GB2425387A - Apparatus for generation of synthetic response when a wireless communications link fails in a traffic control system - Google Patents
Apparatus for generation of synthetic response when a wireless communications link fails in a traffic control system Download PDFInfo
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- GB2425387A GB2425387A GB0607700A GB0607700A GB2425387A GB 2425387 A GB2425387 A GB 2425387A GB 0607700 A GB0607700 A GB 0607700A GB 0607700 A GB0607700 A GB 0607700A GB 2425387 A GB2425387 A GB 2425387A
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- control system
- traffic control
- local response
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- synthetic local
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- 230000004044 response Effects 0.000 title claims abstract description 50
- 238000004891 communication Methods 0.000 title claims abstract description 35
- 230000009118 appropriate response Effects 0.000 claims abstract description 7
- 238000001514 detection method Methods 0.000 claims description 2
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- 101100194362 Schizosaccharomyces pombe (strain 972 / ATCC 24843) res1 gene Proteins 0.000 abstract description 2
- 102100034204 Transcription factor SOX-9 Human genes 0.000 abstract description 2
- 230000011664 signaling Effects 0.000 abstract description 2
- 238000010295 mobile communication Methods 0.000 abstract 1
- 238000010586 diagram Methods 0.000 description 5
- 238000009434 installation Methods 0.000 description 5
- 230000001052 transient effect Effects 0.000 description 4
- RYGMFSIKBFXOCR-UHFFFAOYSA-N Copper Chemical compound [Cu] RYGMFSIKBFXOCR-UHFFFAOYSA-N 0.000 description 2
- 208000032365 Electromagnetic interference Diseases 0.000 description 1
- 230000002411 adverse Effects 0.000 description 1
- 230000005540 biological transmission Effects 0.000 description 1
- 238000012790 confirmation Methods 0.000 description 1
- 229910052802 copper Inorganic materials 0.000 description 1
- 239000010949 copper Substances 0.000 description 1
- 230000000694 effects Effects 0.000 description 1
- 230000007613 environmental effect Effects 0.000 description 1
- 230000007774 longterm Effects 0.000 description 1
- 238000005457 optimization Methods 0.000 description 1
- 230000002035 prolonged effect Effects 0.000 description 1
Classifications
-
- G—PHYSICS
- G08—SIGNALLING
- G08G—TRAFFIC CONTROL SYSTEMS
- G08G1/00—Traffic control systems for road vehicles
- G08G1/07—Controlling traffic signals
-
- G—PHYSICS
- G08—SIGNALLING
- G08G—TRAFFIC CONTROL SYSTEMS
- G08G1/00—Traffic control systems for road vehicles
- G08G1/09—Arrangements for giving variable traffic instructions
- G08G1/095—Traffic lights
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- Physics & Mathematics (AREA)
- General Physics & Mathematics (AREA)
- Traffic Control Systems (AREA)
- Mobile Radio Communication Systems (AREA)
Abstract
A traffic control system comprises first 10 and second 18 units adapted to communicate over a wireless communications link wherein each unit, on receipt of a command signal from the other issues a corresponding response signal. Each of the units has an associated synthetic local response unit 14 and 16 which in the event of the failure of the communications link can provide an appropriate response RES and RES1 to the local unit that issued the command CMD and CMD1. The synthetic response signal is selected according to an expected change of state of the signalling device. The synthetic response unit may also be operable to issue several responses appropriate to local commands when the communication link fails. If the failure of the link lasts beyond a predetermined time then either of the units may output an error condition. The wireless link may be provided by a mobile communications network.
Description
AGD.4.complete 19.04.06.doc Traffic Control System This invention relates
to a traffic control system in which traffic control signals are communicated between two units by means of a wireless communications link, and typically by means of a radio link.
