| 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
-
Ingår i: IEEE Wireless Communications Letters. - 2162-2337. ; , s. 1-6
-
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. |
- Bin Redhwan, Sakib, et al.
(författare)
-
Evaluation of the effect of base station antenna polarization on the performance of CoMP transmission techniques based on synchronous multi-link measurements
- 2016
-
Ingår i: 2016 IEEE 27th Annual IEEE International Symposium on Personal, Indoor and Mobile Radio Communications - (PIMRC). - 9781509032549 - 9781509032556
-
Konferensbidrag (refereegranskat)abstract
- In this paper, the effect of polarization on the downlink achievable sum-rate of multi-user Cooperative Multi-Point (CoMP) systems is studied using synchronous multi-link channel measurements with two different antenna arrangements. In the first setup, four dual-polarized antenna patches with inter-patch distance varied from half wavelength to 8 m are considered at the base station (BS). In the second setup, two BSs located 60 m apart are used, each is provided with dual-polarized antennas spaced half a wavelength apart. Based on the BS antenna element selection, scenarios with different antenna polarizations at the BSs are considered. We consider four virtual users each is equipped with two antennas (V and H-polarized) with half-wavelength inter-element distance. The users are equally spaced with inter-user distance of about 0.5 m and moving in different routes. For each setup, the 8 × 4 MIMO multi-user channels are used to evaluate the achievable sum-rate of the system, where the minimum mean square error (MMSE) beamforming at both the BS and the mobile station (MS) is used. It is found that the performance improvement gained from using dual-polarized antennas at the BS vanishes if the BS antenna elements are distributed over large distance (i.e., having a large antenna array aperture). However, in the measured environment, for the case of having two BSs each of which is provided with co-located antennas, using dual-polarized antennas provide about 40% improvement in the ergodic sum-rate compared to using single-polarized antennas.
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| 3. |
- Bourdoux, Andre, et al.
(författare)
-
D1.2 MaMi Channel Characteristics: Measurement Results
- 2015
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Rapport (övrigt vetenskapligt/konstnärligt)abstract
- This deliverable presents channel measurement results for the scenariosOpen exhibition and Crowded auditiorium. The measurement procedureand equipment are described. Massive MIMO (MaMi) channel characteristicsand key parameters are extracted and used in an extended COST 2100channel model for MaMi. The initial validation performed shows that themodel is capable of reproducing the statistics in terms of temporal behaviorof the user separability, singular value spread, capacity and sum-rate anddirectional characteristics. The model can be used for system and link levelMaMi simulations.
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| 4. |
- 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
-
Ingår i: IEEE Access. - 2169-3536. ; 6, s. 13555-13564
-
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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| 5. |
- Dahman, Ghassan, et al.
(författare)
-
Estimating the Cross-Correlation Properties of Large-Scale Parameters in Multilink Distributed Antenna Systems : Synchronous Measurements Versus Repeated Measurements
- 2017
-
Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 66:9, s. 7633-7642
-
Tidskriftsartikel (refereegranskat)abstract
- It is essential to capture the cross-correlation properties of large-scale parameters (LSPs) among different base station links in cooperative multilink systems in order to make realistic performance assessments. In this work, propagation measurements are used to study the cross-correlation properties of different LSPs, namely large-scale fading, delay spread, azimuth spread, and elevation spread of four links. The interlink cross-correlation coefficients of these LSPs are assessed based on two different measurement approaches: 1) synchronous measurements, where the values of the LSPs of the considered links are estimated from the same measurement run; and 2) repeated measurements, where the values of the LSPs of the considered links are estimated from different measurement runs. Repeated measurements are attractive because they are simpler and less expensive. In this paper, we address the following question: Can repeated measurements be used instead of synchronous measurements in order to estimate the LSPs' cross-correlation properties of different links? Based on analysis of wideband synchronous and repeated multilink measurements in a suburban microcell environment at 2.6 GHz, we found that: 1) the mean values of the cross-correlation coefficients are preserved with repeated measurements, and 2) the estimates of the cross-correlation coefficients from repeated measurements are less spread around the mean value than those from synchronous measurements. These findings are explained based on detailed investigation of specific measured cases and further supported by results obtained from Monte Carlo simulations.
