 |
Description  |
|
|
The present invention relates to methods of and systems and apparatus for
tracking stolen or missing vehicles and the like, being illustratively
described in connection with its important and perhaps primary application
to the recovery of stolen or missing automobiles and the like.
In Letters U.S. Pat. No. 4,177,466 of common assignee with the present
invention, an automobile theft detection system was proposed involving the
concealment in protected automobiles or other vehicles of radio
transceivers or transponders responsive to radio signal transmissions sent
when vehicles are missing, and modulated with a code corresponding to the
missing vehicle identification; each particular missing vehicle
transponder transmitting the same transponder locator signal when its
identification code is received for tracking by a police or other
direction-finder vehicle. To implement a system of this character in
practice, however, far more sophisticated techniques and safeguards are
required, including the use of a single frequency for all transmissions
and the problems of time-sharing dictated thereby, with protection against
transponder transmission while other transmissions on that frequency are
in progress; adaptability for varying the rate of transponder
transmissions once initiated by request of the operator of the tracking
receiver to provide faster or stepped-up periodic reply signals for
homing-in on the vehicle; discrimination of different vehicle transponder
reply transmissions for tracking; checks to insure against false
transponder activation; and the solution of other practical usage problems
such as the required police or other identification information storage
and networking requirements for a universal, nationwide and/or at least
statewide system.
An object of the present invention, accordingly, is to provide an improved
and highly practical method of and apparatus for locating and tracking
stolen or missing vehicles and the like that, while employing prior
underlying concepts of unique signal code-responsive transponders,
provides the added sophistication, security and practical techniques found
essential to enable a commercially useable universal system.
A further object is to provide such a system wherein, for the case of
automobile theft, the vehicle owner need only report the theft, after
which the entire system operates under the direct control of law
enforcement equipment and personnel, with the system virtually insensitive
to disarming or accidental activation
Another object is to provide an improved transponder apparatus for
identifying an object or vehicle with which it is associated and, where
and if desired, permitting location of such object or vehicle
It is a further object of this invention to provide such a transponder
which broadcasts at a variable rate a reply code specific and unique to
that transponder to establish its identity.
It is a further object of this invention to provide such a transponder for
which such broadcast rate is externally controllable.
It is a further object of this invention to provide such a transponder
which permits individual location of simultaneously broadcasting
transponders on the same reply frequency.
It is a further object of this invention to provide such a transponder
apparatus which can receive an activation code and transmit its reply code
on the same frequency.
The invention results, in part, from the realization of a truly effective
vehicle transponder that can detect encoded information, provide a reply
code specific to the transponder, discern the presence of a specific
identification code and a broadcast rate command in the encoded
information, and determine the transmission period for the reply code
based on the broadcast rate command.
Other and further objects will be explained hereinafter and are more fully
delineated in the appended claims.
In summary, however, from its overall aspect, the invention embraces a
method of tracking a computer-registered transponder equipped vehicle and
the like, upon the same being missing, that comprises, checking the
registration of such vehicle to determine that it is computer listed as
transponder-equipped; upon affirmative determination of such transponder
equipment listing, initiating the broadcasting in an appropriate sector of
a radio activation command signal carrying coded identification unique to
said vehicle and its transponder; receiving said command signal at the
vehicle transponder, decoding the identification and verifying that the
same is the unique code of said vehicle and its transponder, and, if so,
causing the transponder to become activated to transmit periodic vehicle
reply signals including unique identification; receiving said periodic
vehicle reply signals in a tracking vehicle and locking onto the same;
thereafter, at the request of the tracking vehicle, modifying the said
sector radio activation command signals to provide increased-rate command
signals to the vehicle transponder; and responding to the increased-rate
command signals at the vehicle transponder to increase the periodicity of
the transmitted transponder vehicle signals to facilitate tracking by the
tracking vehicle.
From other viewpoints, the invention also involves a novel transponder
apparatus for use in identifying the presence of an object interrogated by
broadcasted radio activation command signals on a predetermined RF carrier
carrying coded identification unique to that object and its transponder,
the apparatus having, in combination, means for receiving said command
signal and for decoding the identification and verifying that the same is
the unique code of said object and its transponder; means operable in the
event of such verification, for activating the transponder to transmit
periodic reply signals on the same carrier frequency and including unique
identification thereupon; and means responsive to further command signals
requesting a variation in the rate of such reply signals for thereupon
transmitting the reply signals at such varied rate.
