U.S. patent application number 09/748368 was filed with the patent office on 2002-06-27 for mobile terminal and system and method for determining the geographic location of a mobile terminal.
This patent application is currently assigned to Ericsson Inc.. Invention is credited to Bloebaum, L. Scott, McMahan, David.
Application Number | 20020080063 09/748368 |
Document ID | / |
Family ID | 25009172 |
Filed Date | 2002-06-27 |
United States Patent
Application |
20020080063 |
Kind Code |
A1 |
Bloebaum, L. Scott ; et
al. |
June 27, 2002 |
MOBILE TERMINAL AND SYSTEM AND METHOD FOR DETERMINING THE
GEOGRAPHIC LOCATION OF A MOBILE TERMINAL
Abstract
A mobile terminal and system and method for determining the
geographic location of the mobile terminal. A current cell
identification number is determined for a cell in which the mobile
terminal is located. The geographic location of the mobile terminal
is determined based on data including at least one geographic
position stored in a database and associated in the database with
data representing the current cell identification number. The
database may be updated with the geographic location and the
current cell identification number.
Inventors: |
Bloebaum, L. Scott; (Cary,
NC) ; McMahan, David; (Raleigh, NC) |
Correspondence
Address: |
Donald J. Perreault
HAYES, SOLOWAY, HENNESSEY, GROSSMAN & HAGE, P.C.
175 Canal Street
Manchester
NH
03101
US
|
Assignee: |
Ericsson Inc.
|
Family ID: |
25009172 |
Appl. No.: |
09/748368 |
Filed: |
December 26, 2000 |
Current U.S.
Class: |
342/357.43 |
Current CPC
Class: |
G01S 19/256 20130101;
G01S 19/06 20130101; G01S 19/252 20130101; G01S 19/25 20130101 |
Class at
Publication: |
342/357.1 |
International
Class: |
G01S 005/14 |
Claims
What is claimed is:
1. A mobile terminal comprising: a processor circuit configured to
identify an approximate geographic position of said mobile terminal
by accessing a database comprising data representing a plurality of
geographic positions, said approximate position corresponding to
one of said geographic positions associated in said database with
data representing a current cell identification number for a cell
in which said mobile terminal is located.
2. A mobile terminal according to claim 1, wherein said is database
stored in said mobile terminal.
3. A mobile terminal according to claim 1, wherein said processor
is configured to compute a current geographic position based on
data comprising said approximate position.
4. A mobile terminal according to claim 3, wherein said processor
is configured to update said database with said current geographic
position, said current geographic position being associated in said
database with said current cell identification number.
5. A mobile terminal according to claim 3, wherein said processor
is configured to compute said current geographic position at a
predefined time interval.
6. A mobile terminal according to claim 3, wherein said processor
is configured to compute said current geographic position when
mobile terminal moves from a first cell to a second cell.
7. A mobile terminal according to claim 3, wherein said processor
is configured to compute said current geographic position in
response to a request from application software.
8. A mobile terminal according to claim 3, wherein said processor
is configured to compute said current geographic position in
response to a request received from a radio network.
9. A mobile terminal according to claim 1, wherein said processor
is configured to compute a current geographic position based on
data comprising said approximate position and at least one
positioning signal from at least one positioning signal source.
10. A mobile terminal according to claim 9, wherein said
positioning signal source is a location server for a radio network
communicating with said mobile terminal.
11. A mobile terminal according to claim 9, wherein said
positioning signal source is a positioning system satellite.
12. A mobile terminal according to claim 11, wherein said satellite
is a GPS satellite.
13. A mobile terminal according to claim 9, wherein said
positioning signal source is a terrestrial signal transmitter.
14. A mobile terminal according to claim 1, wherein said database
employs a caching strategy.
15. A mobile terminal according to claim 14, wherein said caching
strategy is selected from the group consisting of: least recently
used, first-in first-out, and random discard.
16. A mobile terminal comprising: a database comprising data
representing a plurality of geographic positions; a communication
processor circuit configured to determine a current cell
identification number for a cell in which said mobile terminal is
located; and a positioning processor circuit configured to identify
an approximate geographic position of said mobile terminal, said
approximate position corresponding to one of said geographic
positions associated in said database with data representing said
current cell identification number.
