U.S. patent application number 09/989091 was filed with the patent office on 2002-06-20 for interface for wireless location information.
Invention is credited to Fitch, James A., Hose, David A., McKnight, Michael.
Application Number | 20020077119 09/989091 |
Document ID | / |
Family ID | 26804055 |
Filed Date | 2002-06-20 |
United States Patent
Application |
20020077119 |
Kind Code |
A1 |
Fitch, James A. ; et
al. |
June 20, 2002 |
Interface for wireless location information
Abstract
Multiple location finding equipment (LFE) inputs are used to
enhance the location information made available to wireless
location-based applications. In one implementation, the invention
is implemented in a wireless network including an MSC (112) for use
in routing communications to or from wireless stations (102), a
network platform (114) associated with the MSC (112), and a variety
of LFE systems (104, 106, 108 and 110). A Location Finding System
(LFS) (116) in accordance with the present invention is resident on
the platform (114). The LFS (116) receives location information
from the LFEs (104, 106, 108 and 110) and provides location
information to wireless location based applications (118). In this
regard, the LFS (116) can receive input information at varying time
intervals. of varying accuracies and in various formats, and can
provide standardized outputs to the applications (118), for
example, depending on the needs of the applications (118). Multiple
inputs may also be co-processed for enhanced accuracy.
Inventors: |
Fitch, James A.; (Edmonds,
WA) ; Hose, David A.; (Boulder, CO) ;
McKnight, Michael; (Westminster, CO) |
Correspondence
Address: |
MARSH, FISCHMANN & BREYFOGLE LLP
3151 SOUTH VAUGHN WAY
SUITE 411
AURORA
CO
80014
US
|
Family ID: |
26804055 |
Appl. No.: |
09/989091 |
Filed: |
November 19, 2001 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
09989091 |
Nov 19, 2001 |
|
|
|
09396235 |
Sep 15, 1999 |
|
|
|
60106816 |
Nov 3, 1998 |
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|
Current U.S.
Class: |
455/456.2 |
Current CPC
Class: |
H04W 88/18 20130101;
H04W 4/029 20180201; G01S 5/12 20130101; H04W 64/00 20130101; H04W
4/02 20130101; H04W 8/08 20130101; G01S 5/02 20130101; G01S 5/0027
20130101 |
Class at
Publication: |
455/456 ;
455/435 |
International
Class: |
H04Q 007/20 |
Claims
What is claimed is:
1. A method for use in a wireless network to obtain requested
location information regarding a wireless station and provide the
requested location information to a wireless location application,
the wireless network being associated with at least a first
location source and a second location source for providing
information regarding locations of wireless stations in the
network, the method comprising the steps of: providing a system for
receiving location information from the first and second location
sources, where the first and second location sources employ first
and second location finding technologies for locating wireless
stations; establishing an interface for communications between said
system and said wireless location application, where said interface
defines a standard for requesting and providing said requested
location information; first receiving, at said system via said
interface, a location request regarding said wireless station from
said wireless location application, said location request
requesting said requested location information in accordance with
said standard of said interface; storing data in memory accessible
by said system relating to said first location input and said
second location input; second receiving, at said system, a first
location input based on first location information provided by said
first location source, and a second location input based on second
location information provided by said second location source;
obtaining said requested location information by selectively
retrieving data from said memory based on said location request;
and outputting said requested location information to said wireless
location application in accordance with said standard of said
interface, wherein said wireless location application is
selectively supported by said first location source and said second
location source via said interface.
Description
CROSS REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation in part of U.S. patent
application Ser. No. 09/396,235 filed on Sep. 15, 1999, entitled
"Multiple Input Data Management For Wireless Location-Based
Applications", which is a continuation in part of U.S. Patent
Application Serial No. 60/106,816 filed on Nov. 3, 1998, entitled
"Data Fusion for Wireless Location-Based Applications". Both of
these applications are incorporated herein by reference in their
entireties.
FIELD OF THE INVENTION
[0002] The present invention relates in general to wireless
location-based applications and, in particular, to a method and
apparatus for use in processing multiple location finding equipment
inputs and making the resulting location information available to
wireless location-based applications.
BACKGROUND OF THE INVENTION
[0003] Wireless communications networks generally allow for voice
and/or data communication between wireless stations, e.g., wireless
telephones (analog, digital cellular and PCS), pagers or data
terminals that communicate using RF signals. In recent years, a
number of location-based service systems have been implemented or
proposed for wireless networks. Such systems generally involve
determining location information for a wireless station and
processing the location information to provide an output desired
for a particular application.
[0004] Examples of such existing or proposed applications include
emergency or "911" applications, location dependent call billing,
cell-to-cell handoff and vehicle tracking. In 911 applications, the
location of a wireless station is determined when the station is
used to place an emergency call. The location is then transmitted
to a local emergency dispatcher to assist in responding to the
call. In typical location dependent call billing applications, the
location of a wireless station is determined, for example, upon
placing or receiving a call. This location is then transmitted to a
billing system that determines an appropriate billing value based
on the location of the wireless station. In handoff applications,
wireless location is determined in order to coordinate handoff of
call handling between network cells. Vehicle tracking applications
are used, for example, to track the location of stolen vehicles. In
this regard, the location of a car phone or the like in a stolen
vehicle can be transmitted to the appropriate authorities to assist
in recovering the vehicle.
