Measuring Propagation Channel Variations and Reciprocity using 28 GHz Indoor Distributed Multi-user MIMO

This paper describes the indoor experimental verifications of a 28 GHz multi-user multiple-input multiple-output testbed considering 5G networks. A base station (BS) of the testbed has eight transceivers and eight distributed antenna units consisting of 15 elements inline antennas. The testbed is built at total reflection circumstances in a shield room. The over-the-air (OTA) experiment with single user equipment (UE) demonstrates that channel quality variations in the UE locations, frequency, and time are decreased by using the eight antenna units. The OTA experiment with two UEs shows uplink to downlink channel reciprocity by using zero-forcing pre-coded signals in millimeter-wave.