| 1. |
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| 2. |
- Al-Ameri, Ali, et al.
(författare)
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A Hybrid Antenna Switching Scheme for Dynamic Channel Sounding
- 2023
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Ingår i: 2023 IEEE 97th Vehicular Technology Conference, VTC 2023-Spring - Proceedings. - 9798350311143 - 9798350311150
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Konferensbidrag (refereegranskat)abstract
- Channel sounding is essential for the development of radio systems. One flexible strategy is the switched-array-based channel sounding, where antenna elements are activated at different time instants to measure the channel spatial characteristics. Although its hardware complexity is decreased due to fewer radio-frequency (RF) chains, sequentially switching the antenna elements can result in aliasing in the joint estimation of angles and Doppler frequencies of multipath components (MPCs). Therefore, pseudo-random switching has been proposed to mitigate such aliasing and increase estimation accuracy in both angular and Doppler domains. Nevertheless, the increased Doppler resolution could cause additional post-processing complexity of parameter estimation, which is relevant when the Doppler frequencies are not of interest, e.g., for spatial channel modeling. This paper proposes an improved hybrid sequential and random switching scheme. The primary purpose is to maintain the estimation accuracy of angles of MPCs while decreasing the resolution of Doppler frequencies for minimized complexity of channel parameter estimation. A simulated-annealing algorithm is exploited to obtain an optimized switching sequence. The effectiveness of the proposed scheme is also demonstrated with a realistic antenna array.
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| 3. |
- Almuktar, Suhad, et al.
(författare)
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Universal Design for Learning (UDL) in Higher Education: A Case Study in LTH
- 2022
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Konferensbidrag (refereegranskat)abstract
- Universal Design for Learning (UDL) is considered an approach to include all students in the university. UDL is based on three main principles providing multiple means of Engagement, multiple means of representation, and multiple means of action and expression. It is relevant for teachers and departments to focus on more flexibility for students to get the required information, expressing their thoughts and knowledge, and enhancing their motivation to learn. This project aims to investigate the possibility of implementing the UDL in the teaching style of the Faculty of Engineering (LTH), Lund University. Two main approaches were considered in this project. The first one was to interview an expert at LTH about the implementation of UDL at LTH. The second one was to analyze three self-experienced teaching situations according to the UDL guidelines. The results of this project stated that LTH management is considerably serious about UDL, and they already planned a seminar series for training teachers at LTH on how to implement UDL in their course design. The analyses for the three different teaching situations showed that the UDL guidelines provide options for making these teaching and learning experiences much better for both teachers and students. We concluded that the UDL is a vital tool to improve teaching in the higher education sector, in Sweden and worldwide.
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| 4. |
- Cai, Xuesong, et al.
(författare)
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A Centralized and Scalable Uplink Power Control Algorithm in Low SINR Scenarios
- 2021
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 70:9, s. 9583-9587
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Tidskriftsartikel (refereegranskat)abstract
- Power control is becoming increasingly essential for the fifth-generation (5G) and beyond systems. An example use-case, among others, is the unmanned-aerial-vehicle (UAV) communications where the nearly line-of-sight (LoS) radio channels may result in very low signal-to-interference-plus-noise ratios (SINRs). The authors in (Chiang et al., 2007) proposed to efficiently and reliably solve this kind of non-convex problem via a series of geometrical programmings (GPs) using condensation approximation. However, it is only applicable for a small-scale network with several communication pairs and practically infeasible with more (e.g., tens of) nodes to be jointly optimized. We therefore in this paper aim to provide new insights into this problem. By properly introducing auxiliary variables, the problem is transformed to an equivalent form which is simpler and more intuitive for condensation. A novel condensation method with linear complexity is also proposed based on the form. The enhancements make the GP-based power control feasible for both small- and especially large-scale networks that are common in 5G and beyond. The algorithm is verified via simulations. A preliminary case study of uplink UAV communications also shows the potential of the algorithm.
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| 5. |
- Cai, Xuesong, et al.
(författare)
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A Switched Array Sounder for Dynamic Millimeter-Wave Channel Characterization: Design, Implementation and Measurements
- 2024
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X.