[0005] From the foregoing, it will be appreciated that
location-based service systems involve location finding equipment
(LFE) and location-related applications. To some extent, the LFEs
and applications have developed independently. In this regard, a
number of types of LFEs exist and/or are in development. These
include so-called angle of arrival (AOA) time difference of arrival
(TDOA) including handset global positioning system (GPS) and the
use of cell/sector location. The types of equipment employed and
the nature of the information received from such equipment vary in
a number of ways. First, some of these equipment types, like GPS,
are wireless station-based whereas others are "ground-based",
usually infrastructure-based. Some can determine a wireless
station's location at any time via a polling process, some require
that the station be transmitting on the reverse traffic channel
(voice channel), and others can only determine location at call
origination, termination, and perhaps registration. Moreover, the
accuracy with which location can be determined varies significantly
from case to case. Accordingly, the outputs from the various LFEs
vary in a number of ways including data format, accuracy and
timeliness.
[0006] The nature of the information desired for particular
applications also varies. For example, for certain applications
such as 911, accuracy and timeliness are important. For
applications such as vehicle tracking, continuous or frequent
monitoring independent of call placement is a significant
consideration. For other applications, such as call billing,
location determination at call initiation and call termination or
during handoff is generally sufficient.
[0007] Heretofore, developers have generally attempted to match
available LFEs to particular applications in order to obtain the
location information required by the application. This has not
always resulted in the best use of available LFE resources for
particular applications. Moreover, applications designed to work
with a particular LFE can be disabled when information from that
LFE is unavailable, e.g., due to limited coverage areas,
malfunctions or local conditions interfering with a particular LFE
modality. In addition, the conventional query and response mode of
operation between applications and the associated LFEs has resulted
in the use by applications of LFE dependent data formats, LFE
limited data contents, and single LFE input location
determinations.
SUMMARY OF THE INVENTION
[0008] The present invention is directed to a method and apparatus
for using multiple LFE inputs to enhance the location information
made available to wireless location-based applications. The
invention allows wireless location-based applications access to
information based inputs from LFEs of different types, thereby
enhancing the timeliness, accuracy and/or reliability of the
requested location information. Moreover, in accordance with the
present invention, applications are independent of particular LFEs
and can access location information from various LFE sources
without requiring specific adaptations, data formats, or indeed
knowledge of the LFE sources employed, in order to access and use
such location information. By virtue of such independence, new
location finding technologies can be readily deployed and existing
applications can exploit such new technologies without
compatibility issues. The invention also allows multiple LFE
inputs, from one or more LFEs, to be used to allow for wireless
station tracking and reduced location uncertainty.
[0009] According to one aspect of the present invention, a method
is provided for using multiple (i.e., two or more) LFEs to support
a wireless location application. The method involves receiving
first and second inputs from first and second LFEs, storing
location information based on the inputs in memory, receiving a
location request regarding a wireless station from a wireless
location application, selectively retrieving the location
information from memory, and outputting a response to the location
request to wireless location application.0
[0010] The first and second LFEs preferably may employ different
location finding technologies, e.g., GPS and other TDOA, AOA, and
cell/sector technologies. The stored location information
preferably includes at least location information and corresponding
time information for particular wireless stations, and may further
include location uncertainty information, travel speed information
and travel direction information. In response to the location
request from the wireless location application, location
information may be retrieved from memory or, alternatively, one or
more of the LFEs may be prompted to obtain location information. In
this regard, the location request may include a specification
regarding the desired location information, for example, indicating
how recent or how accurate the information should be. If the memory
includes information conforming to the specification, then such
information is retrieved and output to the requesting application.
Otherwise, appropriate information may be obtained by prompting one
or more LFEs to locate the wireless station of interest.
[0011] In accordance with another aspect of the present invention,
a processing system is interposed between the LFEs and the wireless
location applications such that the applications can access
location information in a manner that is independent of the
location finding technology employed by the LFEs. The corresponding
process implemented by the processing system involves: receiving
LFE dependent location data (i.e., location data having a content
and/or format dependent on the location finding technology
employed) from multiple LFEs receiving a location request from a
wireless location application seeking LFE independent location data
(i.e., location data having a content and format independent of any
particular location finding technology) and responding to the
location request based on LFE dependent location data. The process
implemented by the processing system may further involve generating
and storing LFE independent location data based on the LFE
dependent data. The processing system may be resident on the
location finding controllers associated with each LFE, on a
separate platform and/or the processing system functionality may be
distributed over multiple platforms.
