On the Information Rate of MIMO Systems with Finite Rate Channel State Feedback and Power On/Off Strategy

TL;DR

This paper analyzes the information rate of MIMO systems with finite feedback and power on/off strategies, deriving asymptotic optimal beam usage ratios and a power efficiency factor to optimize system performance.

Contribution

It introduces a near optimal power on/off strategy with a constant number of on-beams and provides formulas to evaluate power efficiency under imperfect beamforming.

Findings

Optimal on-beam ratio converges to a constant at high SNR.

Power efficiency factor quantifies the impact of beamforming imperfections.

Approximate information rate formula matches simulations across SNR regimes.

Abstract

This paper quantifies the information rate of multiple-input multiple-output (MIMO) systems with finite rate channel state feedback and power on/off strategy. In power on/off strategy, a beamforming vector (beam) is either turned on (denoted by on-beam) with a constant power or turned off. We prove that the ratio of the optimal number of on-beams and the number of antennas converges to a constant for a given signal-to-noise ratio (SNR) when the number of transmit and receive antennas approaches infinity simultaneously and when beamforming is perfect. Based on this result, a near optimal strategy, i.e., power on/off strategy with a constant number of on-beams, is discussed. For such a strategy, we propose the power efficiency factor to quantify the effect of imperfect beamforming. A formula is proposed to compute the maximum power efficiency factor achievable given a feedback rate. The information rate of the overall MIMO system can be approximated by combining the asymptotic results and the formula for power efficiency factor. Simulations show that this approximation is accurate for all SNR regimes.