From still another aspect, the invention provides a transponder apparatus
which detects encoded information, discerns the presence of its specific
and unique identification code and a broadcast rate command in the encoded
information, and transmits a reply code specific to the transponder, while
determining the next time of transmission of the reply code for
periodically repeating such reply transmissions. In one construction, the
transponder monitors RF command signals for predetermined encoded audio
signal carried by the broadcast signal. The audio signal conveys encoded
digital information using different audio frequency signals or tones, to
define the information, which typically includes a broadcast rate command
for the transponder replies and an identification code specific and unique
to that transponder (although in certain instances a universal
identification code such as a universal test code may be substituted for
the specific identification code). The transponder converts the digital
information into digital logic signals and, if the specific identification
code is present, broadcasts a reply code, specific to the transponder,
repeatedly at a rate determined by the externally controlled broadcast
rate code command, which may be changed to vary the transponder reply
rate. Mutual interference with both reception and transmission is avoided
with the preferred single carrier frequency employed, by pseudo randomly
varying the transmission period. A number of activated transmitters,
moreover, can broadcast simultaneously on the same RF frequency as well as
monitor that frequency for additional commands.
And, in another feature, the invention further provides a transponder
vehicle tracking apparatus having, in combination, direction-finding means
for receiving activated vehicle transponder periodic radio reply signals
carrying vehicle identification code information; signal and
microprocessor means for demodulating said identification code information
and for alpha-numerically displaying the same; means also responsive to
the last-named means for simultaneously displaying both the bearing from
which the transponder reply signals are received and the signal strength
thereof; and means for locking onto and displaying only radio reply
signals of a selected vehicle transponder.
Mention should also be made of the feature of using non-volatile memory to
remember the state of the transponder so that if electrical power should
be removed after activation, when electrical power is restored to the
transponder it will continue to transmit a reply code without need for
re-activation.
Preferred and best mode embodiments and apparatus details are later
explained.
The invention will now be described with reference to the accompanying
drawings,
FIG. 1 of which is a system diagram of the preferred vehicle location
system application of the concepts of the invention;
FIGS. 2 and 4 are block circuit diagrams of a transponder or transceiver
apparatus particularly designed for use in the vehicles-to-be-tracked in
the system of FIG. 1;
FIG. 3 is an encoded information sequence useful with the system;
FIG. 5 is a flow chart of the operation of the receiving and transmitting
functions of the transponder of FIGS. 2 and 4;
FIGS. 6 and 7 are block circuit diagrams of a preferred vehicle tracking
receiving and display systems for homing-in on the reply signals of the
transponders of FIGS. 1, 2 and 4; and
FIG. 8 is a data flow diagram of the sector activation computer-controlled
broadcast command system providing radio signals to interrogate and
activate the vehicle transponders of the invention.
A description, first, of the overall philosophy and methodology underlying
the total system operation of the invention in preferred form is in order,
with reference to the system diagram of FIG. 1.
When a vehicle V (or V') equipped with the transponder T (or T') of the
present invention is lost, the owner reports that fact to the local police
department which, in turn, reports to a state computer station system S.
In tests in Massachusetts, this system, as later explained, is termed
LEAPS. This information is sent, as a matter of course, from station S, as
by telephone network or link L, to a master computer file, preferably
maintained, for example, by the National Crime Information Center (NCIC),
a part of the FBI in Washington, D. C., (or at other suitable computer
facilities) and whereat it is intended to have in storage (SVLS--stolen
vehicle location system), a list of the vehicle identification numbers of
registered subscribers to the theft system of the invention. Every stolen
car report that comes in, will be checked against the subscriber list
(SVLS data base), and if a match is found, a computer message will be sent
back at L to the originating station S, with a set of information that
includes a unique activation code and a unique reply code for the
transponder of the stolen vehicle, and a description of the vehicle. This
information, now at the computer (LEAPS) at location S, is used to cause a
controlling computer (SVLS computer) to set up a transmission schedule
and, as by microwave link M, initiating the transmitting of the activation
code from a series of radio broadcasting transmitting antennas B (B'),
operated sequentially or if sufficiently spaced, simultaneously or in
slave fashion, thereby causing the stolen vehicle transponder, if in the
area or section, to activate with a certain probability. The activator
code is broadcast periodically (schematically shown at C) until a report
is received that the car has been retrieved or until some predetermined
time interval has been exceeded. These activation command signals,
broadcast at C, have the activation code of the vehicle transponder,
check-sum digits, and certain command bits that cause turn-on, turn-off
and speed-up, as later explained.
