MODELING AND SIMULATION OF THE AUTOMATIC TRAIN

PROTECTION IN WLAN BASED CBTC SYSTEMS

Xiaomin Zhu and Junyang Li

School of Mechanical, Electronic and Control Engineering, Beijing Jiaotong University, 100044, Beijing, China

Keywords: WLAN, CBTC, Automatic Train Protection.

Abstract: The urban rail transit is playing a more and more role in the social and economic development, building a

suitable ATP system in wireless LAN based CBTC system with low cost and high accuracy has become

increasingly important. Based on the theories of wireless LAN-based CBTC and ATP system, this paper

studies the general structure and modelling of ATP system in wireless LAN based CBTC system, and

accordingly establishes the model of speed-distance brake curve for ATP system which is essential in

optimal design of an ATP system. The model can realize a smooth train stopping and speed protection

function. Meanwhile, strong wireless signal coverage improves the equipment reliability of internal

communications. Comprehensive simulations on labVIEW platform verify the correctness of the model.

1 INTRODUCTION

In recent years, urban rail transit in various cities of

China is developing rapidly. Along with the advance

of computer technology, communication technology

and control technology (generally called the 3C

technologies), the latest train control system —

CBTC (Communication Based Train Control)

formed gradually. CBTC outcomes the shortcomings

that information can only be transferred by trackside

equipment when the train runs, and achieves real-

time two-way communication between the train and

the trackside equipment (Chen et al., 2005). Safety

is an important factor which restricts the

development of CBTC in China. ATP (Automatic

Train Protection) which is responsible for safe

running of trains is the core component of CBTC on-

board equipments. In CBTC, with the characteristics

of wireless broadband, high speed and mobility,

WLAN provides a more reliable medium in data

communications on high-speed trains (Carr et al.,

2005). CBTC automatic train protection system

based on WLAN can further reduce the amount of

trackside equipment of signal system, and improve

the ability of system upgrading and expanding. It has

already become a new development direction of

ATP system in urban rail transit.

In foreign countries, WLAN security technology

has already reached the safety standards in CBTC

system. CBTC system based on WLAN has been

already widely used in urban rail transit (Wu, 2005).

Automatic train protection system is an important

problem to be solved on the way to establish a

CBTC system with independent intellectual property

in China. Due to the characteristics of CBTC

system, the WLAN network performance under the

condition of fast moving traffic on the road should

be considered as a key issue. And we should pay

attention to the problem of automatic train protection

system in CBTC based on WLAN. To ensure the

safety of operation and to improve the efficiency of

transportation, it is urgent to equip advanced, safe

and reliable train control system. Train control

system currently used in China is mainly based on

track circuit (Xu and Tang, 2007). This kind of

system played an important role in the protection of

traffic safety and efficiency. But some problems also

exist, for example, real closed-loop control cannot

be achieved due to the limited amount of

information transmitted by track circuit, the stability

of track circuits influenced by environment and large

investment on repairing the track circuit. To

overcome the shortcomings of train control system

based on track circuit, more and more countries

prefer to use CBTC which is a new generation of

train control technology. Based on communication

technology, CBTC achieves information exchanging

with the station or the train controlling centre

through on-board equipment and site communication

449

Zhu X. and Li J..

MODELING AND SIMULATION OF THE AUTOMATIC TRAIN PROTECTION IN WLAN BASED CBTC SYSTEMS.

DOI: 10.5220/0003594604490458

In Proceedings of the 13th International Conference on Enterprise Information Systems (EIT-2011), pages 449-458

ISBN: 978-989-8425-55-3

 2011 SCITEPRESS (Science and Technology Publications, Lda.)

equipment. There are many advantages when

compared with TBTC, such as a shorter departure

interval, less quantity of hardware, simple

maintenance, more flexible, better security of the

system and a better transmission mode. CBTC train

control system will become a mainstream

technology in the future.

Therefore China should speed up on the research

of train control system, and develop train control

technology with its own intellectual property.

Although China has started the research of CBTC

train control system technology, it is still in infancy

period. Currently, WLAN based on the standard of

IEEE802.11 has become the most widely used data

communication method in urban rail transit

(Grappone and Hubbs, 2007). ATP (automatic train

protection system), which is responsible for the safe

operation of trains, is the core component of CBTC

equipment. Therefore, the study of urban rail transit

ATP system based on WLAN is the main mission in

the research of CBTC. The establishment on the

model of urban rail transit ATP based on WLAN is a

paramount and urgent research work. It is significant

for ensuring the security and stability of CBTC

system. Meanwhile it can help to reduce the project

cost of CBTC systems.

