Channel Characterization for Massive MIMO in Subway Station Environment at 6 GHz and 11 GHz

Massive multiple-input multiple-output (MIMO) has been selected as one of the key technologies of the fifth generation mobile communication system (5G). It can provide high spectral and power efficiency, thus it is suitable to be deployed in different hotspot scenarios. In this paper, a channel measurement campaign using a wideband channel sounder and a 256-element virtual uniform rectangular array (URA) for massive MIMO communications is presented. The measurements were respectively conducted at 6 GHz and 11 GHz, and the subway station environment was considered. The typical channel parameters, root mean square (RMS) delay spread and coherence bandwidth, are analyzed based on the measurements. Moreover, the channel characteristics in angular domain are obtained by applying the space-alternating generalized expectation-maximization algorithm (SAGE). The SAGE estimates are validated by relating them to the physical environment. The overall elevation angle distribution of multipaths is found to be fitted well with Laplace distributions. The global angular spread, including the azimuth spread of departure (ASD) and elevation spread of departure (ESD), are both fitted well with Lognormal distributions. The results in this paper can be fed into the new channel simulator for massive MIMO, and are useful for the design and application of the practical massive MIMO system in the future.