Exploiting Spatial Interference Alignment and Opportunistic Scheduling in the Downlink of Interference Limited Systems

TL;DR

This paper investigates how spatial interference alignment and opportunistic scheduling enhance interference mitigation in multi-antenna downlink systems, providing bounds on outage capacity and analyzing the impact of encoding schemes and user configurations.

Contribution

It introduces a framework combining scheduling and multi-antenna processing that exploits spatial interference alignment for improved interference suppression and capacity optimization.

Findings

Opportunistic scheduling exploits spatial interference alignment for interference mitigation.

Sum outage capacity can be maximized by reducing the multiplexing rate below the maximum.

Real-valued encoding in multi-user spatial multiplexing can outperform complex encoding.

Abstract

In this paper we analyze the performance of single stream and multi-stream spatial multiplexing (SM) systems employing opportunistic scheduling in the presence of interference. In the proposed downlink framework, every active user reports the post-processing signal-to-interference-plus-noise-power-ratio (post-SINR) or the receiver specific mutual information (MI) to its own transmitter using a feedback channel. The combination of scheduling and multi-antenna receiver processing leads to substantial interference suppression gain. Specifically, we show that opportunistic scheduling exploits spatial interference alignment (SIA) property inherent to a multi-user system for effective interference mitigation. We obtain bounds for the outage probability and the sum outage capacity for single stream and multi stream SM employing real or complex encoding for a symmetric interference channel model. The techniques considered in this paper are optimal in different operating regimes. We show that the sum outage capacity can be maximized by reducing the SM rate to a value less than the maximum allowed value. The optimum SM rate depends on the number of interferers and the number of available active users. In particular, we show that the generalized multi-user SM (MU SM) method employing real-valued encoding provides a performance that is either comparable, or significantly higher than that of MU SM employing complex encoding. A combination of analysis and simulation is used to describe the trade-off between the multiplexing rate and sum outage capacity for different antenna configurations.