U.S. patent application number 11/619426 was filed with the patent office on 2007-07-12 for method and apparatus for locating a wireless device.
This patent application is currently assigned to Lockheed Martin Corporation. Invention is credited to J. Claude Caci.
Application Number | 20070161383 11/619426 |
Document ID | / |
Family ID | 32179911 |
Filed Date | 2007-07-12 |
United States Patent
Application |
20070161383 |
Kind Code |
A1 |
Caci; J. Claude |
July 12, 2007 |
METHOD AND APPARATUS FOR LOCATING A WIRELESS DEVICE
Abstract
Disclosed is a method and apparatus for locating a wireless
device especially useful for locating a cellular telephone making a
call from an unknown location. The call may be a request for
emergency assistance, or for location-based commercial services,
for example. Various embodiments may optionally include a mobile
location component, a cellular telephone enabled to
chirp-on-demand, and/or an interferometer link. A mobile location
component may include a directional antenna. The directional
antenna may be mounted on an antenna boom on top of an emergency
vehicle, for example. The mobile location component may alternately
or additionally comprise a hand-held unit. System elements may
cooperate to generate a situation awareness map or other display.
The mobile location component may be moved in the general direction
of a first location calculation associated with a first circular
error of probability. After being moved in the general direction,
the mobile location component may cooperate with other elements to
determine a second location calculation associated with a second
circular error of probability. Second and subsequent location
calculations are of increasing precision, enabling an emergency
vehicle or attendant to zero in on a cellular telephone.
Inventors: |
Caci; J. Claude;
(Baldwinsville, NY) |
Correspondence
Address: |
MILES & STOCKBRIDGE PC
1751 PINNACLE DRIVE
SUITE 500
MCLEAN
VA
22102-3833
US
|
Assignee: |
Lockheed Martin Corporation
Bethesda
MD
|
Family ID: |
32179911 |
Appl. No.: |
11/619426 |
Filed: |
January 3, 2007 |
Related U.S. Patent Documents
|
|
|
|
|
|
Application
Number |
Filing Date |
Patent Number |
|
|
11419843 |
May 23, 2006 |
|
|
|
11619426 |
Jan 3, 2007 |
|
|
|
10695894 |
Oct 30, 2003 |
7050786 |
|
|
11419843 |
May 23, 2006 |
|
|
|
60422202 |
Oct 30, 2002 |
|
|
|
Current U.S.
Class: |
455/457 ;
455/456.2 |
Current CPC
Class: |
G01S 5/02 20130101; G01S
5/0221 20130101; H04W 64/00 20130101; G01C 21/20 20130101 |
Class at
Publication: |
455/457 ;
455/456.2 |
International
Class: |
H04Q 7/20 20060101
H04Q007/20 |
Claims
1-18. (canceled)
19. A method of determining a location of a mobile telephone and
displaying the location on a map, the method comprising: receiving,
at a controller, a first location signal from a single cellphone
tower in wireless communication with the mobile telephone;
receiving, at the controller, a second location signal from a
non-tower source in wireless communication with the mobile
telephone; determining the location of the mobile telephone based
solely on the first and second location signals; generating a
situation awareness map including the determined location and
geographic map data for an area surrounding the determined
location; digitally displaying on a digital display device the
situation awareness map showing the determined location of the
mobile phone on a digital map of a geographic area surrounding the
determined location.
20. A system for determining a location of a mobile telephone and
displaying the location on a map, the method comprising: means for
receiving a first location signal from a single cellphone tower in
wireless communication with the mobile telephone; means for
receiving a second location signal from a non-tower source in
wireless communication with the mobile telephone; means for
determining the location of the mobile telephone based on the first
and second location signals; means for generating a situation
awareness map including the determined location and geographic map
data for an area surrounding the determined location; means for
displaying the situation awareness map showing the determined
location of the mobile phone on a map of the surrounding area.
21. The method of claim 1 wherein the digital display device is a
hand-held wireless communication device.
Description
[0001] This application claims benefit to U.S. provisional patent
application No. 60/422,202 filed Oct. 30, 2002, which is hereby
incorporated by reference.
[0002] The present invention relates generally to wireless
communications, and more particularly to the provisioning of
emergency services and location-based services using a wireless
network.
[0003] Cellular phone user's need prompt, effective emergency
services that require the certain knowledge of a user's location
much the same as wire-line users. In 1996 the Federal
Communications Commission (FCC) concluded a Consensus Agreement
between wireless carriers and public safety representatives to
implement a cellular location service in which carriers are
required to provide the location of cell phones requesting
emergency assistance by dialing 9-1-1. The E-911 Mandate is
structured into two phases. The first phase requires wireless
carriers to provide Public Safety Answering Points (PSAP),
essentially 9-1-1 dispatchers, with information comprising a
telephone number of the call originator and the cellular site
location managing the 9-1-1 call. The second phase, mandatory by
Dec. 31, 2005, implements more location precision through an
Automatic Location Identification (ALI) service.
[0004] One previous attempt at E-911 compliance uses a Geographic
Positioning Service (GPS) receiver in the mobile unit or handset,
classifying it as a handset-centric solution. In this approach, a
mobile unit of a wireless network has a GPS receiver embedded
therein, so that a position coordinate can be fixed using the GPS
satellite network. Once the position coordinate is fixed, it can be
transmitted over the wireless network to the servicing PSAP.
[0005] Another previous attempt at E-911 compliance makes use of a
location Radio Frequency RF) receiver on the cellular
communications tower of a wireless network, classifying it as a
network-centric solution.
[0006] FIG. 1 shows the present inventor's analysis of a Time
Difference Of Arrival (TDOA) method of locating a wireless caller.
System 100 comprises at least three towers 102, 104, 106, each
equipped with at least one overlay location receiver 108, 110, 112,
respectively, for RF detection of emission signals originating from
a caller's mobile unit 120. Each overlay location receiver unit
108, 110, 112, shares the legacy infrastructure of system 100
without interfering with existing base station equipment.
