Communication Based Train Control Research Articles

LTE-U based Train to Train Communication System in CBTC: System Desin and Reliability Analysis

Communication-Based Train Control (CBTC) system is a critical signal system to ensure rail transit’s safe operation. Compared with the train-ground CBTC system, the train control system based on train-to-train (T2T) communication has the advantages of fast response speed, simple structure, and low operating cost. As the core part of the train control system based on T2T communication, the reliability of the data communication system (DCS) is of great significance to ensure the train’s safe and efficient operation. According to the T2T communication system requirements, this paper adopts Long-Term Evolution-Unlicensed (LTE-U) technology to design the DCS structure and establishes the reliability model of the communication system based on Deterministic and Stochastic Petri Nets (DSPN). Based on testing the real line’s communication performance parameters, the DSPN model is simulated and solved by π -tool, and the reliability index of the system is obtained. The research results show that the LTE-U-based T2T communication system designed in this paper meets the train control system’s needs for communication transmission. This paper’s reliability evaluation method can complete the reliability modeling of train control DCS based on T2T communication. The research in this paper will provide a strong practical and theoretical basis for the design and optimization of train control DCS based on T2T communication.

Failure Mode and Effect Analysis for Cyber-Physical Systems

Cyber-Physical Systems (CPS) are a prominent component of the modern digital transformation, which combines the dynamics of the physical processes with those of software and networks. Critical infrastructures have built-in CPS, and assessing its risk is crucial to avoid significant losses, both economic and social. As CPS are increasingly attached to the world’s main industries, these systems’ criticality depends not only on software efficiency and availability but also on cyber-security awareness. Given this, and because Failure Mode and Effect Analysis (FMEA) is one of the most effective methods to assess critical infrastructures’ risk, in this paper, we show how this method performs in the analysis of CPS threats, also exposing the main drawbacks concerning CPS risk assessment. We first propose a risk prevention analysis to the Communications-Based Train Control (CBTC) system, which involves exploiting cyber vulnerabilities, and we introduce a novel approach to the failure modes’ Risk Priority Number (RPN) estimation. We also propose how to adapt the FMEA method to the requirement of CPS risk evaluation. We applied the proposed procedure to the CBTC system use case since it is a CPS with a substantial cyber component and network data transfer.

A Cross-Layer Defense Scheme for Edge Intelligence-Enabled CBTC Systems Against MitM Attacks

While communication-based train control (CBTC) systems play a crucial role in the efficient and reliable operation of urban rail transits, its high penetration level of communication networks opens doors to Man-in-the-Middle (MitM) attacks. Current researches regarding MitM attacks do not consider the characteristics of CBTC systems. Particularly, the limited computing capability of the on-board computers prevents the direct implementation of most existing intrusion detection and defense algorithms against the MitM attack. In order to tackle this dilemma, in this article, we first introduce edge intelligence (EI) into CBTC systems to enhance the computing capability of the system. A cross-layer defense scheme, which includes the detection and defense stages, are proposed next. For the cross-layer detection stage, we propose a Long Short-Term Memory (LSTM) and Support Vector Machine (SVM) based detection method to combine the detection probability calculated from the train control parameter sequence and operation log files. For the cross-layer defense stage, we construct a Bayesian game based defense model to derive the optimal defense policy against MitM attacks. To further improve the accuracy of the defense scheme as well as optimize the communication resource allocation scheme, we propose an optimal communication resource allocation scheme based on the Asynchronous Advantage Actor-Critic (A3C) algorithm at last. Extensive simulation results show that the proposed scheme achieves excellent performance in defending against MitM attacks.

A Reinforcement Learning Empowered Cooperative Control Approach for IIoT-Based Virtually Coupled Train Sets

Virtually coupled train sets (VCTS) have been proposed to increase the transportation capacity and the flexibility of railway organization. Due to the lack of reliable wireless communications and accurate perceptual information, the promotion of VCTS was challenged. With the development of industrial Internet of Things (IIoT), an IIoT-based VCTS is built in the article based on the popular communication-based train control architecture. Considering the dynamic and complex operation environment, it is difficult to achieve the efficient cooperative control of VCTS. The reason is that the traditional method is frequently trapped into a local optimization. To resolve the problem, we apply reinforcement learning (RL) to obtain an optimal policy for the IIoT-based VCTS, where the traditional artificial potential field (APF) is taken to develop the reward function. RL can thus search the global optimal policy, whereas APF can help RL to reduce the computation complexity. This can substantially increase the efficiency of the proposed approach. Simulation results confirmed that the proposed RL-based cooperative control approach would bring excellent performance in the IIoT-based VCTS.