[0012] According to a still further aspect of the present
invention, multiple LFE inputs are utilized to make a location
determination regarding a wireless station. The corresponding
method involves the steps of receiving a first location input from
a first LFE including first location information and first
uncertainty information, receiving a second location input from a
second LFE including second location information and second
uncertainty information and combining the first and second location
inputs to provide a combined location input including combined
location information and uncertainty information based on the first
and second inputs. Preferably, the first and second inputs include
raw location and uncertainty information obtained from LFE
measurements prior to aggregation and related processing. One or
both of the first and second inputs may constitute partial
information, insufficient on its own to yield a location and
uncertainty regarding the wireless station within the requirements
of the wireless location application. For example, in the case of
LFEs that determine location based on readings obtained relative to
two or more cell sites, a reading from one of the cell sites may be
used in conjunction with other location information, e.g., cell
sector information, to make a location determination.
[0013] According to another aspect of the present invention,
multiple LFE inputs, obtained at different times from the same or
different LFEs, are utilized to derive tracking information such as
for obtaining improved location determination accuracy. The
associated method includes the steps of receiving a first LFE input
including first location information and first corresponding time
information for a particular wireless station, receiving a second
LFE input including second location information and second time
information for the wireless station, and using the first and
second inputs to derive tracking information for the wireless
station. The tracking information preferably includes information
regarding the mobile station's speed of travel and direction of
travel. This tracking information can be used in conjunction with
subsequent LFE inputs for the wireless station to improve location
determination accuracy and can also be used to interpolate wireless
station location between location determinations, or to project
future wireless station locations as may be desired for some
applications. It will be appreciated that this tracking function
and other functions are facilitated by the provision of a system
for receiving inputs from one or more LFEs, standardizing such
inputs with regard to data content and format, and storing such
information. In particular, such standardized and stored
information can be readily analyzed to yield derivative information
regarding wireless station position as well as statistical
information for wireless stations of interest in the service
area.
[0014] A system constructed in accordance with the present
invention includes an input facility for receiving inputs from
multiple LFEs, a memory such as a cache for storing information
from the LFE inputs (e.g., a wireless station identification, a
location, a time associated with that location, an uncertainty for
that location, and travel speed and bearing), an interface for
receiving location requests from wireless location applications and
providing responses to such requests, and a processing subsystem
for processing the LFE inputs and location requests. The apparatus
may also include a facility for prompting LFEs to make location
measurements in response to location requests. Among other things,
the processing subsystem may convert the LFE inputs into a standard
format, direct storage of data in the memory, derive tracking or
other derivative information from multiple inputs, analyzing stored
information relative to received location requests to determine
whether the stored information includes information responsive to
the requests and selectively directing the LFEs to make location
measurements. The system may be resident on a single or multiple
platform and the functionality may be spread among multiple
applications.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] For a more complete understanding of the present invention
and further advantages thereof, reference is now made to the
following detailed description taken in conjunctions with the
drawings in which:
[0016] FIG. 1 is a schematic diagram of a wireless network
implementing a location finding system in accordance with the
present invention;
[0017] FIG. 2 is a schematic diagram illustrating a wireless
location-based services system in accordance with the present
invention;
[0018] FIGS. 3a-3e illustrate various location finding technologies
that may be utilized in the context of the present invention;
[0019] FIG. 4 is a graphical illustration of the use of multiple
LFE inputs to reduce location uncertainty in accordance with the
present invention;
[0020] FIG. 5 is a graphical depiction of a location uncertainty
analysis in accordance with the present invention; and
[0021] FIGS. 6-9 illustrate various wireless location interface
signaling sequences in accordance with the present invention.
DETAILED DESCRIPTION
[0022] In the following description, particular embodiments and
implementations of the present invention are set forth in the
context of a telecommunications network. It will be appreciated
however, that various aspects of the invention are more broadly
applicable to other location based services environments.
[0023] Referring to FIG. 1, a wireless telecommunications network
implementing the present invention is generally identified by the
reference numeral 100. Generally, the network includes a mobile
switching center (MSC) 112 for use in routing wireless
communications to or from wireless stations 102, a network platform
114 associated with the MSC 112 for implementing a variety of
subscriber or network service functions, and a variety of location
finding equipment (LFE) systems 104, 106, 108 and 110. In the
illustrated embodiment, the network platform is used to run a
Location Manager (LM)16 in accordance with the present invention
and a number of wireless location applications 118. Although the
illustrated location finding system 116 and wireless location
applications 118 are illustrated as being resident on the network
platform 114, it will be appreciated that the elements 116 and 118
may be located elsewhere in the network 100, may be resident on
separate platforms, or the functionality of each of these elements
116 and 118 may be spread over multiple platforms. In addition,
other applications not depicted in FIG. 1 may be resident on the
platform 114.
