Abstract:
An arrangement for requesting preemption from a vehicle is used in a traffic control system. The arrangement for requesting preemption includes a protocol circuit, a signal control generation circuit, and an optical source. The protocol circuit is adapted to provide a plurality of communication protocols, wherein a plurality of the communication protocols communicate encoded data. The signal control generation circuit is adapted to generate an output signal in accordance with at least one of the plurality of communication protocols. The optical source is adapted to transmit light pulses from the vehicle, wherein the light pulses are generated from the output signal and include the encoded data for said at least one of the plurality of communication protocols.

Description:
FIELD OF THE INVENTION 
     The present invention is generally directed to systems and methods that allow traffic light systems to be remotely controlled using data communication, for example, involving optical pulse transmission from an optical emitter to an optical detector that is communicatively-coupled to a traffic light controller at an intersection. 
     BACKGROUND OF THE INVENTION 
     Traffic signals have long been used to regulate the flow of traffic at intersections. Generally, traffic signals have relied on timers or vehicle sensors to determine when to change the phase of traffic signal lights, thereby signaling alternating directions of traffic to stop, and others to proceed. 
     Emergency vehicles, such as police cars, fire trucks and ambulances, are generally permitted to cross an intersection against a traffic signal. Emergency vehicles have typically depended on horns, sirens and flashing lights to alert other drivers approaching the intersection that an emergency vehicle intends to cross the intersection. However, due to hearing impairment, air conditioning, audio systems and other distractions, often the driver of a vehicle approaching an intersection will not be aware of a warning being emitted by an approaching emergency vehicle. 
     There are presently a number of optical traffic priority systems that permit emergency vehicles to preempt the normal operation of the traffic signals at an intersection in the path of the vehicle to permit expedited passage of the vehicle through the intersection. These optical traffic priority systems permit a code to be embedded into an optical communication to identify each vehicle and provide security. Such a code can be compared to a list of authorized codes at the intersection to restrict access by unauthorized users. However, the various optical traffic priority systems are incompatible because the vehicle identification code for each of the various optical traffic priority systems is embedded in the optical communication using incompatible modulation schemes. 
     Generally, an optical traffic priority system using a particular modulation scheme is independently purchased and implemented in each jurisdiction, such as a city. Thus, the traffic lights and the emergency vehicles for the jurisdiction are equipped to use the particular modulation scheme. However, a neighboring jurisdiction may use equipment that embeds the vehicle identification code using an incompatible modulation scheme. Frequently, a pursuit by a police car or the route of an ambulance may cross several jurisdictions each using an incompatible modulation scheme to embed the vehicle identification information. It may be burdensome and expensive to allow a vehicle to preempt traffic lights in multiple jurisdictions while maintaining appropriate security to prevent unauthorized preemption of traffic lights. 
     SUMMARY OF THE INVENTION 
     The present invention is directed to overcoming the above-mentioned challenges and others that are related to the types of approaches and implementations discussed above and in other applications. The present invention is exemplified in a number of implementations and applications, some of which are summarized below. 
     In connection with one embodiment, the present invention is directed to implementations that allow traffic light systems to be remotely controlled using multiple communication protocols. 
     According to a more particular embodiment, an arrangement for requesting preemption from a vehicle is used in a traffic control system. The arrangement for requesting preemption includes a protocol circuit, a signal control generation circuit, and an optical source. The protocol circuit is adapted to provide a plurality of communication protocols, wherein a plurality of the communication protocols communicate encoded data. The signal control generation circuit is adapted to generate an output signal in accordance with at least one of the plurality of communication protocols. The optical source is adapted to transmit light pulses from the vehicle, wherein the light pulses are generated from the output signal and include the encoded data for the at least one of the plurality of communication protocols. 
     The above summary of the present invention is not intended to describe each illustrated embodiment or every implementation of the present invention. The figures and detailed description that follow more particularly exemplify these embodiments. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       The invention may be more completely understood in consideration of the detailed description of various embodiments of the invention in connection with the accompanying drawings, in which: 
         FIG. 1  is a view of a vehicle approaching and controlling multiple traffic intersections using incompatible communication protocols for preemption of the traffic lights in accordance with the present invention; 
         FIGS. 2A ,  2 B and  2 C illustrate optical pulses transmitted between a vehicle and equipment at an intersection for various example communication protocols in accordance with the present invention; and 
         FIG. 3  is a block diagram of the components of an emitter for optical traffic preemption system for an embodiment in accordance with the present invention. 
