U.S. patent application number 14/959952 was filed with the patent office on 2016-03-24 for indoor positioning using pressure sensors.
The applicant listed for this patent is QUALCOMM Incorporated. Invention is credited to Sai Pradeep Venkatraman.
Application Number | 20160084934 14/959952 |
Document ID | / |
Family ID | 45818491 |
Filed Date | 2016-03-24 |
United States Patent
Application |
20160084934 |
Kind Code |
A1 |
Venkatraman; Sai Pradeep |
March 24, 2016 |
INDOOR POSITIONING USING PRESSURE SENSORS
Abstract
The present disclose relates to position estimation in an indoor
environment. In one example, a location server may receive a
request for reference information from a wireless network device
located in the indoor environment. The location server may
determine a reference altitude and a reference pressure at the
wireless network device. The location server may transmit the
reference altitude and the reference pressure to the wireless
network device for the wireless network device to determine its
altitude in the indoor environment. The location server may also
determine a reference horizontal position, and transmit the
reference horizontal position to the wireless network device for
the wireless network device to determine its horizontal position in
the indoor environment.
Inventors: |
Venkatraman; Sai Pradeep;
(Santa Clara, CA) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM Incorporated |
San Diego |
CA |
US |
|
|
Family ID: |
45818491 |
Appl. No.: |
14/959952 |
Filed: |
December 4, 2015 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
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12885077 |
Sep 17, 2010 |
9234965 |
|
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14959952 |
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Current U.S.
Class: |
342/451 |
Current CPC
Class: |
G01C 21/34 20130101;
G01S 19/10 20130101; G01C 21/206 20130101; G09B 29/00 20130101;
G01S 5/0236 20130101; G01S 5/0257 20130101; G01S 19/48 20130101;
G08B 25/10 20130101; G01S 5/0252 20130101; G09B 29/10 20130101;
G01S 5/0045 20130101; G01C 5/06 20130101; G01C 21/20 20130101; G01S
5/0263 20130101; G01S 5/0063 20130101; G01S 19/46 20130101; G09B
29/008 20130101; G01C 21/08 20130101 |
International
Class: |
G01S 5/02 20060101
G01S005/02; G01S 5/00 20060101 G01S005/00 |
Claims
1. A method for position estimation, the method comprising:
receiving, by a location server, a request for reference
information from a wireless network device located in an indoor
environment; determining, by the location server, a reference
altitude and a reference pressure at the wireless network device;
and transmitting, by the location server, the reference altitude
and the reference pressure to the wireless network device for the
wireless network device to determine its altitude in the indoor
environment.
2. The method of claim 1, wherein said determining a reference
altitude and a reference pressure at the wireless network device
comprises: determining, by the location server, a reference
altitude and a reference pressure associated with a first access
point located in the indoor environment.
3. The method of claim 2, further comprising: determining, by the
location server, multiple pressure and altitude measurements from a
plurality of access points located in the indoor environment; and
transmitting, by the location server, the multiple pressure and
altitude measurements to the wireless network device for the
wireless network device to determine its altitude in the indoor
environment based, at least in part, on the multiple pressure and
altitude measurements.
4. The method of claim 2, wherein said determining the reference
altitude and the reference pressure associated with the first
access point comprises: transmitting, by the location server, a
message to the first access point requesting the first access point
to provide the reference altitude and the reference pressure
associated with the first access point; and receiving, by the
location server from the first access point, the reference altitude
and the reference pressure associated with the first access
point.
5. The method of claim 2, wherein said determining the reference
altitude and the reference pressure associated with the first
access point comprises: receiving, by the location server, the
reference pressure and the reference altitude from the first access
point that the first access point received from a second wireless
network device located in the indoor environment.
6. The method of claim 2, further comprising: determining, by the
location server, a reference horizontal position associated with
the first access point; and transmitting, by the location server,
the reference horizontal position associated with the first access
point to the wireless network device for the wireless network
device to determine its horizontal position in the indoor
environment.
7. The method of claim 6, wherein said determining the reference
altitude, the reference pressure, and the reference horizontal
position associated with the first access point comprises:
receiving, by the location server, a rebroadcast from the first
access point of the reference pressure, the reference altitude, and
the reference horizontal position received from a second wireless
network device located in the indoor environment.
8. The method of claim 1, wherein said determining a reference
altitude and a reference pressure at the wireless network device
comprises: determining a reference altitude of the location server
and a reference pressure at the location server.
9. The method of claim 8, wherein the reference pressure is
determined using a pressure sensor of the location server.
10. The method of claim 1, further comprising: determining, by the
location server, a reference horizontal position, wherein said
determining the reference horizontal position includes one of:
determining, by the location server, a horizontal position of a
first access point located in the indoor environment; or
determining, by the location server, a horizontal position of the
location server.
11. The method of claim 10, further comprising: transmitting, by
the location server, the reference horizontal position to the
wireless network device for the wireless network device to
determine its horizontal position in the indoor environment.
12. The method of claim 1, wherein the location server receives the
request for reference information from the wireless network device
when a first access point located in the indoor environment is not
capable of determining a reference pressure associated with the
first access point.
13. The method of claim 1, further comprising: receiving, by the
location server, contextual information associated with the indoor
environment from the wireless network device; and determining, by
the location server, an altitude of the wireless network device
based, at least in part, on the contextual information.
14. The method of claim 13, wherein the contextual information
includes at least one member selected from the group consisting of
a building level where the wireless network device is located, a
name of a shop closest to the wireless network device, and an image
of the shop closest to the wireless network device.
15. The method of claim 1, further comprising: determining that a
first access point located in the indoor environment is not capable
of determining a reference pressure and a reference altitude
associated with the first access point; determining a pressure and
an altitude associated with a second wireless network device
located in the indoor environment; and using the pressure and the
altitude associated with the second wireless network device as the
reference pressure and the reference altitude of the first access
point.
16. The method of claim 15, further comprising: rebroadcasting the
pressure and the altitude associated with the second wireless
network device to a second access point located in the indoor
environment.
17. The method of claim 1, further comprising: transmitting a
request for reference information from a first access point located
in the indoor environment to a second access point located in the
indoor environment.
18. A location server comprising: a processor; and a memory to
store instructions, which when executed by the processor, cause the
location server to: receive a request for reference information
from a wireless network device located in an indoor environment;
determine a reference altitude and a reference pressure at the
wireless network device; and transmit the reference altitude and
the reference pressure to the wireless network device for the
wireless network device to determine its altitude in the indoor
environment.
19. The location server of claim 18, wherein the instructions that
cause the location server to determine a reference altitude and a
reference pressure at the wireless network device include
instructions that cause the location server to: determine a
reference altitude and a reference pressure associated with a first
access point located in the indoor environment.
20. The location server of claim 19, wherein the instructions,
which when executed by the processor, further cause the location
server to: determine multiple pressure and altitude measurements
from a plurality of access points located in the indoor
environment; and transmit the multiple pressure and altitude
measurements to the wireless network device for the wireless
network device to determine its altitude in the indoor environment
based, at least in part, on the multiple pressure and altitude
measurements.
21. The location server of claim 18, wherein the instructions,
which when executed by the processor, further cause the location
server to: determine a reference horizontal position based, at
least in part, on one of a horizontal position of a first access
point located in the indoor environment or a horizontal position of
the location server.
22. The location server of claim 21, wherein the instructions,
which when executed by the processor, further cause the location
server to: transmit the reference horizontal position to the
wireless network device for the wireless network device to
determine its horizontal position in the indoor environment.
