| 1. |
- Fan, Wen, et al.
(författare)
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Performance Analysis of Cell-Free Massive MIMO Over Spatially Correlated Fading Channels
- 2019
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Ingår i: ICC 2019 - 2019 IEEE INTERNATIONAL CONFERENCE ON COMMUNICATIONS (ICC). - : IEEE. - 9781538680889 - 9781538680896
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Konferensbidrag (refereegranskat)abstract
- Cell-free massive multiple-input multiple-output (MIMO) is a promising network architecture for future wireless systems. This paper investigates the uplink performance of cell-free massive MIMO systems employing the least-square (LS) estimator over spatially correlated fading channels. We first derive a generalized closed-form expression of the spectral efficiency as a function of the number of access point (AP) antennas and the spatial correlation matrices. We use this result to analyze the impact that the fronthaul, number of users and number of APs have on the energy efficiency. Compared to traditional colocated massive MIMO using maximum ratio combining (MRC), our analysis shows that the large performance gain of cell-free massive MIMO with low-complexity linear LS estimators.
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| 2. |
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| 3. |
- Guan, Ke, et al.
(författare)
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Channel Characterization for Intra-Wagon Communication at 60 and 300 GHz Bands
- 2019
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 68:6, s. 5193-5207
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Tidskriftsartikel (refereegranskat)abstract
- © 1967-2012 IEEE. In this paper, the intra-wagon channels at 60 and 300 GHz bands are characterized through measurement-validated ray-tracing (RT) simulations. To begin with, an in-house-developed three-dimensional RT simulator is calibrated and validated by a series of millimeter-wave and Terahertz channel measurements inside a high-speed train wagon. Then, the validated RT simulator is used to conduct extensive simulations with different transmitter (Tx) and receiver deployments. At low frequencies, the channel is strongly influenced by the line of sight (LOS), and therefore, is usually classified into LOS and non-LOS (NLOS) regions. However, the simulation results at 60 and 300 GHz bands show that the first-order reflection also imposes a significant impact on the channel characteristics. This motivates us to further classify the NLOS region into light-NLOS (L-NLOS) and deep-NLOS (D-NLOS) according to the existence of the first-order reflection. Through analyzing the area ratios of LOS, L-NLOS, and D-NLOS regions, we evaluate the Tx deployment strategies and suggest the optimum one. Based on RT simulation results, totally 12 cases (three propagation regions with two Tx deployments at two frequencies) are characterized in terms of path loss, shadow fading, root-mean-square delay spread, Rician K-factor, azimuth/elevation angular spread of arrival/departure, cross-polarization ratio, and their cross correlations. All these parameters are fed into the 3GPP-like quasi-deterministic radio channel generator (QuaDRiGa). The good agreement between QuaDRiGa and RT proves that the 13 tables provided in this paper effectively parameterize the intra-wagon scenario for the standard channel model family. These results provide valuable insights into the system design and evaluation for intra-wagon communications.
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| 4. |
- Guan, Ke, et al.
(författare)
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Channel Sounding and Ray Tracing for Train-to-Train Communications at the THz Band
- 2019
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Ingår i: 13th European Conference on Antennas and Propagation, EuCAP 2019. ; March 2019
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Konferensbidrag (refereegranskat)abstract
- In order to increase railway capacity for passengers and freight, it is necessary to realize virtual coupling technology through train-to-train (T2T) communications. This T2T link requires large bandwidth for high-data rate and low latency, forming a strong motivation to explore terahertz (THz) band. In this paper, the T2T channel is characterized through ultrawideband (UWB) channel sounding and ray tracing at THz band for the first time. To begin with, a series of T2T channel sounding measurements are performed in a train test center at 300 GHz with 8 GHz bandwidth. Correspondingly, Rician K-factor and root-mean-square (RMS) delay spread are extracted from the measured power-delay profile (PDP). After validated by the measurements, a self-developed ray-tracing (RT) simulator is used to physically interpret the propagation mechanism constitution and significant objects in the target scenario. This provides the first hand information of how the communicating trains themselves influence the T2T channel, and therefore, lays the foundation for channel modeling through extended RT simulations in the future.