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Tidskriftsartikel (refereegranskat)abstract
- A prerequisite for the design and evaluation of wireless systems is the understanding of propagation channels. While abundant propagation knowledge exists for bands below 6 GHz, the same is not true for millimeter-wave frequencies. In this paper, we present the design, implementation and measurement-based verification of a re-configurable 27.5-29.5 GHz channel sounder. Based on the switched array principle, our design is capable of characterizing 128×256 dynamic double-directional dual-polarized channels with snapshot times of around 600 ms. This is in sharp contrast to measurement times on the order of tens-of-minutes of sounders by rotating horn antennas. The antenna arrays at both link ends are calibrated in an anechoic chamber with high angular sampling intervals of 3 degrees in azimuth and elevation domains, which enables de-embedding the system responses of the sounder from the propagation channels. This is complemented with a bandwidth of up to 2 GHz, i.e., nanosecond-level delay resolution. The short measurement times and stable radio frequency design facilitate real-time processing of the received wavefronts to enhance measurement dynamic range. After disclosing the sounder design and implementation, we demonstrate its capabilities by presenting a measurement campaign at 28 GHz in an indoor lab environment.
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| 6. |
- Cai, Xuesong, et al.
(författare)
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Characterizing the Small-Scale Fading for Low Altitude UAV Channels
- 2021
-
Ingår i: ICWMC 2021 : The Seventeenth International Conference on Wireless and Mobile Communications - The Seventeenth International Conference on Wireless and Mobile Communications. - 9781612088785 ; , s. 16-19
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Konferensbidrag (refereegranskat)abstract
- In this contribution, a recently conducted measurement campaign in a suburban scenario for the Unmanned Aerial Vehicle (UAV) Air-to-Ground (A2G) radio channel is introduced.The downlink signals in an in-service Long Term Evolution (LTE) network were collected and utilized to extract the Channel Impulse Responses (CIRs). A high-resolution parameter estimation algorithm derived based on the Space-Alternating Generalized Expectation-maximization (SAGE) principle is applied to estimate the delays, Doppler frequencies and complex amplitudes of Multi Path Components (MPCs) from the CIRs. Based on the MPC estimation results, fast fading characteristics of the A2G channels are investigated. It is found that the Rician distribution models the fast fading the best compared to Nakagami, Lognormal and Rayleigh distributions. Rician K factors are also calculated for the A2G channels.
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| 7. |
- Cai, Xuesong, et al.
(författare)
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Dynamic Channel Modeling for Indoor Millimeter-Wave Propagation Channels Based on Measurements
- 2020
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Ingår i: IEEE Transactions on Communications. - 0096-1965. ; 68:9, s. 5878-5891
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Tidskriftsartikel (refereegranskat)abstract
- In this contribution, a recently conducted measurement campaign for indoor millimeter-wave (mm-wave) propagation channels is introduced. A vector network analyzer (VNA)-based channel sounder was exploited to record the channel characteristics at the frequency band from 28-30 GHz. A virtual uniform circular array (UCA) with a radius of 0.25 m was formed using a rotator with 360 steps. Moreover, by taking advantage of fiber-optic technique applied in the channel sounder, measurements at 50 positions were performed from an indoor hall to an indoor corridor along a long pre-defined route. A low-complexity high-resolution propagation estimation (HRPE) algorithm is exploited to estimate the propagation parameters of multipath components (MPCs). Based on the HRPE estimation results, a novel clustering identification and tracking algorithm is proposed to trace clusters. Composite channel characteristics, cluster-level characteristics and dynamic (or birth-death) behaviours of the clusters are investigated, which constitute a dynamic model for the indoor mm-wave channel.
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| 8. |
- Cai, Xuesong, et al.
(författare)
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Dynamic mmWave Channel Emulation in a Cost-Effective MPAC with Dominant-Cluster Concept
- 2021
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X.
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Tidskriftsartikel (refereegranskat)abstract
- Millimeter-Wave (mmWave) massive multiple-input multiple-output (MIMO) has been considered as a key enabler for the fifth-generation (5G) communications. It is essential to design and test mmWave 5G devices under various realisticscenarios since the radio propagation channels pose intrinsic limitations on the performance. This requires emulating realistic dynamic mmWave channels in a reproducible manner in laboratories, which is the goal of this paper. In this contribution, we first illustrate the dominant-cluster(s) concept, where thenon-dominant clusters in the mmWave channels are pruned, for mmWave 5G devices applying massive MIMO beamforming. This demonstrates the importance and necessity to accurately emulate the mmWave channels at a cluster level rather than the composite-channel level. Thus, an over-the-air (OTA) emulationstrategy for dynamic mmWave channels is proposed based on the concept of dominant-cluster(s) in a sectored multiprobe anechoic chamber (SMPAC). The key design parameters including the probe number and the angular spacing of probes are investigated through comprehensive simulations. A cost-effective switch circuit is also designed for this purpose and validated in the simulation. Furthermore, a dynamic mmWave channel measured in an indoor scenario at 28-30 GHz is presented, where the proposed emulation strategy is also validated by reproducing the measured reality.
