On Optimum Power Allocation for the V-BLAST

TL;DR

This paper develops a unified analytical framework for optimal power allocation in V-BLAST systems, deriving compact approximations and analyzing performance gains, robustness, and practical low-complexity solutions.

Contribution

It introduces a unified framework for power allocation in V-BLAST, providing closed-form approximations, performance analysis, and robustness evaluation, including a practical low-complexity power allocation method.

Findings

Optimal power allocation favors lower step transmitters.

SNR gain of optimization is bounded by the number of transmitters.

Robustness of the optimized algorithm is confirmed.

Abstract

A unified analytical framework for optimum power allocation in the unordered V-BLAST algorithm and its comparative performance analysis are presented. Compact closed-form approximations for the optimum power allocation are derived, based on average total and block error rates. The choice of the criterion has little impact on the power allocation and, overall, the optimum strategy is to allocate more power to lower step transmitters and less to higher ones. High-SNR approximations for optimized average block and total error rates are given. The SNR gain of optimization is rigorously defined and studied using analytical tools, including lower and upper bounds, high and low SNR approximations. The gain is upper bounded by the number of transmitters, for any modulation format and type of fading channel. While the average optimization is less complex than the instantaneous one, its performance is almost as good at high SNR. A measure of robustness of the optimized algorithm is introduced and evaluated. The optimized algorithm is shown to be robust to perturbations in individual and total transmit powers. Based on the algorithm robustness, a pre-set power allocation is suggested as a low-complexity alternative to the other optimization strategies, which exhibits only a minor loss in performance over the practical SNR range.