23. The location server of claim 18, wherein the instructions that
cause the location server to determine a reference altitude and a
reference pressure at the wireless network device include
instructions that cause the location server to: determine a
reference altitude of the location server and a reference pressure
at the location server.
24. The location server of claim 23, further comprising a pressure
sensor configured to determine the reference pressure at the
location server.
25. The location server of claim 19, wherein the instructions,
which when executed by the processor, further cause the location
server to: determine a reference horizontal position associated
with the first access point; and transmit the reference horizontal
position associated with the first access point to the wireless
network device for the wireless network device to determine its
horizontal position in the indoor environment.
26. A non-transitory machine-readable storage medium having
instructions stored therein, which when executed by a processor
cause the processor to perform operations that comprise: receiving,
by a location server, a request for reference information from a
wireless network device located in an indoor environment;
determining, by the location server, a reference altitude and a
reference pressure at the wireless network device; and
transmitting, by the location server, the reference altitude and
the reference pressure to the wireless network device for the
wireless network device to determine its altitude in the indoor
environment.
27. The non-transitory machine-readable storage medium of claim 26,
wherein the operations for determining a reference altitude and a
reference pressure at the wireless network device further comprise:
determining, by the location server, a reference altitude and a
reference pressure associated with a first access point located in
the indoor environment.
28. The non-transitory machine-readable storage medium of claim 27,
wherein the operations further comprise: determining, by the
location server, multiple pressure and altitude measurements from a
plurality of access points located in the indoor environment; and
transmitting, by the location server, the multiple pressure and
altitude measurements to the wireless network device for the
wireless network device to determine its altitude in the indoor
environment based, at least in part, on the multiple pressure and
altitude measurements.
Description
RELATED APPLICATIONS
[0001] This application is a continuation of U.S. application Ser.
No. 12/885,077 filed on Sep. 17, 2010.
BACKGROUND
[0002] Embodiments of the inventive subject matter generally relate
to the field of navigation systems and, more particularly, to
indoor positioning using pressure sensors.
[0003] Positioning systems typically receive a set of signals
(e.g., navigation signals from satellites in the case of
satellite-based positioning systems, radio signals from access
points in the case of Wi-Fi based positioning systems, etc.) and
determine a user's position. The positioning systems can analyze
the received signals and determine timing information associated
with the received signals to determine the user's position. Various
techniques based on time of arrival, time difference of arrival,
trilateration, triangulation can be used to determine the user's
position.
SUMMARY
[0004] Various embodiments for position estimation in an indoor
environment are disclosed herein. In one embodiment, a request for
reference information is received by a location server from a
wireless network device located in an indoor environment. The
location server determines a reference altitude and a reference
pressure at the wireless network device. The location server
transmits the reference altitude and the reference pressure to the
wireless network device for the wireless network device to
determine its altitude in the indoor environment.
BRIEF DESCRIPTION OF THE DRAWINGS
[0005] The present embodiments may be better understood, and
numerous objects, features, and advantages made apparent to those
skilled in the art by referencing the accompanying drawings.
[0006] FIG. 1 is an example conceptual diagram illustrating indoor
positioning using pressure sensors
[0007] FIG. 2 is a flow diagram illustrating example operations of
an access point for providing pressure and location information to
a user device;
[0008] FIG. 3 is a flow diagram illustrating example operations of
an access point determining location information;
[0009] FIG. 4 depicts a flow diagram illustrating example
operations for determining location of a navigation device and
routing directions to a destination based on pressure sensors;
[0010] FIG. 5 is a continuation of FIG. 4 and depicts the flow
diagram illustrating example operations for updating the location
of a navigation device and the routing directions to the
destination based on detecting a pressure variation;
[0011] FIG. 6 is a flow diagram illustrating example operations of
a centralized location server enabling a user navigation device to
determine its location;
[0012] FIG. 7 is a block diagram of one embodiment of an electronic
device including a mechanism for indoor positioning using pressure
sensors; and
[0013] FIG. 8 is a block diagram of one embodiment of an access
point including a mechanism for enabling indoor positioning of a
navigation device.
DESCRIPTION OF EMBODIMENT(S)
[0014] The description that follows includes exemplary systems,
methods, techniques, instruction sequences, and computer program
products that embody techniques of the present inventive subject
matter. However, it is understood that the described embodiments
may be practiced without these specific details. For instance,
although examples refer to using wireless local area network (WLAN)
technologies for exchanging location and pressure information
between an access point and a user navigation device, embodiments
are not so limited. In other implementations, the location and
pressure information can be exchanged using other suitable
communication standards and technologies (e.g., ultrawide band
(UWB) communication, cellular communication, etc.). In other
instances, well-known instruction instances, protocols, structures,
and techniques have not been shown in detail in order not to
obfuscate the description.
[0015] A location-based navigation device utilizes precise vertical
positioning for navigation in a multi-level indoor environment
(e.g., in a multi-story building). For example, precise vertical
positioning may be utilized to enable a user at the ground level of
a mall to navigate to a shop on the second level of the mall.
GPS-based navigation devices typically have poor indoor performance
because navigation signals received from GPS satellites become
weakened after propagation through multiple walls and other
obstacles. The sensitivity of the GPS-based navigation devices may
not be high enough to acquire four or more GPS satellites with
relatively good geometry. The accuracy and availability of the GPS
satellites can also be poor at lower levels of a multi-story
building and error in determining the altitude of the navigation
device may be higher than the vertical separation between the
building levels. On the other hand, WLAN based positioning devices
typically use a time of arrival (TOA) method or a time difference
of arrival (TDOA) method to determine the location of the
navigation device. However, calculating a three-dimensional
location--namely a horizontal position (i.e., X-coordinate and
Y-coordinate) and an altitude (i.e., Z-coordinate) of the
navigation device can pose a challenge in the multi-level indoor
environment. This is because altitude estimates determined using
TOA or TDOA may not be very accurate especially if available access
points are on the same plane (i.e., at approximately the same
altitude) as the navigation device. Although altitude information
(e.g., a name of a shop closest to the navigation device, a
building level, an altitude, etc.) can be used to improve the
accuracy of vertical positioning, the user would need to know and
manually enter the altitude information. Errors in vertical
positioning (e.g., an error in determining the building level of
the destination) may result in the navigation device leading the
user to a wrong destination (e.g., a shop at a building level below
the actual building level of the destination). The errors in
vertical positioning may result in the user having to retrace
his/her steps, identify a nearest staircase/elevator/escalator, and
go to the correct building level before finally proceeding to the
destination.
[0016] In some embodiments, a pressure sensor can be incorporated
into the navigation device to improve accuracy of vertical
positioning of the navigation device and to enable determining a
more precise altitude of the navigation device. Because pressure
varies with altitude, different levels in a building (e.g., inside
a mall, a parking garage, etc.) can be identified based on pressure
variations at the different levels. Also, because the access points
are fixed, the altitude and the corresponding pressure at the
access points (preferably in the same environment as the navigation
device) can serve as a reference based on which the altitude of the
navigation device can be calculated. The relative pressure between
the reference pressure at the access points and the measured
pressure at the navigation device can be translated into a precise
altitude difference between the access points and the navigation
device, which can then be used to determine the altitude of the
navigation device. Furthermore, the navigation device can identify
and load a map of the building level on which a user of the
navigation device is, based on knowledge of the altitude of the
navigation device. The horizontal position of the navigation device
can be determined based on the calculated altitude of the
navigation device and based on location coordinates received from
the access points. Based on knowledge of the horizontal position
and the altitude of the navigation device, the navigation device
can determine a three-dimensional route to the destination with
precision. Configuring access points with pressure sensors to
provide reference altitude (and corresponding pressure information
to assist the navigation device) can improve accuracy associated
with estimating the altitude of the navigation device. This, in
turn, can improve precision of routing directions to the
destination.
