Channel Estimation for UPA-Assisted Near-Field Channel in Extremely Large-Scale Massive MIMO Systems

For future 6G communications, extremely large-scale massive multiple-input multiple-output (XL-MIMO) is an effective technology expected to achieve performances break-through. However, the use of large aperture arrays makes it more challenging to acquire accurate channel state information (CSI), especially for the near-field channel under the uniform planar array (UPA) scenario. To address this problem, we propose an effective near-field channel estimation scheme where the base station (BS) deploys the UPA. Specifically, we firstly propose an UPA near-field channel model defining the equivalent elevation-angle (e-angle) and azimuth-angle (a-angle). Then, we propose a dual simultaneous orthogonal matching pursuit (DS-OMP) algorithm to obtain the near-field channel estimation by extracting the parameters from the received signal. Additionally, to reduce the complexity, we propose a single iterative orthogonal matching pursuit (SI-OMP) algorithm further. Finally, numerical results show the superior performances of the proposed scheme compared to the existing channel estimation schemes.