[0007] To locate mobile unit 120, each overlay location receiver
108, 110, 112, measures the time for the RF signals propagating
from mobile unit 120 in a wireless call to reach tower 102, 104,
106. The differences in these temporal measurements are applied to
a triangulation algorithm to identify the location of mobile unit
120 within a general area. Once this area is identified, a mobile
telephone switching office 122 forwards this location information,
along with the mobile number and voice call, to PSAP 124 for
emergency services.
[0008] In FIG. 1, circle 121 represents a circular error of
probability (CEP) that the signal source (mobile unit 120) is
contained within the area. A probability may be associated with the
circle. Points A, B, and C bound circle 121, so this circle is a
three-point CEP. The size of the CEP depends on the signal source
location relative to the three towers 102, 104, and 106.
[0009] Separately, certain commercial location tracker systems are
designed for tracking wildlife. These systems use a radio frequency
chirp beacon transmitter and directional receiver. The user follows
a vector decoded by the directional receiver to the emitting chirp
beacon transmitter.
[0010] In a preferred embodiment of the present invention, a
cooperative element location system includes a cellular telephone
that is located at an unknown location and may be moving. The
system also includes a mobile location component used to zero in on
the cellular telephone's location. The mobile location component
may be mounted in an emergency vehicle equipped with a directional
antenna bar, for example. As the vehicle approaches a first CEP
area, the system elements cooperate to generate second and
subsequent CEP's of increasing accuracy and decreasing size. The
elements may include a mobile location component, one or more
cellular telephone tower location receivers, a cellular telephone,
and an optional chirp-on-demand signal. In this manner, the mobile
location component may provide an emergency vehicle with
increasingly accurate estimates of a cellular telephone location,
as the vehicle moves toward the general area of that location. An
attendant may then take a hand-held device and carry it inside a
building, for example, where the elements continue their
cooperation to lead the attendant precisely to the cell phone
location within the building. An optional interferometer link
between cells may further enhance precision.
DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 is a diagram of a time of arrival solution to
locating an emitter.
[0012] FIG. 2 is a diagram of a cooperative element location system
in the context of a wireless communication network.
[0013] FIG. 3 is an exaggerated graph of a radiation pattern.
[0014] FIG. 4 is a timing diagram of a chirp-on-demand signal.
[0015] FIG. 5 is a diagram of an exemplary geographic information
server.
[0016] FIG. 6 shows a graphical user interface for use with the
present invention.
[0017] FIG. 7 is a diagram of a mobile location component including
an antenna boom.
[0018] FIG. 8 is a graph illustrating radiation patterns for a
directional antenna.
[0019] FIG. 9 is a diagram showing the relationship of time of
arrival to angle of arrival of a signal wave front.
[0020] FIG. 10 showing an antenna and associated electronics.
[0021] FIG. 11 illustrates message flow in a cooperative element
location system.
[0022] FIG. 12 is a diagram of an interferometer link between
representative cells.
[0023] FIG. 13 is a representative diagram showing a series of
Circular Error of Probability estimations of decreasing size.
[0024] FIG. 14 is a flowchart describing the process of using
towers with an interferometer link to locate a cellular
telephone.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0025] Referring now to FIG. 2, a wireless communication network
200 is shown comprising at least one communications tower 202, at
least one mobile unit 120, and a mobile telephone switch/public
telephone network 206.
[0026] Communication tower 202 receives a first signal 208 from
mobile unit 120 when a user of mobile unit 120 initiates a cellular
call. In a preferred embodiment, signal 208 may be a radio
frequency (RF) signal. In accordance with normal cellular
operation, a base station receiver 210, operatively coupled to the
at least one communication tower 202, process signal 208. Using
digital signal processing techniques, base station radio
transceiver 210 analyzes signal 208 to determine whether mobile
unit 120 is authenticated for service.
[0027] Under current cellular protocols, a mobile unit's unique
Electronic Serial Number (ESN) provides the basis for cellular
authentication. Mobile unit 120 transmnits its ESN to tower 202
when a call is initiated. Base station transceiver 210 analyzes
signal 208 to determine the ESN of mobile unit 120. The ESN is
referenced in an authentication database, which indexes the ESN to
a user's account information. Once the ESN is authenticated, base
station radio 210 issues a control channel and channel assignment.
The channel may be assigned in frequency, time, or code
representative of the network technology.
[0028] Upon authentication, base station radio transceiver 210
analyzes signal 208 to retrieve the dialed digit sequence. The call
is connected to mobile telephone switch/public telephone network
206. The dialed digit sequence determines call routing and final
destination.
[0029] Now, in accordance with one embodiment of the invention, a
cooperative element location system 250 comprises a tower location
receiver 252, a Geographic Information Server (GIS) 254, and a
mobile location component 256. Tower location receiver 252 is
operatively connected with communication tower 202, and configured
to determine a first location calculation of mobile unit 120. Tower
location receiver 252 receives signal 208 from mobile unit 120.
Tower location receiver 252 decodes signal 208 to search for a
special predetermined sequence of digits, which indicate a need or
request for an emergency or non-emergency location-based service.
For example, these digits may include 9-1 -1, indicating a request
for emergency services, 4-1 -1, indicating a request for
information services, 5-1 -1, indicating a request for yellow pages
(business directory) services, a sequence of digits for roadside
assistance, or some other predetermined sequence. Preferably, the
sequence may consist of three digits.
[0030] If tower location receiver 252 does not identify any of the
predetermined sequences indicating that there is no request for
emergency or non-emergency location-based services, no further
action is taken. However, if the dialed digits represent a request
for an emergency service or a non-emergency location-based service,
tower location receiver 252 performs a location measurement on
signal 208.
[0031] The location measurement includes a range measurement and
bearing measurement, which in combination can determine an
approximate location of mobile unit 120 relative to the location of
tower 202. GIS 254 converts the measurements to a first location
calculation of mobile unit 120.
[0032] Depending on the nature of environmental circumstances and
the distance of mobile unit 120 from tower 202 at the moment tower
location receiver 252 takes the location measurement, the first
location calculation may not meet E-911 performance and accuracy
requirements. However, the first location calculations will meet
the needs of many non-emergency location-based services.
[0033] The first location calculation is a map space location
comprising a latitude and longitude position of mobile unit
120.
[0034] In one embodiment, GIS 254 may be further configured to
calculate a Circular Error Probability (CEP) measurement. A CEP
measurement provides statistical probabilities as to the accuracy
of the location calculation.
