EP1868175B1

EP1868175B1 - Control station, mobile station and method for communication in object movement control

Info

Publication number: EP1868175B1
Application number: EP06115510A
Authority: EP
Inventors: Nanna Svane Theisen; Mark Motorola Edwards; Ole Hammer
Original assignee: Motorola Inc
Current assignee: Motorola Solutions Inc
Priority date: 2006-06-14
Filing date: 2006-06-14
Publication date: 2010-02-24
Anticipated expiration: 2026-06-14
Also published as: EP1868175A3; DE602006012462D1; ATE458657T1; EP1868175A2

Abstract

A communication system (100) for use in movement control of mobile objects such as transport vehicles includes a first mobile station (106), a second mobile station (107) and a control station (103), wherein the first mobile station is operable to send to the control station, and the control station is operable to receive, a signal including location information relating to a current location of the first mobile station and wherein the second mobile station is operable to send to the control station, and the control station is operable to receive, a signal including location information relating to a current location of the second mobile station, and the control station is operable to detect from the location information received from the first and second mobile stations that the first mobile station is approaching a current location of the second mobile station and to issue an alert signal to either or both of the first and second mobile stations to indicate an alert condition related to the detected approach. The control station may automatically issue the alert signal based on a prediction of a probable collision. The first mobile station may be carried on a train or ship or other transport vehicle and the second mobile station may be a radio of a user who is located in the intended path of the train or ship or other vehicle. Also described is a control station, a mobile station and a method for use in the system.

Description

FIELD OF THE INVENTION

The present invention relates to a wireless communication system and a method of communication for use in movement control of mobile objects. In particular, the invention relates to communication to assist avoidance of collisions between moving transport vehicles such as trains and other mobile objects.

BACKGROUND OF THE INVENTION

Despite ongoing efforts made by transport authorities to improve transport safety, reports are occasionally heard about collisions between transport vehicles travelling along a predetermined path and other mobile objects that are located on the path. For example, such collisions occur between railway trains and maintenance or other railway staff that have to work on or adjacent to railway tracks along which the trains run. An efficient alerting system is needed to indicate to these staff and to the train driver that a train is approaching the location in which these staff are working. The problem is intensified nowadays by the high speeds at which trains can run and the lack of noise made by some modern trains.
Existing alerting and safety systems rely on short range communications between train and staff, on alert signals when trains pass fixed points such as signals and on advanced (ATP) systems which operate to cause automatic braking of trains when their speed exceeds a predetermined speed in certain specified zones.
Existing alert systems produce alarms which may not be adequate in the situations described earlier or may be irrelevant when the train is moving slowly, leaving to a tendency for personnel to whom the alarms are directed to consider all alarms as false alarms, which carries the danger that a genuine alarm might be ignored.
Similar problems can arise in controlled movement of other types of vehicle, such as ships following a pre-determined course which may become occupied for example by smaller boats or other waterborne craft.
JP 2003212121 describes a train approach alarming system which monitors the position of trains and workers and sends an alarm signal to a working spot when a train is approaching it.
WO 01/89905 describes a system for installation in a rail network which seeks to avoid the likelihood of train collisions. Each train determines its own position and communicates with a central controller which works out where each train is on the network.
WO 95/28650 describes a system in which aircraft have a position determining portion and transmit positional and tracking information to a receiving aircraft. A computing portion on the receiving aircraft or in a ground based facility computes a probabilistic future track of the transmitting aircraft.

SUMMARY OF THE INVENTION

According to the present invention in a first aspect there is provided a wireless communication system as defined in claim 1.
According to the present invention in a second aspect there is provided a method as defined in claim 12.
Further features of the invention are defined in the accompanying dependent claims and are disclosed in the embodiments of the invention in the following description.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a block schematic diagram of a radio communication system being used in a railway train movement control.
FIG. 2 is a block schematic diagram of a mobile station operating in the communication system of FIG. 1.
FIG. 3 is a block schematic diagram of a control station operating in the communication system of FIG. 1.
FIG. 4 is a block schematic diagram of a radio communication system being used in ship movement control.