17. A mobile terminal according to claim 16, wherein said
positioning processor is configured to compute a current geographic
position based on data comprising said approximate position.
18. A mobile terminal according to claim 17, wherein said
positioning processor is configured to update said database with
said current geographic position, said current geographic position
being associated in said database with said current cell
identification number.
19. A mobile terminal according to claim 17, wherein said
positioning processor is configured to compute said current
geographic position at a predefined time interval.
20. A mobile terminal according to claim 17, wherein said
positioning processor is configured to compute said current
geographic position when mobile terminal moves from a first cell to
a second cell.
21. A mobile terminal according to claim 17, wherein said
positioning processor is configured to compute said current
geographic position in response to a request from application
software.
22. A mobile terminal according to claim 17, wherein said
positioning processor is configured to compute said current
geographic position in response to a request received from a radio
network.
23. A mobile terminal according to claim 16, wherein said
positioning processor is configured to compute a current geographic
position based on data comprising said approximate position and at
least one positioning signal from at least one positioning signal
source.
24. A mobile terminal according to claim 23, wherein said
positioning signal source is a location server for a radio network
communicating with said mobile terminal.
25. A mobile terminal according to claim 23, wherein said
positioning signal source is a positioning system satellite.
26. A mobile terminal according to claim 25, wherein said satellite
is a GPS satellite.
27. A mobile terminal according to claim 23, wherein said
positioning signal source is a terrestrial signal transmitter.
28. A mobile terminal according to claim 16, wherein said database
employs a caching strategy.
29. A mobile terminal according to claim 28, wherein said caching
strategy is selected from the group consisting of: least recently
used, first-in first-out, and random discard.
30. A communication system comprising: a radio network comprising a
plurality of base stations, each said base station serving a cell
in said radio network; a database comprising data representing a
plurality of geographic positions; and a mobile terminal configured
to receive communication signals from said radio network, said
communication signals comprising data representing a current cell
identification number corresponding to an associated one of said
cells in which said mobile terminal is located; said mobile
terminal being configured to identify an approximate geographic
position of said mobile terminal by accessing said database, said
approximate position corresponding to one of said geographic
positions associated in said database with data representing said
current cell identification number.
31. A system according to claim 30, wherein said database is stored
in said mobile terminal.
32. A system according to claim 30, said system further comprising
a location server configured to communicate with said mobile
terminal through said radio network, said server storing
positioning data and being adapted for selectively transmitting
said positioning data to said mobile terminal.
33. A system according to claim 30, wherein said mobile terminal is
configured to compute a current geographic position based on data
comprising said approximate position.
34. A system according to claim 33, wherein said mobile terminal is
configured to update said database with said current geographic
position, said current geographic position being associated in said
database with said current cell identification number.
35. A system according to claim 33, wherein said processor is
configured to compute said current geographic position at a
predefined time interval.
36. A system according to claim 33, wherein said processor is
configured to compute said current geographic position when mobile
terminal moves from a first cell to a second cell.
37. A system according to claim 33, wherein said mobile terminal is
configured to compute said current geographic position in response
to a request from application software.
38. A system according to claim 33, wherein said mobile terminal is
configured to compute said current geographic position in response
to a request received from said radio network.
39. A system according to claim 30, wherein said system further
comprises at least one positioning signal source, and wherein said
mobile terminal is configured to compute a current geographic
position based on data comprising said approximate position and a
positioning signal from said positioning signal source.
40. A system according to claim 39, wherein said positioning signal
source is a location server configured to communicate with said
mobile terminal through said radio network.
41. A system according to claim 39, wherein said positioning signal
source is a positioning system satellite.
42. A system according to claim 41, wherein said satellite is a GPS
satellite.
43. A system according to claim 39, wherein said positioning signal
source is a terrestrial signal transmitter.
44. A system according to claim 30, wherein said database employs a
caching strategy.
45. A system according to claim 44, wherein said caching strategy
is selected from the group consisting of: least recently used,
first-in first-out, and random discard.
46. A communication system comprising: a radio network comprising a
plurality of base stations, each said base station serving a cell
in said radio network; a database comprising data representing a
plurality of geographic positions; a mobile terminal configured to
receive communication signals from said radio network, said
communication signals comprising data representing a current cell
identification number corresponding to an associated one of said
cells in which said mobile terminal is located; and a location
server configured to communicate with said mobile terminal through
said radio network and to identify an approximate geographic
position of said mobile terminal by accessing said database, said
approximate position corresponding to one of said geographic
positions associated in said database with data representing said
current cell identification number.
