ANALYSIS OF THE ARCHITECTURE AND RELIABILITY

OF DATA TRANSMISSION NETWORK USED FOR

RADIO BASED CAB SIGNALING SYSTEM

Wang Junfeng, Zhang Yong, Wang Huashen and Wang Xishi

School of Electronics and Information Engineering, Beijing Jiaotong University, Beijing, 100044, P. R. China

Keywords: Radio based cab signaling, Communication based train control, Radio transmission, Network

Abstract: The application background and basic structure of train control system based on the combination of Radio

Based Cab Signaling (RBCS) and Automatic Train Protection (ATP) is introduced. The architecture of the

data transmission network used for RBCS is analyzed in detail, together with the reliability of radio data

transmission.

1 INTRODUCTION

Communication Based Train Control (CBTC)

system is the development trend of train control

techniques, which has many advantages compared

with Track circuit Based Train Control (TBTC)

system. For example, bi-directional train-track

communication with large information volume can

be realized; close-looped train control can be formed

to improve train operation safety; moving block or

virtual block can be implemented to enhance traffic

efficiency.

Chinese Ministry of Railways (MOR) is now

advocating CBTC techniques, and has made a

strategy to develop Chinese Train Control System

(CTCS) which is now under stepwise

implementation. CTCS consists of five application

levels, from level 0 to level 4, in which level 3 and

level 4 will be based on CBTC techniques. In the

near future, part of the technique will be applied on

Qinghai-Tibet Railway and Datong-Qinghuangdao

Railway.

The Qinghai-Tibet Railway is built on a plateau

with perennial frozen soil and very harsh climate.

The lowest temperature is –45.2°C and the

maximum temperature difference is 35°C. Under

these conditions, the parameter of track circuit will

change considerably, resulting in the unstable

operation of track circuit. Especially, the insulation

joint of track circuit will be easily damaged. To the

Datong-Qinghuangdao Railway which is a dedicated

coal line, a transport capacity expansion plan will

soon be carried out, with the goal to increase train

weight from 10,000 tons to 20,000 tons. As a result,

the traction current will reach as high as

1000~1500A, causing the unbalanced current to

exceed the standard by a great margin, which will

directly affect the normal operation of track circuit.

In view of above situations, the MOR has

decided to use radio to transmit train control

information, and has started the research on Radio

Based Cab Signaling (RBCS) system, which is now

under experiment.

After giving a brief introduction to the train

control system based on the combination of RBCS

and ATP system, this paper will focus on analyzing

the architecture of the radio transmission network

used for RBCS, together with the reliability of radio

data transmission.

2 RBCS SYSTEM

RBCS is a kind of device that transmits cab signal

and train control information by means of radio. It

consists of two parts: the station control equipment

and the onboard equipment. The transmission

network can use either radio data transceiver,

GSM-R or TETRA as the transmission media.

There are two types of RBCS. One type is called

continuous RBCS because it can provide cab signal

both at stations and in sections; another type is

called approaching continuous RBCS because it can

only provide cab signal when a train is running

within station area.

RBCS can work with onboard ATP equipment,

394

Junfeng W., Yong Z., Huashen W. and Xishi W. (2004).

ANALYSIS OF THE ARCHITECTURE AND RELIABILITY OF DATA TRANSMISSION NETWORK USED FOR RADIO BASED CAB SIGNALING

SYSTEM.

In Proceedings of the First International Conference on Informatics in Control, Automation and Robotics, pages 394-397

DOI: 10.5220/0001126303940397

 SciTePress

interrogator/balise, station interlocking, axle

counters and so on to realize close-looped train

control. As a result, train operation can be

continuously tracked and monitored, thus enhancing

train operation safety, reducing trackside equipment

and lowering maintenance cost.

The working principle of the approaching

continuous RBCS can be briefly described as

following. When a train enters the effective working

area of RBCS, its onboard equipment will apply for

registration to the SCC. Upon receiving the

registration information, the SCC will pick up the

cab signal information related to the train from the

station interlocking and send it to the train. After

receiving the cab signal information, the onboard

equipment will indicate the cab signal to the driver

and relay it to the ATP onboard equipment. At the

same time, train position and speed, the return

receipt of cab signal and so on are sent back to the

SCC in order to verify the correctness of the

transmitted information. When the train exits the

RBCS effective working area, it will be deregistered

by the SCC.

3 THE ARCHITECTURE OF DATA

TRANSMISSION NETWORK

The radio data transmission network is the

foundation of RBCS, and is one of the key technical

issues. Many issues concerning the transmission

network should be properly addressed, such as

network architecture, transmission method,

addressing mode, common frequency interference,

frame collision, data transceiver deadlock, radio

coverage, handover, communication protocol and so

on.

The approaching continuous RBCS uses the

commercial radio data transceiver to form a data

transmission network. There is a onboard radio on

each locomotive, and a base radio station at each

station, with all radios numbered in a unified way.

Thus, a local radio transmission network is formed

by the station base radio and all the onboard radios

equipment within the station area; the whole

transmission network of RBCS is formed by all the

local transmission networks along the railway. Same

frequency is used for the station and all the trains

within its controlled area, to share the channel in a

time multiplexing way.

The basic requirements on the data transmission

network are the reliability and availability, which

include following contents:

(1) To meet the real time requirement of data

transmission, in order to guarantee the response time

of RBCS.

(2) To meet the requirement of information

volume.

(3) To guarantee that a unique communication

channel is established between the station and a

given train.

(4) To meet the error rate and reliability

requirement in data transmission;

(5) To guarantee a reliable radio coverage for all

the trains within the station area.

The characteristics of the radio data transmission

network are described as following.

