  An analytical framework for minimizing the outage probability of a coded
spatial multiplexing system while keeping the rate close to the capacity is
developed. Based on this framework, specific strategies of optimum power and
rate allocation for the coded V-BLAST architecture are obtained and its
performance is analyzed. A fractional waterfilling algorithm, which is shown to
optimize both the capacity and the outage probability of the coded V-BLAST, is
proposed. Compact, closed-form expressions for the optimum allocation of the
average power are given. The uniform allocation of average power is shown to be
near optimum at moderate to high SNR for the coded V-BLAST with the average
rate allocation (when per-stream rates are set to match the per-stream
capacity). The results reported also apply to multiuser detection and channel
equalization relying on successive interference cancelation.
