On optimal detection ordering for coded V-BLAST

Optimum ordering strategies for the coded V-BLAST with capacity achieving temporal codes on each stream are analytically studied in this paper, including optimal power and/or rate allocations among data streams. A compact closed-form solution is obtained for the case of two transmit antennas and necessary optimality conditions are found for the general case. The optimal rate allocation is shown to have a major impact (stronger streams are detected last) while the optimal power allocation does not alter the original Foschini ordering (stronger streams are detected first). A sub-optimal ordering is proposed based on the necessary optimality conditions, which performs very close to the optimal one but has much smaller computational complexity. An SNR gain of ordering is introduced and studied. All the results also apply to a multiple-access channel under successive interference cancelation.