Impact of Residual Transmit RF Impairments on Training-Based MIMO Systems

TL;DR

This paper investigates how residual transmit RF impairments affect training-based MIMO systems, deriving new estimators, analyzing achievable rates, and showing large antenna arrays can mitigate additional training needs caused by impairments.

Contribution

It introduces a new linear channel estimator for MIMO systems with residual RF impairments and analyzes the impact on training and achievable rates, including large-scale MIMO scenarios.

Findings

Residual impairments cause an error floor at high SNRs.

Optimal training length increases with residual impairments.

Large antenna arrays can eliminate extra training requirements.

Abstract

Radio-frequency (RF) impairments, which intimately exist in wireless communication systems, can severely limit the performance of multiple-input multiple-output (MIMO) systems. Although we can resort to compensation schemes to mitigate part of these impairments, a certain amount of residual impairments always persists. In this paper, we consider a training-based point-to-point MIMO system with residual transmit RF impairments (RTRI) using spatial multiplexing transmission. Specifically, we derive a new linear channel estimator for the proposed model, and show that RTRI create an estimation error floor in the high signal-to-noise ratio (SNR) regime. Moreover, we derive closed-form expressions for the signal-to-noise-and-interference ratio (SINR) distributions, along with analytical expressions for the ergodic achievable rates of zero-forcing, maximum ratio combining, and minimum mean-squared error receivers, respectively. In addition, we optimize the ergodic achievable rates with respect to the training sequence length, and demonstrate that finite dimensional systems with RTRI generally require more training at high SNRs than those with ideal hardware. At last, we extend our analysis to large-scale MIMO configurations, and derive deterministic equivalents of the ergodic achievable rates. It is shown that, by deploying large receive antenna arrays, the extra training requirements due to RTRI can be eliminated. In fact, with sufficiently large number of receive antennas, systems with RTRI may even need less training than systems with ideal hardware.