47. A system according to claim 46, wherein said mobile terminal is
configured to compute a current geographic position based on data
comprising said approximate position.
48. A system according to claim 47, wherein said server is
configured to update said database with said current geographic
position, said current geographic position being associated in said
database with said current cell identification number.
49. A system according to claim 47, wherein said mobile terminal is
configured to compute said current geographic position at a
predefined time interval.
50. A system according to claim 47, wherein said mobile terminal is
configured to compute said current geographic position when mobile
terminal moves from a first cell to a second cell.
51. A system according to claim 47, wherein said mobile terminal is
configured to compute said current geographic position in response
to a request from application software.
52. A system according to claim 47, wherein said mobile terminal is
configured to compute said current geographic position in response
to a request received from said radio network.
53. A system according to claim 46, and wherein said mobile
terminal is configured to compute a current geographic position
based on data comprising said approximate position and at least one
positioning signal from at least one positioning signal source.
54. A system according to claim 53, wherein said positioning signal
source is a positioning system satellite.
55. A system according to claim 54, wherein said satellite is a GPS
satellite.
56. A system according to claim 53, wherein said positioning signal
source is a terrestrial signal transmitter.
57. A system according to claim 46, wherein said database employs a
caching strategy.
58. A system according to claim 57, wherein said caching strategy
is selected from the group consisting of: least recently used,
first-in first-out, and random discard.
59. A method of determining the geographic location of a mobile
terminal comprising: creating a database comprising data
representing a plurality of geographic positions; identifying a
current cell identification number corresponding to a cell in which
said mobile terminal is located; and determining said geographic
location based on data comprising one of said geographic positions
associated in said database with data representing said current
cell identification number.
60. A method according to claim 59, wherein said database is stored
in said mobile terminal.
61. A method according to claim 59, wherein said database is stored
in a location server configured to communicate with said mobile
terminal through a radio network.
62. A method according to claim 59, wherein said current cell
identification number is identified based on data received by said
mobile terminal from a radio network.
63. A method according to claim 59, wherein said geographic
position is determined by a processor in said mobile terminal.
64. A method according to claim 63, wherein said processor is
configured to compute said geographic position in response to a
request from application software.
65. A method according to claim 63, wherein said processor is
configured to compute said geographic position in response to a
request received from a radio network.
66. A method according to claim 59, wherein said geographic
position is determined by a location server configured to
communicate with said mobile terminal through a radio network.
67. A method according to claim 59, wherein said data further
comprises at least one positioning signal from at least one
positioning signal source.
68. A method according to claim 67, wherein said positioning signal
source is a location server configured to communicate with said
mobile terminal through a radio network.
69. A method according to claim 67, wherein said positioning signal
source is a positioning system satellite.
70. A method according to claim 69, wherein said satellite is a GPS
satellite.
71. A method according to claim 67, wherein said positioning signal
source is a terrestrial signal transmitter.
72. A method according to claim 59, wherein said data further
comprises data selected from the group consisting of satellite
orbits, time estimates, and ephemeris.
73. A method according to claim 59, said method further comprising:
updating said database with said geographic location.
74. A method according to claim 59, wherein said database employs a
caching strategy.
75. A method according to claim 74, wherein said caching strategy
is selected from the group consisting of: least recently used,
first-in first-out, and random discard.
76. A method according to claim 59, wherein said geographic
location is determined at a predefined time interval.
77. A method according to claim 59, wherein said geographic
location is determined when said mobile terminal moves from a first
cell to a second cell.
Description
BACKGROUND OF THE INVENTION
[0001] This invention relates to a mobile terminal including
geo-location capabilities, and to a system and method system for
determining the geographic location of a mobile terminal.
[0002] Increasingly, mobile terminals are equipped with positioning
receivers that derive geographic position information from external
sources, e.g. a satellite or radio network. Precise location
information is useful for a variety purposes in connection with a
mobile terminal. The location of the mobile terminal may, for
example, be used in determining the billing rate for a particular
telephone call based on a user's calling plan. Location information
is also useful in connection with a variety of ancillary services,
such as locating a user for providing emergency medical assistance,
e.g. in connection with a 911 emergency call, or providing location
information for nearby facilities such as gas stations, hotels,
etc.
