High-speed Train Communication Research Articles

Characterization of Doppler shift in inter-satellite laser link between LEO, MEO, and GEO orbits

Over the past few decades, the development of optical wireless communications (OWC) has led to its application in a wide range of environments, including indoor, outdoor, and space. Optical carriers offer advantages such as high bandwidth, security, and directivity, making it a suitable technology for applications in radio astronomy, remote sensing, cellular networks, high-speed train communications, last-mile access, underwater/terrestrial communications, and satellite communications employing laser links. However, laser links between satellites experience Doppler shift due to their relative motion, and this effect should be taken into account from a system design perspective. This paper presents a study of the Doppler shift characterization in laser links for circular Keplerian orbits. An analytical derivation establishes the relationship between the Keplerian orbital elements and the Doppler shift in laser links. The derived equations provide a more comprehensive understanding of the impact of these orbital elements on the Doppler shift in laser links. Additionally, equations have been derived for the Doppler shift rate and the visibility window condition during satellite communication. Furthermore, we conducted a link failure analysis using simulations to evaluate the effects of the Doppler shift, also identifying the worst-case scenarios for orbits most significantly impacted by this shift. The results showed that among the six Keplerian orbital elements, the semi-major axis, inclination, and right ascension of ascending node contribute to the Doppler shift in circular orbits. While the Doppler shift impact is less significant for laser communication systems employing intensity modulation/direct detection, it can degrade the communication system performance for coherent detection. This work contributes to the effective estimation of Doppler shift from a system design perspective.

Throughput Maximization for Intelligent-Refracting-Surface-Assisted mmWave High-Speed Train Communications

Throughput Maximization for Intelligent-Refracting-Surface-Assisted mmWave High-Speed Train Communications

Reconfigurable Intelligent Surface Assisted High-Speed Train Communications: Coverage Performance Analysis and Placement Optimization

Reconfigurable Intelligent Surface Assisted High-Speed Train Communications: Coverage Performance Analysis and Placement Optimization

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

IRS-Assisted High-Speed Train Communications: Performance Analysis and Optimal Configuration

High-speed train (HST) communications are envisioned to provide diversified broadband services by integrating with 5G while the high mobility induces fast-fading channels and potentially degrades the system performance. To address this issue, we investigate an HST communication network empowered by intelligent reflecting surfaces (IRS) with the multiple-input multiple-output (MIMO) technology. Statistical channel state information (CSI) is exploited to mitigate the impact of the fast time-varying fading. The transceiver beamforming vectors and the IRS phase shift matrix are optimized to improve the system performance in terms of the outage probability and the ergodic capacity considering the channel uncertainty. First, we derive the analytical expression of the outage probability with a generalized Marcum Q-function. Then, we develop an alternating optimization algorithm to minimize the outage probability by capitalizing on the generalized eigenvalue-eigenvectors. Moreover, the ergodic capacity is deduced with statistical CSI and then optimized by analyzing the upper bound with Jensen’s approximation. Extensive simulations show that simulation results are consistent with the theoretical analysis, and the IRS-assisted system significantly outperforms the system without IRS in terms of the outage probability and the ergodic capacity.

Power allocation algorithm for capacity maximization in 5G MIMO systems

The multiple input - multiple output (MIMO) systems have sparked a lot of research interest because of their ability to increase the system capacity without using much bandwidth. The High-Speed Train (HST) communication system's capacity was calculated by assuming that the SNR is unaffected by variations in attenuation and channel losses. Here, considering this optimization problem, a power allocation algorithm using the Water-Filling technique is proposed for the MIMO system with known Channel Side Information (CSI) at the transmitter and receiver. The presented algorithm may be efficiently optimized for improving channel capacity to achieve spectral efficiency (SE).

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.

Cell-Free Massive MIMO-OFDM for High-Speed Train Communications

Cell-free (CF) massive multiple-input multiple-output (MIMO) systems show great potentials in low-mobility scenarios, due to cell boundary disappearance and strong macro diversity. However, the great Doppler frequency offset (DFO) leads to serious inter-carrier interference in orthogonal frequency division multiplexing (OFDM) technology, which makes it difficult to provide high-quality transmissions for both high-speed train (HST) operation control systems and passengers. In this paper, we focus on the performance of CF massive MIMO-OFDM systems with both fully centralized and local minimum mean square error (MMSE) combining in HST communications. Considering the local maximum ratio (MR) combining, the large-scale fading decoding (LSFD) cooperation and the practical effect of DFO on system performance, exact closed-form expressions for uplink spectral efficiency (SE) expressions are derived. We observe that cooperative MMSE combining achieves better SE performance than uncooperative MR combining. In addition, HST communications with small cell and cellular massive MIMO-OFDM systems are compared in terms of SE. Numerical results reveal that the CF massive MIMO-OFDM system achieves a larger and more uniform SE than the other systems. Finally, the train antenna centric (TA-centric) CF massive MIMO-OFDM system is designed for practical implementation in HST communications, and three power control schemes are adopted to optimize the propagation of TAs for reducing the impact of the DFO.

