A Survey on High-Speed Railway Communications: A Radio Resource Management Perspective
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paper_title: A Survey on Methods for Broadband Internet Access on Trains

paper_content:

We present a survey of approaches for providing broadband Internet access to trains. We examine some of the barriers that hinder the use of broadband Internet on trains and then discuss some of the opportunities for broadband deployment to trains. This survey considers some of the basic concepts for providing broadband Internet access and then reviews associated network architectures. The review of network architectures shows that we can subdivide networks for providing broadband Internet access to trains into the train-based network, the access network-for connecting the train to the service provider(s)-and the aggregation network-for collecting user packets generated in the access network for transmission to the Internet. Furthermore, our review shows that the current trend is to provide Internet access to passengers on trains using IEEE 802.11; however, a clear method for connecting trains to the global Internet has yet to emerge. A summary of implementation efforts in Europe and North America serves to highlight some of the schemes that have been used thus far to connect trains to the Internet. We conclude by discussing some of the models developed, from a technical perspective, for testing the viability of deploying Internet access to trains.
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paper_title: Assessment of LTE-R Using High Speed Railway Channel Model

paper_content:

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.
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paper_title: A Multi-Mode Multi-Band and Multi-System-Based Access Architecture for High-Speed Railways

paper_content:

With the rapid development of high-speed railways all over the world, it is very promising to deliver public broadband access to passengers aboard high-speed trains. However, it has been a challenge to support high speed (e.g. above 350 km/h) mobile users with broadband communications, because of rapidly fading radio channels and Doppler frequency shift. This paper presents a review of network architectures providing broadband access to high-speed trains. A novel scheme referred as multimode multi-band and multi-system-based access architecture is proposed in this paper. It consists of three parts: (1) train network part that relays data to large number of users in carriages without changing their own terminals, (2) ground network part that deals with traffic from different operators' networks, and (3) ground-to-train network part that connects the train network and ground network. Moreover, this architecture could support high mobility with broad bandwidth, seamless handover, scalable and cost-effective deployment.
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paper_title: Challenges Toward Wireless Communications for High-Speed Railway

paper_content:

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.
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paper_title: Third-Generation Partnership Project Standards: For Delivery of Critical Communications for Railways

paper_content:

The Global System for Mobile Communications-Railways (GSM-R) is a radio telecommunication network and the bearer technology for the European Train Control System (ETCS). Both GSM-R and ETCS constitute the European Rail Traffic Management System (ERTMS). GSM was adopted by the International Union of Railways (UIC) because it was the only system in commercial operation with a great potential to fulfill the requirements for the transport of railway services, although some features had to be added to the standard. However, as time has passed, GSM-R has proven to have capacity limitations, higher costs, and long development cycle times due to the special features built into standard GSM that have reduced the market for GSM-R equipment. These facts, together with the end of industry support by 2025, are motivating the switch to long-term evolution (LTE)/system architecture evolution technology as the new bearer network for railways. LTE provides higher data capacity than GSM and presents a flat architecture, which reduces deployment and maintenance costs as long as standard elements are used. This article provides an overview of third-generation partnership project (3GPP) systems, services, and their standardization status, which should be implemented to support the transport of railway services over a standard LTE network. Additionally, the quality of service (QoS) requirements for the transport of ETCS data control are compared with the QoS provided by LTE.
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paper_title: LTE for Railways: Impact on Performance of ETCS Railway Signaling

paper_content:

The Global System for Mobile Communications-Railways (GSM-R) is an obsolete mobile technology with considerable shortcomings in terms of capacity and data transmission capabilities. Because of these shortcomings, GSM-R is becoming the element limiting the number of running trains in areas with high train concentration, such as major train stations. Moreover, GSM-R cannot support advanced data services. Hence, modern technologies, such as long-term evolution (LTE), have to be evaluated as possible railway communication technologies to replace GSM-R in the future. This article analyzes the characteristics of the LTE railway radio access network in terms of eNodeB (LTE base station) density and eNodeB transmission power. Based on this analysis, a set of computer-based simulation scenarios (e.g., OPNET) with varying numbers of eNodeBs is evaluated regarding the achieved transfer delay and data integrity of European Train Control System (ETCS) messages.
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paper_title: Position-Based Modeling for Wireless Channel on High-Speed Railway under a Viaduct at 2.35 GHz

paper_content:

This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.
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paper_title: A novel network architecture for train-to-wayside communication with quality of service over heterogeneous wireless networks

paper_content:

In the railway industry, there are nowadays different actors who would like to send or receive data from the wayside to an onboard device or vice versa. These actors are e.g., the Train Operation Company, the Train Constructing Company, a Content Provider, etc. This requires a communication module on each train and at the wayside. These modules interact with each other over heterogeneous wireless links. This system is referred to as the Train-to-Wayside Communication System (TWCS). While there are already a lot of deployments using a TWCS, the implementation of quality of service, performance enhancing proxies (PEP) and the network mobility functions have not yet been fully integrated in TWCS systems. Therefore, we propose a novel and modular IPv6-enabled TWCS architecture in this article. It jointly tackles these functions and considers their mutual dependencies and relationships. DiffServ is used to differentiate between service classes and priorities. Virtual local area networks are used to differentiate between different service level agreements. In the PEP, we propose to use a distributed TCP accelerator to optimize bandwidth usage. Concerning network mobility, we propose to use the SCTP protocol (with Dynamic Address Reconfiguration and PR-SCTP extensions) to create a tunnel per wireless link, in order to support the reliable transmission of data between the accelerators. We have analyzed different design choices, pinpointed the main implementation challenges and identified candidate solutions for the different modules in the TWCS system. As such, we present an elaborated framework that can be used for prototyping a fully featured TWCS.
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paper_title: A Survey on Methods for Broadband Internet Access on Trains

paper_content:

We present a survey of approaches for providing broadband Internet access to trains. We examine some of the barriers that hinder the use of broadband Internet on trains and then discuss some of the opportunities for broadband deployment to trains. This survey considers some of the basic concepts for providing broadband Internet access and then reviews associated network architectures. The review of network architectures shows that we can subdivide networks for providing broadband Internet access to trains into the train-based network, the access network-for connecting the train to the service provider(s)-and the aggregation network-for collecting user packets generated in the access network for transmission to the Internet. Furthermore, our review shows that the current trend is to provide Internet access to passengers on trains using IEEE 802.11; however, a clear method for connecting trains to the global Internet has yet to emerge. A summary of implementation efforts in Europe and North America serves to highlight some of the schemes that have been used thus far to connect trains to the Internet. We conclude by discussing some of the models developed, from a technical perspective, for testing the viability of deploying Internet access to trains.
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paper_title: A Multi-Mode Multi-Band and Multi-System-Based Access Architecture for High-Speed Railways

paper_content:

With the rapid development of high-speed railways all over the world, it is very promising to deliver public broadband access to passengers aboard high-speed trains. However, it has been a challenge to support high speed (e.g. above 350 km/h) mobile users with broadband communications, because of rapidly fading radio channels and Doppler frequency shift. This paper presents a review of network architectures providing broadband access to high-speed trains. A novel scheme referred as multimode multi-band and multi-system-based access architecture is proposed in this paper. It consists of three parts: (1) train network part that relays data to large number of users in carriages without changing their own terminals, (2) ground network part that deals with traffic from different operators' networks, and (3) ground-to-train network part that connects the train network and ground network. Moreover, this architecture could support high mobility with broad bandwidth, seamless handover, scalable and cost-effective deployment.
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paper_title: Making a well-founded choice of the wireless technology for train-to-wayside data services

paper_content:

The provisioning of wireless data services in the railway environment will become increasingly important for train operators and train constructors in the upcoming years. A well-founded choice of the technology to be used for the outdoor network connection is investigated in this paper. Several wireless technologies - including HSPA, E-UTRA and WiMAX - are compared by calculating their wireless ranges for reception outside and inside trains, based on the location of the transceiver. These wireless ranges determine the number of base stations needed to cover a pre-defined area along a railway track. Results show that generally 3G (UMTS-HSPA) and 4G (E-UTRA/LTE) technologies offer the best coverage over a range of data rates, from 2 Mbps to 8 Mbps. These data rates relate to a wide variety of services, from network control data, surveillance, crew services to passenger Internet traffic.
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paper_title: Communications and entertainment onboard a high-speed public transport system

paper_content:

This article discusses architectural design at the conceptual/functional level of communication and entertainment services onboard a high-speed public transport system, such as a high-speed train, a transoceanic cruise ship, or even a mid- to long-range airplane. Existing commercial mobile communication services, such as AMPS and GSM, are inaccessible to passengers onboard these public transport systems. A hierarchical architecture is laid out to provide passengers with communication and entertainment services. Within this framework, the transport system itself becomes an entity of a mobile network whose connection with the infrastructure networks may be interfaced through either a land terrestrial microwave or a satellite communication system. The entire architecture is further divided into the mobile subsystem, the radio transport, and the land backbone network. Potential research topics are outlined.
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paper_title: SWiFT: A Novel Architecture for Seamless Wireless Internet for Fast Trains

paper_content:

It has been a challenge to support high speed (above 200 kms/hr - freeways and high speed train) mobile user with broadband data communication. Research community efforts are underway to develop wide area networks (wireless access and optical backbone) to support broadband to high speed vehicular users. ITU-R has proposed the International Mobile Telecommunication-Advanced (IMT-Advanced) technical requirements for supporting such usage scenarios. IEEE 802.16 m based (WiMAX) standard is working to meet the requirements of IMT-Advanced proposal. In this paper we have proposed a novel technology referred as Seamless Wireless internet for Fast Trains (SWiFT). In particular SWiFT architecture relies on a fast handoff mechanism by layer 2 (L2) triggering using a confidence factor (a probabilistic value evaluated by high speed movement and signal strength, to decide handoff). An interface gateway (IGW) that enables interoperability between WLAN (802.11e) and WiMAX 802.16 m is being designed to support the above handoff. Extensive simulation results by NS-2 shows that, SWiFT handoff latency is 52% less than mobile IPv6 (MIPv6) proposed by IETF.
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paper_title: A novel network architecture for train-to-wayside communication with quality of service over heterogeneous wireless networks

paper_content:

In the railway industry, there are nowadays different actors who would like to send or receive data from the wayside to an onboard device or vice versa. These actors are e.g., the Train Operation Company, the Train Constructing Company, a Content Provider, etc. This requires a communication module on each train and at the wayside. These modules interact with each other over heterogeneous wireless links. This system is referred to as the Train-to-Wayside Communication System (TWCS). While there are already a lot of deployments using a TWCS, the implementation of quality of service, performance enhancing proxies (PEP) and the network mobility functions have not yet been fully integrated in TWCS systems. Therefore, we propose a novel and modular IPv6-enabled TWCS architecture in this article. It jointly tackles these functions and considers their mutual dependencies and relationships. DiffServ is used to differentiate between service classes and priorities. Virtual local area networks are used to differentiate between different service level agreements. In the PEP, we propose to use a distributed TCP accelerator to optimize bandwidth usage. Concerning network mobility, we propose to use the SCTP protocol (with Dynamic Address Reconfiguration and PR-SCTP extensions) to create a tunnel per wireless link, in order to support the reliable transmission of data between the accelerators. We have analyzed different design choices, pinpointed the main implementation challenges and identified candidate solutions for the different modules in the TWCS system. As such, we present an elaborated framework that can be used for prototyping a fully featured TWCS.
---
paper_title: A Survey on Methods for Broadband Internet Access on Trains

paper_content:

We present a survey of approaches for providing broadband Internet access to trains. We examine some of the barriers that hinder the use of broadband Internet on trains and then discuss some of the opportunities for broadband deployment to trains. This survey considers some of the basic concepts for providing broadband Internet access and then reviews associated network architectures. The review of network architectures shows that we can subdivide networks for providing broadband Internet access to trains into the train-based network, the access network-for connecting the train to the service provider(s)-and the aggregation network-for collecting user packets generated in the access network for transmission to the Internet. Furthermore, our review shows that the current trend is to provide Internet access to passengers on trains using IEEE 802.11; however, a clear method for connecting trains to the global Internet has yet to emerge. A summary of implementation efforts in Europe and North America serves to highlight some of the schemes that have been used thus far to connect trains to the Internet. We conclude by discussing some of the models developed, from a technical perspective, for testing the viability of deploying Internet access to trains.
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paper_title: Long term evolution in high speed railway environments: Feasibility and challenges

paper_content:

Long Term Evolution (LTE) is considered to be the natural evolution for the current Global System for Mobile Communications-Railways (GSM-R) in high speed railway environments, not only for its technical advantages and increased performance, but also due to the current evolution of public communication systems. In railway environments, mission critical services, operation assistance services, and passenger services must be supported by reliable mobile communication systems. Reliability and availability are key concerns for railway operators and as a consequence, railway operators are usually conservative adopters of information and communication technologies (ICT). This paper describes the feasibility of LTE as a successor to GSM-R for new railway mobile communication systems. We identify key features of LTE as a technology and analyze its ability to support both the migration of current railway services and the provisioning of potential future ones. We describe the key challenges to address specific requirements for railway communication services including the provisioning of voice service in LTE networks, handover performance, multicast multimedia transmission, and the provisioning of group communications service and railway emergency calls.
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paper_title: Doppler frequency offset estimation and diversity reception scheme of high-speed railway with multiple antennas on separated carriage

paper_content:

The challenges of severe Doppler effects in high-speed railway are considered. By building a cooperative antenna system, an algorithm of joint channel estimation and Doppler frequency offset (DFO) estimation is proposed based on Ricean channel model. First, a maximum likelihood estimation (MLE) algorithm for DFO is designed, showing that the Doppler estimation can be obtained by estimating moving velocity of the train and the path loss with the exploitation of pilots that are placed inside the frame. Then a joint detection algorithm for the receiver is proposed to exploit multi-antenna diversity gains. Last, the theoretical Crammer Rao bound (CRB) for joint channel estimation and DFO estimation is derived. The steady performance of the system is confirmed by numerical simulations. In particular, when the Ricean fading channel parameter equals 5 and the velocities of train are 100 m/s and 150 m/s, the estimation variances of DFO are very close to the theoretical results obtained by using CRB. Meanwhile, the corresponding signal to noise ratio loss is less than 1.5 dB when the bit error rate is 10−5 for 16QAM signals.
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paper_title: Precoding for PAPR Reduction of OFDM Signals With Minimum Error Probability

paper_content:

The precoding technique is an effective and flexible way for reducing the peak-to-average power ratio (PAPR) of orthogonal frequency division multiplexing (OFDM) signals. However, different precoding schemes will increase error probabilities of the system. With the knowledge of the channel information and the receiver filter, we derive a necessary condition on the chosen precoding matrices for minimizing error probability of the OFDM system in the additive white Gaussian noise (AWGN) channel. A systematic procedure in designing such an optimal precoding matrix is provided. With a proper selection, the optimal precoding matrix can meet the requirements of PAPR reduction and achieve the minimum error probability in white Gaussian noise. Our simulation results show that the chosen precoding matrix notably outperforms other general precoding matrices in both AWGN and multipath fading channels. We also proved that the precoding matrix with all the singular values equal to 1 is one of the optimal solutions.
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paper_title: Pilot-Assisted PAPR Reduction Technique for Optical OFDM Communication Systems

paper_content:

