Subspace precoding with limited feedback for the massive MIMO interference channel

A non-iterative two-stage precoding scheme for the multiple-input-multiple-output interference channel (IC) with a large number of transmit antennas is presented. Second stage precoders are used to compress the channel state information (CSI) of interfering links, while keeping the multiplexing gain of the IC constant. First stage precoders zero-force the interference based on the compressed CSI of interfering links. In addition, a proper design of the second stage precoders forces the first stage precoders to span a reduced subspace containing the maximal direct links´ power, resulting in a better zero-forcing solution in terms of sum-rate. For a fixed number of receive antennas and transmitter/receiver pairs, the required feedback amount of interfering links is constant, regardless of the number of transmit antennas. As cooperative algorithms are very sensitive to CSI errors, the proposed scheme offers an attractive solution in case CSI feedback constitutes the system bottleneck.