Optimization and performance analysis of the V-BLAST algorithm

Abstract

Complexity-performance tradeoff in different implementations of the V-BLAST algorithm is discussed. Low-complexity alternatives to the optimal ordering procedure, such as ordering at 1st step, adaptive power allocation and pre-set non-uniform power allocation are proposed. A unified analytical framework for the optimum power allocation in the V-BLAST algorithm is presented. Comparative performance analysis of the optimum power allocation based on various optimization criteria (average and instantaneous block and total error rates) is given. Uniqueness of the optimum power allocation is proven for several scenarios. Compact closed-form approximations for the optimum power allocation and for the optimized error rates are derived. The SNR gain of optimization is rigorously defined and analyzed 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.