Construction of 1-Bit Transmit-Signal Vectors for Downlink MU-MISO Systems With PSK Signaling

We consider a downlink multi-user multiple-input single-output system where the base station has a large number of antennas with cost-effective 1-b digital-to-analog converters. For this system, we first identify that assigning the zero-power to some transmit signals (in short, zero-power allocation) can yield a non-trivial symbol-error-rate performance gain by alleviating an error-floor problem. Likewise the related works on 1-b precoding, finding an optimal transmit-signal vector (encompassing precoding and zero-power allocation) requires an exhaustive search due to its combinatorial nature. Motivated by this, we propose a low-complexity two-stage algorithm to construct such transmit-signal vector directly. In the first stage, we derive a feasible transmit-signal vector via iterative-soft-thresholding algorithm whose output ensures that each user's noiseless observation belong to a desired region (called decision region). In the second stage, a bit-flipping algorithm is performed to refine the feasible vector so that each user's received signal is more robust to additive Gaussian noises. Simulation results demonstrate that the proposed method can yield a more elegant performance-complexity tradeoff than the existing 1-b precoding methods.