Impact of training on mmWave multi-user MIMO downlink

The impact of training on the performance of millimeter wave multi-user multiple-input multiple-output downlink systems based on hybrid analog/digital beamforming is investigated in the regime of a large number of transmit antennas under the uniform random single-path channel model. In particular, the performance loss with respect to the number of training beams is quantified for general training-based data transmission schemes with several different training beam designs when full training is not applicable. Our analysis provides insights into effective training beam design and simulation result validates our analysis.