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

In this paper, we investigate the construction of a transmit signal for downlink multiuser multiple-input single-output (MU-MISO) systems under cost-effective 1-bit digital-to-analog converters (DACs). Due to coarse nonliner property, conventional precoding methods, developed infinite-resolution DACs, could not yield an attractive performance having severe error-floor. Finding optimal signal, moreover, is computationally implausible due its combinatorial nature. This challenging problem has been partially solved in our earlier work focusing on phase-shift-keying constellations. Our major contribution extend it into more practical quadrature-amplitude-modulation constellations non-trivial way. We first derive so-called feasibility condition guarantee that every user's noiseless received belongs desired decision region, and then transform as linear constraints. Taking robustness additive noise account, proposed method formulated mixed integer programming problem. construct efficient algorithm solve (equivalently, generate signal). Via simulation results, demonstrate superiority with respect computational complexity detection performance.