How often channel estimation is needed in MIMO systems

In this paper we develop a unique framework for evaluating the required repetition rate of channel estimation for multiple-input multiple-output (MIMO) systems in slowly fading radio channels. An analytical formula for the interference due to the temporal variation of the channel coefficients is given. This makes it possible to evaluate the time interval in which the channel has to be estimated again, in order to keep the error probability below a desired threshold. This interval depends not only on the Doppler spread of the channel but also on the antenna configuration, detection algorithm and modulation scheme.