Adaptive hybrid precoding and combining in MmWave multiuser MIMO systems based on compressed covariance estimation

In this paper we propose an adaptive multi user (MU) single-cell hybrid precoding strategy that iteratively designs the precoders/combiners exploiting the reciprocity of time division duplex (TDD) millimeter wave systems. The minimum mean square error (MMSE) criterion is considered to design the combiners, which relies on second order statistics of the channel. The covariance of the received signal at the antenna array is estimated online from compressed measurements, leveraging the sparse nature of mmWave channels. The proposed method avoids the explicit estimation of the channel matrix associated to each user, reducing the training overhead, and achieving sum spectral efficiencies comparable to the ones obtained with block diagonalization.