     
    
    
     While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not necessarily to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention as defined by the appended claims. 
     DETAILED DESCRIPTION OF THE EMBODIMENTS 
     The present invention is believed to be applicable to a variety of different communication protocols in an optical traffic preemption system. While the present invention is not necessarily limited to such approaches, various aspects of the invention may be appreciated through a discussion of various examples using these and other contexts. 
       FIG. 1  is a view of a vehicle  102  approaching and controlling multiple traffic intersections  104  and  106  using incompatible communication protocols for preemption of the traffic lights  108  and  110  in accordance with the present invention. Intersection  104  is in jurisdiction  112 , such as a city, and intersection  106  is in jurisdiction  114 . A governmental body for jurisdiction  112 , such as a city government, can install a traffic light control system for traffic light  108  permitting preemption of the normal operation of the traffic light  108  to expedite passage through the intersection  104  by an emergency vehicle  102 . A separate governmental body for jurisdiction  114  can similarly install a traffic light control system for traffic light  110 . 
     Intersection  104  has a traffic light controller  116  that controls the operation of traffic lights  108  and supports preemption of the normal operation of the traffic lights  108 . Typically, the traffic light control system for intersection  104  includes one or more detectors  118  that detect stroboscopic optical light pulses from an emitter  120  of vehicle  102 . Typically, an optical source of the emitter  120  is mounted on the roof of the vehicle  102  orientated to emit the optical light pulses in the direction of travel by the vehicle  102 . Signals from the detector  118  for a requested preemption of the traffic light  108  by vehicle  102  are coupled to the traffic light controller  116 . In response to the requested preemption, the traffic light controller  116  adjusts the phase of the traffic lights  108  to permit passage of the vehicle  102  through the intersection  104 . Intersection  106  may similarly have detectors  122  and controller  124  for traffic light  110 . 
     Jurisdictions  112  and  114  can install traffic light control systems for intersections  104  and  106  that are incompatible. The communication protocol used to communicate a preemption request to traffic light controller  116  via detector  118  can be incompatible with the communication protocol used to communicate a preemption request to traffic light controller  124  via detector  122 . Typically, a vehicle  102  is associated with a jurisdiction, for example, vehicle  102  can be associated with jurisdiction  112 . Jurisdiction  112  can equip vehicle  102  with an emitter  120  that is compatible with each traffic light  108  in jurisdiction  112 ; however, emitter  120  could be incompatible with the traffic lights  110  in jurisdiction  114 . 
     Frequently, an ambulance transporting a patient or a fire truck responding to a fire alarm crosses multiple jurisdictions  112  and  114 . A duplicate of emitter  120  can be installed in vehicle  102  for vehicle  102  to be able to request preemption of both traffic lights  108  in jurisdiction  112  and traffic lights  110  in jurisdiction  114 . The incompatibility between certain traffic light control systems is limited to encoded data embedded in the stroboscopic optical pulses, such as the data value of a vehicle identification code used to authorize and log each preemption request. A jurisdiction  114  can configure traffic light controller  124  to omit authorization and logging of a preemption request from an emitter  120  using an incompatible protocol to embed data values in the stroboscopic optical pulses. However, omission of authorization and logging to enable preemption of traffic lights  110  by vehicles  102  from another jurisdiction  112  makes traffic lights  110  in jurisdiction  114  vulnerable to preemption by unauthorized users and limits the capability to detect preemption by unauthorized users. 
     Various embodiments of the invention provide for preemption of traffic lights  108  and  110  having corresponding communication protocols that are incompatible without duplicating equipment and without sacrificing the authorization and logging of vehicle identification codes. 
     According to a specific example embodiment, the emitter  120  of  FIG. 1  is implemented using a known implementation that is modified to support multiple communication protocols. For example, an Opticom™ Priority Control System (manufactured by 3M Company of Saint Paul, Minn.) can be modified to support one or more communication protocols in addition to the communication protocol for the Opticom™ Priority Control System. Consistent with features of the Opticom™ Priority Control System, one or more embodiments of U.S. Pat. No. 5,172,113 can be modified in this manner. Also according to the present invention, another specific example embodiment is implemented using another commercially-available traffic preemption system, such as the Strobecom II system (manufactured by TOMAR Electronics, Inc. of Phoenix, Ariz.), modified to support one or more additional communication protocols. 