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| 6. |
- Dahman, Ghassan, et al.
(författare)
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Experimental Evaluation of the Effect of BS Antenna Inter-Element Spacing on MU-MIMO Separation
- 2015
-
Ingår i: IEEE International Conference on Communications. - 9781467364324 ; 2015-September
-
Konferensbidrag (refereegranskat)abstract
- In this paper, multiple-input multiple-output (MIMO) channel measurements in an outdoor micro-cell environment are used to study the effect of base-station (BS) inter-element spacing on multi-user MIMO signal separation. Users with two dual-polarized patch antennas at the mobile station (MS), and four equally-spaced dual-polarized patch antennas at the BS are considered. At the BS, the inter-element spacing (i.e., the spacing between the four dual-polarized patch antennas), is varied from half a wavelength to 8 m. For each BS inter-element spacing, the 4×8 MIMO channels are used to evaluate the system's capability separating closely located users. This evaluation is done by means of the correlation matrix distance metric (between each pair of closely located users) and the sum-rate capacity of the system (when 8 equally-spaced closely located users are served simultaneously). It is found that the system is capable of separating closely located users as long as the distance between them and the BS is less than the Fraunhofer distance associated with the BS antenna array. In the measured environment, for both LOS and NLOS propagation conditions, users located as close as 0.5 m from each other, having the same orientation, are separated successfully in the multi-user MIMO sense.
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| 7. |
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| 8. |
- Flordelis, Jose
(författare)
-
Engaging Students in Homework Assignments and Self-Study: A Study Case
- 2015
-
Ingår i: LATHE introduction: Learning and teaching in higher education. ; , s. 61-66
-
Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- This paper discusses teaching and learning activities (TLAs) that foster students’ commitment to homework and self-study. The discussion is illustrated with an exercise class, part of the International Master Programme in Wireless Communications at Lund University. The TLAs favored do not only look after the cognitive state and learning style preferences of the students, but they also take into account the teaching abilities of professors. An incremental approach is advocated for, in which more advanced TLAs are gradually added to the teaching and learning situation as the teacher gains in skills and confidence.
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| 9. |
- Flordelis, Jose, et al.
(författare)
-
Exploiting antenna correlation in measured massive MIMO channels
- 2016
-
Ingår i: 2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications, PIMRC 2016. - 9781509032549
-
Konferensbidrag (refereegranskat)abstract
- We investigate antenna correlation of an M-antenna massive multiple-input multiple-output (MIMO) setup with the purpose of obtaining a low-rank representation of the instantaneous massive MIMO channel. Low-rank representation bases using short-term and long-term antenna correlation statistics are defined, and their performance is evaluated with data sets obtained from channel measurements in both indoor and outdoor environments at 2.6 GHz. Our results indicate that the short-term bases can capture a larger amount of the channel energy compared to the long-term ones, but they have a limited timespan, one coherence time or less. On the other hand, the long-term bases are stable over time-spans of a few seconds. Hence, they can be obtained relatively easily. We also investigate a rank-p vector-scalar LMMSE channel estimator that exploits antenna correlation. Our results show that the investigated estimator can achieve a performance similar to that of full-rank LMMSE at a (2p + 1)/M times lower cost. The investigated estimator may be used in conjunction with estimators that exploit correlation in the frequency and time domains or, alternatively, in situations in which these estimators cannot be used, e.g., when pilot separation is larger than the channel coherence bandwidth or time.
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| 10. |
- Flordelis, Jose, et al.
