High-speed Train Communication System Research Articles

Robust Train-to-Train Transmission Scheduling in mmWave Band for High Speed Train Communication Systems

Robust Train-to-Train Transmission Scheduling in mmWave Band for High Speed Train Communication Systems

FSO communication system for high-speed trains under varying visibility conditions

High-speed train systems are rapidly growing in complexity and coverage, demanding efficient high-speed internet services. Existing radio frequency technology struggles to meet these demands due to handover mechanisms and limited connectivity times. Furthermore, current free-space optics (FSO) techniques require a large number of base stations (BSs), resulting in high costs. This study presents a novel high-speed train communication technique, using FSO, that significantly reduces the number of required BSs while maintaining sufficient coverage and data speeds. The proposed technique can be adapted for fixed or variable representations of transmitted and received power, providing a fixed or variable data rate. The research also investigates the impact of divergence angle on transmitted and received power. By employing the proposed communication technique, a system with a fixed data rate, such as 1.25 Gbps, can be achieved. The results demonstrate the potential of this approach in high-speed train applications, reducing the number of BSs from 113, as reported in the best existing literature, to less than 10. Weather conditions, including clear, haze, thin fog, light fog, and heavy fog, are considered when calculating the required BS locations to achieve a target data rate. Additionally, this work introduces a new handover mechanism and mathematical formulation, providing a more comprehensive solution for high-speed train communication systems. The simulations and evaluations conducted in this study are based on parameters and equations from previous works to ensure a fair comparison.

RIS-Aided Next-Generation High-Speed Train Communications: Challenges, Solutions, and Future Directions

High-speed train (HST) communication is a very challenging scenario in wireless communication systems due to its fast time-varying channels and significant penetration loss. Thanks to its low cost and smart channel reconfiguration ability, the reconfigurable intelligent surface (RIS) has been proposed as a promising technology to solve the aforementioned challenges cost effectively and achieve high spectral and energy efficiency in the next-generation HST communication systems. In this article, we first provide a novel RIS-aided HST wireless communication paradigm, including its main challenges and application scenarios. Furthermore, practical solutions are provided to realize efficient signal processing and resource management in the considered system. Finally, promising research directions of RIS-aided HST communication systems are pointed out to inspire further investigation in future work.

WITHDRAWN: A study on single frequency network on high speed train

Abstract This paper presents a comprehensive study on millimetre wave (mmWave)-based mobile hotspot network (MHN) system for high-speed train (HST) communications, including system design, field trial, channel modeling based on measurement campaign, simulation and validation. Firstly, the physical layer specification and single frequency network (SFN) which includes MHN enhanced design (MHN-E) and the overview of the MHN system is provided. Secondly, For MHN conventional (MHN-C) and MHN-E systems, the prototypes and the overall design is presented and the MHN-C prototype and demonstrations with the MHN-E prototype are analysed with the help of results of field trial which conducted at Seoul subway line 8.Thirdly, the paper presents a characteristics of a measurement campaign investigating channel which is based on rural HST environment. Lastly, the performance of the MHNE system is validated by the help of computer simulation. The simulation is done at the speed of 500 km/h under the QuaDRiGa channel model which is also known as the good method for validation of HST communication systems, since it is impractical by real testbeds now. The simulation results revealed that with a peak data rate which exceeding 5 Gbps at a speed of 500 km/h the MHN-E system can able to provide a broadband mobile wireless backhaul (MWB).

Recent Developments and Future Challenges in Channel Measurements and Models for 5G and Beyond High-Speed Train Communication Systems

The fast developments of high-speed train (HST) and growing communication demands of users pose new challenges for HST communication systems. To provide reliable communication services, key 5G communication technologies, such as millimeter-wave (mmWave) and massive multiple-input multiple-output (MIMO), and potential architectures, such as coordinated multipoint and mobile relay station, are considered in future railway communications. New technologies and architectures will bring new channel propagation characteristics. Accurate channel models that can capture these channel characteristics play a critical role in the design and test of future railway communication systems. This article reviews the HST channel measurements conducted in different scenarios and frequency bands, and the advanced HST channel models. Then a novel HST channel model incorporating the mmWave and massive MIMO propagation characteristics is presented, and its frequency non-stationarity is analyzed. Finally, some future directions are discussed.