The cost of installing the cabling for the signalling between road traffic signals at a junction contributes massively to the cost of installation. The cost of digging up the road, putting in the copper wire and filling in the road again is put at about 300 per metre. These costs arise not only in terms of the labour required for burying the cable but also the consequent costs in terms of administrative and legal costs in obtaining appropriate permissions and also the general interruption to traffic. There have been proposals to replace buried copper with wireless links but these have intended to be in network systems rather than in more simple point to point communications.
However, given the robustness of the control system built into typical traffic contro! installations we have found that it is not realistic simply to replace the fixed cable with a wireless link because of the differences in the nature and operation of wireless links as opposed to fixed cables. It is the nature of fixed cable installations used in urban traffic control installations that any interruption in a signal is indicative of a cable fault and hence is typically recorded as an error by the control system. By contrast, wireless communication links are inherently prone to intermittent interruption due to, for example, electro-magnetic interference, adverse environmental conditions, and antenna occlusion and so on. Simply substituting an existing fixed cable link with a wireless link will result in numerous error conditions being recorded and so will not produce a AGD.4.complete 1904.06.doc satisfactory solution.
Upgrading existing legacy traffic control systems in order to be compatible with such wireless links can prove to be very expensive and indeed is often impractical due to external dependencies.
In addition, in order to reduce the cost of the links it is preferred to use a public network such as the mobile phone network and thereby avoiding the need to take a licence under the Wireless Telegraphy Act. Thus, in addition to the intermittent interruptions as indicated above, the system may experience transient network glitches which in an unmodified system might well trigger an error condition.
Accordingly, in one aspect, this invention provides a traffic control system comprising a first unit and a second unit adapted to communicate data and/or control signals via a wireless communications link, wherein each unit, on receipt of a selected command signal from the other unit, issues a corresponding response signal, the system being characterised fti that at least one of said units has associated therewith a synthetic local response module which, in the event of a failure of the wireless communications link, provides an appropriate response (which may be a response signal) when said unit issues a command signal.
In this manner, in the event of a transient disruption or disturbance to the communications link the synthetic local response module can synthesise or spoof signals that would otherwise be provided by the other unit or units when a given unit issues a command signal, and so the synthetic local response module can maintain appropriate signal states until the communication link is restored.
AGD.4.complete 19.04.06.doc The synthetic local responses will be selected according to the expected state or changes of state. In some instances, the response may be a change of signal level of predetermined delay. Alternatively it may be a pulsed output. The synthetic local response unit may determine the appropriate response based on observation or detection of one or several conditions.
In addition, the synthetic local response module can synthesise appropriate responses to system state changes during the break in communication. These system state changes can be subsequently transmitted by the local response module to the other unit or units (or a synthetic local response module associated therewith) upon restoration of the communications link. In this way, the other unit can be updated with changes that took place whilst the communications link was down.
The various default signal states, command and response protocols, and timings may be pre-configured and programmed into each of the synthetic local response modules. The synthetic local response modules may also be programmed to detect true error conditions so that all signals fail in a safe manner.
In this way a wireless communications link can be substituted for a fixed cable installation with little or no change required to the main traffic controller system.
Preferably, each of said first and second units include respective synthetic local response modules operating in the above fashion. Although the wireless communications link may take many forms, it is preferred for it to be a short-range radio link, and, in a particularly preferred embodiment, the AGD.4compiete 19.04.06.doc communication link uses a mobile telephone communications networks and/or GPRS, or DECT.
Preferably, at least one of said units and/or the respective module or modules is operable to output an error condition in the event that the failure of said communications link lasts longer than a preset period.
Whilst the invention has been described above, it extends to any inventive combination of the features set out above or in the following
description.
By way of example only, a specific embodiment of the invention will now be described, reference being made to the accompanying drawings, in which:Figure 1 is a schematic diagram of a standard configuration of existing traffic control system; Figure 2 is a timing diagram showing the timings of a command signal issued by the junction controller and a response signal returned by the sub- controller; Figure 3 is a schematic diagram of a traffic control system in accordance with this invention where a junction controller and a remote sub-controller communicate via a wireless link each of which includes a synthetic local response module; Figure 4 is a corresponding timing diagram showing issuance of respective command and response signals, and Figure 5 is a schematic diagram representing operation of a Vehicle HoldNehicle Green Confirm.
