GB2218557A - A railway signalling system - Google Patents

Abstract

A signalling system in which 'authority' is given to a train by radio from a central computer base station and location information is derived by the train from wayside transponders and transmitted back to the base station. The authority consists of specifying transponders in the authorised track section. Thus in a digital data coding system, rather than specify every transponder in the authorised section - an indeterminate message format - the sum of the transponder codes is transmitted, together with the identity of the first and last. An on-board processor sums the transponder codes as they arise and at the end of the section a discrepancy between the accumulated sum and the received sum indicates a faulty transponder and the identity of the particular one. Economy of message transmission and constant message format is thus achieved. <IMAGE>

Description

A Railway Signalling System This invention relates to railway signalling systems and particularly to such systems for monitoring and controlling the movement of trains through track sections.

Various systems have been devised for the safe signalling and control of trains using radio data messages between a base station and a radio transmitter/receiver on each train of the system.

In some of these systems, securely-coded data messages, which constitute authority for a particular train to travel over a particular section of track, are sent by radio from a central safe computer system at the base station to a processor on-board the train.

This electronic 'authority' corresponds to the physical tokens of earlier systems, actual possession of a token being essential for the driver to proceed. The data message contains the text of the station names between which the train may travel. The on-board processor checks that the secure coding of the message has been preserved during radio transmission, and if so, displays the text to the train driver.

When the train driver reaches the end of the section for which he has authority, he returns his authority to the central safe computer by another data message over the radio, the on-board processor having previously blanked the text display.

In many of the systems of this type that have been installed to date, the reporting of the position of the train when it returns its authority is accomplished verbally by voice transmission; the train driver tells the central operator the current position of the train, and the operator keys this information into the central safe computer system. This is clearly a process prone to human error.

Others have proposed the use of passive transponders, each having a unique identity, installed on the track at intervals, together with transponder readers on trains, to allow each train in the controlled area to monitor its own position. Such proposals have usually involved a list of transponders that the train may pass over being sent to the train along with the text of its authority. The train, in such proposals, reports its passage over each transponder in turn, by means of further radio data messages. By this means, the central safe computer maintains a record of the location of each train in the system.

Unfortunately, the list of transponder identities will be of variable length, depending on the extent of the authority given to the train. Also, the data messages from each train reporting passage over a transponder tend to use up a significant amount of time on the radio channel, making it unsuitable to be shared between speech and data messages.

An object of the present invention is to provide a railway signalling system employing radio transmission of location information which at least partially overcomes the above problems.

According to one aspect of the present invention, in a railway signalling system in which train equipment comprises a transponder interrogator, a data processor and a radio transmitter/receiver, a base station comprises a radio transmitter/receiver and means for transmitting to the train data authorising the passage of the train through a track section defined by the transmitted data, the track section comprising a plurality of transponders positioned at intervals along the track and each transponder having an identity code which is transmitted to the train on interrogation, the base station comprises means for transmitting to the train a check code derived from a combination of the identity codes of the transponders in an authorised track section and the train equipment is adapted to receive identity codes from transponders as the train proceeds through the authorised track section and provide an Indication when the received identity codes correspond to the check code.

Preferably the base station has means for transmitting, in addition to the check code, the identity code of at least one limit transponder at an end of the authorised track section, the data processor being adapted to compare each transponder code detected on interrogation with that of the limit transponder received from the base station and to produce a train controlling response in the event the detected identity code is beyond the limit transponder and outside the authorised track section.

The base station may have means for transmitting the number of transponders in the authorised track section, the data processor having means for counting the number of transponders detected upon interrogation within the authorised track section and providing an indication of any discrepancy to the train transmitter for transmission to the base station.

The check code may comprise the sum of the identity codes of the transponders in the authorised track section.

The processing of the detected identity codes may comprise a cumulative summation, the train transmitter being arranged to transmit the cummulative sum to the base station, the base station comprising means adapted to subtract the cumulative sum from the check code to obtain the identity code for any transponder that failed to respond.

According to another aspect of the invention, in a railway signalling system in which an authorisation message is transmitted by radio from a base station to a train to permit the train to traverse a track section having a plurality of transponders and in which the exit of the train from the authorised track section is required to be monitored, a method of passing authority from the base station to the train in which the transmitted data authority message comprises the first and last only of the individual transponder identity codes and a constant length check code derived from all of the transponder identity codes, the authority message format being constant irrespective of the number of transponders in the particular section.

A railway signalling system in accordance with the invention will now be described, by way of example, with reference to the accompanying drawings, of which: Figure 1 is a diagram showing the relation between base station, train and transponders; and Figure 2 is a diagram of a track system between a number of stations.

Referring to Figure 1, the track system is divided into a number of sections by transponders 1 mounted adjacent the track at strategic positions along the track. Each transponder is passive to the extent that it is energised only by reception and rectification of an interrogation signal from a passing train. Such interrogation initiates a response from the transponder, a radio signal which identifies the transponder to the interrogator on board the train.

The power of the transponder signal is much too low to be picked up by any other train.

The type of transponder is not of importance in the invention; it may be partially active as above, purely passive as with magnetic elements, or fully active. The transponder is merely required to identify itself to the on-board processor when interrogated.

The central control, or base, station 3 has a radio transmitter and receiver and means for transmitting data messages to selected trains. The data messages incorporate very secure address coding for selection of the train in question while different base stations are separated by means of different carrier frequencies.

The data messsage sent to the train contains the text of the authority to be displayed to the driver, i.e. the station or other location names, and various items of data concerning the transponders.

These data may include: (a) Upper and lower limits for the transponder identities that the train may pass over, thus specifying a permitted range.

