A Cross Layer Optimization Based on Variable-Power AMC and ARQ for MIMO Systems

To improve spectrum efficiency (SE), the adaptive modulation and coding (AMC) and automatic repeat request (ARQ) scheme have been combined for MIMO systems. In this paper, we add variable power subject to power constraint in each AMC mode. We use KKT optimization algorithm to get the optimal transmit power and AMC mode boundaries. The numerical results show that the average SE is increased by about 0.5 bps/Hz for 2 x 2 MIMO systems with Nakagami fading with parameter m = 2 when SNR is around 15 dB and the ARQ retransmission is twice.