Referring initially to Figure 1, in a conventional arrangement a junction AGD.4.complete 19.04.06.doc controller 10 communicates via a buried wire with a remote sub-controller 12. In use, the junction controller 10 asserts a signal CMD and expects a response RES within a specified time range to confirm the command. If the response line assert time (Ti) and the duration time of RES (T2 - Ti) (see Figure 2) are not within specified system limits, then the junction controller will flag an error. In the case of a system where the control signals are carried by wires, it will be appreciated that a break in communications is likely to be permanent and so the system may reasonably assume that the break in communication is not a transient glitch and that the line is likely to be down until it is repaired.
In the present invention the signals between the junction controller and remote sub-controller are sent by a wireless link which may, from time to time, experience transient interruptions in communication which occur for a short period, only and which do not represent a permanent compromise of the integrity of the link.
In the schematic arrangement shown in Figure 3, the junction controller and the remote sub-controller 12 are each shown with short range wireless link devices 14 and 16 which are normally used for transmitting control and response signals between the junction control and the remote subcontroller.
This communication link may be by any suitable wireless link, for example a mobile telephone communications network, GPRS or DECT or any other
suitable medium.
The devices 14 and 16 also include synthetic local response modules which provide a synthetic local response should the radio communication between the units be broken or interrupted for a short period.
AGD.4.complete 19.04.06.doc Thus, as illustrated in Figure 4, in the event that the radio link is interrupted, a command signal CMD asserted by the junction controller 10 is detected by the synthetic local response module in device 14 which returns the appropriate response signal RES. Similarly, at the other end of the interrupted link, when the remote subcontroller 12 issues a command CMD1 the unit 16 returns an appropriate response RES1. In this way the remote sub-controller may continue operation. Thus, the devices 14 and 16 effectively decouple the main signal lines and generate the appropriate signal so that an error condition is averted. If there is a prolonged break in the wireless communication, for e.g. longer than 10 minutes, a fault can be reported back to the junction controller and the system alerted to the problem.
A number of examples of different types of synthetic local responses implemented in the SRWL, namely a first type of response relating to Vehicle Green Hold and Confirm (Pedestrian demand & confirm) where in SCOOT (Split Cycle Offset Optimization Technique) terminology the system is on "PLAN", and a second one related to a Standard Output, where the system is "OFF PLAN" . A synthetic local response providing a pulsed output has also been proposed.
VEHICLE HOLD \ VEHICLE GREEN CONFIRM Under normal operating conditions, the Vehicle Green hold (VGH) signal sent out from the urban traffic control system (UTC) controller via the outstation transmission unit (OTU) to the pedestrian controller is held in an active state, such that the pedestrian controller is inhibited from running its crossing phase.
Under this VGH condition, the pedestrian controller should reply with a vehicle AGD.4.complete 19.04.06.doc green confirm (VGC) reply which is also in the active state, indicating that the pedestrian controller is holding the vehicle phase on.
Every n seconds, where n is a period generated by the UTC system, the VGH signal is sent into the inactive state for, say, 2 seconds, to allow the pedestrian controller to cycle the system and allow pedestrians to cross. if a valid pedestrian demand has been entered, the VGC reply will be set to the inactive state while the crossing phase is implemented. Error checking in the UTC system will flag up a fault if the VGC reply appears too late once the VGH has been set inactive, or if the VG reply appears for too long once the VH has been set inactive, or if the VGC reply appears in the inactive state when the VGH is active. There is no error message generated by the UTC system if no inactive VGC is received when the VGH is active - it is just assumed that there is no pedestrian demand.
In some systems the OTU also has the ability to instruct the pedestrian controller to restrict vehicular traffic by forcing the issue of a pedestrian demand, which has a similar effect to a pedestrian pressing the button at the crossing.