As before stated, the frequency of the broadcast transmitters is the same
as that of every vehicle transponder; namely, for example, a nationally
assigned VHF law-enforcement frequency. But each transponder T (T')
transmits a digital coded response or reply of about a tenth of a second
duration, periodically and preferably at pseudo random intervals, say,
once every ten seconds, roughly. In accordance with a feature of the
invention, however, if the transponder detects another transmission on the
frequency, it waits until that message is completed and then commences its
reply transmission.
A police or other tracking vehicle TR, appropriately equipped with a
direction-finding antenna system A and a tracking receiver and display D,
when within range of the missing vehicle, will display on an indicator
panel the coded response of the vehicle transponder, received along
schematic path(s) R (R'), a five-digit alpha-numeric code corresponding to
the code being transmitted by the vehicle transponder T (T'). When the
police officer sees that display at D, the officer calls into his radio
dispatcher, via RD, who puts an inquiry at P into the state computer
(LEAPS) and inquires as to the status of that code. If it turns out that
this is a vehicle that is stolen or that it is otherwise desired to track,
then the sector broadcast transmitters B (B') will be activated to send
out a different transmission C distinguished from the first activation
signals to vehicle transponders T (T") in that it represents a request to
increase the periodicity or rate of vehicle transponder responses or
replies. The second, step-up or speed-up reply request command signals C
will have the same vehicle identification number. It may or may not have
the same check-sum bits as the first type activation command signals, ut
it will have a different code in the command section of the message,
causing the speed-up, as opposed to just turn-on.
When the vehicle transponder receiver receives this increased rate command
signal, the transponder circuits will cause the transmission of the coded
reply or response message signal from the transponder vehicle to be
accelerated to a faster rate of transmission, say about once per second,
along R (R'), so that those in the tracking vehicle TR, instead of seeing
the coded number once every ten seconds on the display, will see it once
every second or so to aid in homing-in. The transponder will stay in that
speeded-up mode for a period of time, say 30 minutes, and then
automatically return to the regular mode of transmitting once every ten
seconds, the expectation being that within a half hour, the vehicle ought
to have been recovered.
If recovery has not been made, the tracking vehicle can always ask for the
speeded-up vehicle transponder reply command request to be broadcast again
at B (B').
At the tracking vehicle TR, not only are vehicle transponder reply codes
displayed, but a lock select or control (button, for example) is provided
at D to cause the computer processor in the tracking device to display
only signals with a particular reply code from a particular vehicle
transponder, to the exclusion of other vehicle transponder signals as from
other stolen vehicles in the area. In addition to the reply code display,
the tracking vehicle installation is provided with a direction indicator
such as a circle of light-emitting diodes that gives relative bearing or
direction of reception of the transponder signals. The direction-finding
system at the tracking vehicle preferably employs four roof antennas A,
later discussed in connection with the embodiment of FIG. 6, that are
electronically phased to determine the incoming signal by determining the
Doppler shift, as is wellknown, and providing the bearing indication.
In addition to the bearing indication, a bar-graph indicator is further
provided at D that shows relative signal strength and thus a rough
indication of range. This is important in tracking, particularly in urban
environments where the signal can bounce off a building or other vehicles
and trucks that may be close by. The signal that comes from the direction
of the stolen vehicle will usually be the stronger; so that if the tracker
sees the signal strength display in erratic mode, the direction of maximum
signal strength is followed.
