Vehicle location system - Patent Review 3984807

What is claimed is:

1. A vehicle location system for providing a remote site with updated information regarding vehicle location wherein a plurality of stationary low power wayside radio transmitter stations respectively transmit digitally encoded location messages indicative of their respective geographical locations, said vehicles each carrying a radio receiver for receiving said coded message when said vehicle is in the proximity of said transmitter, and a radio transmitter for transmitting digitally encoded location messages to said remote site, wherein the improvement comprises:

means at each of said stationary wayside radio transmitter stations for accompanying said digitally encoded location messages with a first plurality of data bits preceding each digitally coded message and a second plurality of data bits following each digitally coded message, said first and second plurality of data bits encoding respectively different predetermined start and stop code patterns; and

signal verifier means carried by each of said vehicles and coupled to said radio receiver carried by the vehicle which receives the encoded location messages from the wayside transmitter stations, said signal verifier means comprising the comparing start and stop code patterns with stored code formats permanently retained in said signal verifier means, the same code formats being permanently retained in each of said vehicles; said signal verifier means operatively coupled to said radio transmitter carried by the vehicle for inhibiting transmission of said digitally encoded location messages to said remote site unless the predetermined start and stop code patterns compare with said permanently retained code formats.

2. In the vehicle location system of claim 1 which includes:

a radio transmitter carried by each vehicle for transmitting over a radio channel said updated information regarding vehicle location to said remote site,

a radio receiver tuned to the channel over which said messages are transmitted to said remote site, and

means responsively coupled to said receiver for automatically delaying transmission of an encoded message to said remote site until said channel is clear.

3. In the vehicle location system of claim 2 wherein:

said radio receiver includes a squelch system for providing an output signal indicative that said channel is clear, and

means responsive to said output signal for inhibiting transmission of said encoded message to headquarters until said signal is received.

4. In the vehicle location system of claim 1 including:

portable transmitter means for transmitting a radio frequency signal over the same channel as said radio frequency communication links between said wayside stations and vehicles, and

means independent of said signal verifier means responsive to the signal from said portable transmitter means for automatically initiating a predetermined encoded message from said vehicle to said remote headquarters.

5. In the vehicle location system of claim 4 wherein:

said portable transmitter includes a source of clock pulses and timer means for modulating the portable transmitter with said clock pulses for a predetermined length of time, and

said means responsive to said portable transmitter signal uniquely responds to a continuous series of said pulses for a predetermined period of time somewhat less than the interval during which pulses are transmitted for said portable transmitter.

6. In the vehicle location system of claim 1 wherein both audio and digitally encoded messages may be sent from another site to said vehicle, the system including:

an audio speaker carried by a vehicle for communicating said audio messages,

means for minimizing the noise which would otherwise be produced by said digital data in said audio speaker including,

first means responsive to receipt of an encoded data signal at said vehicle, and

second means responsive to said first means for disconnecting said audio speaker during transmission of said encoded data.

7. In the vehicle system of claim 6 wherein said digitally encoded messages sent to said vehicle from another site are preceded by a tone of predetermined frequency, said system including:

a tuned high Q resonant circuit responsive to said predetermined tone frequency, and

switch means responsive to said resonant circuit for disconnecting said audio speaker.

8. In a vehicle location system wherein stationary wayside stations are used to reference the locations of a plurality of vehicles at a given point in time and wireless paths subject to interference and substantial attenuation when any appreciable distance separates the vehicle from a wayside station are used for transmitting digitally encoded messages between said stationary wayside stations and said vehicles, the improvement for maintaining the integrity of said messages by detecting errors resulting from the interference and attenuation of said wireless path comprising:

means for accompanying said digitally encoded messages with a predetermined digital code pattern,

signal verifier means carried by each of said vehicles for comparing said predetermined digital code pattern with a fixed unchanging code format permanently retained in said signal verifier means, said same code format being permanently retained in each of said vehicles, and

means responsive to said signal verifier means for inhibiting utilization of said digitally encoded messages unless the predetermined digital code pattern transmitted over said wireless path compares with said permanently retained code format.

9. In the vehicle location system of claim 8 wherein:

said predetermined digital code pattern comprises a plurality of data bits preceding each digitally coded message, so that errors induced by noise in said wireless path during the initial portion of transmission over said wireless path will be detected in said signal verifier means.