[0024] As shown in FIG. 1, multiple LFE systems 104, 106, 108 and
110 may be associated with the network 100. These LFE systems 104,
106, 108 and 110 may employ any of a variety of location finding
technologies including AOA, TDOA such as GPS and cell/sector
technologies and the various systems 104, 106, 108 and 110 may be
the same as or different from one another. It will be appreciated
that the nature of the data obtained from the LFE systems 104, 106,
108 and 110 as well as the path by which the data is transmitted
varies depending on the type of LFE employed, and the ability to
accommodate a variety of LFEs is an important advantage of the
present invention. Some types of LFEs include LFE equipment in the
handset. Examples include certain GPS and other TDOA systems. In
such cases, location information may be encoded into signals
transmitted from the handset to a cell site or other receiver, and
the information may then be transferred to the platform 114 via the
MSC 112 or otherwise. Other LFE systems, i.e., embedded systems,
use equipment associated with individual cell sites such as
specialized antennae to make location determinations such as by
triangulation and, again, the resulting location information may be
transferred to the platform 114 via the MSC 112 or otherwise. Still
other LFE systems employ a network of dedicated LFE equipment that
is overlaid relative to the wireless network. Such systems may
communicate location information to the platform 114 independent of
the MSC 112 and network cell site equipment. In addition, some LFE
technologies can be implemented via equipment resident in the
handset, in cell sites or other network locations and/or in
dedicated LFE sites such that the data pathway of the location
information may vary even for a given LFE technology.
[0025] Three of the illustrated systems 104, 106 and 108 operate
separate from the MSC 112. For example, such systems may include
network based AOA systems and network based TDOA systems and
external systems such as GPS. Generally, the illustrated network
based systems such as AOA and network TDOA systems determine the
location of a wireless station 102 based on communications between
the wireless station and the cell site equipment of multiple cell
sites. For example, and as will be described in more detail below,
such systems may receive information concerning a directional
bearing of the wireless station 102 or a distance of the wireless
station 102 relative to each of multiple cell sites. Based on such
information, the location of the wireless station 102 can be
determined by triangulation or similar geometric/mathematic
techniques. External systems such as GPS systems, determine the
wireless station location relative to an external system. In the
case of GPS systems, the wireless station 102 is typically provided
with a GPS receiver for determining geographic position relative to
the GPS satellite constellation. This location information is then
transmitted across an air interface to the network 100.
[0026] The illustrated cell sector system 110 may be associated
with cell site equipment for communicating with the wireless
station 102. In this regard, the cell site equipment may include
three or more directional antennas for communicating with wireless
stations within subsections of the cell area. These directional
antennas can be used to identify the subsection of a cell where the
wireless station 102 is located. In addition, ranging information
obtained from signal timing information may be obtained to identify
a radius range from the cell site equipment where the wireless
station 102 is located, thereby yielding a wireless station
location in terms of a range of angles and a range of radii
relative to the cell site equipment. This cell/sector location
information can be transmitted to the LM 116 via the MSC 112 or
possibly via other network information or structure.
[0027] As shown, the LM 116 receives location information from the
various LFE systems 104, 106, 108 and 110. The nature of such
information and handling of such information is described in more
detail below. Generally, however, such information is processed by
the LM 116 to provide location outputs for use by any of various
wireless location applications 118 in response to location requests
from the application 118. Such applications may include any
location-based services applications such as 911, vehicle tracking
and location-based billing programs.
[0028] FIG. 2 illustrates a location-based services system 200 in
accordance with the present invention. An important aspect of the
present invention relates to the operation of the LM 214 to receive
inputs from multiple LFEs 202, 204 and 206 and provide location
outputs to multiple applications 226, 228 and 230. In accordance
with the present invention, the LFEs 202, 204 and 206 may be based
on different technologies, and may therefore provide different
types of location information, in different data formats, with
different accuracies based on different signals.
[0029] A number of different location finding technologies are
depicted in FIGS. 3a-3d for purposes of illustration. FIG. 3a
generally shows the coverage area 300 of a cell sector. As noted
above, the cell site equipment for a particular cell of a wireless
telecommunications system may include a number, e.g., three or
more, of directional antennas. Each antenna thus covers an angular
range relative to the cell site bounded by sides 302. In the case
of a three sector cell, each antenna may cover about
120.degree.-150.degree. relative to the cell site. In addition the
coverage range for the antenna defines an outer perimeter 304 of
the coverage area 300. As shown, the range varies with respect to
angle defining a somewhat jagged outer perimeter 304. Accordingly,
the actual uncertainty regarding the location of a wireless station
located in the illustrated cell sector is defined by the coverage
area 300. The location determination output from a cell/sector LFE
is therefore effectively defined by the coordinates of the coverage
area 300.
[0030] FIG. 3b depicts a TOA based LFE. In this case, the wireless
station's range from a cell sector antenna is determined, based on
time of signal arrival or signal transit time to within a radius
range, e.g., about 1000 meters. Accordingly, the wireless station's
location can be determined to be within an area bounded by sides
306 (based on the angular range of the cell sector antenna) and
inner 308 and outer 310 arcs (defined by the ranging uncertainty).
The output from a TOA based LFE is effectively defined by the
coordinates of the sides 306 and the axes 308 and 310.
[0031] An AOA based LFE is generally illustrated in FIG. 3c. AOA
based LFEs determine the location of a wireless station based on
the angle of arrival of signals, generally indicated by rays 312
and 314, from the wireless station as measured by two or more cell
sites 316 and 318. Each angle measurement has an angular
uncertainty generally indicated by line segments 320 and 322.
Consequently, the uncertainty region for a given location
determination is defined by a polygon having 2n sides, where n is
the number of cell sites 316 and 318 involved in the
measurement.