[0017] FIG. 1 is an example conceptual diagram illustrating indoor
positioning using pressure sensors. FIG. 1 depicts a user
navigation device 102 and an access point (AP) 116. The user
navigation device 102 may be a dedicated GPS receiver or may be
another suitable electronic device (e.g., a mobile phone) with GPS
navigation functionality. The user navigation device 102 comprises
a pressure sensor 104, a location calculation unit 106, and a
routing unit 108. The access point 116 comprises a pressure sensor
122 and an access point positioning unit 120. In one example, the
access point 116 and the user navigation device 102 are located
within a building that comprises three levels--building level one
110, building level two 112, and building level three 114. In FIG.
1, the user navigation device 102 is at building level one 110, the
access point 116 is a fixed access point and is located at building
level two 116, and a destination 124 of the user navigation device
102 is at building level three 114.
[0018] At stage A, the pressure sensor 122 of the access point 116
determines a pressure at the access point 116 ("access point
pressure information"). In some implementations, the pressure
sensor 122 may determine the access point pressure information
every pre-defined interval of time. In another implementation, the
pressure sensor 122 may monitor the access point pressure
information and may record a new value of the pressure on
determining a change in the access point pressure information. In
another implementation, the pressure sensor 122 may determine the
access point pressure information in response to the access point
116 receiving a request from the user navigation device 102.
[0019] At stage B, the access point positioning unit 120 provides
an indication of the location of the access point 116 ("access
point location information") and the access point pressure
information. The access point location information may be a
two-dimensional position of the access point 116 (e.g., a latitude
and longitude) or a three-dimensional position of the access point
116 (e.g., a latitude, longitude, and altitude). In some
implementations, the access point positioning unit 120 may indicate
the altitude of the access point 116 in terms of an absolute
altitude (e.g., in meters, feet, etc.). In another implementation,
the access point positioning unit 120 may indicate the altitude of
the access point 116 in terms of a building level at which the
access point 116 is located. For example, with reference to FIG. 1,
the access point positioning unit 120 can indicate that the access
point 116 is located at building level 112. In one implementation,
the access point location information may be pre-programmed and the
access point positioning unit 120 can read a predetermined memory
address to determine the access point location information. In
another implementation, the access point positioning unit 120 may
estimate the access point location information based on location
information received from other network devices, as will be
described below. In another implementation, the access point
positioning unit 120 can determine the access point location
information using global position system (GPS) technologies, real
time locating, etc., as will be described with reference to FIG. 3.
In some implementations, the access point 116 can broadcast the
access point location information and the access point pressure
information at periodic intervals (e.g., in a beacon message). In
another implementation, the access point 116 can transmit the
access point location information and the access point pressure
information in response to receiving a request for the access point
location information and the access point pressure information from
the user navigation device 102. The access point location
information and the access point pressure information serve as
reference information for the user navigation device 102 to
calculate its altitude and horizontal position, as will be
described in stages C-E.
[0020] At stage C, the pressure sensor 104 of the user navigation
device 102 determines a pressure at the user navigation device 102.
In some implementations, the pressure sensor 104 may determine the
pressure at the user navigation device 102 every pre-defined
interval of time. In another implementation, the pressure sensor
104 may monitor the pressure at the user navigation device 102 and
may record a new value of the pressure on determining a change in
the pressure at the user navigation device 102. In other
implementations, the pressure sensor 104 can obtain multiple
pressure measurements and can calculate an average pressure at the
user navigation device 102. It is also noted that in some
implementations the user navigation device 102 may activate the
pressure sensor 104 on determining that the access point location
information and the access point pressure information were
received.
[0021] At stage D, the location calculation unit 106 of the user
navigation device 102 determines an altitude of the user navigation
device 102 based on the access point location information, the
access point pressure information, and the pressure at the user
navigation device 102. The location calculation unit 106 can
convert the pressure at the user navigation device (determined at
stage C) into an altitude of the user navigation device 102 as will
be described in FIG. 4. It is noted, however, that if the altitude
of the user navigation device 102 cannot be determined (e.g.,
because the access point location information, the access point
pressure information, and/or the pressure at the user navigation
device 102 are not available), various other techniques can be used
to determine the altitude of the user navigation device 102. For
example, contextual information (e.g., name or image of a shop
closest to the user navigation device, a building level associated
with the user navigation device, etc) provided by a user can be
used to query a centralized server (not shown) and to determine the
altitude of the user navigation device 102. As another example, the
location calculation unit 106 can use the contextual information in
conjunction with a map of the indoor environment (e.g., the
building) stored on the user navigation device 102 to determine the
altitude of the user navigation device 102. After the location
calculation unit 106 determines the altitude of the user navigation
device 102, the location calculation unit 106 can implement Wi-Fi
based positioning techniques (e.g., time difference of arrival
(TDOA), time of arrival (TOA), etc.) to determine a horizontal
position (e.g., x-coordinate and y-coordinate) of the user
navigation device 102. For example, the location calculation unit
106 can measure round trip transit times (e.g., time between
transmitting a request for location/pressure information to the
access point 116 and receiving a response from the access point
116) to the access points 116 in range of the user navigation
device 102. In some implementations, if the user navigation device
102 comprises a GPS receiver (not shown), horizontal position of
the user navigation device 102 can be determined using GPS
techniques (e.g., triangulation based on GPS signals received from
three or more GPS satellites).
[0022] At stage E, the routing unit 108 of the user navigation
device 102 determines routing directions to the destination 124.
The routing unit 108 can determine the routing directions to the
destination 124, based on the location of the destination 124 and
the location (i.e., the horizontal position and the altitude) of
the user navigation device 102. In some implementations, the
routing unit 108 may determine whether a map of the indoor
environment of the user navigation device (e.g., a map of the
building) is available. If so, the routing unit 108 can overlay the
routing directions on the map (e.g., present arrows highlighting a
route to the destination 124, etc.). Otherwise, the routing unit
108 can present text directions on the user navigation device 102.
For example, with reference to FIG. 1, the location calculation
unit 106 may determine that the user navigation device is currently
at building level 110. Consequently, the routing unit 108 can
determine whether a map of the building level 110 (depicting shops,
elevators, etc. at building level 110) is available. If so, the
routing unit can load the map of the building level 110 and can
overlay instructions for navigating from building level 110 to
building level 114. It is also noted that the pressure sensor 104
can continue to monitor the pressure at the user navigation device
102. On detecting a change in the pressure, the location
calculation unit 106, in conjunction with the pressure sensor 104,
can determine a new altitude of the user navigation device 102 and
the routing unit 108 can recalculate the routing directions to the
destination 124.
[0023] Although not depicted in FIG. 1, in some implementations,
the access point 116 may also comprise a temperature sensor. In
addition to providing the access point location information and the
access point pressure information, the access point 116 can also
provide an indication of the temperature at the access point 116.
The temperature at the access point 116 can serve as a reference
temperature. The location calculation unit 106 can use the
temperature at the access point 116 to calculate the altitude of
the user navigation device 102 with higher accuracy, as will be
described in FIG. 4.
[0024] FIG. 2 is a flow diagram ("flow") 200 illustrating example
operations of an access point for providing pressure and location
information to a user navigation device. The flow 200 begins at
block 202.