[0035] In an alternative embodiment, the tower location receiver
252 itself may be equipped to calculate the first location
calculation and/or the CEP measurement, which are subsequently
forwarded to GIS 254.
[0036] If mobile unit 120 has requested a non-emergency
location-based service, GIS 254 forwards the location calculation
to mobile telephone switch/public telephone network 206, along with
the digit sequence so network 206 may appropriately route the
location calculation. The location calculation may be routed to a
commercial service providing location-based information to mobile
unit 120. In other embodiments, GIS 254 can provide the commercial
service
[0037] GIS 254 routes the first location calculation and any CEP
measurement to a servicing PSAP GIS network 258. This link can be a
dedicated connection, or alternatively, packet routed through
mobile telephone switch/public telephone switch 206 to PSAP GIS
network 258.
[0038] PSAP GIS network 258 receives the location calculation and
any CEP measurement so that a PSAP operator can analyze location
information, including the location calculation and any CEP
measurement, to efficiently manage the progress to the site of the
emergency.
[0039] PSAP GIS network 258 dispatches a vehicle or attendant over
public safety land mobile network 260 to a general area identified
by the first location calculation in cooperation with any available
CEP accuracy measurement. Public safety land mobile network 260 is
representative of the Private Land Mobile Radio Network used by
police, fire, and medical services in accordance with 47 CFR .sctn.
90. A PSAP operator vocally confers the general location of the
emergency site, which is inherently the location of mobile unit
120, using a first voice channel of an RF signal 262 on public
safety land mobile network 260.
[0040] Mobile location component 256 may for example comprise a
vehicle mount 257 and/or a hand-held device 259. Mobile location
component 256 may be in physical association with an emergency
vehicle or attendant proceeding to the site of an emergency, and is
positioned some distance from mobile unit 120 in accordance with
the first location calculation. Upon receipt of the first location
calculation, mobile location component 256 is moved in the general
direction of mobile unit 120 as indicated by arrow 261.
[0041] Mobile location component 256 is configured to determine a
second location calculation of mobile unit 120. Mobile location
component 256 is configured to receive a second, data channel of RF
signal 262 having parameter exchange protocols for receiving data
necessary for fixing and tracking signal 212 from mobile unit 120.
In a preferred embodiment signal 212 may be an RF signal similar to
signal 208. The data includes the unique ESN of mobile unit 120 and
its control channel and channel assignment issued by base station
transceiver 210. Using this data, mobile location component 256 is
initialized to lock to signal 212.
[0042] It should be appreciated that while mobile location
component 256 is configured to receive both the voice and data
channel of signal 262 in the present embodiment, other embodiments
include a mobile location component configured to receive the data
channel of signal 262, while a separate radio receiver is
configured to receive the voice channel of signal 262.
[0043] In still yet another embodiment, a radio receiver may be
capable of receiving the voice channel and data channel of signal
262.
[0044] Most emergency vehicles or attendants communicate with
dispatchers using two-way data/voice radios communicating over RF
modulation signal 262 to public safety land mobile network 260.
These radios are sophisticated in that they can multiplex several
low rate channels into one high-speed air link. For example, the
Federal Communications Commission (FCC) has opened up the UHF band
for land mobile radios capable of 25.6 Kbp/s. These are commercial
units with a voice channel and multiple RS-232 data channels,
enabling the addition of data protocols to the voice signal
simultaneously without interferences. Accordingly, mobile location
component 256 cooperates with an existing radio configured to
receive the data from public safety land mobile network 260. The
data, which require a low data rate channel, may be transmitted
over one of the multiple RS-232 data channels alternatively, mobile
location component 256 comprises a receiver for receiving the data
directly from signal 262 over public safety land mobile network
260.
[0045] As the emergency vehicle or attendant approaches mobile unit
120 so does the associated mobile location component 256 as shown
by arrow 261. Mobile location component 256 will acquire signal 212
at some distance from mobile unit 120. If tower location receiver
252 performs the first location measurement on a good signal, there
will be sufficient information to engage mobile location component
256 with signal 212 at several miles from mobile unit 120. Once
engaged, mobile location component 256 performs a new location
measurement for determining a second location calculation.
[0046] As the distance decreases between mobile location component
256 and mobile unit 120, mobile location component 256 refines the
measurement, which becomes increasingly more accurate relative to
the actual location of mobile unit 120 as shown by arrow 263. This
process continues until the highest accuracy is achieved as mobile
location component 256 converges upon mobile unit 120 as shown by
arrow 265 mobile location component 256 continuously transmits a
refined measurement over public safety land mobile network 260 to
GIS 254. GIS 254 continuously calculates and refines the second
location calculation of mobile unit 120. Any CEP measurement may
also be refined to reflect the updated location measurement. PSAP
GIS network 258 receives the second location calculation to assist
the PSAP operator in efficiently coordinating emergency
services.
[0047] In the present embodiment, mobile location component 256
includes a beacon transmit unit for transmitting a tracking beacon
signal 264 for determining the present location of mobile location
component 256 and consequently the location of the associated
emergency vehicle or attendant. To initiate the tracking beacon, a
PSAP operator requests a tracking channel be assigned for the
beacon. The request alerts tower location receiver 252 to look for
the tracking beacon signal 264. The request crosses the network
demarcation and is received by GIS 254 and forwarded on to tower
location receiver 252. The tracking channel will be on or near the
frequency channel used by mobile unit 120. Tower location receiver
252 differentiates the modulation of the tracking signal to process
with little interference. Tracking beacon signal 264 is not on
continuously but on for only a low duty cycle to limit its
interference with the voice channel of signal 208. Tracking beacon
signal 264 is specifically designed for location accuracy. In fact,
if the tracking beacon source is moving, this should negate some
propagation path ambiguities providing even more location accuracy.
