Ergodic Capacity, Capacity Distribution and Outage Capacity of MIMO Time-Varying and Frequency-Selective Rayleigh Fading Channels

The ergodic capacity, capacity distribution and outage capacity are investigated for MIMO wireless systems under time-varying and frequency-selective Rayleigh fading channels. Our theoretical results and Monte-Carlo simulations show that: (1) if the frequency-selective Rayleigh fading channel impulse response has no inter-tap correlations, then its ergodic capacity is the same as that of the frequency flat Rayleigh fading channel, otherwise, its ergodic capacity is less than that of the frequency flat Rayleigh fading channel; (2) time variations have no influence on ergodic capacity but have significant impact on the capacity distribution and outage capacity in the case of finite coding length; (3) the maximum diversity level of a MIMO channel is quantified as M ·N ·L ·NDPR , where M,N , and L are the number of receive antennas, the number of transmit antennas, and the channel length, respectively. The fourth-dimensional diversity is provided by time variations due to Doppler spread with the order being NDPR = 1+ 2KFdTs, where K is the coding length, Fd the maximum Doppler, and Ts the symbol period.