This paper will analyze on giving a model of the

core algorithm formula on the speed-distance curve

of the ATP system based on WLAN, and use

modular design method to establish the model of

ATP system and system maintenance and upgrading

will benefit from it. To test the reliability of the

model, the platform of Labview is selected and an

integrated simulation system of ATP is established

in this research. Then simulates this program and

discusses the feasibility and accuracy of the

proposed solution.

The paper follows the steps by question

prompting, theoretical research, practical research,

solution proposing and model establishing to check

the solution. First, the paper points out the necessity

and background of security problems in application

of ATP system, and elaborates practical significance

of this study. Second, the paper defines the basic

theories, targets and principles of establishing

models on applying WLAN to CBTC, and analyzes

the advantages and disadvantages of current ATP

systems, so that to find out the advantages of ATP

system applied to CBTC based on WLAN. Then,

applies WLAN technology based on IEEE 802.11 to

the train control systems, builds the structure of the

entire wireless communication system, and focuses

on modeling the ATP speed-distance curve in

mathematics and dynamics. Next, based on the

established model, simulates the ATP system in

CBTC based on WLAN and discusses the accuracy

and feasibility of the proposed solution. Finally,

summarizes the work on composing the paper.

2 RESEARCH FOUNDATION

AND RELATED THEORIES

2.1 Problems Existed in WLAN

WLAN obeys an open channel standard. Therefore,

it is hard to prevent attackers from eavesdropping

deliberately, tampering and forwarding maliciously.

Information of WLAN transmits in the air through

radio waves. So attackers can receive, interfere,

tamper, forward or even forge information as long as

they have the same receiving equipment while the

sender can’t detect them. It’s easier for attackers to

camouflage to be legal users because users do not

have to connect with the net actually. In addition,

when the radio wave transmits in the air, the signal

attenuates which leads to the missing of information

for various reasons, such as barrier or shield. Radio

coverage area is limited. Wave energy will become

lower and lower when it spreads in the air. Besides,

there may be some obstacles in the communication

environment. When transmitting through the

obstacles, the information may lose, causing data

integrity problems.

When applied to urban rail transit CBTC, the

WLAN’s characteristics mentioned above will cause

some specific security problems. When CBTC

communicates by WLAN, as the environment is

more complex, the speed of the train is fast and there

are all kinds of interference such as signal reflection

in the subway tunnel, shielding and signal

temporarily blind areas, electromagnetic, signals,

human destruction, etc

[5]

. Equipment processing

capacity, network load capacity problems,

communication equipment or media failure, may

lead to insecurity data communication. Unauthorized

users’ accessing, eavesdropping, simulating base

stations and other malicious behaviours are what we

need to consider.

To solve these problems, there have been some

related researches at home and abroad, for example,

obtain the best AP density to ensure relatively

redundancy by modelling and calculating to solve

the problem of data loss. To carry out effective

authentication, Message sequence number, Time

stamp (Cai, 2000), Time-out, Source and destination

identifiers, Feedback message, and Safety code

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450

(Chen and Song, 2007) are used. Dynamic keys or

random keys are used for data encryption.

Currently, there are some products which have

been put into use in foreign CBTC system (Zhou et

al., 2009). However, the related domestic research

has just started. As mature and open DCS

communication security technology and products are

still rare, related products are very expensive.

Besides, the safety of urban rail transit is directly

related to the security of life, property and social

stability. Therefore, train operation control puts

forward higher requirements for reliability, security

and confidentiality of wireless transmission. These

problems seriously affect and restrict the

popularization and application of CBTC technology.

2.2 Characteristics of the ATP System

in CBTC based on WLAN

ATP (He, 2005) system is an important subsystem of

the automatic train control (ATC) system and a key

facility to ensure the operation safety of trains. It is

consisted of the trackside equipment and on-board

equipment. With the advantages of its high accuracy

positioning of trains, two-way high capacity train-

ground data communication and on-board, the ATP

system in CBTC based on WLAN (Zhang and Li,

2008) has become an important and indispensable

part of the development of urban rail transit at home

and abroad.