Tracking beacon signal 264 carries this location data information
at regular intervals to communication tower 202, where tower
location receiver 252 receives tracking beacon signal 264, decodes
tracking beacon signal 264, and forwards the location data to PSAP
GIS network 258. Because there is a chance that more than one
tracking beacon signal 264 is being transmitted if CELS 250 is
servicing other emergencies, each tracking beacon signal 264 is
assigned a unique beacon identification code so tower location
information receiver 252 looks for tracking beacon signal 264 and
appropriately associates the emergency services of mobile unit 120,
and not another mobile unit requesting emergency services. In this
manner, an operator at PSAP GIS network 258 who is handling the
emergency service request from mobile unit 120 will receive the
correct location data of the vehicle or attendant reporting to the
emergency site. The PSAP operator can provide updated progress
reports to the user of mobile unit 120 as to the current location
of the vehicle or attendant reporting to the scene of the emergency
through voice communication. The beacon allows the cell tower
receiver to refine the coefficients used in the location algorithm
and to improve the accuracy.
[0048] In one embodiment, the beacon transmit code is uniquely
built into the beacon transmit unit of mobile location component
256 and associated with the emergency vehicle of the attendant by
way of manual entry into PSAP and forwarded to GIS 254 and
eventually tower location receiver 252 at the appropriate time.
[0049] In another embodiment, the beacon transmit code is uniquely
generated by PSAP GIS network 258 and uploaded to the beacon
transmit unit as needed.
[0050] While the present embodiment discloses the beacon transmit
unit as an integral member of mobile location component 256, the
tracking unit may be independent in alternative embodiments.
[0051] The first location calculation and the second location
calculation performed by GIS 254 is now discussed, including range
and bearing measurements taken for achieving these location
calculations is now described. Referring to FIG. 3, a mobile unit
radiation pattern 308 representative of signal 208 received by
tower location receiver 252 or signal 212 received by mobile
component 256 is shown. Mobile unit radiation pattern 308 is
characterized by radius ("r") 310, length ("l") 314, and height
("h") 312.
[0052] The receive signal level (RSL), from which the bearing and
range measurements can be obtained, should follow the "one over
distance squared" law for a propagating spheroid surface, where
power density is a function of the spheroid surface area. Because
the originating mobile unit signal antenna power generally is
limited to 600 milliwatts, the radiation sphere volume will always
contain the 600 milliwatts. However, as the sphere grows, the
surface energy density in watts per square meter follows the rule
for a spherical sector: A.sub.t=3.pi.r.sup.2 where A.sub.t is the
area of the spherical sector surface, and V = 2 .times. .pi.
.times. .times. r 2 .times. h 3 ##EQU1## where V is the volume of
the spherical sector which estimates free space loss Lf of the
signal.
[0053] In assuming r is the location distance vector, h is assumed
the error. For short distances r, error h will be noteworthy, and
for long distances r, error h will be negligible. However, a sphere
is not always a practical radiation pattern due to the reflection
and absorption properties of Earth's surface. Earth's surface
becomes a reflector under certain conditions and an absorber of
signals under other conditions. The radiation pattern may be more
hemispherical in practice.
[0054] To calculate range and bearing of an RF signal, certain
assumptions need to be made about its power density. Those
assumptions include free space signal loss plus a number of
additional factors. Those factors can be lumped into an average
aggregate value that varies by climate and environmental conditions
or time of year. For example, if rainy weather conditions exist,
signal loss would be expected to be higher. Heavy downpours absorb
more signal than light rainfall, so rainfall rate is an important
factor. Fog and temperature inversions also play a modest part.
Therefore L.sub.p is total propagation loss consisting of free
space loss L.sub.f and climate loss L.sub.c. Most Communication
towers each have several antennas with two or more to a cell face.
Each antenna is connected to at least one channel and space
diversity could apply. By way of example let antenna gains be
respectively G.sub.T1 and G.sub.T2 where T1 represents tower
antenna one and T2 represents tower antenna two and so forth. The
mobile unit's antenna gain is G.sub.p. Total gain per channel
(G.sub.1, G.sub.2, respectively) is then: G.sub.1=G.sub.T1+G.sub.p
and G.sub.2=G.sub.T2+G.sub.p Then RSL for each channel becomes:
RSL.sub.L1=(G.sub.T1+G.sub.p)-(L.sub.f+L.sub.p)+P.sub.t and
RSL.sub.L2=(G.sub.T2+G.sub.p)-(L.sub.f+L.sub.p)+P.sub.t where
P.sub.T is the mobile unit's transmit power. RSL is measured by
tower location receiver 252.
[0055] G.sub.T1 and G.sub.T2 are known variables. While G.sub.p is
not known, it may be accurately estimated by an assumption. G.sub.p
may be a small negative value when using a hand held mobile unit
and a small positive value when using an automotive installation.
L.sub.p can be derived from a signal strength profile such as
published data. Each communication tower has a signal strength
profile from measured values at the time of tower construction, and
are necessary to determine handoff from tower to tower. This data
can also be used to determine propagation losses. Alternatively,
the signal strength profile may be measured by an interferometer or
some other accurate means.
[0056] Although not required by the present invention,
tower-to-tower communications can be used to more accurately
compute propagation losses as part of a rough interferometer setup,
especially under current atmospheric weather conditions. For
example, if a calibrated power level signal is put on a calibrated
transmission line to a calibrated antenna, then path loss could be
measured. Knowing the propagation velocity, location accuracy can
be improved.
[0057] Free space loss may be computed from tower face to tower
face and any extra loss is mostly due to climate and fading
factors. Therefore, all the variables of the RSL.sub.L1 equation
are known except for L.sub.F for which it is solved. Range and
bearing may be calculated therefrom. The range and bearing
measurement provide an estimate of the location of the mobile
unit.
[0058] At this point no provision has been made for noise
interference. However, a noise figure can be included in L.sub.p.
Therefore, an accurate expression can be developed to compute range
and bearing from a single communication tower or a single mobile
location information component. Although not required by the
present invention, multiple communication towers can compute a
range and bearing measurement on a single mobile unit provided that
multiple towers can receive a signal from the mobile unit. This may
improve location accuracy. In this case, the original serving tower
carrying the voice call has a means to indicate that it is the
prime serving location receiver, so as to insure an emergency
request be forwarded to the appropriate PSAP network servicing the
caller's area.
