System and method for transmitting data in an optical traffic preemption system
DCFirst Claim
1. A method of optically transmitting data comprising:
- emitting a stream of light pulses which include priority pulses occurring at a repetition rate and data pulses interleaved with the priority pulses, wherein each light pulse is separated from an adjoining light pulse by one of n predetermined time intervals;
receiving the stream of light pulses;
producing a received signal that represents the stream of light pulses;
identifying received light pulses that are separated from one another by one of the n predetermined time intervals;
sorting data pulses from priority pulses based on the predetermined time intervals separating identified light pulses; and
assembling data derived from the priority pulses, the data pulses and the predetermined time intervals.
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Abstract
A method of optically transmitting data from an optical emitter to a detector mounted along a traffic route is used in an optical traffic preemption system. The method allows variable data to be transmitted in a stream of light pulses by interleaving data pulses between priority pulses. By allowing data to be transmitted in a stream of light pulses, an optical emitter constructed in accordance with the present invention transmits an optical signal that can include an identification code that uniquely identifies the emitter, an offset code that causes a phase selector to create a traffic signal offset, an operation code that causes traffic signal lights to assume at least one phase and a range setting code that causes a phase selector to set a threshold to which future optical transmissions will be compared. Phase selectors constructed in accordance with the present invention are provided with a discrimination algorithm which is able to track a plurality of optical transmissions with each detector channel. Optical emitters constructed in accordance with the present invention are provided with a coincidence avoidance mechanism which causes overlapping optical transmission from separate optical emitters to drift apart. The present invention provides an optical signal format that allows variable data to be transmitted, while maintaining compatibility with prior optical traffic preemption systems.
170 Citations
44 Claims
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1. A method of optically transmitting data comprising:
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emitting a stream of light pulses which include priority pulses occurring at a repetition rate and data pulses interleaved with the priority pulses, wherein each light pulse is separated from an adjoining light pulse by one of n predetermined time intervals; receiving the stream of light pulses; producing a received signal that represents the stream of light pulses; identifying received light pulses that are separated from one another by one of the n predetermined time intervals; sorting data pulses from priority pulses based on the predetermined time intervals separating identified light pulses; and assembling data derived from the priority pulses, the data pulses and the predetermined time intervals. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 18, 19, 20, 21)
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9. The method of claim wherein emitting a stream of light pulses includes:
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representing a first logic state by emitting a data pulse between consecutive priority pulses; and representing a second logic state by not emitting a data pulse at a predetermined point between consecutive priority pulses. - View Dependent Claims (10, 11, 12, 13, 14, 15, 16, 17)
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22. An optical data communication system for use in a traffic signal control system having a traffic signal controller for controlling traffic signal lights that control traffic flow at a traffic intersection, the traffic signal controller being responsive to phase requests, the optical data communication system comprising:
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an emitter for transmitting a stream of light pulses which represent a transmitted signal that includes a preemption request and an identification code that uniquely identifies the emitter; a detector for receiving the stream of light pulses and producing a received signal representing the stream of light pulses; and a phase selector for receiving the received signal from the detector and extracting the preemption request and the identification code from the received signal and issuing a phase request to the traffic signal controller. - View Dependent Claims (23, 24, 25, 26, 27, 28)
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29. An optical data communication system for use in a traffic signal control system that has a traffic signal controller for controlling traffic signal lights which control traffic flow at a traffic intersection, the traffic signal controller being responsive to phase requests to assume at least one of m phases, the optical data communication system comprising:
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an emitter for transmitting a stream of light pulses which represent a transmitted signal that includes an offset code; a plurality of detectors, each detector for producing a received signal representing the stream of light pulses and stationed to receive the stream of light pulses from an approach to the intersection; a phase selector having a plurality of phase selector channels, with each phase selector channel having a channel number and coupled to at least one detector, the phase selector for receiving the received signals from the plurality of detectors, extracting offset codes from the received signals and alternately issuing phase requests to and withdrawing phase requests from the traffic signal controller based upon an offset code extracted from one of the received signals and the channel number of the phase selector channel which is coupled to the detector that received the stream of light pulses representing the transmitted signal that included the offset code. - View Dependent Claims (30, 31, 32)