[0032] FIG. 3d illustrates a TDOA based LFE. Although the
illustrated system is cell site based, the TDOA system may
alternatively be handset based. In TDOA systems, multiple cell
sites measure the time of arrival of signals from a wireless
station. Based on such measurements, each cell site can provide
information regarding wireless station location in terms of a
hyperbola 324 or 326 and an uncertainty, generally indicated by
segments 328 and 330. The resulting uncertainty region is defined
by a multi-sided region (where each wall is curved) having 2n
walls, where n is the number of cell sites involved in the
determination.
[0033] FIG. 3e illustrates a GPS based LFE. In GPS systems, the
wireless station includes a GPS transceiver for receiving signals
indicating the wireless station's location relative to multiple
satellites in the GPS constellation. Based on these signals, the
geographic coordinates of the wireless station's location is
determined to an accuracy of perhaps 20 meters as generally
indicated by circle 332. This information is then transmitted to
the wireless network across an air interface.
[0034] Another type of LFE is network assisted GPS. GPS is a TDOA
system requiring signals from a minimum of three satellites to
locate on a two dimensional surface, e.g., geographical
coordinates. The location is determined as the intersection of the
hyperbolas defined by the range differences between each pair of
satellites. When the number of satellites in view is reduced to a
single pair, the location can be determined by the intersection of
the resulting hyperbola and other geometric figures such as the
serving cell boundaries.
[0035] Referring again to FIG. 2, each of the LFEs 202, 204 or 206
outputs location information to its respective LFC 208, 210 or 212.
The nature of this "raw" LFE output depends in part on the type of
LFE involved. For example, in the case of a cell sector system the
output may be a sector identifier or coordinates; in the case of a
TOA system, the output may be a sector identifier or coordinates
and a radius; in an AOA system the output may be angular
measurements and corresponding cell site identifiers/coordinates;
in TDOA systems the output may define multiple hyperbolae; and in
GPS systems the output may be geographic coordinates.
[0036] The LFCs 208, 210 and 212 collect and aggregate the "raw"
location into a standard format which is then sent to the location
cache (LC) 220 of the LM 214 for storage. Aggregation involves
using the raw data to determine a wireless station location and
uncertainty. For some LFE systems, such as GPS systems, this
process is simple because location coordinates are reported and the
uncertainty is known. For other LFE systems, aggregation is more
involved. For example, in the case of TDOA, aggregation may involve
receiving multiple hyperbola definitions and using these
definitions to define a wireless station location and a multi-sided
uncertainty region. The LFCs 208, 210 and 212 may be provided by
the LFE vendors or their functionality may be incorporated into a
subsystem of the LM 214.
[0037] In the context of the present invention, it is useful to
express the location information in a standard format. Accordingly,
the LFCs 208, 210 and 212 or a cooperating subsystem of the LM 214
associated with the LC 220, may implement a conversion facility for
converting the determined (processed) location information of the
LFCs 208, 210 and 212 into standardized location information
expressed, for example, as geographical location coordinates and a
region of uncertainty. The uncertainty region may be of any shape
(e.g., polygonal) depending, for example, on the nature of the
LFE(s) employed. Once such type of uncertainty region is a circular
region that can be characterized by an uncertainty radius. In the
illustrated embodiment, two dimensional location coordinates are
defined (e.g., latitude and longitude) together with an uncertainty
radius applied relative to the location coordinates. It will be
appreciated that the standard format may allow for altitude
coordinates, non-circular uncertainty regions and other
parameters.
[0038] Referring again to FIGS. 3a-3e, examples of these
coordinates and circular uncertainty regions are graphically
depicted. In particular, in each case, a location "L" and
standardized uncertainty region "C" are geometrically defined such
that the standardized uncertainty region C circumscribes the actual
uncertainty region associated with that location finding
technology. In this regard, the location L may be defined first
(e.g., as the intersection of rays 312 and 314 in FIG. 3c) and then
the minimum radius circle C may be defined to circumscribe the
actual uncertainty region; the standardized uncertainty region C
may be defined first (e.g., as the minimum radius circle required
to circumscribe the actual uncertainty region) and then L be
defined as the center of the circle C; or any other appropriate
geometric solutions/approximations may be employed.
[0039] This standardized location information is then stored in a
database in LC 220. Specifically, the location coordinates for a
wireless station and corresponding uncertainties can be stored in a
field, in a relational database, or can otherwise be indexed to a
wireless station identifier, e.g., a cellular telephone Electronic
Serial Number/Mobile Identification Number (ESN/MIN). The
coordinates and uncertainty may be expressed in terms of any
appropriate units. For example, the coordinates may be expressed as
latitude and longitude values in units of 10.sup.-6 degrees and the
uncertainty may be expressed in units of meters.
