Title of Invention

"DISTRIBUTED TIME SYNCHRONIZATION OF ROAD TRAFFIC SIGNAL CONTROLLERS USING GPS"

Abstract

Distributed time synchronization of road traffic signal controllers using GPS The present invention provides a simple, fast and economic traffic control system using GPS system for distributed time synchronization of road traffic controllers. The system comprising a receiver unit for receiving information from a satellite network; a traffic signal controller unit coupled to the receiver unit, the said controller unit receiving the information from the receiver unit and generating control and synchronization signals; a real time clock operatively coupled to the said controller unit for receiving control and synchronization signals from the controller unit for updating the clock; a plurality of traffic signaling units coupled to the said controller unit, said controller unit controlling the operations of the traffic signaling units.

Full Text

The Present invention relates to a system for controlling the traffic signals by time synchronizing technology. More specifically, this invention relates to a distributed time synchronization of road traffic signal controllers using a GPS for synchronizing the time in the traffic controller with the time from the GPS (Global Positioning System). Background and Prior Art The traffic at the intersection streets is controlled by traffic control lights. These lights are operated in accordance with the predetermined timing sequences by a controller. Various controllers have been developed and used to control traffic lights. Such controllers are electronic controllers, and controllers which include microprocessors to generate various timing and control signals. Synchronized traffic is a technique adopted in road traffic signaling to attain progressive green in a corridor to minimize stops and delays to the main traffic. The synchronized traffic is achieved by maintaining an offset between the stages of the consecutive traffic controllers in a corridor. The offset is based on the ground speed. In the synchronized traffic a vehicle entering the corridor will get right-of-way progressively at the consecutive intersections, if traveled at specified speed. The traveling time from one intersection to the other is known since the distance and speed are known parameters. By displacing the stages for through traffic of the succeeding intersection controllers with this known time, offset, an uninterrupted traffic flow could be attained in the corresponding direction. There are two methods practiced currently to achieve the synchronized traffic. One is cabled synchronization method where all the traffic controller equipments are interlinked with cable on which sync pulse is transmitted every cycle. The receive end traffic controller will wait for the sync pulse to execute the synchronization stage for maintaining the offset between the signals of the previous controller. The sync pulse is sent normally at the start of the synchronization stage of the preceding intersection. This method has the following drawbacks: laying the cable for the entire length of the corridor is very expensive, chances of cable failure due to construction work on the road is very high and a power interruption or mode change at one intersection will put the succeeding intersection in waiting for the sync pulse which could cause unnecessary delay or stops at that intersection. The other method is cable less synchronization, where the system maintains a timetable for the synchronized traffic. This timetable is invoked with respect to the real time clock running at each traffic controller equipments in the corridor. The offset is built into the junction specific plan and timetable. All the problems listed in the cabled synchronization method are avoided in the cable less synchronization, but has a constraint of maintaining the real time clock at each traffic controller without relative drift. RTC running with few second's difference at different controllers could defeat the synchronization in the cable less method. Presently the RTC accuracy is achieved by using a temperature controlled crystal oscillator with high precision. This method also has a drawback that the time is entered manually and an entry error could jeopardize the entire scheme. Also periodic verification is required to ensure validity of the real time clocks as the RTC are battery backed. A weak battery could affect the crystal frequency. Different methods are possible to achieve the time synchronization of the traffic controller equipment in a row or at an area. Few methods are discussed below. Timetable method with cabled synchronization Multi-dropping with RS485 The system time could be transmitted from one controller to another in a master slave method to follow master time in all slave controllers. Normally RS485 serial communication interface is available in most of the modern traffic controller equipments that can transmit/ multi-drop data up to a distance of 4000ft. Multi-dropping is a Master-Slave configuration. The controllers in this configuration are connected in daisy chain. The master can force the slaves to follow the time the master maintains and achieve the timetable based synchronized traffic. The method has a drawback that the distance is limited to 4000ft and the failure of the master could defeat the synchronization plan. Point-to-Point RS 485 Communication In this method the time and date could be relayed from one end to the other. Each controller will have two RS485 ports to communicate with both sides. The transmission will be initiated from one end. The nearby controller will update its RTC with the received time information and transmit the same to the next controller. Here the distance limitation is overcome with the controller-to-controller distance of 4000ft maximum and theoretically no limitation on the number of controllers in the chain. But, this method has a drawback on delay. The time transmitted from the first controller will be received by the second and it updates its own RTC before transmitting the information to the next. With the increase in the number of intersections in a chain, the delay due to retransmission increase in proportion. Also a failure in the communication cable could isolate the remaining intersections. Networking Intersection Controllers Networking the intersection controllers with wire or wireless medium and broadcasting the time information from a common center is another method to achieve the common RTC at different controllers. The provider of the traffic control equipment has to maintain a control station to manage the time and other information to be sent to the individual nodes. Also this requires special equipments. This is a highly expensive approach. The US patent No: 6,133,854 features networking the traffic controller equipments using a satellite channel such as Motorola 'Iridium' through dialup connection. This is only a replacement of wired network or radio network (using line-of-sight transmitters) with the satellite channel. Availability of such services all over the world is another question. The Wireless communication with line-of-sight RF network also has serious drawbacks of sustainable connectivity, limitation in coverage area and initial expense. The traffic controllers are positioned directly at the intersection and achieving a sustainable and reliable connection