This paper investigates the use of a pilot signal in reducing the electrical peak-to-average power ratio (PAPR) of an orthogonal frequency division multiplexing (OFDM) intensity-modulated optical wireless communication system. The phase of the pilot signal is chosen based on the selected mapping (SLM) algorithm while the maximum likelihood criterion is used to estimate the pilot signal at the receiver. Bit error rate (BER) performance of the pilot-assisted optical OFDM system is identical to that of the basic optical OFDM (with no pilot and no PAPR reduction technique implemented) at the desired BER of less than 10-3 needed to establish a reliable communication link. The pilot-assisted PAPR reduction technique results in higher reduction in PAPR for high order constellations than the classical SLM. With respect to a basic OFDM system, with no pilot and no PAPR reduction technique implemented, a pilot-assisted M-QAM optical OFDM system is capable of reducing the electrical PAPR by over about 2.5 dB at a modest complementary cumulative distribution function (CCDF) point of 10-4 for M = 64. Greater reductions in PAPR are possible at lower values of CCDF with no degradation to the system's error performance. Clipping the time domain signal at both ends mildly (at 25 times the signal variance level) results in a PAPR reduction of about 6.3 dB at the same CCDF of 10-4 but with an error floor of about 3 ×10-5. Although it is possible to attain any desired level of electrical PAPR reduction with signal clipping, this will be at a cost of deterioration in the systems's bit error performance.
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paper_title: Time-Frequency Training OFDM with High Spectral Efficiency and Reliable Performance in High Speed Environments

paper_content:

Orthogonal frequency division multiplexing (OFDM) is widely recognized as the key technology for the next generation broadband wireless communication (BWC) systems. Besides high spectral efficiency, reliable performance over fast fading channels is becoming more and more important for OFDM-based BWC systems, especially when high speed cars, trains and subways are playing an increasingly indispensable role in our daily life. The time domain synchronous OFDM (TDS-OFDM) has higher spectral efficiency than the standard cyclic prefix OFDM (CP-OFDM), but suffers from severe performance loss over high speed mobile channels since the required iterative interference cancellation between the training sequence (TS) and the OFDM data block. In this paper, a fundamentally distinct OFDM-based transmission scheme called time-frequency training OFDM (TFT-OFDM) is proposed, whereby every TFT-OFDM symbol has training information both in the time and frequency domains. Unlike TDS-OFDM or CP-OFDM where the channel estimation is solely dependent on either time-domain TS or frequency-domain pilots, the joint time-frequency channel estimation for TFT-OFDM utilizes the time-domain TS without interference cancellation to merely acquire the path delay information of the channel, while the path coefficients are estimated by using the frequency-domain grouped pilots. The redundant grouped pilots only occupy about 3% of the total subcarriers, thus TFT-OFDM still has much higher spectral efficiency than CP-OFDM by about 8.5% in typical applications. Simulation results also demonstrate that TFT-OFDM outperforms CP-OFDM and TDS-OFDM in high speed mobile environments.
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paper_title: Resource allocation for OFDMA system under high-speed railway condition

paper_content:

A dynamic resource allocation algorithm is investigated for the orthogonal frequency division multiplexing access (OFMDA) system under the network architecture of High-Speed Railway (HSR). The mobile base station (MBS) on the top of the train forwards the signal received from the base station (BS) on the ground to the user equipments (UE) in the train. Due to the high mobility in the BS-MBS link, the inter-carrier interference (ICI) caused by the Doppler shift may degrade the system performance. In this paper, we aim to combat the influence of the ICI to improve the system capacity by means of the resource allocation, which includes subcarrier allocation, subcarrier pairing and power allocation. Simulation results demonstrate that the proposed resource allocation algorithm can improve the system performance dramatically.
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paper_title: A novel network architecture for train-to-wayside communication with quality of service over heterogeneous wireless networks

paper_content:

In the railway industry, there are nowadays different actors who would like to send or receive data from the wayside to an onboard device or vice versa. These actors are e.g., the Train Operation Company, the Train Constructing Company, a Content Provider, etc. This requires a communication module on each train and at the wayside. These modules interact with each other over heterogeneous wireless links. This system is referred to as the Train-to-Wayside Communication System (TWCS). While there are already a lot of deployments using a TWCS, the implementation of quality of service, performance enhancing proxies (PEP) and the network mobility functions have not yet been fully integrated in TWCS systems. Therefore, we propose a novel and modular IPv6-enabled TWCS architecture in this article. It jointly tackles these functions and considers their mutual dependencies and relationships. DiffServ is used to differentiate between service classes and priorities. Virtual local area networks are used to differentiate between different service level agreements. In the PEP, we propose to use a distributed TCP accelerator to optimize bandwidth usage. Concerning network mobility, we propose to use the SCTP protocol (with Dynamic Address Reconfiguration and PR-SCTP extensions) to create a tunnel per wireless link, in order to support the reliable transmission of data between the accelerators. We have analyzed different design choices, pinpointed the main implementation challenges and identified candidate solutions for the different modules in the TWCS system. As such, we present an elaborated framework that can be used for prototyping a fully featured TWCS.
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paper_title: Efficient Multiple-Group Multiple-Antenna (MGMA) Scheme for High-Speed Railway Viaducts

paper_content:

The capacity of a multiple-input-multiple-output (MIMO) channel with N transmit and receive antennas for highspeed railways (HSRs) is analyzed based on the 3-D modeling of the line of sight (LOS). The MIMO system utilizes a uniform linear antenna array. Instead of increasing the number of antennas or simply changing the parameters of the antenna array, such as separation and geometry, the capacity gain can be obtained by adjusting the weights of multiantenna array groups, because there are few scatterers in strong LOS environments. On the other hand, it is hard to obtain the array gain of MIMO beamforming for HSRs because of drastic changes in the receiving angle when the train travels across E-UTRAN Node B. Without changing the antenna design of Long-Term Evolution systems, this paper proposes a multiple-group multiple-antenna (MGMA) scheme that makes the columns of such a MIMO channel orthogonal by adjusting the weights among MGMA arrays, and the stable capacity gain can be obtained. The value of weights depends on the practical network topologies of the railway wireless communication system. However, the reasonable scope of group number N is less than 6. In selecting N, one important consideration is the tradeoff between practical benefit and cost of implementation.
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paper_title: Distributed beamforming for High Speed Railway

paper_content:

In this paper, we introduce an algorithm of distributed beamforming for High Speed Railway (HSR) based on the idea of location assistant beamforming. In the new algorithm, the weights are calculated from direction of departure (DOD) of two direct paths since two receive antennas are placed in long distance. The performance of new algorithm with accurate position information and position error under Gaussian and uniform distributions are both evaluated. Simulation results show that distributed beamforming algorithm has better performance and strong robustness against position error.
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paper_title: Distributed Antenna Systems for Mobile Communications in High Speed Trains

paper_content:

With the deployment of high speed train (HST) systems increasing worldwide and their popularity with travelers growing, providing broadband wireless communications (BWC) in HSTs is becoming crucial. In this paper, a tutorial is presented on recent research into BWC provision for HSTs. The basic HST BWC network architecture is described. Two potential cellular architectures, microcells and distributed antenna systems (DASs) based cells, are introduced. In particular, the DAS is discussed in conjunction with radio over fiber (RoF) technology for BWC for HSTs. The technical challenges in providing DAS-based BWC for HSTs, such as handoff and RoF are discussed and outlined.
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paper_title: Radio admission control scheme for high-speed railway communication with MIMO antennas

paper_content:

Along with the wide deployment of high-speed railway at more than 300 km/h, providing various services effectively for users in the train becomes both practical demand and interesting challenge for wireless communication. Due to the specific environment for high-speed railway, existing radio admission control (RAC) algorithms could not suit the requirements such as frequent handover, quick decision-making duration and fast-changing physical transmission condition. The investigation on novel and proper RAC is of great importance. In this paper, we propose an effective radio admission control scheme based on Rician shading model for high-speed railway communication with MIMO antennas. Layered networks access architecture is designed in which Rician channel is used to analyze physical transmission condition. The effect of bit error rate on data rate at high moving speeds is taken into account for the RAC decision-making to get better quality of service (QoS). Moreover, different priorities for different services are considered to resolve simultaneous multiple users' access requests. Simulation results have proved that the proposed scheme may improve QoS obviously compared to the scheme that does not consider bit error rate and service priority.
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paper_title: RADIATE: radio over fiber as an antenna extender for high-speed train communications

paper_content:

With the explosive growth of Internet-based applications and services, people are relying on the Internet in their daily life. This drives a significant demand for provisioning broadband Internet services in high-speed trains. In this article, we propose a novel solution named RADIATE for high-speed train communications. RADIATE utilizes cellular networks as backhauls to avoid the expensive capital expenditure in provisioning broadband Internet services in high-speed trains. RADIATE, by applying radio over fiber, deploys on-roof antennas and optimally operates these antennas to address the drawbacks of utilizing cellar networks as backhauls. Thus, RADIATE provides a cost-effective and high-quality communications solution for provisioning broadband Internet services in high-speed trains.
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paper_title: Analysis of distributed antenna system over high-speed railway communication

paper_content:

Provision of high data rate services on train has attracted a great attention recently. In this paper, the issues of time division duplex (TDD) DAS, including coverage of remote antenna units (RAUs), echo channel effect and system deployment cost were analyzed. The timing drift problem while solving echo channel effect with moving cell concept in DAS was also depicted in detail. Furthermore, the frequency response, propagation model, and time dispersion parameters of the RoF-DAS channel will be analyzed with simulation. This paper provided analyzed RoF-DAS channel profile over high-speed railway communication system for future researches.
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paper_title: Broadband wireless communications on high speed trains

paper_content:

This tutorial paper provides a comprehensive overview on the recent development in broadband wireless communications for high speed trains. Starting with the introduction of the two-hop network structure, radio-over-fiber (RoF) based cell planning is described in detail. Moreover, based on the analysis of differences between conventional cellular systems and the one for high speed trains, promising techniques are recommended to improve the performance of handover, which is one of the main challenges in high speed train communications. Finally, in order to combat the fast fading caused by the high mobility, robust algorithms are needed in physical layer signal processing, including synchronization, channel estimation, modulation/demodulation, and so on.
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paper_title: Coverage Efficiency of Radio-Over-Fiber Network for High-Speed Railways

paper_content:

Due to the rapid development of high-speed railways all over the world, it is very promising to deliver public broadband wireless network to passengers aboard high-speed trains. However, deploying conventional cellular network along the railway will lead to low coverage efficiency and radio resource waste, where a large part of service coverage area may not have any users' traffic at all. A model of analyzing the coverage efficiency of the conventional network and Radio over Fiber (RoF) network is presented in this paper. Based on certain parameters of Chinese high-speed railway scenario, simulation results demonstrate that the coverage efficiency of the RoF network improves greatly compared with the conventional network. In addition, the number of Remote Antenna Units (RAUs) mounted along the railway may be less than the number of antennas installed on the roof of the high-speed train due to initial infrastructure cost. The optimal match of the antennas and RAUs is proposed to maximum the coverage efficiency in this paper. The conclusions provide observations to guide RoF cell planning for high-speed railways.
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paper_title: Experimental analysis of beamforming in high-speed railway communication

paper_content:

The demand of broadband high-mobility communication increased dramatically with the rapid development of high speed railway system. A beamforming platform through changing transmitter antenna direction base on real time receiver Global Positioning System (GPS) information was proposed to improve communication quality. Experiments were carried out over Taiwan High Speed Railway (THSR) train to analysis the tracking capability and path loss model. The results show that the received signal strength indicator (RSSI), carrier to interference plus noise ratio (CINR) and throughput were improved.
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paper_title: Seamless Dual-Link Handover Scheme in Broadband Wireless Communication Systems for High-Speed Rail

paper_content:

Due to frequent handovers in broadband wireless communications in high-speed rail, communication interruption during handover could seriously degrade the experiences of passengers on the train. Aiming to reduce the interruption time, this paper proposes a seamless handover scheme based on a dual-layer and dual-link system architecture, where a Train Relay Station is employed to execute handover for all users in a train and two antennas are mounted at the front and rear of a train. In the proposed scheme, the front antenna executes handover while the rear antenna is still communicating with BS, so that the communication can keep non-interruptive throughout the handover. Moreover, bi-casting is adopted to eliminate the data forwarding delay between the serving BS and target BS. A complete handover protocol is designed and the performance of the proposed scheme is analyzed. It can be seen from analytical results that the handover failure probability decreases as cell overlap increases and the communication interruption probability decreases with the decrease of train handover location and the increase of cell overlap. The simulation results show that in the proposed scheme, the communication interruption probability is smaller than 1% when the handover location is properly selected and the system throughput is not affected by handover. In conclusion, both theoretical and simulation results show that the proposed scheme can efficiently perform seamless handover for high-speed rail with low implementation overhead.
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paper_title: Scaling up MIMO: Opportunities and Challenges with Very Large Arrays

paper_content:

Multiple-input multiple-output (MIMO) technology is maturing and is being incorporated into emerging wireless broadband standards like long-term evolution (LTE) [1]. For example, the LTE standard allows for up to eight antenna ports at the base station. Basically, the more antennas the transmitter/receiver is equipped with, and the more degrees of freedom that the propagation channel can provide, the better the performance in terms of data rate or link reliability. More precisely, on a quasi static channel where a code word spans across only one time and frequency coherence interval, the reliability of a point-to-point MIMO link scales according to Prob(link outage) ` SNR-ntnr where nt and nr are the numbers of transmit and receive antennas, respectively, and signal-to-noise ratio is denoted by SNR. On a channel that varies rapidly as a function of time and frequency, and where circumstances permit coding across many channel coherence intervals, the achievable rate scales as min(nt, nr) log(1 + SNR). The gains in multiuser systems are even more impressive, because such systems offer the possibility to transmit simultaneously to several users and the flexibility to select what users to schedule for reception at any given point in time [2].
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paper_title: On the Uplink Capacity of High Speed Railway Communications with Massive MIMO Systems

paper_content:

This paper studies the performance and design of high speed railway communications that employ massive MIMO systems. The users onboard the train communicate with the BS by using antennas mounted on top of the train as gateways. Two antenna layouts on the train are considered, one has co-located antennas (CA) at the center of the train, and the other has distributed antennas (DA) uniformly placed along the train. The analytical uplink ergodic capacities for both layouts are derived by averaging over all the locations in a cell. For the CA layout, the average uplink cell capacity is concave in the number of antennas on the train, and the optimum number of antennas on the train is identified by maximizing the average uplink capacity. For the DA layout, the average cell capacity is upper and lower bounded by two concave functions, which are then used to find a sub-optimum value of the number of antennas on the train. Both analytical and numerical results demonstrate that the CA layout has a higher average cell capacity while the DA layout has less variations in terms of uplink capacity at different locations inside a cell.
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paper_title: Capacity of MIMO Rician channels

paper_content:

This paper presents exact results on the capacity of multiple-input-multiple-output (MIMO) Rician channels when perfect channel state information (CSI) is assumed at the receiver but the transmitter has neither instantaneous nor statistical CSI. It first derives the exact expression for the average mutual information (MI) rate of MIMO Rician fading channels when the fading coefficients are independent but not necessarily identically distributed. The results for the independent and identically distributed (i.i.d.) MIMO Rician and Rayleigh fading channels are also obtained as special cases. These results are derived using a different approach than the one used by Telatar for the i.i.d. Rayleigh case. The complementary cumulative distribution function (CCDF) of the MI is also obtained using a Gaussian approximation. The CDF of MI can serve as an upper bound to the outage probability of nonergodic MIMO Rician channels. Numerical results confirm that for a fixed channel gain, a strong tine-of-sight component decreases the channel capacity due to the lack of scattering.
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paper_title: Field trial results for integrated WiMAX and radio-over-fiber systems on high speed rail

paper_content:

As high speed rails become more and more popular, providing broadband internet access on high speed rails is not widespread due to the large inter-carrier interference, terrestrial obstacles and inherent carriage shielding. In this paper an integrated Worldwide Interoperability for Microwave Access-Radio over Fiber (WiMAX-RoF) system is proposed and deployed along Taiwan High Speed Rail (THSR) rail tracks. Field trial and laboratory experiment results are presented. According to the field trial results, excessive delay induced by unequal fiber length deteriorates the throughput performance and can be overcome by equalizing the fiber length. On the other hand, rate adaptation for maximum throughput is challenging at high mobility. Careful calibration is needed to tradeoff the throughput gain against robustness to signal fluctuations. Laboratory experiments distinguish the impact of echo channel and remote antenna unit (RAU) distance from others. The results give insights in the analysis of field trial results.
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paper_title: Multidimensional resource allocation strategy for high-speed railway MIMO-OFDM system

paper_content:

With the wide deployment of high-speed railway at more than 300 kilometers per hour, providing various services effectively for users in the train becomes both practical demand and interesting challenge for wireless communication. Resource allocation problem in high-speed railway communication system is one of the key issues to improve the efficiency of resource utilization. In this paper, we propose a multidimensional resource allocation strategy for high-speed railway downlink orthogonal frequency-division multiplexing (OFDM) system with multiple-input multiple-output (MIMO) antennas. Sub-carrier, antenna, time slot, and power are considered jointly, which is modeled as a nonlinear integer programming problem. The effect of the moving speed on inter-carrier interference is analyzed to calculate the transmitted power. The objective is to minimize the total transmitted power while satisfying quality of service requirement of each user. Moreover, optimal and approximate solutions are obtained by linearization and quadratic fitting, respectively. Simulation results have proved that approximate solution has lower total transmitted power than optimal solution while the computation complexity is higher.
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paper_title: Channel Measurements and Models for High-Speed Train Communication Systems: A Survey

paper_content:

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.
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paper_title: Channel Characteristics in High-Speed Railway: A Survey of Channel Propagation Properties

paper_content:

In this article, we give an overview of recent research on propagation properties in high-speed railways (HSRs). The channel fading in HSRs is a big challenge for wireless access. It is essential to understand the channel-fading behavior before the system design. The novel results of propagation and channel models are presented. The details of channel characteristics, such as path loss, shadow fading, and Ricean K- factor, are discussed in each scenario. A comprehensive picture of propagation and channel-modeling research in railways is shown.
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paper_title: Position-Based Modeling for Wireless Channel on High-Speed Railway under a Viaduct at 2.35 GHz

paper_content:

This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.
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paper_title: Challenges Toward Wireless Communications for High-Speed Railway

paper_content:

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.
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paper_title: Short-Term Fading Behavior in High-Speed Railway Cutting Scenario: Measurements, Analysis, and Statistical Models

paper_content:

Cuttings are widely used in high-speed railway (HSR) transportation to ensure the flatness of rails. The special structure of cuttings results in rich reflection and scattering, and creates dense multipath components. This paper presents a series of measurements of the propagation channel at 930 MHz conducted along the “Zhengzhou-Xi'an” HSR of China, to characterize the small-scale fading behavior of rail-cutting scenarios as a function of the geometry of cuttings, including crown width and bottom width. Raw data are collected in six cuttings (five cuttings are used for developing the model, while the other one is used for validation) in rural and suburban environments. We propose a set of effective methods to statistically model the spatial/temporal variations – including fade depth (FD), level crossing rate (LCR), average fade duration (AFD), and Ricean ${K}$ -factor – as a function of the structural parameters of cuttings. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale fading. In addition, the rich multipath and directionality of the transmitting antennas lead to a non-monotonous dependence of the ${K}$ -factor on the distance between transmitter and receiver. The autocovariance function of the deviation of the extracted ${K}$ -factors from the proposed model is presented and the coherence length is investigated. Our results show that even though a cutting is a scenario with severe fading, a “wide” cutting (i.e., with both wide crown and bottom widths) is conducive to the reduction of the severity of fading.
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paper_title: Measurements and Modeling of Distributed Antenna Systems in Railway Tunnels

paper_content:

This paper covers some of the work carried out in the planning of the global system for mobile communication for railway (GSM-R) of the tunnels on the new high-speed trains in Spain. Solutions based on distributed antenna systems have been tested by installing several 900-MHz transmitters inside and outside of a 4000-m tunnel and measuring the propagation in different conditions. The measurements have been used to model the effects of tunnel propagation, including curves, trains passing from the outside to the inside, and the effect of two trains passing inside the tunnel. All cases have been tested by comparing solutions using isofrequency and multifrequency distributed transmitters inside the tunnel. The improvements of signal-to-noise ratio and the reduction of the blocking effects of two trains passing have demonstrated the advantages of using isofrequency distributed antenna systems in tunnels. Finally, a complete propagation model combining both modal analysis and ray tracing has been applied to predict the propagation loss inside and outside these tunnels, and results have been compared with the measurements. The model has proven to be very useful for radio planning in new railway networks.
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paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

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.
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paper_title: Position-Based Modeling for Wireless Channel on High-Speed Railway under a Viaduct at 2.35 GHz

paper_content:

This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.
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paper_title: Radio Wave Propagation Scene Partitioning for High-Speed Rails

paper_content:

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.
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paper_title: Efficient Multiple-Group Multiple-Antenna (MGMA) Scheme for High-Speed Railway Viaducts

paper_content:

The capacity of a multiple-input-multiple-output (MIMO) channel with N transmit and receive antennas for highspeed railways (HSRs) is analyzed based on the 3-D modeling of the line of sight (LOS). The MIMO system utilizes a uniform linear antenna array. Instead of increasing the number of antennas or simply changing the parameters of the antenna array, such as separation and geometry, the capacity gain can be obtained by adjusting the weights of multiantenna array groups, because there are few scatterers in strong LOS environments. On the other hand, it is hard to obtain the array gain of MIMO beamforming for HSRs because of drastic changes in the receiving angle when the train travels across E-UTRAN Node B. Without changing the antenna design of Long-Term Evolution systems, this paper proposes a multiple-group multiple-antenna (MGMA) scheme that makes the columns of such a MIMO channel orthogonal by adjusting the weights among MGMA arrays, and the stable capacity gain can be obtained. The value of weights depends on the practical network topologies of the railway wireless communication system. However, the reasonable scope of group number N is less than 6. In selecting N, one important consideration is the tradeoff between practical benefit and cost of implementation.
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paper_title: Finite state Markov modelling for high speed railway wireless communication channel

paper_content:

How to provide reliable, cost-effective wireless services for high-speed railway (HSR) users attracts increasing attention due to the fast deployment of HSRs worldwide. A key issue is to develop reasonably accurate and mathematically tractable models for HSR wireless communication channels. Finite-state Markov chains (FSMCs) have been extensively investigated to describe wireless channels. However, different from traditional wireless communication channels, HSR communication channels have the unique features such as very high speed, deterministic mobility pattern and frequent handoff events, which are not described by the existing FSMC models. In this paper, based on the Winner II physical layer channel model parameters, we propose a novel FSMC channel model for HSR communication systems, considering the path loss, fast fading and shadowing with high mobility. Extensive simulation results are given, which validate the accuracy of the proposed FSMC channel model. The model is not only ready for performance analysis, protocol design and optimization for HSR communication systems, but also provides an effective tool for faster HSR communication network simulation.
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paper_title: A Standardized Path Loss Model for the GSM-Railway Based High-Speed Railway Communication Systems

paper_content:

High-speed railway (HSR) has been widely introduced to meet the increasing demand for passenger rail travel. While it provides more and more conveniences to the people, the huge cost of the HSR has laid big burden on the government finance. Reducing the cost of HSR has been necessary and urgent. Optimizing the arrangement of the base stations (BS) by improving the prediction of the communication link is one of the most effective methods, which could reduce the number of the BSs to a reasonable number. However, it requires a carefully developed propagation model, which has been largely neglected before in the research on the HSR. In this paper, we propose a standardized path loss model for HSR channels based on an extensive measurement campaign in 4594 HSR cells of the "Zhengzhou-Xian" HSR line. The measurements are conducted using a practically deployed and operative GSM-Railway (GSM-R) system to reflect the real conditions of the HSR channels. The proposed model is validated by the measurements conducted in another operative railway - "Beijing-Shanghai" HSR line. The results are helpful for the HSR communications system designers to gain a better tool in the system planning, and propagation researchers to assess where the most pressing needs in the modeling of HSR channels lie.
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paper_title: Short-Term Fading Behavior in High-Speed Railway Cutting Scenario: Measurements, Analysis, and Statistical Models

paper_content:

Cuttings are widely used in high-speed railway (HSR) transportation to ensure the flatness of rails. The special structure of cuttings results in rich reflection and scattering, and creates dense multipath components. This paper presents a series of measurements of the propagation channel at 930 MHz conducted along the “Zhengzhou-Xi'an” HSR of China, to characterize the small-scale fading behavior of rail-cutting scenarios as a function of the geometry of cuttings, including crown width and bottom width. Raw data are collected in six cuttings (five cuttings are used for developing the model, while the other one is used for validation) in rural and suburban environments. We propose a set of effective methods to statistically model the spatial/temporal variations – including fade depth (FD), level crossing rate (LCR), average fade duration (AFD), and Ricean ${K}$ -factor – as a function of the structural parameters of cuttings. Akaike's Information Criterion (AIC)-based evaluation indicates that the Ricean distribution is the best to describe small-scale fading. In addition, the rich multipath and directionality of the transmitting antennas lead to a non-monotonous dependence of the ${K}$ -factor on the distance between transmitter and receiver. The autocovariance function of the deviation of the extracted ${K}$ -factors from the proposed model is presented and the coherence length is investigated. Our results show that even though a cutting is a scenario with severe fading, a “wide” cutting (i.e., with both wide crown and bottom widths) is conducive to the reduction of the severity of fading.
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paper_title: Wayside Communications: CBTC Data Communications Subsystems

paper_content:

This article will focus on how data communications subsystems (DCSs) provide radio frequency (RF) coverage, how they deal with and mitigate RF interference and multipath fading, and how they make use of sophisticated signal-processing techniques to improve performance in the face of a harsh propagation environment. The various DCSs used on many ?communications-based train control (CBTC) system projects planned and in service throughout North America, Europe, and Asia are surveyed. The article will also focus on the RF characteristics of the DCS so as to highlight the similarities and common challenges that all DCSs face with a view to presenting best practice and innovative design.
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paper_title: Finite-State Markov Modeling for High-Speed Railway Fading Channels

paper_content:

Developing an accurate and mathematically tractable high-speed railway (HSR) channel model is a key issue to provide reliable, cost-effective wireless services for the HSR operators and users. Although finite-state Markov chain (FSMC) has been extensively investigated to describe fading channels, most of FSMC channel models are designed based on the first-order Markov chain, which are no longer valid when the transceivers operate in high mobility scenarios, specially in HSR communications. In this letter, an advanced FSMC channel model for HSR is proposed, which incorporates the impacts of moving speed on the temporal channel statistical characteristic. The closed-form expressions of state transition probabilities between channel states are derived. The accuracy of the proposed FSMC channel model is validated via extensive measurements conducted on the Zhengzhou-Xi’an HSR line in China.
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paper_title: Measurement of Distributed Antenna Systems at 2.4 GHz in a Realistic Subway Tunnel Environment

paper_content:

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.
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paper_title: An Empirical Path Loss Model and Fading Analysis for High-Speed Railway Viaduct Scenarios

paper_content:

Based on the narrowband 930-MHz measurements taken along the “Zhengzhou-Xi'an” high-speed railway in China, an empirical path loss model is proposed. It is applicable to high-speed railway viaduct scenarios, considering the influences of viaduct height H and base station antenna relative height h, which are not well-covered by existing large-scale models. The path loss exponents are investigated, based on which the influence of viaduct on propagation is discussed. The fading depth up to 15.96 dB and the Ricean K -factor with mean value of 3.79 dB are obtained.
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paper_title: Position-Based Modeling for Wireless Channel on High-Speed Railway under a Viaduct at 2.35 GHz

paper_content:

This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.
---
paper_title: Efficient Multiple-Group Multiple-Antenna (MGMA) Scheme for High-Speed Railway Viaducts

paper_content:

The capacity of a multiple-input-multiple-output (MIMO) channel with N transmit and receive antennas for highspeed railways (HSRs) is analyzed based on the 3-D modeling of the line of sight (LOS). The MIMO system utilizes a uniform linear antenna array. Instead of increasing the number of antennas or simply changing the parameters of the antenna array, such as separation and geometry, the capacity gain can be obtained by adjusting the weights of multiantenna array groups, because there are few scatterers in strong LOS environments. On the other hand, it is hard to obtain the array gain of MIMO beamforming for HSRs because of drastic changes in the receiving angle when the train travels across E-UTRAN Node B. Without changing the antenna design of Long-Term Evolution systems, this paper proposes a multiple-group multiple-antenna (MGMA) scheme that makes the columns of such a MIMO channel orthogonal by adjusting the weights among MGMA arrays, and the stable capacity gain can be obtained. The value of weights depends on the practical network topologies of the railway wireless communication system. However, the reasonable scope of group number N is less than 6. In selecting N, one important consideration is the tradeoff between practical benefit and cost of implementation.
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paper_title: Doppler frequency offset estimation and diversity reception scheme of high-speed railway with multiple antennas on separated carriage

paper_content:

The challenges of severe Doppler effects in high-speed railway are considered. By building a cooperative antenna system, an algorithm of joint channel estimation and Doppler frequency offset (DFO) estimation is proposed based on Ricean channel model. First, a maximum likelihood estimation (MLE) algorithm for DFO is designed, showing that the Doppler estimation can be obtained by estimating moving velocity of the train and the path loss with the exploitation of pilots that are placed inside the frame. Then a joint detection algorithm for the receiver is proposed to exploit multi-antenna diversity gains. Last, the theoretical Crammer Rao bound (CRB) for joint channel estimation and DFO estimation is derived. The steady performance of the system is confirmed by numerical simulations. In particular, when the Ricean fading channel parameter equals 5 and the velocities of train are 100 m/s and 150 m/s, the estimation variances of DFO are very close to the theoretical results obtained by using CRB. Meanwhile, the corresponding signal to noise ratio loss is less than 1.5 dB when the bit error rate is 10−5 for 16QAM signals.
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paper_title: Radio environment map-based cognitive Doppler spread compensation algorithms for high-speed rail broadband mobile communications

paper_content:

Recently, there is an increasing yet challenging demand on broadband mobile communications for high-speed trains. In this article, cognitive Doppler spread compensation algorithms are proposed for high-speed rail broadband mobile communications, which make use of the dedicated radio environment map (REM) for railway to compensate the time-varying Doppler spread. The dedicated REM for high-speed rail can be viewed as a spatial-temporal database consisting of the radio channel parameters along a given railway. The performance of the proposed Doppler spread compensation algorithms are evaluated with a typical OFDM-based broadband mobile system. Simulation results show that the link-level performance of high-speed rail broadband mobile communications can be improved significantly due to the REM-enabled radio channel condition awareness and the cognitive Doppler spread compensation algorithms. The REM-based cognitive radio approach presents a new paradigm for systems design of high-speed rail broadband mobile communications.
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paper_title: Performance analysis of high-speed railway communication systems subjected to co-channel interference and channel estimation errors

paper_content:

The performance of high-speed railway wireless communication systems is studied in the presence of co-channel interference and imperfect channel estimation in the uplink. The authors derive exact closed-form expressions for the outage probability and investigate the impact of fading severity. New explicit expressions are derived for both the level crossing rate and average outage duration for illustrating the impact of mobile speed and channel estimation errors on the achievable system performance. Our results are generalised and hence they subsume a range of previously reported results.
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paper_title: Position-Based Modeling for Wireless Channel on High-Speed Railway under a Viaduct at 2.35 GHz

paper_content:

This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.
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paper_title: Radio Resource Management for Wireless Networks

paper_content:

This article describes comparison of two intelligent methods used for channel selection for MANET, 5G technology or 802.11 networks. The main point is to show how channel selection influences speed and quality of data routing in wireless, sensor or ad-hoc networks. The article shows the basics of new trends in multi access networks, where effective spectrum is not an option, but a requirement. The article compares differences between fuzzy logic and game theory in channel selection. Each of these methods has some advantages and disadvantages to calculate results. Simulation shows how channels can be assigned to each node in wireless networks based on input parameters. The process of channel and node selection is important in 5G technology and beyond with so many access nodes in networks.
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paper_title: Call admission control in wireless networks: a comprehensive survey

paper_content:

Radio resource management (RRM) plays a major role in Quality of Service (QoS) provisioning for wireless communication systems. The performance of RRM techniques has a direct impact on each user's individual performance and on the overall network performance. Arriving (new and handoff) calls are granted/denied access to the network by the call admission scheme (CAC) based on predefined criteria, taking the network loading conditions into consideration. CAC in wireless networks has been receiving a great deal of attention during the last two decades due to the growing popularity of wireless communications and the central role that CAC plays in QoS provisioning in terms of the signal quality, call blocking and dropping probabilities, packet delay and loss rate, and transmission rate. In the first and second generation of wireless systems, CAC has been developed for a single service environment. In the third generation and beyond wireless systems, multimedia services such as voice, video, data, and audio are to be offered with various QoS profiles. Hence, more sophisticated CAC schemes are developed to cope with these changes. This article provides a comprehensive survey of CAC schemes in modern wireless networks.
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paper_title: Radio admission control scheme for high-speed railway communication with MIMO antennas

paper_content:

Along with the wide deployment of high-speed railway at more than 300 km/h, providing various services effectively for users in the train becomes both practical demand and interesting challenge for wireless communication. Due to the specific environment for high-speed railway, existing radio admission control (RAC) algorithms could not suit the requirements such as frequent handover, quick decision-making duration and fast-changing physical transmission condition. The investigation on novel and proper RAC is of great importance. In this paper, we propose an effective radio admission control scheme based on Rician shading model for high-speed railway communication with MIMO antennas. Layered networks access architecture is designed in which Rician channel is used to analyze physical transmission condition. The effect of bit error rate on data rate at high moving speeds is taken into account for the RAC decision-making to get better quality of service (QoS). Moreover, different priorities for different services are considered to resolve simultaneous multiple users' access requests. Simulation results have proved that the proposed scheme may improve QoS obviously compared to the scheme that does not consider bit error rate and service priority.
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paper_title: Access control schemes for high-speed train communications

paper_content:

With the fast deployment of high-speed railways of more than 300 km/h, providing quality of service of multimedia applications for users in the train is a key issue in wireless communications. The more challenging problem rests on the need to trade-off two performance metrics: the handover call dropping probability and the new call blocking probability. In this paper, we propose some prioritized access control schemes. These schemes take the advantages of the high-speed railway communication scenario. A position-based access factor is introduced to decrease the handover call dropping probability. In addition, separating resource reservation schemes are also proposed for both handovers and new calls. The system resource utilization has also been taken into account. Simulation results show that the proposed schemes may improve quality of service compared with schemes that do not apply the access factor and separating resource reservations.
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paper_title: A cross-layer admission control scheme for high-speed railway communication system

paper_content:

In high-speed railway communication system, due to its intrinsic features, on-going services are more prone to drop than in common communication systems. Therefore, existing admission control (AC) schemes designed for common communication systems cannot be directly used, otherwise the service dropping probability (SDP) requirement cannot be guaranteed. In this paper, a cross-layer AC scheme is designed to improve system SDP performance in high-speed railway communication system. Firstly, we clearly classify the main potential origins of service dropping into two types: modulation and coding scheme (MCS) changed service dropping and handoff service dropping. And then corresponding adaptive resource reservation algorithms are proposed to improve SDP performance, where the influence of MCS change and the unique characteristics of high-speed railway communication are taken into account. Simulation results show that compared with traditional cutoff AC scheme, the proposed AC scheme can effectively improve SDP performance while maintaining fairly desirable performance of service blocking probability and system bandwidth utilization.
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paper_title: Mobility-Aware Call Admission Control Algorithm With Handoff Queue in Mobile Hotspots

paper_content:

In this paper, we propose a mobility-aware call admission control (MA-CAC) algorithm with a handoff queue (HQ) in mobile hotspots, where different admission control policies are employed, depending on the vehicle mobility. Specifically, when a vehicle is static, a handoff priority scheme with guard channels is studied to protect vehicular handoff users because handoff users may get on the vehicle. In addition, an HQ is examined during stopping to further accept handoff users. On the other hand, for a moving vehicle, no guard channels for handoff users are allocated to maximize channel utilization. By means of Markov chains, we evaluate MA-CAC with an HQ in terms of new-call blocking probability (NCBP), handoff-call dropping probability (HCDP), handoff-call waiting time in the HQ, and channel utilization. Analytical and simulation results demonstrate that MA-CAC with an HQ can lower both the HCDP and the NCBP while maintaining high channel utilization.
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paper_title: Spring model-based call admission control mechanism for high-speed railway environment

paper_content:

Call admission control in mobility environment is a challenging issue. For high-speed railway environment, call admission control mechanism needs to be designed in order to admit more users when system bandwidth resource becomes scare. In this paper, a call admission control mechanism based on spring model is proposed. Although system bandwidth resource is occupied by existing users, a part of bandwidth resource can still be borrowed from them on condition that their lowest qualities of service could be guaranteed. Therefore, every existing service is regarded as a spring that can be compressed to some extent. Handover users who have higher priority than new users can be admitted by the above bandwidth resource borrowing strategy. Moreover, birth-death process is used to analyze dropping probability and blocking probability. Simulation results show that dropping probability of handover users is lower than blocking probability of new users. In addition, dropping probability of voice service is lower than that of data and video services.
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paper_title: Analysis and Optimization of Resource Control in High-Speed Railway Wireless Networks

paper_content:

This paper considers a joint optimal design of admission control and resource allocation for multimedia services delivery in high-speed railway (HSR) wireless networks. A stochastic network optimization problem is formulated which aims at maximizing the system utility while stabilizing all transmission queues under the average power constraint. By introducing virtual queues, the original problem is equivalently transformed into a queue stability problem, which can be naturally decomposed into three separate subproblems: utility maximization, admission control, and resource allocation. A threshold-based admission control strategy is proposed for the admission control subproblem. And a distributed resource allocation scheme is developed for the mixed-integer resource allocation subproblem with guaranteed global optimality. Then a dynamic admission control and resource allocation algorithm is proposed, which is suitable for distributed implementation. Finally, the performance of the proposed algorithm is evaluated by theoretical analysis and numerical simulations under realistic conditions of HSR wireless networks.
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paper_title: Radio admission control scheme for high-speed railway scenario: an optimal accepted service number approach

paper_content:

Long term evolution for railway (LTE-R) is commonly believed to be the next generation wireless communication system for high-speed railway. However, existing radio admission control (RAC) scheme in conventional LTE system can't be used directly. The main objective of this paper is to design a RAC scheme that suits to this special environment. Considering that RAC scheme in LTE-R system should have better ability to admit huge services, in the proposed RAC scheme a resources preemption algorithm is introduced to a complete-sharing resources allocation model to maximize the number of admitted services while guaranteeing the related quality of service requirements of each service class. Complete-sharing resources allocation model can guarantee the full use of system bandwidth resource; resources preemption algorithm can make sure that all on-going services occupy optimum system bandwidth resource with their related QoS. Furthermore, the expressions of admitted service number, service blocking probability and service blocking probability are deduced using 3-dimensional Markov model. Simulation results show that the performance of the proposed scheme outperforms that of existing scheme.
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paper_title: Admission control and handover management for high‐speed trains in vehicular geostationary satellite networks with terrestrial gap‐filling

paper_content:

Following a recent upgrade, the Digital Video Broadcasting—Return Channel Satellite (DVB-RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite–terrestrial architecture for the provision of broadband services onboard high-speed trains, in which terrestrial cellular networks are seen as viable gap-fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB-RCS-cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high-speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed-point approximation, we show performance improvements with respect to stand-alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2-based DVB-RCS packet-level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly. Copyright © 2009 John Wiley & Sons, Ltd.
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paper_title: Access control schemes for high-speed train communications

paper_content:

With the fast deployment of high-speed railways of more than 300 km/h, providing quality of service of multimedia applications for users in the train is a key issue in wireless communications. The more challenging problem rests on the need to trade-off two performance metrics: the handover call dropping probability and the new call blocking probability. In this paper, we propose some prioritized access control schemes. These schemes take the advantages of the high-speed railway communication scenario. A position-based access factor is introduced to decrease the handover call dropping probability. In addition, separating resource reservation schemes are also proposed for both handovers and new calls. The system resource utilization has also been taken into account. Simulation results show that the proposed schemes may improve quality of service compared with schemes that do not apply the access factor and separating resource reservations.
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paper_title: A cross-layer admission control scheme for high-speed railway communication system

paper_content:

In high-speed railway communication system, due to its intrinsic features, on-going services are more prone to drop than in common communication systems. Therefore, existing admission control (AC) schemes designed for common communication systems cannot be directly used, otherwise the service dropping probability (SDP) requirement cannot be guaranteed. In this paper, a cross-layer AC scheme is designed to improve system SDP performance in high-speed railway communication system. Firstly, we clearly classify the main potential origins of service dropping into two types: modulation and coding scheme (MCS) changed service dropping and handoff service dropping. And then corresponding adaptive resource reservation algorithms are proposed to improve SDP performance, where the influence of MCS change and the unique characteristics of high-speed railway communication are taken into account. Simulation results show that compared with traditional cutoff AC scheme, the proposed AC scheme can effectively improve SDP performance while maintaining fairly desirable performance of service blocking probability and system bandwidth utilization.
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paper_title: Mobility-Aware Call Admission Control Algorithm With Handoff Queue in Mobile Hotspots

paper_content:

In this paper, we propose a mobility-aware call admission control (MA-CAC) algorithm with a handoff queue (HQ) in mobile hotspots, where different admission control policies are employed, depending on the vehicle mobility. Specifically, when a vehicle is static, a handoff priority scheme with guard channels is studied to protect vehicular handoff users because handoff users may get on the vehicle. In addition, an HQ is examined during stopping to further accept handoff users. On the other hand, for a moving vehicle, no guard channels for handoff users are allocated to maximize channel utilization. By means of Markov chains, we evaluate MA-CAC with an HQ in terms of new-call blocking probability (NCBP), handoff-call dropping probability (HCDP), handoff-call waiting time in the HQ, and channel utilization. Analytical and simulation results demonstrate that MA-CAC with an HQ can lower both the HCDP and the NCBP while maintaining high channel utilization.
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paper_title: Spring model-based call admission control mechanism for high-speed railway environment

paper_content:

Call admission control in mobility environment is a challenging issue. For high-speed railway environment, call admission control mechanism needs to be designed in order to admit more users when system bandwidth resource becomes scare. In this paper, a call admission control mechanism based on spring model is proposed. Although system bandwidth resource is occupied by existing users, a part of bandwidth resource can still be borrowed from them on condition that their lowest qualities of service could be guaranteed. Therefore, every existing service is regarded as a spring that can be compressed to some extent. Handover users who have higher priority than new users can be admitted by the above bandwidth resource borrowing strategy. Moreover, birth-death process is used to analyze dropping probability and blocking probability. Simulation results show that dropping probability of handover users is lower than blocking probability of new users. In addition, dropping probability of voice service is lower than that of data and video services.
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paper_title: Analysis and Optimization of Resource Control in High-Speed Railway Wireless Networks

paper_content:

This paper considers a joint optimal design of admission control and resource allocation for multimedia services delivery in high-speed railway (HSR) wireless networks. A stochastic network optimization problem is formulated which aims at maximizing the system utility while stabilizing all transmission queues under the average power constraint. By introducing virtual queues, the original problem is equivalently transformed into a queue stability problem, which can be naturally decomposed into three separate subproblems: utility maximization, admission control, and resource allocation. A threshold-based admission control strategy is proposed for the admission control subproblem. And a distributed resource allocation scheme is developed for the mixed-integer resource allocation subproblem with guaranteed global optimality. Then a dynamic admission control and resource allocation algorithm is proposed, which is suitable for distributed implementation. Finally, the performance of the proposed algorithm is evaluated by theoretical analysis and numerical simulations under realistic conditions of HSR wireless networks.
---
paper_title: Radio admission control scheme for high-speed railway scenario: an optimal accepted service number approach

paper_content:

Long term evolution for railway (LTE-R) is commonly believed to be the next generation wireless communication system for high-speed railway. However, existing radio admission control (RAC) scheme in conventional LTE system can't be used directly. The main objective of this paper is to design a RAC scheme that suits to this special environment. Considering that RAC scheme in LTE-R system should have better ability to admit huge services, in the proposed RAC scheme a resources preemption algorithm is introduced to a complete-sharing resources allocation model to maximize the number of admitted services while guaranteeing the related quality of service requirements of each service class. Complete-sharing resources allocation model can guarantee the full use of system bandwidth resource; resources preemption algorithm can make sure that all on-going services occupy optimum system bandwidth resource with their related QoS. Furthermore, the expressions of admitted service number, service blocking probability and service blocking probability are deduced using 3-dimensional Markov model. Simulation results show that the performance of the proposed scheme outperforms that of existing scheme.
---
paper_title: Admission control and handover management for high‐speed trains in vehicular geostationary satellite networks with terrestrial gap‐filling

paper_content:

Following a recent upgrade, the Digital Video Broadcasting—Return Channel Satellite (DVB-RCS) standard sets up to support terminal mobility. In this scenario, integration with terrestrial systems becomes a primary concern to ensure network connectivity in urban areas. This article proposes an integrated satellite–terrestrial architecture for the provision of broadband services onboard high-speed trains, in which terrestrial cellular networks are seen as viable gap-fillers for discontinuous satellite coverage. We derive an analytical model of the hybrid DVB-RCS-cellular system by exploiting analogies between the mobility pattern predictability of LEO constellations and that of high-speed trains. Terminals whose QoS cannot be guaranteed by the satellite segment are proposed to temporarily divert the connections towards the terrestrial infrastructure, where available. Using an iterative approach based on the Erlang fixed-point approximation, we show performance improvements with respect to stand-alone satellite systems in terms of handover failure probability and overall resource utilization. The analytical model is also validated via our ns2-based DVB-RCS packet-level simulator. Detailed modelling of synchronization and signalling mechanisms confirms the accuracy of the analytical results, and shows that topology and mobility information can contribute to refine radio resource utilization optimality when used jointly. Copyright © 2009 John Wiley & Sons, Ltd.
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paper_title: TDD-based mobile communication solutions for high-speed railway scenarios

paper_content:

Mobile communication solutions for highspeed railway scenarios aim at providing seamless coverage, high system capacity and a high data rate for end users, which in turn face the challenges of Doppler frequency shift, penetration loss, mobility management and system capacity planning. Because the scarcity of frequency resources and increasing wireless broadband requirements have become very serious problems worldwide, increasing attention has been focused on time-division duplexing based technology, on which we focus in this article. Time-division synchronous code-division multiple access based and time-division Long Term Evolution based solutions are introduced with appropriate technology analysis. The experimental results of TD-SCDMA-based solutions in the Shanghai maglev high-speed network environment and the simulation results of TD-LTE-based solutions are presented. Finally, to improve performance, we discuss an enhanced solution based on mobile relays with performance evaluation, which is considered as a more comprehensive solution for high-speed railway scenarios.
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paper_title: Mobility and handoff management in vehicular networks: a survey

paper_content:

Mobility management is one of the most challenging research issues for vehicular networks to support a variety of intelligent transportation system (ITS) applications. The traditional mobility management schemes for Internet and mobile ad hoc network (MANET) cannot meet the requirements of vehicular networks, and the performance degrades severely due to the unique characteristics of vehicular networks (e.g., high mobility). Therefore, mobility management solutions developed specifically for vehicular networks would be required. This paper presents a comprehensive survey on mobility management for vehicular networks. First, the requirements of mobility management for vehicular networks are identified. Then, classified based on two communication scenarios in vehicular networks, namely, vehicle-to-vehicle (V2V) and vehicle-to-infrastructure (V2I) communications, the existing mobility management schemes are reviewed. The differences between host-based and network-based mobility management are discussed. To this end, several open research issues in mobility management for vehicular networks are outlined. Copyright © 2009 John Wiley & Sons, Ltd.
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paper_title: Location Updating Schemes for High-Speed Railway Cellular Communication Systems

paper_content:

High-speed railway private cellular network provides voice and data services for passengers. It brings much signaling cost as a great many of mobile subscribers ask for location updating simultaneously. Moreover, it leads to plenty of control signaling channel requests. This paper presents two novel location updating schemes, that is, “clustering location management” and “mobile group location management” to solve the problems caused by the existing location updating scheme in high speed railway cellular private network. These two schemes can realize location updating without occupying more frequency resources. In addition, it does not impact the mobile subscribers’ paging. Then it analyses the performance of two improved schemes, such as channel request number of stand-alone dedicated control channel (SDCCH), average waiting time of location updating, cost of location updating, and paging. The result indicates that both schemes can utilize the SDCCH channel resource effectively.
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paper_title: Efficient On-Demand Data Service Delivery to High-Speed Trains in Cellular/Infostation Integrated Networks

paper_content:

In this paper, we investigate on-demand data services for high-speed trains via a cellular/infostation integrated network. Service requests and acknowledgements are sent through the cellular network to a content server, while data delivery is achieved via trackside infostations. The optimal resource allocation problem is formulated by taking account of the intermittent network connectivity and multi-service demands. In order to achieve efficient resource allocation with low computational complexity, the original problem is transformed into a single-machine preemptive scheduling problem based on a time-capacity mapping. As the service demands are not known a priori, an online resource allocation algorithm based on Smith ratio and exponential capacity is proposed. The performance bound of the online algorithm is characterized based on the theory of sequencing and scheduling. If the link from the backbone network to an infostation is a bottleneck, a service pre-downloading algorithm is also proposed to facilitate the resource allocation. The performance of the proposed algorithms is evaluated based on a real high-speed train schedule. Compared with the existing approaches, our proposed algorithms can significantly improve the quality of on-demand data service provisioning over the trip of a train.
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paper_title: An Optimized Seamless Dual-Link Handover Scheme for High-Speed Rail

paper_content:

In high-speed rail (HSR) with Long-Term Evolution (LTE) technology, the wireless communication quality of service (QoS) is enormously degraded because of the unstable signal and frequent handover. Recently, a seamless handover using two antennas on the top of a train has been introduced to provide a better user experience. The two antennas are mounted on the front and the rear of the train, respectively, so that one performs handover, and the other is communicating. A bicasting mechanism is adopted to eliminate the delay and overhead of data forwarding. In this paper, we consider a new algorithm to optimize the handoff opportunity by investigating not only the hysteresis exceeding level but the signal strength of both antennas as well. The parameter selection in the algorithm is analyzed based on a probability model. Furthermore, a set of new handover procedures, which optimize the utilization of the two antennas, is proposed to decrease the overhead and improve the QoS of the users. Accordingly, numerical results show that the handover failure probability (HFP) and the communication interruption probability (CIP) are both obviously reduced.
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paper_title: Seamless Wireless Connectivity for Multimedia Services in High Speed Trains

paper_content:

The recent advent of high speed trains introduces new mobility patterns in wireless environments. The LTE-A (Long Term Evolution of 3GPP - Advanced) networks have largely tackled the Doppler effect problem in the physical layer and are able to keep wireless service with 100Mpbs throughput within a cell in speeds up to 350 km/h. Yet the much more frequent handovers across cells greatly increases the possibility of service interruptions, and the problem is prominent for multimedia communications that demand both high-throughput and continuous connections. In this paper, we present a novel LTE-based solution to support high throughput and continuous multimedia services for high speed train passengers. Our solution is based on a Cell Array that smartly organizes the cells along a railway, together with a femto cell service that aggregates traffic demands within individual train cabins. Given that the movement direction and speed of a high-speed train are generally known, our Cell Array effectively predicts the upcoming LTE cells in service, and enables a seamless handover that will not interrupt multimedia streams. To accommodate the extreme channel variations, we further propose a scheduling and resource allocation mechanism to maximize the service rate based on periodical signal quality changes. Our simulation under diverse network and railway/train configurations demonstrates that the proposed solution achieves much lower handover latency and higher data throughput, as compared to existing solutions. It also well resists to network and traffic dynamics, thus enabling uninterrupted quality multimedia services for passengers in high speed trains.
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paper_title: Handover Scheme for 5G C/U Plane Split Heterogeneous Network in High-Speed Railway

paper_content:

Being a promising technology for fifth-generation (5G) communication systems, a novel railway communication system based on control/user (C/U) plane split heterogeneous networks can provide a high-quality broadband wireless service for passengers in high-speed railways with higher system capacity, better transmission reliability, and less cochannel interference. However, due to its special architecture where the C-plane and the U-plane must be split and supported by a macro Evolved Node B (eNB) and a phantom eNB, respectively, it would suffer more serious handover problem, particularly in intermacrocell handover, which directly degrades its applicability and availability in high-speed railways. Moreover, no technical specification has been released about this network architecture. Therefore, this paper focuses on redesigning and analyzing technical details and handover procedures based on Long-Term Evolution (LTE) specifications to guarantee the proposed system's practicability and generality and its analytical tractability. To resolve the handover problem, this paper proposes a handover trigger decision scheme based on GM(1, $n$) model of the grey system theory. By this scheme, the received signal quality from the $(N + hbox{1})$th measurement report can be predicted from the $N$th measurement period, and the predicted values can be then utilized to make the handover trigger decision. The simulation results show that the proposed scheme is capable of triggering handover in advance effectively and of enhancing handover success probability remarkably.
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paper_title: A CoMP soft handover scheme for LTE systems in high speed railway

paper_content:

With the development of high-speed railway and public growing demand on data traffic, people pay much more attention to provide high data rate and high reliable services under high mobility circumstance. Due to the higher data rate and lower system latency, long-term evolution (LTE) has been chosen as the next generation's evolution of railway mobile communication system by the International Union of Railways. However, there are still many problems to be solved in the high mobility applications of LTE, especially the higher handover failure probability, which seriously degrades the reliability of railway communication. This article proposes an optimized handover scheme, in which the coordinated multiple point transmission technology and dual vehicle station coordination mechanism are applied to improve the traditional hard handover performance of LTE. The scheme enables the high speed train to receive signals from both adjacent base stations and obtain diversity gain when it moves through the overlapping areas, so it improves the quality of the received signal and provides reliable communication between train and ground eNodeBs. Numerical analysis and simulation results show that the proposed scheme can decrease the outage probability remarkably during handover and guarantee the reliability of train to ground communication.
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paper_title: Distributed Antenna Systems for Mobile Communications in High Speed Trains

paper_content:

With the deployment of high speed train (HST) systems increasing worldwide and their popularity with travelers growing, providing broadband wireless communications (BWC) in HSTs is becoming crucial. In this paper, a tutorial is presented on recent research into BWC provision for HSTs. The basic HST BWC network architecture is described. Two potential cellular architectures, microcells and distributed antenna systems (DASs) based cells, are introduced. In particular, the DAS is discussed in conjunction with radio over fiber (RoF) technology for BWC for HSTs. The technical challenges in providing DAS-based BWC for HSTs, such as handoff and RoF are discussed and outlined.
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paper_title: An Enhanced Handover Scheme for Mobile Relays in LTE-A High-Speed Rail Networks

paper_content:

Recently, the mobile relay technique has been discussed to support communication services for Long-Term Evolution Advanced (LTE-A) high-speed rail networks. In the network, there are several mobile relays in a train. User equipment (UE) devices connect to in-car mobile relays instead of outside evolved NodeBs (eNBs). Mobile relays establish backhaul links with the serving donor eNBs (DeNBs) and coordinate control and data flows for UE devices. Since the train travels in high speed, mobile relays suffer from frequent handovers between DeNBs. We observe that the defined handover procedures in LTE-A specifications may incur message overhead and lengthen handover time. In this paper, we propose an enhanced handover scheme, which contains two procedures. The first procedure is an enhanced measurement procedure, which can accelerate the measurement procedure when the mobile relay knows that the train is moving toward some neighbor DeNBs. The second procedure is a group in-network handover procedure, which can aggregate similar in network handover procedures in the core network. Performance evaluations indicate that our design can conserve both time and messages when handover.
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paper_title: Seamless Handover for High-Speed Trains Using Femtocell-Based Multiple Egress Network Interfaces

paper_content:

High-speed rail systems are becoming increasingly popular among long-distance travelers. With the explosive growth in the number of mobile devices, the provision of high-quality telecommunication and Internet access services on high-speed trains is now a pressing problem. Network mobility (NEMO) has been proposed to enable a large number of mobile devices on a vehicle to access the Internet; however, several issues must be solved before it can be put into practice, e.g., frequent handovers, long handover latency, and poor quality of service. To resolve these problems, we propose an LTE femtocell-based network mobility scheme that uses multiple egress network interfaces to support seamless handover for high-speed rail systems called MEN-NEMO. The results of simulations show that the proposed MEN-NEMO scheme reduces the handover latency and transmission overhead of handover signaling substantially.
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paper_title: A seamless dual-link handover scheme suitable for high-speed rail

paper_content:

LTE with large capacity and high speed is the most promising standard of wireless data communications technology to be used in Chinese high-speed rail(HSR). Because of over-frequent handover in HSR, the experience of passengers is highly degraded. Wireless Quality of Service (QoS) provisioning in such high speed movement is more difficult to be tackled than in a fixed-wired environment. Seamless handover attempts to provide a given QoS during the process of migration from one cell to another. It can reduce the interruption period to nearly zero. In this paper, we revised an existent seamless dual-link handover scheme where the Train Relay Station relays the data of users in the train and two antennas are mounted in the top of the train and designed a set of new handover procedures suitable for HSR communications. We defined a velocity threshold(VT). If the speed of train exceeds VT, two target base stations are prepared for user equipment(UE) when handover is triggered. The simulation results show that in the proposed scheme the communication interruption probability is under 0.01 when the train is at speed of 350 kilometers per hour.
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paper_title: Improving Handover and Drop-off Performance on High-Speed Trains With Multi-RAT

paper_content:

Provisioning commercial mobile telecommunications service on a high-speed train (HST) faces several challenges. In particular, when an HST quickly passes through the radio coverage of the base stations, frequent handovers may result in serious communication interruption. Methods such as the hierarchical two-hop network and the seamless dual-link handover scheme were proposed to address these challenges. This paper proposes the multiple radio access technology (multi-RAT) to resolve the HST handover issue, which allows the HST to simultaneously connect to two or more heterogeneous mobile networks (e.g., the Universal Mobile Telecommunications System and Long Term Evolution). With this approach, the handover process can be improved by keeping multiple heterogeneous network links of the HST at the same time and maintaining the connection through one link during the handover process of the other link. We show that multi-RAT can effectively enhance HST communications by reducing the impact of handover failure. This approach can work together with other solutions such as the dual-link scheme to further enhance the performance of the HST communications.
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paper_title: Mobile Relay Based Fast Handover Scheme in High-Speed Mobile Environment

paper_content:

There are a lot of handovers failed in high-speed mobile environment because the handover can't be completed in time although the field strength values are sufficient availability along the tracks. A mobile relay based fast handover scheme is proposed which is suitable for high-speed mobile environment. Two reference points are introduced to ensure handover in time. Pre-preparation and packet bi-casting is introduced to reduce communication interruption time and realize seamless handover. The performance of the proposed scheme is analyzed in terms of handover delay, communication interruption time and bi-casting time.
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paper_title: Broadband wireless communications on high speed trains

paper_content:

This tutorial paper provides a comprehensive overview on the recent development in broadband wireless communications for high speed trains. Starting with the introduction of the two-hop network structure, radio-over-fiber (RoF) based cell planning is described in detail. Moreover, based on the analysis of differences between conventional cellular systems and the one for high speed trains, promising techniques are recommended to improve the performance of handover, which is one of the main challenges in high speed train communications. Finally, in order to combat the fast fading caused by the high mobility, robust algorithms are needed in physical layer signal processing, including synchronization, channel estimation, modulation/demodulation, and so on.
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paper_title: The cross layer RMPA handover: a reliable mobility pattern aware handover strategy for broadband wireless communication in a high-speed railway domain

paper_content:

Enhancing the handover process in broadband wireless communication deployment has traditionally motivated many research initiatives. In a high-speed railway domain, the challenge is even greater. Owing to the long distances covered, the mobile node gets involved in a compulsory sequence of handover processes. Consequently, poor performance during the execution of these handover processes significantly degrades the global end-to-end performance. This article proposes a new handover strategy for the railway domain: the RMPA handover, a Reliable Mobility Pattern Aware IEEE 802.16 handover strategy “customized” for a high-speed mobility scenario. The stringent high mobility feature is balanced with three other positive features in a high-speed context: mobility pattern awareness, different sources for location discovery techniques, and a previously known traffic data profile. To the best of the authors’ knowledge, there is no IEEE 802.16 handover scheme that simultaneously covers the optimization of the handover process itself and the efficient timing of the handover process. Our strategy covers both areas of research while providing a cost-effective and standards-based solution. To schedule the handover process efficiently, the RMPA strategy makes use of a context aware handover policy; that is, a handover policy based on the mobile node mobility pattern, the time required to perform the handover, the neighboring network conditions, the data traffic profile, the received power signal, and current location and speed information of the train. Our proposal merges all these variables in a cross layer interaction in the handover policy engine. It also enhances the handover process itself by establishing the values for the set of handover configuration parameters and mechanisms of the handover process. RMPA is a cost-effective strategy because compatibility with standards-based equipment is guaranteed. The major contributions of the RMPA handover are in areas that have been left open to the handover designer’s discretion. Our simulation analysis validates the RMPA handover decision rules and design choices. Our results supporting a high-demand video application in the uplink stream show a significant improvement in the end-to-end quality of service parameters, including end-to-end delay (22%) and jitter (80%), when compared with a policy based on signal-to-noise-ratio information.
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paper_title: Handover schemes and algorithms of high-speed mobile environment: A survey

paper_content:

Abstract With lower energy consumption, less environmental pollution, larger capacity, and higher safety, the high-speed railway is playing an important role in mass transportations. The development of high-speed railways makes people’s life more and more convenient. Meanwhile, it puts forward much higher demands on high-speed railway communications. Therefore, new solutions are desired to keep up with this unprecedented growth. However, communications in high-speed environment have particular characteristics such as fast and frequent handover, high penetration loss, and high Doppler frequency shift. Current researches mainly focus on providing broadband wireless network access for high-speed mobile terminals. This article presents an overview of the latest technical developments on handover schemes and handover algorithms targeting high-speed mobile scenarios. In addition, this paper suggests the most appropriate techniques which can efficiently communicate in high-speed mobile scenarios. Finally, we discuss future trends of handover researches in high-speed mobile environments.
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paper_title: A fast handover scheme based on GPS information for IEEE 802.16e on high-speed railway

paper_content:

As the high-speed train moves forward at a high speed, inevitably, it will go across the cell in a short time. In order to keep communication always on, the MS is required to perform handover operation at a short time. For IEEE 802.16e, there exists a serial of problems such as ambiguous timing of scanning and unnecessary memory resource consumption during scanning duration. Furthermore, for high-speed railway BWA system, some operations in the conventional handover procedure are redundant. To resolve those problems, according to the GPS information, we propose a cell reselection and handover decision algorithm, and also propose a handover scheme to omit the scanning operation and greatly shorten the operation time of the whole HO procedure.
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paper_title: An Effective Handover Scheme Based on Antenna Selection in Ground–Train Distributed Antenna Systems

paper_content:

