Low complexity algorithm for rate and power quantization in extended V-BLAST

Using multiple antennas at both the transmitter and receiver, BLAST exploits the multipath characteristics of a wireless channel to enable very large capacities. In an extended VBLAST, those capacities are approached with singledimensional coding and rate adaptation. However, such results require infinite precision for rate and power, which is not implementable due to a limited data rate on the feedback channel. In this paper, we show that discretising the rates to QAM constellations causes a 3-5 dB penalty. We then propose SQPC (Successive Quantization with Power Control), an ad-hoc low-complexity algorithm that reduces that penalty to 1-3 dB. We show that SQPC closely approaches the performance limit attainable with discrete QAM rates, which we find numerically by exhaustive search.