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

Research output: Contribution to journalArticle

Abstract

We investigate the ability of Massive multiple-input multiple-output (MIMO) systems to spatially separate up to eighteen users located close to one another in line-of-sight (LOS) propagation conditions, in both indoor and outdoor environments. For that, we use fully-synchronous measured channels at 2.6 GHz of single-antenna users moving within a small area and concurrently communicating with a base station (BS) equipped with a compact 128-port array. To quantify the degree of spatial user separability, we use three scalar metrics, namely, the achievable sum-rates, the condition number of the channel matrix, and the angle to interference factor. Our results show that Massive MIMO with zero-forcing (ZF) or regularized ZF (RZF) can spatially separate nine, even eighteen, concurrent users at practical SNR values even in the challenging case of dominant LOS propagation. In particular, signal-to-noise ratio losses relative to ideal (non-interfering and equally strong) channels can be reduced dramatically compared with standard multiuser MIMO systems, which typically have the same number of users as BS antennas. Our findings suggest that with RZF or ZF the ratio of BS antennas to number of served users should be at least three to four, to harvest most of the available spatial gains that the environment can offer. Although orthogonality and array gains complement each other, for the suggested ratios of antennas to users, the main contribution to improving system performance, measured in sum-rates, comes from the orthogonality gain.

Details

Authors
Organisations
External organisations
  • University of Electronic Science and Technology of China
  • École de technologie supérieure ETS
Research areas and keywords

Subject classification (UKÄ) – MANDATORY

  • Communication Systems

Keywords

  • Channel measurements, Massive MIMO, spatial separation
Original languageEnglish
Article number8408797
Pages (from-to)40253-40266
Number of pages14
JournalIEEE Access
Volume6
Publication statusPublished - 2018 Jul 8
Publication categoryResearch
Peer-reviewedYes

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