10. In the vehicle location system of claim 8 wherein:

said predetermined digital code pattern comprises a plurality of data bits following each digitally coded message, so that errors induced by noise in said wireless path during the latter portion of transmission over said wireless path will be detected in said signal verifier means.

11. In the vehicle location system of claim 8 wherein:

said signal verifier means includes means for registering the digital code pattern which accompanies said digitally coded message, and

means for converting said registered code pattern to the same format as said permanently retained code format.

12. In the vehicle location system of claim 11 wherein:

said permanently retained code format is a number in the decimal system, and

said means for converting said registered code format comprises a binary-to-decimal converter which provides an output transmit enable signal only when the decimal value encoded by said accompanying bits corresponds to said decimal number stored in said converter means.

13. In the vehicle location system of claim 8 which includes:

means responsive to said signal verifier means for automatically retransmitting said digitally encoded message upon receipt of a transmit enable signal from said signal verifier means.

14. A vehicle location system for providing a remote site with updated information regarding vehicle location wherein a plurality of stationary low power wayside radio transmitter stations respectively transmit digitally encoded location messages indicative of their respective geographical locations, said vehicles each carrying a radio receiver for receiving said coded message when said vehicle is in the proximity of said transmitter, and a radio transmitter for transmitting digitally encoded location messages to said remote site, wherein the improvement comprises:

means at each of said stationary wayside radio transmitter stations for accompanying said digitally encoded messages with a first plurality of data bits preceding each digitally coded message and a second plurality of data bits following each digitally coded message, said first and second plurality of data bits encoding respectively different predetermined start and stop code patterns;

signal verifier means carried by each of said vehicles and coupled to said radio receiver carried by the vehicle which receives the encoded location messages from the wayside transmitter stations, said signal verifier means comparing the predetermined start and stop code patterns with stored code formats permanently retained in said signal verifier means, the same code formats being permanently retained in each of said vehicles;

a keyboard in said vehicle for selecting a predetermined message;

means coupled to said radio transmitter for storing a vehicle designation, the keyboard selected message, and the digitally encoded location message; and

means operatively coupling said signal verifier means to said radio transmitter carried by the vehicle for inhibiting transmission of said stored messages to said remote site unless the predetermined start and stop code patterns compare with said permanently retained code formats.

15. A vehicle location system for providing a remote site with updated information regarding vehicle location wherein a plurality of stationary low power wayside radio transmitter stations respectively transmit digitally encoded location messages indicative of their respective geographical locations, said vehicles each carrying a radio receiver for receiving said coded message when said vehicle is in the proximity of said transmitter, a radio transmitter for transmitting digitally encoded location messages to said remote site, and a radio receiver for receiving messages from said remote site having a squelch system for providing an output signal indicative that the transmit-receive radio frequency channel between the vehicle and said remote site is clear, wherein the improvement comprises:

means at each of said stationary wayside radio transmitter stations for accompanying said digitally encoded messages with a first plurality of data bits preceding each digitally coded message and a second plurality of data bits following each digitally coded message, said first and second plurality of data bits encoding respectively different predetermined start and stop code patterns;

signal verifier means carried by each of said vehicles and coupled to said radio receiver carried by the vehicle which receives the encoded location messages from the wayside transmitter stations, said signal verifier means comparing the predetermined start and stop code patterns with stored code formats permanently retained in said signal verifier means, the same code formats being permanently retained in each of said vehicles; said signal verifier means operatively coupled to said radio transmitter carried by the vehicle for inhibiting transmission of said digitally encoded location messages to said remote site unless the predetermined start and stop code patterns compare with said permanently retained code formats;

means carried by each of said vehicles responsively coupled to said output signal of the squelch system of said receiver and operatively coupled to said radio transmitter for automatically delaying transmission of said digitally encoded location message to said remote site until the transmit-receive channel is clear; and

means for transmitting both audio and digitally encoded messages over the same channel from said remote site to said vehicle including in each vehicle (i) an audio speaker coupled to said receiver for communicating said audio message and (ii) means coupled to said receiver and said speaker for detecting receipt of an encoded data signal at the vehicle and automatically disconnecting said speaker during transmission of said encoded data.