The tracking vehicle personnel, as they home-in, thus know the relative
direction, the relative signal strength and a complete description of the
vehicle being sought; and, of course, other information that may be
pertinent such as whether the car may have been involved in an armed
robbery or some other important aspect. After finding and securing the
sought vehicle, the personnel of the tracking vehicle will report that the
car has been retrieved so that the system may cancel the stolen car report
in the NCIC and other computer files. Again, in accordance with preferred
features of the invention, this is also automatically effected, with the
software at NCIC checking and issuing a new set of command instructions
which causes the turn-off of the command signals previously broadcasted in
the search sector Other aspects of preferred refinements in the best mode
of practice of the system of the invention include the following. Messages
that come in to the computer controlling the broadcast transmitters are
queued up before being transmitted because it takes a certain amount of
time for the transmitter to build up to full intensity, which amount of
time is of the same order of magnitude as the messages-to-be-sent. The
sector broadcast transmitters will send out their activation signals and
codes on a periodic bases, perhaps once an hour or so, as before
indicated, until the vehicle is either recovered or a certain period of
time has gone by, which may, for example, be set at a month.
From a practical viewpoint, it is important to have some way of checking
out the transponder system once it is installed in the car. This may be
effected by an installation test unit, later described in connection with
the functional or operational diagram of FIG. 5. This installation test
unit is capable of sending a signal to the transponder receiver portion
T-RX which the transponder recognizes as a signal coming from the test
device and which causes the transmitter section T-TX of the transponder T
to go into a low power mode, in response also to another safeguard signal
that it picks up on it's DC power line, simultaneously.
In this preferred nationwide cooperative system illustrated in FIG. 1,
(though the invention is also useful for smaller sectors, states, group of
states or other sector sub-divisions as well), thus, each vehicle
transponder or transceiver assembly is part of a national (or at least
wide-area) stolen vehicle location system, as above indicated, shown as
preferably coordinated with the National Crime Information Center, NCIC.
When a vehicle such as automobile(s) V (V') is reported stolen, information
such as the license is entered through terminals P at any of a number of
terminals disposed throughout the area being monitored, such as in local
police stations or other municipal buildings, all such cooperating with
the before-mentioned LEAPS computer which has access to information as to
the manufacturer's vehicle identification number, description, etc. This
is a procedure followed in recent testing of the invention in
Massachusetts. The LEAPS computer interacts via L with the SVLS data base,
to determine if the vehicle is equipped with a vehicle transponder T
according to this invention. The vehicle identification number is sent
through the federal communications telephone or other networking L to the
NCIC computer in Washington, D.C., where, according to the preferred mode
of the invention, once the vehicle is identified (from comparison with
stored data) as a subscriber equipped with such transponders, the SVLC
software accesses the SVLS data base at NCIC to determine the unique
activation code for the vehicle V (V') and the unique reply code which
that transponder will broadcast upon activation. The activation code and
reply code information are returned automatically through network L to the
LEAPS computer which engages the SVLS computer and as through microwave
control link M, relays the code information to the radio transmitter at B
to broadcast an RF carrier command signal containing on its carrier
frequency the vehicle activation code and including the specific unique
vehicle identification code and a command for the transponder to reply at
a particular rate.
Let it be assumed that vehicle transponders T and T', hidden within cars V
and V', respectively, are both in range of sector activation transmitter
B, as shown. Only transponder T, however, will respond to the unique
identification code broadcast along C by transmitting antenna B. Upon
activation, transponder T then broadcasts its reply code unique to it
which is then received at D by the tracking vehicles such as a police
cruiser TR. The code name for car V is thus displayed on a console at D.
The tracking officer relays this code name along radio link RD to the
police dispatcher, who accesses the LEAP and SVLS computers at S to obtain
a description of the vehicle V, which is then radioed back to cruiser TR
so that the officer can visually identify the vehicle V.
As before stated, homing-in can be facilitated by step-up or increase of
the periodicity of transponder reply signals as the tracking cruiser
enters the vicinity of the stolen vehicle V. By requesting such speed-up
via link RD, the SVLS will control the before-mentioned increased rate
request, causing the signals broadcast at C to command such step-up in
transponder reply rate.
