Impact of RF Processing and Switching Errors in Lens-Based Massive MIMO Systems

Lens-based massive multiple-input multiple-output (MIMO) systems have considerable potential to reduce signal processing cost at millimeter-wave frequencies. As a result, they are able to lower the effective channel dimension via beam selection, realized with a network of radio-frequency (RF) switches. However, lens arrays suffer from the inherent quantization of the beamspace, as well as errors due to imperfections in the lens construction itself. Unlike prior works, we model the above effects in the context of a Rotman lens-enabled massive MIMO system. Assuming line-of-sight propagation, we derive analytical approximations of the expected (average) signal-to-interference-plus-noise-ratio (SINR) of a terminal and ergodic sum spectral efficiency of the system. Our analysis caters for spillover losses in the Rotman lens and imperfections in the RF switching matrix, caused by impedance mismatches, as well as poor port isolation. The presented numerical results show large degradation in the expected SINR and ergodic spectral efficiency when considering the above imperfections, yielding more accurate performance assessment of lens-based massive MIMO systems.