       FIG. 2  illustrates optical pulses transmitted between a vehicle and equipment at an intersection for various example communication protocols in accordance with the present invention. A first communication protocol can have optical pulse stream  200  and a second communication protocol can have optical pulse stream  220 . A third communication protocol can have optical pulse stream  240  that combines the features of optical pulse streams  200  and  220 . 
     Optical pulse stream  200  has major stroboscopic pulses of light  202  occurring at a particular frequency that typically is nominally either 10 Hz or 14 Hz. Between the major pulses, optional data pulses  204 ,  206 , and  208  embed the encoded data values in the optical pulse stream  200 . For example, if pulse  204  is present then an encoded data value has a first bit of one, and if pulse  204  is absent then the encoded data value has a first bit of zero. If pulse  206  is present then the encoded data value has a second bit of one, and if pulse  206  is absent then the encoded data value has a second bit of zero. Similarly, if pulse  208  is present then the encoded data value has a third bit of one, and if pulse  208  is absent then the encoded data value has a third bit of zero. Typically, the optional pulses  204 ,  206 , and  208  are half-way between the major pulses  202 . Optical pulse stream  200  may correspond to the communication protocol of an Opticom™ Priority Control System. 
     Optical pulse stream  220  has stroboscopic pulses of light that nominally occur at a particular frequency that typically is approximately either 10 Hz or 14 Hz, but the pulses are displaced from the nominal frequency to embed the encoded data values in the optical pulse stream  220 . For example, after an initial pulse  222 , only one or the other of pulses  224  and  226  is present and if an early pulse  224  is present then an encoded data value has a first bit of zero and if late pulse  226  is present then the encoded data value has a first bit of one. Only one or the other of pulses  228  and  230  is present and if early pulse  228  is present then the encoded data value has a second bit of zero and if late pulse  230  is present then the encoded data value has a second bit of one. Similarly, only one or the other of pulses  232  and  234  is present and if early pulse  232  is present then the encoded data value has a third bit of zero and if late pulse  234  is present then the encoded data value has a third bit of one. 
     Typically, each pulse  224  through  234  is separated from the prior pulse with a nominal time period corresponding to the nominal frequency with the actual separation between a pulse and the prior pulse being slightly less or slightly more than the nominal time period. An early pulse with a separation from the prior pulse of slightly less than the nominal time period embeds a data bit of zero and a late pulse with a separation from the prior pulse of slightly more than the nominal time period embeds a data bit of one. For example, if pulse  224  is present then a second bit of zero is embedded when pulse  228  is separated from pulse  224  by slightly less than the nominal time period, and if pulse  226  is present then a second bit of zero is embedded when pulse  228  is separated from pulse  226  by slightly less than the nominal time period. Such an optical pulse stream may correspond to the communication protocol of a Strobecom II system. 
     Optical pulse stream  240  combines pulse positions of optical pulse streams  200  and  220 , allowing more encoded data or duplicated encoded data to be transmitted within a given time interval. After an emitter transmits an initial pulse  242 , the presence or absence of pulse  244  respectively provides a first bit of one or zero, and the presence of either pulse  246  or pulse  248  respectively provides a second bit of zero or one. The additional bits three through six are similarly embedded by pulses  250  through  260 . 
     In one embodiment, pulses  244 ,  250 , and  252  are transmitted by a multiple-protocol emitter one-half of the nominal period after the previous pulse. For example, if pulse  246  is present then pulse  250  is transmitted one-half of the nominal period after pulse  246  and if pulse  248  is present then pulse  250  is transmitted one-half of the nominal period after pulse  248 . In another embodiment, pulses  244 ,  250 , and  252  are transmitted half-way between the previous and following pulses. 
     A traffic light control system can have emitters on vehicles with one timing generator, such as a crystal oscillator, and controllers at intersection with another timing generator. To account for the possible timing differences between the timing generators at the emitter and controller, a controller designed to receive optical pulse stream  200  can have a tolerance for the nominal frequency for pulses  202 . Thus, a controller designed to receive optical pulse stream  200  can accept a range of frequencies for pulses  202  that encompasses the nominal frequency for pulses  202 . 