Turning, now, to details of preferred implementation of the various
components of the system of the invention, a useful transponder or
transceiver configuration T is illustrated in FIG. 2, wherein an antenna
1, hidden in the vehicle V (as inside the seat backs, dashboards, etc.),
is connected to a switch 3, such as conventional PIN diodes or the like,
for switching the antenna to the receiving or transmitting circuits of the
apparatus at appropriate times.
Assuming that the switch 3 is in the receiving function, the antenna 1 is
then connected to an RF amplifier and then a mixer so-labelled, which,
with the mixing of a local oscillator (1st L.O. takes the carrier
frequency of the activation command signals C broadcast by B (B') down to
a first intermediate frequency, say from a specified VHF carrier
(narrow-band FM audio FSK signal) to an intermediate frequency of 10.7MHz.
This is filtered and then applied to demodulator, so-labelled, that
basically extracts the audio from the signal. That audio comprises two
tones, one of which corresponds to a logical "zero" and the other of which
corresponds to a logical "one". The purpose of the modem 5 receiving these
filtered tones is to convert the tones into digital voltage levels,
corresponding to the "zero" and "one". The converted logic levels are
applied to a microprocessor 5' which serves as a control device.
When the vehicle code has been identified, as later explained, and it is
desired to reply or respond with unique vehicle code periodic transmitted
signals, as before explained, the microprocessor 5' generates logical
levels which it then feeds to the modem 5 to convert those logic levels
back into tones which are fed into a modulator so-labelled, in the
transmitter (bottom) portion of FIG. 2. The modulator modulates the
transponder transmitter T-TX consisting of an oscillator, a frequency
tripler to bring the frequency to that of the input command signal
carrier. The transmitter is a driver and a power amplifier (power amp),
adapted to feed the transponder antenna to transmit the reply signals R
(FIG. 1) on the same carrier frequency as the broadcast activation command
signals C, when the switch 3 connects to the power amplifier under the
control (via 3') of the microprocessor 5'. A high-power switch (Hi-power),
is also shown controlled by the microprocessor 5' to bypass the last-named
power amplification stage (power amp) so that a mode for low-power test
and installation transmissions is provided.
An example of coded information originally carried by the broadcast command
activation signals C as FM-modulation and received by the vehicle
transponder T is shown in FIG. 3. The preamble I comprises initially
sequential digital logic "ones" and "zeros" which allow modem 5, before
mentioned, to synchronize with the signal. The next block II, labelled
"Flag", indicates the commencement of the following data frame containing
the information conveyed by the two audio tones (say, of 1200 and 1800 Hz
frequency) representing logical "ones" and "zeros". When the signal C is
intended solely for the transponder T of missing vehicle V, the
transponder code III represents the unique digital address for transponder
T. The rate command portion IV is an activation command, a deactivation
command, or a step-up transponder reply periodicity command represented by
one or more values in binary form. Lastly, the frame may further include
conventional redundancy checks V, shown dotted, such as cyclic redundancy
checks, vertical redundancy checks, or longitudinal redundancy checks
which permit error correction and detection of transceiver code III and
rate command IV.
Using the code information of FIG. 3 as exemplary, the corresponding
encoded information may be traced through the transponder circuit of FIG.
2, as follows. When the FM-RF signal C having the preselected carrier
frequency is received, the same is demodulated, as before explained,
producing the carried audio signals representing the desired digital
information. The modem 5 converts the audio signals into digital signals,
as previously stated, and microprocessor 5' receives the digital
information when the audio signal is, say, in the range of 1100 to 1900
Hz. The modem 5, such as, for example, Type 409 of MX-COM Inc., of
Winston-Salem, N.C., outputs a logical "one" for one cycle of 1200 Hz, and
a digital "zero" for one and one-half cycles of 1800 Hz in the above
example. Microprocessor 5', such as, for example, Type MSM5840RS of OKI
Semiconductor, Inc., Santa Clara, Calif., processes the encoded digital
information as follows. A non volatile memory 7, such as an EEPROM
(electrically erasable programmable read-only memory) or other PROM
cooperates with the microprocessor 5' and contains the specific vehicle
transponder identification code, to be compared with the encoded digital
information III, FIG. 3, and the matching transponder reply code. To
conserve power, this memory 7 is provided with power only when retrieval
of its information is required. In combination with the feature that
intermittent or periodic transponder reply signals are generated only upon
command, as described, the transponder efficiently conserves power. The
car battery +,- or other battery provides power at twelve volts to a power
regulator 9 which maintains a five-to-six-volt power output to the
microprocessor 5'. A voltage level detection circuit 11 resets the
microprocessor 5' when the voltage drops below a predetermined voltage,
thereby allowing it to complete routine housekeeping while sufficient
power remains. As an example, the most recent rate command can thereby be
stored in the non volatile memory 7 before power is totally lost.