LTE-Assisted Multi-Link MIMO Channel Characterization for High-Speed Train Communication Systems

The performance of wireless systems and transmission technologies is ultimately limited by radio channels. This paper characterizes multi-link multiple-input multiple-output (MIMO) channels for future high-speed train (HST) communication systems. The channel characterization is based on field measurements in a dedicated long-term evolution (LTE) network along a high-speed railway line of China. The raw channel data are collected by an LTE sounder with two antenna ports in the multi-link region between neighboring remote radio units of the network, which are further processed by a time-delay-window-based partitioning approach to acquire multi-link MIMO channel impulse responses. Before investigating the multi-link channel properties, MIMO channel characteristics for each single link in a plain viaduct scenario are analyzed and compared in terms of root mean square angular spread and spatial correlation. Then, the dual-link MIMO channel characteristics, such as correlation matrix collinearity and sum rate capacity, are newly presented and discussed. These results can provide the reference for realistic performance assessment of cooperative MIMO HST communication systems.

A Comprehensive Study on mmWave-Based Mobile Hotspot Network System for High-Speed Train Communications

This paper presents a comprehensive study on millimeter-wave-based mobile hotspot network (MHN) system for high-speed train (HST) communications, including system design, field trial, channel modeling based on measurement campaign, simulation, and validation. First, an overview of the MHN system and the design of an MHN enhanced (MHN-E) system including physical layer specification and single frequency network are provided. Second, the overall design of prototypes for MHN conventional (MHN-C) and MHN-E systems is presented, and then the recent experimental results of a field trial conducted at Seoul subway line 8 with the MHN-C prototype and demonstrations with the MHN-E prototype are analyzed. Third, this paper presents a measurement campaign investigating channel characteristics of a rural HST environment and a QuaDRiGa-based channel model developed based on the parameters extracted from the measurement. Finally, a computer simulation is conducted to validate the performance of the MHN-E system at high mobility of up to 500 km/h under the QuaDRiGa channel model, which suggests a good methodology for the validation of HST communication systems at the highmobility since it is impractical to be tested by real testbeds as of now. The simulation results revealed that the MHN-E system is capable of providing a broadband mobile wireless backhaul with a peak data rate exceeding 5 Gb/s at a speed of 500 km/h.

A Novel Non-Stationary High-Speed Train (HST) Channel Modeling and Simulation Method

With the rapid development of high-speed train (HST), the HST wireless communication systems have been attracting an increasing amount of attention. For the design, optimization, and evaluation of HST communication systems, it is vital to have an accurate channel model that can mimic the non-stationary characteristics of HST communication links. In this paper, we propose a new geometry-based stochastic channel model (GSCM) for rural macrocell scenarios by exploiting the sum-of-frequency-modulated signals method. The time-variant (TV) theoretical autocorrelation function (ACF) and Doppler power spectrum density of the proposed GSCM under von-Mises scattering environments are also derived by employing the Wigner distribution function. Moreover, a new simulation method is developed to reproduce the proposed GSCM. To reconstruct the non-stationary characteristic precisely, we also develop a low complexity parameter computation approach with linear variation. Finally, the simulation results demonstrate that the TV train's velocity leads to the non-stationary characteristic in the channel model. Meanwhile, the simulated ACF agrees well with the theoretical and measured ones, showing the correctness of the theoretical derivation and the simulation method.

Multidomain Index Modulation for Vehicular and Railway Communications: A Survey of Novel Techniques

Vehicular communications have recently attracted considerable attention due to a range of new applications and valueadded features. Compared to conventional communication systems, vehicular communications suffer from graver challenges due to the high-Doppler spread caused by the mobility of vehicles. In this context, index modulation (IM) constitutes a promising design alterative for vehicular communications due to its appealing benefits. A key feature of IM is that it conveys the information bits using the specific indices of the transmit resources, such as antenna, subcarrier, precoder, and channel-path indices. The resulting transmission signals tend to be sparse in one or several of the resource domains, which increases their robustness and reduces the detection complexity. In this article, we introduce the basic IM concept and highlight the applications of IM in the context of road vehicle-to-infrastructure (V2I), vehicle-to-vehicle (V2V), and conventional railway and high-speed train communication systems. Finally, some design challenges of IM-based vehicular communications are listed for future studies.

