Angular spread measurement and modeling for 3D MIMO in urban macrocellular radio channels

When planar antenna arrays are introduced at the base stations (BSs) of cellular networks, accurate modeling of the spatial radio channel in there-dimension (3D) will become crucial. In this paper, a field measurement campaign was conducted to characterize the 3D spatial propagation to the BS in urban street canyon environments. Using a wideband channel sounder with two uniform planar antenna arrays, the angular spread (AS) in both azimuth and elevation domains at the BS was measured with the user equipment (UE) located at 100 different positions in LOS scenario and 95 positions in NLOS scenario. Contrary to the expected simple correlation between the large-scale fading (like path loss) and AS, our measurements have shown much more complicated relationship between AS and the surrounding environment. It is demonstrated that, in LOS scenario, the AS has positive correlation with the UE-to-BS distance in wide street, but negative correlation in narrow street. In NLOS scenario, the correlation between AS and the transceiver distance is positive when the UE is too close to a building to have 'Quasi-LOS' path (diffracted over the building roof) propagation. However, if 'Quasi-LOS' path is strengthened, the correlation is reversed. These observations lead to the need of more sophisticated models on the angular characteristics in urban radio channels. Based on the collected data, we also present the Laplacian distribution models of AS in both azimuth and elevation domains.