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Symbol Error Rate Minimization Based Constructive Interference Precoding for Multi-User Systems

Symbol level precoding based on the concept of constructive interference has been recognized as an advanced version of conventional interference-avoidance precoding for multi-user transmission. With the full knowledge of channel state information (CSI) and symbol information, inter-user interference is adjusted to bring constructive effect to the desired signal. However, the existing schemes are limited within the concept of channel pre-equalization which could be further improved. In this paper, we propose a symbol error rate (SER) minimization based constructive interference precoding scheme for multi-user systems. The constructive interference region is firstly defined based on the analysis of the SER expression, which implies that the proposed scheme is essentially a symbol pre-detection scheme. Then, we prove that the optimal precoded signal for SER minimization shall be the linear combination of the channel vectors. Accordingly, a modified feasible direction algorithm is developed to handle the complex expression of SER, where an extra projection step is proposed to enhance the efficiency of the feasible direction. Finally, the proposed scheme is further extended for transmit power optimization and imperfect CSI cases. Simulation results highlight the efficiency of the modified feasible direction, and the superiority of the proposed scheme in terms of SER and transmit power.