High-speed railway (HSR) brings convenience to peoples' lives and is generally considered as one of the most sustainable developments for ground transportation. One of the important parts of HSR construction is the signaling system, which is also called the “operation control system,” where wireless communications play a key role in the transmission of train control data. We discuss in detail the main differences in scientific research for wireless communications between the HSR operation scenarios and the conventional public land mobile scenarios. The latest research progress in wireless channel modeling in viaducts, cuttings, and tunnels scenarios are discussed. The characteristics of nonstationary channel and the line-of-sight (LOS) sparse and LOS multiple-input-multiple-output channels, which are the typical channels in HSR scenarios, are analyzed. Some novel concepts such as composite transportation and key challenging techniques such as train-to-train communication, vacuum maglev train techniques, the security for HSR, and the fifth-generation wireless communications related techniques for future HSR development for safer, more comfortable, and more secure HSR operation are also discussed.

Challenges Toward Wireless Communications for High-Speed Railway

To improve safety on the roads, next-generation vehicles will be equipped with short-range communication technologies. Many applications enabled by such communication will be based on a continuous broadcast of information about the own status from each vehicle to the neighborhood, often referred as cooperative awareness or beaconing. Although the only standardized technology allowing direct vehicle-to-vehicle (V2V) communication has been IEEE 802.11p until now, the latest release of long-term evolution (LTE) included advanced device-to-device features designed for the vehicular environment (LTE-V2V) making it a suitable alternative to IEEE 802.11p. Advantages and drawbacks are being considered for both technologies, and which one will be implemented is still under debate. The aim of this paper is thus to provide an insight into the performance of both technologies for cooperative awareness and to compare them. The investigation is performed analytically through the implementation of novel models for both IEEE 802.11p and LTE-V2V able to address the same scenario, with consistent settings and focusing on the same output metrics. The proposed models take into account several aspects that are often neglected by related works, such as hidden terminals and capture effect in IEEE 802.11p, the impact of imperfect knowledge of vehicles position on the resource allocation in LTE-V2V, and the various modulation and coding scheme combinations that are available in both technologies. Results show that LTE-V2V allows us to maintain the required quality of service at even double or more the distance than IEEE 802.11p in moderate traffic conditions. However, due to the half-duplex nature of devices and the structure of LTE frames, it shows lower capacity than IEEE 802.11p if short distances and very high vehicle density are targeted.

On the Performance of IEEE 802.11p and LTE-V2V for the Cooperative Awareness of Connected Vehicles

The application scenarios and requirements are more diverse in the fifth-generation (5G) era than before. In order to successfully support the system design and deployment, accurate channel modeling is important. Ray-tracing (RT) based deterministic modeling approach is accurate with detailed angular information and is a suitable candidate for predicting time-varying channel and multiple-input multiple-output (MIMO) channel for various frequency bands. However, the computational complexity and the utility of RT are the main concerns of users. Aiming at 5G and beyond wireless communications, this paper presents a comprehensive tutorial on the design of RT and the applications. The role of RT and the state-of-the-art RT techniques are reviewed. The features of academic and commercial RT based simulators are summarized and compared. The requirements, challenges, and developing trends of RT to enable the visions are discussed. The practices of the design of high-performance RT simulation platform for 5G and beyond communications are introduced, with the publicly available high-performance cloud-based RT simulation platform as the main reference. The hardware structure, networking, workflow, data flow and fundamental functions of a flexible high-performance RT platform are discussed. The applications of high-performance RT are presented based on two 5G scenarios, i.e., a 3.5 GHz Beijing vehicle-to-infrastructure scenario and a 28 GHz Manhattan outdoor scenario. The questions on how to calibrate and validate RT based on measurements, how to apply RT for mobile communications in moving scenarios, and how to evaluate MIMO beamforming technologies are answered. This tutorial will be especially useful for researchers who work on RT algorithms development and channel modeling to meet the evaluation requirements of 5G and beyond technologies.

The Design and Applications of High-Performance Ray-Tracing Simulation Platform for 5G and Beyond Wireless Communications: A Tutorial

Railway communications has attracted significant attention from both academia and industries due to the booming development of railways, especially high-speed railways (HSRs). To be in line with the vision of future smart rail communications, the rail transport industry needs to develop innovative communication network architectures and key technologies that ensure high-quality transmissions for both passengers and railway operations and control systems. Under high mobility and with safety, eco-friendliness, comfort, transparency, predictability, and reliability. Fifth-generation (5G) technologies could be a promising solution to dealing with the design challenges on high reliability and high throughput for HSR communications. Based on our in-depth analysis of smart rail traffic services and communication scenarios, we propose a network slicing architecture for a 5G-based HSR system. With a ray tracing-based analysis of radio wave propagation characteristics and channel models for millimeter wave (mmWave) bands in railway scenarios, we draw important conclusions with regard to appropriate operating frequency bands for HSRs. mymargin Specifically, we have identified significant 5G-based key technologies for HSRs, such as spatial modulation, fast channel estimation, cell-free massive multiple-input–multiple-output (MIMO), mmWave, efficient beamforming, wireless backhaul, ultrareliable low latency communications, and enhanced handover strategies. Based on these technologies, we have developed a complete framework of 5G technologies for smart railways and pointed out exciting future research directions.