DESCRIPTION OF EMBODIMENTS OF THE INVENTION

The present invention provides a mobile communications system, and a control station, mobile station and method for use therein, which allows alerting of personnel via mobile radio terminals (mobile stations or 'MSs') by signals from a control station that a moving object such as a transport vehicle is approaching them. The transport vehicle may for example be a railway train and the personnel may for example be railway maintenance or other operational staff. In addition, an alert signal may be sent to a mobile station carried on a moving vehicle, e.g. train, to alert the driver to reduce the speed of the vehicle or stop the vehicle. The invention is not limited to use in railways and may for example be used in control of movement of other types of vehicle, e.g. shipping to warn navigators of small boats and other vessels that a ship is approaching along a pre-determined shipping lane or in control of movement of other types of land vehicles or airborne vehicles.
FIG. 1 is a block schematic diagram of a communication system 100 deployed to provide communications in a railway system. The communication system 100 is a wireless communication system, either narrowband or broadband. For example, the communication system 100 may be a trunked system designed to operate in accordance with industry standard protocols for wireless communication, such as the TETRA (Terrestrial Trunked Radio) standard protocols as defined by the European Telecommunications Standards Institute. Alternatively, the communication system 100 could be built to operate using proprietary protocols.
The communication system 100 includes a fixed infrastructure 101 including a BTS (base transceiver station) 102. A control station 103 is connected by a link 104 to the infrastructure 101. The control station 103, which is described in more detail later, controls movement of railway trains and other objects in the railway system at least in a geographical region of the railway system. The link 104 may be a wired or cable link or may be a wireless link, e.g. via one or more other base transceiver stations in a wide area, e.g. nationwide, communication network. Where the control station 103 is located close to the infrastructure 101 the control station 103 and the infrastructure 101 or part of the infrastructure 101 may be located in the same building.
A moving railway train 105 carries a MS (mobile station) 106 which is a radio communication unit fitted inside the train 105, e.g. in a cabin dedicated to the train's driver. A MS which is a similar unit is carried by other trains operating in the same railway transport system. The MS 106 and other similar MSs (not shown) in other trains include a radio transceiver which sends and receives radio signals. The MS 106 sends signals to the control station 103. These signals are sent from the MS 106 over the wireless connection to the BTS 102 and then to the control station 103 via the fixed infrastructure 101 and the link 104. These signals sent by the MS 106 to the control station 103 include information useful in control of the movement of trains in the railway system by the control station 103. These signals include location information including an estimate of the current location of the MS 106 indicating the current location of the train 105. This estimate, which is being updated regularly, preferably substantially continuously, may for example have been obtained using a GPS (Global Positioning System) receiver included in the MS 106. Alternatively, the MS 106 may include a processor which, in a known manner, estimates the current location by another known location estimating technology, such as by timing synchronised known signals from at least three base transceiver stations of known location (e.g. including the BTS 102) to provide measures of the respective distances of the MS 106 from the base transceivers stations and then by calculating the location of the MS 106 by triangulation from the distance measurements.
The minimum sending frequency of the signals indicating current location, i.e. the number of signals sent per unit of time, is desirably calculated and optimised for the performance characteristics needed for a specific implementation of the system 100 and the MS 106, but can be expected to be in the order of seconds for most train speeds. The sending frequency of these signals may be variable and for example may beneficially be increased with an increase in speed of the train 105, e.g. with the sending frequency being proportional to a detected speed of the MS 106.
A MS (mobile station) 107 and a MS 108 are present in the path of the train 105. The MSs 107 and 108 may for example be portable radios carried by railway track maintenance personnel working on a part of the track along which the train 105 is travelling. The MSs 107 and 108 also contain location detection technology enabling the respective locations of the MSs 107 and 108 also to be reported to the control station 103. The MSs 106, 107, 108 operate in a similar manner to the MS 106 which will now be described in more detail with reference to FIG. 2 as follows.
