Design and Analysis of LoS-MIMO Systems With Uniform Circular Arrays

We consider the design of a uniform circular array (UCA) system under array misalignment over line-of-sight (LoS) channels. UCAs have been considered as useful array structures since their LoS channels can be diagonalized without the channel state information at the transmitter (Tx). However, such a characteristic holds only when transceiver arrays are perfectly aligned. To overcome this difficulty, we propose an optimal design method and transceiver architectures for UCA systems under array misalignment that achieve channel capacity without knowledge of misalignment angles. To this end, we first verify that the singular values of the misaligned UCA system are independent of tilting and center-shift and small relative array rotation, but fluctuate with the Radii Product to Distance Ratio (RPDR). Using the result, we present an optimal design method for UCA systems that performs an one-dimensional search for the RPDR to maximize channel capacity, and we show that a simple zero-forcing (ZF) receiver can achieve the maximum channel capacity because of the channel characteristic at the optimal design criteria. Additionally, we propose a low-complexity precoding scheme for UCA systems in which the optimal design criteria cannot be fulfilled. The simulation results demonstrate the validity of the proposed design method and transceiver architectures.