Note: Descriptions are shown in the official language in which they were submitted.
~ w096/02007 2 ~ 7 I 3 ~ 3 PCT~S95/08527
, APPARAT~S AND M~ FOR ~OCATING r~rrm-~ TE~h~N~S
AND SIMIr-AR TRANSh~ ~KS
S
Bac~lou.,d o~ the Invention
Field of the Invention
The present invention generally relates to the
function of locating cellular telephones and other mobile
transmitters, and particularly, to a method and apparatus
which use a two stage approach including a long range,
variable accuracy technique in combination with a short
range, high accuracy technigue.
IS 8tatement of the Prior Art
The proliferation of cellular telephones, or cell
phones, and their technology and usage, has revealed
various applications for the ability to locate cell
phones and similar transmitters. These applications
include ~911~ calls, tourist and travel information, the
tracking of commercial, government and stole Yehicles,
and the identification of unauthorized cell ~-~one usage
and illegal activities, to name a few. The basic cell
phone systems can only determine the nearest cell phone
base station, which locates the cell pho~e to within 3 to
10 miles.
A goal of any such system for use with cellul~
phones is the use of as much existing eguipment as
possible or at least compatibility with existing
eguipment. Examples of this are use with unmodified
cellular phones and compatibility with existing cellular
base stations.
A great deal of technoloqy already exists concerning
the tracking or locating of radio transmitters. One
W096/02007 3 PCT~S~5/~85~.7
least in such applications as LORAN and GPS. The
application of this process to cell phones includes
accurately measuring the time of arrival of the same
signal at a multiplicity of base stations and comparing
5 the times to determine the difference between
transmission times to each base station. Tdoa techni~ues
do not re~uire any modifications of the transmitters,
because they operate on the ordinary signal transmitted.
Tdoa techni~ues are also compatible with existing
10 omnidirectional cell phone, base station antennas.
One such application of tdoa technology combined
with direction finding and applied to cellular phones is
described in US Patent No. 5,317,323. The system
described therein uses GPS timing signals at the
15 receivers to determine the time of signal reception.
Direction f;n~;ng is used to reduce multipath and co-
channel interference. Unfortunately, the use of
direction finding requires the use of a steerable antenna
or array and i8 thus not compatible with the existinq
20 omnidirectional antenna structures used in the cell phone
industry. Even sectored antennas, which may be used for
cell phones, do not provide sufficient accuracy. The
patent does show the importance of ~-.~ving multipath
interference. Thus, it is a goal of any such locating
system for cellular telephones to distinguish between a
direct signal from a cell phone and multipath reflections
of the same signal from buildings and other reflectors.
Reflected signals, which take a longer and unknown path
to the receiver, provide less accurate location
30 information.
A similar approach to locating cell ~hone~ is 6
described in US Patent No. 5,327,144. This approach
employs tdoa techni~ues by collecting all data
transmitted by cell rho~es on the rever~e control channel
~ w096/02007 21 71333 PCT~S~S/~8~27
and cross correlating that data to identify and locate
those cell phones. This approach demonstrates an
inherent deficit in using the tdoa techni~ue alone with
unmodified cell phones in that the signal which is being
S measured is limited to a 30 KHz transmission channel.
This limited bandwidth limits the accuracy of the tdoa
measurement under ideal conditions to a theoretical 300
feet. Whenever any sort of multipath or co-channel
interference is encountered, this accuracy deteriorates
significantly.
S~MM~Y OF THE lN V~. .lON
Accordingly, it is a object of the present invention
to provide an apparatus and method for determ; n; ng the
location of cellular telephones and similar transmitters
which provides a hi~h degree of accuracy.
It is a further object of the present invention to
perform such location f;n~;ng on ordinary cell phones and
similar transmitters which are not specially modified.
It is still a further object of the present
invention to perform such location f;n~;ng in the
presence of high levels of multipath reflected signals.
It is yet a further object of the present invention
to perform such location f;n~; n~ using antennas and
antenna structures which are normally used for typical
cell phone operation.
In one embodiment, the present invention provides a
method for determ;n;ng the location of a cellular
telephone or similar transmitter, comprising the steps of
30 detPrm; n; ng the general location of the phone or
transmitter within a predetermined range by receiving
transmissions thereof at a plurality of locations and
signal processing the received signals, receiving
tr~ncmission signals from the phone or transmitter with a
wo~ 0~7 2~333 PCT~595108527 ~
portable receiver located within the predetermined range
of the phone or transmitter, and determ;ning the precise
location of the cell phone or transmitter in response to
the transmission signals received by the portable
S receiver. ~,
In another embodiment, the present invention
provides an apparatus for determin;ng the location of a
cell phone or similar transmitter, comprising means for
determ; n; n~ the general location of the phone or
transmitter within a predetermined range thereof
including means for receiving transmissions therefrom at
a plurality of locations and means for signal processing
the received signals, and portable receiver means adapted
for movement to within the predetermined range of the
lS phone or transmitter for receiving tr~n~mi~sion signals
from the phone or transmitter and including means for
determining the precise location of the cell phone or
transmitter in response to the received transmission
signals.
