Channel Estimation via Subcarrier Grouping for Wideband mmWave Hybrid Massive MIMO-OFDM Systems

This paper studies the channel estimation of millimeter-wave massive multiple-input multiple-output orthogonal frequency division multiplexing systems with a wide bandwidth and a hybrid structure. By considering the influence of the frequency-spatial wideband effect and the channel sparsity, the subcarriers are grouped, the support as well as the angle of each group are estimated. Based on the angle estimate, the support of each subcarrier is deduced. The computational complexities are analyzed and compared, which show the proposed method has a lower computational complexity. The Cramér-Rao bound (CRB) and the spectral efficiency are also analyzed. The analysis shows that the spectral efficiency increases logarithmly with the increase of the signal-to-noise ratio when channel estimation is perfect but is limited otherwise. The simulations show the proposed method gets closer to the CRB in channel estimation error and achieves higher spectral efficiency than the existing one.

I. Introduction

The millimeter-wave (mmWave) massive multiple-input multiple-output (MIMO) system has obvious effects in improving the capacity of wireless communication. This is because the mmWave can provide a very wide bandwidth, and a large number of antennas can provide diversity gains [1], [2], [3], [4]. However, as the bandwidth and the number of antennas are large, the spatial-wideband effect occurs and the beam squint is caused [5], [6], which makes channel estimation in wideband mmWave massive MIMO systems challenging.