BRIEF SUMMARY OF THE INVENTION
[0003] A mobile terminal consistent with the invention is provided
with a processor circuit configured to identify an approximate
geographic position of the mobile terminal by accessing a database
including data representing a plurality of geographic positions.
The approximate position corresponds to one of the geographic
positions in the database associated with data representing a
current cell identification number for a cell in which the mobile
terminal is located.
[0004] A communication system consistent with the invention
includes a radio network having a plurality of base stations, each
base station serving a cell in the radio network; a database
including data representing a plurality of geographic positions;
and a mobile terminal configured to receive communication signals
from the radio network. The communication signals include data
representing a current cell identification number corresponding to
an associated cell in which the mobile terminal is located. The
mobile terminal is configured to identify an approximate geographic
position of the mobile terminal by accessing the database. The
approximate position corresponds to one of the geographic positions
associated in the database with data representing the current cell
identification number. In another embodiment, a location server
configured to communicate with the mobile terminal through the
radio network may be configured to identify the approximate
geographic position.
[0005] A method of determining the geographic location of a mobile
terminal consistent with the invention includes: creating a
database including data representing a plurality of geographic
positions; identifying a current cell identification number
corresponding to a cell in which the mobile terminal is located;
and determining the geographic location based on data including at
least one of the geographic positions associated in the database
with data representing the current cell identification number.
BRIEF DESCRIPTION OF THE DRAWINGS
[0006] Advantages of the present invention will be apparent from
the following detailed description of exemplary embodiments
thereof, which description should be considered in conjunction with
the accompanying drawings, in which:
[0007] FIG. 1 is a block diagram of an exemplary system consistent
with the present invention;
[0008] FIG. 2 is a block diagram of an exemplary mobile terminal
consistent with the present invention;
[0009] FIG. 3 is a graphical representation of an exemplary
database consistent with the present invention;
[0010] FIG. 4 is a graphical representation of another exemplary
database consistent with the present invention;
[0011] FIG. 5 is a flowchart illustrating operation of exemplary
system consistent with the present invention;
[0012] FIG. 6 is a flowchart illustrating operation of another
exemplary system consistent with the present invention; and
[0013] FIG. 7 is a flowchart illustrating operation of yet another
exemplary system consistent with the present invention.
DETAILED DESCRIPTION OF THE INVENTION
[0014] With reference to FIG. 1, there is illustrated an exemplary
system 100 for locating a mobile terminal 110 consistent with the
present invention. For ease of explanation and to convey its
mobility, the mobile terminal 110 is graphically represented in
FIG. 1 by an illustration of an automobile. It is to be understood,
however, that the term "mobile terminal", as used herein, may
include a cellular radiotelephone with or without a multi-line
display; a Personal Communications System (PCS) terminal that may
combine a cellular radiotelephone with data processing, facsimile
and data communications capabilities; a PDA that can include a
radiotelephone, pager, Internet/intranet access, Web browser,
organizer, calendar and/or a positioning receiver, such as a GPS
receiver; and a conventional laptop and/or palmtop receiver or
other appliance that includes a radiotelephone transceiver.
[0015] Also, it should be understood that the principles of the
present invention may be applied to any cellular or wireless system
utilizing air interfaces, such as GSM, TDMA, CDMA or FDMA. It
should further be understood that the principles of the present
invention may be utilized in hybrid systems that are combinations
of two or more of the above air interfaces. In addition, a mobile
terminal, in accordance with the present invention, may be designed
to communicate with a base station transceiver using any standard
based on GSM, TDMA, CDMA, FDMA, a hybrid of such standards, or any
other standard.
[0016] As shown, a system 100 consistent with the invention may
include a radio network comprising a core network 102 and a radio
access network (RAN) 101. The RAN 101 may include a collection of
base stations 103, 104, 105, each of which serves a region or cell
106, 107, 108, respectively, in the network 101. An example of such
a network is a cellular telephone network, including commercially
operational networks based on well-known industry standards such as
GSM, TDMA or CDMA.
