Near-Field Channel Estimation for Hybrid Massive MIMO-OFDM Systems

This paper proposes inclusive polar-domain simultaneous orthogonal matching pursuit (inclusive P-SOMP) method to estimate near-field channel for the hybrid massive multiple-input multiple-output (MIMO)-orthogonal frequency division multiplexing (OFDM) systems. In contrast to the far-field region, where the wavefronts take on a planar shape, wavefronts originating from the near-field region exhibit angle-range dependent spherical waveforms. Therefore, it is imperative to jointly consider both angles and ranges for precise channel estimation. In OFDM systems, the channel values of different subcarriers are also dependent on the ranges, indicating that frequency selectivity is determined by these ranges. The proposed method comprehensively addresses this point. We begin by vectorizing the received pilot signal and generating a dictionary to assess the sparsity of the channel in this form. Subsequently, we employ an inclusive P-SOMP approach to estimate the near-field channel. The numerical results demonstrate that the proposed method surpasses P-SOMP, particularly in terms of range estimation. This performance improvement positions the proposed method as an effective approach for near-field channel estimation.