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BACKGROUND OF THE INVENTION

This invention relates to a system for referencing the location of vehicles with respect to a plurality of stationary wayside stations.

There presently exists a need for a reliable economical system for periodically referencing the respective locations of a plurality of vehicles operating in the field. In general, such systems have relied upon the vehicle operator routinely advising a remote headquarters as to his geographical whereabouts. Obvious examples are the policeman in a patrol car and the cab driver. Human problems often interfere with the effectiveness of this type of system. Since people forget or neglect to report their locations, it is not uncommon for a vehicle to be "lost" for all intents and purposes since its location is unknown at a critical time. Also, emergency situations may prevent a patrolman from reporting his location at the very time that updated information as to his location may be the most critical.

Although a number of different kinds of systems have been devised which in theory provide a satisfactory vehicle location system, such systems have either been entirely too expensive for most government and private applications or they have had some inherent insurmountable problems. For example, it has been proposed heretofore to position low power transmitters at predetermined locations and have the vehicle receive a radio frequency signal when it is proximate to such transmitter indicative of the transmitter location. However, such systems have, heretofore, been impractical since the vehicle is constantly moving into and out of fringe reception areas. The number of error signals received is intolerable in these systems and obviously in many instances, inaccurate location information is worse than no information at all.

SUMMARY OF THE INVENTION

In its preferred embodiment, the present invention utilizes a plurality of stationary wayside radio transmitters each periodically transmitting a low power digitally coded message indicative of the geographical location thereof. In addition to a unique geographical location code, this signal also incorporates a start code preceding the station location message and a stop code which follows the station location message. These start and stop codes are keyed to a message verifier system within the vehicle which guard against reception of an erroneous location signal. Unless these start and stop codes correspond to a predetermined known code stored in the message verifier, the message is discarded. By bounding the location message within such start and stop codes, the integrity of the message is safeguarded, whether the vehicle is moving into or out of a fringe receiving area. Thus, when the vehicle is moving in such an area, noise may interfere with reception of a portion of the signal. Such noise however causes errors in the start and stop codes and thus results in the entire message being discarded. Similarly, when the vehicle is entering or leaving the location of a transmitter, a portion of the location message signal may well have noise interference but the same noise also generally causes errors in the start and stop codes. Such errors are detected in the message verifier system which causes the entire message to be discarded.

Upon receipt of a verified location message, the system automatically transmits a message from the vehicle to headquarters including the encoded location message received from the wayside station and in addition a unique vehicle identification code. In the preferred embodiment described herein, the communication may further include a status message entered on a keyboard mounted within the vehicle.

Special precoded messages such as an emergency communication may be transmitted to headquarters in two different ways. Within each vehicle, a keyboard includes one or more keys which when depressed transmit a coded message to headquarters. In addition, a portable transmitter which advantageously may be worn on the belt of a person, includes an actuator switch which, when depressed, transmits a signal to the vehicle. Systems within the vehicle decode this signal and cause an appropriate message to be automatically transmitted to headquarters.

The system of this invention permits operation with a minimum number of communication channels while providing for monitoring the location of a substantial number of vehicles. In the preferred embodiment, the audio and digital messages to and from the vehicle and headquarters are conducted over the same channel without interference. This is accomplished by automatically sensing the presence or absence of a transmitted signal on this channel and delaying transmission from the vehicle until the channel is clear.

The unpleasant and distracting sounds which result when a digital signal is applied to an audio speaker within the vehicle are substantially obviated in the present invention by automatically detecting transmission of a digital signal and turning off the audio speaker circuit during reception of these signals.

