Maximizing the Cutoff Rate in a Quantized MIMO Wireless System with AGC

We investigate the effects of quantization and AGC (Automatic Gain Control) in MIMO (Multiple Input Multiple Output) wireless systems. We derive the cutoff rate equations for a deterministic MIMO channel with quantization at the receiver inputs and demonstrate by numerical simulation the dependence of the cutoff rate on the receiver AGC settings. Then we propose a fast AGC algorithm to maximize the cutoff rate for each channel realization and use it in numerical simulations to evaluate the quantized MIMO system performance in a Rayleigh channel. We find that even quite low resolution quantizers yield cutoff rates very close to those of equivalent unquantized systems when the fast AGC algorithm is applied. Results are presented for BPSK and QPSK modulations for a 2×2 MIMO configuration in deterministic and Rayleigh channels.