Low complexity millimeter-wave LOS-MIMO precoding systems for uniform circular arrays

In this paper we investigate low complexity millimeter-wave communication systems for uniform circular arrays (UCAs) in line-of-sight (LOS) multiple-input multiple-output (MIMO) channels. We first demonstrate that the MIMO channel matrices for UCAs in LOS-MIMO channels are circulant matrices. Then, we show that the channel matrices can be made orthogonal by choosing the array diameters appropriately as a function of range and wavelength for the 3×3 and 4×4 UCAs. We also derive simple analytical expressions of eigenvalues as a function of array design. Finally, we propose a high performance LOS-MIMO precoding system which combines forward error correction (FEC) codes and spatial interleaver with fixed precoding matrix. Unlike the SVD based eigenmode system, the proposed precoding system does not require CSI estimation, SVD calculation and feedback of precoding matrix owing to the properties of circulant matrices. Simulation results show that the proposed low complexity system can obtain excellent performance in various link ranges.