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| 5. |
- Guan, Ke, et al.
(författare)
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Measurement, simulation, and characterization of train-To-infrastructure inside-station channel at the terahertz band
- 2019
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Ingår i: IEEE Transactions on Terahertz Science and Technology. - 2156-342X .- 2156-3446. ; 9:3, s. 291-306
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Tidskriftsartikel (refereegranskat)abstract
- © 2011-2012 IEEE. In this paper, we measure, simulate, and characterize the train-To-infrastructure (T2I) inside-station channel at the terahertz (THz) band for the first time. To begin with, a series of channel measurements is performed in a train test center at 304.2 GHz with 8 GHz bandwidth. Rician K-factor and root-mean-square (RMS) delay spread are extracted from the measured power-delay profile. With the aid of an in-house-developed ray-Tracing (RT) simulator, the multipath constitution is physically interpreted. This provides the first hand information of how the communicating train itself and the other train on site influence the channel. Using this measurement-validated RT simulator, we extend the measurement campaign to more realistic T2I inside-station channel through extensive simulations with various combinations of transmitter deployments and train conditions. Based on RT results, all cases of the target channel are characterized in terms of path loss, shadow fading, RMS delay spread, Rician K-factor, azimuth/elevation angular spread of arrival/departure, cross-polarization ratio, and their cross correlations. All parameters are fed into and verified by the 3GPP-like quasi-deterministic radio channel generator. This can provide the foundation for future work that aims to add the T2I inside-station scenario into the standard channel model families, and furthermore, provides a baseline for system design and evaluation of THz communications.
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| 6. |
- Guan, Ke, et al.
(författare)
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Millimeter-wave communications for smart rail mobility: From channel modeling to prototyping
- 2019
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Ingår i: 2019 IEEE International Conference on Communications Workshops, ICC Workshops 2019 - Proceedings.
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Konferensbidrag (refereegranskat)abstract
- In this paper, we present an integration solution from channel modeling to prototyping, to realize millimeter-wave (mmWave) communications for smart rail mobility. In order to involve the railway features in the channel models, two mmWave channel models are established based on ray-tracing simulations in realistic railway scenarios. Moreover, the challenges raised by mmWave directional network under high mobility is overcome by our solutions concerning handover scheme, random access procedure, and beamforming strategies. By integrating these key enabling technologies, we prototype the mobile hotspot network (MHN) system which realizes 1.25 Gbps downlink data throughput in a subway line with the train speed of 80 km/h.
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| 7. |
- Guan, Ke, et al.
(författare)
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Towards realistic high-speed train channels at 5G millimeter-wave band - Part I: Paradigm, significance analysis, and scenario reconstruction
- 2018
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 67:10, s. 9112-9128
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Tidskriftsartikel (refereegranskat)abstract
- The upcoming fifth-generation (5G) mobile communication system is expected to support high mobility up to 500 km/h, which is envisioned in particular for high-speed trains. Millimeter wave (mmWave) spectrum is considered as a key enabler for offering the 'best experience' to highly mobile users. Despite that channel characterization is necessary for the mmWave system design and validation, it is still not feasible to directly do extensive mmWave mobile channel measurements on moving high-speed trains (HST) at a speed up to 500 km/h in the present. Thus, rather than conducting mmWave HST channel sounding directly with high mobility, this study proposes a viable paradigm for realizing the realistic HST channels at the 5G mmWave band. We first propose the whole paradigm. Then, we define the scenario of interest and select the main objects and materials. Afterwards, the electromagnetic and scattering parameters of the materials are measured and estimated between 26.5 GHz and 40 GHz. With this information, the most influential materials are determined through significance analysis. Correspondingly, we reconstruct the three-dimensional mmWave outdoor HST and tunnel scenario models. Through extensive ray-tracing simulations, we determine the main propagation mechanisms in these two scenarios, the channel models based on that are validated by measurements. This verifies the whole paradigm proposed in this paper.
