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TWO WAY TRACKING SYSTEM AND METHOD USING AN EXISTING
WIRELESS NETWORK
FIELD OF THE INVENTION
The present invention relates to a two way tracking system and method for
locating vehicles, objects, animals or humans that are provided with a
wireless
transceiver.
DESCRIPTION OF THE PRIOR ART
The present invention is an improvement over US patent no. 5.895.436 to Savoie
et al. That patent discloses a vehicle tracking method and system using the
cellular network infrastructure. According to Savoie a cellular transceiver is
installed in a vehicle which requires tracking, and operates on a continuously
stand-by mode, to remain accessible to the cellular security provider. The
cellular
transceiver is turned on to an active mode when tracking of the vehicle is
initiated.
The general location of the stolen vehicle can be determined by paging the
cellular
transceiver located in the stolen vehicle to identify one or more cell sites
located
near the stolen vehicle. The information is then relayed to a tracking vehicle
which
makes use of a radio direction finder to obtain an accurate bearing on the
location
of the stolen vehicle. In another embodiment, the tracking vehicle which is
provided with a radio direction finder can determine using a global
positioning
system receiver its location with respect to one or more cell sites identified
as
being close to the stolen vehicle such that the tracking vehicle can quickly
travel to
the area identified by the selected cell sites.
One of the main issues of that patent is conserving the integrity and security
of the
on-board system. In fact, the on-board system must be hidden from view, so as
to
prevent a potential thief from disarming the system.
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SUMMARY OF THE INVENTION
One of the objects of the present inven~._ion is to provide a
two-way trackimg system similar t:~, the one disclosed in
U.S. patent no. 5.89~~.43t~, ,.z:;irm~ an existing wireless
network to locate a variety of objects, persons or animals.
According to yet another aspect of the invention, there is
provided a system for tracking an object, person or animal,
the object, per:~on or animal being pr~ov~ded with a tracking
wireless transceiver, comprising:
- receiver means for receiving an indication that the
object, person or animal needs to xae t: racked;
- wireless radio means for w~.reles~ly c:ommun.icating with
the tracking wireless transceiver;
- means for estimating co::~rciinates of the object, person
or animal based on a locat~i.on of ~ane or more sites
communicating with the tracking wia:-e:less transceiver; and
- at least one wireless device prc:~ridf~d with the object,
person or animal., for ~airele~;sly communicating with the
tracking wireless transceivfar_ ;
- wherein the at least one wire7_ess device includes:
- a receiver for rE,ceiving -nessag~:s from the tracking
wireless transceiver; and
- an interface connec.tec~ t:o the rf~c~esiver, for generating a
message indicat ing that the obj ec:~t , p~:~rson or animal is
being tracked.
According to yet another a~pec:t: of 1-.lae invention, there is
provided a systE:m for track:inc~ ar-: ,~b-.yf~c:t., person or animal,
the object, person or animal ~:~eir.g gz~c>vided with a tracking
wireless transceiver, compr.~si.n<~:
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- receiver means for rec:eiv~ng an indication that the
object, person or animal needs to be tracked;
- wireless radio means for wire~.es~~ly communicating with
the tracking wireless transceivE:a_-;
- means for estimating coordinates of the object, person
or animal based on a l~:~cation c~f cane or more sites
communicating with the tracking wi.r_elt~s:~ transceiver; and
- at least one wireless device provided with the object,
person or animal, for ~.nrir_~elessly c~:~mrr~unicating with the
tracking wireless transceiver;
and further comprising:
-- a sensor_ connected to the trackincx w:i..reless transceiver,
for detecting a change and sending a sensor signal to the
tracking wireless transceiver; and
- a token included i.n the- at :Least: ore wireless device,
for receiving a signal from the tracking wireless
transceiver if the sensor ha::~ detf-~ctc_~d the change, and
transmitting a modif~_ed response s:i.gn,;~.1 to the tracking
wireless transceiver.
