Cell-free Massive MIMO with multi-antenna access points and user terminals

The objective of the paper is to discuss the optimization of "cell-free" massive MIMO (CF-MaMIMO), in which antennas are distributed among access points (APs) throughout the service area, specifically for the case of multiple antennas at user terminals (UTs). We also focus on millimeter-wave (mmW) systems, where the array gain is important in compensating for the large free space path loss and channels are likely to be relatively sparse. We discuss the importance of channel state information (CSI) at the UTs, and propose an approach using SVD-based precoding with zero-forcing to eliminate inter-user interference. We show that in the case of perfect CSI this approach can asymptotically achieve the single user bound on capacity.