Due to frequent handovers in broadband wireless communications for the high-speed railway system, communication interruption caused by handover failures could seriously degrade the users' experience. Aiming at reducing the handover failure probability, this paper proposes an effective handover scheme based on the distributed antenna system (DAS) and mobile-relay-aided two-link architecture, i.e., ground-relay link and relay-onboard link, where the mobile relay is mounted on top of the moving train. In addition, an antenna selection scheme with optimal power allocation is proposed to improve handover performance. Our simulation and analysis results show that the DAS structure with macrodiversity can reduce the unnecessary handovers, as well as reduce the handover failure and link outage probabilities compared with the traditional cell without DAS. In addition, the proposed DAS with an antenna selection scheme performs better in terms of handover failure and link outage probabilities than that of DAS with a equal power allocation (EPA) scheme.
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paper_title: Broadband communication on the highways of tomorrow

paper_content:

Consumer demands for broadband communications at highway speeds will not likely be met by next-generation proposals. Although solutions exist for incremental improvements in capacity and bandwidth, the wireless industry has not yet offered an economical method for providing the broadband channels demanded by mobile consumers on the highway. The article examines a proposed high-capacity infrastructure with moving base stations for providing broadband communication services that are not limited by a user's speed. Moving base stations provide moving communication cells to mobile users traveling along a roadway. This broadband solution provides communication services with data rates of 20 Mb/s or more at any vehicular speed at costs comparable to wireline. In addition to presenting a general technical description of the proposed infrastructure, the discussion includes an overview of wireless technology and obstacles encountered in designing a high-capacity system providing high-bandwidth channels to users traveling at highway speeds.
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paper_title: Seamless Dual-Link Handover Scheme in Broadband Wireless Communication Systems for High-Speed Rail

paper_content:

Due to frequent handovers in broadband wireless communications in high-speed rail, communication interruption during handover could seriously degrade the experiences of passengers on the train. Aiming to reduce the interruption time, this paper proposes a seamless handover scheme based on a dual-layer and dual-link system architecture, where a Train Relay Station is employed to execute handover for all users in a train and two antennas are mounted at the front and rear of a train. In the proposed scheme, the front antenna executes handover while the rear antenna is still communicating with BS, so that the communication can keep non-interruptive throughout the handover. Moreover, bi-casting is adopted to eliminate the data forwarding delay between the serving BS and target BS. A complete handover protocol is designed and the performance of the proposed scheme is analyzed. It can be seen from analytical results that the handover failure probability decreases as cell overlap increases and the communication interruption probability decreases with the decrease of train handover location and the increase of cell overlap. The simulation results show that in the proposed scheme, the communication interruption probability is smaller than 1% when the handover location is properly selected and the system throughput is not affected by handover. In conclusion, both theoretical and simulation results show that the proposed scheme can efficiently perform seamless handover for high-speed rail with low implementation overhead.
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paper_title: Position-assisted fast handover schemes for LTE-advanced network under high mobility scenarios

paper_content:

Two position-assisted fast handover schemes, scheme A and scheme B, for LTE-A system under very high mobility scenarios, are proposed, together with their performance evaluation. Scheme A is designed to reduce handover delay by making handover preparation before handover starts. Scheme B aims at reducing unnecessary handovers and improving handover success rate, by calculating the geographically best target handover cell, which makes it easier for mobile terminals to access the target cell. A system level simulation is conducted to evaluate the performance of these two schemes. It is shown that, scheme A could reduce inter-site handover delay by about 50 ms, while scheme B could cut down nearly 50% of all handovers when time-to-trigger (TTT) is 0 ms. Besides, as TTT gets larger, Scheme B has much better success rate.
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paper_title: Beamforming and positioning-assisted handover scheme for long-term evolution system in high-speed railway

paper_content:

As the railway industry expands and trains speed-up, the reliability and efficiency of wireless communication systems in high-speed railway have to face the severe challenges. The high-speed brings about more severe Doppler effect, the postponement of handover triggering location and more frequent handover. Therefore the influence caused by the high-speed decreases the reliability of wireless communication network. In this study, considering the decision of `global system for mobile communication for railway` evolution to long-term evolution for railway (LTE-R) by International Union of Railways, a scheme based on the beamforming and positioning information is proposed to improve the system handover performance for the LTE system which is being applied to the high-speed railway. In the overlapping region, both the current serving eNodeB and the target eNodeB start to use beamforming with different gain factors to improve handover success probability. The results have shown that the proposed scheme increases the handover success probability effectively.
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paper_title: A 60 GHz Radio-Over-Fiber Network Architecture for Seamless Communication With High Mobility

paper_content:

We demonstrate a 60 GHz broadband picocellular Radio-over-Fiber network architecture that enables seamless connectivity for highly mobile end-users. Its seamless communication capabilities arise by the supported handover scheme that relies on a novel Moving Extended Cell (MEC) concept. MEC exploits user-centric virtual groups of adjacent cells that transmit the same data content to the user and utilizes a switch mechanism for restructuring the virtual multi-cell area according to the user's mobility pattern, so that a virtual antenna group moves together with the mobile user. We present the theoretical formulation for MEC and show that it can provide zero packet loss and call dropping probability values in high-rate wireless services for a broad range of mobile speeds up to 40 m/sec, independently of the fiber link distances. We also demonstrate the physical layer network architecture and switch mechanism both for a RoF network with a single 60 GHz radio frequency (RF) over each wavelength, as well as for a RoF configuration supporting simultaneous multi-RF channel transmission over each optical wavelength. The performance of the multi-RF-over-lambda network implementation is evaluated via simulations showing successful 100 Mb/s radio signal transmission over fiber links longer than 30 km. To this end, MEC can enable seamless connectivity and bandwidth guarantees in 60 GHz picocellular RoF networks being also capable of serving multiple users over the same wavelength in a RF frequency-division-multiplexed (FDM) approach.
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paper_title: Coordinated of multi-point and bi-casting joint soft handover scheme for high-speed rail

paper_content:

The high mobility of high-speed train brings great challenges to the current wireless communication, especially to the handover. How to reduce the interrupt time and enhance the handover performance is becoming a serious problem for high-speed rail (HSR). In this study, a coordinated of multi-point (CoMP) and bi-casting joint soft handover scheme for HSR is proposed, which is based on long-term evolution network architecture, and without any change to the existing network and the train. In the scheme, CoMP is used on air interface and bi-casting is used on S1 interface. With the binding triggering of CoMP and bi-casting, only one suit of signalling is needed and the system complexity is much simplified. Meanwhile, as much handover related information is stored in corresponding entity during the joining process of CoMP and bi-casting, the handover process is much simplified and converted into update of serving eNodeB. Compared with traditional handover scheme, it can be seen from theoretical analysis and simulation results that the handover delay is reduced remarkably and the handover performance is improved greatly.
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paper_title: Delay-Aware Dynamic Resource Management for High-Speed Railway Wireless Communications

paper_content:

With the fast development of high-speed railway (HSR), the demand for mobile communication on high-speed trains is increasingly growing. This leads to significant attention on the study of resource management in HSR wireless communications with limited bandwidth. Resource management is a challenging problem due to heterogenous quality of service (QoS) requirements and dynamic characteristics of HSR wireless communications. In this article, we first provide a state-of-the-art overview on HSR wireless communications and the existing resource management schemes. Then a location-aware cross-layer optimization framework is developed for the dynamic resource management with realistic system model, where the train location information is exploited to facilitate dynamic design. Next we demonstrate the applications of stochastic network optimization theory in solving the dynamic resource management problem in HSR wireless communications. Finally, we highlight some future research directions for location-aware dynamic resource management in the conclusion.
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paper_title: Finite state Markov modelling for high speed railway wireless communication channel

paper_content:

How to provide reliable, cost-effective wireless services for high-speed railway (HSR) users attracts increasing attention due to the fast deployment of HSRs worldwide. A key issue is to develop reasonably accurate and mathematically tractable models for HSR wireless communication channels. Finite-state Markov chains (FSMCs) have been extensively investigated to describe wireless channels. However, different from traditional wireless communication channels, HSR communication channels have the unique features such as very high speed, deterministic mobility pattern and frequent handoff events, which are not described by the existing FSMC models. In this paper, based on the Winner II physical layer channel model parameters, we propose a novel FSMC channel model for HSR communication systems, considering the path loss, fast fading and shadowing with high mobility. Extensive simulation results are given, which validate the accuracy of the proposed FSMC channel model. The model is not only ready for performance analysis, protocol design and optimization for HSR communication systems, but also provides an effective tool for faster HSR communication network simulation.
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paper_title: Exploiting the forecast channels for power allocation in High-Speed Railway communications

paper_content:

A High-Speed Railway (HSR) communication system also has its own advantages compared to a conventional cellular system due to the fixed railway infrastructure and a priori known position of the trains. Based on the measurement results and analysis regarding the propagation channels for HSR communications in literature, this paper distinguishes and analyses the permanent and temporary elements affecting the channels. The characteristics of the channel at the positions when the train will pass in a short time (called here “future” channel) can be forecast based on the permanent elements and therefore provide a novel method to minimize the total transmit power and range for transmitting uplink packets with a certain time-to-live (TTL) period. A power reduction up to 20 dB can be achieved for packets with TTL period of 200ms.
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paper_title: Optimal Power Allocation With Delay Constraint for Signal Transmission From a Moving Train to Base Stations in High-Speed Railway Scenarios

paper_content:

Widespread deployment of high-speed railways in recent years has created huge demand for high-mobility broadband wireless communications. To provide broadband wireless access for passengers on the train, a well-acknowledged approach is to apply a two-hop architecture, under which passengers communicate with base stations (BSs) via an access point (AP) installed in the train. We consider the uplink transmission from the AP to the BSs on the ground along the railway. The key problem we discuss is how to match user-data arrival process and time-varying channel service process with a delay constraint at the AP. We first assume the constant-rate data arrival and the wireless channel affected only by large-scale fading in high-speed railway scenarios. We present the optimal power-allocation policy given the delay constraint. Based on the policy, we show that there exists a power–delay tradeoff in our system model, with the delay within a limited range. Besides, we find that the average transmit power and the train velocity have a tradeoff, which is similar to the power–delay tradeoff. Besides, given average transmit power constraint, the delay constraint is inversely proportional to the train velocity. Finally, when small-scale fading is considered, we modify the optimal power-allocation policy and provide a convenient approach to counteract Nakagami- $m$ fading in high signal-to-noise ratio (SNR) regimes. The modified power-allocation policy can be well adapted to different fading statistics in different terrestrial environments experienced by the high-speed train.
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paper_title: Bounds on the average transmission rate in high speed railway wireless communications

paper_content:

Different from traditional cellular communication, the transmission rate will vary greatly when the train is moving in a high speed railway system. In fact, the transmission rate is primarily determined by the distance between the train and the base station. As a result, the data transmission between the base station and the tain can only be measured in term of average transmission rate. This paper investigates the influence of train speed on system performance. As shown, the average transmission rate is independent of train speed. However, the total service that the train receives from a certain base station is inversely proportional to train speed. A lower bound as well as an upper bound on the average transmission rate are also presented.
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paper_title: Analysis and Optimization of Resource Control in High-Speed Railway Wireless Networks

paper_content:

This paper considers a joint optimal design of admission control and resource allocation for multimedia services delivery in high-speed railway (HSR) wireless networks. A stochastic network optimization problem is formulated which aims at maximizing the system utility while stabilizing all transmission queues under the average power constraint. By introducing virtual queues, the original problem is equivalently transformed into a queue stability problem, which can be naturally decomposed into three separate subproblems: utility maximization, admission control, and resource allocation. A threshold-based admission control strategy is proposed for the admission control subproblem. And a distributed resource allocation scheme is developed for the mixed-integer resource allocation subproblem with guaranteed global optimality. Then a dynamic admission control and resource allocation algorithm is proposed, which is suitable for distributed implementation. Finally, the performance of the proposed algorithm is evaluated by theoretical analysis and numerical simulations under realistic conditions of HSR wireless networks.
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paper_title: Energy-Efficient Mobile Data Uploading from High-Speed Trains

paper_content:

Recent decades have witnessed the fast development of high-speed railway systems in many countries, which have significantly shortened the travel time between distant cities. Accompanied with this convenience is the challenge for cell phone vendors to provide broadband Internet access for passengers, particularly considering the fast changing channel conditions in high-speed trains and the limited battery of cell phones, which often cannot be re-charged in trains. In this paper, inspired by the unique spatial-temporal characteristics of wireless signals along high-speed railways, we propose a novel energy-efficient scheduling approach for uploading data from cell phones, both with soft deadlines (e.g., documents) and hard deadlines (e.g., video streaming). Our solution effectively predicts the signal strength through its spatial-temporal periodicity in this new application scenario, and smartly adjusts the transmission rate to maximize the overall data transmission rate and yet conserves the energy consumption. Performance evaluation based on realistic railway scenarios and H.264 video traces demonstrate the effectiveness of our solution and its superiority as compared to the existing solutions.
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paper_title: Utility-based resource allocation in high-speed railway wireless networks

paper_content:

In this paper, we investigate the utility-based resource allocation problem at a base station in high-speed railway (HSR) wireless networks, jointly taking into account the power allocation along the time and the packet allocation among services. The problem to maximize the total utility under the average power constraint is formulated as a mixed-integer non-linear programming (MINLP) problem. Through the integer constraint relaxation, the MINLP problem can be simplified into a convex optimization problem. The detailed analysis reveals that the relaxed problem can be equivalently decomposed into power allocation problem along the time and packet allocation problem among services, which can reduce the problem size. When the optimality of the relaxed problem is achieved, the power allocation along the time and the packet allocation along the time for each service are both proportionally fair. Since the integer relaxation causes a non-integer solution not implementable in practice, a greedy algorithm is proposed to obtain a near-optimal integer solution of the MINLP problem. Finally, the performance of the proposed algorithm is analyzed by simulations under realistic conditions for HSR wireless networks.
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paper_title: Resource allocation for high-speed railway downlink MIMO-OFDM system using quantum-behaved particle swarm optimization

paper_content:

Resource allocation problem in high-speed railway wireless communication networks is one of the key issues to improve the efficiency of resource utilization. However, traditional resource allocation methods cannot be directly applied to this special communication system. In this paper, we propose a resource allocation approach for high-speed railway downlink orthogonal frequency-division multiplexing (OFDM) system with multiple-input multiple-output (MIMO) antennas. Sub-carriers, antennas, time slots, and power are jointly considered, which is formulated as a mixed-integer nonlinear programming problem. The effect of the moving speed on Doppler shift is analyzed to calculate the inter-carrier interference power. The objective is to maximize the throughput under the constraint of total transmission power. In order to reduce computational complexity, suboptimal solution to the optimization problem is obtained by quantum-behaved particle swarm optimization. Simulation results show that the proposed resource allocation strategy has a better performance compared with an existing one.
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paper_title: Dynamic Resource Allocation in High Speed Mobile OFDMA System

paper_content:

A novel dynamic resource allocation algorithm is proposed for matching the OFDMA system in high speed mobile environment, which suffers from high inter-carrier interference and large dynamic range of mobile speed for versatile users. With the non-linear optimization, the objective function of the transmission power can be directly mapped with the variables, such as the mobile speed of users, channel state information, modulation and coding schemes etc. Compared with the hitherto resource allocation algorithms in IEEE 802.16e, the proposed scheme has even more comprehensive capability depicting the features for high speed mobile and better performance in BER and QoS guarantee, especially in case the speed is more than 300 km/h.
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paper_title: Performance analysis of high-speed railway communication systems subjected to co-channel interference and channel estimation errors

paper_content:

The performance of high-speed railway wireless communication systems is studied in the presence of co-channel interference and imperfect channel estimation in the uplink. The authors derive exact closed-form expressions for the outage probability and investigate the impact of fading severity. New explicit expressions are derived for both the level crossing rate and average outage duration for illustrating the impact of mobile speed and channel estimation errors on the achievable system performance. Our results are generalised and hence they subsume a range of previously reported results.
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paper_title: Effective Uplink Interference Avoidance Scheme for High-Speed Railway Communications

paper_content:

In this paper, an effective resource allocation mechanism aiming to avoid the uplink interference between the macro cell and the mobile relay (MR) cell is proposed. We firstly formulate this problem as a mixed integer nonlinear programming (MINLP). Such an optimization problem is hard to solve, we therefore propose an alternative heuristic scheme by which the bad resource blocks (BRBs) and suitable RBs are allocated separately between these two subsystems and then the optimal power is determined to maximize the system sum throughput. Implementation details are shown in a practical Long Term Evolution (LTE) system and simulations prove the efficacy of our provided approach.
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paper_title: Resource allocation for OFDMA system under high-speed railway condition

paper_content:

A dynamic resource allocation algorithm is investigated for the orthogonal frequency division multiplexing access (OFMDA) system under the network architecture of High-Speed Railway (HSR). The mobile base station (MBS) on the top of the train forwards the signal received from the base station (BS) on the ground to the user equipments (UE) in the train. Due to the high mobility in the BS-MBS link, the inter-carrier interference (ICI) caused by the Doppler shift may degrade the system performance. In this paper, we aim to combat the influence of the ICI to improve the system capacity by means of the resource allocation, which includes subcarrier allocation, subcarrier pairing and power allocation. Simulation results demonstrate that the proposed resource allocation algorithm can improve the system performance dramatically.
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paper_title: Multidimensional resource allocation strategy for high-speed railway MIMO-OFDM system

paper_content:

With the wide deployment of high-speed railway at more than 300 kilometers per hour, providing various services effectively for users in the train becomes both practical demand and interesting challenge for wireless communication. Resource allocation problem in high-speed railway communication system is one of the key issues to improve the efficiency of resource utilization. In this paper, we propose a multidimensional resource allocation strategy for high-speed railway downlink orthogonal frequency-division multiplexing (OFDM) system with multiple-input multiple-output (MIMO) antennas. Sub-carrier, antenna, time slot, and power are considered jointly, which is modeled as a nonlinear integer programming problem. The effect of the moving speed on inter-carrier interference is analyzed to calculate the transmitted power. The objective is to minimize the total transmitted power while satisfying quality of service requirement of each user. Moreover, optimal and approximate solutions are obtained by linearization and quadratic fitting, respectively. Simulation results have proved that approximate solution has lower total transmitted power than optimal solution while the computation complexity is higher.
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paper_title: Stochastic Delay Analysis for Train Control Services in Next-Generation High-Speed Railway Communications System

paper_content:

The communication delay of train control services has a great impact on the track utilization and speed profile of high-speed trains. This paper undertakes stochastic delay analysis of train control services over a high-speed railway fading channel using stochastic network calculus. The mobility model of high-speed railway communications system is formulated as a semi-Markov process. Accordingly, the instantaneous data rate of the wireless channel is characterized by a semi-Markov modulated process, which takes into account the channel variations due to both large- and small-scale fading effects. The stochastic service curve of high-speed railway communications system is derived based on the semi-Markov modulated process. Based on the analytical approach of stochastic network calculus, the stochastic upper delay bounds of train control services are derived with both the moment generating function method and the complementary cumulative distribution function method. The analytical results of the two methods are compared and validated by simulation.
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paper_title: A QoS-Aware Scheduling Algorithm for High-Speed Railway Communication System

paper_content:

With the rapid development of high-speed railway (HSR), how to provide the passengers with multimedia services has attracted increasing attention. A key issue is to develop an effective scheduling algorithm for multiple services with different quality of service (QoS) requirements. In this paper, we investigate the downlink service scheduling problem in HSR network taking account of end-to-end deadline constraints and successfully packet delivery ratio requirements. Firstly, by exploiting the deterministic high-speed train trajectory, we present a time-distance mapping in order to obtain the highly dynamic link capacity effectively. Next, a novel service model is developed for deadline constrained services with delivery ratio requirements, which enables us to turn the delivery ratio requirement into a single queue stability problem. Based on the Lyapunov drift, the optimal scheduling problem is formulated and the corresponding scheduling service algorithm is proposed by stochastic network optimization approach. Simulation results show that the proposed algorithm outperforms the conventional schemes in terms of QoS requirements.
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paper_title: Delay-Aware Online Service Scheduling in High-Speed Railway Communication Systems

paper_content:

We investigate the downlink service scheduling problem in relay-assisted high-speed railway (HSR) communication systems, taking into account stochastic packet arrivals and quality-of-service (QoS) requirements. The scheduling problem is formulated as an infinite-horizon average cost constrained Markov decision process (MDP), where the scheduling actions depend on the channel state information (CSI) and the queue state information (QSI). Our objective is to find a policy that minimizes the average end-to-end delay through scheduling actions under the service delivery ratio constraints. To address the challenge of centralized control and high complexity of traditional MDP approaches, we propose a distributed online scheduling algorithm based on approximate MDP and stochastic learning, where the scheduling policy is a function of the local CSI and QSI only. Numerical experiments are carried out to show the performance of the proposed algorithm.
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paper_title: Goodput performance improvement in high-speed railway communication systems: A link adaptation approach

paper_content:

Providing reliable and quality of service (QoS) guarantee service is basic requirement for communication system. However, the intrinsic features of high-speed railway communication (HSRC), such as serious channel distortion, lack of perfect channel state information (CSI), severe Doppler effect, and sensitive to algorithm computation complexity, make this requirement hard to be met. In this paper, considering the intrinsic features of HSRC, a novel link adaptation scheme is proposed to improve HSRC systems goodput while guaranteeing prescribed error rate target. We formulate the link adaptation as a partially observable Markov decision process (POMDP). With this stochastic optimization formulation, the proposed link adaptation scheme can tackle the imperfect CSI and has very low computation complexity. In addition, cross-layer design methodology is exploited, where diversity/multiplexing gain selection in physical layer and frame size in link layer are considered together to improve system goodput. Simulation results demonstrate the effectiveness of the proposed link adaptation scheme.
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paper_title: Delay-aware fair scheduling in relay-assisted high-speed railway networks

paper_content:

In this paper, we consider delay-aware fair downlink scheduling with heterogeneous packet arrivals and delay requirements for a relay-assisted high-speed railway (HSR) network. Data packets from multi-users requests are delivered via the two-hop network architecture to achieve a high data transmission rate instead of direct transmission. Our objective is to find a policy that minimizes the average weighted end-to-end (e2e) delay through packet scheduling under the user fairness constraint. The policy is a two-dimensional vector with the scheduling indexes in the two-hop link as its elements. We model the problem as an infinite-horizon average reward constrained Markov decision problem (CMDP) when the data arrival process and the channel process are Markovian. To address the challenge of huge complexity of MDP problems, we propose a heuristic and low-complexity algorithm. Simulation results show that the proposed algorithm outperforms the other existing schemes in terms of average weighted delay performance and user fairness.
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paper_title: Radio Resource Allocation for OFDMA Systems in High Speed Environments

paper_content:

In high speed train (HST) system, real-time multimedia entertainments are very important applications in which a data stream often contains packets with different quality of service requirements. For example, video stream encoded with scalability contains the base layer packets with high quality (HQ) bit error rate (BER) requirement and enhancement layers' packets with low quality (LQ) BER requirement. When a conventional allocation approach, which only considers one BER constraint for one data stream, is applied to orthogonal frequency division multiple access (OFDMA) systems, the BER constraint will be the strictest one among multiple requirements from different types of packets, which leads to inefficient allocation when each data stream has multiple BER requirements. This paper aims to develop novel resource allocation approach by considering multiple BER requirements for different types of packets in one data stream. In order to not only simplify the resource allocation, but also to compensate for the channel estimation error caused by Doppler shift in the HST environment, a proper number of contiguous subcarriers are grouped into chunks and spectrum is allocated chunk by chunk. Simulation results show that the developed resource allocation scheme outperforms the conventional scheme, particularly when the BER ratio of HQ packets to LQ packets is larger than one. Furthermore, in order to reduce the complexity of resource allocation further, an empirical allocation scheme is proposed to allocate better chunks to HQ packets. It is shown that the performance of the empirical allocation scheme is quite close to that of the optimal scheme.
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paper_title: Optimal Scheduling for Wireless On-Demand Data Packet Delivery to High-Speed Trains

paper_content:

In this paper, we consider a cellular/infostation integrated network that supports on-demand data service delivery over a wireless link to users in a high-speed train. For the requests with different lifetimes and prices that they are willing to pay, we develop the optimal packet schedule that aims at earning the maximum revenue. To this end, we formulate the problem as an integer linear program (ILP). The problem cannot be solved efficiently by existing ILP solvers with guaranteed polynomial-time complexity in the worst case. By exploring the special structure of the formulated ILP, we propose a novel Checker algorithm and prove that this algorithm is guaranteed to find the offline optimal schedule in polynomial time. Based on the relevant insights, we further develop a class of online Checker algorithms that require only causal knowledge of service demands and wireless channel capacities. It is established that these online algorithms have a worst-case competitive ratio of 1/2, i.e., total revenue earned by them is at least half as much as the revenue earned by an offline optimal schedule that knows the complete a priori knowledge of future requests and channel conditions. Simulation results are provided to demonstrate the merit of the proposed algorithms.
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paper_title: Efficient On-Demand Data Service Delivery to High-Speed Trains in Cellular/Infostation Integrated Networks

paper_content:

In this paper, we investigate on-demand data services for high-speed trains via a cellular/infostation integrated network. Service requests and acknowledgements are sent through the cellular network to a content server, while data delivery is achieved via trackside infostations. The optimal resource allocation problem is formulated by taking account of the intermittent network connectivity and multi-service demands. In order to achieve efficient resource allocation with low computational complexity, the original problem is transformed into a single-machine preemptive scheduling problem based on a time-capacity mapping. As the service demands are not known a priori, an online resource allocation algorithm based on Smith ratio and exponential capacity is proposed. The performance bound of the online algorithm is characterized based on the theory of sequencing and scheduling. If the link from the backbone network to an infostation is a bottleneck, a service pre-downloading algorithm is also proposed to facilitate the resource allocation. The performance of the proposed algorithms is evaluated based on a real high-speed train schedule. Compared with the existing approaches, our proposed algorithms can significantly improve the quality of on-demand data service provisioning over the trip of a train.
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paper_title: Quality of Service Improvement for High-Speed Railway Communications

paper_content:

With the fast development of high-speed railways, a call for fulfilling the notion of communication at"anytime, anywhere"for high-speed train passengers in the Train Operating Control System is on the way. In order to make a realization of that, new railway wireless communication networks are needed. The most promising one is the Long Term Evolution for Railway which will provide broadband access, fast handover, and reliable communication for high mobility users. However, with the increase of speed, the system is subjected to high bit error rate, Doppler frequency shift and handover failure just like other system does. This paper is trying to solve these problems by employing MIMO technique. Specifically, the goal is to provide higher data rate, higher reliability, less delay, and other relative quality of services for passengers. MIMO performance analysis, resource allocation, and access control for handover and various services in a two-hop model are proposed in this paper. Analytical results and simulation results show that the proposed model and schemes perform well in improving the system performances.
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paper_title: Analysis and Optimization of Resource Control in High-Speed Railway Wireless Networks

paper_content:

This paper considers a joint optimal design of admission control and resource allocation for multimedia services delivery in high-speed railway (HSR) wireless networks. A stochastic network optimization problem is formulated which aims at maximizing the system utility while stabilizing all transmission queues under the average power constraint. By introducing virtual queues, the original problem is equivalently transformed into a queue stability problem, which can be naturally decomposed into three separate subproblems: utility maximization, admission control, and resource allocation. A threshold-based admission control strategy is proposed for the admission control subproblem. And a distributed resource allocation scheme is developed for the mixed-integer resource allocation subproblem with guaranteed global optimality. Then a dynamic admission control and resource allocation algorithm is proposed, which is suitable for distributed implementation. Finally, the performance of the proposed algorithm is evaluated by theoretical analysis and numerical simulations under realistic conditions of HSR wireless networks.
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paper_title: A resource allocation scheme for VoIP traffic under high speed train scenario

paper_content:

This paper investigates the resource allocation schemes for Voice over Internet Protocol (VoIP) traffic under high speed train scenario, in which 2-state VoIP traffic model based on Markov chain is considered. Unlike the full-buffer traffic, in which the transmitter buffer is always full of data to be transmitted, VoIP traffic can be characterized by small packets in regular intervals with tight delay constraints. Considering this, two different resource allocation schemes are discussed in this paper. One is an existing scheme adopting fixed Modulation and Coding scheme (MCS) without packet-bundling, which is commonly used for VoIP scheduling in traditional cellular networks; the other one is our proposed scheme, which uses adaptive MCS with packet-bundling and is suitable for broadband wireless communication under high-speed train scenario. System-level simulation is conducted and the simulation results show that the proposed scheme outperforms the conventional resource allocation scheme in terms of the VoIP outage probability and VoIP capacity under high-speed train scenario.
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paper_title: Position-Based Limited Feedback Scheme for Railway MU-MIMO Systems

paper_content:

In future railway communications, the system architecture is highly likely to be based on the mobile relay structure. However, during the transition period, onboard passenger equipment can only directly connect to wayside public mobile networks to get wireless services. As an efficient technology to increase the capacity widely used in Long-Term Evolution (LTE) public mobile networks, multiuser multiple input–multiple output (MU-MIMO) requires channel state information (CSI) of users at base stations to suppress interuser interference, which poses a bandwidth burden on feedback links. Thus, how to reduce the MU-MIMO feedback load becomes an urgent problem. In railway scenarios, onboard passenger equipment of a user set almost has the same signal-to-noise ratio (SNR), which provides a new way to reduce the MU-MIMO feedback overheads. Accordingly, we propose a position-based limited feedback scheme for railway MU-MIMO systems, in which dedicated feedback resource positions are preassigned to codebook vectors. A resource position where users feed back channel quality indicators (CQIs) indicates a special codebook vector. Then, overheads due to precoding matrix index (PMIs) are saved. Even if bandwidth resources assigned to feedback positions may be insufficient to supply every user with a feedback chance, it still has little impact on the total capacity for whether the user with the largest CQI in an active user set is selected in highly populated railway scenarios. Moreover, a novel performance criterion called feedback efficiency is proposed. Simulation results demonstrate that the proposed scheme can achieve higher feedback efficiency compared with the conventional scheme.
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paper_title: Radio environment map-based cognitive Doppler spread compensation algorithms for high-speed rail broadband mobile communications

paper_content:

Recently, there is an increasing yet challenging demand on broadband mobile communications for high-speed trains. In this article, cognitive Doppler spread compensation algorithms are proposed for high-speed rail broadband mobile communications, which make use of the dedicated radio environment map (REM) for railway to compensate the time-varying Doppler spread. The dedicated REM for high-speed rail can be viewed as a spatial-temporal database consisting of the radio channel parameters along a given railway. The performance of the proposed Doppler spread compensation algorithms are evaluated with a typical OFDM-based broadband mobile system. Simulation results show that the link-level performance of high-speed rail broadband mobile communications can be improved significantly due to the REM-enabled radio channel condition awareness and the cognitive Doppler spread compensation algorithms. The REM-based cognitive radio approach presents a new paradigm for systems design of high-speed rail broadband mobile communications.
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paper_title: Position-assisted fast handover schemes for LTE-advanced network under high mobility scenarios

paper_content:

