Capacity and coding for quantized MIMO systems

In this paper, the effects of receive signal quantization on the channel capacity and the performance of error control coding in multi-input multi-output (MIMO) systems are investigated. The receive antennas of a MIMO system experience a channel-dependent superposition of modulated signals originating from all transmit antennas. A fine-granular analog to digital conversion of the resulting irregular constellation is difficult to obtain in practice. The quantization is therefore likely to be rather coarse. It turns out, however, that the loss in channel capacity due to coarse quantization is surprisingly small. On the other hand, existing coding schemes do not seem to tolerate coarse quantization gracefully, producing rather high error floors. Closing the huge gap between information theoretic opportunities offered by coarse quantized MIMO systems on the one hand, and the actual poor performance of coding schemes which are designed without signal quantization in mind, remains a challenging task.