5G Key Technologies for Smart Railways

Road safety is an active area of research for the automotive industry, and certainly one of ongoing interest to governments around the world. The intelligent transportation system (ITS) is one of several viable solutions with which to improve road safety, where the communication medium (e.g., among vehicles and between vehicles and the other components in an ITS environment, such as roadside infrastructure) is typically wireless. A typical communication standard adopted by car manufacturers is IEEE 802.11p for communications. Thus, this paper presents an overview of IEEE 802.11p, with a particular focus on its adoption in an ITS setting. Specifically, we analyze both MAC and PHY layers in a dedicated short-range communication (DSRC) environment.

A Review on IEEE 802.11p for Intelligent Transportation Systems

In this paper, a physical (PHY) layer performance comparison for 3GPP Long Term Evolution (LTE) and IEEE 802.11p in a realistic urban street intersection scenario is presented. For this approach standard compliant link level simulation tools in combination with ray-optical channel modeling are utilized. Results are analyzed with respect to an intersection collision warning application where a suitable performance metric is derived to analyze the individual performances with respect to the packet error ratio in the downlink. In the absence of a line of sight (LOS) path for a Vehicle-to-Vehicle (V2V) link, the results show promising potential of LTE to outperform a dedicated IEEE 802.11p based communication link even when considering full buffer intercell-interference condition.

Physical Layer Performance Comparison of LTE and IEEE 802.11p for Vehicular Communication in an Urban NLOS Scenario

Today's cellular radio networks offer so many parameters that can be configured, that it is virtually impossible to configure such a system manually. To overcome this problem, operators and vendors put their trust in SON. But still, how can a SON function evaluate all potential parameter variations in short time and in a realistic manner in order to make the right decision? The herein presented Simulator for Mobile Networks (SiMoNe) is capable of performing system-level simulations within realistic network scenarios. By offering the capability of parallel simulations of parameter variations, a multitude of different settings can be evaluated. It allows for simulations based on time variant maps as well as for simulations with a large number of individual user traces which follow different mobility pattern like vehicular or indoor mobility.

SiMoNe - Simulator for Mobile Networks: System-Level Simulations in the Context of Realistic Scenarios

There is a need to characterize the radio channel for vehicular communication systems including the derivation of adequate channel models for specific traffic situations. Deterministic channel modeling approaches like ray tracing may become of greater interest since they take the individual characteristics of the environment into account and help reveal the most relevant radio propagation phenomena. However, a detailed and accurate database of objects like buildings influencing radio propagation is required. The aim of this paper is to encourage the propagation research community to consider public-domain OpenStreetMap (OSM) data for the purpose of deterministic channel modeling focusing on urban vehicular environments.We present a guideline on how to make use of OSM data and answer the question whether the building data can provide a satisfying accuracy required for adequate channel modeling.

On the use of OpenStreetMap data for V2X channel modeling in urban scenarios

Femto cells in LTE are attracting more and more attention since they are expected to provide substantial indoor network coverage. In contrast, the interference level on the outside increases with every new indoor base station, so that it is crucial to gain in-depth knowledge of the propagation phenomena from indoor to outdoor environments. Therefore, an exhaustive measurement campaign has been carried out to prove the usability of femto cells. Furthermore, a prediction model has been set up that considers the dominant effects in femto cell deployments, namely transmission and vertical diffraction.

Indoor to outdoor propagation — Measuring and modeling of femto cells in LTE networks at 800 and 2600 MHz

Indoor network coverage has become more important since the majority of mobile data traffic is delivered to indoor environments. With the deployment of femto cells, the way in which signals penetrate into buildings and interfere on the inside with others has become a central aspect, because high data rates rely on good SINR. Therefore, an exhaustive measurement campaign has been carried out in order to prove the usability of classical models and to discover supplementary key facts. In addition, a prediction model has been set up that considers the dominant effects.

Dennis M. Rose

Papers

Physical Layer Performance Comparison of LTE and IEEE 802.11p for Vehicular Communication in an Urban NLOS Scenario

SiMoNe - Simulator for Mobile Networks: System-Level Simulations in the Context of Realistic Scenarios

On the use of OpenStreetMap data for V2X channel modeling in urban scenarios

Indoor to outdoor propagation — Measuring and modeling of femto cells in LTE networks at 800 and 2600 MHz

Outdoor-to-indoor propagation — Accurate measuring and modelling of indoor environments at 900 and 1800 MHz