A Precoding Scheme Based on Semidefinite Relaxation for MIMO Downlinks

The way of controlling transmit power, in a precoding method based on maximal Signal-to- Leakage-plus-Noise Ratio (SLNR) for multiuser MIMO downlinks，is not efficient to ensure each users available SLNR value, so a precoding scheme pursuing design goal that minimizes total transmit power under each users SLNR constraint is proposed. The goal issues can be successfully solved by using SemiDefinite Relaxation (SDR) techniques, and power constraint condition added in goal issues can efficiently reduce total transmit power of the base station. Simulation results show that the proposed scheme that satisfies large SLNR thresholds, has better Bit Error Rate (BER) and lower total transmit power than the maximal SLNR based precoding method. Moreover, the higher the system Signal-to-Noise Ratio (SNR), the lower the total transmit power of the scheme.