is very difficult. This is because the adjacent buildings and hoardings near to the receiving station often intercept the line-of-sight transmission. Also, the maximum height possible to place the receiving antenna at the intersection is of the height of the signal pole. FMRDS RDS, standing for the Radio Data System, is adding a basic data and text service to FM radio. Many FM stations are supporting the RDS that transmit time and date every second. With special decoders this data could be extracted to update the traffic controller RTC. Problem with this approach is that the service is not supported by every FM stations and at all cities. Therefore this approach could not be considered as a generic solution Summary of the Invention The present invention overcomes the above drawbacks and provides a simple, fast and economic traffic control system with provisions for distributed time synchronization of road traffic controllers, eliminating the need for base station in the traffic control system. It is an object of the present invention to provide a traffic control system capable of using a GPS for distributed time synchronizing the road traffic controllers. In one embodiment of the present invention provides a traffic control system comprising: a receiver unit for receiving time, date and day of the week information from a satellite network; a traffic signal controller unit coupled to the said receiver unit, said controller unit receiving the said information from the receiver unit and generating control and synchronization signals; a real time clock operatively coupled to the said controller unit, said real time clock receiving control and synchronization signals from the controller unit for updating the clock; a plurality of traffic signaling units coupled to the said controller unit, said controller unit controlling the operations of the traffic signaling units. In another embodiment of the present invention the satellite network is the Global Positioning System (GPS). In another embodiment of the present invention the receiver is a Global Positioning System (GPS) receiver. In another embodiment of the present invention the receiver sends data to said traffic controller according to NMEA standard. In another embodiment of the present invention the real time clock is updated during startup and at every cycle switching. In another embodiment of the present invention the traffic signal control unit has a control card capable of receiving time, date and day of the week information from the receiver unit, processing said information and generating synchronization signal for the real time clock. In another embodiment of the present invention the control card comprises a glue logic and firmware to extract the required information from the data provided by the GPS receiver. In another embodiment of the present invention the control card comprises a communication interface unit between the GPS receiver and the glue logic circuitry. In another embodiment of the present invention the control card comprises a local RTC which receives RTC updates from the glue logic circuitry. In another embodiment of the present invention the control card comprises a signal control logic processing signal information and providing lamp control signals to traffic signaling units. Statement of invention: Accordingly the present invention provides a traffic control system comprising: a receiver unit for receiving time, date and day of the week information from a satellite network; a traffic signal controller unit coupled to the said receiver unit, said controller unit receiving the said information from the receiver unit and generating control and synchronization signals; a real time clock operatively coupled to the said controller unit, said real time clock receiving control and synchronization signals from the controller unit for updating the clock; a plurality of traffic signaling units coupled to the said controller unit, said controller unit controlling the operations of the traffic signaling units. Brief description of the drawings The invention will be better understood from a reading of the following detailed description in conjunction with the drawings in which like reference numerals designate like elements and which. Fig. 1 shows a timetable system for cabled synchronization Fig. 2 shows a system for point-to-point RS485 communication Fig. 3 shows a system for Networking Intersection Controllers Fig. 4 schematic diagram for synchronized traffic Fig .5 shows the traffic controllers enabled by GPS Fig. 6 shows the block diagram of present system configuration in accordance with the principles of the invention. Fig. 7 shows the Functional block diagram of the Traffic Controller Equipment Control Card Fig. 8 shows the synchronization Time-Space Diagram. Detail description of the preferred embodiments Fig.l shows a system to achieve the time synchronization of the traffic control equipment. The system time could be transmitted from one controller to another in a master slave system to follow master time in all slave controllers. Normally RS485 serial communication interface is available in most of the modern traffic controller equipments that can transmit/ multi-drop data up to a distance of 4000ft. Multi-dropping is a master-slave configuration. The controllers in this configuration are connected in daisy-chain. The master (101) can communicate with a maximum of 16 slaves (102-117) (32 slaves in the improved RS489 standard) within a distance of 4000ft. The master can force the slaves to follow the time the master maintains and achieve the timetable based synchronized traffic. This system has a serious drawback that the total distance is limited to 4000ft (approximately 1.2Km). Also the failure of the master could defeat the synchronization plan. Fig. 2 shows a system for point-to-point RS485 communication, in this system the time and date could be relayed from one end to the other. Each controller will have two RS485 ports to communicate with both sides. The transmission will be initiated from one end. The nearby controller will update its RTC with the received time information and transmit the same to the next controller. Fig. 3 shows a system for Networking Intersection Controllers through satellite. Networking through wired or other wireless medium also is possible. In all the cases provider of the traffic control equipment has to maintain a control station to manage the time and other information to be sent to the individual nodes. The US patent no. 6,133,854 features networking the traffic controller equipments using a satellite channel such as Motorola 'Iridium' through dialup connection. This is only a replacement of wired network or radio network (using line-of-sight transmitters) with the satellite channel. The wireless communication with line-of-sight RF network has serious drawbacks of sustainable connectivity, limitation in coverage area and initial expense. The traffic controllers are positioned directly at the intersection and achieving a sustainable and reliable connection is very difficult. This is because the adjacent buildings and hoarding near to the receiving station often intercept the line-of-sight transmission. Also, the maximum height possible to place the receiving antenna at the intersection is of the height of the signal pole. Fig 4 shows a schematic diagram of synchronized traffic. When the vehicle entering