For testing purposes, the microprocessor 5' may broadcast a test reply
signal when a universal RF test signal is received simultaneously with an
electrical signal of predetermined special frequency on the unit's D.C.
power supply (as detected by a power signal detection circuit 13). The
special signal is of frequency high enough so that the impedance of
battery +,- does not interfere with signal detection, and low enough so
that a test signal does not create RF interference. The special electrical
signal is required so that the test device cannot be used by an authorized
person to locate cars equipped with the transponder of the invention.
Returning to the normal operation, when the proper identification code is
received, microprocessor 5' recalls its specific reply code from the
nonvolatile memory 7, stores it in RAM, and submits the information to the
modem 5 which converts the digitally encoded information back into an
audio signal. As before explained, with antenna switch 3 disabling
connection to the receiving part (T-RX) of the transponder, the
transmitter portion (T-TX) on activation of the transmit switch 15, under
control from the microprocessor 5', transmits on the same carrier
frequency the reply FM signals carrying the audio code reply signal; but
only if the microprocessor 5', controlling antenna and transceiver
switches 3 and 15, does not receive indication from modem 5 that the
receiver portion is still receiving a transmission on the carrier
frequency; otherwise, the control signal awaits absence of such carrier
frequency. As before stated, the use of the non-volatile memory enables
the transponder to continue replying after an interruption in replying
caused by power failure.
The microprocessor 5' includes an operation for interpreting the broadcast
rate command when received with the identification code specific to a
particular vehicle transponder T. A schematic implementation of this part
of the operation in hardware form is shown in FIG. 4, such being
considered as effectively incorporated in the processor 5' of FIG. 2. In
actual practice, of course, conventional software control will be
provided, the hardware explanation, however, more facilely describing the
operational functions. Specific identification (ID) code comparator 17
matches the received identification code with the identification code
stored in RAM, after it is accessed from the non volatile memory 7 of FIG.
2. If the identification codes match, the broadcast rate command is
provided to rate interpreter circuit 19 which selects a reply broadcast
rate at switch SW. If the rate command is "00", FIG. 4, for example,
pseudo random generation circuit 21 is accessed, this circuit periodically
receiving a pulse from a clock 23 and delaying signalling
transmitter-enable circuit 25 by an additional amount of time represented
by a pseudorandomly generated number. For example, clock 23 may provide a
pulse every 8 seconds, and circuit 21 may generate an additional delay
period of 0 to 4 seconds, resulting in the about once per ten second rate
of periodic reply signals as the enable circuit 25 is signalled to command
transmission of the replies.
When a step-up or increased reply rate command is received ("01"), such as
after a police cruiser nears the stolen vehicle, a step-up clock 27 is
accessed, as by switch SW effectively moving to the position shown in FIG.
4, the clock 27 generating a pulse at short, regular intervals, such as
once every second, which triggers enable circuit 25 to continue
transponder transmission at that rate and also steps up the pseudo random
circuit.
After a predetermined period of time, clock 27 signals rate interpreter
circuit 19 through line 27' to return to the normal broadcast rate (SW
position "01"), whereupon normal reply activation rate continues until a
deactivation command "02" is received, at which time switch SW contacts
ground to cease transmissions.
One suitable operation logic for the transponder T is shown in FIG. 5. In
receiver T-RX, the frequency of the incoming carrier signals C is
monitored, represented by operational step 29, and unless received, the
monitoring continues at step 31. If the received carrier frequency is
valid and the audio signal thereupon is within the preselected frequency
range, step 33, the encoded information enters the modem 5 and
microprocessor 5' for processing (RX-AUDIO IN, FIG. 2).