Systems constructed in accordance with the present invention not only serve the needs in an urban environment, such as police, fire, cab service and delivery service, but also because of their reliability and relative low cost permit application of a vehicle location system to new and different environments. One such environment, for example, is a large open pit mine in which the system of this invention automatically supplies updated information as to the whereabouts and status of the ore hauling trucks to a remote headquarters.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a perspective view of the system of the invention used as a police patrol car location system, particularly illustrating the relationship between the wayside stations, vehicles, portable transmitters and headquarters;

FIG. 2a illustrates graphically the pulse waveforms of a binary one and a binary zero in the exemplary embodiment of the invention;

FIG. 2b is a graphical representation of the digitally encoded waveform generated at a wayside station;

FIG. 3 is a simplified block diagram of the exemplary embodiment of this invention, particularly illustrating the communication paths connecting the wayside stations, vehicles, emergency transmitters and headquarters;

FIG. 4 is a detailed block diagram of the wayside station, emergency transmitter and message verifier portions of a vehicle location system constructed in accordance with this invention;

FIG. 5a illustrates graphically the pulse waveform of an emergency call from the emergency transmitter to the patrol car;

FIGS. 5b, 5c and 5d illustrate waveforms within the portion of the system of FIG. 4 for decoding an emergency call;

FIG. 6 is a detailed block diagram of the vehicle message transmission portion of a vehicle location system constructed in accordance with this invention; and

FIG. 7 is a detailed block diagram of the vehicle message receiving portion of a vehicle location system constructed in accordance with this invention .

OVERALL DESCRIPTION OF PATROL CAR LOCATION SYSTEM

Referring to FIG. 1, a plurality of stationary wayside stations 10a, 10b, 10c, 10d and 10e strategically located at predetermined geographical locations. In the specific embodiment described herein of a police patrol car location system, these wayside stations are conveniently mounted to structures already existing in a municipality such as street lamps 11 and stop and go lights 12. As a patrol car 13a, 13b, 13c or 13d is driven past a wayside station, the location of the vehicle is referenced at that point in time by virtue of receiving a low power digitally encoded message from the wayside station. The encoded message corresponds to the geographical location of the wayside station. Advantageously as shown, the encoded location message received by the vehicle is in turn transmitted from the vehicle to a remote headquarters 14 where the message is decoded and presented on a visual display 15. The positions of all patrol cars in use are conveniently displayed on a map 16 of the environment in which the system is installed.

In addition, the system of this invention provides for a portable transmitter 20a, 20b small enough to be conveniently carried on an individual patrolman when he leaves the patrol car. By merely depressing an activator button on the unit, the patrolman is able to transmit to a patrol car such as car 13d and thence over a high power radio frequency link to the remote headquarters 14 a precoded emergency message and last known vehicle location and thus inform headquarters that an emergency condition exists.

The operation of the system of FIG. 1 depends upon limiting the communication paths between the wayside stations 10 and the vehicles 13 so that a vehicle 13 receives a particular encoded location signal only when it is in the proximity of the station sending the signal. A convenient manner for achieving this is to provide each of the wayside stations with a very low power radio transmitter so that the effective radius of transmission is limited to a predetermined distance, for example, some 200 feet, represented by numerals 21, 22 and 23. Advantageously, this transmitted low power level at each wayside station may be adjusted to conform to the particular location of the wayside station. Thus, the transmitted power levels of stations 10a and 10b whose respective signals 21, 22 must be received by vehicles traveling along a pair of intersecting streets should be higher than station 10d whose signal 23 need only blanket the street area immediately adjacent this wayside station.

Such low power transmission as is provided by the wayside station 10 ordinarily produces serious communication problems since a driven vehicle 13 is constantly entering and leaving a fringe area of reception at the outer periphery of the radio transmitter zones, e.g. 21, 22 or 23; during which time noise may produce significant error signals. A significant feature of this invention is that these errors are successfully detected by a message verifier system located within each vehicle 13 so as to avoid transmitting erroneous location messages to the headquarter display 15.

As shown in FIG. 3, the wayside station 10 includes a low power 75 MHz radio transmitter coupled to an antenna 25. A vehicle within receiving range of this antenna receives a digitally encoded location message transmitted from the wayside station 10 on vehicle mounted antenna 26 coupled to a 75 MHz receiver 27. The validity of each received location message is determined in the location message verifier 28 and a valid location is retained in message store 29. Message store 29 also retains any status communication selected by the patrolman on the keyboard-display 30.

The portable transmitter 20 advantageously operates on the same 75 MHz radio channel to provide on its antenna 35 a signal received on the vehicle antenna 26. The precoded message provided by the portable transmitter is verified by the emergency signal verify 36 which automatically actuates the keyboard-display 30.

