Outdoor 5G Radio Access Experiments on Downlink Distributed MIMO Separation Distance with Beamforming in 28 GHz Frequency Band.

Based on a 5G cellular radio access system, this paper presents experimental results of line-of-sight (LoS) outdoor field measurements clarifying the 4-by-8 multiple-input multiple-output (MIMO) throughput performance when applying distributed MIMO with narrow antenna-beam tracking in the 28-GHz frequency band in the downlink. To investigate the influence of the separation distance between distributed transmission points (TPs), deployments of distributed MIMO with various TP separation distances from 0.115 m to 20 m are investigated. The throughput and average rank selectivity increases throughout the area as the separation distance increases indicating that the channel correlation decreases as the distance increases. When the separation distance is 20 m, throughput performance exceeding 11 Gbps is observed with a high average rank of nearly 4. For the distributed MIMO gain in terms of throughput, the throughput gain of 50% is confirmed in the downlink at the cumulative distribution function of 60% compared to that without separation. In addition, the degree of additional improvement in the throughput performance is smaller when the distance between TPs becomes greater than 4 m, indicating that 4 m is sufficient to support a 100 m LoS distance with good throughput performance.