[0040] The stored, standardized information can be used to perform
a number of multiple input analyses. Three examples of such
facilities are generally indicated by the velocity 216, multi-input
processing 217 and tracking 218 facilities of LM 214. The velocity
facility 216 involves determining and storing speed information and
direction (bearing) information for a wireless station based on
multiple LFE inputs for the station. Because of the standardized
format, such determinations can be easily made relative to inputs
from the same or different LFEs 104, 106 and/or 108. The velocity
information can be obtained based on knowledge of the change in
position and the change in time (determined by way of the time
stamps associated with the location information) and may be
expressed in terms of latitudinal and longitudinal velocity
components in units of meters per second, together with velocity
uncertainty terms. The direction information can be directly
obtained from the location information, or can be based on a ratio
of the velocity components, using standard trigonometric
principles. It will be appreciated that such speed and direction
information may be useful for a variety of applications such as
vehicle tracking.
[0041] The multi-input processing facility 217 can be used to
improve location accuracy based on multiple inputs from the same
or, more preferably, different LFEs 202, 204 and/or 206. That is,
if two locations with two uncertainties can be obtained for a given
wireless station at a given time, a reduced uncertainty can be
calculated as the overlap of the two original uncertainties. A
complicating factor is that the locations and uncertainties stored
in the LC 220 for a given wireless station will typically not
represent location determinations for the same time. Because
wireless stations are generally mobile, an additional element of
uncertainty is introduced.
[0042] The illustrated multi-input processing facility 217 takes
time into account. This is accomplished by:
[0043] 1. accessing the LC 220 to obtain two (or more) sets of
location information for a given wireless station;
[0044] 2. identifying a location, uncertainty and time for each set
of information;
[0045] 3. determining a time difference between the times of the
information sets;
[0046] 4. calculating an element of location uncertainty associated
with the time difference; and
[0047] 5. applying the calculated element of location uncertainty
to the earlier location information to obtain time translated
location information.
[0048] This time translated location information can then be
compared to the later location information in an uncertainty
overlap analysis, as described below, to obtain a reduced
uncertainty.
[0049] Various processes can be employed to calculate the
additional, time-related element of location uncertainty. A simple
case involves assuming a maximum rate of travel. For example, a
maximum rate of travel of 70 miles per hour may be assumed to
account for travel of a mobile phone in a vehicle. The uncertainty
associated with an earlier location determination may then be
expanded by a value determined by multiplying the maximum rate of
travel by the time difference between the two measurements to be
compared. Different maximum travel rates may be assumed for
different conditions, for example, a lower rate may be assumed for
city locations than for suburban locations, a lower rate may be
assumed for peak traffic periods, or a lower rate may be assumed
for mobile stations that are not generally used on fast moving
vehicles. Also, wireless station speed and direction information as
described above or other tracking information as described below
may be used to reduce the time-related element of uncertainty.
[0050] Once such a time translation process has been employed to
normalize multiple LFE inputs relative to a given time, an
uncertainty overlap analysis can be implemented. Such an analysis
is graphically illustrated in FIGS. 4 and 5. Referring first to
FIG. 4, the smaller circle represents a location and uncertainty
associated with a later LFE input taken to be at time t.sub.1. The
larger circle 402 represents a location and uncertainty associated
with a time translated location information based on an earlier LFE
input taken to be at time t.sub.0. Circle 402 is illustrated as
having a larger uncertainty than circle 400 to account for the
additional time and travel related element of uncertainty
associated with the time translation. The shaded overlap area 404
represents the reduced uncertainty achieved by using multiple
inputs. That is, statistically, if circle 400 represents a 95%
confidence level regarding the position of the station at t.sub.1
and circle 402 represents a nearly 95% confidence level regarding
the position of the station at t.sub.1, the position of the station
can be determined to be in the shaded area 404 with a high level of
confidence.
[0051] FIG. 5 illustrates a mathematical process for combining the
original uncertainties to obtain a more accurate position and
uncertainty. Mathematically, the problem is to compute the
intersection of the circular uncertainty regions, and express the
result as a location with an uncertainty (e.g., a circular
uncertainty circumscribing the intersection region). To simplify
the mathematics, the geometric arrangement of FIG. 4 is translated
to provide a first axis (x in FIG. 5) that extends through the
centerpoints of the circular uncertainty regions 500 and 502
(generally, the coordinates of the originally determined locations)
and an orthogonal axis (y) intersecting the center of the larger
(in this case later) circular uncertainty region 502. The
mathematical equations for the boundaries of circular uncertainty
regions 500 and 502 are:
x.sup.2+y.sup.2=r.sub.1.sup.2 (1)
(x-x.sub.0).sup.2+y.sup.2=r.sub.2.sup.2 (2)
[0052] It will be appreciated that the values of r.sub.1, r.sub.2
and x.sub.0 are known as these are the uncertainty of the time
translated information, the uncertainty of the later LFE input and
the difference between r.sub.1 and r.sub.2, respectively. Equations
(1) and (2) can then be simultaneously solved to obtain x and y,
where x is the new location and y is the radius of the new
uncertainty region. Finally, these values can be translated back
into Earth coordinates. This mathematical analysis can be used for
cases where x.ltoreq.x.sub.0 and x.sub.0.ltoreq.r.sub.1+r- .sub.2.
In other cases, the most recent or most accurate of the LFE inputs
can be utilized.
