Optimal Training Length for MIMO Systems with Transmit Antenna Correlation

By maximizing a derived lower bound on the ergodic capacity, the optimal design of training length is given for Multiple-Input Multiple-Output (MIMO) systems. The channel is assumed to be flat fading in presence of spatial fading correlation only at the transmitter, which is known a priori by both ends. Different from the case of independent and identically distributed channel, the optimal training length no longer equals the number of transmit antennas but is just the same as the rank of transmit correlation matrix. The stronger the channel correlation is, the less the optimal training length is. This coincides with the fact that the accuracy of channel estimation is being improved when the channel correlation increases under equal training intervals.