According to yet another aspect. o~ the invention, there is
provided a system for tracking arr c:~b;lect , person or animal,
the object, per:~on or animal beirng pr-e.w~.ded with a tracking
wireless transceiver, comprising:
receiver means fo~~~ r~ecei.vinc~ an indication that the
object, person or animal needs to be tracked;
- wireless radio means for wirrlesaly c~ommunicatirlg with
the tracking wireless transc,eiwer ;
- means for estimating coordinates of the object, person
or animal based on a location a; t- ~_.:,ne or more sites
communicating with the: t:ra:.:k.~ng v~~irf->:le.~s transceiver; and
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- at least one wireless device provided with the object,
person or animal, fc~r wiw~el.ess~~y cvc~mrnunieating with the
tracking wireless trransceiver;
and further comprising:
- local emitters inc'~uded in the at the least one wireless
device for wirelessly ccimmunicar.inq with the tracking
wireless t.ranscf~iver; anc~
- a central location cvirelessl.y c~omnuunicating with the
tracking wireless transceiver for determining which of the
local emitters is cl~~ser tc3 t:~~e r_racking wireless
transceiver.
According to yet another aspect of the invention, there is
provided a system for tracking an object, person or animal,
the object, person or animal being ~>r.~ov:i.ded with a tracking
wireless transceiver, comprising:
- receiver means for ~:eceiving an. indication that the
object, person or animal needs to be tracked;
wireless radio means for wi.reles~~-ly commun.icating with
the tracking wireless transweiver~;
- means for estimating coordinates of the object, person
or animal based on a lcacat:i_c-n r_.~f. ~:~r:e or more sites
communicating with the tracking wireless transceiver; and
- at least one wireles~~ device prawTids:~d wi.t~h the object,
person or animal., for wixeles:;7_y ~:rc~mrnuni<~ating with the
tracking wireless transceiver;
a.nd further. comprising
- positioning means for determining a location of a search
vehicle with respect t.o c:~ne o~:~ mores ~~:i.t.es;
- radio means for manir_ox-ing i~F ~~.lc~n~::~~.s emitted by the
wireless transceiver and recei.wed at. t.:he search vehicle;
and
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- radio location finder means for tracking the object,
person or animal based on a c::~i.rcet~ic~rn for travel of the RF
signals emitted by the= w::ireles~a t:x~a:~:-ace a ve-r and received at
the search vehicle.
According to yet another aspect of the invention, there is
provided a system for tr~~ck ing an o:ka j ect: , per.°son or animal ,
the object, person or an:~ma.l.:bei.ng pr:av::zded with a tracking
wireless transceiver, comprising:
- receiver means for r_eceivi.n~ are indicatloTl that the
object, person or animal needs to be tracked;
- wireless radio means for w:irel..essly <~ommunicating with
the tracking wireless transceiver; az~d
- means for estimating coordinates of the object, person
or animal based on a 1<acat-~.on of ~me or more sites
communicating with the t:rackizxg wireless transceiver, the
improvement wherein:
- the wireless transceiver is further wirelessly in
communication with at. least cone wi.re:.l.ess device on the
object, person or animal; and
- the wireless transceiver can be used to communicate with
the at least one wireless de~ri.cc on thf:-~ objecr_, person or
animal wherein the at least one wi~~eiess device includes:
- a receiver far re~ce:i.ving mc:.s~a~~s from the tracking
wireless transceiver; arid
- an interface connected to the receivNr, for generating a
message indicating tl;at tlue oby ec::t~ ~ pc:m-son or animal is
being tracked.
According to yet another aspect of the invention, there is provided a method
for
tracking an object, person or animal" the object, laerson or animal being
provided
3 o with a tracking wireless~transceiver, the method cr~mprising the steps of;
estatzlishing a~wireiess comrnunicatian with the wireless transceiver;
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estimating coordinates of the abject, person or animal based on a location
of one or more sites communicating with the wireless transceiver;
receiving an indication that the abject, pErson or animal needs to be tracked
at the wireless transceiver; and
sending a wireless signal from the wireless transceiver to at least one
wireless device on the abject, person or animal.
According to a further aspect of the invention, there is provided a method for
tracking an object, person or animal, the object, perscan or animal being
provided
1 o with a tracking wireless transceiver, the method comprising the steps of:
establishing a wireless communication with the-wireless transceiver;
estimating coordinates of the abject, person or animal based on a location
of one or more sites communicating with the wireless transceiver;
sending a wireless signal from the wireless transceiver to at least one
wireless device on the abject, person or animal; and
determining that the abject, person or animal needs to he tracked based on
a response of the at feast one wireless device received at the wireless
transceiver.