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| 9. |
- Cai, Xuesong, et al.
(författare)
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Empirical Low-Altitude Air-to-Ground Spatial Channel Characterization for Cellular Networks Connectivity
- 2021
-
Ingår i: IEEE Journal on Selected Areas in Communications. - 0733-8716. ; 39:10, s. 2975-2991
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Tidskriftsartikel (refereegranskat)abstract
- Cellular-connected unmanned aerial vehicles (UAVs) have recently attracted a surge of interest in both academia and industry. Understanding the air-to-ground (A2G) propagation channels is essential to enable reliable and/or high-throughput communications for UAVs and protect the ground user equipments (UEs). In this contribution, a recently conducted measurement campaign for the A2G channels is introduced. A uniform circular array (UCA) with 16 antenna elements was employed to collect the downlink signals of two different Long Term Evolution (LTE) networks, at the heights of 0-40m in three different, namely rural, urban and industrial scenarios. The channel impulse responses (CIRs) have been extracted from the received data, and the spatial, including angular, parameters of the multipath components in individual channels were estimated according to a high-resolution-parameter-estimation (HRPE) principle. Based on the HRPE results, clusters of multipath components were further identified. Finally, comprehensive spatial channel characteristics were investigated in the composite and cluster levels at different heights in the three scenarios.
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| 10. |
- Cai, Xuesong, et al.
(författare)
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Enhanced Effective Aperture Distribution Function for Characterizing Large-Scale Antenna Arrays
- 2023
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Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X. ; 71:8, s. 6869-6877
-
Tidskriftsartikel (refereegranskat)abstract
- Accurate characterization of large-scale antenna arrays is growing in importance and complexity for the fifth-generation (5G) and beyond systems, as they feature more antenna elements and require increased overall performance. The full 3D patterns of all antenna elements in the array need to be characterized because they are in general different due to construction inaccuracy, coupling, antenna array's asymmetry, etc. The effective aperture distribution function (EADF) can provide an analytic description of an antenna array based on a full-sphere measurement of the array in an anechoic chamber. However, as the array aperture increases, denser spatial samples are needed for EADF due to large distance offsets of array elements from the reference point in the anechoic chamber, leading to a prohibitive measurement time and increased complexity of EADF. In this paper, we present the EADF applied to large-scale arrays and highlight issues caused by the large array aperture. To overcome the issues, an enhanced EADF is proposed with a low complexity that is intrinsically determined by the characteristic of each array element rather than the array aperture. The enhanced EADF is validated using experimental measurements conducted at 27-30 GHz frequency band with a relatively large planar array.
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| 11. |
- Cai, Xuesong, et al.
(författare)
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Power Allocation for Uplink Communications of Massive Cellular-Connected UAVs
- 2023
-
Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 72:7, s. 8797-8811
-
Tidskriftsartikel (refereegranskat)abstract
- Cellular-connected unmanned aerial vehicle (UAV) has attracted a surge of research interest in both academia and industry. To support aerial user equipment (UEs) in the existing cellular networks, one promising approach is to assign a portion of the system bandwidth exclusively to the UAV-UEs. This is especially favorable for use cases where a large number of UAV-UEs are exploited, e.g., for package delivery close to a warehouse. Although the nearly line-of-sight (LoS) channels can result in higher powers received, UAVs can in turn cause severe interference to each other in the same frequency band. In this contribution, we focus on the uplink communications of massive cellular-connected UAVs. Different power allocation algorithms are proposed to either maximize the minimal spectrum efficiency (SE) or maximize the overall SE to cope with severe interference based on the successive convex approximation (SCA) principle. One of the challenges is that a UAV can affect a large area meaning that many more UAV-UEs must be considered in the optimization problem, which is essentially different from that for terrestrial UEs. The necessity of single-carrier uplink transmission further complicates the problem. Nevertheless, we find that the special property of large coherent bandwidths and coherent times of the propagation channels can be leveraged. The performances of the proposed algorithms are evaluated via extensive simulations in the full-buffer transmission mode and bursty-traffic mode. Results show that the proposed algorithms can effectively enhance the uplink SEs. This work can be considered the first attempt to deal with the interference among massive cellular-connected UAV-UEs with optimized power allocations.
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| 12. |
- Cai, Xuesong, et al.