The transponder may include a testing feature, indicated in dotted lines as
step 35, where an RF test signal carrying a test code within the correct
audio range may trigger the transponder T-TX to broadcast a test reply
signal, step 37. For test step 35 to be satisfied, a preselected signal
detection circuit 13 of FIG. 2, earlier described must detect the
appropriate signal on the D.C. power line.
If the testing feature or the criteria for entering its subroutine are not
present, the specific transponder code for the vehicle V is recalled from
memory in step 39 and compared to the converted audio tone digital
information on the incoming signal. When the specific transponder code is
not present, monitoring continues, step 31; but if the specific
transponder code is discerned, the rate command is relayed, line 61, and
is distinguished within the transmission command procedure 41 to determine
transmission of the reply code by the transponder transmitting portion
T-TX. When a deactivation command is present from the broadcast signal C,
step 43, the transponder T ceases broadcasting replies, 45, and then, as
indicated by line 59, resumes monitoring, step 31.
The presence of the transponder activation command of broadcast signal C is
determined in step 51, and of the reply rate step-up request command, at
47. The transponder is activated to reply, or it receives the step-up rate
command to replay at a greater periodic rate. The step-up command, as
before explained, may remain in effect until a deactivation command is
received or until a predetermined period of time has elapsed.
When the activation command is received, a broadcast-enable is generated
pseudo randomly, step 53, at an average rate which is slower than the
step-up rate; for example, "enables" may be generated in step 49 once
every second, as before discussed, whereas the normal reply "enable" may
be generated, step 53, once every 10 seconds or so, including plus or
minus a random number, thereby minimizing the chance of overlap with the
reply broadcasts of other activated transponders. Preferably, after each
new rate command is received, it is stored in non volatile memory, shown
dotted at 55, and corresponding to the memory 7 of FIG. 2. Conventional
error correction and detection can be performed on the incoming data in
steps 39 and 41 by means of well-known vertical, longitudinal, and cyclic
redundancy checks, as previously mentioned.
It is now in order to examine the necessary type of circuits for the
tracking vehicle receiver equipment TR, FIG. 1, a preferred form of which
is illustrated in FIG. 6. The tracking receiver has two main parts; a
radio-receiving, power and processing portion; and a display, portion D.
The receiving portion comprises an RF summer 2 that multiplexes the inputs
from four antennae of the tracking vehicle direction - finding antenna
system A (FIG. 1): J 4, J5, J6, and J7. The sum of the four inputs
generates the signal from which the user is able to determine the
direction of either a vehicle transponder T being tracked or any device
that may be jamming the vehicle/transponder. The summer output contains
the very high frequency carrier signal of the vehicle transponder coded
reply with response signals and is fed to a narrow band FM receiver 4
which "strips off" the information-carrying signals in the audio range
(1200 and 1800Hz and the Doppler modulation frequency from the
direction-finding, such as 422 Hz), and supplies that demodulated audio
signal to the tracker's microprocessor and signal processor 6. The
microprocessor portion decodes the reply code of the vehicle being tracked
and the signal processor determines the car's direction, as later
discussed.
The receiver also provides the signal strength level that indicates the
stolen car's distance from the tracking vehicle, as also hereinafter more
fully explained.
The power for the tracking receiver, which may range from 11.5 to 14.5
volts, is supplied by the police or other tracking vehicle in which the
device is mounted. The power supply, and SP clock and filter circuit board
10 supplies all the power necessary for the functioning of the tracking
device, contains the master clock for the signal processor 6, and does
some preliminary filtering of the signal for the signal processor.
The signal processor board 6 has two functional parts: a control voltage
waveform generator and an audio signal processor. The control voltage
waveform generator portion provides the signals (VCA, VCB, VCC, VCD) that
are necessary for the RF summer 2 to multiplex smoothly from one of the
four antenna signals to the next, in conventional fashion. These four
signals, which are all identical, are shifted 90 degrees according to a
precise curve calculated from PROMs contained on the board. The audio
signal processor portion, on the other hand, takes the filter signal from
the power supply board and performs additional filtering, which serves to
make apparent the before-mentioned Doppler shift that indicates the
direction of the car being tracked.