According to yet another aspect of t:he invention, there is
20 provided a system for trr~c~;ing an c>hjeci_, person or animal,
the object, person or animal being provided with a tracking
wireless transceiver, comprising:
- receiver means for rec~eiv:i.x~g an :~ ndlr_ation that the
object, person or animal needs t.;.> be ~ra~cl~ed;
- wireless radio means for wirel.e=,:ly communicating with
the tracking wireless tr~~nscei~~ei ; and
- means for estimating coordiraates of the object, person
or animal based on a l~:~cation <,f :one or more sites
communicating with the l~r~ickinc~ c~ri~v::el.es~ transceiver, the
3 0 improvement whe:re.in
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- the wireless transceiver is further wirelessly in
communication with at Least one w~.reLess device on the
object, person or animal; and
- the wireless transceivez~ can rye used to communicate with
the at least one wireless device on the abject, person or
animal; and further comprising:
- a sensor connected to tr::e tracking wireless transceiver,
for detecting a physical change and sen;~ing a sensor signal
to the tracking wireless transceiz~er; arid
- a token included in tlne at least one wireless device for
receiving a signal from tlue t:racki.ng wireless transceiver
if the sensor has detected the ph~;rsical change, and
transmitting a modified response si..gn~l to the tracking
wireless transceiver.
According to yet another aspect of the invention, there is
provided a system for tr<~cking are, olaject. , person or animal,
the object, person or animal being prova_ded with a tracking
wireless transceiver, compris.in.g:
- receiver means for receiving an indication that the
object, person or animal needs t~:~ be tra:zcked;
- wireless radio means fc:r wirelessly communicating with
the tracking wireless transceiver;
- means for estimating ceardinatr_=s of the object, person
or animal based an a l~~cat.iom c.~f.: -~zle or more sites
communicating with the tracking wi.re~:l.~~s:transceiver; and
- at least one wire7.es~, device f~rc,vidF.>cl with the object,
person or animal., far wi.~_elessly uomrriunicating with the
tracking wireless transc~>iver; and
- further comprising : a s;~usor cot:~mecfi ed to the wireless
tracking transceiver for detecting a change and sending a
sensor signal. to t:he t:rac:v:king wi re iec~:~ t ransceiver; <~nd
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at least one automatic tr<~nsmitter for receiving a signal
from the tracking wireless trar~scei.vei: if the sensor has
detected the physical. c;rvant~e, arnd 1:~.=r C~mir_ting a signal to
the tracking wireless tr<~nCmitt:~r.
BRIEF DESCRIPTION OF~THE DRAWiNC~S
The present invention and its advantages will be more easily understood after
reading the fo~llnwing nan-restrictive description of preferred embodiments
thereof,
made with reference to the following drawings in which:
1 o Fig. 1 is a black diagram of a tracking wireless transceiver with a
wireless
device according to the present invention;
Fig. 2 is an illustration of the vehicle tracking system of the present
invention;
Fig. 3 is a diagram illustrating haw a stolen vehicle or abject, can be
tracked
with a system of Fig. 2;
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Fig. 4a is a block diagram of the vehicle tracking equipment provided on a
search vehicle;
Fig. 4b is a diagram illustrating the location or direction finding GPS and
transceiver antennae used with the system of Fig. 4a;
Fig. 5 is a schematic. illustration of the wireless transceiver of the present
invention operatively connected to a motion sensor and to an engine kill and
in
wireless communication with a token; and
Fig. 6 is a schematic representation of the tracking device of the present
invention where local emitters designated as home and school periodically
transmit an ID to the tracking device, which is also in communication with a
central
location.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS
Referring to figure 1, there is shown a block diagram of a tracking wireless
transceiver 10. The wireless transceiver 10 illustrated is of the cellular
type, but it
should be understood by those skilled in the art that other types of wireless
transceivers may be used and that the present description although giving
examples of cellular transceivers, is not limited thereto. The wireless
transceiver
10 can be installed in a vehicle 20 (shown in figure 2), but can also be worn
by a
person, an animal or be installed in or on almost any object.
In case the transceiver 10 is installed in the vehicle 20, it can be connected
directly
to a constant 12 volt power source, such as the car battery and may be
provided
with a back-up battery 32 to prevent the transceiver 10 from being disabled if
the
cables to the car battery are disconnected. The transceiver 10 is designed to
operate full-time in a standby mode. The transceiver 10 is designed to draw a
minimum amount of current such that it can be maintained in a standby mode
continuously once installed. Similarly, even in an active mode, when the
transceiver 10 is required to operate at higher transmit power, very little
current will
be drawn from the car battery. The transceiver 10 can be designed to operate
in
the same way as a standard telephone transceiver in that it will respond to
queries
from the cellular network at periodic intervals to provide the network with an
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indication of its operating status. The transceiver 10 will respond to
standard
commands and queries from the network such as when the RSSI level with
respect to a particular cell site is required. It can also receive commands
from the
cellular network if the transceiver transmit power level needs to be changed,
such
5 as when the transceiver 10 is paged. The power level can vary from a minimum
of
0.2 watts to a maximum of 0.6 watts such as is currently used in standard
cellular.
telephones.