(författare)
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Toward 6G with Terahertz Communications: Understanding the Propagation Channels
- 2024
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Ingår i: IEEE Communications Magazine. - 0163-6804. ; 62:2, s. 32-38
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Tidskriftsartikel (refereegranskat)abstract
- This article aims at providing insights for a comprehensive understanding of THz propagation channels. Specifically, we discuss essential THz channel characteristics to be well understood for the success of THz communications. The methodology of establishing realistic and 6G-compliant THz channel models based on measurements is then elaborated on, followed by a discussion on existing THz channel measurements in the literature. Finally, future research directions, challenges and measures to enrich the understanding of THz channels are discussed.
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| 13. |
- Ebrahimizadeh, Javad, et al.
(författare)
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RCS-Based 3D Millimeter-Wave Channel Modeling Using Quasi-Deterministic Ray Tracing
-
Ingår i: IEEE Transactions on Antennas and Propagation. - 0018-926X.
-
Tidskriftsartikel (refereegranskat)abstract
- This paper introduces a low-complexity ultra-wideband quasi-deterministic ray tracing (QD-RT) method for statistical analysis of wireless channels. This model uses a statistical distribution to model the bistatic radar-cross-section (RCS) of irregular objects such as cars and pedestrians, instead of a deterministic propagation model, i.e., applying the exact values of bistatic RCSs. It is shown that the quasi-deterministic propagation model benefits from a low complexity compared with a deterministic model while keeping the accuracy. The proposed QD-RT method is applied in a realistic street canyon scenario in the millimeter wave frequency band, and the performance of the QD-RT method is verified by the deterministic propagation method, where the second-order statistics including root-mean-square (RMS) delay spread and angular spread and the first-order statistic transfer function yield good agreements. Finally, the application of the QD-RT in stochastic channel modeling is demonstrated by developing a 3GPP-like statistical channel model for street canyon scenarios.
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| 14. |
- Huang, Ziwei, et al.
(författare)
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A Mixed-Bouncing Based Non-Stationarity and Consistency 6G V2V Channel Model with Continuously Arbitrary Trajectory
-
Ingår i: IEEE Transactions on Wireless Communications. - 1536-1276.
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a novel three-dimensional (3D) irregularshaped geometry-based stochastic model (IS-GBSM) is proposedfor sixth-generation (6G) millimeter wave (mmWave) massivemultiple-input multiple-output (MIMO) vehicle-to-vehicle(V2V) channels. To investigate the impact of vehicular trafficdensity (VTD) on channel statistics, clusters are divided into staticclusters and dynamic clusters, which are further distinguishedinto static/dynamic single/twin-clusters to capture the mixed bouncingpropagation. A new method, which integrates thevisibility region and birth-death process methods, is developedto model space-time-frequency (S-T-F) non-stationarity of V2Vchannels with time-space (T-S) consistency. The continuouslyarbitrary vehicular movement trajectory (VMT) and soft clusterpower handover are modeled to further ensure channel T-Sconsistency. From the proposed model, key channel statistics arederived. Simulation results show that S-T-F non-stationarity ofchannels with T-S consistency is modeled and the impacts of VTDand VMT on channel statistics are analyzed. The generality ofthe proposed model is validated by comparing simulation resultsand measurement/ray-tracing (RT)-based results.
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| 15. |
- Huang, Ziwei, et al.
(författare)
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A Non-Stationary 6G V2V Channel Model with Continuously Arbitrary Trajectory
- 2023
-
Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545. ; 72:1, s. 4-19
-
Tidskriftsartikel (refereegranskat)abstract
- In this paper, a novel three-dimensional (3D) massive multiple-input multiple-output (MIMO) millimeter wave (mmWave) geometry-based stochastic model (GBSM) is proposed for sixth-generation (6G) vehicle-to-vehicle (V2V) channels. In the proposed GBSM, clusters in the environment are divided into static clusters and dynamic clusters. Furthermore, the time-variant acceleration together with the integration of time during the transmission distance update are exploited. As a result, the continuously arbitrary trajectory of the transceiver and dynamic clusters is successfully captured. To jointly model space-time-frequency (S-T-F) non-stationarity of 6G V2V channels, a new method, which properly integrates the frequency-dependent factor, birth-death (BD) process, and selective evolution of static and dynamic clusters, is developed. Key channel statistics, including the space-time-frequency correlation function (STF-CF), time stationary interval, and Doppler power spectral density (DPSD) are obtained. Simulation results demonstrate that S-T-F non-stationarity is modeled and the impacts of vehicular traffic density (VTD) and vehicular movement trajectory (VMT) on channel statistics are further analyzed thoroughly. Finally, the generality and accuracy of the proposed GBSM are validated through the comparison of simulation results and available measurement data.
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| 16. |
- Huang, Zeyu, et al.