(b) The number of transponders that the train should encounter during its travel over the authorised section of the line, l.e. the transponder 'count'.

(c) The sum of the identities of all the transponders the train should encounter, this sum constituting a check code.

Each of these items has, or may be arranged to have, a constant word length irrespective (within limits) of the number of transponders involved. Thus the sum of the identity codes has a constant word length comparable to that of each transponder code. The overall format of the 'authority', i.e. the data message, can thus be maintained constant irrespective of the length of the authorised section. The absence of lists of transponder identities in the authority also provides an economy of transmission time.

Figure 2 shows a track system connecting stations A, B, C and D and a typical transponder numbering system over the various single and double track portions.

Also shown in Figure 2 is a typical list of data messages transmitted to a train. Each message consists of a portion displayed to the driver, giving the extent of the authority granted by the names of the terminal stations, e.g. A - B, and a portion received only by the on-board processor and comprising the identity code of the lower limit transponder, the upper limit transponder, the transponder count over the authorised section, and the sum of the transponder identity codes encountered.

In operation, each time the train passes over a transponder, the on-board processor checks the identity of the transponder against the range information Eitem (a) above] received from the central computer. In the event of the transponder being outside the authorised range, the processor may take appropriate action, such as applying the train brakes.

The processor also keeps a count of the transponders passed since the receipt of that authority, and the sum of their identities.

When the train reaches the end of the authorised section, the driver recognising the terminal station, he returns his authority (by initiating a keyed-in verbal signal transmission), the display is blanked and a data message is sent back to the base station computer.

Included in this data message are the following: (a) The identity of the last transponder passed over (which should be the 'upper limit' or 'lower limit' transponder above). This identifies the current position of the train.

(b) The difference between the expected and actual number of transponders passed during travel over the route. This information can be used by the central computer for diagnostic purposes; a failed transponder in that section of line will result in a non-zero value for this data.

(c) The difference between the expected and actual sums of the identities of transponders passed during travel over the route. This difference is used by the base station processor in a diagnostic operation. A failed transponder in the authorised section of line will result in a value for this data corresponding to the identity of the failed transponder.

The above method of using transponders offers several advantages over other methods: (1) The data sent to and from the train by radio is of fixed format, whatever the extent of the authority.

(2) In spite of the fact that the identities of all the individual transponders in the section are not transmitted to the train, the central computer at the base station is made aware of the failure and identity of any transponder, so that a technician can be sent to replace the device.

(3) If logical sequences of numbers for transponders are used on the railway, there is redundancy of information sent to the train, enabling the on-board processor to carry out checks on the validity of the data, and of the correctness of each transponder passed. Thus, in the example shown in Figure 2, all transponder identities are multiples of 5 and each section has a constant first two digits (of a four digit code).

Particular transponders can be used as triggers for actions by the on-board processor, in one of two ways: The identity of the trigger transponder can be transmitted to the train in the data message containing the authority details; and, if a logical sequence of transponder identities is used, the trigger transponder identity can be derived by the on-board processor (e.g. an audible warning on the approach to the end of the authority could be triggered by passage over a transponder with an identity within some limit of the maximum or minimum of the range).

A major advantage of the system described above is that the on-board processor can be a relatively low-cost processor since it merely has to deal with limited data of constant format. The n jority of the data security procedures can therefore be built into the base station processor, leaving the on-board processor to perform minimal processing with minimal security.

Claims (8)

1. In a railway signalling system in which train equipment comprises a transponder interrogator, a data processor and a radio transmitter/receiver, a base station comprises a radio transmitter/receiver and means for transmitting to the train data authorising the passage of the train through a track section defined by the transmitted data, said track section comprising a plurality of transponders positioned at Intervals along the track and each transponder having an identity code which is transmitted to the train on interrogation, said base station comprises means for transmitting to the train a check code derived from a combination of the identity codes of the transponders in an authorised track section and said train equipment is adapted to receive identity codes from transponders as the train proceeds through the authorised track section and provide an indication of the correspondence between the received identity codes andd said check code after passage through said authorised track section.

2. A railway signalling system according to Claim 1, wherein said base station has means for transmitting, in addition to said check code, the identity code of at least one limit transponder at an end of the authorised track section, said data processor being adapted to compare each transponder code detected on interrogation with that of said limit transponder received from the base station and to produce a train controlling response in the event the detected identity code is beyond said limit transponder and outside said authorised track section.

3. A railway signalling system according to Claim 1 or Claim 2, wherein said base station has means for transmitting the number of transponders in said authorised track section, said data processor having means for counting the number of transponders detected upon interrogation within said authorised track section and providing an indication of any discrepancy to the train transmitter for transmission to said base station.

4. A railway signalling system according to any preceding claim, wherein said check code comprises the sum of the identity codes of the transponders in the authorised track section.

5. A railway signalling system according to Claim 4, wherein the processing of the detected identity codes comprises a cumulative summation, said data processor being adapted to subtract said cumulative sum from said check code to obtain the identity code for any transponder that failed to respond.

6. In a railway signalling system in which an authorisation message is transmitted by radio from a base station to a train to permit the train to traverse a track section having a plurality of transponders and in which the exit of the train from the authorised track section is required to be monitored, a method of passing authority from the base station to the train in which the transmitted data authority message comprises the first and last only of the individual transponder identity codes and a constant length check code derived from all of the transponder identity codes, the authority message format being constant irrespective of the number of transponders in the particular section.

7. A railway signalling system substantially as hereinbefore described with reference to the accompanying drawings.

8. A method of signalling authority messages between a base station and a train substantially as hereinbefore described with reference to the accompanying drawings.