Multiuser 1-Bit Precoding for Downlink MISO Systems with QAM Constellations

In this paper, we investigate a construction of transmit signal vector for a base station (BS) with a massive number of antenna arrays under cost-effective 1-bit digital-to-analog converters (DACs). Because of the coarse nonlinear property, conventional precoding schemes could not provide a satisfactory performance. Unfortunately, finding an optimal transmit signal vector is computationally implausible due to its combinatorial nature. We first derive a feasibility condition which ensures that each user's noiseless observation belongs to a desired decision region, and then formulate it as linear constraints. Additionally including the robustness to a noise, we formulate a linear programming (LP) problem with a relaxed constraint, and properly refine the LP solution using an efficient greedy algorithm to satisfy the 1-bit constraint. We further compare the computational complexities of the proposed and existing methods. Simulation results validate the computational complexity and the detection performance of the proposed method in symbol error rate.