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33. An optical data communication system for use in a traffic signal control system that has a traffic signal controller for controlling traffic signal lights which control traffic flow at a traffic intersection, the traffic signal controller being responsive to a phase request to assume at least one of m phases, the optical data communication system comprising:
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an emitter for transmitting a stream of light pulses which represent a transmitted signal that includes an operation code; a plurality of detectors, each detector for producing a received signal representing the stream of light pulses and stationed to receive the stream of light pulses from an approach to the intersection; a phase selector having a plurality of phase selector channels, with each phase selector channel coupled to at least one detector, the phase selector for receiving the received signals from the plurality of detectors, extracting operation codes from the received signals and issuing a phase request to the traffic signal controller to assume at least one of the m phases based upon an operation code extracted from one of the received signals and irrespective of the detector that received the stream of light pulses representing the transmitted signal that included the operation code. - View Dependent Claims (34, 35)
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36. An optical data communication system for use in a traffic signal control system, the optical data communication system comprising:
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an emitter for transmitting a stream of light pulses which represent a transmitted signal that includes a range setting code; a detector for receiving the stream of light pulses and producing a received signal representing the stream of light pulses; a phase selector for receiving the received signal from the detector, extracting the range setting code from the received signal and responding to the range setting code by determining an amplitude based on the received signal and using the amplitude as a threshold to which future received signals will be compared, wherein future received signals having an amplitude exceeding the threshold will be acted upon and future received signals having an amplitude less than the threshold, and not including the range setting code, will not be acted upon.
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37. A method of optically preempting a normal sequence of traffic signal lights comprising:
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emitting a stream of light pulses which include priority pulses occurring at a repetition rate and data pulses interleaved with the priority pulses, wherein each light pulse is separated from an adjoining light pulse by one of n predetermined time intervals; receiving the stream of light pulses; producing a signal that represents the stream of light pulses; identifying received light pulses that are separated from one another by one of the n predetermined time intervals; sorting data pulses from priority pulses based on the predetermined time intervals separating identified light pulses; assembling data derived from the priority pulses, the data pulses and the predetermined time intervals; issuing phase requests based on the data; evaluating phase requests; and controlling traffic signal lights to assume phases based on issued phase requests.
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38. A method for uniquely identifying an emitter in a traffic signal control system comprising:
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transmitting a stream of light pulses which represent a transmitted signal that includes a preemption request and an identification code that uniquely identifies the emitter; receiving the stream of light pulses and producing a received signal representing the stream of light pulses; extracting the preemption request and the identification code from the received signal; and controlling traffic flow at a traffic intersection by issuing a phase request based upon the received signal and evaluating phase requests to determine whether the phase requests should be granted. - View Dependent Claims (39, 40, 41)
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42. A method for issuing phase requests in a traffic signal control system comprising:
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transmitting a stream of light pulses which represent a transmitted signal that includes an operation code; producing a plurality of received signals, wherein each received signal is identified by a channel number and represents light pulses received from an approach to an intersection; receiving a received signal that represents the stream of light pulses and extracting the operation code from the received signal; and issuing a phase request to a traffic signal controller to assume at least one of m phases based upon the operation code extracted from the received signal and irrespective of the channel number associated with the received signal. - View Dependent Claims (43)
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44. A method of setting a range in an optical traffic preemption system comprising:
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transmitting a stream of light pulses which represent a transmitted signal that includes a range setting code; receiving the stream of light pulses and producing a received signal representing the stream of light pulses; extracting the range setting code from the received signal; and responding to the range setting code by determining an amplitude based on the received signal and using the amplitude as a threshold to which future received signals will be compared, wherein future received signals having an amplitude exceeding the threshold will be acted upon and future received signal having an amplitude less than the threshold, and not including a range setting code, will not be acted upon.
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Specification