The main functions of ATP system in CBTC

based on WLAN exists in following aspects:

security parking point protection; speed monitoring

and speeding protection; measurement of distance

and speed to control the safe running of the train;

gate controlling to prevent opening the door outside

the station, opening the wrong door inside the station

and preventing the train from starting with the door

open in order to ensure the safety of passengers;

interval controlling to prevent the train from rear

collision.

There have been some fixed necessary

engineering data in the computer of ATP system

such as route slope, length of track circuit, speed

limit and so on. According to the existing data and

operating conditions of the route, ATP computer

follows a certain algorithm to calculate the

maximum allowable curve of the train (Hong, 2006).

Shown in Figure 1.

The information of the position or the danger

point of the train ahead (named A) transmits to the

follow-up train B which is running in the line

interval through the wireless communication system.

For train B, position of train A is a danger point.

Train B calculates the maximum allowable speed to

the danger point. With train A moving forward, the

safe parking point of train B (stations do not belong

to safe parking points) also changes. Train B

calculates the speed-distance curve to the parking

points at real-time. When actual speed exceeds the

maximum allowable speed, the system alerts and

requires the train to decelerate. If the train fails to

decelerate to the maximum allowable speed within

the given time, the system will implement

emergency brake to ensure the safety of the train.

Figure 1: Operation principal of ATP system.

3 MODELING OF ATP SYSTEM

STRUCTURE

3.1 The General Model of ATP System

Now build the model of ATP system according to

section 2.2. The model mentioned in this paper takes

WLAN which is based on the standard of

IEEE802.11 to communicate between train and

ground (Hu, 2002). Use the advantages of WLAN

technology such as flexible using, convenient

installation, economic, easy extension to connect

ground equipment and on-board equipment through

the information transmitting platform. We can

achieve not only fast and real-time transmitting of

high capacity information but also closed loop

testing of train-ground information. The system will

be more advanced when supplied by positioning and

checking equipment (Chen et al., 2007). The general

model of ATP system in CBTC based on WLAN

includes 3 parts: regional control centre, on-board

equipment of the train and train-ground two-way

transmitting system (

Mirtchev, 2005). The general

model is shown in Figure 2.

3.2 Design of Regional Control Centre

The regional control centre is established in the

station where there is a bifurcation so that to

MODELING AND SIMULATION OF THE AUTOMATIC TRAIN PROTECTION IN WLAN BASED CBTC SYSTEMS

451

interlock this station with neighbouring bifurcated

stations and to control the ATP system. The control

targets are turnouts, protective signal equipments

and digital track circuits. The designed capacity of

this centre is: controlling range ≤5km; system

treatment cycle time200~250ms; the number

collected by relay (digital input) ≤500points; the

number controlled by relay (digital output)

≤500points (

Lamborn and Thomas, 2005); the

communication channel with neighbouring centres is

redundant fiber channel; the number of centres

whose interfaces can be connected ≤3.

Communication mode: two-way serial

communication; communication cycle time

(transmission) 200~250ms (Wang et al., 2005).

The wireless regional control centre which must

be operated safely is the core part of the entire ATP

system. Here redundant measurement, disperse and

isolate measurement are carried out. Redundant

measurement includes 3 levels (Xu and Tang, 2007):

system redundancy, net redundancy and power

supply redundancy. Disperse and isolate

measurement distributes control to all I/O modules

in order to reduce the burden on the host system by

I/O modules intellectualization. Meanwhile board-

level state testing and failure diagnosing are

implemented.

3.3 Construct of WLAN

Communication System

3.3.1 Structure of WLAN Communication

System

As the development of urban rail transit, data

communication system based on WLAN will

become the most widely used communication

system in CBTC considering of the advantages of

WLAN based on the standard IEEE802.11, for

example, it can be applied to the situation that needs

to connect with the net when moving and roaming; it

supports distant data processing and uneasy wiring

areas; its flexible using, convenient installation,

economic, easy extension and so on (Xu and Li,

2006). The wireless data communication network

consists of wired backbone network and wireless

mobile network. Its network structure is shown in

Figure 3.

WLAN communication system is the data

transmission platform between different parts of

ATP system (Zhang, 2007). The whole data

communication system includes 3 levels: Core level,

i.e., the backbone network. It’s the central of data

Figure 2: General model of ATP system.