     An emitter can transmit optical pulse stream  240  with the frequencies for mutually exclusive pulses  246  and  248  within the tolerance range of frequencies for pulses  202 . When an emitter transmits an optical pulse stream  240  to a controller designed to receive optical pulse stream  200 , this controller can recognize either pulse  246  or pulse  248 , regardless of which of pulses  246  and  248  is actually transmitted, as a corresponding pulse  202 . Thus, existing and future controllers designed to receive optical pulse stream  200  may ignore the frequency shifting of pulses  246  and  248 . An emitter transmitting optical pulse stream  240  is compatible with a controller designed to receive optical pulse stream  200  when pulses  244 ,  250 , and  252  are present or absent in a manner corresponding to pulses  204 ,  206 , and  208 , respectively. 
     Generally, pulses  244 ,  250 , and  252  are ignored by a controller designed to receive optical pulse stream  220 . An emitter transmitting optical pulse stream  240  is compatible with existing and future controllers designed to receive optical pulse stream  220  when pulses  246  or  248 ,  254  or  256 , and  258  and  260 , are positioned to correspond to pulses  224  or  226 ,  228  or  230 , and  232  or  234 , respectively. 
     An emitter that transmits optical pulse stream  240  has the advantages of supporting a higher data communication rate and/or being compatible with either or both of optical pulse streams  200  and  220 . In one embodiment, the data values transmitted for bits one, three, and five are always zero corresponding to the absence of pulses  244 ,  250 , and  252 , to produce an optical pulse stream  240  that is compatible with optical pulse stream  220 . In another embodiment, the data values transmitted for bits two, four, and six are all always zero or all always one, corresponding to a constant frequency shift, to produce an optical pulse stream  240  that is compatible with optical pulse stream  200 . It will be appreciated that elimination of the frequency shifting can improve compatibility. In these two embodiments, an emitter transmitting optical pulse stream  240  is compatible with one or the other, but not both, of a controller designed to receive optical pulse stream  200  and a controller designed to receive optical pulse stream  220 . When an emitter is configurable to implement either of these two embodiments, only one type of emitter needs to be designed, to have inventory stocked, and to be supported. 
     An emitter transmitting optical pulse stream  240  can concurrently activate preemption of two traffic lights having controllers designed to receive optical pulse stream  200  for one traffic light and optical pulse stream  220  for the other traffic light. For example, two adjacent traffic lights a block apart can be situated within different jurisdictions that have installed controllers designed to receive optical pulse stream  200  for one traffic light and optical pulse stream  220  for the other traffic light. An emergency vehicle approaching both traffic lights can concurrently activate preemption at both traffic lights when the emergency vehicle is equipped with an emitter transmitting optical pulse stream  240 . 
     In one embodiment, each jurisdiction manages the assignment of a vehicle identification code to each vehicle authorized to activate preemption of traffic lights within the jurisdiction. A vehicle can be assigned two vehicle identification codes, with one vehicle identification code assigned by a first jurisdiction with traffic lights controllers designed to receive optical pulse stream  200  and another vehicle identification code assigned by a second jurisdiction with traffic light controllers designed to receive optical pulse stream  220 . An emitter for the vehicle may transmit a preemption request with one vehicle identification code embedded as encoded data in pulses such as pulses  244 ,  250 , and  252 , and the other vehicle identification code embedded as encoded data in pulses such as pulses  246  and  248 ,  254  and  256 , and  258  and  260 . The optical pulse stream  240  with the two embedded vehicle identification codes can concurrently activate preemption in both jurisdictions. 
     In another embodiment, vehicle identification codes are cooperatively assigned by the jurisdictions, possibly with each emergency vehicle being assigned a single vehicle identification code. An emitter for a vehicle may transmit a preemption request with the vehicle identification code embedded as encoded data in pulses, such as pulses  244 ,  250 , and  252 , and the same vehicle identification code embedded as encoded data in pulses, such as pulses  246  and  248 ,  254  and  256 , and  258  and  260 . The optical pulse stream  240  with the duplicated embedding of the vehicle identification code can concurrently activate preemption in both jurisdictions. 
