On the Impact of the Radiation Pattern of the Antenna Element on MU-MIMO Indoor Channels

This paper presents an analysis of the effect that the radiation pattern of the antenna element that makes up the base station array has on the structure of multi-user multiple-input multiple-output (MU-MIMO) channels. In this paper, the analysis focuses on the uplink. It is well known that the antennas are an inseparable part of the radio channel. The use of more or less directional antennas as elements of the base station array of a MIMO system influences the channel in two fundamental parameters that affect the performance of MU-MIMO systems: on the one hand, the coherence bandwidth, which determines the necessary overhead in the channel estimation; and, on the other hand, the orthogonality of the subchannels between the multiple users and the base station, which influences the degree with which the condition of “favorable propagation” is fulfilled. Based on an experimental analysis using both omnidirectional and directional antennas, conclusions are drawn about how these two parameters are affected and their influence on the spectral efficiency obtainable. The measurement campaign was carried out in an indoor environment in the 3 to 4 GHz band.