[0017] As will be described in greater detail below, a location
server 109 in the radio network may provide aiding data to the
positioning-enabled mobile terminal 110. This aiding data may be,
for example, data indicating the current cell in which the mobile
terminal is positioned. Other types of aiding data, e.g. satellite
ephemeris, time estimates, etc. may also be provided. The data may
be provided to improve the performance of the mobile terminal 110,
such as reducing time-to-first-fix (TTFF), or increasing the
sensitivity of the mobile terminal 110 so that signals from the
positioning satellite 112 (e.g. a GPS satellite) may be acquired by
the mobile terminal in difficult radio propagation environments.
Providing a position of the current cell of the mobile terminal 110
is helpful in this regard, even if the position is relatively
inaccurate (e.g. the geographical coordinates of the base
station).
[0018] The location server 109 may capture the aiding data from a
variety of sources, e.g. a GPS receiver 115 that is accessible
through a network or locally attached, as shown in FIG. 1. The
server 109 may have access either locally or through a network to a
database 111 containing cell position information, which it
delivers as aiding data based on the unique identity of the current
cell in which the requesting mobile terminal 110 resides.
[0019] A positioning application 113, e.g. a software program may
be provided either within or outside of the radio network. Also,
although the positioning application 113 in the illustrated
embodiment is external to the mobile terminal, it is to be
understood that the application may be stored in the mobile
terminal. An example of a positioning application is a
location-dependent information service (e.g. for locating the
nearest restaurant). Those skilled in the art will recognize a
variety of system architectures for employing a positioning
application. In one embodiment of the invention, for example, one
or more positioning applications may execute on one or more
application servers. If the positioning application 113 resides
outside of the network, it may communicate with the core network
102 through a particular gateway. In addition, the application 113
may also communicate with the location server 109 either through
the core network 102 or through an external network 114.
[0020] Turning now to FIG. 2, there is provided a block diagram of
an exemplary mobile terminal 200 consistent with the invention. For
ease explanation, the illustrated mobile terminal 200 comprises a
radiotelephone and positioning receiver in combination. Those
skilled in the art will recognize, however, that other functional
elements may be included in a mobile terminal consistent with the
invention. For example, a mobile terminal consistent with the
invention may also include a radiotelephone transmitter.
[0021] A radiotelephone portion of the terminal may include a
radiotelephone receiver 201, which receives information-bearing
signals from, for example, a radio network 202 via an antenna 203.
The radiotelephone receiver 201 may utilize a well-known
superheterodyne or homodyne architecture. Those skilled in the art
will recognize, however, that a variety of receiver types may be
incorporated into an embodiment consistent with the invention.
[0022] In the illustrated exemplary embodiment, the radiotelephone
receiver 201 filters and translates the information-bearing signal
to center its frequency spectrum at a low, or zero, frequency. This
signal may then be coupled to a communication processor (CoP) 204
in sampled and quantized format. The CoP 204 may extract the
information from the signal and process it consistent with the type
of information carried therein, e.g. speech or data. Optionally,
the CoP 204 may utilize an automatic frequency control (AFC) 212 to
adjust the receiver's frequency reference 205 (in the embodiment
shown, a temperature-controlled crystal oscillator) in order to
keep it tuned to the desired channel.
[0023] A positioning section of the mobile terminal 200 contains a
positioning receiver 206, which may receive positioning signals
from a plurality of positioning signal sources 207 via an antenna
208. While one or more GPS satellites, as shown in FIG. 2, are one
example of a positioning signals source, it is understood by those
skilled in the art that the positioning receiver may also receive
positioning signals, other satellite or terrestrial positioning
systems, or a combinations thereof. Also, the positioning receiver
206 may have many different embodiments, including the well-known
superheterodyne and homodyne architectures.
[0024] The down-converted signal from the positioning receiver 206
may be coupled to a positioning processor (PoP) 209 in sampled and
quantized format. The PoP 206 processes these signals to generate
the measurements required to compute a position estimate. In a GPS
receiver embodiment, this may involve correlating the incoming
signal with pseudonoise (PN) codes to determine time-of-transit
from the respective GPS satellites to the receiver 206.
[0025] A frequency synthesizer 211 may be provided for locking the
synthesized frequencies of the CoP 204 and/or the PoP 209 to the
frequency reference signal 205. In the embodiment shown, the
frequency synthesizer 211 is capable of providing a multiplicity of
local oscillators from a single reference source, such that the
local oscillator signals are simultaneously provided for several
concurrent operations (e.g. telephone signal reception and
transmission and GPS signal reception). Although a single frequency
synthesizer 211 is shared between the CoP and PoP in the
illustrated exemplary embodiment, other configurations are
possible. For example, the CoP and PoP may use separate
synthesizers.
