On Differential Modulation in Downlink Multiuser MIMO Systems

TL;DR

This paper introduces a low-complexity downlink MU-MIMO scheme using differential modulation and precoding techniques that do not require channel knowledge at transmitters or receivers, enhancing performance and simplicity.

Contribution

It proposes a novel combination of downlink precoding, differential modulation, and orthogonal spreading to eliminate the need for channel knowledge in MU-MIMO systems.

Findings

Effective interference cancellation with block diagonalization

Achieved low complexity transceivers

Demonstrated good performance through simulations

Abstract

In this paper, we consider a space time block coded multiuser multiple-input multiple-output (MU-MIMO) system with downlink transmission. Specifically, we propose to use downlink precoding combined with differential modulation (DM) to shift the complexity from the receivers to the transmitter. The block diagonalization (BD) precoding scheme is used to cancel co-channel interference (CCI) in addition to exploiting its advantage of enhancing diversity. Since the BD scheme requires channel knowledge at the transmitter, we propose to use downlink spreading along with DM, which does not require channel knowledge neither at the transmitter nor at the receivers. The orthogonal spreading (OS) scheme is employed in order to separate the data streams of different users. As a space time block code, we use the Alamouti code that can be encoded/decoded using DM thereby eliminating the need for channel knowledge at the receiver. The proposed schemes yield low complexity transceivers while providing good performance. Monte Carlo simulation results demonstrate the effectiveness of the proposed schemes.