(författare)
-
Initial Characterization of Massive Multi-User MIMO Channels at 2.6 GHz in Indoor and Outdoor Environments
- 2015
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The channel properties have a large influence on user separability in massive multi-user multiple-input multiple-output (massive MIMO) systems. In this paper we present spatio-temporal characteristics obtained from massive MIMO channel measurements at 2.6 GHz. The results are based on data acquired in both indoor and outdoor scenarios where a base station equipped with 64 dual-polarized antenna elements communicates simultaneously with nine single-antenna users. In the outdoor scenarios the base station is placed at two rooftops with different heights and the users are confined to a five-meter diameter circle and move rando mly at pedestrian speeds. In the indoor scenarios, the users are located close to each other in a lecture theater and the base station is placed at various locations in the room. We report on the observed distribution of the delay spreads and angular spreads. Furthermore, the multi-user performance in terms of singular value spread of the MU-MIMO channel is also reported. Finally, statistics of the coherence time and coherence bandwidth of the propagation channel in various scenarios are given. The results are important for the design and analysis of massive MU-MIMO systems, as well as in the development of realistic massive MU-MIMO channel models.
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| 11. |
- Flordelis, Jose, et al.
(författare)
-
Massive MIMO Extensions to the COST 2100 Channel Model : Modeling and Validation
- 2020
-
Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276. ; 19:1, s. 380-394
-
Tidskriftsartikel (refereegranskat)abstract
- To enable realistic studies of massive multiple-input multiple-output systems, the COST 2100 channel model is extended based on measurements. First, the concept of a base station-side visibility region (BS-VR) is proposed to model the appearance and disappearance of clusters when using a physically-large array. We find that BS-VR lifetimes are exponentially distributed, and that the number of BS-VRs is Poisson distributed with mean proportional to the sum of the array length and the mean lifetime. Simulations suggest that under certain conditions longer lifetimes can help decorrelating closely-located users. Second, the concept of a multipath component visibility region (MPC-VR) is proposed to model birth-death processes of individual MPCs at the mobile station side. We find that both MPC lifetimes and MPC-VR radii are lognormally distributed. Simulations suggest that unless MPC-VRs are applied the channel condition number is overestimated. Key statistical properties of the proposed extensions, e.g., autocorrelation functions, maximum likelihood estimators, and Cramer-Rao bounds, are derived and analyzed.
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| 12. |
- Flordelis, Jose, et al.
(författare)
-
Massive MIMO Performance - TDD Versus FDD : What Do Measurements Say?
- 2018
-
Ingår i: IEEE Transactions on Wireless Communications. - : IEEE-INST ELECTRICAL ELECTRONICS ENGINEERS INC. - 1536-1276 .- 1558-2248. ; 17:4, s. 2247-2261
-
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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| 13. |
- Flordelis, Jose, et al.
(författare)
-
Measurements of Large-Scale Parameters of a Distributed MIMO Antenna System in a Microcell Environment at 2.6 GHz
- 2013
-
Ingår i: Antennas and Propagation (EuCAP), 2013 7th European Conference on. - 2164-3342. ; , s. 747-3026
-
Konferensbidrag (refereegranskat)abstract
- Multi-site multi-antenna measurements for semiurban microcell environment at 2.6 GHz are performed with four base stations (BSs) and one mobile station (MS). Three BSs are provided with four antenna elements in closely spaced copolarized configuration, and one BS is provided with a single antenna element. The MS is equipped with a cylindrical uniform array consisting of 64 dual-polarized antenna elements and moves along some predefined routes. The values of large-scale fading (LSF) from 19 measurement runs with a total of 1900 snapshots at different locations are extracted. The cross-correlation properties of the LSF between different BS links are analyzed. It was found that, in the selected propagation environment, the influence of the BS location on the LSF cross-correlation properties is negligible. However, the location of the MS has a significant influence on the LSF cross-correlation properties of the different BS links.
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| 14. |
- Flordelis, Jose, et al.