(författare)
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Optimal Phasors for Wideband RIS Transmissions
- 2023
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Ingår i: 2023 IEEE Conference on Antenna Measurements and Applications, CAMA 2023. - 2474-1760 .- 2643-6795. - 9798350323047 ; , s. 250-254
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Konferensbidrag (refereegranskat)abstract
- Configuring reconfigurable intelligent surfaces (RISs) based on a practical RIS model is a fundamental problem in RIS-assisted wireless transmission. In this work, we propose a concept named optimal phasor (OP), a latent quantity that can considerably help the practical model-based RIS configuration. Under such a concept, we can design versatile algorithms that are applicable to different RIS models. As an example, we formulate the optimization problem of frequency selectivity reduction and develop an OP-based algorithm, allowing us to reach a remarkable performance based on the practical one-bit RIS model.
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| 17. |
- Khosravi, Hedieh, et al.
(författare)
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Experimental Analysis of Physical Interacting Objects of a Building at mmWave Frequencies
- 2024
-
Ingår i: 18th European Conference on Antennas and Propagation, EuCAP 2024. - 9788831299091
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Konferensbidrag (refereegranskat)abstract
- Understanding the evolution of multipath components (MPCs) in real radio channels is crucial to enhancing channel modeling and multipath-assisted positioning. This paper provides an experimental analysis of the behavior of MPCs originating from a standard building facade at millimeter wave (mmWave) frequencies. Utilizing a high-resolution channel parameter estimation method alongside a joint clustering and tracking technique, we identify physical interacting objects and analyze their lifetimes and quantities. The building wall under study is shown to have many distributed distinct backscattering points and reflection contributions due to the windows. Our findings shed light on the reflection and scattering patterns from standard building elements, highlighting the importance of including them in channel models, positioning methods, and ray tracing simulations.
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| 18. |
- Kong, Dexin, et al.
(författare)
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Base-Station and RIS Deployment Optimization for Indoor Coverage Enhancement
- 2023
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Ingår i: 2023 IEEE Conference on Antenna Measurements and Applications, CAMA 2023. - 9798350323047 ; , s. 246-249
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Konferensbidrag (refereegranskat)abstract
- Reconfigurable intelligent surfaces (RISs) are promising to improve energy efficiency and coverage for 6G [1]. In this paper, we aim to optimize the deployment of BSs and RISs for enhanced coverage in terms of received power. Specifically, an active RIS structure [2] with tuneable power amplification is applied, and a framework of mixed integer linear programming (MILP) is proposed for the optimization problems. Furthermore, an indoor scenario is simulated using ray tracing tools. Based on the simulated channels, we apply the proposed framework to enhance the indoor coverage for slightly-shadowed and heavily-shadowed cases, respectively. The main outcome of this paper is that deploying RISs in appropriate positions can reduce the number of deployed BSs significantly.
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| 19. |
- Li, Xuhong, et al.
(författare)
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A Belief Propagation Algorithm for Multipath-based SLAM with Multiple Map Features: A mmWave MIMO Application
- 2024
-
Annan publikation (övrigt vetenskapligt/konstnärligt)abstract
- In this paper, we present a multipath-based simultaneous localization and mapping (SLAM) algorithm that continuously adapts mulitiple map feature (MF) models describing specularly reflected multipath components (MPCs) from flat surfaces and point-scattered MPCs, respectively. We develop a Bayesian model for sequential detection and estimation of interacting MF model parameters, MF states and mobile agent's state including position and orientation. The Bayesian model is represented by a factor graph enabling the use of belief propagation (BP) for efficient computation of the marginal posterior distributions. The algorithm also exploits amplitude information enabling reliable detection of weak MFs associated with MPCs of very low signal-to-noise ratios (SNRs). The performance of the proposed algorithm is evaluated using real millimeter-wave (mmWave) multiple-input-multiple-output (MIMO) measurements with single base station setup. Results demonstrate the excellent localization and mapping performance of the proposed algorithm in challenging dynamic outdoor scenarios.
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| 20. |
- Marinsek, Alexander, et al.
