Note: Descriptions are shown in the official language in which they were submitted.
1333635
The present invention relates to transponder vehicle tracking
apparatus, being illustratively described in connection with its important and
perhaps primary application to the recovery of stolen or missing automobiles and
the like.
This application is a divisional application of C~n~di~n Application
Serial No. 533,481 filed March 31, 1987.
In U.S. Letters Patent 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 when 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
rn/
~k
133363~
as the required police or other identification information storage and networking
requirements for a universal, nationwide and/or at least state-wide system.
A feature of the invention is to provide an improved transponder
apparatus for identifying an object or vehicle with which it is associated and,
where and if desired, pelmi~ g location of such object or vehicle.
It is another feature 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 feature of this invention to provide such a transponder for
which such broadcast rate is externally controllable.
It is another feature of this invention to provide such a transponder
which permits individual location of simultaneously broadcasting transponders on
the same reply frequency.
It is a feature 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 features of the invention will be explained hereinafter and are
more fully delineated in the appended claims.
rn/ ~ ~
-3- 13336~
The invention 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 identifica-
tion 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
transponder it will continue to transmit reply code
without need for re-activation.
Preferred and best mode embodiments and apparatus
1333~3S
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. l;
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 syseem
providing radio signals to interrogate and activate the
vehicle transponders of the invention.
- 1333633
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 svstem diagram of Fig. 1.
When a vehicle V (or V') equipped with the trans-
ponder 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
13336~
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 informa-
tion, 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 sufficently 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 trans-
ponder; namely, for example, a nationally assigned VHF
133363~
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
133363~
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, but 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 track-
ing 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
1 3 3 3 6 3 ~
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 par-
ticular 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 incom-
lng signal by determining the Doppler shift, as is well-
`- 1~336~
--10--
known, 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
1333G3~
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 refine-
ments 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 trasmitter 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
133363~
--12 --
the transponder receiver portion-T-RX which the trans-
ponder recognizes as a signal coming from the test device
and which causes the transmitter section T-T~ of the
transponder T to go into a low power mode, in response
also to another safeguard signal that it pick`s up on it r 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 build-
ings, all such cooperating with the before-mentioned LEAPS
computer which has access to information as to the
manufacturer's vehicle identification number, description,
133363~
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
accordin~ to this invention. The vehicle identification
number is sent through the federal communications tele-
phone 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
1333635
-14-
reply at a particular rate.
Let it be assumed that vehicle transponder-s 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 identi-
fication 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 re~uest, causing the signals broadcast at C
to command such step-up in transponder reply rate.
133363~
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 func-
tion, 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 LØ), 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
133363~
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 modu-
lator so-labelled, in the transmitter (bottom) portion of
Fig. 2. The modulator modulates the transponder trans-
mitter T-TX consisting of an oscillator, a frequency
tripler to bring the frequency to that of the input com-
mand signal carrier. The transmitter is a driver and a
power amplifier (power amp), adapted to feed the trans-
ponder 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-
, ,. ,~ ;
-- 133363~
named power amplification stage (power amp) so that a mode
for low-power test and installation transmissions is pro-
vided.
An e~ample of coded information originally carried by
the broadcast command activation signals C as FM-modu-
lation 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 com-
mand portion IV is an activation command, a deactivation
command, or a step-up transponder reply periodicitycommand
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,
. ,,, , ~,
133363~
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 represent-
ing the desired digital information. The modem 5 converts
the audio signals into digital signals, as previously
stated, and microprocessor 5' receives the digital infor-
mation 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, North Carolina, 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,
California, processes the encoded digital information as
follows. A nonvolatile memory 7, such as an EEPROM
(electrically erasable programmable read-only memory) or
other PROM cooperates with the microprocessor 5' and
. ,. c: . . ~, ~
133363~
--19 --
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 combin-
ation 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 main-
tains a five-to-six-volt power outpout to the micropro-
cessor 5'. A voltage level detection circuit 11 resets
the microprocessor 5' when the voltage drops below a pre-
determined 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 nonvolatile memory 7 before power is totally
lost.
For testing purposes, the microprocessor 5' may
-
1333~3~
-20-
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
133363~
-21-
reply signal; but only if the microprocessor S' controll-
ing 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 pro-
cessor 5' of Fig. 2. In actual practice, of course, con-
ventional software control will be provided, the hardware
explanation, however, more facilely describing the opera-
tional 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 nonvolatile memory 7 of Fig. 2. If the
1333~3~
-22-
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, pseudorandom generation circuit
21 is accessed, this circuit periodically receiving a
pulse from a clock 23 and delaying signalling trans-
mitter-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 O 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
133363a
signals rate interpreter circuit 19 through line 21' 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, represented by opera-
tional step 39, the frequency of the incoming carrier
signals C is monitored, and unless received, the monitor-
ing continues at step 31. If the received carrier fre-
quency 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 11, 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 b~oadcast a test reply
signal, step 37. For test step 35 to be satisfied, a pre-
selected signal detection circuit 13 of Fig. 2, earlier
described must detect the appropriate signal on the D.C.
power line.