Figure 3: Schematic diagram of wireless data

communication network.

communication system which is implemented by

redundant optical network with the characteristics of

high bandwidth and high reliability. Centre control

system and regional control system access to the

wired backbone optical network directly; Middle

level, i.e., the trackside network. It connects

backbone network and wireless network system. The

network extents following the route by network

switch which has accessed to the backbone network.

In this way the trackside network formed. This

network connects with wireless railside unit (WRU).

Thereby, the wireless access point (AP) can access

in it; Mobile level, i.e., the wireless network. This

network supports train-ground two-way mobile

communication. The trackside AP and on-board

wireless units (OBRU) on moving trains

communicate by wireless way. In this way, it

constructs a link between ground and moving trains.

One side of the wireless link is AP and the other side

ICEIS 2011 - 13th International Conference on Enterprise Information Systems

452

is on the train which connects with OBRU. WLAN

communication doesn’t mean totally wireless. There

are wired fiber between different regional control

centres. The equipment of whole communication

system includes: optical backbone network, AP,

wireless on-board equipment, interlocking

centralized station, switch in control centre and

router.

3.3.2 WLAN Ethernet Train-ground

Communication System

(1)Trackside Wireless Unit

One side of the wireless link is AP and the other side

is on the train which connects with OBRU. There is

an identification gateway for every switch’s ports

and OBRU. This gateway certificates the

identification of DCS message. To implement the

redundant of wireless network, every port of every

WRU connects with different switches. So a series

of redundant local network is supplied to WRU.

The switch of trackside network connects with

the supply chain of local WRU. This chain is

consisted of fiber. Considering of technology

demand and cost, multimode fiber is used generally.

WRUs are installed following the route about 250

per meter. Actual distance depends on detailed

survey, including terrain, tunnel structure, local

standard, antenna type and so on. Every AP on

WRU connects with Ethernet switches through local

servo chains. Every AP has two directional antennas

facing opposite directions.

Special transmit condition at the channel bend

and between distant stations should be considered

when arranging AP antennas. We should install

antennas according to the actual measured wireless

covered range whether it is channels or outdoors.

This way most factors that may influence signal

transmission would be involved so that there won’t

be any gaps under the cross covering by wireless

signals.

(2)OBRU

There’s an OBRU with moving wireless radio (MR)

station on each side of the train. In order to

implement the redundancy between trackside and

the train, these two OBRUs both connect with

VOBC. In addition, to diverse the receiving mode of

the signal, all MRs connect with 2 on-board

antennas. Each MR can search out at least 2 AP

signals at any time because of overlapping coverage.

To enhance the signal strength and reduce the

number of devices, these antennas are oriented.

3.4 On-board Subsystem

3.4.1 Structure of On-board Subsystem

ATP on-board equipment regard the information

received from the ground as a basis and generate a

speed Hijack curve to compare with the actual

speed. If actual speed exceeds the speed control

curve, on-board equipment will brake automatically.

According to principles of ATP on-board subsystem

and its mission, this paper refines it into different

functional modules. The train can protect itself

automatically by mutual coordination between all

functional modules. Main processor is the central

part to carry out different functional calculates. It

calculates output according to the settings of

application program and information from different

modules and drive corresponding parts using these

outputs.

3.4.2 Structure of Train Positioning

Technology System

Real-time, precise train positioning technology is a

premise to implement moving block urban rail

transit and is the basis for ATP system. This model

uses a technology called Wireless Spread Spectrum

Communication Location to implement real-time,

precise, train positioning and tracking under

complex environment. This technology includes

advanced wireless spread spectrum communication,

pseudo code ranging and computer information

processing technology. Wireless spread spectrum

communication location system accord with the

demand of ATP system based on WLAN. It can

locate precisely and is a completely independent

positioning system.

Set ranging base central controlling station on

the ground along with the trackside radios. Install

wireless spread spectrum communication transmitter

on both sides of the train. The transmitter sends

positioning information to the ranging base station

on the ground; after receiving the information, the

ranging base station calculates pseudo-range using

digital signal processing technology and transmits to

the central controlling station to precede data

processing through wireless or wired links. The

positioning result displays on e-maps and transmits

to trains by wireless way. The position of trackside

radio stations are fixed after accurate measurement.

All the radio stations are synchronization accurately

by synchronous clock. Trackside computers or on-

board computers will calculate the position of the

train according to the transmitting delay time of

different radios.

