A Novel Spatial Multiplexing Architecture with Finite Rate Feedback

The V-BLAST (vertical Bell Labs layered Space-Time) architecture with equal rate and power per antenna and a fixed order of detection is known to suffer from poor performance; in a multi-input multi-output (MIMO) Rayleigh fading channel with Mt transmit antennas and Mr receive antennas (Mr ≥ Mt), the diversity order is only Mr ≥ Mt + 1. There are two remedies available, namely, (a) channel ordered detection at the receiver and (b) allocation of rates and powers at the transmitter. However, given independent coding/decoding at each layer, the diversity gain of V-BLAST even by applying these remedies is fundamentally upper bounded by Mr. In this paper, we show that the story would be dramatically different if the receiver is allowed to feed a few bits of channel state information (CSI) back to the transmitter. We develop an approach of jointly designed ordered detection at the receiver and rate/power allocation at the transmitter. Herein the receiver feeds back a finite number of bits (=log2(Mt!)) to the transmitter regarding the detection order. In particular, we propose what we call the Greedy ordering Rate Tailored V-BLAST (GRT-VB) scheme which, with independent coding/decoding on each layer, is shown to have the diversity-multiplexing (D-M) gain tradeoff which is close to the optimal one (e.g. it has the maximal diversity gain of MrMt). The simulation result validates the superior performance of the proposed scheme.