[0026] The CoP 204 may include a processing unit, such as a
microprocessor or digital signal processor, and one or more
memories used to store software, e.g. a positioning application,
executed by the processor. Typical embodiments include non-volatile
memory containing the executable program and fixed data values, and
volatile random access memory (RAM) containing variable data values
stored and used by the program. In one embodiment of the present
invention, the CoP 204 is capable of updating the data values in
non-volatile memory, such as flash memory. The PoP 209 may have the
same architecture as the CoP 204, or, alternatively, the PoP 209
and the CoP 204 may be merged and share common program and/or data
memories.
[0027] In the illustrated embodiment, a location database 210, i.e.
a digital record that is stored in a volatile or non-volatile
memory, is included for storing location information, which may be
retrieved and utilized by the PoP 209 and/or the CoP 204. While the
database 210 in FIG. 2 is shown as being external to the PoP 209
and the CoP 204, the database may be stored in the memory of either
the PoP 209 or the CoP 204, as well as in a memory circuit
peripheral to both of these processor units but accessible by one
or both processors. An example of one such memory circuit is a
Subscriber Identity Module (SIM) used in Global System for Mobile
Communications (GSM) cellular phones.
[0028] The databases includes data representing a plurality of
geographic positions, each of which may be indexed by one or more
cell identification numbers (cell-IDs). Due to the general
limitation of resources in a GPS mobile terminal, which is
typically designed to minimize complexity to be a commercially
viable consumer product, the database may be of finite size and
relatively small with respect to the number of cells in radio
networks worldwide. Of course, the database may be more
comprehensive if size and cost considerations are not present.
Also, position information may be stored in a variety of formats,
including Cartesian earth-centered earth-fixed (ECEF) coordinates
or latitude/longitude/altitude.
[0029] FIG. 3 schematically illustrates an exemplary embodiment 300
of a database 210 consistent with the present invention. In the
illustrated embodiment, the database 300 comprises a plurality of
entries, each entry directly mapping a given position 302 of the
mobile terminal to a cell-ID 301. The current cell-ID may be
provided to the database by the mobile terminal, and the position
302 may be provided through the positioning processor, e.g.
processor 209. Each time the positioning processor computes a
position, the cell-ID of the current cell may be combined with the
position and stored in the database 300. Also, instead of updating
the database at every position fix, caching strategies such as
least recently used (LRU), first-in first-out (FIFO), random
discard, or other appropriate strategies may be used to keep the
size of the database within a boundary, thereby conserving database
resources.
[0030] The frequency of database updates may also be reduced in a
number of other ways. Prior to each update of the database, for
example, the processor accessing the memory where the database 210
is stored, e.g. the PoP 209 or the CoP 204, may check the database
for the existence of an entry for the current cell-ID. If an entry
already exists for the current cell-ID, then no update may be made.
Since positions are typically only approximate, any valid position
for a given cell-ID may be presumed to be as accurate as any
other.
[0031] In another embodiment, the processor may fill the database
with entries for each unique cell-ID encountered until it is full.
After the database is full, the processor may not overwrite
existing entries. With enough entries, the database will be
adequate for normal usage by many GPS mobile terminal users, with
the exception of highly mobile users. Also, the processor may add a
database entry only if the geographic distance for the current
cell-ID is more than a predefined distance from locations of
existing entries.
[0032] Another embodiment 400 involving the use of "one-to-many"
relationships, is illustrated in FIG. 4. As shown, the database 400
is divided into two tables: the position table 402, which contains
a plurality of mobile terminal positions 405; and the ID table 401,
which contains a plurality of cell-IDs 403 and a plurality of
indices 404 into the position table 402. Many cell-IDs 403 are thus
associated with a relatively small number of positions 405, thereby
exploiting the assumption that the required accuracy for the
estimated position is larger than the area covered by a single
cell.