[0059] While not required by the above-disclosed embodiment, the
present invention may additionally or alternately incorporate a
mobile unit configured to transmit a cooperating chirp-on-demand
signal to improve location performance. This chirp-on-demand signal
significantly improves the accuracy of the first location
calculation, as well as the fine location calculation. A
chirp-on-demand signal would offer additional accuracy not
available with normal RF emissions from mobile unit 120 and a
single communication tower solution. While emergency services will
benefit from a chirp-on-demand signal, it is especially significant
to commercial services that most likely do not have the benefit of
implementing mobile location component 256. The chirp signal,
consisting of a known frequency and a calibrated time duration
between chirp bursts, provides a reasonable accurate location
determination resolving enough location ambiguity for commercial
revenue generation using a single communication tower 202. These
"radar-like" chirp signals provide resilience to RF interference
and to low quality RF path propagation. The chirp-on-demand signal
does not interfere with ongoing functions even while within signal
208 or signal 212 of mobile unit 120. The chirp-on-demand signal
weaves into a voice call while one is ongoing.
[0060] Chirp-on-demand works by varying the amplitude and frequency
of signal 208 and signal 212 from mobile unit 120 in a known,
accurate pattern. Tower location receiver 252, or optionally,
mobile location component 256, can extract known propagation
variables from signal 208 or signal 212 using digital signal
processing techniques. By analyzing these additional propagation
variables, the RSL can be calculated to a more precise
measurement.
[0061] In this alternative method, mobile unit 120 is capable of
providing a calibrated chirp-on-demand signal. With respect to
government performance and accuracy requirements, the chirp method
may be able to meet the accuracy specification without the use of a
mobile location component 256 in many situations such as, for
example, flat terrain areas.
[0062] FIG. 4 shows an example of a segmented, calibrated chirp
signal 400 weaved into signal 208. In order to alter the frequency
pattern of signal 400, a calibrated time and calibrated time
interval T.sub.1, T.sub.2, . . . T.sub.x has been added.
[0063] In one embodiment of chirp-on-demand, mobile unit 120 is
configured to uplink or receive absolute time as part of the RF
protocol then some form of system synchronization is possible. Time
intervals T.sub.1, T.sub.2, . . . T.sub.x may also be added by
mobile unit 120 itself. Knowing absolute time and time intervals
T.sub.1, T.sub.2, . . . T.sub.x, the propagation path then can be
thought of as an unknown delay line. At ingress of this delay line,
the calibrated time signal is injected, eventually yielding
calculated information about path range. Propagation velocity
variations across the cell space will be minimal because
propagation velocity generally will be uniform. Propagation
velocity can be measured from tower to tower as part of a rough
interferometer setup.
[0064] With knowledge of the propagation velocity and time
intervals T.sub.1, T.sub.2, . . . T.sub.x of chirp signal 400,
range accuracy is improved.
[0065] Frequency likewise sometimes detects changes in path length
and direction. Changes in RSL due to chirp frequency variations
would help average out the measured RSL.
[0066] Likewise, calibrated chirp amplitude variations A.sub.1 . .
. A.sub.x will help average out RSL amplitude deviations. If, for
example, a chirp code comprises a 3 dB change in amplitude, but the
tower receiver only receives a 2.5 dB change in amplitude, then
most likely diffraction is deducting from the measured RSL and
would be 0.5 dB higher than the computed RSL. This helps to improve
RSL accuracy.
[0067] This demonstrates that chirp-on-demand can improve range
accuracy as measure by the cell tower location receiver and add
improvement to commercial location services.
[0068] Referring now to FIG. 5, one embodiment of GIS 254 is shown.
GIS 254 integrates between commercial and emergency services by
providing a common denominator for both.
[0069] A demarcation point may exist between PSAP GIS network 258,
which is a publicly serviced network, and GIS 254, which would most
likely be privately serviced by a wireless carrier. GIS 254
comprises a tower location receiver data link 501, a PSAP network
data link 503, and a mobile telephone switch/public telephone
switch data link 505. A common message format enables
interoperability and the transfer of data from one network to the
other. The common message format standard could be agreed upon by
PSAP interest groups and wireless carrier interest groups.
[0070] GIS 254 comprises interface software 502 that establishes a
common message format. Interface software provides protocols for
the transfer of data including a range and bearing measurement, a
latitude and longitude position, a CEP measurement, unique codes,
RF signal intercept data, or other data as well, across tower
location receiver data link 501, PSAP data link 503, and mobile
telephone switch/public telephone switch data link 505.
[0071] Where GIS 254 is at a demarcation point between a wireless
carrier's network and PSAP GIS network 258, interface software 502
implements the appropriate protocols for communication
therebetween. Interface software 502 facilitates communication of
GIS 254 with tower location information receiver 252, PSAP GIS
network 258, and mobile location component 256.
[0072] GIS 254 comprises a geographic location engine (GLE) 504
configured to generate a map space location from the first
measurement from tower location receiver 252 and, in the case of an
emergency service request, the second measurements from mobile
location component 256.
[0073] GIS 254 includes a communication tower location database 506
comprising a unique identification number for each of a plurality
of communication towers and corresponding geographic locations.
These geographic locations are in a map space, comprising latitude
and longitude positions. In this manner, a single GIS may service a
plurality of communication towers.
[0074] Interface software 502 receives a location measurement from
tower location receiver 252 along with the identification number of
servicing tower 202. GLE 504 generates the location calculation of
mobile unit 120 by searching database 506 for the identification
number and upon finding a matching identification number,
calculating the location calculation from the corresponding
geographic location of servicing tower 202 and the location
measurement.
[0075] In some embodiments, GLE 504 will geocode the latitude and
longitude position to a street address using methods familiar in
the art. This is most likely useful for commercial services, or for
third party commercial vendors who do not provide their own
geocoding software offsite. GLE 504 may geocode to street addresses
for emergency services, although this is more likely to be handled
by PSAP GIS network 258 to comply with specific geocoding
performance standards.
[0076] Non-emergency services software 508 provides non-emergency
location-based services that may be requested by mobile unit 120.
These services may include navigation directions, commercial
location information on restaurants or retail outlets in the
geographic area of mobile unit 120, etc. GIS 254 may log such
transactions in a commercial location services accounting database
510, such as by the ESN of requesting mobile unit 120 for
accounting purposes. Alternatively, if a subscriber business
methodology is employed, GIS 254 first references the requesting
ESN in commercial accounting database 510, and upon a match,
non-emergency services software 508 provides the requested
service.
