Performance Comparison of Constant Envelope and Zero-forcing Precoders in Multiuser Massive MIMO

TL;DR

This paper compares constant envelope and zero-forcing precoders in massive MIMO systems, showing that CE precoders can significantly outperform ZF precoders in terms of SINR when power amplifiers operate near saturation, enhancing energy efficiency.

Contribution

It introduces an efficient computation method for CE precoders and demonstrates their superior performance over ZF precoders in realistic PA saturation scenarios.

Findings

CE precoders reduce PAPR, enabling more efficient PA operation.

CE precoders can achieve 5-6 dB higher SINR than ZF precoders.

Large gains in SINR improve spectral and energy efficiency.

Abstract

In this article, the adoption and performance of a constant envelope (CE) type spatial precoder is addressed in large-scale multiuser MIMO based cellular network. We first formulate an efficient computing solution to obtain the antenna samples of such CE precoder. We then evaluate the achievable CE precoder based multiuser downlink (DL) system performance and compare it with the corresponding performance of more ordinary zero-forcing (ZF) spatial precoder. We specifically also analyze how realistic highly nonlinear power amplifiers (PAs) affect the achievable DL performance, as the individual PA units in large-array or massive MIMO systems are expected to be small, cheap and operating close to saturation for increased energy-efficiency purposes. It is shown that the largely reduced peak-to-average power ratio (PAPR) of the PA input signals in the CE precoder based system allows for pushing the PA units harsher towards saturation, while allowing to reach higher signal-to-interference-plus-noise ratio (SINRs) at the intended receivers compared to the classical ZF precoder based system. The obtained results indicate that the CE precoder can outperform the ZF precoder by up to 5-6 dBs, in terms of the achievable SINRs, when the PA units are pushed towards their saturating region. Such large gains are a substantial benefit when seeking to improve the spectral and energy-efficiencies of the mobile cellular networks.