FIG. 2 is a block schematic diagram showing more detail of one form of the MS 106. The MS 107 and the MS 108 are constructed and operate in a similar manner except of course that the MS 106 is fitted inside the train 105 whereas the MSs 107 and 108 are portable and are carried by a person. The main operations of the MS 106 are controlled by a controller 201, e.g. a digital signal processor, which operates in conjunction with a timer 209 which synchronises operations within the MS 106 and a memory 210 which stores data and programs used within the MS 106. A processor 202 processes information included in RF signals sent and received by a transceiver 203. The processor 202 may also be a digital signal processor and in practice may operate together with the controller 201 in a single device. The processor 202 extracts information from a received RF signal detected by a transceiver 203 and passes the information to an appropriate output transducer. Similarly, the processor 202 receives input information for transmission from an appropriate input transducer and delivers the information to the transceiver 203 for transmission in the form of an RF signal by the transceiver 203. As in a conventional mobile radio terminal, the MS 106 includes (as an optional component) an output transducer which is an audio output 204, e.g. a speaker, which converts signals received which represent speech information to an output audible form for delivery to a user. The MS 106 also includes (as an optional component) an input transducer which is an audio input 205 which converts an input audio signal, e.g. in the form of speech, into an electrical form in a well known manner. The electrical signal is delivered to the processor 202 described above. A keypad 212 serves as a user interface and allows a user to enter control signals for delivery to the controller 201 to operate functions of the MS 106. The keypad 212 also acts as another input transducer allowing entry of alphanumeric data for delivery to the processor 202 for processing to send in radio communications by the transceiver 203. A display 207 operated by a display driver 206 under control of the controller 201 provides displayed information to a user of the MS 106 in a known manner. A battery 211 provides electrical power to all operational components of the MS 106.
An alarm 213 provides a warning or alarm signal to a user of the MS 106, e.g. the train driver, when the alarm 213 is operated by a signal from the controller 201 triggered by an alert signal from the control station 103 in a manner described later. For example, the alarm 213 may be a warning light and/or a device providing a loud audible alarm sound such as buzzer or may provide an audible message to the driver to slow down or stop. As described later, warning signals of at least two different types may be produced by the alarm 213 depending on the severity of the warning needed to given to the user as detected by the controller 201.
The signal from the controller 201 to operate the alarm 213 may be employed in conjunction with a primary safety control system in which the brakes of the train 105 are automatically applied when the severity of the warning reaches a certain critical level. Such a use would require special adaptation into the design of the safety control system.
The MSs 107 and 108 produce alarm or warning signals in a manner similar to the MS 106. Thus, the signals generated by the controller 201 of the MSs 107 and 108 in response to an alert signal from the control station 103 operate the alarm 213 of the MSs 107 and 108 and the users of the MSs 107 and 108 are thereby warned that they should move to a position of safety.
The transceiver 203 of the MS 106 provides RF communications to and from other transceivers operating within the system 100 such as the BTS 102 and, when able to operate in a direct communication mode, with the MS 107, the MS 108. The transceiver of the MSs 107 and 108 provides similar communications. The MS 106 also includes a location detector. In the form shown in FIG. 2, the MS 106 includes a GPS (Global Positioning System) receiver as an example of the location detector. The GPS receiver 208 can receive GPS signals from GPS satellites (not shown) in a known manner. Information extracted by the GPS receiver 208 is passed to the processor 202. The processor 202 thereby extracts current location information from the GPS receiver 208 in a known manner and provides the same information to the memory 210 for storage in the memory 210.
In addition, the controller 201 instructs the processor 202 to prepare a data message which includes the current location information. The format of this message may include a code to be understood by a receiving terminal indicating what is included in the message. This message is sent as an RF signal by the transceiver 203 to the infrastructure 101 via the BTS 102 and is delivered by the infrastructure 101 to the control station 103 via the link 104. The RF signal may for example include a network destination address by which the signal is routed to the control station 103. The MSs 107, 108 collect and send signals including current location information in a similar manner.
In the above embodiments, the message including the location information sent by the transceiver 203 (of the MS 106, 107 or 108) to the control station 103 also includes a time indication ('timestamp') of the precise time of the message generation and/or transmission, e.g. for recordal, calculation and investigation purposes at the control station 103 where it is received.