An Extended Object-Oriented Petri Net Model for Vulnerability Evaluation of Communication-Based Train Control System

Communication-based train control systems (CBTCs) have been widely used as crucial systems in urban rail transit networks. CBTCs typically utizes different levels of symmetry structure according to different geographic deployments. While, in practice, CBTCs crashes have destroyed the transportation systems of the whole city level for many times. Based on the extended object-oriented Petri net (EOOPN), this paper proposes a vulnerability model and an evaluation procedure, which are capable of considering the vulnerability factors in both inner system level and equipment level. On the system level, it establishes a complex dynamic communication structure model among the distributed subsystems, while on the equipment level, it details the equipment changing state during train operation. The searching algorithm of EOOPN depicts possible failed paths of CBTCs via the token transition among train¬–ground communication EOOPN subnets. The vulnerability calculation is applied to the metro company’s in situ CBTCs to illustrate the effectiveness of the approach.

Performance Analysis of DCF- Two Way Handshake vs RTS/CTS During Train-Trackside Communication in CBTC based on WLAN802.11b

Background:Wireless Local Area Network (WLAN) is used primarily in CBTC because of easy availability of commercial WLAN equipment. In present scenario, WLAN Medium Access Control (MAC) protocol is a well-known protocol which is used to satisfy real-time traffic and delay- sensitive applications. The bidirectional train-trackside communication is the fundamental key of train control in CBTC.Methods:DCF describes two basic techniques used for packet transmission: First technique is a Two Way Handshake (TWH) mechanism and another is Four Way Handshake (FWH) mechanisms. RTS/CTS FWH protocol specified by IEEE802.11b is introduced to rectify the Hidden Node Problem (HNP) encounters in TWH protocol. That is why the TWH mechanism of DCF technique suffers from higher average packet delay time when this protocol is applied to CBTC. DCF- Four Way Handshake (FWH), Request To Send (RTS) and Clear To Send (CTS) delay model is proposed to develop Communication Based Train Control (CBTC) system.Results:FWH is applied in CBTC to overcome the packet delay and throughput limitations of Two Way Handshake (TWH) mechanism of distributed coordination function (DCF) based technique. An experiment is designed to simulate and compare the performance of RTS/CTS delay model against TWH mechanism of DCF.Conclusion:It was found that the Average packet delay is slightly higher and throughput is lesser in RTS/CTS in comparison to TWH method. By comparing the performance of these two medium access mechanism in CBTC it was found that for multiple retransmissions with various data rates the RTS/CTS model had better packet delay time than TWH.

Cross-Layer Defense Methods for Jamming-Resistant CBTC Systems

Communication-based Train Control (CBTC) systems are the burgeoning directions for developing future train control systems. With the adoption of wireless communication and network techniques, train control systems are more vulnerable to cyber-attacks. Notably, the jamming attacks, aiming at the handoff process that is the weakest part of train ground communication systems, will cause long disruption of communication. It will have a severe impact on train control operation efficiency. Current research regarding industry control system security is hard to model the impact of the jamming attacks on the train control system quantitatively, and current countermeasure schemes against jamming attacks are not designed for the operating mechanism of train control systems. This paper first builds the train control security state transition probability model under jamming attacks. A cross-layer defense scheme is then proposed from the aspect of the physical layer, the cyber layer and the management layer. In the physical layer, this paper designs a model prediction control algorithm to track dynamic target signals, in the hopes of eventually tracking the dynamic target quickly and smoothly. In the cyber layer, a multi-stage and zero-sum stochastic game model is built for the channel selection for the attack and the defense, whereby the channel selection randomized policy will be obtained. In the management layer, a dynamic train travel speed profile generation algorithm is proposed to mitigate the jamming attacks’ impact on train control systems. Extensive simulation results are shown that jamming attack impact on CBTC can be mitigated effectively with our proposed cross-layer defense scheme.

