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 M_t transmit antennas and M_r receive antennas (M_rgesM_t), the diversity order is only M_r-M_t+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 M_r. 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(M_t!)) 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 M_rM_t). The simulation result validates the superior performance of the proposed scheme.