Energy- and Spectral-Efficiency Tradeoff in Beam Domain Massive MIMO Downlink with Statistical CSIT

We investigate energy- and spectral-efficiency trade-off by optimizing resource efficiency (RE) for single-cell massive multiple-input multiple-output (MIMO) downlink transmission with only statistical channel state information available at the transmitter (CSIT). We first show that beam domain transmission is favorable for RE optimization in massive MINIO downlink, by deriving a closed form solution for the eigenvectors of the optimal transmit covariance matrices. With this conclusion, the RE optimization precoding design is reduced to a real-valued power allocation problem. Exploiting sequential optimization and random matrix theory, we further propose a low-complexity two-layer water-filling-structured power allocation algorithm. Numerical results demonstrate the effectiveness of our proposed statistical CSI aided RE optimization approach.