All-Digital Massive MIMO Uplink and Downlink Rates under a Fronthaul Constraint

TL;DR

This paper analyzes the maximum achievable uplink and downlink rates in a massive MIMO system with a fronthaul constraint, optimizing hardware parameters and considering both perfect and imperfect channel information.

Contribution

It introduces a novel rate expression for systems with imperfect channel knowledge and determines optimal hardware configurations under fronthaul limitations.

Findings

Optimal ADC/DAC resolution and antenna count maximize rates.

Derived rate expressions for perfect and imperfect CSI.

Quantified impact of fronthaul constraints on system performance.

Abstract

We characterize the rate achievable in a bidirectional quasi-static link where several user equipments communicate with a massive multiple-input multiple-output base station (BS). In the considered setup, the BS operates in full-digital mode, the physical size of the antenna array is limited, and there exists a rate constraint on the fronthaul interface connecting the (possibly remote) radio head to the digital baseband processing unit. Our analysis enables us to determine the optimal resolution of the analog-to-digital and digital-to-analog converters as well as the optimal number of active antenna elements to be used in order to maximize the transmission rate on the bidirectional link, for a given constraint on the outage probability and on the fronthaul rate. We investigate both the case in which perfect channel-state information is available, and the case in which channel-state information is acquired through pilot transmission, and is, hence, imperfect. For the second case, we present a novel rate expression that relies on the generalized mutual-information framework.