Spatial Separation of Closely-Located Users in Measured Massive MIMO Channels

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Abstract

We investigate the ability of massive multiple-input multiple-output (MIMO) systems to spatially separate signals sent to users located close to each other in line-of-sight (LOS) propagation conditions. The analysis is based on fully-synchronous channel measurements of 9 single-antenna users conducted in both indoor and outdoor environments at 2.6 GHz. The users are confined to a small area and communicate concurrently with a 128-antenna base station (BS). We examine the channel condition number, achievable sum rates and number of simultaneously served users in various setups and for various numbers of antennas and precoding schemes. Our results indicate that massive MIMO with 128 antennas and zero forcing (ZF) precoding can simultaneously serve all 9 users with low transmit power values, and with low sum rate losses relative to optimal dirty-paper coding (DPC). This leads us to conclude that users can be spatially separated with massive MIMO, also in tricky scenarios such as the one studied here. However, our results do not support the use of maximum ratio transmission (MRT) precoding for spatial multiplexing of users in the scenarios considered. We also study the physical propagation mechanisms that facilitate spatial separation of users, and the role of antenna polarization at the BS. Our findings are relevant to the design of future 5G communication systems.

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  • Telecommunications
Original languageEnglish
JournalIEEE Transactions on Wireless Communications
StateSubmitted - 2016 Jun 23
Peer-reviewedYes