Simulation results show that the proposed two power control schemes can provide BER lower than that of the equal power allocation and the existing suboptimal scheme under imperfect CSI.

In this paper, a low-complexity precoding scheme for minimizing the bit error rate (BER) subject to fixed power constraint for distributed antenna systems with non-Kronecker correlation over spatially correlated Rayleigh fading channels is presented. Based on an approximated BER bound and a newly defined compressed signal-to-noise ratio (CSNR) criterion, closed-form expressions of power allocation and beamforming matrix are derived for the developed precoding scheme. This scheme not only has the calculation of the power allocation less than and also obtain the BER performance close to that of the existing optimal precoding scheme. Simulation results show that the proposed scheme can provide BER lower than the equal power allocation and single mode beamforming scheme, has almost the same performance as the existing optimal scheme.