| 1. |
- Bengtsson, Erik L, et al.
(författare)
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A Case Study on the Influence of Multiple Users on the Effective Channel in a Massive MIMO System
- 2019
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Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; , s. 1-6
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Tidskriftsartikel (refereegranskat)abstract
- We investigate the importance of weak clusters when modeling a wireless massive MIMO channel. We do this by studying the influence of densely spaced terminals and the number of base-station antennas for a zero-forcing precoded massive MIMO system. In particular, we focus on the influence on the correlation and imbalance between the signals at the terminal antennas, the effective channel-gain, the eigenvalue distributions and the number of clusters.The study is based on measured radio-channels from terminal prototypes with integrated antennas connected to a massive MIMO testbed.We further evaluate the advantage of using block-diagonalized zero-forcing compared to conventional zero-forcing in a massive MIMO system. Unexpectedly, terminals with low antenna envelope correlation coefficient may benefit significantly from block-diagonal zero-forcing in a massive MIMO system.The main conclusion is that weaker clusters are important when modeling multi-user scenarios.
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| 2. |
- Bengtsson, Erik L., et al.
(författare)
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A Simulation Framework for Multiple-Antenna Terminals in 5G Massive MIMO Systems
- 2017
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Ingår i: IEEE Access. - 2169-3536. ; 5, s. 26819-26831
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Tidskriftsartikel (refereegranskat)abstract
- The recent interest in massive MIMO has spurred intensive work on massive MIMO channel modeling in contemporary literature. However, current models fail to take the characteristics of terminal antennas into account. There is no massive MIMO channel model available that can be used for evaluation of the influence of different antenna characteristics at the terminal side. In this paper, we provide a simulation framework that fills this gap. We evaluate the framework with antennas integrated into Sony Xperia handsets operating at 3.7 GHz as this spectrum is identified for the 5G new radio standard by 3GPP. The simulation results are compared with measured terminal performance when communicating with the Lund University’s massive MIMO testbed under the same loading conditions. Expressions are derived for comparison of the gain obtained from different diversity schemes computed from measured far-field antenna patterns. We conclude that the simulation framework yields results close to the measured ones and that the framework can be used for antenna evaluation for terminals in a practical precoded massive MIMO system.
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| 3. |
- Bengtsson, Erik L, et al.
(författare)
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Simulation of Multiple-Antenna Terminal Performance in Massive MIMO Systems based on Indoor Measurements
- 2020
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 69:1, s. 418-427
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Tidskriftsartikel (refereegranskat)abstract
- In massive MIMO systems the uplink pilot signalstransmitted by a terminal define the channel seen by the basestation. This gives the terminal some degree of freedom selectingan uplink pilot transmission strategy. In this paper, we investigatethe benefit of different pilot transmission strategies when increasingthe number of antennas in the terminal. Building on previouswork on a simulation framework for Multiple-antenna terminalsin 5G massive MIMO systems, this paper presents simulatedperformance results for various transmission schemes. The resultsare calibrated to reflect a real communication situation in a largeauditorium. Emulating the measurement set-up, we show that theframework can be tuned to generate channel distributions thatmatch measured data. Under generalized conditions, we performsimulations for different terminal transmission-strategies, bothrelated to single stream and multiple streams. All evaluations arebased on terminals with four antennas integrated into real SonyXperia smartphone-chassis, tuned to 3.7 GHz. The measurementsare conducted by using the Lund University Massive MIMOtestbed with its 100 antennas. The results clearly show theadvantage of increasing the antenna-count also at the terminalside in massive MIMO systems.
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| 4. |
- Dahman, Ghassan, et al.
(författare)
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On the probability of non-shared multipath clusters in cellular networks
- 2015
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Ingår i: IEEE Wireless Communications Letters. - 2162-2345. ; :99
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Tidskriftsartikel (refereegranskat)abstract
- In Space Division Multiple Access (SDMA) systems, users are separated based on their positions. The base-station (BS) signals typically reach the users through multipath clusters. The goal of this work is to find the probability that a randomly selected user will receive the signal from the BS via at least one nonshared (by any other user) multipath cluster. This probability, referred to as PSuccess, provides (under some conditions) the limit of the probability that the BS is able to communicate successfully with a randomly selected user using SDMA without causing significant interference to other users. In order to find PSuccess, we first derive a model describing the probability distribution function (pdf) of the non-overlapping area of a set of circles, that have the same radius and are spatially distributed according to a Poisson distribution. Then, the proposed model for this pdf is used to express PSuccess as a function of the user’s intensity and the clusters’ intensity. Simulations, using the COST 2100 model, for outdoor and indoor scenarios, are used to validate the derived expression for PSuccess with a very good agreement, where the maximum error was 0:04.
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| 5. |
- Flordelis, Jose, et al.
(författare)
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Massive MIMO Performance - TDD Versus FDD : What Do Measurements Say?
