Scheduling and Pre-Conditioning in Multi-User MIMO TDD Systems

TL;DR

This paper explores scheduling and pre-conditioning strategies in multi-user MIMO TDD systems, addressing the challenges of channel estimation and throughput maximization in high-mobility, interference-limited environments.

Contribution

It introduces new scheduling and pre-conditioning schemes tailored for reciprocal channels, improving sum capacity bounds and net throughput in heterogeneous user scenarios.

Findings

Derived a lower bound on sum capacity for homogeneous users.

Optimized training sequence length to maximize net throughput.

Proposed a modified pre-conditioning method for heterogeneous users.

Abstract

The downlink transmission in multi-user multiple-input multiple-output (MIMO) systems has been extensively studied from both communication-theoretic and information-theoretic perspectives. Most of these papers assume perfect/imperfect channel knowledge. In general, the problem of channel training and estimation is studied separately. However, in interference-limited communication systems with high mobility, this problem is tightly coupled with the problem of maximizing throughput of the system. In this paper, scheduling and pre-conditioning based schemes in the presence of reciprocal channel are considered to address this. In the case of homogeneous users, a scheduling scheme is proposed and an improved lower bound on the sum capacity is derived. The problem of choosing training sequence length to maximize net throughput of the system is studied. In the case of heterogeneous users, a modified pre-conditioning method is proposed and an optimized pre-conditioning matrix is derived. This method is combined with a scheduling scheme to further improve net achievable weighted-sum rate.