A Stochastic Confocal Elliptic-Cylinder Channel Model for 3D MIMO in Millimeter-Wave High-Speed Train Communication System

Massive MIMO technology is among the most promising solutions for achieving higher gain in 5G millimeter-wave (mmWave) channel models for high-speed train (HST) communication systems. Based on stochastic geometry methods, it is fundamental to accurately develop the associated MIMO channel model to access system performance. These MIMO channel models could be extended to massive MIMO with antenna arrays in more than one plane. In this paper, the proposed MIMO 3D geometry-based stochastic model (GBSM) is composed of the line of sight component (LOS), one sphere, and multiple confocal elliptic cylinders. By considering the proposed GBSM, the local channel statistical properties are derived and investigated. The impacts of the distance between the confocal points of the elliptic cylinder, mmWave frequencies of 28 GHz and 60 GHz, and non-stationarity on channel statistics are studied. Results show that the proposed 3D simulation model closely approximates the measured results in terms of stationary time. Consequently, findings show that the proposed 3D non-wide-sense stationary (WSS) model is better for describing mmWave HST channels in an open space environment.

Discrete FBMC-based orthogonal time frequency space in wireless communications considering different prototype filters

Designing a proper multicarrier signaling technique for the next generation of mobile network communications is one of the challenging fields of study. Orthogonal Frequency Division Multiplexing (OFDM) as the standard multicarrier technique in 5G suffers from the out-of-band (OOB) leakage where using the filter-based multicarrier techniques like Filter Bank Multi-Carrier (FBMC) could reduce the OOB emission. Also, due to the requirement of serving under high mobility conditions such as vehicle to vehicle (V2V) and high-speed train communications, employing a functional multicarrier technique like Orthogonal Time Frequency Space (OTFS) is quite desirable. Besides, to gain good frequency localization, it is required to have a long symbol duration where the more longer symbol duration provides the less robustness of the waveform to mobility. Hence, the combination of OTFS and FBMC could be interesting to fit in at the same time and frequency localization, and support the mobility. As a phenomenal property, OTFS could be understood as a pre- and post-processing steps for the OFDM-based techniques which enables OTFS to cooperate with them. Therefore, to achieve a better performance, we extended the FBMC by applying the OTFS and implemented the FBMC-based OTFS technique which benefits from both OTFS and FBMC qualities. Besides, to reduce the computational complexity of the continuous form and contributing more analytical results, the discrete FBMC-based OTFS formulation is provided. Our accomplished analyses and simulated results certificate the FBMC-based OTFS superiority over different schemes in Peak to Average Power Ratio (PAPR) and error probability terms.

Physical Layer Enhancement for Next-Generation Railway Communication Systems

This paper presents an overview of the challenges and state-of-the-art physical layer enhancement designs for next-generation railway communication, also known as high-speed train (HST) communication. The physical layer design for the HST should adapt from its counterpart in the general-purpose network because of the harsh propagation environment and extreme conditions, stringent latency and reliability requirements of dedicated railway applications, and frequency band scarcity caused by regulation. In this survey, we examine how conventional multiple-input-multiple-output (MIMO) family techniques such as beamforming, multi-cell MIMO, and relays can enhance the physical layer performance for HST. Physical layer enhancement assisted by novel reconfigurable intelligent surface (RIS) technology was also analyzed from different perspectives. Dedicated control channels, reference signals, waveforms, and numerology designs for train-to-infrastructure (T2I) and train-to-train (T2T) communication in sidelinks are also reviewed. Finally, a brief introduction to artificial intelligence (AI)/machine learning (ML)-aided HST physical layer design is provided. Several promising research avenues have also been suggested.

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.

Resource Allocation for High-Speed Train Communication Based on Deep Reinforcement Learning

With the advent of high-speed railway era, users’ demands for high link capacity and high reliability are increasing. In this paper, a resource allocation algorithm based on deep reinforcement learning (DRL) is proposed in the high-speed railway (HSR) scenario. The communication link between high-speed train and high-speed train (T2T) is taken as an agent, and the link capacity and packet transmission success probability (PTSP) are taken as optimization objectives, which are mapped into the reward function. The agents gain experience by constantly interacting with the HSR communication environment to update the neural networks in DRL and eventually learned the optimization policy. The simulation shows that when the trains’ speed is 350km/h and the transmission packet size is 2385Bits, the high reliability of T2T link can still be maintained, and the capacity of high-speed train to Infrastructure (T2I) link is improved by 1Mbps compared with the baseline, which proves that the proposed algorithm can mitigate the interference introduced by spectrum reuse and doppler shift.

