Channel Recovery for Asymmetrical Uplink and Downlink Transceivers in Massive MIMO Systems with UPAs

The asymmetrical transceiver architecture has shown potential in reducing hardware complexity and cost in massive multiple-input multiple-output (MIMO) systems. However, channel recovery is necessary for the asymmetrical transceiver to acquire excellent transmission performance. Although the uniform planar array (UPA) is widely deployed in practical systems, the compact form of UPAs will result in high computational complexity due to the inherent high-dimensional nature of the array. The angle ambiguity problem also arises when directly extending the uniform linear array channel recovery method into the UPAs. To address these challenges, we propose a low-complexity gridless channel recovery method in this paper. First, the concept of the mixed angle for UPAs is introduced to deal with the low elevation angular resolution originating from the compact array form. After that, an antenna selection algorithm is designed to construct a virtual array based on the mixed angle to maximize the virtual array aperture with a minimal number of antennas. Finally, a low-complexity UPAbased modified newtonized orthogonal matching pursuit channel recovery algorithm is developed to mitigate angle ambiguity, thus enabling accurate reconstruction of the full downlink channel state information. Numerical results demonstrate the superiority of the proposed method in significantly reducing the number of receive uplink radio frequency chains while ensuring satisfactory channel recovery performance.