Dedicated Mobile Communications for High-speed Railway

High-speed railway (HSR) communications will become a key feature supported by intelligent transportation communication systems. To the end of 2015, the operating mileage of China railway has reached 121,000 km, and the operating mileage of China HSR has reached 19,000 km, which accounting for more than 60% of the world’s HSR operation mileage, and ranking the first all over the world. Within the past few decades, HSR has been widely introduced to meet the increasing demand for passenger rail travel. HSR becomes more competitive in areas of higher population density due to its faster than normal speed of operation. Meanwhile, a reliable communication system with high capacity and security is a challenging task for HSR. This chapter briefly reviews the development of HSR communication system and explores the necessity and significance for future HSR communications.

HSR has been developed rapidly all over the world, which puts forward requirements for a reliable and efficient wireless communication system between the moving train and the ground. According to International Union of Railways (UIC) E-Train Project, the train-ground wireless communication services for HSR system mainly include the train control services, the train monitoring services, and the passenger services from/to Internet. The train control and monitoring services are special services for train needs and provided by train operators mainly using Global System for Mobile Communications-Railway (GSM-R), which is an international wireless communications standard for railway communication and applications. With the rapid growth of HSR services, GSM-R has been unable to support the broadband communication systems. Therefore, from GSM-R to long-term evolution for railway (LTE-R) is the essential trend to guarantee a reliable communication systems. By introducing and comparing the network architecture and key technologies of GSM-R and LTE-R system, this chapter discusses the development of the next-generation HSR broadband communication systems.

In this chapter, we study radio propagation and wireless channels for railway communications. The first part of the chapter focuses on definitions of propagation scenarios. To begin with, high-speed railway propagation scenarios are partitioned, and the characteristics of each scenario are described in detail. Then, traditional concepts of railway communications and vehicular communications are summarized together to constitute a more general concept—wide-sense V2X (WSV2X). In this manner, the vehicles, trains, and infrastructures build up a wireless network enabling them to exchange controlling and traffic information, such as road obstacles, accidents, and so forth, via the wireless communication links. Correspondingly, all the propagation scenarios of WSV2X communications are defined in detail.

In the second part of the chapter, we shift our focus to high-speed railway channel measurements. Both narrowband and wideband measurement methods and systems are surveyed. Then, various measurement campaigns on high-speed railways are depicted and discussed in detail.

In the last part of the chapter, we study narrowband channel characteristics, i.e., path loss, shadow fading, and small-scale fading, for high-speed railways. Afterwards, we study wideband characteristics for high-speed railways in terms of delay characteristics, Doppler characteristics, and angular characteristics.

In recent years, a new paradigm for communication called cooperative communications has been proposed for which initial information theoretic studies have shown the potential for improvements in capacity over traditional multi-hop wireless networks. Cooperative communication involves exploiting the broadcast nature of the wireless medium to form virtual antenna arrays out of independent single-antenna network nodes for transmission. The field of telecommunication networks involves exchange of information messages among a collection of terminals, links, and nodes that are connected together. The field has advanced tremendously and has generated many breakthroughs in research and technology innovations in the past century. The fundamental goals that have driven communications and networking research and technology developments mainly solve two problems: how to increase communication rates over a communication link connecting two nodes and how to increase the communication reliability to minimize the errors in information delivery. The first goal often refers to spectral efficiency, measured by bits per second per hertz. The second goal often refers to information multi-capacity or channel capacity, measured by the bits per second that can be achieved with arbitrarily small error probability. Emerging classes of wireless networks, such as ad hoc and sensor networks and cellular networks with multiple hops, often consist of a large number of nodes in different geometric locations. Compared with classical point-to-point systems, these new types of networks are extremely difficult to analyze and optimize. Therefore, new theoretical and practical techniques are needed to augment classical communication and networking theory and practice. The current spectrum allocation policy is highly inefficient, which is one of the main reasons that lead to significant underutilization of spectrum in the face of explosive growth in demand. The radio spectrum is the radio frequency (RF) portion of the electromagnetic spectrum, which is a natural resource used by the transmitter and receiver to transmit signals. In order to solve the shortage in spectrum resources and to improve the spectrum utilization, cognitive radio (CR) has been proposed, which allows a secondary user (unlicensed user) to exploit spectrum holes at a given time and location and transmit. The spectrum hole is the frequency band that is unoccupied by the primary user (licensed user), and can be exploited temporally, spectrally, and spatially. The concept of cognitive radio was first proposed by Mitola in 1999, whereby a radio can adapt and dynamically reconfigure itself based on its RF environment. After a decade of research, cognitive radio has attracted a lot of interest. Recently, cognitive radio has been considered as a promising candidate technique in the upcoming 5G wireless systems. In this chapter, we start from the introduction of fundamental cooperation and cognition, followed by a brief review of the application in railway communications.

High-speed railway (HSR) communications will become a key feature supported by intelligent transportation communication systems. The increasing demand for HSR communications leads to significant attention on the study of radio resource management (RRM), which enables efficient resource utilization and improved system performance. RRM design is a challenging problem due to heterogenous quality of service (QoS) requirements and dynamic characteristics of HSR wireless communications. The objective of this chapter is to provide an overview on the key issues that arise in the RRM design for HSR wireless communications. We provide a literature survey on state-of-the-art RRM schemes for HSR wireless communications, with an in-depth discussion on various RRM aspects including admission control, power control, and resource allocation. The studies on joint power control and resource allocation problem, and dynamic resource management problem are presented. Finally, this chapter outlines the current challenges and open issues in the area of RRM design for HSR wireless communications.

Recently, high-speed railway (HSR) has been developed rapidly all over the world, which puts forward requirements for a reliable and efficient wireless communication system between the moving train and the ground. It is important to design the next generation HSR communications system based on LTE technology while addressing the specific challenges of HSR environment, such as high mobility speeds and stringent QoS requirement of some railway-specific signaling,. Such a wireless communications system is commonly referred to as LTE-Railway (LTE-R). LTE-R system has the significant characteristics of wide bandwidth, low delay, all-IP network architecture and so on. This book is devoted to the discussion of LTE-R network services, architecture, and performance evaluation issues.

In this chapter covers security schemes of dedicated mobile communications for railway. Due to the control signal is transmitted via wireless channel, communication security is crucial to the whole rail transit system. Although currently the mobile communication infrastructure in railway is based on public cellular mobile communications, considering the rail transit has characteristics of ultra-high moving velocity and high reliability and safety demand, traditional security mechanism is unable to satisfy the basic requirements of the rail transit scenario. On the one hand, there are still some threats remained in GSM-R. On the other hand, the future dedicated mobile network for railway is heterogeneous and complicated, including 2G, 3G, 4G, WLAN networks, and mobile relays. How to achieve fast authentic handover scheme across domains is a problem that must be solved. In this chapter, we first introduce the security problems in mobile communications. Next, we describe in detail the key improvements of railway communication technology. Finally, we introduce some key technologies in heterogeneous network environment and give a brief prospect of the future research.

The railway broadband mobile communication systems are required to be continuous, high capable, extremely reliable, and bidirectional [1–2]. Unlike wired channels, the radio channels between train and Infrastructure are random dynamic and unpredictable [3–4]. Thus, it is important to evaluate the performance for railway broadband mobile communication systems.