3.1 Dynamic Network Organization

and Network Mobility

A train approaching a station has to register to enter

the local transmission network of a station, and a

train leaving the station is deregistered to exit the

network. Because a train moves along the line

continuously, the members of the station local

network are not fixed. On the contrary, it is a

dynamic joining and splitting process. In this sense,

the whole network formed by all the local networks

along the line is mobile.

3.2 Star Shape Network Structure

The station local network is a star shape network,

with the station base radio at the center, and all

onboard radios as the network nodes.

3.3 Using Different Frequencies

Alternatively in Different Stations

As shown in figure 1, every three stations use a

frequency group, to avoid common frequency

interference between stations. Each station has two

radios, one is used for up running direction, and the

other for down running direction, with two different

frequencies for each running direction respectively.

For example, frequency F

, F

are used for up

running direction, and F

, F

for down running

direction.

The frequency used for a train to communicate

with the next station can be pre-stored in a balise.

When an outbound train passes the balise, the

onboard interrogator will pick up the frequency

information from the balise and pass it to the

onboard control equipment of RBCS, which will

accordingly set the frequency of the onboard radio

to the new value.

ANALYSIS OF THE ARCHITECTURE AND RELIABILITY OF DATA TRANSMISSION NETWORK USED FOR

RADIO BASED CAB SIGNALING SYSTEM

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3.4 Addressing Mode

The radio data transceiver used for RBCS works in

addressing mode, because all the radio stations

within the station area use the same frequency.

Therefore, the network address of the radio should

be included in the data frame. When a data

transceiver receives a data frame, it will compare the

address contained in the frame with its own address.

If two addresses match, the data frame will be

passed to the main controller for further processing;

otherwise the data frame will be rejected.

3.5 Data Frame Collision and

Communication Jam

Data frame collision can be avoided by adopting

time multiplexing and communication protocol. The

communication protocol will put strict constraint on

the time slot, the communication sequence of the

time slot, as well as the master-slave relationship

between the station radio and the onboard radio, in

order to guarantee the orderly communication

between station and train. During communication,

the onboard radio and the station radio may be

deadlocked for some reasons. In order to avoid the

interruption of the communication, overtime

detection circuit is designed to reset the radio.

3.6 Using Changeable Data Frame

The information transmitted by RBCS is divided

into three classes. Class I includes the basic train

control information; Class II includes the number of

the route for train receiving/departure, train number,

train actual speed and maximum allowed speed,

train position, etc. These above two classes of

information are vital train control information.

Furthermore, if permitted by time delay. The third

class of non-vital information used for the

engineering department, communication and

signaling department as well as locomotive

department can be transmitted. Therefore, different

frame format with long, medium and short length

can be chosen according to different requirements.

4 RELIABILITY OF RADIO DATA

TRANSMISSION

Because RBCS is used as a warrant for train

operation on main lines, its reliability, availability,

maintainability and safety (RAMS) is very important.

The transformation from TBTC to CBTC, is actually

the transformation of information transmission

channel. Therefore, the unreliable factors caused by

the transformation should be properly addressed in

system design. In the approaching continuous RBCS,

following measures are adopted to guarantee the

reliability.

(1) Any transmitted information is constrained by

the limitation of target address. In RBCS, the

information is transmitted via radio channel in the

open space, therefore, each station and on-board

control equipment of RBCS must be assigned a

unique network address.

(2) Time stamp is used to guarantee the time

validity of the information. In RBCS, information is

transmitted on time division multiplexing basis,

which may be interfered or attacked intentionally or

unintentionally, therefore, time stamp is used in the

bi-directional communication between train and

station, namely, the sender of the information should

attach the transmitted information with a time stamp;

upon receiving the information, the receiver will

check the time stamp for time validity. If the time

stamp expires, the information is regarded as invalid

and will not be executed

(3) Train registration method. Any train in the

controlled area of the dispatcher is assigned a unique

train number according to traffic plan. The train

number is associated with a registration number. So,

only a registered train can perform valid information

Figure 1: Frequency distribution in RBCS

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transmission in the radio channel.

The three-dimension control puts a strict

constraint on the bi-directional communication,

namely, only when the information has qualified for

the three constraints of address, time stamp and

registration number can it be regarded as valid. In

the effective working area of RBCS, each train

occupies a fixed space at any time, and is assigned a

unique registration number.

5 CONCLUSION

The result of the field test of RBCS has proved that

the structure of the transmission network and the

reliability of RBCS can meet the requirement of

train control. The constitution of data transmission

network by such methods as dynamic network

organization, star shape network, alternative

frequency used for different stations, and addressing

mode is reasonable and practicable. The

three-dimension control technique proposed in the

paper can enhance the reliability remarkably.

REFERENCES

Wang Junfeng, 2001, Analysis about the Reliability of

Wireless Data Transmission for High Speed Train in

Strong Interference Environment, IEEE 54

VEHICULAR TECHNOLOGY CONFERENCE, VTC

FALL 2001, VOLS 1-4, PROCEEDINGS, 168-172

Wang Junfeng, 2001, Research on the Application of

Interwoven Techniques to improve the Real Time

Performance of Transmitting Train Control

Information by Radio, Mobile Communication, No.2

pp38-40.

Wang Junfeng, 2001, Analysis of the Safety of Train

Control System for Qinghai-Tibet Railway, Journal of

Safety Science of China, Vol.11, No.5, pp53-57, 2001

Wang Junfeng, Zhang Yong et al, 2002, Research on the

Radio Based Cab Signalling System used for

Qinghai-Tibet Railway, Journal of Railways, Vol.24,

No.3, pp22-27

Wang Junfeng, Zhang Yong et al, 2003, Analysis of the

Safety of The Train Control System of Qinghai-Tibet

Line, Proceedings of WCRR2003, Edinburgh, UK.

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RADIO BASED CAB SIGNALING SYSTEM

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