Enhanced Multiple Angles-of-Arrival Detection Using Non-uniform Sub-connection in Hybrid Beamforming Systems

Due to the high cost and power consumption of the radio frequency (RF) chains in massive multiple-input multiple-output (MIMO) systems, the hybrid beamforming (HBF) architecture is a promising candidate for future wireless networks. The massive MIMO systems rely on accurate channel information to maximize the throughput, and the angle-of-arrival (AOA) information is an important part of the channel information, especially in the millimeter wave (mmWave) band. The AOA information is also crucial to positioning which is featured in the next generation mobile communication networks. In this paper, we intend to exploit the enhanced degrees of freedom (DOF) of non-uniform array/connection in HBF systems. A HBF structure with interleaved sub-connection based on nested array geometry is proposed for underdetermined multi-source AOA estimation. This HBF structure can estimate the AOAs of more sources than the number of RF chains and avoid the angle ambiguity issue seen in the AOA estimation in some existing HBF schemes. For the proposed HBF structure as well as the existing schemes, the unequal spatial pattern caused by the sub-arrays may degrade the AOA estimation performance. This issue is also investigated and a phased sub-array design that retains the performance is provided.