Investigations on Millimeter-Wave Massive MIMO Scenarios by Bidirectional Ray-Tracing Using Stationary-Phase Point Approximation

A bidirectional ray-tracing algorithm based on the identification of stationary-phase points is utilized to investigate the average downlink user data rate and the signal-interference characteristics in a millimeter-wave massive multiple-input multiple-output (MIMO) urban scenario. The ray-tracing simulations rely on the conventional bidirectional ray-tracing technique for collecting the information about the incident rays and corresponding wavefronts, then a stationary-phase point approximation is employed for evaluating the antenna transfer function by the reciprocity integral. Maximum-ratio combining and regularized zero-forcing precoding schemes are considered in a single cell massive MIMO scenario where a frequency of 28 GHz is assumed. Relevant comparisons are made with a carrier frequency of 7 GHz as well, where the lower frequency transmission is found beneficial in noise-limited scenarios, due to the smaller transfer function attenuation. In interference-limited scenarios, the millimeter-wave transmission performs similar to the 7 GHz carrier for a comparable base station antenna arrangement, which can, however, be considerably smaller in absolute size. Another important advantage of the millimeter-wave band is of course the larger available absolute frequency bandwidth.