[0077] If cooperative element location system 250 employs the
chirp-on-demand capability, GIS 254 is operatively configured to a
chirp code database 512. Chirp code databases 512 accommodates a
pool of chirp codes. When a request for emergency or non-emergency
location-based service is received, tower location receiver 252
decodes the dialed digit sequence and engages location-based
services by sending the ESN to servicing GIS 254 via data link 501.
GIS 254 receives the ESN at connection 514 and a database is
searched for a matching ESN to identify whether requesting mobile
unit 120 is chirp capable.
[0078] If no match is found, a message indicating that the chirp
feature is not possible is sent back to tower location receiver
252. Tower location receiver 252 takes bearing and range
measurements without searching for a chirp signal. G1S 254
calculates the first location calculation as previously
described.
[0079] However, if a match is found indicating mobile unit 120 has
the chirp-on-demand capability, GIS 254 retrieves a chirp code from
the chirp code pool in database 512. GIS 254 sends this chirp code
to base station radio transmitter 210 to transmit the code to
mobile unit 120.
[0080] Mobile unit 120 receives the chirp code and transmits the
chirp code in signal 208 and signal 212 so that tower location
receiver 252 can make the first location measurement and, in the
case of an emergency service request, mobile location component 256
can make the second location measurement.
[0081] In the case of the emergency service request, the chirp
signal continues intermittently until mobile location component 256
converges upon mobile unit 120, indicating that the emergency
attendant has reached mobile unit 120, or is terminated by PSAP GIS
network 258. In the case of a non-emergency service request, the
chirp signal continues intermittently until tower location receiver
252 completes the first location measurement. In either case, GIS
254 notifies mobile unit 120 via communication tower 202 to kill
its chirp. GIS 254 returns the chirp code to the available chirp
code pool in database 512.
[0082] In the case of an emergency service request, PSAP GIS
network 258 is configured to receive location information from GIS
254 via PSAP network data link 503 to generate a situation
awareness map.
[0083] FIG. 6 shows one embodiment of a situation awareness map
graphical user interface (GUI) 600 for use by a PSAP operator of
PSAP GIS network 258. GUI 600 updates the PSAP operator as the
emergency situation develops. The geographic map data of GUI 600
may be provided by PSAP GIS network 258.
[0084] GUI 600 includes map space location data, including a
location icon 602 of mobile unit 120 layered with geographic
data.
[0085] Mobile unit location icon 602 is first displayed in
accordance with the first location calculation, and adjusted
according to the continual updates from the second location
calculation received by GIS 254. GLTI 600 displays a CEP
measurement 604 to the operator, each outlying circle representing
an area with an associated location probability of mobile unit 120.
For example, GUI 600 shows a CEP measurement comprising two CEP
estimations 604a-b. Innermost CEP estimation 604a may represent a
60% probability that mobile unit 120 is within the encirclement.
Outermost CEP estimation 604b may represent a 90% probability that
mobile unit 120 is within the encirclement.
[0086] GUI 600 shows communication tower icon 606 in accordance
with the map space location of servicing communication tower 202.
Communication tower icon 606 is complemented with the tower
identification number, so that the PSAP operator has this
information readily available if needed.
[0087] GUI 600 displays a mobile component location icon 608 in
accordance with the map space location of mobile location component
256 assists the PSAP operator in initially vectoring the emergency
attendants to a signal intercept area represented by signal
intercept circle (SIC) 609. The PSAP operator vectors the emergency
attendant to SIC 609, at which point, mobile location component 256
should pick up signal 208 of mobile unit 120 for performing the
second location calculation.
[0088] GUI 600 optionally shows dispatch unit identification 610, a
unique identifier of the attending dispatcher unit.
[0089] GUI 600 optionally shows a channel and code number 614 over
which the PSAP operator is communication on the public safety land
mobile network 260 to the emergency attendant.
[0090] Referring now to FIG. 7, one embodiment of mobile location
component 256 is shown. Mobile location component 256 may be a
vehicular unit and/or a hand-held unit. The vehicular unit fits
into an emergency vehicle without requiring significant
modifications to the vehicle. The vehicular unit will generally be
more sensitive to RF emissions from mobile unit 120 than a handheld
unit because a vehicular unit can be operatively coupled with a
lager antenna size. A handheld unit may be appropriate to function
inside buildings or between buildings where a vehicular unit proves
impractical. If target mobile unit 120 is in an area that is hard
to see or navigate, or in a high-rise building, the emergency
attendant can easily switch from a vehicular unit to a handheld
unit when necessary.
[0091] In one embodiment, mobile location component 256 is a
hand-held unit that plugs into a vehicle-mounted antenna. For
example, a vehicle may have a cradle for placing a hand-held device
in communication with a directional antenna bar on the roof. When
desired, the hand-held device may be removed from the cradle and
employ its own built-in antenna for use outside the vehicle.
[0092] Mobile location component 256 preferably comprises a mobile
location receiver 702, a beacon transmitter 704, an antenna 706, a
plurality of channels 708, and a display 710. Mobile location
receiver 702 may also include or be operatively coupled to a land
mobile radio 712 which can transmit voice communication using
antenna 706 over public safety land mobile network 260.
[0093] Mobile location receiver 702 is operatively configured to
receive signal 208 with antenna 706 through channels 708 for making
the second location measurement. This may be done using a boom
servo technique.
[0094] As shown in FIG. 1, antenna 706 may be directional, and may
be placed on an emergency vehicle. For example, antenna 706 may
comprise a left directional antenna 714 and a right directional
antenna 716. A navigation solution requires two components, a
bearing and a range. A mobile platform such as mobile location
component 256 can make successively accurate measurements just by
traveling in the direction of increasing signal level. As an
alternative to simple directional antennas, omnidirectional
antennas consisting of two or more each spatially separated
(Reference FIG. 9) at the antenna boom ends coupled with time of
arrival and angle of arrival computation techniques can provide
bearing information. They can also be used together as shown in
this example of FIG. 7. RSL computations provide range information.