Messages encoding the vehicle location, vehicle number and status are automatically transmitted from the vehicle 13 to headquarters 14 over another communications link which in the exemplary embodiment is a 150 MHz radio channel. These messages are automatically transmitted whenever: (i) an updated location message is contained in message store 29, (ii) the patrolman activates the portable transmitter 20, or (iii) the patrolman actuates his keyboard-display unit 30 within the vehicle. When any one of these events occurs, a signal is supplied from either the location message verifier 28 or the keyboard-display 30 to the transmitter control logic 37. This logic is also responsive to the presence of another 150 MHz signal on vehicle mounted antenna 38 and received by vehicle mounted receiver 39 so that the 150 MHz vehicle transmitter 40 is keyed-on only when the 150 MHz channel is clear. The data stored in the message store 29 is then transmitted from antenna 41 to headquarters 14 on the 150 MHz channel. While transmitter 40 is keyed-on, a signal on lead 46 turns off vehicle receiver 39.

Communications from the headquarters 14 to vehicles 13 are provided via headquarters 150 MHz receiver-transmitter 42 which transmits over antenna 43 a signal received on the antenna 38 of all patrol vehicles. Encoded communications are selected by the dispatcher at headquarters on keyboard 44. These messages are received on the vehicle receiver 39 and displayed on vehicle keyboard-display 30. The encoded location and status messages transmitted from the vehicle are displayed on the headquarters vehicle location and status display 45.

For convenience, the 150 MHz receiver 39 and transmitter 40 and their respective antennas 38 and 41 are shown as separate elements herein. It will be understood that combinations of these units are commercially available as transceivers. Also, a single antenna installed on the vehicle would ordinarily be used to both transmit and receive the 150 MHz radio signals.

In the exemplary embodiment, the wayside stations include individual radio transmitters which produce low power signals received on vehicle mounted antenna 26. Another embodiment of the invention not shown includes a low power transmitter mounted on each vehicle for transmitting the vehicle identification numbers and status to receivers located at each wayside station. Passage of a vehicle proximate to a wayside station automatically provides an updated location message back to headquarters 14. In such embodiment the location message verifier 28 is located at the wayside station 10 rather than in the vehicle 13 and operates in an identical manner as described below to protect the integrity of the signal, especially when the vehicle and wayside station are so situated as to result in fringe reception at the wayside station receiver.

It will further be apparent that this invention is not limited to a system in which radio links provide the entire communication path from the wayside station or vehicle to the headquarters. The invention may, for example, be used advantageously in systems wherein the communication links between the vehicle and wayside station are wireless paths subject to interference and substantially attenuated when any appreciable distance separates the vehicle from the wayside station. Thus, modulated light waves encoding a digital message may transmit information between the vehicle and wayside station. Telephone lines may be used to transmit messages between the wayside station and the remote headquarters. Although specific radio frequencies are given herein for exemplary purposes, it will be understood that these values are exemplary values and specific channels will be generally determined by the availability of frequencies in accordance with the F.C.C. regulations.

DETAILED DESCRIPTION OF WAYSIDE STATION

As shown in FIG. 4, each wayside station 10 includes a timer 49 periodically activating repetitive code generator 50 and low power 75 MHz RF modulator-transmitter 51. When generator 50 and modulator-transmitter 51 are activated, a digitally coded message produced by generator 50 is transmitted over the 75 MHz channel on antenna 25.

Exemplary encoded waveforms produced by the repetitive code generator 50 are shown in FIGS. 2a and 2b. As shown in FIG. 2a, binary ones and zeros are distinguished by the time spacing between the leading edges of a pulse train. Thus, a five millisecond spacing between the leading edges 53, 54 of adjacent pulses defines a binary one whereas a 2 millisecond spacing between the leading edges 54, 55 defines a binary zero. The respective pulses are typically 1/2 millisecond long.