at junction 1 at time to reach at junction 2 at time t0+20 Sec and Junction 3 at time to+50 sec. the signal plans at junction 2 and junction 3 are so adjusted to give a right of way for the incoming traffic from junction 1 through displacement of signal plan by 20seconds and 50seconds respectively, with respect to the signal plan at junction 1. The prime requisite for achieving this is to have a common RTC on all the intersection controllers. Fig. 5 described according to the present invention that time synchronizing the road traffic controllers (501-n) to solve the all drawbacks in all the system discussed above and also shows how the all the GPS enabled traffic controllers will receive the same time, date and day of week information from the satellite. The GPS Space segment consists of 24 satellites in six circular orbits 20,200 km (10,900 NM) above the earth at an inclination angle of 55 degrees with a 12-hour period. The satellites are spaced in orbit so that at any time a minimum of 6 satellites will be in view of users anywhere in the world. The satellites continuously broadcast position and time data to users throughout the world. Fig 6 describes that the GPS receiver (603) receives the signals from the satellites (601) and present the data in NMEA (National Marine Electronics Association) standard to the traffic controller equipment (604). This data has several information of the satellite (601) from which the signals are received and the location data; the traffic controller equipment (604) extracts only the required information. Fig 7 describes a traffic control system (700) according to one of the embodiments of the invention GPS receiver (702) receives time, date and day of the week information from one of the GPS satellites and the data according to NMEA standard is communicated to a traffic controller equipment control card (701) which is a part of the traffic controller unit. The controller card (701) comprises a glue logic circuit to extract required information from the data provided from the GPS receiver (702), the glue logic circuit (704) provides RTC updates to a local RTC (705) and updates the local RTC (705) with the correct date, time and day information. A communication interface (703) is provided for interfacing GPS receiver (702) with the glue logic circuit. The controller card (701) also comprises a signal control logic (708). The signal control logic (708) receives input signals from timetable (706) maintaining signal on/off time information and a stage offset (707) providing offset values and the local RTC (705). The signal control logic (708) provides lamp control signals as input to the signal lamps. Fig 8 shows the synchronized time-space diagram. In the time-space diagram, the Green bands represent Stages for synchronized traffic. Stage timings are plotted on X-axis and distance between intersections on Y-axis. A vehicle starting at time to from junction 1 towards junction 2 will take toffset time to reach junction 2. A relation between the intersection controllers will be maintained to give green signal at junction 2 for the vehicles approaching from junction 1 by the time they reach junction 2. This could be extended to any number of intersections and in the reverse direction too. Stage switching is done with respect to a real time clock maintained in the intersection controller. To provide consistency in every cycle, the prime requirement is to maintain the real time clock in every intersection controllers without relative time drift. All the traffic controllers within the synchronized scheme will be operating on same cycle time for maintaining repeatability. Thus all the traffic control equipments at various traffic junctions will maintain same date, time and day of the week without any relative drift thus achieving distributed time synchronization. One advantage of using the GPS for Time Synchronizing Traffic Signal Equipments is that special network is not required to get the data at individual nodes. Yet another advantage of using the GPS for time synchronizing Traffic Signal Equipments is that there is no need to maintain separate base station control. Yet another advantage of using the GPS for time synchronizing Traffic Signal Equipments is that the system is available all the time, around the world, all nodes in a time zone follows same time without any drift. Yet another advantage of using the GPS for time synchronizing Traffic Signal Equipments is that the system offers an accuracy of better than l/100th of a second Yet another advantage of using the GPS for time synchronizing Traffic Signal Equipments is Economical and reliable compared to all other solutions and also need not maintain battery backup for the local RTC. Although a few embodiments of the present invention have been shown and described, it would be appreciated by those skilled in the art that changes may be made in these embodiments without departing from the principles and spirit of the invention, the scope of which is defined in the claims and their equivalents. We claim: 1. A traffic control system comprising: a receiver unit for receiving time, date and day of the week information from a satellite network; a traffic signal controller unit coupled to the said receiver unit, said controller unit receiving the said information from the receiver unit and generating control and synchronization signals; a real time clock operatively coupled to the said controller unit, said real time clock receiving control and synchronization signals from the controller unit for updating the clock; a plurality of traffic signaling units coupled to the said controller unit, said controller unit controlling the operations of the traffic signaling units. 2. The traffic control system as claimed in claim 1, wherein the satellite network is a Global Positioning System (GPS). 3. The traffic control system as claimed in claim 1, wherein the receiver unit is a Global Positioning System (GPS) receiver. 4. The traffic control system as claimed in claim 1, wherein the receiver unit sends data to said traffic controller according to NMEA standard. 5. The traffic control system as claimed in claim 1, wherein the real time clock is updated during startup and at every cycle switching. 6. The traffic control system as claimed in claim 1, wherein the traffic signal control unit has a control card capable of receiving time, date and day of the week information from the receiver unit, processing said information and generating synchronization signal for the real time clock. The traffic control system as claimed in claim 6, wherein the control card comprises a glue logic and firmware to extract the required information from the data provided by the GPS receiver. The traffic control system as claimed in claim 6 and 7, wherein the control card comprises a communication interface unit between the GPS receiver and the glue logic circuitry. The traffic control system as claimed in claim 6 to 8, wherein the control card comprises a local RTC which receives RTC updates from the glue logic circuitry. The traffic control system as claimed in claim 6 to 9, wherein the control card comprises a signal control logic processing signal information and providing lamp control signals to traffic signaling units. A traffic control system substantially as herein described with reference to accompanying drawings. Dated this the 07th day of November, 2005