[0053] The illustrated LM 214 also includes a tracking facility
218. Such tracking involves using historical information (at least
two sets of location information) and using such information to
reduce the uncertainty associated with current measurements. That
is, by tracking movement of a wireless station, information can be
obtained that is useful in analyzing the uncertainty of current
measurements. In a simple case, where tracking information
indicates that a wireless station is moving in a straight line (or
otherwise on a definable course) or at a constant speed, then curve
fitting techniques or other simple algorithms can be employed to
obtain a degree of confidence concerning current location.
Moreover, interpolation and extrapolation techniques can be
employed to determine location at times between measurements or in
the future. Such information may be useful to determine when a
wireless station crossed or will cross a boundary as may be
desired, for example, for location-based billing applications or
network management applications (for handling hand-off between
adjacent cells). It will thus be appreciated that the information
stored in the LC 220 may include wireless station identifiers,
locations, uncertainties, confidence levels, travel speeds, travel
directions, times and other parameters. Data may be purged from the
LC upon reaching a certain age in order to remove visitor data and
other unnecessary data.
[0054] The velocity facility 216, multi-input processing facility
217, and tracking facility 218 may use the raw information data
transmitted from the LFEs 202, 204 and 206 to the LFCs 208, 210 and
212 in place of, or in addition to, the LFC outputs. For example,
the multi-input processing facility 217 may use a hyperbola
definition from a TDOA system in combination with an angle from an
AOA system (or other combination of partial LFE outputs) if such
combination yields an improved location accuracy or otherwise
provides a suitable location determination. Similarly, it may be
preferred to use the raw data for velocity or tracking calculations
as such data is mathematically closer to the moving wireless
station and may more accurately reflect station movement.
[0055] Information residing in the network for the purposes of
handover management, e.g., Network Measurement Report (NMR) and
Mobile Assisted Hand-Off (MAHO) can be used to locate the mobile
unit inside the serving cell boundary and reduce the uncertainty to
a fraction of the cell size. The intersection of potential serving
cells provides a location estimate with a Circular Error
Probability (CEP) that is significantly smaller than the CEP of the
serving cell. Alternatively, matching the received signal strengths
from theses cells with accurate predictions results in estimates
with even smaller CEP. The intersection of any of these uncertainty
circles with the GPS hyperbola provides a new estimate of
location.
[0056] Using this, the mobile unit is positioned at the center of
the hyperbola segment bounded by the uncertainty circle. The
uncertainty in this new estimate is confined to the area bounded by
that circle and the uncertainty hyperbolas around the nominal
value. The area of the ellipsoid that contains this figure is
smaller than the area of the CEP. Thus, the accuracy of the new
estimate is higher than either of its components by themselves.
[0057] The above process and conclusions apply also to GPS/AFLT,
which replaces lost satellites with signals from base stations.
[0058] Another use of multiple location sources is related to
situations when there is no overlap between two independently
obtained location estimates (taking into account the uncertainty
associated with each estimate) such as GPS and NMR. In such a
situation a weighting can be applied to each estimate to derive a
new location and uncertainty estimate that is different than each
independently obtained estimate. However, another approach is to
re-query the network to obtain new location estimates based on the
premise that the reason for the lack of an overlap between the two
estimates is that one of these location estimates is incorrect.
Depending on the results of the new query a new estimate can be
determined which may be a weighted average of the two, the
intersection of the two or in some case a decision may be made to
only use one of the estimates.
[0059] Referring again to FIG. 2, the illustrated system 200
includes a wireless location interface (WLI) 224 that allows
wireless location applications 226, 228 and 230 to selectively
access information stored in the LC 220 or prompt one or more of
LFEs 202, 204 and/or 206 to initiate a location determination. The
WLI 224 provides a standard format for submitting location requests
to the LM 214 and receiving responses from the LM 214 independent
of the location finding technology(ies) employed. In this manner,
the applications can make use of the best or most appropriate
location information available originating from any available LFE
source without concern for LFE dependent data formats or
compatibility issues. Moreover, new location finding technologies
can be readily incorporated into the system 200 and used by the
applications 226, 228 and 230 without significant accommodations
for the existing applications 226, 228 and 230, as long as
provision is made for providing data to the LC 220 in the form
described above.
[0060] The WLI 224 of the illustrated implementation allows the
applications to include a specification with a location request
regarding the desired location information. For example, the
specification may include one or more of the following: the
timeliness of the location information (e.g., not older than [date
stamp parameter]), the accuracy of the information (e.g.,
uncertainty not exceeding [uncertainty parameters]), confidence
(confidence at least equal to [confidence parameter]).
Alternatively, the request may specify the use of the most recent
available information, most accurate available information, etc. In
addition, the location request can specify whether the request is
for one-time only location information or ongoing monitoring of a
mobile station, whether the LM 214 should wait for the next
available update or force a location determination, whether
redundant or unnecessary updates should be filtered (e.g., do not
send updates more often than once a minute or if wireless station
has moved less than 50 meters), and what the priority of the
request is. In this manner, ongoing monitoring may be employed, for
example, by applications such as vehicle tracking and 911, and
event triggered requests can be used for other applications such as
location based billing. In each case, the desired location
parameters can be specified.