A processor of the MS 106, which may be the processor 202 or the controller 201, may calculate the current speed of the train 105 by monitoring the variation of the location information with time. The current speed may be indicated in each of the signals sent to the control station 103. The current speed may also be used to adjust the sending frequency of the signals sent to the control station 103. The sending frequency may be increased as the speed of the train 105 increases and may be reduced as the speed is reduced. The sending frequency may be adjusted in steps or as a linearly proportional response to changes of the speed.
Signals which are incoming alert signals sent from the control station 103 as described in more detail later via the BTS 102 are received by the transceiver 203 and are passed to the processor 202. The processor 202 recognises that the signals have to be passed to the controller 201. The controller 201 is programmed automatically to recognise the signals, e.g. because they contain a special code, and automatically to issue signals to operate the alarm 213 in response. As described later, the controller 201 may recognise different types of received alert signal in this way and in response may issue control signals of different types causing different warnings to be provided to a user via the alarm 213, to provide warnings of different severity levels.
FIG. 3 is a block schematic diagram of the control station 103. The control station 103 includes a transceiver 301 which receives and sends signals via the link 104 and the infrastructure 101. The control station 103 also includes a server 302 which processes received signals and prepares signals for sending. The server 302 also includes a database to store current information about the railway system including information about the current location of trains and other objects in the railway system and other useful pre-programmed information such as route and timetable information. The server 302 is also able to make intelligent calculations and predictions as described later. A control console 303 is operably connected to the server 302. The control console 303 includes a keyboard 304 for data entry by a user, a display screen 305 to display information relevant to control of the railway transport system, a radio dispatcher unit 306 to allow radio communications to be made via the link 104 and the infrastructure 101 and a telephone 307 to allow standard landline telephone communications to be made to and from a person operating the control console 303. The display screen 305 may for example display when selected a map which shows a layout of the railway system and the current location of trains and other mobile objects present in the railway system.
Incoming signals received by the transceiver 301 include: (i) a first signal giving information relating to the current location of the MS 106 on the moving train 105; (ii) a second signal giving information relating to the current location of the MS 107; and (iii) a third signal giving information relating to the current location of the MS 108. In practice, the transceiver 301 may receive signals from many communication units mounted on other trains as well as from other mobile stations carried by other relevant moving objects such as maintenance staff.
The transceiver 301 receives the incoming signals from each of the specified sources regularly, e.g. at a rate that is proportional to the speed at which each source is moving. For a control station 103 that is monitoring many MSs this is likely to result in a plurality of signals per second being received at the transceiver 301. The transceiver 301 decodes the signals and delivers the information contained in them to the server 302. The information includes an identifier of the terminal (e.g. the MS 106, the MS 107 or the MS 108) which has sent the signal containing the information as well as a time indication ('timestamp') of the precise time of the message generation and/or transmission. As mentioned earlier, the received signal may also include an estimation of the speed of travel of the sending terminal. The received information is used to update information held in the database of the server 302 on a regular or substantially continuous basis.
The server 302 comprises a processor which uses the identification and location information it receives to carry out calculations of (a) the current trajectories of all moving objects from which it is receiving location information; (b) the predicted trajectories of those objects for a period of time into the future; and (c) a probability that there will be an intersection between two or more of the predicted trajectories. Information produced from the calculations may be employed for display in graphical form, e.g. having a map as background, on the display screen 305. The display in graphical form may be regularly or substantially updated automatically by use of signals from the server 302 relating to the calculations it makes.
The trajectory of an object in the context of the calculations made by the server 302 is in practice a set of object velocity measurements, i.e. discrete measurements of the speed of an object and the direction in which it is heading at selected points in time. This set contains some historical data which are measurements from a period which has just taken place, say the previous 60 seconds, to help in estimating the object's current heading direction. Other data such as historical data retrieved from a memory of the server 302 relating to previous movement patterns of moving objects as well as the identity of the MSs 106, 107 or 108 or their users may be used in the calculations. Of course, if one of the objects is not moving its 'trajectory' will be detected as a stationary position.