MODELING AND SIMULATION OF THE AUTOMATIC TRAIN PROTECTION IN WLAN BASED CBTC SYSTEMS

453

A WLAN is constructed by distributed radio

stations. Under most conditions, the area between

different stations can be covered by wireless reliably

and have redundancy. This kind of redundancy is a

self healing structure. When a radio station fails to

work, the system can rearrange and report the

location or number of the failed radio automatically.

So it won’t influence communication and train

controlling. Information of one radio station will be

received by 2 or even 3 radios generally. Spread

spectrum technology is design for military

application initially. It has the ability to transmit

under harsh electromagnetic environment. The

position of a train can be tested every 0.5s and the

positioning precision can reach to ±5m (

Stadlmann,

2008).

4 MODELING OF ATP

SPEED-DISTANCE BRAKING

CURVE

After building the model of ATP structure, this

section will research on ATP core algorithm

modelling, speed-distance braking curve modelling.

Train braking curve is the basis of over speed

protection of ATP system in CBTC based on WLAN.

The traction and braking force involved in this

model is determined according to “Order of train

traction calculation” (The Ministry of Railways of

The People’s Republic of China) promulgated by the

PRC Railway Ministry.

4.1 ATP Protection Curve

The function of braking is to ensure the train to stop

at a certain position or to limit the speed in a certain

range, i.e., the so-called “rash advance protection”

and “speeding protection”. Rash advance protection

is a special condition of speeding protection when

the limit terminal velocity equals to 0. But there are

some differences, for example, the result will be

different when distinguishing the braking safety

distance. In our design, all conditions are treated as

“speeding protection” because moving-blocking

method is used here. Expanse and adjust it to satisfy

precise controlling of all parameters. The train

braking distance formula after adjusting is shown as

formula (1).









jchh

vvTv

1000

)(17.4

6.3



(1)

Where:

, v

—initial and terminal velocity of braking;

—conversion friction coefficient of brake shoes;

—conversion rate of train braking;

—common used braking coefficient;

—unit basic resistance of the train;

—additional slop thousandths at braking section.

ATP system of urban rail transit monitors the

speed continuously to prevent from speeding. Firstly,

ATP system works out the maximum allowable

speed of the train at any time, i.e., the safe running

speed. If actual speed exceeds this speed, ATP

system will brake so that the actual speed can

decrease to safe speed in given time. In this process,

ATP speed-braking curve model is a most important

basis for speeding protection.

4.2 Algorithm to Determine

the Maximum Allowable Speed

There have been some fixed necessary engineering

data in ATP system such as route, slope, length of

track circuit, speed limit and so on. On-board ATP

equipment stores basic data about the train such as

mass and performance characteristics. First,

determine the position of the train by on-board

positioning system. On-board wireless equipment

transmits information including position code to

regional control centre through track WLAN. Then

regional control centre sends fixed engineering data

of the train position to on-board ATP equipment

through WLAN. On-board ATP computers work out

the maximum allowable speed curve based on this

model algorithm.

4.3 ATP Speeding Protection Process

After calculating the maximum speed and generating

the maximum allowable speed curve, on-board ATP

computers monitor the running speed and position of

the train. If actual speed curve exceeds the

maximum speed protection interface, ATP system

will cut off the train traction power immediately to

carry out protection braking.

The maximum allowable speed varies as the train

position changes. On-board ATP equipment makes

real-time and two-way communication with regional

control centre through WLAN. So ATP speeding

protection system is dynamic and real-time. This is

just the advantages of ATP system based on CBTC.

ICEIS 2011 - 13th International Conference on Enterprise Information Systems

454

5 SIMULATION OF ATP SYSTEM

OF CBTC BASED ON WLAN

In Section 3 and 4 we’ve built the models of ATP

system and ATP braking curve. The combination of

them can implement the main function of ATP

system, i.e., designated parking, speed monitoring,

speeding protection, distance and speed measuring,

gate controlling and interval controlling. Now build

a simulation platform based on LabVIEW to verify

the effect of this model.

5.1 Function of ATP System based on

WLAN

According to the main function of ATP system in

CBTC based on WLAN, this paper designs it into 4

functional modules:

(1)Basic data input subsystem

It is mainly used to set basic parameters for the

entire ATP system including 2 parts: structure of

route data and train data. Structure of route data

includes slop segment data, curve data and speed

limiting data. Structure of train data includes traction

braking characteristic curve data, mechanical

property data of the train and parameters.

