Ke Guan

Assessment of LTE-R Using High Speed Railway Channel Model

Long Term Evolution for Railway (LTE-R) is commonly believed to be the next generation wireless communication system for high speed railway. The main objective of this paper is to assess the performance of LTE-R under realistic conditions using a hybrid high speed railway channel model involving WINNER II Channel Model that was refined and validated using measurements made within the WP1 Channel Model work package in Europe, high speed train channel model in 3GPP and large-scaled models based on a group of measurements on Zhengzhou-Xian passenger dedicated line in China. The paper presents a detailed evaluation of the BER and PSD for LTE-R suitably dimensioned for the high speed railway channel. The investigation includes analysis of the Doppler shift caused by the velocity of transmitter and receiver, the multipath interference due to reflections and diffractions from terrains in the radio service coverage area, and other serious impairing factors. The results show that LTE-R has promising potential to be used in a high speed railway environment.

Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

Accurate characterization of the radio channel in tunnels is of great importance for new signaling and train control communications systems. To model this environment, measurements have been taken at 2.4 GHz in a real environment in Madrid subway. The measurements were carried out with four base station transmitters installed in a 2-km tunnel and using a mobile receiver installed on a standard train. First, with an optimum antenna configuration, all the propagation characteristics of a complex subway environment, including near shadowing, path loss, shadow fading, fast fading, level crossing rate (LCR), and average fade duration (AFD), have been measured and computed. Thereafter, comparisons of propagation characteristics in a double-track tunnel (9.8-m width) and a single-track tunnel (4.8-m width) have been made. Finally, all the measurement results have been shown in a complete table for accurate statistical modeling.

Future railway services-oriented mobile communications network

The future development of the railway is highly desired to evolve into a new era where infrastructure, trains, travelers, and goods will be increasingly interconnected to provide high comfort, with optimized door-to-door mobility at higher safety. For this vision, it is required to realize seamless high data rate wireless connectivity for railways. To improve the safety and comfort of future railways, wireless communications for railways are required to evolve from only voice and traditional train control signaling services to various high data rate services including critical high-definition (HD) video and other more bandwidth-intensive passenger services, such as onboard and wayside HD video surveillance, onboard real-time high data rate services, train multimedia dispatching video streaming, railway mobile ticketing, and the Internet of Things for railways. Corresponding mobile communications network architecture under various railway scenarios including inter-car, intra-car, inside station, train-to-infrastructure and infrastructure- to-infrastructure are proposed in this article. Wireless coverage based on massive MIMO for railway stations and train cars is proposed to fulfill the requirement of high-data-rate and high spectrum efficiency. The technical challenges brought by the massive MIMO technique are discussed as well.

High-Speed Railway Communications: From GSM-R to LTE-R

High-speed railways (HSRs) improve the quality of rail services, yield greater customer satisfaction, and help to create socioeconomically balanced societies [1]. This highly efficient transport mode creates significant challenges in terms of investment, technology, industry, and environment. To handle increasing traffic, ensure passenger safety, and provide real-time multimedia information, a new communication system for HSR is required. In the last decade, public networks have been evolving from voice-centric second-generation systems, e.g., Global System for Mobile Communications (GSM) with limited capabilities, to fourth-generation (4G) broad-band systems that offer higher data rates, e.g., long-term evolution (LTE). It is thus relevant for HSR to replace the current GSM-railway (GSM-R) technology with the next-generation railway-dedicated communication system providing improved capacity and capability.

Propagation Measurements and Modeling of Crossing Bridges on High-Speed Railway at 930 MHz

Bridges that cross a railways right-of-way are one of the most common obstacles for wave propagation along a highspeed railway. They can lead to poor coverage or handover failure but have been rarely investigated before. To describe the influence of this nonnegligible structure on propagation, measurements have been taken at 930 MHz along a real high-speed railway in China. Based on different mechanisms, the entire propagation process is presented by four zones in the case of an independent crossing bridge (ICB) and two zones in the case of groups of crossing bridges. First, all the propagation characteristics, including extra propagation loss, shadow fading, small-scale fading, and fading depth, have been measured and extracted. The results are shown in a complete table for accurate statistical modeling. Then, two empirical models, i.e., ICB and crossing bridges group (CBG), are first established to describe the extra loss owing to the crossing bridges. The proposed models improve on the state-of-the-art models for this problem, achieving a root mean square error (RMSE) of 3.0 and 3.7 dB, respectively.