An alert message is automatically generated by the server 302 for sending to the MS 106 and/or to the MSs 107 and 108. Thus, using the location and other information extracted from incoming signals and a pre-programmed calculation and prediction procedure as described above, the server 302 generates an alert signal when it detects a probability of collision between the MS 106 and the MS 107 and/or the MS 108. When the probability reaches a pre-determined level, e.g. when the server 302 calculates that there is a minimum safe distance between the train 105 and the users of the MS 107, 108, the server 302 issues an alert signal. The server 302 may automatically send the alert signal to the MSs involved in the possible collision, i.e. to the MS 106 and to the MSs 107, 108, e.g. using addresses known from the signals received. The alert signal may itself be in the form of a data message. For example, this data message may comprise a special 'PDU' (packet data unit) data message. Desirably, the message can be extracted and understood without further interpretation at the receiving terminal (i.e. the MS 106, the MS 107 or the MS 108). Alternatively, the alert signal may include a short code which an intelligent controller at the receiving terminal, e.g. the controller 201 of the MSs 106, 107 and 108, can recognise and can convert into an alert message in words an/or can employ to operate an alarm such as the alarm 213 of the MS 106.
In an enhanced embodiment of the invention, the server 302 may automatically issue appropriate alert signals to MSs whose users are at risk wherein the alert signals are graded according to the probability of collision. So, for example, a more urgent and prominent alert signal may be sent if a collision is very likely in the next 20 seconds, but a less urgent and prominent alert signal may be sent where a collision is not likely in the next 20 seconds but might happen in the next few minutes. The infrastructure 101 may beneficially be programmed to recognize one of these alert signals sent by the control station 103, particularly one required to be delivered urgently and prominently, and to give the signal the required priority of delivery. Similarly, the receiving MSs, e.g. the MSs 106, 107 and 108, may operate by a suitable program run in the controller 201 of each MS to recognize different forms of alert signal according to the likelihood of collision and generate different forms of warning or alarm signal accordingly.
A person who is a control manager of the railway system (at least in a particular defined region thereof) can also monitor information displayed on the display screen 305, in the form of a map highlighting the monitored objects, to monitor that the train movement is operating satisfactorily. The control manager can also monitor for potential problems that may arise. The control manager is able to communicate with the relevant people, e.g. a driver of the train 105 or a user of the MS 107 and a user of the MS 108. The control manager may for example issue a message from the console 303 as a data message by entry via the keyboard 304 or by pressing a single button or key on the keyboard 304 which causes a standard alert message to be produced by the server 302. Alternatively, the control manager may issue a spoken message, e.g. from the local radio dispatcher unit 306 via the infrastructure 101 or by the telephone 307. The message is delivered to the target terminal (e.g. MS 106) via the transceiver 301 and the infrastructure 101.
For example, in addition to a message automatically generated and sent by the server 302, an alert message may be sent by the control manager from the control station 103 to the driver of the train 105 and to the users of the MSs 107 and 108 via the MSs 106, 107 and 108 to warn the driver and those users that the train 105 is approaching the location where those users are. As indicated earlier, the message may be a speech message or a data message. Such a message may include for example information giving the current location and speed of approach of the train 101. It may also give the identity of the train and the direction of approach. Where the message is a data message it may include a component which is recognised automatically to trigger an alarm at the receiving terminal. Where the message is received by the MS 106, MS 107 or MS 108, the controller 201 of the MS 106, 107 or 108 may recognise a code included in the particular received message and may automatically issue a signal to operate the alarm 213. Supplementary warning information may also be provided visually via the display 207 and/or audibly via the audio output 204 to the user of the MS 107.