[0025] At block 202, a request for access point location
information and corresponding pressure information is received at
an access point. For example, in FIG. 1, the access point 116 can
receive the request for access point location information and
corresponding pressure information from the user navigation device
102. The flow continues at block 204.
[0026] At block 204, pressure at the access point is measured. For
example, the pressure sensor 122 can measure the pressure at the
access point 116. In some implementations, the pressure sensor 122
can determine the access point pressure information in response to
receiving the request at block 202. However, in other
implementations, the access point 116 may automatically trigger the
pressure sensor 122 to measure the pressure at the access point 116
after a pre-determined time interval elapses. In another
implementation, the access point 116 may retrieve previously
measured access point pressure information. The flow continues at
block 206.
[0027] At block 206, the access point location information is
determined. For example, the access point positioning unit 120 can
determine the access point location information. The access point
location information can comprise a horizontal position
(X-coordinate and Y-coordinate, latitude and longitude, etc.) and
an altitude of the access point 116. In some implementations, the
access point location information may be pre-defined and may be
stored in a location information database (not shown) or may be
hardwired as part of the access point 116. In another
implementation, the access point positioning unit 120 may determine
the access point location information using GPS techniques (as will
be further described below with reference to FIG. 3). In another
implementation, the access point positioning unit 120 may estimate
the access point location information based on location information
received from other wired/wireless network devices in the vicinity
of the access point 116. For example, as will be further described
below, the access point positioning unit 120 may receive location
information from WLAN devices through a viral broadcast. The flow
continues at block 208.
[0028] At block 208, the access point location information and the
access point pressure information are provided to the user
navigation device. For example, the access point 116 can provide
the access point location information and the access point pressure
information to the user navigation device 102. In some
implementations, the access point 116 can provide the access point
location information and the access point pressure information in
response to a request (e.g., the request received at block 202)
from the user navigation device 102. In another implementation, the
access point 116 can broadcast the access point location
information and the access point pressure information every
pre-determined interval of time (e.g., in a beacon frame). It is
noted that in some implementations, the access point 116 may only
transmit the altitude (and not the horizontal position) of the
access point and the pressure at the access point to the user
navigation device. From block 208, the flow ends.
[0029] Although not described in FIG. 2, it is noted that because
atmospheric pressure fluctuates with weather conditions (e.g.,
temperature, humidity, etc.), the access point 116 can execute
operations to ensure that the access point pressure information
provided to the user navigation device 102 is a most recent value
of the pressure at the access point 116. Prior to transmitting the
access point pressure information to the user navigation device
102, the access point 116 can read a timestamp associated with the
access point pressure information received from the pressure sensor
122. The access point 116 can calculate a time difference between
the timestamp and a current time. The access point 116 can transmit
the access point pressure information to the user navigation device
102 if the difference time is less than a predetermined time
threshold. The access point 116 can discard the access point
pressure information if the difference time is greater than the
predetermined time threshold. It is also noted that because the
atmospheric pressure can fluctuate with temperature, in some
implementations, the access point 116 can comprise a temperature
sensor. The access point 116 can trigger the temperature sensor to
determine the temperature at the access point 116 and can provide
access point temperature information (at block 208) along with the
access point location and pressure information to the user
navigation device 102. As will be described in FIG. 4, the
temperature at the access point 116 can be used to improve accuracy
in determining the altitude of the user navigation device 102.
[0030] In some implementations, the access point 116 may be unaware
of its location (e.g., because pre-programmed access point location
information is unavailable at the access point 116). In such cases,
if the access point 116 comprises a GPS receiver (or other location
detection unit), the access point 116 can determine the access
point location information as will be described in FIG. 3.
[0031] FIG. 3 is a flow diagram 300 illustrating example operations
of an access point determining location information. The flow 300
begins at block 302.
[0032] At block 302, it is determined that location information is
not available at the access point. For example, the access point
positioning unit 120 can determine that access point location
information is not available. In one implementation, the access
point positioning unit 120 can check the status of a flag to
determine whether the access point location information is
pre-programmed at the access point 116. In another implementation,
the positioning unit 120 can determine whether previously
calculated values of the access point location information are
available at the access point 116. The flow continues at block 304
if the access point positioning unit 120 determines that the access
point location information is not available at the access point
116.
[0033] At block 304, it is determined whether the access point has
the ability to determine the access point location information. For
example, the access point positioning unit 120 can determine
whether the access point 116 comprises a GPS receiver or other
location detection module capable of determining the access point
location information. In some embodiments, the GPS receiver or
other location detection module may be implemented as part of the
positioning unit 120. In another embodiment, the GPS receiver or
other location detection module may be distinct from the access
point positioning unit 120. If it is determined that the access
point 116 has the ability to determine the access point location
information, the flow continues at block 306. Otherwise, the flow
continues at block 318.
[0034] At block 306, a loop begins for each location measurement at
the access point. For example, the access point positioning unit
120 initiates a loop to perform operations described in blocks
308-310 for each location measurement at the access point 116. A
location measurement is an estimate of the access point location
information (e.g., the horizontal position and the altitude of the
access point) at a specified time instant based on navigation
signals received at the specified time instant. The access point
positioning unit 120 can determine the access point location
information based on comparing different location measurements as
will be described in blocks 314-316. The access point positioning
unit 120 can obtain a set of location measurements based on
navigation signals received from visible navigation satellites to
determine the access point location information. In one
implementation, the navigation satellites may be global positioning
system (GPS) satellites. The access point positioning unit 120 can
obtain each location measurement at different instants of time to
account for movement of GPS satellites in the sky, visibility of
the GPS satellites and GPS satellite geometry at different instants
of time, etc. In one implementation, the access point positioning
unit 120 may obtain a predetermined number of location
measurements. In another implementation, the access point
positioning unit 120 may obtain a location measurement every
predetermined time interval to obtain the predetermined number of
location measurements. For example, the access point positioning
unit 120 may obtain a location measurement every 30 minutes until
the access point positioning unit 120 obtains 10 location
measurements. The flow continues at block 308.
[0035] At block 308, the location measurement is determined based
on navigation satellites visible at the access point. For example,
the access point positioning unit 120 can determine the location
measurement based on navigation satellites visible at the access
point 116. The access point positioning unit 120 can receive the
navigation signals from one or more visible navigation satellites.
The access point positioning unit 120 can use triangulation
techniques to obtain the location measurement (i.e., an estimate of
the position of the access point 116). For example, the access
point positioning unit 120 may receive GPS signals from visible GPS
satellites. The access point positioning unit 120 may determine
whether a sufficient number of GPS satellites are visible (e.g., 3
GPS satellites to estimate the horizontal position, 4 GPS
satellites to determine the horizontal position and the altitude of
the user navigation device, etc.). In some implementations, if an
insufficient number of GPS satellites are visible, the access point
positioning unit 120 may not obtain a location measurement at the
current time instant. Instead, the access point positioning unit
120 may wait for a predefined time interval (e.g., until the
geometry and position of the GPS satellites in the sky changes)
before obtaining another GPS measurement. The flow continues at
block 310.