Radio Wave Propagation Scene Partitioning for High-Speed Rails

Radio wave propagation scene partitioning is necessary for wireless channel modeling. As far as we know, there are no standards of scene partitioning for high-speed rail (HSR) scenarios, and therefore we propose the radio wave propagation scene partitioning scheme for HSR scenarios in this paper. Based on our measurements along the Wuhan-Guangzhou HSR, Zhengzhou-Xian passenger-dedicated line, Shijiazhuang-Taiyuan passenger-dedicated line, and Beijing-Tianjin intercity line in China, whose operation speeds are above 300 km/h, and based on the investigations on Beijing South Railway Station, Zhengzhou Railway Station, Wuhan Railway Station, Changsha Railway Station, Xian North Railway Station, Shijiazhuang North Railway Station, Taiyuan Railway Station, and Tianjin Railway Station, we obtain an overview of HSR propagation channels and record many valuable measurement data for HSR scenarios. On the basis of these measurements and investigations, we partitioned the HSR scene into twelve scenarios. Further work on theoretical analysis based on radio wave propagation mechanisms, such as reflection and diffraction, may lead us to develop the standard of radio wave propagation scene partitioning for HSR. Our work can also be used as a basis for the wireless channel modeling and the selection of some key techniques for HSR systems.

Deterministic Propagation Modeling for the Realistic High-Speed Railway Environment

In a realistic high-speed railway environment, the track, terrain, vegetation, cuttings, barriers, pylons, buildings, and crossing bridges are the main sources of reflection, diffraction, and scattering. Moreover, the radiation pattern and the polarization of the transmitting and receiving antennas considerably influence the propagation. This paper presents a deterministic modeling approach covering all the effects in a realistic highspeed railway environment for the first time. The antenna influence and the mechanisms of transmission, scattering, and reflection are evaluated by developing a 3D ray-optical tool. The diffraction loss is obtained by the multi-edge diffraction models using raster databases. This approach compensates the limitation of the existent empirical and stochastic models used for the high-speed railway, and promotes the deterministic modeling towards to the realistic environment. Therefore, it allows a detailed and realistic evaluation and verification of the train control communications systems.

Propagation Measurements and Analysis for Train Stations of High-Speed Railway at 930 MHz

Train stations are one of the most common structures along a high-speed railway. They can block the line of sight (LOS), generate multiple reflected and scattered waves, and aggravate the fading behavior; however, these effects have been rarely investigated. This paper presents a group of 930-MHz measurements conducted on train stations of high-speed railways in China. The whole process of a train passing stations has been measured with two typical types of stations. The results indicate that, when the station is far from the transmitter (Tx), the semi-closed station (in which the awnings cover both the platforms and the rails) influences the propagation much more seriously than the open station (in which the awnings only cover the platforms supporting a clear free space over the tracks). When the station is near the Tx, the fact of whether the train keeps the LOS and stays inside the station determines the propagation for both types of stations. All the propagation characteristics, including extra propagation loss, shadow fading, small-scale fading, level crossing rate (LCR), average fade duration (AFD), and fading depth (FD), have been measured and computed for the first time. Specific findings of propagation characteristics in the train station scenario are provided. Afterward, by filling the gap of the train station scenario, a table is made to establish the comprehensive understanding of main scenarios in the high-speed railway. Furthermore, comparisons of the propagation characteristics between the train station scenario and ten standard scenarios are made to emphasize the significance of the modeling exclusively for the train station scenario. Finally, rules of the influence of four conditions are quantitatively revealed. The measured results and quantitative analysis are significant for leading the simulation and design of signaling and train control communications systems toward the reality.

Complete Propagation Model in Tunnels

The wave propagation in tunnels does not only depend on the carrier frequency and properties of the tunnel, but also differs along with the distance between transmitter (Tx) and receiver (Rx). This letter presents a complete structure and model for propagation in tunnels. Compared to existing models, the complete model unifies different academic viewpoints, reveals all possible propagation mechanisms, and localizes all the dividing points between every two adjacent propagation mechanism zones. When the user is close to the Tx, the propagation is dominated by the free-space mechanism, then the multimode mechanism is established. Afterwards, when the high-order modes have been largely attenuated, the fundamental-mode guided propagation is dominant. Finally, when the user is extremely far away, the waveguide effect vanishes because of attenuation of reflected rays. Measurements and simulations validate the model. This complete structure and model can be essential to establish a comprehensive understanding of the propagation in tunnels and can be applied for network planning and interference analysis of advanced communication systems.

Measurements and Analysis of Large-Scale Fading Characteristics in Curved Subway Tunnels at 920 MHz, 2400 MHz, and 5705 MHz

Wave propagation characteristics in curved tunnels are of importance for designing reliable communications in subway systems. This paper presents the extensive propagation measurements conducted in two typical types of subway tunnels - traditional arched “Type I” tunnel and modern arched “Type II” tunnel - with 300- and 500-m radii of curvature with different configurations - horizontal and vertical polarizations at 920, 2400, and 5705 MHz, respectively. Based on the measurements, statistical metrics of propagation loss and shadow fading (path-loss exponent, shadow fading distribution, autocorrelation, and crosscorrelation) in all the measurement cases are extracted. Then, the large-scale fading characteristics in the curved subway tunnels are compared with the cases of road and railway tunnels, the other main rail traffic scenarios, and some “typical” scenarios to give a comprehensive insight into the propagation in various scenarios where the intelligent transportation systems are deployed. Moreover, for each of the large-scale fading parameters, extensive analysis and discussions are made to reflect the physical laws behind the observations. The quantitative results and findings are useful to realize intelligent transportation systems in the subway system.