Applying Safety Concepts and Principles in Vital Controller Design

A vital controller is safety critical and its failures, if not mitigated in time, can contribute to hazards in the application system. With electronics advancing and automation increasing, the expanding complexity of a vital controller creates challenges in designing it and assessing its safety integrity level. Typically, traditional safety engineering approaches are not effective for providing systematic guidance to design vital controllers and also not cost efficient for justifying their safety integrity. Through practice on developing multiple Communications-Based Train Control systems, we have identified an approach to using a set of safety concepts as guidance for both safety critical controller design and its safety integrity assessment. These safety concepts are categorized as intrinsic fail-safe, reactive fail-safe, and composite fail-safe. An effective combination of them is applying the composite fail-safe concept in checked redundancy techniques for designing the architecture of a controller, the reactive safety concept for identifying self-testing and monitoring mechanisms in each checked redundant channel, and the intrinsic fail-safe concept for ensuring safe interfaces to other controllers and controlled devices. This paper presents the approach for using these safety concepts and discusses their application principles and verification factors for achieving high safety integrity level of a controller.

Functional safety verification of train control procedure in train-centric CBTC by colored petri net

Communication-based Train Control (CBTC) system is a widely-used signaling system. There is an increasing demand for innovating the traditional ground-centric architecture. With the application of train-train communication, object control and other advanced techniques, Train-centric CBTC (TcCBTC) system is expected to be the most promising tendency of train control system. The safe tracking interval would be reduced as well as the life-cycle costs. Formal methods play an essential role in the development of safety-critical systems, which provides an early integration of the verifiable design process. In the paper, the architecture design of TcCBTC is first analyzed. The official system specification of TcCBTC has not issued, so it takes efforts to perform the systematic summarization of the functional requirements. Secondly, we propose an integrated framework that combines the Colored Petri Net (CPN) models with the functional safety verification of the underlying systems. Functional safety depends on the logic accuracy and is a part of overall safety. The framework also specifies what kinds of functions, behaviors or properties need to be verified. The train control procedure of TcCBTC is regarded as the link among new functional modules, thus it is chosen as the modelling content. Thirdly, the scenarios and the color sets are prepared. Models are established with the novel design thought from top to bottom. Simulation and testing are implemented during the model establishment to discover the apparent errors. Lastly, the model checking by state space is performed. All possible states are checked in detail. Standard behavioral properties and other user-defined properties are verified by state space report and ASK-CTL (Computation Tree Logic) queries, respectively. Verification results reveal that the models are reasonable to depict the dynamic behaviors of train control procedure. The functional safety properties are satisfied and prepared for further drafting the system functional specification.

A Method of Generating Engineering Test Sequence for Urban Rail Transit CBTC System Based on Formalization

In recent years, with the rapid development of urban rail transit, Communication Based Train Control system is very important to improve the operation efficiency and ensure the traffic safety. Before urban rail transit lines are put into operation, they need to be tested strictly. In view of the lack of unified test standards, specifications and low test efficiency, a formal test sequence generation method for CBTC system is proposed. Firstly, the test line is divided into several test segments; secondly, analyze the constraint conditions of test cases and get the expression of constraint relationship of test cases; thirdly, analyze the characteristic quantity that can represent the line characteristics, and get the line characteristic expression; and then match test cases with test segments using matching algorithm; finally, concatenate test cases into test sequences using the concatenation algorithm. The results show that the test sequences generated by this method meets the test requirements of CBTC system. The test sequences cover all test cases. And the method can effectively improve the test efficiency.

열차간 통신기반 열차자율주행제어시스템의 주행안전기능 설계 및 구현: Part Ⅱ

본 논문은 이전 연구결과인 Part I[9] 이어서 열차자율주행제어시스템의 ATP 차상장치 주행안전기능을 설계 및 구현한다. Part I 에서는 열차자율주행제어시스템의 주행안전기능 중에 열차 간의 최소한의 안전 간격을 유지하기 위해서 열차의 위치를 결정하고, 이동권한을 계산하는 기능을 구현 및 테스트 하였다. 이 논문에서는 열차자율주행제어시스템의 주행안전기능 중에 안전감속도를 계산하고 동적속도프로파일을 생성 및 감시하는 기능을 설계하고 구현하였다. 또한 각 기능별 모듈을 테스트케이스를 통해 검증하고 Part I 의 구현 기능과 통합하여 주행안전기능을 시뮬레이션하였다. 이를 위해 안전성 및 신뢰성있는 소프트웨어를 제작하기 위한 소프트웨어 개발툴인 SCADE를 활용한다.