(2)Speed controlling subsystem

It is used for speed monitoring, distance and

speed measuring and speeding protection. This

subsystem can prevent the train from speeding and

ensure the actual speed lower than allowable speed

which is determined by route, turnout, train and safe

controlling curve so that the train can run safely.

(3)Position testing and interval controlling

subsystem

It is used to protect the safe parking point and

control the running interval. This subsystem can

check running state of the train automatically and

generate a corresponding curve according to the

route environment so that the train can stop at safe

regions and rear collision can be avoided.

(4)Gate protection subsystem

It is used for protecting the safety of opening or

closing the door. This subsystem controls the

platform screen doors and safety doors to ensure the

security of passengers when the train stops or leaves.

5.2 Input and Output Design for ATP

System based on WLAN

Input and output design includes speed controlling,

position testing and interval controlling and gate

protection subsystem. The following example shows

the speed controlling subsystem.

5.2.1 Function Description

Speed controlling subsystem involves basic data

input system and speed controlling sub module.

Here is the train speed controlling sub module

simulation-IPO (Input-Process-Output) diagram, as

is shown in Figure 4.

Called by：

System name：ATP system in WLAN based CBTC

Calls for：

Initial input：line and curve data

Actual input：

current speed

running distance

work mode of ATP

drawing or braking choice

Choose curve data

End

Local data：Vo—ideal speed，Fi—drawing/braking force of last minute，Ni—speed series

index of drawing/braking characteristic curve，Nil—force series index of drawing/braking

characteristic curve

Module name：

Speed controlling subsystem

Basic data input subsystem

current speed limit of ATP

Actual output：

force series

start

current traction

Final output：null

Every 300ms

Obtain current speed limit，work mode of ATP and current speed，running distance

Make choice of drawing，coasting or braking according to current and ideal speed

Manually selection of drawing/braking series is available，default series is 1

Calculate drawing/braking force using interpolation method

Pass result of the choice，force series，current drawing force

Algorithm explanation：

Figure 4: IPO diagram of speed controlling subsystem.

5.2.2 Algorithm Explanation

Use interpolation method to calculate

traction/braking force: assume (V

, F

) and (V

, F

)

are two known points on the traction curve. Point

, F

) is a point whose speed is known but force is

unknown and should be worked out.

When V

12 1

()()

FV V







(2)

Where:

—traction/braking force of the unknown point

(KN);

—current speed (km/h).

5.3 System Simulation and Calculation

5.3.1 Simulation Environment

Use LabVIEW virtual instrument development

platform of NI to develop the system. LabVIEW

MODELING AND SIMULATION OF THE AUTOMATIC TRAIN PROTECTION IN WLAN BASED CBTC SYSTEMS

455

(Zhang and Zhang, 2007) is currently a unique

worldwide graphical programming environment

based on data flow. According to the program of

simulation and test, this paper chooses LabVIEW

PDS, Measurement Studio, Signal Express and

LabVIEW add-on tools in NI Developer Suite.

ATP system of CBTC based on WLAN includes

initial parameter setting, speed controlling, position

testing, and interval controlling and gate protection.

Speed controlling is the central module of the entire

ATP system. It generates fixed or temporary speed

limit curve after inputting basic train information

and route information. It can also generate braking

curve according to the information from the control

centre.

The train and route parameters of this simulation

come from Rail Transit Line 2 of the straddling

monorail train and line data in Chongqing and are

simplified according to the model. Here, a section of

1.2km is chosen to simulate. In order to better reflect

the logic of the model all speed limits are attributed

to one parameter-interval speed limit which is set as

85km/h. In order to reflect the ability of the model to

adapt to various situations, all input data involved in

the software, including interval speed limit, can be

manually set to facilitate the testing of the system.

5.3.2 Simulation Result

Initial state: the train ahead runs under a constant

speed 85km/h and stops smoothly at 1.1km. The

distance between the train behind and the train ahead

is 0.5km. The train behind regards the front train as

target distance and target speed to adjust the

protection curve. The simulation result is shown in

Figure 5.

Figure 5: Braking curve of the train.

In this figure the red curve represents for interval

speed limit data. It’s obtained from reading data

which is set before the software runs. The green

curve represents for protection curve. It’s generated

by the model of ATP system. The blue curve

represents for target speed. It’s obtained by

decreasing the speed of protection curve by 3-7km/h.

