Construction of 1-Bit Transmit Signal Vectors for Downlink MU-MISO Systems: QAM Constellations

In this paper, we investigate the construction of transmit signal 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 methods could not yield satisfactory performances. Moreover, finding an optimal transmit signal is computationally implausible due to its combinatorial nature. Thus, it is still an open problem to construct a 1-bit transmit signal efficiently. 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. Taking into account the robustness to a noise, we develop a mixed-integer-linear-programming (MILP) problem. Also, we propose an efficient algorithm to solve it (equivalently, to generate a 1-bit transmit vector). We further compare the computational complexities of the proposed and existing methods. Simulation results validate the computation complexity and the detection performance of the proposed method.