(författare)
-
On The Coherence Time of Fiber-Based Distributed Antenna Systems
- 2014
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- The possibility of using radio over fiber (RoF) analog transmissions to characterize the wireless propagation channel of distributed antenna systems is investigated. In particular, the coherence time of kilometer-long, fiber-based networks is analyzed. Joint measurements of the phase noise of parallel links to the same site (intra-site) and to different sites (inter-site) in such a network are presented. The coherence time of the phase noise and phase noise difference between links is evaluated by means of the Allan time deviation. Measurements are performed at a frequency of 2.3 GHz under both stationary and non-stationary temperature conditions, for a duration of ten hours.In the setup analyzed, the phase noise was found to be white, with a phase drift component that determines the coherence time of the link. Coherence times between two to six minutes have been measured for a phase offset of 10 degrees Celcius. Values of the correlation coefficient r for intra-site phase noise processes higher than 0.99 have been measured, while correlation coefficients for inter-site links exhibit lower values, r >0.87. All phase noise processes display a strong, negative correlation with the local environment temperature, with r <-0.75 and temperature drift coefficients in the range of -20$ degrees to -30 degrees per Celcius degree. On the other hand, phase noise difference between links showed weak correlation with temperature, where coherence times were in the order of 15 minutes for inter-site links and 60 minutes for intra-site links. Moreover, it was found that hardware imbalances between links, as well as temperature gradients of several Celcius degrees per hour can considerably reduce coherence times.The results of this investigation suggest that, when parallel fiber optic links are used, the phase coherence of the measurement system might prevent the double-directional characterization of the wireless propagation channel, unless care is taken to minimize variations in the (distributed) temperature environment. Alternatively, phase offsets can be measured several times per hour.
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| 15. |
- Flordelis, Jose, et al.
(författare)
-
Spatial Separation of Closely-Located Users in Measured Massive MIMO Channels
- 2018
-
Ingår i: IEEE Access. - 2169-3536. ; 6, s. 40253-40266
-
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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| 16. |
- Flordelis, Jose, et al.
(författare)
-
Spatial Separation of Closely-Spaced Users in Measured Massive Multi-User MIMO Channels
- 2015
-
Ingår i: 2015 IEEE International Conference on Communications (ICC). ; , s. 1441-1446
-
Konferensbidrag (refereegranskat)abstract
- Fully-synchronous measurements of a massive multi-user multiple-input multiple-output (MU-MIMO) radio propagation channel are presented. We evaluate the ability of a massive MIMO system to spatially separate users located close to each other in line-of-sight (LOS) propagation conditions. The system consists of a base-station (BS) antenna array equipped with 64 dual-polarized antenna elements (128 ports) arranged in a cylindrical configuration, and eight single-antenna users. The users are confined to a five-meter diameter circle and move randomly at pedestrian speeds. The BS antenna array is located on top of a 20 m tall building and has LOS to the users. We examine user separability by studying singular value spread of the MU-MIMO channel matrix for several subsets of BS antenna array ports, along with sum-rate capacity and achievable sum-rates with both zero-forcing and matched-filtering linear precoders. We also analyze the performance of the user with the lowest rate. Finally, a comparison between the performance offered by the massive MIMO system and that of a conventional MU-MIMO system is provided. To the best of our knowledge, this is the first report of fully-synchronous dynamic measurements of a massive MIMO system. Our investigation shows that even users located close to each other in LOS propagation conditions can be spatially separated in a massive MIMO system.
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| 17. |
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| 18. |
- Gao, Xiang, et al.
(författare)
-
Massive MIMO Channel Modeling - Extension of the COST 2100 Model
- 2015
-
Konferensbidrag (övrigt vetenskapligt/konstnärligt)abstract
- As massive MIMO is currently considered a leading 5G technology candidate, channel models that capture important massive MIMO channel characteristics are urgently needed. In this paper we present an attempt for massive MIMO channel modeling based on measurement campaigns at 2.6 GHz in both outdoor and indoor environments, using physically-large arrays and with closely-spaced users. The COST 2100 MIMO channel model is adopted as a general framework. We discuss modeling approaches and scopes for massive MIMO, based on which we suggest extensions to the COST 2100 model. The extensions include 3D propagation, polarization, cluster behavior at the base station side for physically-large arrays, and multi-path component gain functions for closely-spaced users. Model parameters for these extensions in massive MIMO scenarios are reported. Initial validation against the measurements are also performed, which shows that the model is capable of reproducing the channel statistics in terms of temporal behavior of the user separability, singular value spread and sum-rate/capacity.
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| 19. |
- Gunnarsson, Sara, et al.
