Transmit Power Allocation for the V-BLAST Algorithm

Optimum power allocation for the V-BLAST algorithm, which is based on various criteria (average and instantaneous block and total error rates (BLER and TBER)), is considered. Closed-form solutions are derived for high-SNR case in a Rayleigh fading channel. They are shown to be robust to small variations in allocated power and average SNR. It is demonstrated that the optimization "on average" is only slightly worse than the instantaneous one, albeit the latter requires an instantaneous feedback and hence is of higher complexity. The generic upper-bound for the SNR gain of any power allocation technique is derived. The BLER and TBER optimization criteria result in the same performance. Power optimization (of unordered BLAST) and optimal ordering result in almost the same performance improvement at high SNR

Performance Analysis of V-BLAST with Optimum Power Allocation

Comprehensive performance analysis of the unordered V-BLAST algorithm with various power allocation strategies is presented, which makes use of analytical tools and resorts to Monte-Carlo simulations for validation purposes only. High-SNR approximations for the 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 any type of fading This upper bound is achieved at high SNR by the considered optimization strategies. 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, including compact closed-form approximations. 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

On Optimum Power Allocation for the V-BLAST

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.Comment: Accepted by IEEE Transactions on Communications, Apr. 200