Interference Exploitation Precoding Based on Multiple Space–Time Line Codes for MU-MIMO Systems

This letter proposes a new precoding method by combining the symbol-level precoding (i.e., interference exploitation precoding) with the multiple space-time line codes (MSTLC) in the downlink communications with multiuser multiple-input multiple-output systems. Considering the channel-dependent encoding and fixed decoding of MSTLC systems, we derive an equivalent signal model represented as multiuser transmission to multiple single-antenna users. Then, an optimization problem is formulated with respect to constellation rotation and perturbation vectors to maximize the detection signal-to-noise ratio under the total transmit power constraint. Since the optimization problem is non-convex, a block coordinate descent method is employed to find the solution by separately updating the constellation rotation and perturbation vectors. Numerical simulations show that the proposed method is beneficial over existing block- and symbol-level precoding schemes.