Hybrid Precoding Using Projection-aided Block Diagonalization for mmWave MU-MIMO Systems

For next generation wireless networks, hybrid precoding has overcome high path-loss issue in millimeter wave (mmWave) multi-user multiple-input multiple-output (MU-MIMO) communication system. In this paper, we propose a fully connected hybrid precoding scheme for downlink mmWave MU-MIMO systems. In the first step, we design the unconstrained fully digital precoder. To eliminate inter-user-interference (IUI), we use projection matrices on the users' null spaces with employing the information about the angle of departure (AoD). In the second step, we calculate the baseband precoder and radio frequency (RF) precoder through matrix decomposition (MD) of the unconstrained precoder. While the proposed algorithm reduces the dominant computational complexity by approximately 30%, the total sum rate of the simulation is close to 99% as compared with iterative matrix decomposition (IMD-) aided block-diagonalization (BD) algorithm. In addition, the proposed hybrid precoder shows a good performance in a multi-streams environment, and outperforms the traditional BD based scheme by the sum rate of approximately 50%.