[0033] The exemplary database 400 makes efficient use of limited
database storage space, for example, in the event a position
element 405 is large in relation to an index 404. The proportion of
space between the two tables should be selected based on average
expected cell size, position accuracy requirements, available
database space, and the amount of space required to hold entries
for each of the tables. While LRU, FIFO and other caching
strategies are still applicable in this embodiment, purging entries
and maintaining database consistency is more complicated due to the
"one-to-many" relationships. Thus, in view of the principle that
removing the minimum number of links retains the maximum amount of
information, one approach would be to select deletions based upon
the minimum number of links for an entry in the position table 402.
Consistent with this approach, the processor would check the
database 400 for consistency between tables each time an entry
deletion occurs in either table, ensuring that the processor
maintains data most likely to be needed when the mobile terminal
moves about a localized area.
[0034] Turning now to FIG. 5, there is shown the process flow for
an exemplary system consistent with the present invention. As
shown, the process is initiated by a request for position from an
application 501, e.g. a positioning application such as a
location-dependent information service or a network application for
requesting a geographic position. The application may request the
position 501 directly from the PoP, transparent to the CoP. After
receiving the request, the PoP sends a message 502 to the CoP
requesting the identity of the current radio network cell serving
the mobile terminal. The CoP responds 503 with the current cell-ID
information, and the PoP checks its location database 504 to
determine if it contains a position entry matching the cell-ID
identified by the CoP.
[0035] If the database contains a position entry matching the
current cell-ID, the PoP utilizes the position entry to compute a
current position estimate 508, e.g. using position information from
a positioning satellite. The PoP may also use other information
(e.g. satellite orbits and/or time estimate) in computing a
position estimate. Once the current position estimate is
calculated, the PoP returns 509 it to the requesting application
509. The PoP also updates 510 the database with the calculated
position estimate to provide the database with a new position entry
for the associated cell-ID.
[0036] If there is no position entry in the database corresponding
to the current cell-ID, the PoP may request assistance 505 from a
location server, e.g. server 109, which responds 506 with a
position corresponding to the cell-ID specified in the request from
the PoP. The PoP may request and the server may respond with other
information 507, such as the location of positioning signal
sources, e.g. orbits of GPS satellites. The PoP then utilizes this
information for the current position calculation 508, the result of
which is returned 509 by the PoP to the application and provided
510 to the database to provide and entry for the cell-ID.
[0037] FIG. 6 illustrates the process flow in another exemplary
embodiment consistent with the invention in which the position
request from the application is provided to the CoP. Those skilled
in the art will recognize a number of applications for such an
embodiment. One example would be an application including a
protocol between the mobile terminal and the radio network that is
executed by the CoP and includes the capability for query and
response of position information.
[0038] In the illustrated exemplary embodiment, the application
requests a position directly from the CoP 601. The CoP passes the
request 602 along with the identity of the current cell to the PoP.
The PoP checks its location database 603 to determine if it
contains an entry matching that cell-ID. If the database contains a
position entry matching the current cell-ID, the PoP utilizes the
position entry to compute a current position estimate 607, which it
returns 608 to the CoP. As discussed above, the position estimate
may be calculated based on position information derived from a
positioning satellite, and using other information, such as
satellite orbits or time estimates. The CoP returns 609 the
calculated position estimate to the requesting application, and the
PoP updates 610 the database with the calculated position estimate
to provide the database with a new position entry for the
associated cell-ID.
[0039] If there is no entry in the database corresponding to the
current cell-ID, then the PoP may request assistance 604 from a
location server, e.g. server 109, which responds 605 with a
position corresponding to the cell-ID specified in the request from
the PoP. The server may also respond with further information 606,
such as the location of positioning signal sources, e.g. orbits of
GPS satellites. The PoP then utilizes this information to compute
607 a current position estimate. The PoP returns 608 the position
estimate to the CoP, which, in turn, returns 609 the position
estimate to the requesting application. The PoP also uses this
position estimate or computed position to update its location
database 610 with a new position entry.
[0040] As discussed above, the location database 210 may reside in
the mobile terminal, i.e. it may be stored in the memory of either
the PoP 209 or the CoP 204, as well as in a memory circuit
peripheral to both of these processors. Interactions between the
elements similar to those described above might take place in an
alternate embodiment, in which the cell-indexed location database
is stored in the CoP. Thus, as the mobile terminal user roams about
the radio network, a cell-indexed location database capable of
aiding in position computation is built and updated.