A Geometry-Based Stochastic Channel Model for the Millimeter-Wave Band in a 3GPP High-Speed Train Scenario

This paper presents a geometry-based stochastic channel model (GSCM) for a 3GPP millimeter-wave (mmWave) high-speed train (HST) scenario. An important demand of the mmWave HST channel model is the spatial consistency during movement. In order to meet this requirement, the environment pattern containing the most effective geometry information is proposed, which is useful for generating an integral and accurate channel geometry. Since the measurement of a mmWave channel is deficient for high mobility, the proposed channel model is developed using a ray-tracing (RT) simulator that is validated with the channel measurements performed in the HST scenario at 93.2 GHz. The paper gives a full parameterization for the proposed model and its implementation for channel simulation. The verification is made through a comparison of the proposed model and the measurement-validated RT simulations in terms of the power delay profile, the Ricean $K$ -factor, and the second-order statistics for the delay and angle domains. Finally, for the design of mmWave HST communication systems, the time-varying channel characteristics are evaluated in the delay and Doppler domains.

Position-Based Interference Elimination for High-Mobility OFDM Channel Estimation in Multicell Systems

Orthogonal frequency-division multiplexing (OFDM) and multicell architecture are widely adopted in current high-speed train (HST) systems for providing high-data-rate wireless communications. In this paper, a typical multiantenna OFDM HST communication system with multicell architecture is considered, where the intercarrier interference (ICI) caused by high mobility and the multicell interference (MCI) are both taken into consideration. By exploiting the train position information, a new position-based interference elimination method is proposed to eliminate both the MCI and the ICI for a general basis expansion model. We show that the MCI and the ICI can be completely eliminated by the proposed method to get the ICI-free pilots at each receive antenna. In addition, for the considered multicell HST system, we develop a low-complexity compressed channel estimation method and consider the optimal pilot pattern design. Both the proposed interference elimination method and the optimal pilot pattern are robust to the train speed and position, as well as the multicell multiantenna system. Simulation results demonstrate the benefits and robustness of the proposed method in the multicell HST system.

Performance Improvement of LeastSquares Adaptive Filter for High-Speed Train Communication Systems

The downlink communication channel from high-altitude platform (HAP) to high-speed train (HST) in the Ka-band is a slowly time-varying Rician distributed flat fading channel with 10-25 dB Rician K factor. In this respect, the received signal is mainly affected by the Doppler shift of the line-of-sight (LOS) link. In order to increase receiver performance, we propose to firstly compensate the Doppler shift of the received signal before least-squares (LS) adaptive filtering is pursued. Implementing the proposed method requires a priori knowledge of the time-varying phase of the LOS component. This is justified since signalling between the train and the controller exists such that the train velocity and location are predictable. Implementing the proposed method to the recursive LS (RLS) received beamforming algorithm shows reduction of mean square error (MSE) and bit error rate (BER).

Simulation and Analysis of Scattering Channel Models in Three-Dimensional High-Speed Mobile Environment

A three-dimensional (3D) statistic channel model based on scattering characteristics is proposed to describe accurately the wireless channel under the scenarios of high-speed train (HST). This paper derives scattering density distribution function and scattering coefficient to represent the channel impulse response (CIR) of HST communication system, and deduces closed expressions of Doppler power spectrum (DPS) of mobile terminal. Expressions are also provided for categorizing and quantizing the scattering characteristics of wireless channels. By analyzing the Doppler spread of HST and comparing the effects of scattering environment and mobile velocity on DPS, these works contribute to understand deeply the wireless scattering channel of HST. Numerical and simulation results demonstrate that the proposed scattering channel models can effectively depict the physical characteristics of HST wireless channel, which provide a reliable method to analyze and estimate channel parameters. Moreover, the channel realization in this paper is more straightforward and concise to study the scattering channel characteristics, which can also be utilized as a reference for experimental measurement campaigns and reducing the modeling errors of scattering channel model effectively.