This paper compared the simulation result with

actual auto protection curve obtained in the test

phase of Rail Transit Line 2 of the straddling

monorail train in Chongqing. Sampling point is

chosen as every 0.1km. The comparison result is

shown in Table1 and Table2.

5.3.3 Simulation Result Analysis

The braking curve, i.e., the speed-distance curve

indicates that if the train wants to stop at a certain

safe parking point with a certain initial speed, it

should start braking at a certain position to ensure

the train arriving right there according to braking

curve.

Table 1: Comparison of simulation speed and actual data.

Sampling

points

(km)

Protec-

tion

speed

(km/h)

Target

speed

(km/h)

Simula-

tion

speed

(km/h)

Actual

speed

(km/h)

0 85 80 0 79.52

0.1 85 80 57.61 78.98

0.2 85 80 72.09 78.76

0.3 85 80 77.94 78.03

0.4 85 80 77.47 77.57

0.5 85 80 76.89 77.08

0.6 85 80 77.00 76.65

0.7 82.17 76.44 74.13 76.12

0.8 77.19 71.05 69.38 73.78

0.9 67.23 60.19 59.97 68.43

1.0 45.86 38.61 38.54 45.57

1.1 0 0 0 0.01

1.2 — — — —

Table 2: Comparison of simulation stopping distance and

actual data.

ATP

stopping

distance(m)

Target

stopping

distance(m)

Simulation

stopping

distance(m)

Actual

stopping

distance(m)

1100 1098 1097.8 1098.5

Figure 5 shows that this model of ATP system

can implement the function of smooth parking and

speed protection. It can be found from Table1 that

the simulation speed is always lower than the target

speed and changes smoothly. The goal of controlling

the train to be safe and satisfying the comfort

requirement is able to achieve. At the point of 0.8km,

the actual speed is 73.78km/h. Although this speed

hasn’t reached ATP protection speed 77.19km/h, it

has exceeded target speed 71.05km/h already. As

soon as the actual speed exceeds the target speed,

the train will start to brake. It’s easy to cause

emergency brake. Thus, it doesn’t satisfy with the

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456

comfort requirement. However, ATP system in

CBTC based on WLAN in this paper improved the

situation that actual speed exceeds target speed when

the train runs because of transmission delay or

equipment limits. Table2 shows that this system is

able to satisfy the function of designated parking and

rash advance protection.

We can conclude after comparing the train

operation diagram and data:

(1)ATP system in CBTC based on WLAN

applies WLAN to CBTC so that it can communicate

wirelessly. It overcomes the disadvantages of

traditional ATP systems such as one-way

transmission, high cost and hard maintenance.

(2)The model build in this paper can calculate

the data of protection curve at real-time according to

two-way communication of WLAN and display

directly.

(3)ATP speed protection model, working as a

speed monitor, controls the train to run according to

the target speed curve. Running curve and protection

curve fits well.

(4)Under the monitor of ATP protection model,

the train meets the demand of protected parking. If

the train exceeds the parking section when entering

the station parking circle range, ATP system will

carry out full brake and monitor the train to ensure it

parking in front of the parking spot.

(5)This system takes hardware redundant of key

modules to satisfy with the reliable designing

requirements of single unit equipment. It also takes

advanced WLAN technology to implement strong

covering of wireless signals and improve the

reliability of internal communication.

(6)This system takes distributed network

structure, standard communication protocol, typical

division of module function and other measures to

improve equipment expansibility. It can meet some

special functional requirements of urban rail trains.

6 CONCLUSIONS

The research of CBTC based on WLAN has been a

research focus in the entire rail transit industry. In

this paper, we mainly focus on modelling of ATP

system in CBTC based on WLAN and propose

related frame structure and principle model

according to the study of ATP system and WLAN

technology combining with private ideas and

literature summary. We also focus on ATP speed-

distance curve modelling in detailed mathematics

and dynamics. Finally, we make simulation on the

ATP system in CBTC based on WLAN. The

functional modules of simulation, data structure and

IPO were designed for implementation of

simulation. And we also focus on simulation of

speed controlling module and analyze the simulation

result to verify the correctness of the model.

There are still imperfections that need further

study for the simulation of ATP system in CBTC

based on WLAN. A research of simulation on

channel establishment of the entire wireless

communication system in ATP has not been given

yet. Meanwhile, the signal security and system

stability problems are not solved. These are to be

researched for the next step.