[0036] At block 310, a measurement error associated with the
location measurement is calculated. For example, the access point
positioning unit 120 can calculate the measurement error associated
with the location measurement. Based on the position of the visible
GPS satellites (e.g., coordinates of the visible GPS satellites in
space), the access point positioning unit 120 can calculate a
dilution of precision (DOP) associated with the location
measurement. Dilution of precision is a measure of the effect of
GPS satellite geometry on the precision/accuracy of the location
measurement and of the quality of the GPS signals received from the
GPS satellites. The precision of the location measurement may be
affected by the position of the GPS satellites relative to each
other. For example, if visible GPS satellites are close together in
the sky, the geometry is considered to be weak and consequently a
dilution of precision value associated with the location
measurement may be high. A low dilution of precision value
associated with the location measurement can represent a high
accuracy of the location measurement (e.g., because of a wide
angular separation between the visible GPS satellites used to
obtain the location measurement). Obstacles (e.g., buildings,
foliage, etc.) in a line of sight path between the access point
positioning unit 120 and the visible GPS satellites may affect the
precision of the location measurement and consequently the dilution
of precision value associated with the location measurement. The
number of visible GPS satellites may also influence the precision
of the location measurement. In one implementation the access point
positioning unit 120 may calculate and monitor a vertical dilution
of precision (VDOP) because the location measurements typically
exhibit more fluctuation in altitude estimates than in horizontal
position estimates. For example, a high vertical dilution of
precision value can represent less certainty in the altitude
estimates solutions and indicate that the GPS satellites are at a
low elevation. It is noted that in other implementations, various
other techniques for estimating the measurement error associated
with the location measurement can be implemented. After the access
point positioning unit 120 determines the measurement error
associated with the location measurement, the flow continues at
block 312.
[0037] At block 312, it is determined whether additional location
measurements are to be obtained at the access point. For example,
the access point positioning unit 120 can determine whether
additional location measurements are to be obtained and analyzed at
the access point 116. As described above, the access point
positioning unit 120 can obtain a predetermined set of location
measurements. The access point positioning unit 120 can also obtain
a location measurement every predetermined time interval based on
GPS signals received from visible GPS satellites. At block 312, the
access point positioning unit 120 can determine whether the
predetermined set of location measurements have been obtained
and/or whether a pre-determined time duration during which location
measurements are to be obtained has elapsed. If it is determined
that additional location measurements are to be obtained, the flow
loops back to block 306 where a next location measurement is
determined and analyzed in accordance with the operations described
in blocks 308-310. If it is determined that a requisite number of
location measurements are already obtained, the flow continues at
block 314.
[0038] At block 314, a location measurement associated with a
smallest measurement error is identified. For example, the access
point positioning unit 120 can identify the location measurement
associated with the smallest measurement error. In one
implementation, the access point positioning unit 120 can compare
the dilution of precision value associated with each of the
location measurements and can identify the location measurement
associated with the smallest dilution of precision value. In
another implementation, the access point positioning unit 120 can
monitor the vertical dilution of precision value associated with
each of the location measurements, because the vertical dilution of
precision is a measure of the accuracy of the altitude component of
the location measurement. The access point positioning unit 120 can
identify the location measurement associated with the smallest
vertical dilution of precision value. In another implementation,
the access point positioning unit 120 can monitor the horizontal
dilution of precision value associated with each of the location
measurements. The horizontal dilution of precision is a measure of
the accuracy of the horizontal component of the location
measurement. The access point positioning unit 120 can identify the
location measurement associated with the smallest horizontal
dilution of precision value. The flow continues at block 316.
[0039] At block 316, the location measurement associated with the
smallest measurement error is stored as the access point location
information. For example, the access point positioning unit 120 can
store the location measurement associated with the smallest
measurement error as the access point location information. In one
implementation, the access point positioning unit 120 can designate
the altitude component of the location measurement (e.g.,
z-coordinate of a location measurement) associated with the
smallest vertical dilution of precision value (determined at block
314) as the altitude of the access point 116. The access point
positioning unit 120 can designate the horizontal component of the
location measurement (e.g., x-coordinate and y-coordinate of a
location measurement) associated with the smallest horizontal
dilution of precision value (determined at block 314) as the
horizontal position of the access point 116. It is noted that the
location measurement associated with the smallest vertical dilution
of precision value may be different from the location measurement
associated with the smallest horizontal dilution of precision
value. Once the altitude and the horizontal position of the access
point 116 are determined, the access point positioning unit 120 can
transmit the altitude and horizontal position as the access point
location information to the user navigation device 102.
Additionally, as described above, the access point positioning unit
120 can also transmit access point pressure (and temperature)
information. It is noted that the access point positioning unit 120
need not repeatedly perform operations described with reference to
flow 300 every time a request for access point location information
is received. The access point positioning unit 120 can access the
stored access point location information (determined at block 316)
and can provide the access point location information to the user
navigation device 102, a location server (not shown), and/or other
network devices that request the access point location information.
In some implementations, the access point positioning unit 120 may
re-execute the operations described with reference to FIG. 3 if the
access point 116 is reset or restarted. From block 316, the flow
ends.
[0040] At block 318, the access point location information is
determined from another network device. The flow moves from block
304 to block 318 if it is determined that the access point 116 does
not have the ability to determine the access point location
information (e.g., if the access point 116 does not comprise a GPS
receiver). In one implementation, the access point positioning unit
120 can receive a location of the user navigation device 102 in
response to a location request broadcasted to other network devices
in the vicinity of the access point 116. In another implementation,
the access point positioning unit 120 can receive the location of
the user navigation device 102 in a viral broadcast from the user
navigation device 102. The access point 116 can use the location of
the user navigation device 102 as the access point location
information. In another implementation, the access point 116 can
request the access point location information from a remote
location server. From block 318, the flow ends.
[0041] FIG. 4 and FIG. 5 depict a flow diagram 400 illustrating
example operations for determining location of a navigation device
and routing directions to a destination. The flow 400 begins at
block 402.
[0042] At block 402, an indication of access point location
information and corresponding pressure information is received from
an access point at a user navigation device. For example, with
reference to FIG. 1, the user navigation device 102 receives the
access point location information and the access point pressure
information from the access point 116. In one implementation, the
user navigation device 102 may receive the access point location
and pressure information in response to a request transmitted by
the user navigation device 102 to the access point 116. In another
implementation, the user navigation device 102 may receive the
access point location and pressure information in a periodically
broadcast message (e.g., a beacon message) from the access point
116. In one implementation, the user navigation device 102 (e.g.,
the location calculation unit 106 of the user navigation device
102) can broadcast a request message for access point location and
pressure information from all access points within a predefined
range of the user navigation device 102. The access points that
receive the request message can determine and transmit their
respective access point location and pressure information to the
user navigation device 102. In another implementation, the user
navigation device 102 can detect one or more access points within
the predefined range of the user navigation device 102 (e.g., based
on receiving beacon messages from the one or more access points).
The user navigation device 102 can transmit specific request
messages (e.g., as part of a probe request frame) to each of the
one or more detected access points. Accordingly, the one or more
access points that receive the request messages can transmit their
respective access point location and pressure information in a
response message (e.g., as part of a probe response message) to the
user navigation device 102. The flow continues at block 404.
[0043] At block 404, a pressure at the user navigation device is
measured. For example, the pressure sensor 104 of the user
navigation device 102 measures the pressure at the user navigation
device 102. In one implementation, the location calculation unit
106 can enable the pressure sensor 104 on receiving the access
point location and pressure information at block 402. In another
implementation, the location calculation unit 106 can trigger the
pressure sensor 104 to measure the pressure at the user navigation
device 102. In response, the pressure sensor 104 can determine the
pressure at the user navigation device 102. In some
implementations, the pressure sensor 104 can obtain a predefined
number of pressure measurements within a predefined measurement
duration and/or separated by a predefined time interval. The
location calculation unit 106 can calculate an average pressure at
the user navigation device 102 based on receiving the predefined
number of pressure measurements. As will be described below, the
pressure sensor 104 can continuously monitor the pressure, record a
new value of the pressure and cause operations described in the
flow 400 to be initiated on determining a change in the pressure at
the user navigation device 102. The relative pressure between the
access point 116 and the user navigation device 102 can be
translated into a precise altitude difference, which can then be
used to determine the altitude of the user navigation device 102 as
will be described below. The flow continues at block 406.