Documents:

1619-CHE-2005 AMENDED CLAIMS. 11-08-2014.pdf

1619-CHE-2005 AMENDED PAGES OF SPECIFICATION 11-08-2014.pdf

1619-CHE-2005 CORRESPONDENCE OTHERS. 04-12-2014.pdf

1619-CHE-2005 EXAMINATION REPORT REPLY RECEIVED. 11-08-2014.pdf

1619-CHE-2005 FORM-1 07-12-2011.pdf

1619-CHE-2005 FORM-1. 11-08-2014.pdf

1619-CHE-2005 FORM-3 04-12-2014.pdf

1619-CHE-2005 OTHER PATENT DOCUMENT 04-12-2014.pdf

1619-CHE-2005 POWER OF ATTORNEY 07-12-2011.pdf

1619-CHE-2005 CORRESPONDENCE OTHERS 07-12-2011.pdf

1619-CHE-2005 POWER OF ATTORNEY 04-12-2014.pdf

1619-che-2005-abstract.pdf

1619-che-2005-claims.pdf

1619-che-2005-correspondnece-others.pdf

1619-che-2005-description(complete).pdf

1619-che-2005-drawings.pdf

1619-che-2005-form 1.pdf

1619-che-2005-form 3.pdf

1619-che-2005-form 5.pdf

Form 1.pdf

FORM 13.pdf