Performance of In-band Transmission of System Information in Massive MIMO Systems

TL;DR

This paper investigates how massive MIMO systems can reliably transmit system information to inactive users without channel state information, using specialized precoding and space-time coding to improve outage performance.

Contribution

It introduces a novel downlink transmission scheme employing orthogonal space-time block codes and reduced-dimension precoding for reliable info delivery in massive MIMO.

Findings

Massive MIMO outperforms single-antenna systems in all scenarios.

Space-time coding enhances reliability under limited diversity.

Precoding reduces pilot overhead and improves outage rates.

Abstract

We consider transmission of system information in massive MIMO. This information needs to be reliably delivered to inactive users in the cell without any channel state information at the base station. Downlink transmission entails the use of downlink pilots and a special type of precoding that aims to reduce the dimension of the downlink channel and the pilot overhead, which would otherwise scale with the number of base station antennas. We consider a scenario in which the base station transmits over a small number of coherence intervals, providing little time/frequency diversity. The system information is transmitted with orthogonal space-time block codes to increase reliability and performance is measured using outage rates. Several different codes are compared, both for spatially correlated and uncorrelated channels and for varying amount of time/frequency diversity. We show that a massive MIMO base station can outperform a single-antenna base station in all considered scenarios.