[0044] At block 406, an altitude of the user navigation device is
calculated based, at least in part, on the access point location
information, the access point pressure information, and the
pressure at the user navigation device. For example, the location
calculation unit 106 can calculate the altitude of the user
navigation device 102. Because ambient temperature influences the
access point pressure information, the location calculation unit
106 can also receive a temperature at which the access point
pressure information was determined. In other words, a temperature
sensor at the access point 116 can record the temperature at the
access point 116 and can provide the temperature at the access
point 116 to the user navigation device 102. The pressure,
temperature, and altitude at the access point 116 are considered to
be the reference pressure (P.sub.R) represented in Pascal, the
reference temperature (T.sub.R) represented in Kelvin (K), and the
reference altitude (h.sub.R) represented in meters, respectively.
Based on the reference pressure, the reference temperature, and the
reference altitude, the location calculation unit 106 can convert
the pressure (P) at the user navigation device 102 into an altitude
(h) of the user navigation device 102, as depicted in Eq. 1.
Additionally, in Eq. 1, L represents the temperature lapse rate and
has a value of -0.0065 K/m, go represents the gravitational
acceleration constant and has a value of 9.80665 m/s.sup.2, M
represents the molar mass of air and have a value of 0.0289644
kg/mol, and R represents the universal gas constant and has a value
of 8.31432 Nm/(molK).
P = P R [ T R T R + L ( h - h R ) ] g o M R L Eq . 1
##EQU00001##
[0045] It is noted that the Eq. 1 does not take dynamic pressure
due to motion of the user navigation device 102 into account. In
determining the altitude of the user navigation device 102 based on
Eq. 1, the location calculation unit 106 assumes that the velocity
of the user navigation device 102 in the indoor environment (e.g.,
the velocity of a pedestrian user) is too small to significantly
impact the pressure at the user navigation device 102. However, if
velocity of the user navigation device 102 is significant to cause
a significant fluctuation in the pressure at the user navigation
device 102, the location calculation unit 106 may prompt the user
of the user navigation device 102 to calibrate the pressure sensor
104 when the user navigation device 102 is stationary to mitigate
the impact of dynamic pressure on pressure measurements captured by
the pressure sensor 104. The flow continues at block 408.
[0046] At block 408, a horizontal position of the user navigation
device is determined. For example, the location calculation unit
106 can determine the horizontal position of the user navigation
device 102. In one implementation, as described with reference to
block 402 of FIG. 4, the location calculation unit 106 can receive
the access point location information from the access point 116. In
addition to the altitude of the access point 102 (used at block 406
to determine the altitude of the user navigation device 102), the
access point location information can also indicate a horizontal
position of the access point as Cartesian coordinates (e.g.,
X-coordinate and Y-coordinate), as latitude and longitudes, etc.
The location calculation unit 106 can measure round trip transit
times to the access point 116 (e.g., time between transmitting a
request for access point location information and receiving the
access point location information from the access point 116). The
location calculation unit 106 can calculate the horizontal position
of the user navigation device 106 based on the altitude of the user
navigation device 102 (determined at block 406) and based on
measured round-trip transit times to the access point 116. Prior to
calculating the horizontal position of the user navigation device
106, the location calculation unit 106 can determine the number of
available access points (e.g., the number of access points from
which the user navigation device 102 can receive access point
location information). Typically, to determine a three-dimensional
location of the user navigation device 102, the location
calculation unit 106 needs to receive access point location
information from at least four access points. However, because the
location calculation unit 106 already calculated the altitude of
the user navigation device (at block 406), the location calculation
unit 106 can determine the horizontal position of the user
navigation device 102 if at least three access points are
available. The location calculation unit 106 can implement a least
squares positioning algorithm, a time of arrival algorithm, a time
difference of arrival algorithm, etc., to calculate the horizontal
position of the user navigation device 102. In some
implementations, if less than three access points are available,
the location calculation unit 106 may estimate the horizontal
position of the user navigation device 102. For example, if only
two access points are available, the location calculation unit 106
can estimate the horizontal position of the user navigation device
102 by calculating a weighted average of coordinates of the
available access points. As another example, if only one access
point is available, the location calculation unit 106 can designate
the horizontal position of the access point 116 as the horizontal
position of the user navigation device 102. However, it is noted
that if the location calculation unit 106 does not receive the
access point location information, the location calculation unit
106 can determine the horizontal position and/or the altitude of
the user navigation device 102 (e.g., using GPS techniques) in
accordance with operations described with reference to FIG. 3. The
flow continues at block 410.
[0047] At block 410, routing directions to a destination are
determined based on the horizontal position of the user navigation
device and the altitude of the user navigation device. For example,
the routing unit 108 of the user navigation device 102 determines
routing directions to the destination 124 based on the location of
the user navigation device 102. The location of the user navigation
device 102 comprises the horizontal position of the user navigation
device 102 (determined at block 408) and the altitude of the user
navigation device 102 (determined at block 406). The routing unit
108 can use any suitable routing algorithm (e.g., distance vector
routing algorithm) to determine the routing directions from the
user navigation device 102 to the destination 124. The routing unit
108 may also determine the routing directions subject to various
constraints such as routing via a shortest path, routing via a
specified intermediate point (e.g., via a specified shop at an
intermediate point in the shopping mall), etc. The flow continues
at block 412.
[0048] At block 412, it is determined whether a map at the altitude
of the user navigation device 102 is available. For example, the
routing unit 108 determines whether the map of the indoor
environment at the altitude of the user navigation device 102 is
available. In one implementation, the routing unit 108 can convert
the altitude of the user navigation device 102 into building level
information. For example, based on knowledge that the floor to
ceiling distance in a building is 6 meters and that the altitude of
the user navigation device is 2 meters, the routing unit 108 can
determine that the user navigation device 102 is at the building
level 1 of FIG. 1. In another implementation, the location
calculation unit 106 may convert the altitude of the user
navigation device 102 into building level information and may
communicate the building level associated with the user navigation
device 102 to the routing unit 108. Accordingly, the routing unit
108 can determine whether a map corresponding to the building level
associated with the user navigation device 102 is available. In one
implementation, the routing unit 108 can access a map database of
the user navigation device 106 to determine whether the map
corresponding to the building level associated with the user
navigation device 102 is available. In another implementation, the
routing unit 108 can query a remote server to determine whether the
map corresponding to the building level associated with the user
navigation device 102 is available. If the map is available, the
routing unit 108 may download the map from the remote server and
may present the map on the user navigation device 102. It is noted
that if the map corresponding to the building level associated with
the user navigation device 102 is not available, the routing unit
108 may not present the map on the user navigation device 102.
Instead, the routing unit 108 may present step-by-step directions
from a current location of the user navigation device 102 to the
destination 124 (e.g., in a text format on the user navigation
device 102, as audio instructions, etc.). If it is determined that
the map that corresponds to the altitude of the user navigation
device available, the flow continues at block 414. Otherwise, the
flow continues at block 416 in FIG. 5.
[0049] At block 414, the map that corresponds to the altitude of
the user navigation device is identified and is presented on the
user navigation device. For example, the routing unit 108
identifies and presents the map that corresponds to the altitude of
the user navigation device 106. Additionally, the routing unit 108
may overlay routing directions and other information (e.g., shop
names at the shopping mall, etc.) on the map presented on the user
navigation device 106. The flow continues at block 416 in FIG.
5.