(författare)
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Channel Hardening in Massive MIMO-A Measurement Based Analysis
- 2018
-
Ingår i: 2018 IEEE 19th International Workshop on Signal Processing Advances in Wireless Communications, SPAWC 2018. - 9781538635124 ; 2018-June
-
Konferensbidrag (refereegranskat)abstract
- Wireless-controlled robots, cars and other critical applications are in need of technologies that offer high reliability and low latency. Massive MIMO, Multiple-Input Multiple-Output, is a key technology for the upcoming 5G systems and is one part of the solution to increase the reliability of wireless systems. More specifically, when increasing the number of base station antennas in a massive MIMO systems the channel variations decrease and the so-called channel hardening effect appears. This means that the variations of the channel gain in time and frequency decrease. In this paper, channel hardening in massive MIMO systems is assessed based on analysis of measurement data. For an indoor scenario, the channels are measured with a 128-port cylindrical array for nine single-antenna users. The analysis shows that in a real scenario a channel hardening of 3.2-4.6 dB, measured as a reduction of the standard deviation of the channel gain, can be expected depending on the amount of user interaction. Also, some practical implications and insights are presented.
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| 20. |
- Gunnarsson, Sara, et al.
(författare)
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Channel hardening in massive mimo : Model parameters and experimental assessment
- 2020
-
Ingår i: IEEE Open Journal of the Communications Society. - 2644-125X. ; 1, s. 501-512
-
Tidskriftsartikel (refereegranskat)abstract
- Reliability is becoming increasingly important for many applications envisioned for future wireless systems. A technology that could improve reliability in these systems is massive MIMO (Multiple- Input Multiple-Output). One reason for this is a phenomenon called channel hardening, which means that as the number of antennas in the system increases, the variations of channel gain decrease in both the time- and frequency domain. Our analysis of channel hardening is based on a joint comparison of theory, measurements and simulations. Data from measurement campaigns including both indoor and outdoor scenarios, as well as cylindrical and planar base station arrays, are analyzed. The simulation analysis includes a comparison with the COST 2100 channel model with its massive MIMO extension. The conclusion is that the COST 2100 model is well suited to represent real scenarios, and provides a reasonable match to actual measurements up to the uncertainty of antenna patterns and user interaction. Also, the channel hardening effect in practical massive MIMO channels is less pronounced than in complex independent and identically distributed (i.i.d.) Gaussian channels, which are often considered in theoretical work.
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| 21. |
- Papaioannou, Panagiotis, et al.
(författare)
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Performance evaluation of CoMP transmission schemes using measurements versus the COST 2100 channel model
- 2016
-
Ingår i: 2016 IEEE 27th Annual International Symposium on Personal, Indoor, and Mobile Radio Communications, PIMRC 2016. - 9781509032549
-
Konferensbidrag (refereegranskat)abstract
- Coordinated Multi Point (CoMP) transmission and reception techniques are used in order to improve the performance of single or multiple cells in wireless systems. A system using CoMP techniques is capable of jointly optimizing its transmission and/or reception and, hence, achieving higher performance. In this work, performance evaluation of three CoMP techniques are performed based on simulations using the COST 2100 channel model and also based on measured channels collected from a synchronous multi-link measurement campaign at Lund University. The contribution of this work is twofold. First, the performance evaluation of different CoMP transmission techniques, namely, the Joint Processing, the Partial Joint Processing and the Coordinated Beamforming, are presented. Second, the capability of the COST 2100 model in predicting the relative performance of different CoMP techniques is assessed. It was found that the COST 2100 model is capable of estimating the relative performance of the studied CoMP schemes well. Moreover, detailed comparison highlighting the agreements and discrepancies between the performance results based on the measured channels and those based on the COST 2100 model are reported.
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| 22. |
- Salous, Sana, et al.