Respective binary ones and zeros are combined to provide an encoded signal from each wayside station 10 shown in FIGS. 1, 3 and 4. As shown in FIG. 2b, the 8 bits defining a digitally encoded location message are accompanied by a predetermined digital code pattern which in the exemplary embodiment comprises an initial 4 bits defining a start code and a following 4 bits defining a stop code. In general, the start and stop codes will be common to all wayside stations, whereas a pre-programmed wayside station location is indicative of a unique geographical location. Thus, the complete encoded message shown in FIG. 2b communicates both the location of the station and a binary coded signal common to all stations. As described below, the coding of the start and stop codes is keyed to a location message verifier 28 (FIGS. 3 and 4) within the vehicle so as to guard against reception of an erroneous location signal. This is particularly important in a vehicle locating system in which, as shown in FIG. 1, the vehicles are constantly moving within a fringe receiving area.

After transmission of the encoded signal of FIG. 2b, the modulator-transmitter 51 is caused to be turned off by the timer 49 for a predetermined time interval. This interval and the transmission radius of the wayside station are selected so that any vehicle operating at its maximum velocity past a station will receive at least two complete coded messages.

DETAILED DESCRIPTION OF MESSAGE VERIFIER SYSTEM

The encoded message of FIG. 3 is received on vehicle mounted antenna 26 (FIG. 4) coupled to the 75 MHz RF receiver and demodulator 27 mounted within the vehicle. The demodulator output signal is connected to a decoder 62 which distinguishes between an encoded binary one and a binary zero. A common form of decoder 62 produces a series of clock pulses on one output 63 with the presence or absence of a pulse on a second output 64 in time coincidence with a clock pulse indicative of a binary one or zero. Such decoders are common in the art and therefore are not shown in further detail in the Figure.

The output of the decoder 62 is coupled to the location message verifier 28 which includes a multiple stage, serial load shift register 65 adapted to hold the entire message from the repetitive code generator 50. As shown, the shift register 65 includes a four stage storage capacity for the 4 start bits, an eight stage storage capacity for the 8 bits wayside station location message and a four stage storage capacity for the 4 bits of stop code.

After an entire message has been entered into the shift register 65 in serial fashion, the entire message is analyzed in parallel fashion to detect whether or not the received signal is a true or erroneous signal. The four stages storing the 4 bits of the start code are respectively connected to a first binary-to-decimal converter 70. Similarly, each of the four stages storing the 4 bits of the stop code are connected to a second binary-to-decimal converter 71. Each of the converters 70, 71 convert the code pattern registered in the start and stop stages of shift register 65 into another code format. Thus, these converters have respective unique outputs 72 and 73 coupled to an AND gate 74. These unique outputs correspond to a pair of numbers programmed at and common to all of the repetitive code generators 50. Thus, in the exemplary message shown in FIG. 3, the start code bites in the binary 0100 pattern digitally encode the decimal number 4 and the stop code bits in the binary 0011 pattern digitally encode the decimal number 3. Each time these start and stop codes are received and stored in the first four and last four stages of the shift register 65, binary-to-decimal converter 70 supplies a signal on its output 72 corresponding to the decimal digit 4 and binary-to-decimal converter 73 supplies a signal on its output 73 corresponding to the decimal digit 3. Simultaneous energization of output 72 and 73 provide an "enable" signal at the output 75 of AND gate 74. As described below, the location message in the shift register is discarded if no signal appears at this enable output.

The operation of the location message verifier 28 so far described for protecting the integrity of the transmitted message may be appreciated by assuming that the vehicle 13 is in a fringe receiving area during a portion of the time interval in which the message is transmitted by the wayside station and received by the vehicle. In this hypothetical situation, noise pulses may erroneously result in a message being stored in the shift register in which the first 4 bits encode a start code number other than 4 and/or the last 4 bits encode a stop code number other than 3. In such instance, no output signal is supplied to output 72 and therefore no enable signal appears on AND gate output 75.

Quite conceivably, the noise which causes an error in the start or stop code also produces an error in the station location message. However, such erroneous location message is discarded by virtue of there being no enable signal produced at output 75. Since the vehicle 13 is normally in a fringe receiving area because it is moving toward or away from a wayside station 10, the error detector system described will guard against errors in both situations. Thus, when a vehicle is in a fringe area, a portion of the message may contain errors. Such errors are avoided by use of the start and stop codes. It is extremely unlikely that the vehicle is so located that the start and stop codes would be received without error and the intervening station location message received without errors.

The signal integrity may be further protected by store register 80 and digital comparator 81. These components provide sti