28 GHz Downlink Multi-User MIMO Experimental Verification using 360 Element Digital AAS for 5G Massive MIMO

This paper describes the indoor experimental verification testing results and discussion of a 28 GHz multi-user (MU) multiple-input multiple-output (MIMO) using the 360 element full-digital massive MIMO active antenna system (AAS) for 5G base station applications. AAS accommodates 24 channels 28 GHz transceiver chains and FPGA based on 1-bit direct-IF digital transmitters. The antenna array consists of full digitally controlled 24 streams of 15 elements inline sub-arrays. The simultaneous four beams are generated and the average Effective Isotropically Radiated Power (EIRP) is 59.4 dBm. The throughputs are measured by maximum-ratio-combining (MRC) method and zero-forcing (ZF) method by steering control. The achieved user-equipment (UE) throughputs are 0.996 Gbps with single beam, 0.655 Gbps to 0.857 Gbps with four users by MRC, and 0.673 Gbps to 0.873 Gbps by ZF. The four user cell throughputs are 2.884 Gbps and 3.134 Gbps by MRC and ZF respectively. The achieved spectrum efficiency is 10.4 bps/Hz/cell using 300 MHz OFDM signal. As par author's knowledge, this is a first report for experimental verification of multi-user MIMO using 28 GHz digital AAS.