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).

High Speed Train Communications in 5G: Design Elements to Mitigate the Impact of Very High Mobility

5G wireless technology is expected to provide much improved performance in terms of data rate, reliability, latency, and mobility in various use cases and deployment scenarios. One of these promising 5G deployment scenarios is the high speed train scenario, which aims to offer broadband access to passengers on a high speed train running up to 500 km/h. Such very high mobility imposes considerable technical challenges to be dealt with during the 5G standardization phases. This article introduces the technical specifications of 5G NR with particular attention on the high speed train scenario. Based on the concrete high speed train scenario description, various NR design elements to achieve such very high mobility are discussed including numerology, frame structure, reference signals, multi-antenna schemes, cell search, random access, and mobility support. Discussions on the challenges and perspectives for high speed train communications of Beyond 5G are also provided.

A Beamforming Scheme With Doppler Suppression for High-Mobility Wireless Communications

In this letter, we consider the high-mobility wireless communications between a high speed train (HST) and a base station (BS) and propose a beamforming scheme with Doppler suppression for the stationary node BS. The typical Rician channel model is assumed, which occupies most of the HST communication scenarios. Based on the fact that the channel time-variation induces interference to the standard time-invariant signal model, the beamforming is then designed to maximize the signal-to-interference-plus-noise ratio (SINR) for both uplink and downlink transmissions. Simulation results are provided to verify that the channel time-variation can be effectively suppressed by the stationary BS through the proposed beamforming scheme.

Analysis and Optimization of Real-time Performance of High-speed Train Communication Network

With the expansion of the scale of network system, the structure of high-speed railway train is more and more complex. The problems of real-time and reliability of network need to be solved. In this paper, aiming at the traditional train network communication mechanism, multi-objective particle swarm optimization algorithm is used to optimize the network design. The real-time performance of the network before and after optimization is simulated by OPNET. The experimental results show that the optimization algorithm in this paper can improve the real-time performance and reliability of the network.

Space-Time Correlation for Three-Dimensional MIMO Channel Model Using Leaky Coaxial Cables in Rectangular Tunnel

The rapid development of high-speed train and Metro communications has provided new challenges for the application of MIMO technologies. Therefore, we propose a three-dimensional (3D) multiple-input multiple-output (MIMO) channel model using leaky coaxial cable (LCX) in a rectangular tunnel. The channel model is based on geometry-based single-bounce (GBSB) channel model and the electric field distribution of LCX in the tunnel environment. The theoretical expressions of channel impulse response (CIR) and space-time correlation function (CF) are also derived and analyzed. The CFs for different model parameters (moving velocity and moving time) and different regions of the tunnel are simulated by Monte Carlo method to verify the theoretical derivation at 1.8 GHz. In the same parametric configuration of nonstationary tunnel scenarios, the time delay of the first minimum value of CFs for LCX-MIMO is 1/5 of the time delay of the minimum value of CFs for dipole antennas MIMO when the train moving velocity is 360 km/h. It is shown that, for MIMO system, the performance of using LCXs is better than using dipole antennas.

Millimeter-Wave System for High-Speed Train Communications Between Train and Trackside: System Design and Channel Measurements

This paper introduces the design of a 41 GHz mmWave system dedicated for high-speed train communications between train and trackside. A novel frame structure is provided for the acquirement of channel state information as well as for the transmission of user data. Based on the proposed design principles, a system prototype has been established and employed in extensive measurement campaigns. The channel measurement results obtained from a recent measurement campaign under high-speed mobile conditions where the relative velocity between the transmitter and the receiver reaches 170 km/h are presented in this paper. Channel characteristics, including the power delay profile, RMS delay spread, fade depth, small-scale fading statistics, Ricean K factor, autocovariance function, coherence time, level crossing rate, and average fading duration are analyzed in detail. Moreover, the bit-error-rate performance for the proposed system under the channel whose characteristics are obtained from the measurements is simulated. Based on the simulation results, the key parameters for the proposed frame structure are determined to improve the system's robustness in fast varying channels and in the mean time achieve high spectrum efficiency. Besides, the throughput of the system prototype recorded during the transmission of three high-definition video streams is presented. Finally, the outage probability as a function of transmission distance and path loss exponent is estimated based on the channel measurement results.

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.