The communication system 100 described with reference to FIG.s 1 to 3 may be used in conjunction with other known location and/or movement monitoring technologies to supplement the location and timing information generated in the system 100 in the manner described above. For example, monitoring of personnel by one or more video surveillance cameras (not shown) may also be used to determine if the personnel are currently in a safe or dangerous position, e.g. to monitor if the personnel are on a platform adjacent to a railway track or on the track itself. The image detected by the video camera(s) may be applied to a program run on an imaging server (not shown) which can automatically detect movement of humans (or other mobile objects) outside a pre-defined safety boundary, e.g. off an edge of a railway station platform. The monitoring server may then issue an alert signal automatically. This may be sent to the control station 103 automatically. The server 302 may use the information in the calculation of a probability that a person whose image has been detected is in danger. The server 302 may then issue an alert signal to the train driver in a manner as described above or to some other official, e.g. a manager at a station where the image is detected. Alternatively, or in addition, a manager who is monitoring the image may send a warning signal to an MS carried by any person in a dangerous position and/or to the control station 103.
In the above embodiments of the invention one or more of the personnel who have MSs which receive a radio message to inform them of the approach of a train may send to the control station 103 an acknowledgment message, which may be generated automatically by pressing a button or key of the MS, to acknowledge the received message, e.g. to indicate that they have moved to a position out of danger. Alternatively, one or more of the personnel may send a message to indicate that they cannot move to avoid collision. This may result in a lower level alarm signal from the control station 103 being upgraded to an emergency signal.
The information recorded by the server 302 may be used to generate a "near-miss" trend analysis and report. This may be used for example to raise an alert to a shift manager. So, if there is a series of near misses happening in a particular location in a short space of time, the analysis and report can indicate a serious problem, e.g. track workers are not being properly supervised, working to an incorrect schedule etc.
In the embodiments of the invention described above, the invention has been described in terms of its application in a railway transport system. Use of the invention is not however limited to railways. The invention may be employed in any system for vehicle movement in which the paths of certain moving vehicles is pre-determined. FIG. 4 illustrates an alternative use of the invention in a maritime shipping environment. In FIG. 4, a communication system 400 includes a fixed infrastructure 401, a BTS 402 and a control station 403 connected to the infrastructure 401 by a link 404. The infrastructure 401, the BTS 402, the control station 403 and the link 404 operate respectively in a manner similar to the infrastructure 101, the BTS 102, the control station 103 and the link 104 described with reference to FIG. 1. A ship 405 carrying an MS 406 is following a pre-determined course. A smaller sailing vessel 409, e.g. a boat, is carrying a MS 407 and a smaller sailing vessel 410 is carrying a MS 408. The vessels 409 and 410 are in the projected path of the ship 405. The MSs 406, 407 and 409 operate respectively in a manner similar to the MSs 106, 107 and 108 in the system 100 of FIG. 1. Thus, a signal may be sent from the control station 403 to a pilot of the ship 405 and to the navigators of the vessels 409, 410 to provide an alert, e.g. to be indicated as an alarm signal to the pilot or navigator at the receiving terminal ( MS 406, 407 or 408), in one of the ways described earlier, of the approach of the ship 405 toward the vessels 409, 410.
The embodiments of the invention described above show certain benefits over the existing alerting systems employed to indicate approach of a transport vehicle such as a train or ship to a particular location along a pre-determined path. Firstly, by constantly gathering location data and related time information, the control station in the embodiments of the invention monitors and records movement of vehicles and other moving objects such as people and is able to make calculations and intelligent predictions about the probability of collisions occurring and to issue signals automatically based on the information, calculations and predictions to provide alerts and warnings about possible collisions. Furthermore, the control station is able to record incidents and near misses unlike the prior art where no central record is normally maintained. Also, the control station may beneficially be capable of alerting emergency services on the occasion of an imminent collision, or when a collision has apparently just occurred. In contrast, using known procedures, valuable time is often lost just after a collision has taken place, e.g. before the driver or passengers involved in a train collision can call for help. Sometimes an alarm even has to be raised by passers-by if the driver and passengers are not able to raise the alarm themselves).
It should be emphasised that the invention is not intended to replace any of the primary safety critical control systems which operate within a transport system such as a railway or shipping system. It is on the other hand intended to provide an additional alerting system, for example by making use of a radio communication system which may already be employed within the transport system to allow normal communications which are not emergency communications to be made.