BRIEF DESCRl, ~10~ OF THE DRAWIN~S
The present invention is illustratively described in
reference to the appended drawings in which:
Fig. 1 is a system block diagram of an apparatus
constructed in accordance with a portion of one
embodiment of the present invention.
DETATr~r~!n DEgCR'CPTION OF ~HE DRAWING~g
Fig. 1 shows one embodiment of a cell phone locating
system 10 which would take advantage of existing cell
phone base stations and antennas. System 10 generally
includes a multiplicity of existing cellular ba~e
stations 12-14, to which apparatus of the present
invention is added. Base stations 12-14 make use of
WO 96/02007 PCT/US95/08527
21 713~3
existing transmit and receive antennas 16 which may be
identical in form and function. Added to each base
station is an additional GPS (Global Positioning System)
antenna 18 which receives timing signals from the
S existing civilian GPS for use in the locating function.
Each of the base stations includec further equipment
for performing the locating function. This equipment
generally includes means for sampling or digitizing the
signals received from the cell phone or transmitter 22
and time stamping the resulting data with signals derived
from the received GPS signal.
Com~l~nication lines 19 are shown connecting at least
two remote base stations 12,13 with a central base
station 14. Central base station 14 includes equipment
lS not present in the remote base stations 12,13 in the form
of tdoa CPU 20 for proce~cing signals received by all
base stations 12-14. Tdoa CPU 20 may be located at any
one of the base stations or m~y be located separately
from such base stations. Such separate location would
include the interconnection of all comm. lines 19
directly between the base stations and tdoa CPU 20.
Tdoa CPU 20 receives the digitized, time stamped
data from each of the receiving base stations and cross
correlates similar data. The time ~tamps on the
correlated data thereupon provide time difference of
arrival data between the correlated data and the
correspondin~ base stations, which have known locations.
The general location of cell phone or transmitter 22 may
then be determined in accordance with well known
techniques.
The tdoa system described above provides a meAnc for
det~nm; ni ng a general location of a cell phone or similar
transmitter 22 within a predetermined range represented
by circle 24. This general location function may be
w096/02007 PCT~S95/08S27
333
provided by any other suitable technique such as
direction finding. One acceptable tdoa method is
described in US Patent Application Number 08/272,725
filed July 8, 1994 for APPARATUS AND METHOD FOR LOCATING
5 CELLULAR TELEPHONES by the same inventor hereof, the
contents of which are hereby incorporated by reference
herein.
Once the general location of circle 24 is known, a
portable receiver 26 may be transported to that area and
used for precisely locating the phone or transmitter 22.
Where a local police force carries the portable receiver
in a number of patroling police cars, such a portable
reciever may already be located within the general
location of circle 24. The size of circle 24 technically
lS depends upon the accuracy of the location e~uipment
described above. However, it is much more practical if
the size of circle 24 is ~ curate with the receiving
capability of the portable receiver 24. Due to the
limited elevation of the portable receiver 26, terrain
will have an impact upon receiver performance.
The portable receiver 26 may also be of any suitable
type and make. One such type is described in US Patent
Application No. 08/272,724, Filed July 8, 1994 entitled
APs?ARATUS AND sYETHOD FOR FINDING A SIGNAL EMISSION SOURCE
by David I.. Herrick and William F. Matthews III, the
contents of which are hereby incorporated by reference
herein. The portable receiver in ~Sestion u~es relative
-lovc...e5lt between the receiver and the phone or
transmitter 22 to determine the general direction
thereof. The described techni~ue is useful in high
multipath enviLol55--c5lts such as buildings. Other fors~s of
direction finding may also be suitable.
In order for the portable receiver 26 to accurately
locate the cell phone or transmitter 22, it will be
WO 96/02007 l 333 PCTlUS9~i/08S~7
necessary to determine the transmitting frequency of the
phone or transmitter 22 and receive that signal. In the
case of a cellular phone 22, the transmission frequency
will depend upon a channel allocation from the local cell
S phone system. To determine the proper channel allocation
it may be preferable to establi~h a co~un;cation link
between receiver 26 and the local cellular system to
receive the channel assignment.
The locating system thus provided overcomes any
inaccuracies present in the long range system without
requiring significant additional expen~e. Such
inaccuracies may even be impossible to avoid in high
multipath enviro~llel~ts. The addition expense of a high
accuracy system located in cellular base stations is
significant given the number of operating base stations.
The embodiments described above are intended to be
taken in an illustrative and not a limiting sense.
Various modifications and changes may be made to the
above embodiments by per~ons skilled in the art without
departing from the scope of the present invention as
defined in the appended claims.
