Precoding Design for Multi-user MIMO Systems with Delay-Constrained and -Tolerant Users

TL;DR

This paper introduces a precoding design for MU-MIMO systems with mixed delay-constrained and delay-tolerant users, optimizing spectral efficiency while respecting latency constraints, and demonstrates superior performance over baseline methods.

Contribution

It proposes a novel GPI precoding algorithm for heterogeneous MU-MIMO systems with delay constraints, extending to multiple time slots for improved spectral efficiency.

Findings

Proposed methods outperform baseline schemes in simulations.

Spectral efficiency for delay-tolerant users is maximized under latency constraints.

Lower bounds for spectral efficiency of delay-constrained users are established.

Abstract

In both academia and industry, multi-user multiple-input multiple-output (MU-MIMO) techniques have shown enormous gains in spectral efficiency by exploiting spatial degrees of freedom. So far, an underlying assumption in most of the existing MU-MIMO design has been that all the users use infinite blocklength, so that they can achieve the Shannon capacity. This setup, however, is not suitable considering delay-constrained users whose blocklength tends to be finite. In this paper, we consider a heterogeneous setting in MU-MIMO systems where delay-constrained users and delay-tolerant users coexist, called a DCTU-MIMO network. To maximize the sum spectral efficiency in this system, we present the spectral efficiency for delay-tolerant users and provide a lower bound of the spectral efficiency for delay-constrained users. We consider an optimization problem that maximizes the sum spectral efficiency of delay-tolerant users while satisfying the latency constraint of delay-constrained users, and propose a generalized power iteration (GPI) precoding algorithm that finds a principal precoding vector. Furthermore, we extend a DCTU-MIMO network to the multiple time slots scenario and propose a recursive generalized power iteration precoding algorithm. In simulation results, we prove proposed methods outperform baseline schemes and present the effect of network parameters on the ergodic sum spectral efficiency.