Claims

A wireless communication system (100) comprising a control station (103) for use in movement control of mobile objects, and an infrastructure (101) operable to provide communications between mobile stations, the control station being operable to receive from a first mobile station (106) via the infrastructure a signal including location information relating to a current location of the first mobile station and to receive from a second mobile station (107, 108) via the infrastructure a signal including location information relating to a current location of the second mobile station, to detect from the location information received from the first and second mobile stations that the first mobile station is approaching a current location of the second mobile station and to issue an alert signal for delivery to either or both of the first and second mobile stations to indicate an alert condition related to the detected approach, wherein the control station (103) is operable to issue different alert signals that are graded according to a probability of collision of the first mobile station (106) and the second mobile station (107, 108) and characterised in that the infrastructure (101) is operable to recognise an alert signal issued by the control station required to be delivered urgently and prominently and to give the alert signal a priority of delivery to either or both of the first and second mobile stations.
A system according to claim 1 including the first mobile station (105) and the second mobile station (107, 108) wherein each of the first mobile station and the second mobile station has a wireless communication link to a base transceiver station (102) of the infrastructure
A system according to claim 1 for claim 2 wherein the control station includes a processor (302) which is operable automatically to detect an alert condition by monitoring received information relating to current location of the first and second mobile stations.
A system according to claim 3 wherein the processor (302) is operable to detect the alert condition by calculating a probability that a collision is about to take place and to issue an alert signal when the calculated probability reaches a pre-determined threshold level.
A system according to claim 3 or claim 4 wherein the processor (302) is operable to issue an alert signal when a minimum distance between the first and second mobile stations is estimated.
A system according to any one of the claims 2 to 5 wherein the processor is operable to calculate a probability that a collision is about to take place by predicting trajectories of the first and second mobile stations.
A system according to any one of claims 1 to 6 wherein the first mobile station is a radio communication unit mounted on a railway train (105) or other mobile land vehicle and the alert signal provides warning of the train or other vehicle approaching another mobile object.
A system according to claim 7 wherein the first mobile station is mounted on a railway train (105) and the second mobile station is carried by a person wherein the system further includes a video camera operable to produce an image to monitor a position of the person and an imaging server operable to receive the image from the video camera and to run a program to determine if the person is outside a pre-defined safety boundary and to issue and to send to the control station an alert signal when the person is determined to be outside the pre-defined safety boundary and the control station is operable to issue in response the alert signal to the first mobile station.
A control station according to any one of claims 1 to 6 wherein the first mobile station is a radio communication unit (406) mounted on a vehicle (405) which is a mobile waterborne vehicle and the signal provides warning of the vehicle approaching another mobile object (409).
A system according to any one of claims 2 to 9 wherein each of the first (106) and second (107, 108) mobile stations is operable to run a program to recognize different forms of alert signal received from the control station (103) according to the likelihood of collision and is operable to generate different forms of warning or alarm signal accordingly.
A system according to any one.of the preceding claims wherein the wireless communication system (100) is a TETRA, Terrestrial Trunked Radio, system.
A method of communication in a wireless communication system (100) for use in movement control of mobile objects including a first mobile station (106) sending to a control station (103) via an infrastructure (101) of the system a signal including location information relating to a current location of the first mobile station, a second mobile station (107, 108) sending to the control station (103) via the infrastructure (101) a signal including location information relating to a current location of the second mobile station, the control station (103) detecting from the location information received from the first and second mobile stations that the first mobile station is approaching a current location of the second mobile station and the control station issuing an alert signal for delivery to either or both of the first and second mobile stations to indicate an alert condition related to the detected approach, wherein the control station (103) issues different alert signals that are graded according to a probability of collision of the first mobile station (106) and the second mobile station (107, 108) and characterised by the infrastructure (101) recognising an alert signal issued by the control station required to be delivered urgently and prominently and to give the alert signal a priority of delivery to either or both of the first and second mobile stations.