ACKNOWLEDGEMENTS

This paper is partially supported by a fund of

Chinese Ministry of Railways with contract number

of “2010X001”.

REFERENCES

Cai, M.J., 2000. Automatic train protection and automatic

driving. Electronic Engineer, 26(8), 30-33.

Carr, D.W. Ruelas, R. Gutierrez- Ramirez, J.F. Salcedo-

Becerra, H., 2005. An Open On-Board CBTC

Controller Based on N-Version Programming. In:

International Conference on Computational

Intelligence for Modelling. Vienna November 2005.

Chen, H.F., Liu L., Xu S., 2005. Communication based

train control (CBTC) system. Railway Signalling &

Communication Engineering, 1,21.(In Chinese)

Chen, L., Ning, B., Xu, T.H., 2007. Research on

Modelling and Simulation of Vehicle-on-board

Automatic Train Protection Subsystem of

Communication Based Train Control System. In:

IEEE International Conference on Vehicular

Electronics and Safety, Proceedings.

Chen, G.F., Song, Q., 2007. Analysis of IEEE 802.11

based Wireless LAN Security. Guangdong

Communication Technology, 27(5), 35-39.(In Chinese)

Grappone, V.F., Hubbs, G.P., 2007. The Long Island Rail

Road Signal Strategy and its joint effort with New

York City Transit on communication-based train

control. IEEE, 33-34.

He, Z.T., 2005. ATP on-board equipment design principle

and implementation. Railway Signalling &

Communication, 41(C00), 19-21.(In Chinese)

Hong, D.C., 2006. Train-ground data communication of

urban rail transit ATP system. Railway Signalling &

Communication Engineering, 3(4), 14-15,19.(In

Chinese)

Hu, Y.H., 2002. Analysis and research of train protection

system under the condition of China train speed.

Chinese Railways, (8), 28-31.(In Chinese)

MODELING AND SIMULATION OF THE AUTOMATIC TRAIN PROTECTION IN WLAN BASED CBTC SYSTEMS

457

Lamborn, M., Thomas, M., 2005. Using fiber optic-to-

radio frequency (RF) conversion for communication-

based train control. In: Proceedings of the 2005

ASME/IEEE Joint Rail Conference. 2005, 181-186.

Mirtchev, A., 2005. Automatic Restart for Communication

Based Train Control Systems. In: Proceedings of the

2005 ASME/IEEE Joint Rail Conference. 2005, 177-

179.

Stadlmann, B., 2008. Basic Train Control System for

Regional Branch Lines - field Test Report. Computers

in Railways Xi- Computer System Design and

Operation in the Railway and Other Transit Systems,

253-262.

The Ministry of Railways of The People’s Republic of

China, 1999. Train traction calculation procedures.

Beijing: China Railway Publishing House. TBT1407.

Wang, C.L., Xiao, P., Kang, T.P., 2005. Train Control

System Security Model and Research Technology.

Journal of Transportation Engineering and

Information, 3(1), 36-39,56.(In Chinese)

Wu, X.Y., 2005. Analysis and Research on CBTC

algorithm for mobile ad hoc networks. Radio

Communications Technology, 31(6), 101-102.(In

Chinese)

Xu, G., Li, J.,2006. Development of wireless transmission

system in the automatic train control. Railway Survey

and Design, 5,35-38,44.(In Chinese)

Xu, T.H., Tang, T., 2007. The modeling and Analysis of

Data Communication System (DCS) in

Communication Based Train Control (CBTC) with

Colored Petri Nets. In: 8

International Symposium on

Autonomous Decentralized Systems.

Zhang, H., 2007. Wireless LAN applications in urban

mass transit. Urban Mass Transit, 10(2), 61-65.(In

Chinese)

Zhang, X.H., Zhang, Y.P., 2007. LabVIEW 8.20

Programming From Novice to Professional. Beijing:

Tsinghua University Press.(In Chinese)

Zhang, T.A., Li, L., 2008. Analysis of CBTC application

in subway though Guangzhou subway signal system.

Rail Transit, 11, 70-72.(In Chinese)

Zhou, P., Xu, H.Z., Hou, J.J., 2009. One Method to

Evaluate the Safety of Train Control Centre. In:

International Asia Conference on Informatics in

Control, Automation, and Robotics, Proceedings.

Thailand February 2009.

ICEIS 2011 - 13th International Conference on Enterprise Information Systems

458