Together they provide navigation information which can be overlaid
on a map. As signals from mobile unit 120 reach antennas 714, 716,
mobile location receiver 702 uses a time difference of arrival
algorithm that measures an offset time to determine a bearing
measurement. Alternatively, an angle of arrival algorithm or other
algorithm may be employed. Mobile location receiver 702 calculates
the RSL to arrive at a range measurement, providing the range
required for the second navigation component.
[0095] The velocity of propagation in the atmosphere is slightly
slower than in free space. The velocity of propagation in free
space has been accurately determined to be 2.99792458*10.sup.8
meters per second by national standards groups. A very small
percentage error in the atmospheric velocity calculation will
generate a large position error. Atmospheric propagation speeds are
dependent on atmospheric air pressure, humidity and temperature.
Air pressure and temperature in turn depend on elevation and
climatology. Air density is a function of air temperature, altitude
and humidity. These factors affect the size of the antenna boom. To
make the boom length practical for vehicles and hand held units,
mobile location receiver adds a second channel with offset timing
signal. In this example the second timing signal is offset from the
first by some 300 picoseconds in round numbers or a third of a
nanosecond. Small accurate delays can be achieved a number of ways
using circuitry components. The important point is to delay the
second channel relative to the first by a controlled amount so FIG.
9 can be computed with precision. Delay can be controlled by a
number of methods for example extra circuitry path length in one
timing signal relative to the other. It could be generated by an
extra gate in a FPGA circuit. It can even be crafted by surface
acoustic wave devices. In the case where antenna 706 is
directional, antenna 706 may have a directional antenna pattern as
shown in FIG. 8, for example. An omni-directional antenna (e.g.
directional antennas 714 and 716) may have directional pattern 804.
Null point 806 occurs when the antenna boom 707 is on a heading
directly toward the mobile unit.
[0096] In this example the 500-picosecond time delay gives the
ability to run two antennas on a shortened boom to perform wave
front angle of arrival computations. In our example of above that
would be in this example roughly a meter. The short boom means the
antenna boom can fit on a car roof or be hand carried into
buildings. Note that the offset time is not fixed but must be
variable by some fine level of increments. To detect the wave
front, the measured complex signal needs to be exactly the same
value on both antennas. To find this point, the offset is varied
from a small value to larger values until the antenna signals
match. This point is a constant wave front and the delay is the
time it took for the wave front to travel to the second antenna.
The time delay is related to the boom length. The offset then
becomes a normalized angle with respect to the boom and gives
direction. When the signal direction is straight ahead of the boom
the signal path is the same for both antennas mounted at the boom
ends. When the emitter is off to one side, it takes longer for the
wave front to reach the farther antenna. By measuring how long it
takes we can compute the angle to the boom. When the wave front is
at right angles to the boom, boom length divided by signal
propagation velocity should roughly equal the maximum system offset
time.
[0097] FIG. 9 shows the time of arrival to angle of arrival
relationship. Three angles are shown in FIG. 9: Angle of arrival
902, angle of normal vector to wave front propagation direction
vector 904 and angle of antenna boom 707 to normal vector 906. The
antenna boom 707 has a north antenna center point 912 and a south
antenna center point 916. The responding emergency vehicle is
traveling with a direction vector 918. The wave front at time
t.sub.1 910 and at time t.sub.2 908 is shown. The wave front
propagation direction vectors 914 are also shown. The elapsed time
from the reception of wave front at south antenna center point 916
to the reception at the north antenna center point 912 is used to
calculate angle of arrival 902. Multiplying the time between
reception of wave front 910 and reception of wave front 908 it is
possible to calculate the length of side 922 which represents the
extra measured distance the wavefront must travel to reach the
second antenna to be at the same value point as measured by the
first antenna. By applying trigonometric functions to the known
values length of antenna boom 707, the angle of normal vector 920,
and the length of side 922, it is possible to compute the value of
the angle of arrival 902. The angle of arrival 902 indicates the
direction that the radio frequency waves are emanating from.
[0098] An alternative method is mounting the boom on a calibrated
servo 750 and rotating the boom to null the signal as shown in FIG.
8. Note that a handheld receiver with boom would not require a
servo as the person holding the system could move the boom while
walking and thus keep the boom aimed at the null until arriving at
the mobile unit 120 location. The time of arrival technique means
an omni directional antenna can be used on the boom. Directional
antennas can also be used on the boom. The advantage of using
directional antennas is that once the vehicle is headed directly
onto the location the null V as shown in FIG. 8 will be easier to
use.
[0099] The mobile location receiver 702 will need readout display
to update the users in making progress. In FIG. 7, the CELS mobile
location receiver 702 shows a display 710 with minimal information.
Minimal information is the bearing and range to the mobile unit
120. More information can be added such as street address or if the
mobile unit 120 is mobile the Highway identification and heading.
This information could come from the PSAP operator over the Public
Safety Land Mobile Network 260.
[0100] In the display 710 is shown two readouts, Fixed and Mobile.
In practice only one would be active at a time. The field denotes
whether the target mobile unit 120 is moving or fixed. If it is
fixed and can be tied to an address, the address is given. If it
cannot be tied to an address, the closest tangent point to a
highway is given. It may be given as latitude/longitude or distance
to the nearest intersection. If the target cellular telephone were
in an open space such as an over grown vacant lot or open space but
difficult to see and navigate, the first responders would switch to
the handheld location receiver and continue the final location. The
same is true if the first responder came to a high rise building.
In the case of a high rise, the map would show the high rise within
the CEP so there would be advanced knowledge that a handheld
location receiver is required.
[0101] FIG. 10 is a schematic showing logic for performing angle of
arrival computations for wave fronts impinging antenna 706. Timing
signal is delayed some number of nanoseconds behind the first
signal. Integrated circuits in multi-tap delay line 1008 provide
delay taps for a range of values, such as for example 0.3
nanoseconds to 30 nanoseconds. Such delay taps are commercially
available, such as DS1110 from Dallas Semiconductor. When channel 2
is delayed to channel 1, the boom 707 looks port side. When channel
1 is delayed to channel 2, the boom 707 looks at the starboard
side.
