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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. - 9798350311150 - 9798350311143
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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
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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
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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 ; , 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
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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
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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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