The transceiver 10 is provided with standard components, such as an antenna
11,
a power supply 13, memory and processor circuits 14, RF circuit 15 and an 10
circuit 16.
The 10 16 circuit is further connected to an second antenna 21 that allows
wireless
communication with a wireless device 22. The wireless device 22 has less
components than the transceiver 10 and is therefore typically smaller in both
size
and weight. The wireless device 22 is further connected to an antenna 23 and
can
have an LCD or pixel screen 24. Furthermore, since the wireless device 22 is
separate from the transceiver 10, it can be easily hidden, while the
transceiver 10
can remain apparent to other people. A person that is to be tracked must be in
proximity of both the transceiver 10 (which can be worn on a belt for example)
and
the wireless device 22 (which can be hidden in a pocket for example).
The 10 circuit 16 can also be provided to connect a variety of sensors 17 to
detect
that an alarm has been triggered on the vehicle 20 or that the ignition 18 has
been
activated by an unauthorized user. Other options, such as, remote engine kill,
car
starter and remote door locks can also be used as well. The 10 circuit 16 can
also
be connected to an audio source 19 such as a microphone to enable the security
service provider to hear any conversation persons might be having in the
vehicle
20.
Referring now to figures 2 and 3, there is shown a diagram illustrating a
tracking
system for tracking the transceiver 10. In this example, the transceiver 10
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illustrated in figure 1 is installed in the vehicle 20. The transceiver 10
would be
provided, as any other cellular telephone, with a unique identifier such as a
MIN.
The identity of the vehicle owner or operator and the transceiver's unique
identifier
are added to a customer database of the security service provider. The
installation
of the transceiver 10 and registration of the unique identifier would of
course be
done via a security service provider authorized by the cellular service
provider to
assign new cellular accounts, such as is currently done with the purchase of
cellular phones.
Normally, when calls to and from a cellular transceiver are made, the cellular
network will verify the cellular transceiver's 10-digit telephone number (NAM,
Number Assigned Mobile) and ESN (Electronic Serial Number) before allowing the
call to go through. Each cellular telephone is provided with a unique
telephone
number (MIN) which corresponds to a unique ESN.
With the system of the present invention, the transceiver 10 will provide its
ESN
when queried by the network. As will be described further below, only the
transceiver having the correct ESN and MIN will respond to queries from the
cellular network, even if each locating transceiver makes use of the same
unique
MINs.
Once the transceiver 10 is installed and in operation, the user becomes
registered
with the security service provider. The security provider enters the
transceiver's
ESN in a database with the customer's personal information, such as
residential
address, telephone number, vehicle description and serial number, etc. The
transceiver 10 which is now in vehicle 20 operates in a passive or standby
mode
within the wireless network infrastructure. From time to time, at
predetermined
intervals, the transceiver 10 will be queried by the network to provide an
indication
of its location within the network. For example, in figures 2 and 3, the
transceiver
10 of vehicle 20 will be paged from time to time over a paging channel 31. The
paging request is generated from any one of the cell sites A, B or C. Upon
receiving the paging request, the transceiver 10 switches over to an active
mode
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to transmit a response to the nearest cell site to identify amongst other
things, the
signal quality or RSSI level. This way, the service provider 32 can keep track
of
various cellular telephones within the network and their locations, such that
when
an incoming call arrives, the call can be directed to a cell site located
nearest to
the cellular telephone user. This information is updated from time to time in
a
database 33. The response may or may not be used by the network, according to
the need to keep track of individual transceivers.
If a third party wishes to report that a person wearing the transceiver 10
needs to
be tracked, then the third party can contact the security service provider 34
by
making a call to a predetermined phone number. When the security service
provider 34 receives the indication that transceiver 10 needs to be tracked.
