Channel Rank Analysis of an Outdoor-to-Indoor Massive MIMO Measurement

Massive multiple-input multiple-output (MIMO) communication often assumes propagation with a dense scattering environment. In this context, we performed an outdoor-to indoor massive MIMO channel measurement. To analyze the multipath components (MPCs) we apply the concept of a double directional radio channel. We evaluate the two-dimensional angular power-spectral density, which shows the amount of power that was carried over a certain Direction of Departure (DOD) Direction of Arrival (DOA) pair. The estimation of the angular power-spectral density is achieved by an conventional beamformer. The beamforming results lead to the conclusion that the channel may be described by a low number of MPCs. To analyze the rank of the wireless channel, we compare the achievable rate for the measured channel with low rank approximated versions. The result shows that the measured outdoor-to-indoor MIMO channel is approximated well with a low rank channel model.