A Framework for One-Bit and Constant-Envelope Precoding over Multiuser Massive MISO Channels

TL;DR

This paper introduces a unified framework for multiuser precoding in massive MIMO systems with one-bit and constant-envelope constraints, optimizing symbol-error rates efficiently.

Contribution

It develops a novel SEP-based precoding design with a penalty method and a fast non-convex optimization algorithm for various hardware constraints.

Findings

Significantly improved bit-error rate performance over existing methods.

Efficient algorithm handles large-scale decision variables quickly.

Framework unifies one-bit and constant-envelope precoding design.

Abstract

Consider the following problem: A multi-antenna base station (BS) sends multiple symbol streams to multiple single-antenna users via precoding. However, unlike conventional multiuser precoding, the transmitted signals are subjected to binary, unit-modulus, or even discrete unit-modulus constraints. Such constraints arise in the one-bit and constant-envelope (CE) massive MIMO scenarios, wherein high-resolution digital-to-analog converters (DACs) are replaced by one-bit DACs and phase shifters, respectively, for cutting down hardware cost and energy consumption. Multiuser precoding under one-bit and CE restrictions poses significant design difficulty. In this paper we establish a framework for designing multiuser precoding under the one-bit, continuous CE and discrete CE scenarios---all within one theme. We first formulate a precoding design that focuses on minimizations of symbol-error probabilities (SEPs), assuming quadrature amplitude modulation (QAM) constellations. We then devise an algorithm for our SEP-based design. The algorithm combines i) a novel penalty method for handling binary, unit-modulus and discrete unit-modulus constraints; and ii) a first-order non-convex optimization recipe custom-built for the design. Specifically, the latter is an inexact majorization-minimization method via accelerated projected gradient, which, as shown by simulations, runs very fast and can handle a large number of decision variables. Simulation results indicate that the proposed design offers significantly better bit-error rate performance than the existing designs.