     In yet another embodiment, pulses  244  through  260  can embed a single preemption request that can transfer more encoded data bits between an emitter and a controller in a given period of time. An emitter can be configurable to enable transmission of an optical pulse stream  240  that is only compatible with controllers designed to receive optical pulse stream  200 , only compatible with controllers designed to receive optical pulse stream  220 , concurrently compatible with controllers designed to receive either optical pulse stream  200  or  220 , and/or compatible with controllers designed to receive optical pulse stream  240  at a higher data transfer rate than optical pulse streams  200  and  220 . The additional encoded data can be used to provide additional operations, to enhance the security using encryption employing an encryption key, and/or enhance robustness by adding error detection or correction without increasing the response time of the optical traffic control system. 
     The nominal frequency used to transmit pulses of an optical pulse stream  200 ,  220 , and  240  can determine a priority. For example, a frequency of approximately 10 Hz can correspond to a high priority for an emergency vehicle and a frequency of approximately 14 Hz can correspond to a low priority for a mass transit vehicle. 
       FIG. 3  is a block diagram of the components of an emitter for optical traffic preemption system for an embodiment in accordance with the present invention. An optical source  302 , such as a Xenon flash tube or high intensity light emitting diode, on a vehicle emits short pulses of light that are received by a detector of a traffic light controller to request preemption of the normal operation of the traffic light to expedite passage of the vehicle through the traffic light. 
     A signal generation circuit  304  generates an output signal to control the flashes of light from optical source  302 . The signal generation circuit  304  can include a transformer used to generate an output signal having high-voltage pulses that each trigger a Xenon strobe light to emit a pulse of light. Data specifying the timing of the pulses of the output signal can be provided by protocol circuit  306 , with the pulses of the output signal corresponding to one or more optical communication protocols, which each can have a corresponding traffic light controller implementing a detection protocol. When the pulses of the output signal correspond to more than one optical communication protocol, the pulses can concurrently communicate all of the optical communication protocols. 
     Protocol circuit  306  can generate the timing specification for the pulses of light emitted by optical source  302 . Protocol circuit  306  can generate the timing specification of the pulses of light emitted by optical source  302  by generating the data values to be embedded in the optical pulse stream and encoding these data values to generate the timing specification for the pulses. The data values embedded in the optical pulse stream can include information specified at user interface  308 . 
     In one embodiment, interface  308  includes an input device used by an operator or administrator of the vehicle carrying emitter  300  to specify one or more vehicle identification codes. Example input devices include thumbwheel switches and keyboards. An operator setting up a vehicle identification code can additionally specify an operating mode for the emitter  300 . For example, one digit of a multi-digit vehicle identification code can specify that emitter  300  should emit an optical pulse stream compatible with a subset of all the optical communication protocols supported by the emitter. For ease of usage by an operator, the operator can be unaware that a portion of each vehicle identification code actually selects an operating mode instead of or in addition to being embedded in the transmitted optical pulse stream. In another embodiment, interface  308  includes a mechanism to specify default operation of the emitter or to configure operation of the emitter after manufacture, such as jumper settings within the enclosure of the emitter or externally configurable non-volatile storage. 
     Protocol circuit  306  can generate a specification of the optical pulse stream, including embedding a vehicle identification code received from user interface  308 . Protocol circuit  306  can include storage circuits  310  providing protocol information for various optical communication protocols. In one embodiment, each optical communication protocol has a corresponding storage circuit  310 . In another embodiment, a single storage circuit  310  provides protocol information for all of the optical communication protocols. 
     In one embodiment, the information in a storage circuit  310  can be a protocol algorithm, such as protocol state transition diagrams or processor-executable code. The protocol circuit  306  can include a processor, such as a microprocessor, that executes the processor-executable code to create data, such as a specification of the optical pulse stream according to the communication protocols. 
     In another embodiment, the information in storage circuit  310  can be a logic implementation, such as a programmable logic array or programmable logic device configured with programming data for the communication protocols. In yet another embodiment, the information in storage circuit  310  can be protocol tables, such as the next state and outputs as a function of the current state and inputs. Combinations of a protocol algorithm, a logic implementation, and tables can be used by protocol circuit  306  in alternative embodiments. The contents of storage circuit  310  can be externally accessible to allow the manufacturer or an administrator of a fleet of vehicles to update the communication protocols supported by protocol circuit  306 .