Throughput Analysis of Massive MIMO Uplink with Low-Resolution ADCs

TL;DR

This paper analyzes the uplink throughput of massive MIMO systems with low-resolution ADCs, proposing novel channel estimation and rate approximation methods, demonstrating near-infinite resolution performance with few-bit ADCs, and assessing robustness to power imbalances.

Contribution

It introduces a new Bussgang-based channel estimator and an accurate rate approximation for low-resolution ADCs in massive MIMO uplink systems, applicable to various input constellations.

Findings

Reliable multi-user communication with 1-bit ADCs using pilot-based estimation and standard detection methods.

Near-infinite resolution throughput achievable with only a few ADC bits.

Low-ADC resolution systems are robust against user power imbalances.

Abstract

We investigate the uplink throughput achievable by a multiple-user (MU) massive multiple-input multiple-output (MIMO) system in which the base station is equipped with a large number of low-resolution analog-to-digital converters (ADCs). Our focus is on the case where neither the transmitter nor the receiver have any a priori channel state information. This implies that the fading realizations have to be learned through pilot transmission followed by channel estimation at the receiver, based on coarsely quantized observations. We propose a novel channel estimator, based on Bussgang's decomposition, and a novel approximation to the rate achievable with finite-resolution ADCs, both for the case of finite-cardinality constellations and of Gaussian inputs, that is accurate for a broad range of system parameters. Through numerical results, we illustrate that, for the 1-bit quantized case, pilot-based channel estimation together with maximal-ratio combing or zero-forcing detection enables reliable multi-user communication with high-order constellations in spite of the severe nonlinearity introduced by the ADCs. Furthermore, we show that the rate achievable in the infinite-resolution (no quantization) case can be approached using ADCs with only a few bits of resolution. We finally investigate the robustness of low-ADC-resolution MU-MIMO uplink against receive power imbalances between the different users, caused for example by imperfect power control.