Delay Testing Method for Off-Site Asynchronous LTE Networks Based on Singular Value Removal

This paper presents an experimental campaign of transmission delay measurements under asynchronous condition for the communication-based train control (CBTC) systems. A three-stage asynchronous clock correction method is proposed. Before and after the working stage, the clock difference between transmitter and the receiver is calculated, moreover the relative offset and relative skew between two terminals of the working stage are derived, and it further leads towards the experimental verification of the transmission delay. In order to improve the measurement accuracy, the singular values are distinguished and eliminated in the test. Using this method, the transmission delay of the Long-Term Evolution for Metro (LTE-M) communication between the train and the signalling room in Shanghai Zhangjiang Metro Training Line is measured successfully, which demonstrates the effectiveness of the proposed one-way transmission delay test.

열차간 통신기반 열차자율주행제어시스템의 주행안전기능 설계 및 구현: Part I

본 논문에서는 열차간 통신기반 열차자율주행제어시스템의 ATP 차상장치 주행안전기능을 설계 및 구현한다. 열차자율주행제어시스템의 주행안전기능은 열차 간의 최소한의 안전 간격을 유지하기 위해서 열차의 위치를 결정하고, 이동권한 계산, 속도프로파일을 생성하고, 열차의 속도를 속도프로파일 내에서 감시하는 기능이다. 이를 위해 안전성 및 신뢰성있는 소프트웨어를 제작하기 위한 소프트웨어 개발툴인 SCADE를 활용한다. 본 논문에서는 열차자율주행제어시스템 주행안전기능의 요구사양에 따라 SCADE를 이용하여 주행안전기능을 모델링하고, 모델에 대한 테스트를 통해 기능을 검증한다. 검증된 모델을 소스코드로 생성하고, 테스트환경을 구축하여 정상 동작 결과를 확인한다.

A Novel Intrusion Detection Model Using a Fusion of Network and Device States for Communication-Based Train Control Systems

Security is crucial in cyber-physical systems (CPS). As a typical CPS, the communication-based train control (CBTC) system is facing increasingly serious cyber-attacks. Intrusion detection systems (IDSs) are vital to protect the system against cyber-attacks. The traditional IDS cannot distinguish between cyber-attacks and system faults. Furthermore, the design of the traditional IDS does not take the principles of CBTC systems into consideration. When deployed, it cannot effectively detect cyber-attacks against CBTC systems. In this paper, we propose a novel intrusion detection method that considers both the status of the networks and those of the equipment to identify if the abnormality is caused by cyber-attacks or by system faults. The proposed method is verified on a hardware-in-the-loop simulation platform of CBTC systems. Simulation results indicate that the proposed method has achieved 97.64% true positive rate, which can significantly improve the security protection level of CBTC systems.

Robust Distributed Cruise Control of Multiple High-Speed Trains Based on Disturbance Observer

This paper investigates the robust distributed cruise control problem of multiple high-speed trains under external disturbances. First, by modeling each train as a cascade of point masses connected by spring-like couplers, the longitudinal interaction between adjacent cars are represented by the connected topological graph. Then, under the framework of the communication-based train control technology, the interaction of desirable speed information among trains and the wayside control center is described by the directed topological graph. Next, a distributed cruise controller is designed by taking advantages of the graphic theory such that the multiple trains track different target speeds, and both the distance of neighboring cars and the headway of successive trains are kept in appropriate ranges. Finally, to eliminate the influence of external disturbances, we adopt the disturbance observer to approximate the perturbations, and present a sufficient condition for the existence of the distributed control strategy and the observer gain parameter in form of the linear matrix inequality (LMI). Numerical experiments illustrate that the composite control law is effective in inhibiting the external disturbances, and guaranteeing the safety, efficiency and comfort of high-speed trains’ movement.

Towards Safety-Risk Prediction of CBTC Systems With Deep Learning and Formal Methods

Communication-Based Train Control System (CBTC) system is an automated system for train control based on bidirectional train-ground communication. Safety-risk estimation is a vital approach that strives to guide the CBTC system to guarantee the safe operation of vehicles. We propose a deep learning method to predict safety-risk states that combined with formal methods. First, the impact factors are selected, and the movement authorization (MA) failure rate is calculated by statistical model checking. Then, we use a deep neural network to model the relationship between the safe-risk states and the train operation status. Experimental results show that our method can achieve an accuracy of 97.4% on safety-risk prediction, and exceeds the baseline methods.