(författare)
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Channel Performance Metrics and Evaluation for XR Head-Mounted Displays with mmWave Arrays
- 2024
-
Ingår i: IEEE Transactions on Communications. - 0090-6778. ; , s. 1-1
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Tidskriftsartikel (refereegranskat)abstract
- Millimeter-wave (mmWave) technology holds the potential to revolutionize head-mounted displays (HMDs) by enabling high-speed wireless communication with nearby processing nodes, where complex video rendering can take place. However, the sparse angular profile of mmWave channels, coupled with the narrow field of view (FoV) of patch-antenna arrays and frequent HMD rotation, can lead to poor performance. We introduce six channel performance metrics to evaluate the performance of an HMD equipped with mmWave arrays. We analyze the metrics using analytical models, discuss their impact for the application, and apply them to 28 GHz channel sounding data, collected in a conference room using eight HMD patch-antenna arrays, offset by 45° from each other in azimuth. Our findings confirm that a single array performs poorly due to the narrow FoV, and featuring multiple arrays along the HMD’s azimuth is required. Namely, the broader FoV stabilizes channel gain during HMD rotation, lessens the attenuation caused by line of sight (LoS) obstruction, and increases the channel’s spatial multiplexing capability. In light of our findings, we conclude that it is imperative to either equip the HMD with multiple arrays or, as an alternative approach, incorporate macroscopic diversity by leveraging distributed access point (AP) infrastructure.
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| 21. |
- Marinsek, Alexander, et al.
(författare)
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Impact of Array Configuration on Head-Mounted Display Performance at mm Wave Bands
- 2023
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Ingår i: 2023 Joint European Conference on Networks and Communications and 6G Summit, EuCNC/6G Summit 2023. - 9798350311020 ; , s. 192-197
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Konferensbidrag (refereegranskat)abstract
- Immersing a user in life-like extended reality (XR) scenery using a head-mounted display (HMD) with a constrained form factor and hardware complexity requires remote rendering on a nearby edge server or computer. Millimeter-wave (mmWave) communication technology can provide sufficient data rate for wireless XR content transmission. However, mmWave channels exhibit severe sparsity in the angular domain. This means that distributed antenna arrays are required to cover a larger angular area and to combat outage during HMD rotation. At the same time, one would prefer fewer antenna elements/arrays for a lower complexity system. Therefore, it is important to evaluate the trade-off between the number of antenna arrays and the achievable performance to find a proper practical solution. This work presents indoor 28 GHz mmWave channel measurement data, collected during HMD mobility, and studies the dominant eigenmode (DE) gain. DE gain is a significant factor in under-standing system performance since mm Wave channel sparsity and eigenmode imbalance often results in provisioning the majority of the available power to the DE. Moreover, it provides the upper performance bounds for widely-adopted analog beamformers. We propose 3 performance metrics - gain trade-off, gain volatility, and minimum service trade-off - for evaluating the performance of a multi-array HMD and apply the metrics to indoor 28 GHz channel measurement data. Evaluation results indicate, that 3 arrays provide stable temporal channel gain. Adding a 4th array further increases channel capacity, while any additional arrays do not significantly increase physical layer performance.
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| 22. |
- Nie, Yifang, et al.
(författare)
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无线信道建模中二分 K 均值聚类多径分簇算法
- 2023
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Ingår i: Dianbo Kexue Xuebao/Chinese Journal of Radio Science. - 1005-0388. ; 38:2, s. 284-291
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Tidskriftsartikel (refereegranskat)abstract
- In order to rationally allocate multi-path component (MPC) of wireless channels to different clusters, a multi-path clustering algorithm based on Bisecting K-means clustering was proposed for millimeter-wave channels to solve the problem of partial optimization of traditional K-means clustering methods. The MPC clustering was implemented based on the cluster split and iteration computation strategy, when the Mahalanobis distance (MD) was regarded as the multipath component distance (MCD). The experiment measurement in indoor millimeter-wave channel was conducted to verify the effectiveness and feasibility of the proposed method. The experimental results show that the clustering result of proposed method is more rational than those of traditional K-means clustering methods, and the highly correlated MPCs are reasonably and uniquely allocated to the same cluster.
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| 23. |
- Sandra, Michiel, et al.
(författare)
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Antenna Array Configuration for Reliable Communications in Maritime Environments
- 2022
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Ingår i: The 2022 IEEE 95th Vehicular Technology Conference.
-
Konferensbidrag (refereegranskat)abstract
- The performance and reliability of wireless communications at sea are often limited by the deep fades caused by the coherent sea surface reflection. In this paper, we show that by employing multiple antennas at the base station, the deep fades can be mitigated within a large communication range if the antennas are carefully spaced in the vertical direction. We derive a bound for the range where mitigation of deep fading is guaranteed and evaluate this bound through numerical searching methods utilizing a realistic channel model that considers the curvature of the earth. The numerical results show that the proposed scheme leads to a better system performance compared with a free space scenario in terms of signal-to-noise ratio, if four or more antennas are employed at the base station.
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| 24. |
- Sandra, Michiel, et al.