13336~a
-24-
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 infor-
mation on the incoming signal. When the specific trans-
ponder 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 trans-
mitting 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 trans-
ponder 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 pre-
determined period of time has elapsed.
1333~3~
_25_
When the activation command is received, a broad-
cast-enable is generated pseudorandomly, step 43, 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 nonvolatile
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
133363S
-26-
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 infor-
mation-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.
1333~3S
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 direc-
tion of the car being tracked.
133363~
-2~-
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 O 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 displays (D1) and one for the display
logic (D2).
The display D2, 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 wheeher
the bar graph display is on the local or distant display
range.
1333635
_29_
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 (G~, 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 G1 - G3 from the microprocessor logic
demodulator 8, receives information for the compass point
1 33363s
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 dis-
play 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
13~363~
-31-
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 communi-
cates 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
13336~
-32-
"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 of the reported
vehicle so that this vehicle transponder may be activated
for tracking. The state police computer (LEAPS of Fig. 1)
would pass that request to the SVLS computer of Figs. 1
and 8 linked up with the terminals of all the police
agencies in the state and receiving (from P7 to P5)
request for P5 to process such activation request (or a
deactivation when the police recover a stolen vehicle and
report such). When P5 receives such request, three things
happen. First of all, the request is logged at D5. Then
an entry is put into a queue D7 for immediate action, with
such queue being serviced, say, one entry every 15 seconds
either to broadcast activation command signal C or to
place the request into the periodic action queue D3. Such
activation signals will be broadcast unless there are
others waiting, in which case, it has to wait its turn.
Thirdly, the request is received in an active file D1
which consists of all business relating to activations and
de-activations that are currently in process. An
,
133363~
activation request goes into the file Dl for, say, 30
days, so that over the ne~t month, activation command
signals will be broadcasted. Deactivations are handled
the same wav, although the time limit may be only 24
hours.
Function P2 removes records from the active file Dl
older than 30 days if they are not active; and other than
24 hours, if they are not active, logging its activity.
P6, which represents the broadcaster control signals
developed by SVLS Computer, services the immediate action
queue D7 once every 15 seconds as earlier mentioned, and
causes the periodic sector broadcast command signals C to
be transmitted from a local transmitter E3 and/or slave
transmitters E4 (B and B' in Fig. 1). The P4 (develop
action queues function) operates every hour to renew the
active file Dl and a local file D2, later described, and
an hours worth of broadcasting material. Old records may
be removed from the local file at P3.
The below-mentioned local file D2 contains data which
comes from Pl (process local transactions) originating at
the console El of the SVLS computer, containing a file of
vehicle transponders which have been entered locally as
133363~
-34-
for test and other special purposes. The console El
itself is protected by a system of passwords (D12, Dll)
and date and time entries (D10) so that unauthorized com-
mands cannot be entered. Conventional print-out may be
available as at E5.
While necessary and designed particularly for the
purposes of the present invention, the transponder
apparatus of the invention may also more generally be
employed where transponder or transceiver operation is
useful with a reply code specific or unique to that
transponder and which it broadcasts at a variable and
externally-controllable or - commanded rate. The
identification of vehicles or, more generally, objects
so-equipped, for example, is of utility in some apparatus,
altogether apart from tracking the same.
Though the invention has been described, moreover, in
its preferred mode of operation as a national system,
clearly, as before stated, the vehicle identification code
material and the like may be stored and supplied within
the state or other locale without cooperation with NCIC.
Other well-known circuits and apparatus and conven-
tionally derived software for performing the stated func-
133363~
-35-
tions than those shown may also be used, as may certain
functions be omitted if not desired; and while specified
features of the invention may be shown in some drawings
and not others, this is for convenience and clarity of
description only, it being understood that each feature
may be combined with any or all of the other features of
the invention. Similarly the particular selection of
frequency reply rates, type of encoding, audio tone range,
etc., types of tracking, communication and broadcasting
antennas, etc., are illustrative of what is believed to be
preferred and what has been successfully experimentally
tested; but further modifications will occur to those
skilled in this art, and such are considered to fall with-
in the spirit and scope of the invention as defined in the
appended claims.