When this happens a Pedestrian Waiting confirmation signal must be received by the OTU within a prescribed time limit or an error condition occurs.
The Synthetic Local Response behaviour is applied to both of these pairs of signals to: 1. ensure that error conditions do not occur at the OTU for intermittent losses in wireless communications.
2. ensure that error conditions do occur for long term loss in communication.
AGD.4.complete 19.04.06.doc 3. ensure that the pedestrian crossing continues to operate satisfactorily in the event of any communication loss.
The VGH \ VGC synthetic local response is normally initialised in the master subsystem. The input bit is set to whichever input is connected to the VGH signal from the OTU, the output bit is set to whichever output is connected to the VGC reply to the OTU. The activate edge parameter is set to whichever logic level indicates that the VGH signal has gone inactive'. The reply polarity parameter is set to whichever logic level indicates that the VGC reply has gone inactive'. The W parameter is set to the maximum time which can be allowed between VGH going inactive and VGC replying with an inactive state (normally I second setting of 8). The P parameter is set to the maximum time for which the VGC reply can be in the inactive state (normally either set to 1.5 x expected value in UTC system, or 60 seconds (60 seconds setting of 480)).
If the master subsystem determines that the radio link is either not present, or is sending messages which are too old' to be useful, then if either of the timing conditions above are exceeded, the VGH output will be set into the active state immediately, and no further changes in VGC will be sent to the OTU until the radio link has been restored (or is operating correctly) and another VGH signal has been received (which resets the timers).
STANDARD OUTPUT
Standard output can be initialised for an output in either the master or slave subsystem, and is used to prevent an output from sticking' in the active state should the radio link drop out or send old' messages. The output bit is set to whichever output is to be monitored, the activate edge parameter is set to AGD.4.complete 19.04.06.doc whichever logic level indicates that the output has gone active', and the P parameter is set to the maximum time for which the output can be in the active state.
If the system determines that the radio link is either not present, or is sending messages which are too old' to be useful, then if the output has been in the active state for longer that the time set by the P parameter, the output in question will be set into the inactive state immediately, and no further changes in output will be passed to the OTU or controller until the radio link has been restored (or is operating correctly) and another active output signal (which resets the timers) has been received.
Pulsed Output In other situations, this synthetic local response module may have a pulsed output option, whereby an output can be set to pulse for a particular length of time, at a particular interval. This could be used in a situation where the link is not present, and it is desirable to be periodically generating the vehicle hold (VGH) signal at the pedestrian controller, to allow the pedestrian demand to be processed.
Claims (13)
- AGD.4.complete 19.04.06.doc Claims 1. A traffic control system comprisinga first unit and a second unit adapted to communicate data and/or control signals via a wireless communications link, wherein each unit, on receipt of a selected command signal from the other unit, issues a corresponding response signal, the system being characterised h-i that at least one of said units has associated therewith a synthetic local response module which, in the event of a failure of the wireless communications link, provides an appropriate synthetic local response when said unit issues a command signal.
- 2. A traffic control system according to Claim 1, wherein the synthetic local response is selected according to the expected state or change of state.
- 3. A traffic control system according to Claim 2, wherein the sythentic local response is a change of signal level of predetermined delay.
- 4. A traffic control system according to Claim 2, wherein the synthetic local response is a pulsed output.
- 5. A traffic control system according to any preceding Claim, wherein the synthetic local response is based on observation or detection of one or several conditions.
- 6. A traffic control system according to any preceding Claim, wherein the synthetic local response module is operable to synthesise appropriate responses to system state changes during the break in communication.
- 7. A traffic control system according to Claim 6, wherein the synthetic local response module is operable to transmit to the other unit data representing said system state changes.AGD.4.complete 19.04.06.doc
- 8. A traffic control system according to any preceding Claim, wherein selected default signal states, command and response protocols, and timings are programmed into the or each of the synthetic local response modules.
- 9. A traffic control system according to any preceding Claim, wherein the or each synthetic local response modules is programmed to detect true error conditions so that all signals fail in a safe manner.
