Channel Modeling and Channel Estimation for Holographic Massive MIMO With Planar Arrays

In a realistic wireless environment, the multi-antenna channel usually exhibits spatially correlated fading. This is more emphasized when large number of antennas densely deployed, known as holographic massive MIMO (multiple-input multiple-output). first part this letter, we develop model for by considering both non-isotropic scattering and directive antennas. With antennas, it difficult to obtain full knowledge spatial correlation matrix. case, estimation conventionally done using least-squares (LS) estimator that requires no prior information statistics or array geometry. second propose novel scheme exploits geometry identify subspace reduced rank covers eigenspace any The proposed outperforms LS estimator, without user-specific statistics.