[0050] At block 416, it is determined whether a change in pressure
is detected at the user navigation device. In one implementation,
the pressure sensor 104 of the user navigation device 102 can
monitor the pressure at the user navigation device 102. The
pressure sensor 104 can transmit a notification (e.g., to the
location calculation unit 106) to indicate the change in the
pressure at the user navigation device 102. In another
implementation, the pressure sensor 104 may be a passive sensing
device. The pressure sensor 104 may obtain a pressure measurement
at the user navigation device 102 every predetermined interval of
time and may communicate the pressure measurement to the location
calculation unit 106. The location calculation unit 106, in turn,
can compare a current pressure measurement with a last received
pressure measurement and determine whether there was a change in
the pressure at the user navigation device 102. If a change in the
pressure at the user navigation device 106 is not detected, the
location calculation unit 106 can assume that the altitude of the
user navigation device 106 has not changed (i.e., that the user has
not moved to a different level within the building). Accordingly,
the location calculation unit 106 may only track the horizontal
position of the user navigation device 102 and may not recalculate
the altitude of the user navigation device 102. If a change in
pressure is detected at the user navigation device, the location
calculation unit 106 can assume that the altitude of the user
navigation device 106 has changed and the flow continues at block
418. Otherwise, the flow ends.
[0051] At block 418, a new altitude of the user navigation device
is calculated based, at least in part, on the access point location
information, the access point pressure information, and a new
pressure at the user navigation device 102. For example, the
location calculation unit 106 can calculate the new altitude of the
user navigation device 102 as described with reference to block 406
of FIG. 4. In some implementations, the user navigation device 102
may broadcast a new request for access point location and pressure
information. In another implementation, the location calculation
unit 106 can use previously received access point location and
pressure information to calculate the new altitude of the user
navigation device 102. The location calculation unit 106 can also
use the new altitude of the user navigation device 102 to calculate
and track the horizontal position of the user navigation device 102
as described with reference to block 408 of FIG. 4. The location
calculation unit 106 can provide the new altitude and a current
horizontal position of the user navigation device 102 to the
routing unit 108. The flow continues at block 420.
[0052] At block 420, it is determined whether the routing
directions to the destination should be updated. For example, the
routing unit 108 can determine whether the routing directions to
the destination 124 should be updated. The routing unit 108 can
determine whether the current horizontal position and the new
altitude of the user navigation device 102 are in accordance with
the route determined at block 410 of FIG. 4. If it is determined
that the routing directions to the destination should be updated,
the flow continues at block 422. Otherwise, the flow continues at
block 424.
[0053] At block 422, the routing directions to the destination are
updated and are presented on the user navigation device. For
example, the routing unit 108 can update the routing directions to
the destination 124 based on the current horizontal position and
the new altitude of the user navigation device 102. The routing
unit 108 can recalculate the routing directions to the destination
124 as described with reference to block 410 of FIG. 4. The routing
unit 108 can present the updated routing directions on the user
navigation device 102. The flow continues at block 424.
[0054] At block 424, it is determined whether a map at the new
altitude of the user navigation device is available. For example,
the routing unit 108 determines whether a map of the indoor
environment at the new altitude of the user navigation device 102
is available as described with reference to block 412 of FIG. 4. If
it is determined that the map that corresponds to the new altitude
of the user navigation device 102 is available, the flow continues
at block 426. Otherwise, the flow ends.
[0055] At block 426, the new map that that corresponds to the new
altitude of the user navigation device 102 is identified and is
presented on the user navigation device. For example, the routing
device 108 identifies and presents the new map on the user
navigation device 102 as described with reference to block 414 of
FIG. 4. From block 426, the flow ends.
[0056] It is noted that although FIG. 4 and FIG. 5 depict the flow
400 ending after the new map is presented on the user navigation
device 102 (at block 426) or after it is determined that the
pressure at the user navigation device was unchanged (at block
416), embodiments are not so limited. In some implementations, the
pressure sensor 104 can continue to monitor the pressure at the
user navigation device 102. On detecting a change in the pressure
at the user navigation device 102, the location calculation unit
106 can determine a new altitude of the user navigation device 102
as described in FIGS. 4 and 5.
[0057] It is noted that although FIGS. 1-5 describe a distributed
positioning system where access points in a building comprise
pressure sensors and are capable of transmitting reference location
and pressure information to the user navigation device 102,
embodiments are not so limited. In some embodiments, a centralized
positioning system may be implemented where the user navigation
device 102 may communicate with a centralized location server to
determine the location of the user navigation device 102 as will be
described with reference to FIG. 6. This can enable the user
navigation device 102 to determine its location when the access
points are legacy WLAN access points and/or have limited
capabilities (e.g., when the access points do not comprise pressure
sensors)
[0058] FIG. 6 is a flow diagram 600 illustrating example operations
of a centralized location server enabling a user navigation device
to determine its location. The flow 600 begins at block 602.
[0059] At block 602, a request for reference location and pressure
information is received at a location server from a user navigation
device. For example, the location server (not shown in FIG. 1) can
receive the request from the user navigation device 102 of FIG. 1.
The user navigation device 102 can establish a connection to the
location server and can transmit the request for the reference
location and pressure information to the location server. In one
implementation, the user navigation device 102 may transmit the
request for the reference location and pressure information to a
location server if one or more access points do not comprise a
pressure sensor. In another implementation, the user navigation
device 102 may communicate with the location server for security
purposes (e.g., as part of a communication protocol, to protect the
location of the access points, etc.). The flow continues at block
604.
[0060] At block 604, it is determined whether the location server
is in the same environment as the access points. For example, the
location server may determine whether the location server is in the
same building as the access points 116 and the user navigation
device 102, in a controlled environment that mirrors the
environment in which the access points are located, etc. The
location server may check the status of a flag to determine whether
the location server in the same environment as the access points.
For example, flag=0 can indicate that the location server is the
same environment as the access points. If it is determined that the
location server in the same environment as the access points 116
and the user navigation device 102, the flow continues at block
606. Otherwise, the flow continues at block 612.
[0061] At block 612, location and pressure information associated
with one or more access points is retrieved. The flow 600 moves
from block 604 to block 612 on determining that the location server
is not in the same environment as the access points and the user
navigation device 102. In some implementations, the location server
can provide a last known reference access point location and
pressure information to the user navigation device. In another
implementation, the location server can transmit a message to the
access points requesting a current access point location and
pressure information. In another implementation, the location
server can communicate with another server collocated with the
access points to determine the access point location and pressure
information for each of the access points. It is noted that in some
implementations, the access points may not comprise pressure
sensors. In such a situation, the pressure at the access points may
be pre-programmed (e.g., during an access point installation stage)
at the access point and/or at the location server. In some
implementations, access points that are equipped with pressure
sensors can communicate the access point pressure information to
the location server. The one or more access points may not directly
transmit the access point location and pressure information to the
user navigation device 102 if the access points are unable to
communicate with the user navigation device (e.g., because of
software or protocol limitations, security concerns, etc.). In some
implementations, the location server may provide only one reference
pressure value and the corresponding reference altitude to enable
the user navigation device 102 to calculate its altitude. In
another implementation, the location server can provide multiple
reference pressure values and the corresponding altitude to the
user navigation device 102. The user navigation device 102, in
turn, can determine an altitude measurement corresponding to each
combination of the reference pressure and reference altitude. The
user navigation device 102 can calculate an average of the multiple
altitude measurements to determine the altitude of the user
navigation device 102. The flow continues at block 614.
[0062] At block 606, a pressure at the location server is
determined. The flow 600 moves from block 604 to block 606 on
determining that the location server is in the same environment as
the access point 116. The location server being in the same
environment as the access points can indicate that the pressure
measured at the location server can be provided as a reference
pressure instead of the pressure at the access point 116. A
pressure sensor implemented on the location server can be enabled
and the pressure sensor can determine the pressure at the location
server as described with reference to block 202 of FIG. 2. The flow
continues at block 608.
