Spatial Non-Stationarity and Polarization Complementarity of Extra-Large Massive MIMO Channel for a Laboratory Indoor Scenario at 3.4 GHz

In this paper, a radio channel measurement campaign at 3.4 GHz with an Extra-Large Massive Multiple Input Multiple Output (XL-MIMO) array was performed in a laboratory indoor environment. This study investigates the near-field channel characteristics of a XL-MIMO system with vertically and horizontally polarized antennas at the receiver (RX) side, focusing on Spatial non-Stationarity (SnS) and polarization complementarity. Through detailed analysis of Power Delay Profiles (PDPs) across the antenna array, we observed significant spatial and temporal variations of Line-Of-Sight (LOS), Obstructed Line-of-Sight (OLOS) and Non-Line-Of-Sight (NLOS) states, which are classified by using K-factor. These findings highlight the SnS of the near-field XL-MIMO channels, influenced by spherical wavefronts and dynamic environmental factors. The spatial discontinuity phenomenon was discovered, since the significant K-factor disparities exceeding 30 dB have been observed between adjacent antenna elements. Furthermore, the complementary behaviors of the two polarizations in both temporal and spatial domain were found, which can be used to enhance spatial diversity, as one polarization often compensates when the other transitions to OLOS/NLOS. Our results can provide valuable insights for developing advanced channel models and optimizing near-field XL-MIMO systems, leveraging polarization diversity to address the challenges for the XL-MIMO laboratory indoor scenarios.