Two position-assisted fast handover schemes, scheme A and scheme B, for LTE-A system under very high mobility scenarios, are proposed, together with their performance evaluation. Scheme A is designed to reduce handover delay by making handover preparation before handover starts. Scheme B aims at reducing unnecessary handovers and improving handover success rate, by calculating the geographically best target handover cell, which makes it easier for mobile terminals to access the target cell. A system level simulation is conducted to evaluate the performance of these two schemes. It is shown that, scheme A could reduce inter-site handover delay by about 50 ms, while scheme B could cut down nearly 50% of all handovers when time-to-trigger (TTT) is 0 ms. Besides, as TTT gets larger, Scheme B has much better success rate.
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paper_title: Energy-Efficient Mobile Data Uploading from High-Speed Trains

paper_content:

Recent decades have witnessed the fast development of high-speed railway systems in many countries, which have significantly shortened the travel time between distant cities. Accompanied with this convenience is the challenge for cell phone vendors to provide broadband Internet access for passengers, particularly considering the fast changing channel conditions in high-speed trains and the limited battery of cell phones, which often cannot be re-charged in trains. In this paper, inspired by the unique spatial-temporal characteristics of wireless signals along high-speed railways, we propose a novel energy-efficient scheduling approach for uploading data from cell phones, both with soft deadlines (e.g., documents) and hard deadlines (e.g., video streaming). Our solution effectively predicts the signal strength through its spatial-temporal periodicity in this new application scenario, and smartly adjusts the transmission rate to maximize the overall data transmission rate and yet conserves the energy consumption. Performance evaluation based on realistic railway scenarios and H.264 video traces demonstrate the effectiveness of our solution and its superiority as compared to the existing solutions.
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paper_title: Location information-assisted opportunistic beamforming in LTE system for high-speed railway

paper_content:

Communication systems of high-speed railway have inherent disadvantages and advantages. The estimation error of direction-of-arrival (DOA) of desired users caused by channel feedback delay and high moving speed make the common beamforming technique of smart antennas work abnormally. Instead, the opportunistic beamforming (OBF) with dumb antennas which does not need channel feedback is proper for high-speed railway. As the system has linear topology, regular movement as well as predictable location and speed information, the OBF can be improved to adapt to this scenario. In this article, conventional OBF is first introduced to the communication systems of high-speed railway. By multiplying random complex on each transmit antenna, the channel fluctuation dynamic range is extended so that multiuser diversity can be exploited. And then location information is employed to assist the conventional one. Communication systems in high-speed railway have the advantage of predictable location and speed information. The improved OBF can perform closer to the performance of coherent beamforming. Numerical analysis and simulation results show that both two algorithms can improve the system performance significantly.
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paper_title: Position-Based Modeling for Wireless Channel on High-Speed Railway under a Viaduct at 2.35 GHz

paper_content:

This paper presents a novel and practical study on the position-based radio propagation channel for High-Speed Railway by performing extensive measurements at 2.35 GHz in China. The specification on the path loss model is developed. In particular, small scale fading properties such as K-factor, Doppler frequency feature and time delay spread are parameterized, which show dynamic variances depending on the train location and the transceiver separation. Finally, the statistical position-based channel models are firstly established to characterize the High-Speed Railway channel, which significantly promotes the evaluation and verification of wireless communications in relative scenarios.
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paper_title: Cross-Layer Design for Video Transmissions in Metro Passenger Information Systems

paper_content:

In metro passenger information systems (PISs), frequent train handoffs can cause severe video distortion. In this paper, we take an integrated design approach to jointly optimize application-layer parameters and handoff decisions to improve video transmission quality over PISs. We present a train-ground video communication network based on fountain codes and IEEE 802.11p for metro PISs. The metro PIS channel is modeled as a finite-sate Markov chain, and the channel-state transition probability matrix is calculated from the data that were measured in real field tests. The handoff decision and application-layer parameters adaptation problem is formulated as a stochastic semi-Markov decision process (SMDP). Minimizing the end-to-end total video distortion is the objective in our model. Simulation results show that the proposed SMDP-based optimization algorithm can significantly improve the end-to-end video transmission quality in metro PISs.
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paper_title: A Survey on High Mobility Wireless Communications: Challenges, Opportunities and Solutions

paper_content:

Providing reliable broadband wireless communications in high mobility environments, such as high-speed railway systems, remains one of the main challenges faced by the development of the next generation wireless systems. This paper provides a systematic review of high mobility communications. We first summarize a list of key challenges and opportunities in high mobility communication systems, then provide comprehensive reviews of techniques that can address these challenges and utilize the unique opportunities. The review covers a wide spectrum of communication operations, including the accurate modeling of high mobility channels, the transceiver structures that can exploit the properties of high mobility environments, the signal processing techniques that can harvest the benefits (e.g., Doppler diversity) and mitigate the impairments (e.g., carrier frequency offset, intercarrier interference, channel estimation errors) in high mobility systems, and the mobility management and network architectures that are designed specifically for high mobility systems. The survey focuses primarily on physical layer operations, which are affected the most by the mobile environment, with some additional discussions on higher layer operations, such as handover management and control-plane/user-plane decoupling, which are essential to high mobility operations. Future research directions on high mobility communications are summarized at the end of this paper.
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paper_title: Analysis and Optimization of Resource Control in High-Speed Railway Wireless Networks

paper_content:

This paper considers a joint optimal design of admission control and resource allocation for multimedia services delivery in high-speed railway (HSR) wireless networks. A stochastic network optimization problem is formulated which aims at maximizing the system utility while stabilizing all transmission queues under the average power constraint. By introducing virtual queues, the original problem is equivalently transformed into a queue stability problem, which can be naturally decomposed into three separate subproblems: utility maximization, admission control, and resource allocation. A threshold-based admission control strategy is proposed for the admission control subproblem. And a distributed resource allocation scheme is developed for the mixed-integer resource allocation subproblem with guaranteed global optimality. Then a dynamic admission control and resource allocation algorithm is proposed, which is suitable for distributed implementation. Finally, the performance of the proposed algorithm is evaluated by theoretical analysis and numerical simulations under realistic conditions of HSR wireless networks.
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paper_title: Dynamic Green Communication Strategy for Railway Cellular Network

paper_content:

Green communication is ecological, economic and essential but seldom discussed in railway cellular network because safety is always the focus and has the highest priority. By analyzing the train scheduling and railway communication characteristics, we find that railway cellular network, especially for radio base station, has a big potentiality for energy saving to reduce carbon footprint without interrupting the safety rules. In this paper, we propose a simple train detection strategy by HANDOVER procedure under 3GPP specification. To implement this strategy under railway system model, we define cells' state along the railway. Then the cells are allocated to different orthogonal groups, which form a series of clusters identified by Finite states. A flexible and effective solution is designed based on mealy-type finite state machine to transit every cell between energy saving mode and full running mode. Our evaluation results show that a significant ratio, approximately up to 33% energy can be saved, by employing the configuration data for an actual high- speed railway line in China.
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paper_title: Efficient On-Demand Data Service Delivery to High-Speed Trains in Cellular/Infostation Integrated Networks

paper_content:

In this paper, we investigate on-demand data services for high-speed trains via a cellular/infostation integrated network. Service requests and acknowledgements are sent through the cellular network to a content server, while data delivery is achieved via trackside infostations. The optimal resource allocation problem is formulated by taking account of the intermittent network connectivity and multi-service demands. In order to achieve efficient resource allocation with low computational complexity, the original problem is transformed into a single-machine preemptive scheduling problem based on a time-capacity mapping. As the service demands are not known a priori, an online resource allocation algorithm based on Smith ratio and exponential capacity is proposed. The performance bound of the online algorithm is characterized based on the theory of sequencing and scheduling. If the link from the backbone network to an infostation is a bottleneck, a service pre-downloading algorithm is also proposed to facilitate the resource allocation. The performance of the proposed algorithms is evaluated based on a real high-speed train schedule. Compared with the existing approaches, our proposed algorithms can significantly improve the quality of on-demand data service provisioning over the trip of a train.
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paper_title: Social Network Services for Rail Traffic Applications

paper_content:

With the rapid development of high-speed railway, subway, city railway, and intercity rail, how to ensure the reliability, safety, and comfort of such rail traffic transportation systems becomes the focus. Meanwhile, the social network service (SNS) is advancing so fast all over the world. How to combine the characteristics of rail traffic transportation systems with that of the social networks, which enable them to play an important role in the rail traffic operations, will become one of the core problems in the future development of intelligent rail traffic transportation systems. Based on the business requirements, the reliable transmission of information, and the characteristics of the rail traffic transportation systems, this article proposes a new concept of "dedicated social network" whose information are exchanged within the internal intranet. A novel social network architecture for rail traffic transportation system is proposed, including the SNS Management Center, a dedicated social network for internal information exchanges among the drivers, the dispatchers, and the train control center, the SNS for the information exchanges among the train marshals, crews, and passengers. The proposed framework attempts to exploit social networks in an active manner in the field of rail traffic transportation systems to make the system safer, more secure, reliable, comfortable, and humane.
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paper_title: Energy-Efficient Mobile Data Uploading from High-Speed Trains

paper_content:

Recent decades have witnessed the fast development of high-speed railway systems in many countries, which have significantly shortened the travel time between distant cities. Accompanied with this convenience is the challenge for cell phone vendors to provide broadband Internet access for passengers, particularly considering the fast changing channel conditions in high-speed trains and the limited battery of cell phones, which often cannot be re-charged in trains. In this paper, inspired by the unique spatial-temporal characteristics of wireless signals along high-speed railways, we propose a novel energy-efficient scheduling approach for uploading data from cell phones, both with soft deadlines (e.g., documents) and hard deadlines (e.g., video streaming). Our solution effectively predicts the signal strength through its spatial-temporal periodicity in this new application scenario, and smartly adjusts the transmission rate to maximize the overall data transmission rate and yet conserves the energy consumption. Performance evaluation based on realistic railway scenarios and H.264 video traces demonstrate the effectiveness of our solution and its superiority as compared to the existing solutions.
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paper_title: A Mobile Proxy Architecture for Video Services Over High-Speed Rail Environments in LTE-A Networks

paper_content:

With the rapid developments in wireless communication technology, people access Internet applications anytime and anywhere. Recently, academics and industry researchers have been paying increasing attention to the video streaming services over high-speed rail environments. For providing the quality of service of video streaming, we present a novel mobile proxy architecture for improving the system performance over high-speed trains in Long Term Evolution–Advanced networks. The mobile proxy not only saves the wireless bandwidth consumption between the base station and the high-speed train but also reduces the starting delay time of the video. Moreover, we propose a score-based replacement scheme in the memory management of the proxy server based on the feature of the video. Our simulation results demonstrate that the proposed scheme provides a better performance than other existing cache management schemes.
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paper_title: WDM RoF-MMW and linearly located distributed antenna system for future high-speed railway communications

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In this article, we propose dual-hop network architecture capable of providing high-speed communications to high-speed trains (HSTs). The system uses a seamless fiber-millimeterwave system for backhaul transmission from a central station to antennas on trains, and a highspeed in-train Wi-Fi network. The system can be combined with signal processing and network control technologies to compensate for interference and the Doppler effect, and to reduce the number of handovers. It can realize seamless connectivity between the inside and outside of trains to avoid penetration loss and help organize the in-train network optimally to increase coverage and data rate. We present and discuss the possible network architecture and technologies that can help realize the proposed network. We also present a proof-of-concept demonstration on a high-performance seamless fiber- MMW system that can be applied for applications in backhaul networks. The proposed network can be an attractive solution to provide broadband services such as video on demand and high-speed mobile signals to users on HSTs.
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paper_title: Challenges Toward Wireless Communications for High-Speed Railway

paper_content:

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.
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paper_title: Control and data signaling decoupled architecture for railway wireless networks

paper_content:

Current implementations of narrowband Global System for Mobile Communications for railway systems are facing significant challenges in meeting the emerging massive capacity demands of passenger services. To extend the capacity, this article presents a control and data signaling decoupled architecture, namely, C/U-plane decoupled architecture for railway wireless networks, in which the relatively important C-plane of passenger services is kept on high-quality lower frequency bands to handle mobility, while the corresponding U-plane is moved to higher frequency bands to gain broader spectra. In this railway wireless network with C/U-plane decoupled architecture, the U-plane and C-plane handovers are also physically decoupled. To achieve the seamless and soft U-plane handover, we introduce a handover scheme based on coordinated multi-point transmission and reception and bi-casting. In addition, channel mappings and physical layer frames are redesigned to facilitate the design. Our study has demonstrated that by decoupling the C/U planes, the network performance is greatly enhanced, leading to a more effective way to provide high speed communications for railway systems.
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paper_title: Future railway services-oriented mobile communications network

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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.
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paper_title: On the Uplink Capacity of High Speed Railway Communications with Massive MIMO Systems

paper_content:

This paper studies the performance and design of high speed railway communications that employ massive MIMO systems. The users onboard the train communicate with the BS by using antennas mounted on top of the train as gateways. Two antenna layouts on the train are considered, one has co-located antennas (CA) at the center of the train, and the other has distributed antennas (DA) uniformly placed along the train. The analytical uplink ergodic capacities for both layouts are derived by averaging over all the locations in a cell. For the CA layout, the average uplink cell capacity is concave in the number of antennas on the train, and the optimum number of antennas on the train is identified by maximizing the average uplink capacity. For the DA layout, the average cell capacity is upper and lower bounded by two concave functions, which are then used to find a sub-optimum value of the number of antennas on the train. Both analytical and numerical results demonstrate that the CA layout has a higher average cell capacity while the DA layout has less variations in terms of uplink capacity at different locations inside a cell.
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paper_title: Uplink Design of Millimeter-Wave Mobile Communication Systems for High-Speed Trains

paper_content:

Passengers in a high-speed train (350 km/h) experience very poor multimedia services and discontinuous connections due to the much more and simultaneous handovers in the cellular networks. To handle these problems, a millimeter-wave mobile communication system for high-speed trains was introduced and its downlink structure was presented. This paper proposes the uplink structure appropriate to the millimeter-wave mobile communication system. It also describes the frame structure, the multiple access method, and the pilot deployment of the uplink channel. Especially, the uplink pilot was designed to solve the Doppler problem in order to achieve a higher spectrum efficiency. The simulation results of the uplink channel show the spectral efficiency of 4.18 bps/Hz even in 400 km/h under the Rician fading channel conditions.
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Title: A Survey on High-Speed Railway Communications: A Radio Resource Management Perspective

Section 1: Introduction
Description 1: Briefly introduce the necessity and evolution of high-speed railway communications, focusing on GSM-R and LTE-R, and their applications and limitations.

Section 2: Heterogeneous Network Architecture
Description 2: Describe the heterogeneous network architecture for high-speed railway (HSR) communications, including the aggregation network, access network, and train network.

Section 3: Radio Resource Management
Description 3: Provide an overview of Radio Resource Management (RRM) in HSR communications, discussing its importance and the four key elements: admission control, mobility management, power control, and resource allocation.

Section 4: HSR Channel Characterization
Description 4: Analyze the unique characteristics of the HSR wireless channel, such as multiple scenarios, line-of-sight (LOS) dominance, and Doppler shift and their effects on RRM design.

Section 5: Admission Control
Description 5: Survey existing admission control schemes in HSR communications, explaining level-based, handover-based, and priority-based admission control.

Section 6: Mobility Management
Description 6: Discuss the strategies for mobility management in HSR networks, focusing on location management, handover management, and group mobility.

Section 7: Power Control
Description 7: Explore power control techniques in HSR communications, examining different power allocation schemes and their effectiveness under various conditions.

Section 8: Resource Allocation
Description 8: Examine various resource allocation schemes in HSR communications, including interference-aware, QoS-aware, and cross-layer dynamic resource allocation.

Section 9: Challenges and Open Issues
Description 9: Identify and discuss the challenges and open research issues in RRM for HSR communications, emphasizing location-aware RRM, cross-layer-based RRM, energy-efficient RRM, robust RRM, and advanced RRM for 5G communications.

Section 10: Conclusions
Description 10: Summarize the key points from the survey, highlighting the importance of effective RRM in improving the performance of HSR wireless communications and addressing future research directions.