LoS spatial multiplexing and beamforming using uniform circular array of subarrays

摘要

We propose the use of uniform circular array of subarrays (UCA-SAs) for millimeter wave (MMW) communication systems over line of sight (LoS) channels and design beamforming coefficients for each subarray. Specifically, for a UCA-SA consisting of N_s subarrays, which are M × M square arrays, the beamforming coefficients are designed so that the N_s × N_s effective channel becomes circulant. To this end, we first show that the UCA-SA can be decomposed into M~2 concentric UCAs having N_s antenna elements. Then, based on this result, we show that the set of beamforming coefficients making the effective channel circulant consist of identical values. The proposed UCA-SA system employs this type of beamformers, called the constant beamformers. The effective channel of the proposed UCA-SA system can be diagonalized by the discrete Fourier transform (DFT) precoder and the inverse DFT (IDFT) combiner, without the knowledge of channel state information (CSI) at the transmitter. This indicates that constant beamformers are optimal beamformers maximizing the N_s × N_s effective channel's mutual information. Simulation results show that the proposed UCA-SA can outperform the conventional UCA with N_sM~2 antenna elements which are equally spaced on a ring.