At this
point, a preliminary query is made to determine the current location of the
transceiver 10 within the network. A general estimate of the location of the
transceiver 10 can be determined, say, within a 120 degree area of a cellular
cluster, namely by identifying the cell site sector communicating with the
transceiver 10. The security service provider dials the pre-selected telephone
number, i.e. common NAM associated with tracking wireless transceivers. The
call
is processed as a normal incoming cellular call by the network operator. The
cellular network operator receives the dialed digits, checks its database for
the
associated ESN, then transmits, on the cellular network, a new paging signal
containing the common NAM and unique ESN of the transceiver 10. The only
transceiver to respond will be the one associated with the vehicle 20 and a
voice
channel illustrated by arrow 36 is opened between the transceiver 10 of the
vehicle 20 and a nearby cell site. This voice channel is kept open, as if a
normal
conversation was taking place. However, the security service provider is now
in
control of the opened voice channel and will keep it open until the
transceiver 10 is
located. In this example, cell site A is currently communicating with the
transceiver
over voice channel 36.
Furthermore, the concerned third party may wish to send a message to the
person
to be tracked through the wireless device 22 via the transceiver 10.
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One way of sending messages in an inexpensive manner is to encode
predetermined messages within the transceiver 10. The transceiver 10 is
adapted
to recognize which message to send based on, for example, the duration of call
set up, i.e. the number of rings, without having the transceiver 10 actually
answer
the call. In the case where the transceiver 10 is a cellular (or PCS) unit,
the person
wishing to send a message would essentially first decide which message is to
be
sent. This message, in encoded form, is sent to the transceiver 10. The
transceiver 10, based on the duration of the call set up, i.e. the number of
rings,
recognizes the message to be transmitted to the wireless device 22. The
transceiver 10 then sends a wireless signal to the device 22 to display a
given
message. The message selector (not shown) in the transceiver 10 may be a
circuit
that is programmed to perform such a function. The advantage to this approach
is
that it does not repuire airtime (thus no fees), and the integrity of the
transceiver
10 is maintained.
The wireless device 22 can be provided with a receiver (not shown) connected
to
the antenna 23 which receives the messages from. the transceiver 10. Even
though a LCD screen or display screen 24 has been shown, other types of
interfaces may be connected to the receiver to generate a message indicating
that
the person is being tracked. For example, the interface may also be an audio
interface. Furthermore, as described above, other messages types may be
displayed on the interface of the wireless device 22.
Referring to figure 5, the transceiver 10 can be provided with a motion sensor
60
installed on the vehicle 20. As soon as the motion sensor detects that the
vehicle
20 is in motion, it sends a signal to the transceiver 10. The transceiver 10
then is
adapted to send a signal to a token 62. The token 62, which can take the form
of a
circuit integrated on a key chain, for example, receives the signal from the
transceiver 10 and modifies it in some way. The transceiver 10, detecting this
modification of the sent signal, recognizes that the proper owner is in the
vehicle
20. However, should the transceiver 10 not detect the modification of the sent
signal, it could arm itself automatically and identify itself to a central
location as
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being in need of being tracked. Alternatively, the transceiver 10 can also
incorporate a feature such as engine kill 64, to prevent the vehicle 20 from
travelling too far. Also alternatively, the transceiver 10 can be programmed
to
contact one or more predetermined numbers, such as a dispatcher, and to
provide
the end user with Internet access, so as to contact the owner of the tracked
item or
parent of the person directly. It should be understood that in this
embodiment, the
invention is not limited to motion sensors, but is equally applicable to any
type of
sensor. Furthermore, the presence of a sensor is not essential, as a simple
exchange between tokens and transceiver may be sufficient upon detecting a
change such as starting the engine.
As can be appreciated, the system of the present invention can be armed or
disarmed through the token 62 (or an automatic pulsing transmitter). Such a
system protects the "stealthness" of the system, and minimizes the risks
associated with a user not properly arming or disarming the system.
Referring to figure 6, the present system can be used to determine with
precision
where a person or object is. This is achieved by first having a user contact a
central to register cell site, cell site sector and signal strength.
Afterwards,
definitive location confirmation is achieved by placing local emitters 66, 68
at
specific locations, such as home, school, office, vehicle, etc. The local
emitter
sends its ID to the tracking device at predetermined intervals. The
transceiver 10
has a receiver on board capable of determining which emitter is transmitting,
and
relaying this information back to the central 70, so that tracking can be
effected.
The central 70 is then able to determine that the tracking device is closer to
school
than to home.