The primary function of the logic/demodulating board 8 is to take the
signal strength from the receiver 4 and convert it into digital form. It
performs that function by demodulating the received signal into a stream
of 0 and 1 bits that contain both the reply code of the car being tracked
and a number of error detection and correction bits. The logic board also
reads and controls the system display D.
That display/control portion D, which may be mounted on the dashboard of
the tracking police car, contains two boards: one for display logic
(D.sub.1) and one for the display (D.sub.2).
The display D.sub.2, more particularly delineated in FIG. 7, consists of an
array of LEDs, arranged in a circle 12 and representing compass points, as
well as a central LED 12' that serves as a point of reference
(particularly at night) for those around the circle's edge. There is also
a bar graph BG with LEDs that indicate relative signal strength by the
height of the lighted display. Another LED 12 placed next to the bar graph
BG indicates whether the bar graph display is on the local or distant
display range.
At the upper center of the display is a 5-character alphanumeric display CD
that shows the reply code of the car being tracked.
There is also a lock-unlock switch 14 that enables the user to lock onto a
particular reply code. When the switch is not in the lock position, each
code from all of a multiplicity of vehicle transponders within range of
the tracking vehicle shows for one second.
The preferred alphanumeric display at CD is effected from data clocked from
the microprocessor 8 (GO, FIG. 7) into a pair of 8-bit shift registers SR,
the first bits controlling which of the LED dot-matrix display unit of CD
are used to display a given character (left), and the following comprise
the code for a given character, so as to produce an alphanumeric display
containing the unique code or serial number of the vehicle transponder
which is sending the reply signals R to the tracking vehicle. In a
practical implementation, a thirty-five bit shift register SR', controlled
by clock C', which is in turn supplied with control outputs G.sub.1 -
G.sub.3 from the microprocessor logic demodulator 8, receives information
for the compass point LED display 12, the on/off (power) control LED 12',
the local/distance LED 12" and the bar graph BG--all as clocked
sequentially into the shift register SR'. On the 36th clock pulse from the
clock C', the data is latched and outputted to the appropriate LED's.
In summary, when the tracking vehicle equipment TR is turned on, but is not
receiving a signal, the direction indicator display 12 (FIG. 7) is blank,
the signal strength indicator display BG reads 0, and the code display CD
is blank. In this mode, any received vehicle transponder signal R of
proper carrier frequency will trigger the TR. When such a signal is
received, the tracking indicator 12 illuminates to show the bearing of the
received signal and the signal strength indicator BG indicates a relative
signal strength value.
If the received signal is a coded vehicle transponder signal, a five
character identifier for that vehicle transponder appears in the digital
display CD. As the tracking vehicle approaches the vehicle, the signal
strength increases. If the distance is increasing, the signal strength
will decrease. In urban areas and other places where there are standing
waves and reflections, the signal strength may not give a reliable
indication of relative distance at all times, but provides homing-in
assistance eventually. In case more than one vehicle transponder is being
received, the lock switch 14 can be operated when the desired vehicle's
code identifier is displayed at CD. This causes the TR to track only that
specified vehicle. When, moreover, the TR displays a normal message from a
vehicle transponder, the center LED 12' of the direction display is
illuminated.
Finally, the data flow operation for the sector activation transmitter(s) B
(B', etc.), FIG. 1, will now be addressed, with reference to FIG. 8 and
with common letter part identification with FIG. 1, and with the
assumption that the operation will be a national system with NCIC reports
on stolen vehicles which go into the national vehicle file DG at NCIC. The
stolen vehicle report is entered by local police and dispatcher terminals
P (E6, E7) to the state LEAPS computer (P7) which communicates with NCIC
along lines L as discussed in connection with FIG. 1. With the
implementation of the present invention, NCIC also would store from data
entries E8 and master file up-dating P10, the master file D4 of vehicles
equipped with the transponders of the invention, labelled "SVLS data base"
in FIG. 1. If the reported vehicle was equipped with the invention, NCIC
would send back at L not only their normal reply, but an extra message
giving the transponder activation and reply codes o | | |