(författare)
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Measurement-Based Wideband Maritime Channel Characterization
- 2023
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Ingår i: 17th European Conference on Antennas and Propagation, EuCAP 2023. - 9788831299077
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Konferensbidrag (refereegranskat)abstract
- Maritime communication is one of the 5G vertical domains and is attracting more attention. Advanced channel models that accurately characterize the wideband maritime propagation channels are essential for the development of modern maritime communication technologies. To this end, we measured the propagation channel at 5.6GHz with a sailing boat, capturing the channel with a bandwidth of 250MHz, both in the harbor and the open sea. Based on the measurement results, we evaluated the Rician K-factor, coherence bandwidth and path loss. We concluded that in the maritime environment various types of power delay profiles can occur, and that the Rician K-factor and coherence bandwidth can vary significantly within a short period of time.
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| 25. |
- Song, Jian, et al.
(författare)
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Bounded Path-Loss Model for UAV-to-UAV Communications
- 2021
-
Ingår i: ICWMC 2021 : The Seventeenth International Conference on Wireless and Mobile Communications - The Seventeenth International Conference on Wireless and Mobile Communications. - 9781612088785
-
Konferensbidrag (refereegranskat)abstract
- In this paper, we focus on ultra-dense network modelingwhere both the Base Stations (BSs) and Mobile Terminals(MTs) are UAVs. In this case, two communication nodes canbe very close to each other. However, existing cellular networkanalyses typically use the standard unbounded path loss modelwhere received power decays like r^beta over a distance r. Thisstandard model is a good approximation for the path-loss inwireless communications over large values of r but is not validfor small values of r due to the singularity at 0. This model is oftenused along with a random uniform node distribution, even thoughin a group of uniformly distributed nodes some may be arbitrarilyclose to one another, thus, it will lose accuracy and may benot applicable for UAV-to-UAV communications. To tackle thisproblem, by using mathematical tool behind stochastic geometry,we propose tractable analytical frameworks of coverage and ratebased on the novel unbounded path-loss model with a constantdistance factor r_0 for analyzing the UAV-to-UAV communications.
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| 26. |
- Tian, Guoda, et al.
(författare)
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Deep-Learning Based Channel Estimation for OFDM Wireless Communications
- 2022
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Ingår i: 2022 IEEE 23rd International Workshop on Signal Processing Advances in Wireless Communication (SPAWC).
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Konferensbidrag (refereegranskat)abstract
- Multi-carrier technique is a backbone for modern commercial networks. However, the performances of multi-carrier systems in general depend greatly on the qualities of acquired channel state information (CSI). In this paper, we propose a novel deep-learning based processing pipeline to estimate CSI for payload time-frequency resource elements. The proposed pipeline contains two cascaded subblocks, namely, an initial denoise network (IDN), and a resolution enhancement network (REN). In brief, IDN applies a novel two-steps denoising structure while REN consists of pure fully-connected layers. Compared to existing works, our proposed processing architecture is more robust under lower signal-to-noise scenarios and delivers generally a significant gain.
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| 27. |
- Tian, Guoda, et al.
(författare)
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Deep-Learning Based High-Precision Localization with Massive MIMO
- 2023
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Ingår i: IEEE Transactions on Machine Learning in Communications and Networking. - 2831-316X.
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Tidskriftsartikel (refereegranskat)abstract
- High-precision localization and machine learning (ML) are envisioned to be key technologies in future wireless systems. This paper presents an ML pipeline to solve localization tasks. It consists of multiple parallel processing chains, each trained using a different fingerprint to estimate the position of the user equipment. In this way, ensemble learning can be utilized to fuse all chains to improve localization performance. Nevertheless, a common problem of ML-based techniques is that network training and fine-tuning can be challenging due to the increase in network sizes when applied to (massive) multiple-input multiple-output (MIMO) systems. To address this issue, we utilize a subarray-based approach. We divide the large antenna array into several subarrays, feeding the fingerprints of the subarrays into the pipeline. In our case, such an approach eases the training process while maintaining or even enhancing the performance. We also use the Nyquist sampling theorem to gain insight on how to appropriately sample and average training data. Finally, an indoor measurement campaign is conducted at 3.7 GHz using the Lund University massive MIMO testbed to evaluate the approaches. Localization accuracy at a centimeter level has been reached in this particular measurement campaign.
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| 28. |
- Tian, Guoda, et al.