An Unscented Kalman Filter-based Synchronization Control Approach for Communication-Based Train Control Systems

Communication-based train control (CBTC) system is an advanced train signalling and control technology which is developed using the moving block signalling (MBS) framework. The CBTC system has been shown to be capable of improving the operational efficiency, line capacity and safety of the railway operation. The main objective in implementing the MBS framework in CBTC system is to minimize the train headways through the utilization of an inter-train continuous communication system that determine and control the position of each train more precisely. One important challenge in such an implementation is the fulfillment of the necessary requirement of having highly accurate train localization method to ensure the safety of the short headway operation. This paper describes the results from experimental examination and application of a synchronization control strategy for the CBTC system using an unscented Kalman filter (UKF)-based sensor fusion approach as the localization method. In the proposed approach, the train localization task is performed using an UKF-based sensor fusion method which fuses measurement data from speed sensors and radio frequency identification tags. A synchronization control approach to ensure the safety movement of the train convoy in curved railway tracks under the MBS scheme is then proposed. The results presented in this paper show that the proposed localization and synchronization control methods can significantly improve the localization accuracy and reduce the inter-train headways.

Intelligent Hazard-Risk Prediction Model for Train Control Systems

Although there has been substantial research in system analytics for risk assessment in traditional methods, little work has been done for safety risk prediction in communication-based train control (CBTC) system, especially intelligently predicting risk caused by the uncertainty in the system operation. Risk prediction and assessment of hazards in train control systems are vital for the safety and efficiency of urban rail transit. In this paper, we propose an intelligent hazard-risk prediction model based on a deep recurrent neural network for a new communication-mode CBTC system. First, a train-to-train communication-based train control (T2T-CBTC) system is proposed to improve the drawback of CBTC in information-exchanging mode. Then we design a risk prediction feature selection and generation method and estimate a critical function feature in the T2T-CBTC system by statistical model checking. Finally, we construct our intelligent hazard-risk prediction model based on a deep recurrent neural network using a long-short-term memory (LSTM) network. The model had excellent risk prediction classification results and performance in our experiment, even for unbalanced data set. This model consistently outperforms the deep belief network trained in Accuracy, Precision, Recall and F1-score for the hazard-risk prediction problem. Specifically, the mean accuracy is 97.2% and mean F1-score is 93.9% in overall performance of model. The improvements of our model against DBN model are 8.2% for Precision, 7% for Recall and 8% for F1-score.

Reliability Evaluation for LTE Based CBTC Train Ground Communication Systems

Nowadays, most communication based train control systems (CBTC) use Wireless Local Networks (WLAN) technology for information transmission. However, because of the high running speed of the train in urban rail transit, WLAN technology cannot fully satisfy the information transmission under the condition of train operation at a high speed. Long term evolution (LTE) technology has a high transmission speed, which can better meet the real-time requirements of train and ground information transmission. Therefore, LTE technology has become an emphasis on the research of communication technology in today’s urban rail transit. Although there is a lot of research on the application of LTE technology in urban rail transit, there is little research on the reliability of LTE based train ground communication systems using experimental data. In this paper, the reliability of train ground communication is firstly defined. Then the train ground communication environment was established in the laboratory, and the performance parameters of train ground communication based on LTE technology were obtained in the test. Finally, the reliability is calculated and analyzed according to the experimental results, and a storage method of train data in actual operation is proposed, which can be used to analyze the reliability of train information transmission. The results show that the reliability of train ground communication based on LTE technology meets CBTC requirements.

Evaluate the shielding effectiveness of driver’s cab for metro and its influence on electromagnetic exposure safety

In order to study the shielding effectiveness of metro driver cab and its impact on the safety of driver high frequency electromagnetic exposure, this paper construct the high frequency electromagnetic environment model of metro cab under the radiation of external and internal exposure sources, its shielding effect is simulated correspond, and the safety of high frequency electromagnetic exposure of metro driver is analysed. The simulation results show that the under digital trunked system antenna (external exposure source) radiation, the peak value of electric field strength inside the metro cab without aluminium alloy body is 1.7214 V/m, which 322 times higher than that of aluminium alloy cab; under the communication based train control system antenna (internal exposure source) radiation, the peak value of electric field strength inside the aluminium alloy material metro cab is 3.1625×10−1 V/m, which 26 times higher than that of without aluminium alloy body. The compared results reveal that the shielding effect of metro cab on the external exposure source is significantly greater than the internal exposure source. Although the radiation dose absorbed by the metro driver varies by 4 to 125 times in different situation, still lower than the international occupational electromagnetic exposure limit, which indicate that the shielding effect of metro cab in the above situation will not cause health hazards to the driver.