| 1. |
- Dahman, Ghassan, et al.
(författare)
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Cross-Correlation of Large-Scale Parameters in Multi-Link Systems : Analysis using the Box-Cox Transformation
- 2018
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Ingår i: IEEE Access. - 2169-3536. ; 6, s. 13555-13564
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Tidskriftsartikel (refereegranskat)abstract
- Spatially distributed transmission points connected to the same source, known as distributed antenna systems, can improve system performance compared to single-link traditional systems. However, the anticipated gain depends heavily on the cross-correlation properties of the large-scale parameters (LSPs) of the different links. Usually, measured LSPs—except the large-scale fading—have non-Gaussian distributions. Therefore, in order to study their multi-link cross-correlation properties, scenario- and parameter-specific adhoc transformations are applied such that the LSPs have Gaussian distributions in the transform domain [1], [2]. In this work, we propose using the Box-Cox transformation as a general framework for homogenizing this conversion step. The Box-Cox transformation is by nature not distribution specific; therefore, it can be used regardless of the empirical distributions of the studied LSPs. We demonstrate the applicability of the proposed framework by studying multi-link fully-coherent propagation measurements of four base stations and one mobile station in a suburban microcell environment at 2.6 GHz. The inter- and intra-link crosscorrelation of four LSPs—the large-scale fading, and the delay, azimuth, and elevation spreads—are analyzed and their distributions are modeled. Based on our analysis, it is found that, for the investigated environment: 1) the LSPs of the different links can be modeled using unimodal and bimodal Gaussian distributions, and 2) the inter- and intra-link cross-correlation coefficients of the different studied LSPs can be modeled using the Truncated Gaussian distribution. The proposed models are validated using the Kolmogorov-Smirnov test and their parameters are provided.
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| 2. |
- Flordelis, Jose, et al.
(författare)
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Spatial Separation of Closely-Located Users in Measured Massive MIMO Channels
- 2018
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Ingår i: IEEE Access. - 2169-3536. ; 6, s. 40253-40266
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Tidskriftsartikel (refereegranskat)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.
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| 3. |
- Shekhan, Ahmad, et al.
(författare)
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Experimental Evaluation of the Performance of CoMP Systems for Closely-Located Users Including Users' Body Influence
- 2018
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Ingår i: 2018 IEEE 87th Vehicular Technology Conference, VTC Spring 2018 - Proceedings. - 9781538663554 ; 2018-June, s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Based on multi-link synchronous propagation measurements, we study the downlink performance of Coordinated Multi-point (CoMP) systems. The propagation measurements took place in an outdoor micro-cellular environment with two base stations (BSs) located 60 m apart, each equipped with two cross-polarized co-located antennas. We focus on the challenging case of having closely-located users with 0.5 m inter- user distance. We consider four virtual users, each equipped with two antennas, moving along various routes. The patterns of the users' antennas, including the user's body influence, are measured in static scenarios with an upper body phantom and a handset mockup in the LTE 2.5-2.7 GHz band. The users' composite channel matrices are constructed based on: 1) the propagation channel represented by the multipath components extracted from the propagation measurements and 2) the user- influenced antenna pattern. We first analyze the effect of the BS antenna polarization on the collinearity among the users' channel matrices. Then, we evaluate the effect of the BS antenna polarization on improving the system performance, where the performance is evaluated based on two criterion: the number of users that the system is able to serve in the same time-frequency resource, and the achievable sum-rate. It is found that using cross- polarized BS antenna improves the fairness and the sum-rate of the system. It is also found that, in contrast to the case of conventional co-located MIMO, the improvement gained by CoMP systems (with per-BS power control) from using cross-polarized BS antennas is mainly attributed to improving the multiplexing gain of the system while the system's effective power gain has insignificant contribution.
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