Experimental Validation of Massive MIMO Linearity Enhancement with DPD in Low-SHF-Band for 5G

Abstract

Massive multi input and multi output (MIMO) for use in 5th Generation (5G) radio access network (RAN) systems has drawn attention as a key technology. Our research focuses on utilizing massive MIMO as an active antenna system (AAS) in the low super-high-frequency (SHF) band, which is expected to be used for 5G commercial bands relatively soon, and on enhancing spectrum efficiency by spatial multiplexing. In this paper, we introduce our latest developed massive MIMO system which has flexible AAS unit configuration, a newly embedded high-performance digital pre-distortion (DPD) scheme to maintain high signal quality even in the high transmission power range, and improves the spatial multiplexing performance of two AAS units (128 antenna elements) by comparison with that of one AAS unit (64 antenna elements).　We evaluate downlink　(DL) multi-user　(MU) MIMO performance in an anechoic chamber, connecting up to a maximum of eight user equipment (UEs) with 16 layers, with two different dense UE allocation scenarios. From the results, we confirmed a greater performance improvement for two AAS units, particularly in the case of the "congested" eight UEs allocation scenario, where the DL SINR reaches 22.9 dB, which has a 4.5 dB gain compared to the DPD-disabled case and a 14.9 dB gain compared to one AAS unit with the DPD-enabled case, respectively. We also confirmed that the developed massive MIMO system can optimize the performance with minimum configuration of AAS units, appropriately according to the environment.