[0061] FIGS. 6-9 show messaging sequences for various location
request situations. Specifically, FIG. 6 shows a series of messages
for a location request where the application waits for the next
available location determination. The process is initiated by
transmitting a WLARequestedLocationInvoke message from one of the
WLAs to the LC. This message may include parameter fields for
Wireless Station Identification, WLA Identification, Location
Request Filter, Location Request Mode (check LC or force LFE
location determination), Geographic Extremes (where to look for
wireless station), Request Priority (processing priority relative
to other pending requests) and Fallback Timeout (time that WLA will
wait for a current location determination before accepting the
information stored in the LC).
[0062] In the case of FIG. 6, where the WLA waits for the next
available location determination, the next message may be a system
access or other triggering signal from the wireless station to the
LFE. In response, the LFC sends raw location measurement
information to the LFE which, in turn, provides a location update
to the LC. The LM then responds to the location request from the
WLA with a WLARequestLocationReturnResult message. This message may
include the following parameters: Geographic Location, Location
Uncertainty, Location Determination Technology, Time Stamp,
Velocity, Velocity Uncertainty, and Fallback Timeout Occurred
Flag.
[0063] FIG. 7 illustrates a sequence of messages associated with a
forced LFE access. The illustrated sequence is initiated by a
WLARequestLocationInvoke as described above. In response, the LM
transmits a QueryLocationInvoke message to the LFC to force an LFE
determination, and the LFC confirms receipt of this message with a
QueryLocationReturnResult message. The parameters of the
QueryLocationInvoke message may include Wireless Station ID,
Geographic Extremes and Measurement Priority (relative to other
pending measurement requests). The LFC then sends a One-time
Measurement Request message to the LFE to instruct the LFE to
obtain location information for the wireless station of interest.
In cases where ongoing monitoring is desired, this message may be
sent repeatedly or periodically as indicated by multiple arrowheads
in the Figure. In order to obtain a location measurement, it is
generally necessary to cause the wireless station to transmit an RF
signal for detection by the LFE or to communicate location data to
the wireless network. This can be achieved by conducting a polling
process using an LRF which requests all wireless stations to
register. In this regard, the LFC issues a Force System Access
message to the LRF which, in turn, transmits the Force System
Access message to the wireless station. In response, a system
access signal is transmitted by the wireless station and detected
by the LFE. The LFE then transmits Location Measurement Information
to the LFC. This may be repeated in the case of ongoing monitoring.
The LFC provides a Location Update to the LC and, finally, the LM
transmits a WLARequestLocationReturnResult as described above to
the WLA.
[0064] FIG. 8 represents the case where a location request can be
responded to based on the data stored in the LC. This occurs, for
example, where the cached data satisfies the request specification
or the request specifically seeks data from the LC. Very simply,
the illustrated message sequence involves transmission of a
WLARequestLocationInvoke message from the WLA to the LM and a
responsive WLARequestLocationReturnR- esult. It will be appreciated
that this case allows for a very fast response. Moreover, it is
anticipated that the cached data will be sufficient in many cases
for many WLAs.
[0065] FIG. 9 shows a typical message sequence for the case where a
WLA requests ongoing updates regarding the location of a wireless
station. The update period is initiated upon transmission of a
WLARequestRegisterInvoke message from the WLA to the LM and
receiving a WLARequestRegisterReturnResult in confirmation; and
terminates upon transmission of a WLARequestUnregisterInvoke
message and receiving a WLARequestUnregisterReturnResult in
confirmation. The parameters included in the Register message can
include the wireless station ID, update interval, whether wireless
station access should be forced, etc. As shown in the Figure, the
LM receives Location Updates from time-to-time from the Location
Determination Technology (LDT). It will be noted that only those
Updates occurring between Registration and Unregistration are
communicated to the WLA. In this regard, the Updates are
communicated from the LM to the WLA via a LMLocationUpdateInvoke
message and a LMLocationUpdateReturnResult is transmitted in
confirmation.
[0066] The system 200 also includes a Geographic Information System
(GIS) based module 222 for use in correlating geographic coordinate
information to mapping information, e.g., street addresses, service
area grids, city street grids (including one-way or two-way traffic
flow information, speed limit information, etc.) or other mapping
information. For example, it may be desired to convert the
geographic coordinates of a 911 call to a street address for use by
a dispatcher, or to correlate a call placement location to a
wireless network billing zone. In this regard, the GIS module 222
may communicate with the LFCs 208, 210, and 212, the LFC 214 and/or
the WLAs 226, 228 and 230 to correlate location information to GIS
information, and to correlate GIS information to
application-specific information such as wireless network billing
zones. A suitable GIS based module 222 is marketed under the
trademark MAPS by SignalSoft Corporation of Boulder, Colo.
[0067] While various embodiments of the present invention have been
described in detail, it is apparent that further modifications and
adaptations of the invention will occur to those skilled in the
art. However, it is to be expressly understood that such
modifications and adaptations are within the spirit and scope of
the present invention.
* * * * *