(författare)
-
Urban Radio Access Networks
- 2016
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Ingår i: Cooperative Radio Communications for Green Smart Environments. - 9788793379152 - 9788793379145 ; 47, s. 17-70
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Bokkapitel (övrigt vetenskapligt/konstnärligt)abstract
- The increase in demand for high-data rates on the move in the complex urbanenvironment requires either the allocation of new spectrum such as availablecontiguous spectrum in the mm-wave band or the use of novel configurationssuch as the application of massive multiple-input multiple-output (MIMO)technology. To enable the design of efficient wireless networks, an understandingof the propagation phenomena in the diverse urban environments isfundamental. In this chapter, we present results of studies related to fourthgeneration (4G) and future 5G radio systems both outdoor and outdoor-toindoor.Classifications include rural and highway, BS to pedestrian users,vehicular-to-vehicular, vehicular-to-infrastructure, container terminals, vegetation,and high-speed mobility such as trains. Results for path loss (PL)and shadow fading are presented from various studies of stochastic anddeterministic channel models based in outdoor, indoor-to-outdoor, hotspots,vehicular, and train environments. Relay stations and the impact of antennaplacement in vehicles, antenna terminal height, and the presence of pedestriansare discussed. Results of angular spread and rms delay spread of widebandchannels are presented for the frequency bands below 6 GHz allocated for4G networks, and preliminary results in the mm-wave band, envisaged for5G networks, including prediction of the impact of rain. To facilitate thesimulation of radio networks in urban environments the Hannover Scenariois proposed to give a common simulation environment.
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| 23. |
- Sanchez, Juan, et al.
(författare)
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Optimal, Low-Complexity Beamforming for Discrete Phase Reconfigurable Intelligent Surfaces
- 2021
-
Ingår i: 2021 IEEE Global Communications Conference, GLOBECOM 2021 - Proceedings. - 9781728181042
-
Konferensbidrag (refereegranskat)abstract
- Reflective reconfigurable intelligent surface (RIS) technology is regarded as an innovative, cost- and power-effective solution that aims at influencing the wireless channel through controlled scattering. The technology can be realized by using metamaterials and/or resonant elements that scatter electromagnetic waves with a configurable phase shift. Most of the previous work on beamforming techniques for RIS assumes ideal hardware and, thus, continuous phase shifts. However, hardware constraints limit the phase shift resolution, manifested into the amount of discrete phase shifts that can be configured into each RIS element. This paper aims to offer a discrete phase shift beamforming algorithm for reflective RISs that targets minimization of the quantization error resulting from discretization of continuous phase shifts. The beamforming solution proves to be optimal under perfect channel knowledge for any discrete set of uniformly distributed phase shifts. The required complexity to find the optimal beamforming vector for our approach is found to be linear with the number of RIS elements, the minimum needed to obtain optimal results. Simulated behavior is validated by measurements, showing robustness against angle misalignments and distance variations.
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| 24. |
- 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
-
Ingår i: 2018 IEEE 87th Vehicular Technology Conference, VTC Spring 2018 - Proceedings. - 9781538663554 ; 2018-June, s. 1-6
-
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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| 25. |
- Zhang, Bei, et al.
(författare)
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Empirical evaluation of indoor multi-user MIMO channels with linear and planar large antenna arrays
- 2018
-
Ingår i: 2017 IEEE International Symposium on Personal, Indoor and Mobile Radio Communications : Engaged Citizens and their New Smart Worlds, PIMRC 2017 - Conference Proceedings - Engaged Citizens and their New Smart Worlds, PIMRC 2017 - Conference Proceedings. - 9781538635315 ; 2017-October, s. 1-6
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Konferensbidrag (refereegranskat)abstract
- Channel measurements of large-scale multiuser multiple-input multiple-output (MU-MIMO) radio propagation channels are presented. In the setup, three users with patch antennas communicate simultaneously with a base station (BS) equipped with a large antenna array in an indoor environment. Both a uniform linear array (ULA) and a uniform planar array (UPA) are used, and their relative ability to separate MU-MIMO signals is examined. At the mobile station (MS) side, the effect of inter-user spacing (i.e., the spacing between different users) is investigated. This evaluation is done by means of the correlation matrix distance metric (between each pair of users) and the singular value spread of the system. Our investigation shows that the users can be spatially separated in a large antenna array system in line-of-sight propagation conditions even when they are located close to each other. Furthermore, the users tend to be more separable when a ULA is adopted, compared to using a UPA. Finally, we also confirm that larger user separation distance results in increased channel orthogonality by measurements.
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