Abstract: An explicit formula for the ergodic capacity of orthogonal frequency division multiplexing (OFDM)-based multiple-input multiple-output(MIMO) systems under correlated frequency selective Rayleigh fading channels is derived, by simplifying the channel response matrix in the frequency domain into the so-called “Kronecker” model composed of three kinds of correlations, i.e., multipath tap gain correlation and spatial fading correlations at both the transmitter and the receiver. The derived formula is very simple and convenient for one to estimate the effects of all three kinds of correlations on MIMO-OFDM capacity. If taps are independent, there exists a simple expression for the ergodic capacity. In the case of tap correlation, the capacity formula could be further given in an integral expression. Both the validity of the new formula is verified and the effects of correlations, delay spread as well as the number of subcarriers on the ergodic capacity are evaluated via Monte Carlo simulations.

Key words: MIMO, OFDM, Kronecker product, ergodic capacity, channel correlation