Continuous flat-fading MIMO channels: achievable rate and optimal length of the training and data phases

In this paper, we propose a simple framework for evaluating the required repetition rate of channel estimation for multiple-input multiple-output (MIMO) systems in continuous slowly fading radio channels. An analytical formula for the interference due to the temporal variation of the channel coefficients is given and verified by link level simulations based on synthetic and measured impulse responses. The proposed interference model makes it possible to optimize the lengths of the training and data phases under different performance criteria. As an example, we investigate the bit-error rate performance of MIMO systems with zero-forcing detection and determine the time interval, after which the channel has to be estimated again in order to keep the error probability below a desired threshold. In the second part, the lengths of the training and data phases is optimized based on the information-theoretical capacity. It is shown that these lengths depend not only on the Doppler spread of the channel, but also on the antenna configuration and noise power.