Outage Analysis and Optimization for Multiaccess/V-BLAST Architecture over MIMO Rayleigh Fading Channels

We consider multi-input multi-output (MIMO) Rayleigh block fading channels and examine the V-BLAST architecture proposed for point-to-point communications over such channels. The results obtained are also applicable to the MIMO multiaccess channel. We derive the outage probabilities or upper bounds to outage probabilities, obtained with the optimum decoder and various successive decoders, namely, the decorrelating decision feedback decoder (D-DFD), the minimum mean-squared error decision feedback decoder (MMSE-DFD) and their generalizations, the group decision feedback decoders. The derivations bring out the intimate connection between the outage probability and the frame error probability (FEP) by establishing achievability and converse results. We then consider the problem of determining the optimal channel dependent grouping rule under a maximum group size constraint such that the resulting outage probability is the minimum among all grouping rules satisfying the maximum group size constraint. We show that an optimal solution can be obtained through a greedy strategy. Finally, we obtain the diversity versus multiplexing tradeoff curves for this architecture for the various decoders considered.