- 10. A traffic control system according to any of the preceding Claims, wherein each of said first and second units include a respective synthetic local response module operating in the above fashion.
- 11. A traffic control system according to any of the preceding Claims, wherein the wireless communications link uses a mobile telephone communications network.
- 12. A traffic control system according to any of the preceding Claims, wherein at least one of said units and/or the respective synthetic local response module or modules is operable to output an error condition in the event that the failure of said communications link lasts longer than a preset period.
- 13. A traffic control system substantially as hereinbefore described with reference to, and as illustrated in, any of Figures 3 to 5 of the accompanying drawings.
Applications Claiming Priority (1)
| Application Number | Priority Date | Filing Date | Title |
|---|---|---|---|
| GBGB0507872.0A GB0507872D0 (en) | 2005-04-19 | 2005-04-19 | Traffic control system |
Publications (3)
| Publication Number | Publication Date |
|---|---|
| GB0607700D0 GB0607700D0 (en) | 2006-05-31 |
| GB2425387A true GB2425387A (en) | 2006-10-25 |
| GB2425387B GB2425387B (en) | 2008-10-15 |
Family
ID=34630909
Family Applications (2)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GBGB0507872.0A Ceased GB0507872D0 (en) | 2005-04-19 | 2005-04-19 | Traffic control system |
| GB0607700A Expired - Fee Related GB2425387B (en) | 2005-04-19 | 2006-04-19 | Traffic control system |
Family Applications Before (1)
| Application Number | Title | Priority Date | Filing Date |
|---|---|---|---|
| GBGB0507872.0A Ceased GB0507872D0 (en) | 2005-04-19 | 2005-04-19 | Traffic control system |
Country Status (1)
| Country | Link |
|---|---|
| GB (2) | GB0507872D0 (en) |
Cited By (1)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010022179A1 (en) * | 2008-08-19 | 2010-02-25 | University Of Idaho | Advanced accessible pedestrian system for signalized traffic intersections |
Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1538288A (en) * | 1977-09-29 | 1979-01-17 | Hb Modules Ltd | Traffic light control equipment |
| JP2003272092A (en) * | 2002-03-14 | 2003-09-26 | Hitachi Kokusai Electric Inc | Radio control type traffic signal system |
| WO2004088610A2 (en) * | 2003-04-01 | 2004-10-14 | Wireless Traffic Technologies Pty Limited | Traffic control system |
-
2005
- 2005-04-19 GB GBGB0507872.0A patent/GB0507872D0/en not_active Ceased
-
2006
- 2006-04-19 GB GB0607700A patent/GB2425387B/en not_active Expired - Fee Related
Patent Citations (3)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| GB1538288A (en) * | 1977-09-29 | 1979-01-17 | Hb Modules Ltd | Traffic light control equipment |
| JP2003272092A (en) * | 2002-03-14 | 2003-09-26 | Hitachi Kokusai Electric Inc | Radio control type traffic signal system |
| WO2004088610A2 (en) * | 2003-04-01 | 2004-10-14 | Wireless Traffic Technologies Pty Limited | Traffic control system |
Cited By (2)
| Publication number | Priority date | Publication date | Assignee | Title |
|---|---|---|---|---|
| WO2010022179A1 (en) * | 2008-08-19 | 2010-02-25 | University Of Idaho | Advanced accessible pedestrian system for signalized traffic intersections |
| US8797184B2 (en) | 2008-08-19 | 2014-08-05 | University Of Idaho | Advanced accessible pedestrian system for signalized traffic intersections |
Also Published As
| Publication number | Publication date |
|---|---|
| GB0507872D0 (en) | 2005-05-25 |
| GB0607700D0 (en) | 2006-05-31 |
| GB2425387B (en) | 2008-10-15 |
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Legal Events
| Date | Code | Title | Description |
|---|---|---|---|
| PCNP | Patent ceased through non-payment of renewal fee |
Effective date: 20110419 |