Adaptive Modulation for MIMO Systems in Time-Varying Channels

In this report, we investigate the adaptive modulation issue for MIMO systems in timevarying channels and propose a low complexity rate quantization scheme, which is called ERQ (Enhanced Rate Quantization). Without any exhaustive numerical search, the ERQ with square QAM constellations of 5 rate levels achieves the spectral efficiency within 0.2dB of the efficiency obtained with the optimal continuous rate and power adaptation. In addition, with ERQ algorithm, the BER and average transmit power constraint are satisfied well. ERQ can be also applied to V-BLAST system, where the optimal adaptive modulation scheme is very hard to be found due to OSD (Optimum Successive Decoding) at the receiver. The results show that the spectral efficiency with ERQ is about 1.5 dB greater than other recently proposed rate quantization for V-BLAST. We also propose another rate quantization scheme for V-BLAST, called TSQPC, which performs comparable to ERQ in V-BLAST.