- 2018
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Ingår i: IEEE Transactions on Wireless Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1276 .- 1558-2248. ; 17:4, s. 2247-2261
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Tidskriftsartikel (refereegranskat)abstract
- Downlink beamforming in Massive MIMO either relies on uplink pilot measurements--exploiting reciprocity and time-division duplexing (TDD) operation, or on the use of a predetermined grid of beams with user equipments reporting their preferred beams, mostly in frequency-division duplexing (FDD) operation. Massive MIMO in its originally conceived form uses the first strategy, with uplink pilots, whereas there is currently significant commercial interest in the second, grid-of- beams. It has been analytically shown that with isotropic scattering (independent Rayleigh fading) the first approach outperforms the second. Nevertheless, there remains controversy regarding their relative performance in practical channels. In this contribution, the performances of these two strategies are compared using measured channel data at 2.6 GHz.
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| 6. |
- 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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| 7. |
- Gao, Xiang, et al.
(författare)
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Massive MIMO performance evaluation based on measured propagation data
- 2015
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 14:7, s. 3899-3911
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Tidskriftsartikel (refereegranskat)abstract
- Massive MIMO, also known as very-large MIMO or large-scale antenna systems, is a new technique that potentially can offer large network capacities in multi-user scenarios. With a massive MIMO system, we consider the case where a base station equipped with a large number of antenna elements simultaneously serves multiple single-antenna users in the same time-frequency resource. So far, investigations are mostly based on theoretical channels with independent and identically distributed (i.i.d.) complex Gaussian coefficients, i.e., i.i.d. Rayleigh channels. Here, we investigate how massive MIMO performs in channels measured in real propagation environments. Channel measurements were performed at 2.6 GHz using a virtual uniform linear array (ULA) which has a physically large aperture, and a practical uniform cylindrical array (UCA) which is more compact in size, both having 128 antenna ports. Based on measurement data, we illustrate channel behavior of massive MIMO in three representative propagation conditions, and evaluate the corresponding performance. The investigation shows that the measured channels, for both array types, allow us to achieve performance close to that in i.i.d. Rayleigh channels. It is concluded that in real propagation environments we have characteristics that can allow for efficient use of massive MIMO, i.e., the theoretical advantages of this new technology can also be harvested in real channels.
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| 8. |
- Harrysson, Fredrik, et al.
(författare)
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Efficient experimental evaluation of a MIMO handset with user influence
- 2010
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Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 9:2, s. 853-863
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Tidskriftsartikel (refereegranskat)abstract
- The immediate environment of handset antennas, including the casings and the users holding the handsets, has a strong impact on the radio channel in mobile communication. In this paper we investigate a composite channel method that synthetically combines double-directional measurements of the userless propagation channel with measured super-antenna patterns, i.e., patterns of the combined antenna-casing-user arrangement. We experimentally evaluate the method by comparing results (power, capacity, and eigenvalue distribution) obtained from this composite method with direct measurements in the same environment. The measurements were done in two static 8 × 4 MIMO scenarios at 2.6 GHz, with the user indoors and the base station located outdoors and indoors, respectively. A realistic user phantom together with a “smart-phone” handset mock-up with four antenna elements was used, and different configurations and orientations were tested. The method gives statistical distributions of the MIMO eigenvalues, that are close to the measured. By using the composite method, we found that the user, apart from introducing hand and body loss that mainly decreases the SNR of the channel, slightly increases the correlation between the fading at the antenna elements.
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| 9. |
- Harrysson, Fredrik, et al.
(författare)
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Experimental Investigation of the Directional Outdoor-to-In-Car Propagation Channel
- 2013
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Ingår i: IEEE Transactions on Vehicular Technology. - 1939-9359. ; 62:6, s. 2532-2543
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- Abstract in UndeterminedThe demand for wireless channel models including realistic user environments is increasing. This motivates work on more detailed models that are reasonably simple and tractable but with adequatestatistical performance. In this paper, we present an investigation of the spatial outdoor-to-in-car radio channel at 2.6 GHz. Specifically, we investigate the performance of a multiple antenna smartphone mockup in the hand of a user. We evaluate and utilize a composite channel approach to combine measured antenna radiation patterns with an estimated spectral representation of the multipath channel outside and inside the car in two different scenarios. The performance of the method is investigated and comparisons with direct channel measurements are performed. Statistical and directional properties of the outdoorto-in-car channel are presented and analyzed. It is found that the composite method, despite nearfieldproblems when estimating plane-wave channel parameters in a very narrow environment, constitutes a tool that provides reasonably viable statistical results. In addition, we have found that the introduction of the car in the propagation environment increases scattering and eigenvalue dispersion while it decreases pairwise antenna signal correlation. These statistical properties are found to slightly increase the possible diversity and the spatial multiplexing gains of multiple antenna terminals when located inside cars. Thispositive effect, however, is small compared to the negative effect of car penetration loss.
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| 10. |
- Rusek, Fredrik, et al.
(författare)
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Scaling up MIMO : Opportunities and Challenges with Very Large Arrays
- 2013
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Ingår i: IEEE signal processing magazine (Print). - : IEEE. - 1053-5888 .- 1558-0792. ; 30:1, s. 40-60
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Tidskriftsartikel (refereegranskat)abstract
- Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].
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