[0102] For determining the second location calculation of mobile
unit 120 from the second location measurement, the current location
position of mobile location component 256 should be determined. For
example, to determine the current location position of mobile
location component 256, beacon transmitter 704 sends the unique
beacon transmit signal to half wave whip transmit antenna 720 for
reception by communication tower 202, and eventually for processing
by tower location receiver 252. Using signal-processing techniques
known in the art, the map space location of mobile location
component 256 can be derived from the beacon signal by GIS 254
using communication tower location database 506. The second
location calculation of mobile unit 120 then can be calculated in
combination with the second location measurements.
[0103] Display 710 of mobile location component 256 updates
progress made by the emergency attendant in locating mobile unit
120. Information displayed includes bearing and range measurements
of mobile unit 120. More information can be added such as street
address or if mobile unit 120 is moving, the highway identification
and heading. The situation awareness map illustrated as GUI 600in
FIG. 6 may also be displayed on display 710, for example. This
additional information may come from PSAP GIS network 258 over
public safety land mobile network 260.
[0104] FIG. 11 illustrates message flow in an exemplary embodiment
of the present invention. Tower location receiver 252 transmits to
the GIS 254 messages of the following types: tower e911 cellular
telephone coarse position data; request for chirp data; RF signal
parameter message including unique cellular telephone electronic
identification number/electronic serial number (EID/ESN), control
channel, and channel assignment for PSAP GIS network 258; and tower
e911 refined position data using chirp results. GIS 254 transmits
to PSAP G6S network 258 messages of the following types: e911
cellular telephone position location data; tracking beacon location
data; and e911 RF signal parameters including unique cellular
telephone EID/ESN, control channel and channel assignment for
mobile unit 256. PSAP GIS network 258 transmits to mobile unit 256,
via public safety land mobile network 260, messages of the
following types: mobile cellular telephone initial position
location text and graphic message for display; and RF signal
parameter exchange message including unique cellular telephone
EID/ESN, control channel, and control channel assignment for
location receiver. GIS 254 and PSAP GIS network 258 are
interconnected at the network demarcation 1106.
[0105] FIG. 12 illustrates the optional addition of an
interferometer link between cells of a cellular telephone network.
This may be useful in the context of the current invention to
further enhance precision, but is not strictly necessary.
[0106] An interferometer link can be formed between any two cell
points that can see each other. It is used to establish a means to
compute accurately propagation velocity, propagation time, and
distance between points in real time. A calibrated link will detect
the type and variance of transmission losses associated with
atmospheric conditions.
[0107] In FIG. 12, cell towers 1202, 1204, and 1206 are linked by a
precision time and synchronization network 1208 which is linked to
a precise time source 1210 and distributes data to all cells in a
region. Precise time and time interval calibrated transmission
bursts 1212 are communicated between cell towers 1204 and 1206, for
example.
[0108] The interferometer function provides information about
propagation loss factors so an accurate estimate of basic
transmission loss can be used to compare with an unknown received
signal level. Tower location receiver 252 may use this comparison
to more accurately compute range and bearing of mobile unit
120.
[0109] FIG. 14 shows a flowchart that describes the process of
using the optional interferometer link to calculate distance from a
tower to a cellular telephone. In step 1402, a test signal is
transmitted from a first tower on a calibrated line. In step 1404,
a second tower receives the calibrated test signal. In step 1406,
the second tower measures the propagation characteristic of the
test signal. In step 1408, the propagation characteristic is stored
for future use. In step 1410, a communications signal is sensed
from a cellular telephone. In step 1412, the system determines
whether a recalculation of the propagation characteristic is
needed. If a recalculation is needed, steps 1414-1420 are
performed. These steps are the same as steps 1402-1408 described
above. Otherwise, step 1422 is performed. In step 1422, the
propagation characteristic of the sensed signal is measured. In
step 1424, the calculated propagation characteristic is compared
against the measured propagation characteristic to determine a
distance to the cellular telephone.
[0110] FIG. 12 shows the addition of an interferometer capability
to an existing cellular system. Note that it is not necessary to
add interferometer capability to all cell sites. The network that
carries the precision time and sync data can also carry the
interferometer data to all cells within a geographical location.
For example a geographic region as large as 500 miles could be
served from one representative interferometer link. The
interferometer provides useful information in the form of
corrections for the path predication calculations. It is a fact
that propagation loss does not exactly match the 1/r.sup.2 loss
model. It is in fact somewhere between 1/r.sup.2 and 1/r.sup.3.
What the interferometer does is allow the link equipment to measure
the loss at the time and compute an accurate 1/r.sup.x where
2.ltoreq.x.ltoreq.3. The other way to compute propagation loss in
excess of the 1/r.sup.2 model is use information from publications
like NBS Technote 101 that contain tables of climate loss values
and pull those values that match the current climatic situation and
enter them into the prediction model. The prediction model is used
to compute the estimated range and in turn location of the mobile
unit 120.
[0111] FIG. 13 shows the operation of a cooperative element
location system 1300 designed to locate a mobile unit 120. A coarse
CEP 1321 provides the initial dispatch point defined by two point
circle A, B. Targeted mobile unit 120 is located somewhere within
coarse CEP 1321. Determination of this coarse CEP requires only one
cell tower 1302, for example. Mobile location component 256 may
include vehicle mount 257 and/or hand-held device 259. A location
beacon 1310 is transmitted from emergency vehicle 1304 to cell
tower 1302.
[0112] Emergency vehicle 1304 receives transmission 1308 including
information identifying coarse CEP 1321. In response, emergency
vehicle travels in the direction of CEP 1321. As emergency vehicle
1304 travels closer to target mobile unit 120 located in coarse CEP
1321, cooperative element location system 1300 is able to provide a
fine location solution of a smaller circle bounded by points C and
D. The smaller circle represents fine CEP 1323 which is a two point
circle contained within coarse CEP 1321. Target mobile unit 120 is
now known to be located in fine CEP 1323. This process may be
reiterated until target mobile unit 120 is located.
[0113] If necessary, handheld location receiver 259 may be used to
go places where emergency vehicle 1304 cannot travel, such as
inside a building. In that case, handheld location receiver 259
receives transmission 1318 containing increasingly accurate
information regarding the location of target mobile unit 120.
* * * * *