(författare)
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High-Precision Machine-Learning Based Indoor Localization with Massive MIMO System
- 2023
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Ingår i: ICC 2023 - IEEE International Conference on Communications. - 9781538674635 - 9781538674628 ; , s. 3690-3695
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Konferensbidrag (refereegranskat)abstract
- High-precision cellular-based localization is one of the key technologies for next-generation communication systems. In this paper, we investigate the potential of applying machine learning (ML) to a massive multiple-input multiple-output (MIMO) system to enhance localization accuracy. We analyze a new ML-based localization pipeline that has two parallel fully connected neural networks (FCNN). The first FCNN takes the instantaneous spatial covariance matrix to capture angular information, while the second FCNN takes the channel impulse responses to capture delay information. We fuse the estimated coordinates of these two FCNNs for further accuracy improvement. To test the localization algorithm, we performed an indoor measurement campaign with a massive MIMO testbed at 3.7 GHz. In the measured scenario, the proposed pipeline can achieve centimeter-level accuracy by combining delay and angular information.
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| 29. |
- Zhang, Guojin, et al.
(författare)
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A Scatterer Localization Method Using Large-Scale Antenna Array Systems
- 2022
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Ingår i: 2022 IEEE Conference on Antenna Measurements & Applications. - 9781665490375
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Konferensbidrag (refereegranskat)abstract
- As ultra-massive multiple-input multiple-output (UM-MIMO) has emerged as a key technology for millimeter-wave and terahertz communications, the spherical wave propagation should be considered for channel modeling. Therefore, it is critical to identify the locations and evolving behaviors of scatterers, i.e., the sources of the spherical wavefronts. In this contribution, a novel space-alternating generalized expectation-maximization (SAGE) based scatterer localization algorithm is proposed, where a large-scale antenna array is divided into multiple sub-arrays. Due to the decreased aperture of each sub-array, plane wave assumption can be applied to estimate the angles of departure/arrival, delays and amplitudes of multipath components (MPCs). Based on the angle variations of MPCs observed at different sub-arrays, the corresponding scatterers can be located. The proposed algorithm is verified in a simulation using a large-scale uniform circular array (UCA) system. Moreover, we apply this algorithm to an indoor measurement campaign conducted at 27-29\,GHz in a hall scenario. Dominant scatterers are identified, which can be used for the development of further geometry-based stochastic channel models.
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| 30. |
- Zhang, Guojin, et al.
(författare)
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Geometry-Based Clustering Characteristics for Outdoor Measurements at 28-30 GHz
- 2022
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Ingår i: IEEE Antennas and Wireless Propagation Letters. - 1548-5757. ; 21:9, s. 1797-1801
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Tidskriftsartikel (refereegranskat)abstract
- This paper presents an analysis of channel characteristics for an outdoor scenario at the frequency band of 28-30 GHz. A geometry-based clustering algorithm is proposed to group the measured multipath components (MPCs) based on the interaction points on the surrounding walls or objects obtained from Ray Tracing 3-D simulations, which is more physically interpretable than the traditional clustering algorithm. The cluster-level characteristics at a total of 15 positions along a pre-defined route covering both line-of-sight (LoS) and non-LoS (NLoS) scenarios are investigated. Moreover, power contributions of MPCs with multiple bounces (up to 7 bounces in NLoS condition) from the interaction objects (IOs) are also investigated.
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| 31. |
- Zhu, Hong, et al.
(författare)
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Affordable Quality of Service Assessment for Cellular-Connected UAV Communications
- 2021
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Ingår i: ICWMC 2021 : The Seventeenth International Conference on Wireless and Mobile Communications - The Seventeenth International Conference on Wireless and Mobile Communications. - 9781612088785
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Konferensbidrag (refereegranskat)abstract
- In recent years, Unmanned Aerial Vehicles (UAVs)have been used extensively in military and civilian fields, making the research on cellular-connected UAVs a popular topic forFifth Generation (5G) and beyond communications. In order to support the increasing amount of applications, it is essential to evaluate the performance of UAV communications. In this work, the end-to-end delay, packet success rate, and through put of Air-to-Ground (A2G) communications are evaluated based on a realistic channel model obtained from measurements. The measurement campaign, conducted in a suburban environment, includes both Line-of-Sight (LoS) and Obstructed Line-of-Sight(OLoS) scenarios. From the results, it can be seen that architectural elements close to the flight route can severely decrease the communications performance even when the visibility between the Base Station (BS) and the UAV is permanently ensured. Moreover, we have shown that the Quality of Service (QoS) requirements for critical communications proposed by 3rd Generation Partnership Project (3GPP) can be fulfilled by establishing a threshold on the received Signal to Interference and Noise Ratio (SINR). This way, the SINR can be used as a condense dperformance metric for the design of safe flight routes for critical communications for UAVs.
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