Compressed Channel Estimation With Position-Based ICI Elimination for High-Mobility SIMO-OFDM Systems

Orthogonal frequency-division multiplexing (OFDM) is widely adopted for providing reliable and high-data-rate communication in high-speed train (HST) systems. However, with increasing train mobility, the resulting large Doppler shift introduces intercarrier interference (ICI) in OFDM systems and greatly degrades channel estimation accuracy. Therefore, it is necessary and important to investigate reliable channel estimation and ICI mitigation methods in high-mobility environments. In this paper, we consider a typical HST communication system and show that the ICI caused by large Doppler shifts can be mitigated by exploiting the train position information and the sparsity of the basis expansion model (BEM)-based channel model. Then, we show that for the complex-exponential BEM (CE-BEM)-based channel model, the ICI can be completely eliminated to get the ICI-free pilots at each receive antenna. After that, we propose a new pilot pattern design algorithm to reduce system coherence to improve the compressed-sensing-based channel estimation accuracy. The proposed optimal pilot pattern is independent of the number of receive antennas, the Doppler shifts, train position, or train speed. Simulation results confirm the effectiveness of the proposed scheme in high-mobility environments. The results also show that the proposed scheme is robust to the speed of the moving train.

Channel Measurements and Models for High-Speed Train Communication Systems: A Survey

The recent development of high-speed trains (HSTs) as an emerging high mobility transportation system, and the growing demands of broadband services for HST users, introduce new challenges to wireless communication systems for HSTs. Accurate and efficient channel models considering both large-scale and non-stationary small-scale fading characteristics are crucial for the design, performance evaluation, and parameter optimization of HST wireless communication systems. However, the characteristics of the underlying HST channels have not yet been sufficiently investigated. This paper first provides a comprehensive review of the measurement campaigns conducted in different HST scenarios and then addresses the recent advances in HST channel models. Finally, key challenges of HST channel measurements and models are discussed and several research directions in this area are outlined.

Admission control scheme for handover service in high-speed train communication system

Admission control in high-speed train communication system is quite different from admission control in traditional cellular networks. Conventional admission control strategies cannot be directly applied to this special communication scenario. In this paper, the problem of admission control for handover service is investigated in high-speed train communication environment. An admission control scheme considering bit error rate (BER) and bandwidth borrowing strategy is proposed. On the basis of admission control decision rule taking BER into account, a part of bandwidth obtained by compressing variable rate service in the networks is provided for handover services. The admission control scheme can admit handover services as more as possible while it guarantees the lowest data rate of different services in the networks. Simulation results show that the proposed admission control scheme has a better performance than existing admission control schemes.

Noisy chaotic neural network for resource allocation in high-speed train OFDMA system

High-speed train communication system is a typical high-mobility wireless communication network. Resource allocation problem has a great impact on the system performance. However, conventional resource allocation approaches in cellular network cannot be directly applied to this kind of special communication environment. A multi-domain resource allocation strategy was proposed in the orthogonal frequency-division multiple access (OFDMA) of high-speed. By analyzing the effect of Doppler shift, sub-channels, antennas, time slots and power were jointly considered to maximize the energy efficiency under the constraint of total transmission power. For the purpose of reducing the computational complexity, noisy chaotic neural network algorithm was used to solve the above optimization problem. Simulation results showed that the proposed resource allocation method had a better performance than the traditional strategy.

Exploiting cooperative multipath–Doppler diversity in relay-assisted high-speed train communications

Severe doubly selective channel fading, or the time- and frequency-selective fading, prevailing in high-speed train (HST) communications, has been a critical issue that hinders the improvement of system efficiency and reliability. In this paper, a relay-assisted HST communication system is considered, and a low-complexity but effective scheme is proposed to cooperatively exploit the joint multipath–Doppler diversity of both the direct link and the relay link and thus to mitigate the negative effect of channel fading and improve the system reliability. In particular, using a special precoding structure followed by two-dimensional Fourier transform, the transmit signal is generated which in effect parallelizes the doubly selective fading channel. As a result, in the transform domain, pointwise combining and equalization, which are of linear complexity, become feasible and diversity gain is obtained. The maximal diversity order is then analyzed under the amplify-and-forward relay settings, which reveals that by cooperative relaying the joint multipath–Doppler diversity of both links can be well exploited. Simulation results verified our analysis.