Furthermore, in order to precisely track the transceiver 10 of the vehicle 20,
the
security service provider 34 can forward the identity of the vehicle 20 to a
security
response team located in a tracking vehicle 37 (also shown in figure 4b). The
team
is provided with the current location of vehicle 20 based on the closest cell
site
sector where the vehicle is located. That information may either be provided
by
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means of a building name or address, where the antenna cell site sector
antenna
is located, a street address, or in the preferred embodiment, by means of a
latitude
and longitude coordinates provided by a global positioning system. The GPS
system is used by tracking vehicle 37 to establish its position with respect
to the
5 cell site sector that has been identified.
Once the identity and general location of the vehicle 10 is received at the
tracking
vehicle 37, the tracking vehicle 37 can monitor the open voice channel 36 and
travel in the general direction identified by the security service provider.
Once the
10 tracking vehicle 37 reaches the general location of the vehicle 20, the
security
response team makes use of a radio direction finder which is tuned to the
voice
channel 36 to precisely identify the location of the vehicle 20. Once the
precise
location of the vehicle 20 has been confirmed, the security response team can
alert the authorities to recover the vehicle 20.
The tracking vehicle 37 is provided with a cellular telephone system to
communicate with the security service provider 34. The radio direction finder
consists of a number of antennae 39 connected to radio direction finder
equipment
to locate precisely the direction of arrival of an RF signal emitted by the
vehicle 20
on the voice channel 36 and received by cell site A as well as tracking
vehicle 37.
Referring now to figure 4a, we have shown a block diagram of the tracking
equipment which is provided in the tracking vehicle and which is used by the
security response team to track the precise location of the vehicle 20. The
equipment includes a standard cellular transceiver 50 which enables the
security
response team to communicafie with the security service provider to coordinate
the
search and tracking of the vehicle. As indicated above, the vehicle may be
provided with a GPS antenna 51 connected to a GPS receiver 52 and computer
53 to enable the operator to determine the location of the tracking vehicle 37
with
respect to the coordinates of the cell site communicating with the vehicle.
GPS
receiver 52 will provide a direction the tracking vehicle should follow in
order to
reach the cell site. This is achieved by entering the coordinates of the cell
site. The
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GPS receiver 52 can then provide an indication of the route to follow to the
tracking vehicle which receives positioning data from a satellite via GPS
antenna
51.
Once the tracking vehicle is dispatched and rolling towards the cell site
serving or
communicating with the cellular transceiver of the vehicle, the specialized
cellular
band RF receiver 55 locks onto the forward voice channel 31 (the frequency
used
to communicate from the tower to the cellular transceiver) currently in use
based
on the combination of ESN and NAM or a specified channel pointed out by the
operators at the MTSO. The four quarter wave antenna of the radio direction
finder
56 can then determine the direction of arrival of the RF signal emitted by the
cellular tower. This provides the recovery team with a bearing towards the
cell
tower A (figure 2) it necessary. Once in the vicinity, the RF receiver is set
to the
reverse voice channel (the frequency used to communicate from the cellular
transceiver to the tower) 31. This is done by dropping the frequency by
exactly 45
Mhz on the tuner. The information provided by the quarter wave antennae 57 can
then be used at a display or monitor 58 to determine the exact location of the
stolen vehicle. As shown in figure 4b, the four quarter wave antennae are
mounted
at the corners of a square on the roof of a tracking vehicle 37. The output of
each
of the quarter wave antennae are fed into an antenna adder/coupler 59 and
applied to the input of RF receiver 55. A radio direcfiion finder such as
described
above is available from Doppler Systems Inc. The cellular tracking system as
identified at reference numeral 54 is available from Allen Telecom Group Inc.
In the event that the tracking wireless transceiver is removed from the
vehicle, one
or multiple miniature wireless transceivers will be activated, at that time
enabling
the tracking vehicle to home it on the vehicle. This is important if the
tracking
wireless transceiver becomes defective or is removed by a thief. The miniature
wireless transceivers essentially monitor the transmitter pulse sector of the
tracker's device. If the miniature wireless transceiver does not detect the
pulse of
the transmitter in a predetermined length of time or detects a coded pulse
from the
transmitter within the tracking device, the miniature wireless transceiver
begins
CA 02395843 2002-06-26
WO 01/59472 PCT/CA01/00130
12
sending its signal indicating a defective tracking wireless transceiver or a
missing
one.
Although preferred embodiments of the present invention have been described in
detail herein and illustrated in the accompanying drawings, it is to be
understood
that the invention is not limited to these precise embodiments and that
various
changes and modifications may be effected therein without departing from the
scope or spirit of the present invention.
s
