Experimental Analysis of Multipath Characteristics in Indoor Distributed Massive MIMO Channels

Distributed massive multiple-input multiple-output (MIMO), also known as cell-free massive MIMO, has emerged as a promising technology for sixth-generation (6G) wireless networks. This letter introduces an indoor channel measurement campaign designed to explore the behavior of multipath components (MPCs) in distributed massive MIMO channels. Fully coherent channels were measured between eight distributed uniform planar arrays (128 elements in total) and a 12-meter user equipment route. Furthermore, a method is introduced to determine the order (single- or multi-bounce) of MPC interaction by leveraging map information and MPC parameters. In addition, a Kalman filter-based framework is used for identifying the MPC interaction mechanisms (reflection or scattering/diffraction/mixed). Finally, a comprehensive MPC-level characterization is performed based on the measured channels, including the significance of the single-bounce MPCs, the spherical wavefront features, the birth-and-death processes of the MPCs, and the spatial distribution of reflections. The findings serve as a valuable reference for understanding MPC propagation behavior, which is necessary for accurate modeling of indoor distributed massive MIMO channels.