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| 8. |
- Guan, Ke, et al.
(författare)
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Towards realistic high-speed train channels at 5G millimeter-wave band - Part II: Case study for paradigm implementation
- 2018
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Ingår i: IEEE Transactions on Vehicular Technology. - 0018-9545 .- 1939-9359. ; 67:10, s. 9129-9144
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Tidskriftsartikel (refereegranskat)abstract
- © 1967-2012 IEEE. In this paper, we present two case studies for generating realistic high-speed train (HST) channels at fifth-generation (5G) millimeter-wave (mmWave) band. The first one is the tunnel environment at relatively low 5G mmWave band, 30 GHz band, whereas the second one is the outdoor HST environment at relatively high 5G mmWave band, 90 GHz band. Both case studies include the following steps: ray-tracing simulations, stochastic channel modeling and realization, verification with ray-tracing simulations, and validation with a reduced set of measurements. A profound and insightful conclusion is reached that by employing the proposed paradigm, realistic channels can be realized for the design and evaluation of 5G mmWave communication systems in high-speed railways, even without the support of sufficient channel sounding data.
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| 9. |
- He, Ruisi, et al.
(författare)
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Measurement-based analysis of relaying performance for vehicle-to-vehicle communications with large vehicle obstructions
- 2017
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Ingår i: 2016 IEEE 84th Vehicular Technology Conference, VTC Fall 2016 - Proceedings. - 9781509017010
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Konferensbidrag (refereegranskat)abstract
- It has been widely recognized that relaying is an important method for increasing the reliability and spectral efficiency of communications systems, and it is thus helpful for improving the performance of vehicle-to-vehicle (V2V) communication systems. However, designing and evaluating V2V relay networks require understanding the effect of shadowing, as this critically impacts the performance of the relay system. Even though the theoretic performances of various relaying schemes have been well investigated, there is a lack of empirical test that incorporates realistic shadowing effects. In this paper, we analyze the performance of relaying transmission in V2V scenarios based on measurements in scenarios where shadowing occurs through large vehicles such as buses. We investigate several potential locations for the relay nodes, and the measurements are performed with two static transmitters (TX) and one dynamic receiver (RX). Outage probabilities of several relaying schemes such as multi-hop decode-and-forward, multi-hop amplify-and-forward, and diversity-amplify-and-forward are estimated and discussed based on the measured instantaneous end-to-end signal-to-noise ratio (SNR). It is found that: (i) shadowing effect caused by the bus between V2V line-of-sight (LOS) links increases the outage probability for the non-LOS (NLOS) direct transmission; (ii) using relay node on the bus roof can significantly improve transmission, however, a strong shadowing effect may reduces the acceptable communication distance of relaying scheme; and (iii) the diversity-amplify-and-forward relaying scheme generally has the best performance. Our results can be used to design a relay system for V2V communications.
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| 10. |
- He, Ruisi, et al.
(författare)
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Vehicle-to-vehicle channel models with large vehicle obstructions
- 2014
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Ingår i: [Host publication title missing]. ; , s. 5647-5652
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Konferensbidrag (refereegranskat)abstract
- Vehicle-to-Vehicle (V2V) communication is an en-abler for improved traffic safety and congestion control. As for any wireless system the ultimate performance limit is determined by the propagation channel. A particular point of interest is the shadowing effect of large vehicles such as trucks and buses, as this might affect the communication range significantly. In this paper we present measurement results and model the propagation channel in which a bus acts as a shadowing object between two passenger cars. The measurement setup is based on a WARP FPGA software radio as transmitter, and a Tektronix RSA5106A real-time complex spectrum analyzer as receiver. We analyze the influence of the bus location and car separation distance on the large-scale path loss, shadowing, and small-scale fading. The main effect of the bus is that it is acting as an obstruction creating an additional 15-20 dB attenuation. A Nakagami distribution is found to describe the statistics of the small-scale fading, by using Akaike's Information Criterion and the Kolmogorov-Smirnov test. The distance-dependency of the path loss is analyzed, and a stochastic model is developed to reflect the impact.
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