[0041] The PoP (or the CoP, if it holds the database) may be
configured to obtain an initial position estimate from an external
source (e.g. server), even if it has a database entry for the
current cell. For example, if a one-to-many structure is employed
in the database, a single stored location may not provide
sufficient location information. The PoP may also be configured to
elect to update and refine the reference location associated with a
particular cell-ID by determining the most likely location of the
mobile terminal in the cell, such as by averaging multiple position
results computed in that cell.
[0042] A variety of additional embodiments or combination of
embodiments are possible. For example, instead of the mobile
terminal requesting assistance from a location server, as
illustrated in FIGS. 5 and 6, the mobile terminal may instead
compute the position on its own, e.g. in the PoP, using one or more
positioning signal sources, without assistance from a location
server. The computed position would be written into the database to
a position corresponding to the cell-ID.
[0043] Also, the CoP may be configured to routinely notify the PoP
when the mobile terminal is "handed off" to a new cell, or at a
predetermined time interval thereafter. In this configuration, the
PoP may then compute its own position using one or more positioning
signal sources, without assistance from a location server, and the
position may be written into the database next to the new cell-ID.
This embodiment would require that the mobile terminal have
sufficient hysterisis in its cell-handoff algorithm to ensure that
the position computed by the mobile terminal corresponds to the
correct cell. In another possible embodiment, the PoP may compute
the position on its own periodically, at a predetermined time
interval, using one or more positioning signal sources, without
assistance from a location server.
[0044] Turning again to FIG. 1, a location database 210a may
accessible and developed by the server, rather than the mobile
terminal. While the database 210a in FIG. 1 is shown as being
external to the server 109, the database may be stored in the
memory of the server 109, as well as in a memory circuit peripheral
to server but accessible to the server. An example of one such
memory circuit is a Subscriber Identity Module (SIM) used in Global
System for Mobile Communications (GSM) cellular phones.
[0045] FIG. 7 illustrates the operation of an exemplary embodiment
wherein the database 210a is developed in a memory that is directly
accessible by the server. In such an embodiment, a server requests
701 the position of the mobile terminal. The mobile terminal
computes 702 a position estimate, and returns 703 the position
estimate and identity of the current cell with which it is
communicating. The server then stores 704 this information in its
memory, which it can then use to assist other mobile terminals
calling from that cell. As subsequent mobile terminals respond with
other positions related to the particular cell, the server may
refine its estimate of the centroid of the cell relative to call
locations, for example, by averaging positions received from
multiple mobile terminals. This continually refined position
estimate may be fed back to mobile terminals requesting assistance
while in that cell. A method consistent with this embodiment thus
allows a server to provide position assistance without having prior
information regarding base station locations in the network.
[0046] Those skilled in the art will recognize that the present
invention may be embodied as cellular communication systems,
methods, and/or computer program products. Accordingly, the present
invention may be embodied in hardware and/or in software (including
firmware, resident software, micro-code, etc.). Furthermore, the
present invention may take the form of a computer program product
on a computer-usable or computer-readable storage medium having
computer-usable or computer-readable program code embodied in the
medium for use by or in connection with an instruction execution
system. In the context of this document, a computer-usable or
computer-readable medium may be any medium that can contain, store,
communicate, propagate, or transport the program for use by or in
connection with the instruction execution system, apparatus, or
device. The computer-usable or computer-readable medium may be, for
example, but not limited to, an electronic, magnetic, optical,
electromagnetic, infrared, or semiconductor system, apparatus,
device, or propagation medium. More specific examples (a
non-exhaustive list) of the computer-readable medium would include
the following: an electrical connection having one or more wires, a
portable computer diskette, a random access memory (RAM), a
read-only memory (ROM), an erasable programmable read-only memory
(EPROM or Flash memory), an optical fiber, and a portable compact
disc read-only memory (CD-ROM). It is noted that the
computer-usable or computer-readable memory could even be paper or
another suitable medium upon which the program is printed, as the
program can be electronically captured, via, for instance, optical
scanning of the paper or other medium, then compiled, interpreted,
or otherwise processed in a suitable manner, if necessary, and then
stored in a computer memory.
[0047] The embodiments that have been described herein, however,
are but some of the several which utilize this invention and are
set forth here by way of illustration but not of limitation. It is
obvious that many other embodiments, which will be readily apparent
to those skilled in the art, may be made without departing
materially from the spirit and scope of the invention.
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