Predictive quantization of bit loading for MIMO time-correlated channels with limited feedback

In this paper we consider variable-rate transmission for time-correlated MIMO (multi-input multi-output) channels with limited feedback. The number of bits loaded on each subchannel of the MIMO system is dynamically assigned according to the current channel condition and fed back to the transmitter. As the channel is time-correlated, so is bit loading. We propose to feedback bit loading using predictive coding, which is known to be a powerful technique for quantizing correlated signals. Assuming the channel is a first-order Gauss-Markov random process, we derive the optimal predictor for the bit loading to be coded. We show that the subchannels prediction errors are approximated Gaussian and thus can be quantized using quantizers designed for Gaussian random variables. Simulations demonstrate that the proposed predictive coding can achieve a very good approximation of the desired transmission rate with a very low feedback rate.