The 3D Spatial Non-Stationarity and Spherical Wavefront in Massive MIMO Channel Measurement

With the rapid development of wireless communications, the understanding of three-dimensional (3D) propagation channels becomes essential for design and testing of new wireless technologies. In this paper, an elaborate channel measurement campaign for massive multiple-input multiple-output (MIMO) is presented. The measurement was conducted at 11 GHz in a lobby environment. Two different types of 256-element virtual uniform rectangular arrays (URAs) (i.e. the 4 x64 virtual URA and the 64 x 4 virtual URA) were used in the measurements. The parameters of the multipath components (MPCs), including power, delay, azimuth of departure, and elevation of departure, are estimated by space-alternating generalized expectation-maximization algorithm (SAGE). Based on the observations from realistic measurements, it is suggested that the channel characteristics in both azimuth and elevation dimensions, and the spatial non-stationary phenomenon observed across the large-scale array in both the horizontal and vertical directions, should be taken into consideration in massive MIMO channel modeling. Moreover, spherical wavefront phenomenon which is reflected by the angle offset of MPCs across the array should be also incorporated. In addition, dominant scattering objects in the environment are identified in the paper. These findings are useful for the development of the cluster/geometry-based channel model for massive MIMO communications.