[0063] At block 608, an altitude of the location server is
determined. In one implementation, the location server may
determine a pre-programmed altitude of the location server. In
another implementation, the location server can comprise a GPS
receiver and can determine the altitude of the location server (as
described with reference to FIG. 3) based on GPS signals received
from GPS satellites. The altitude of the location server can be
provided as a reference altitude that corresponds to the reference
pressure determined at block 606. The location calculation unit 106
of the user navigation device 102 can determine the altitude of the
user navigation device based, in part, on the reference pressure
(determined at block 606) and the reference altitude (determined at
block 608) as described with reference to FIGS. 4-5. The flow
continues at block 610.
[0064] At block 610, location information associated with one or
more access points is retrieved. For example, as described above
with reference to block 612, the location server can retrieve the
location information associated with one or more access points. The
location information may comprise a horizontal position of the
access points and an altitude of the access points. The flow
continues at block 614.
[0065] At block 614, the reference location and pressure
information are transmitted to the user navigation device. The flow
600 moves from block 610 to block 614 on determining the pressure
and altitude of the location server and after the location
information associated with one or more access points is retrieved.
The flow 600 moves from block 612 to block 614 after the reference
location and pressure information associated with one or more
access points are retrieved. As described above, the user
navigation device 102 can use the reference location and pressure
information to calculate the horizontal position and the altitude
of the user navigation device 102. From block 614, the flow
ends.
[0066] It should be understood that the depicted diagrams (FIGS.
1-6) are examples meant to aid in understanding embodiments and
should not be used to limit embodiments or limit scope of the
claims. Embodiments may perform additional operations, fewer
operations, operations in a different order, operations in
parallel, and some operations differently. For example, although
FIG. 6 describes the location server providing access point
location and pressure information to the user navigation device,
and the user navigation device 102 calculating its horizontal
position and altitude, embodiments are not so limited. In some
implementations, the user navigation device 102 can transmit
radio-signal measurements and the pressure at the user navigation
device to the location server. The location server can receive
reference location and pressure information from the access points
and can calculate the altitude and the horizontal position of the
user navigation device 102. The location server can communicate the
altitude and the horizontal position of the user navigation device
102 to the user navigation device.
[0067] It is noted that although FIG. 3 describes the access point
116 executing operations for calculating access point location
information based on identifying a location measurement with the
smallest measurement error, embodiments are not so limited. In
other embodiments, the user navigation device 102 can execute
operations described with reference to FIG. 3 to determine location
of the user navigation device 102 ("user navigation device location
information"). The user navigation device 102 can then provide the
user navigation device location information to the access point
116. In one implementation, the user navigation device 102 can
broadcast the user navigation device location information and
corresponding pressure information to location-unaware access
points through a viral broadcast scheme. In the viral broadcast
scheme, the user navigation device 102 can broadcast the user
navigation device location information and corresponding pressure
information to any access point in the vicinity of the user
navigation device 102 without associating with the access point.
The access point that receives the user navigation device location
information and corresponding pressure information via the viral
broadcast scheme can use the information from the user navigation
device 102 as an approximation of the access point location and
pressure information. The access point 116 can rebroadcast the
received location and pressure information to other wireless
network devices (e.g., WLAN devices, other access points, a
location server, etc.). In another implementation, the user
navigation device 102 may only transmit the user navigation device
location information and corresponding pressure information to the
access point 116 with which the user navigation device 102 has
associated. The access point 116 can use the user navigation device
location information to determine whether calculated access point
location information is correct/valid. The access point 116 can
also use the user navigation device location information as the
access point location information if the access point 116 does not
have the ability to determine its location (e.g., if the access
point 116 does not comprise a GPS receiver).
[0068] It is noted that resolution and accuracy of the pressure
sensor can vary depending on internal temperature at the access
point 116 (e.g., temperature of the access point chip). Therefore,
in some implementations, the access point 116 can comprise a
temperature compensator. The temperature compensator can determine
the difference between the ambient temperature at the access point
116 and the internal temperature and compensate for the difference
in temperature. The access point 116 can then provide the
compensated ambient temperature as a reference temperature
(represented by T.sub.r in Eq. 1) to the user navigation device
102. In other implementations, the user navigation device 102 can
comprise the temperature compensator. The temperature compensator
at the user navigation device 102 can receive the reference
temperature from the access point 116. The temperature compensator
can compare the reference temperature with the temperature at the
user navigation device 102. If the reference temperature is
different from the temperature at the user navigation device 102,
the temperature compensator can compensate for the difference in
temperature.
[0069] In some implementations, the pressure sensor 104 of the user
navigation device 102 can identify whether the user navigation
device 102 is in an indoor or an outdoor environment based on the
pressure at the user navigation device 102. Once the user
navigation device 102 leaves the indoor environment, the calibrated
altitude of the user navigation device 102 may no longer be
accurate. Therefore, knowledge of whether the user navigation
device 102 is in the indoor environment or the outdoor environment
may be exploited to turn on/off the GPS receiver (if any) of the
user navigation device 102 to extend battery life or to turn off
the pressure sensor 104. The pressure sensor can also enable
detection of illegal entry to sealed doors, broken car windows,
cargo container breach, property theft, intruder detection, etc. by
detecting a sudden spike or dip in the pressure. If the pressure
sensor comprises a Wi-Fi communication interface, the pressure
sensor can trigger an alert via the Wi-Fi communication interface.
A GPS receiver or other positioning system if collocated with the
pressure sensor can provide location information with the
alert.
[0070] Lastly, it is noted that although FIGS. 1-6 depict the user
navigation device 102 calculating its altitude and horizontal
position based on reference pressure and reference location
information received from one or more access points, embodiments
are not so limited. In some implementations, cellular networks can
be used instead of (or in conjunction with) Wi-Fi access points to
enable the user navigation device 102 to calculate its altitude and
horizontal position. A pressure sensor at a cellular tower can
determine pressure at the cellular tower. The cellular tower can
communicate the determined pressure and corresponding altitude to
the user navigation device 102. The user navigation device 102 can
receive multiple sets of pressure and altitude information--each
from a different cellular tower and can calculate the altitude of
the user navigation device 102.
[0071] Embodiments may take the form of an entirely hardware
embodiment, an entirely software embodiment (including firmware,
resident software, micro-code, etc.) or an embodiment combining
software and hardware aspects that may all generally be referred to
herein as a "circuit," "module" or "system." Furthermore,
embodiments of the inventive subject matter may take the form of a
computer program product embodied in any tangible medium of
expression having computer usable program code embodied in the
medium. The described embodiments may be provided as a computer
program product, or software, that may include a machine-readable
medium having stored thereon instructions, which may be used to
program a computer system (or other electronic device(s)) to
perform a process according to embodiments, whether presently
described or not, since every conceivable variation is not
enumerated herein. A machine-readable medium includes any mechanism
for storing or transmitting information in a form (e.g., software,
processing application) readable by a machine (e.g., a computer). A
machine-readable medium may be a non-transitory machine-readable
storage medium, or a transitory machine-readable signal medium. A
machine-readable storage medium may include, for example, but is
not limited to, magnetic storage medium (e.g., floppy diskette);
optical storage medium (e.g., CD-ROM); magneto-optical storage
medium; read only memory (ROM); random access memory (RAM);
erasable programmable memory (e.g., EPROM and EEPROM); flash
memory; or other types of tangible medium suitable for storing
electronic instructions. A machine-readable signal medium may
include a propagated data signal with computer readable program
code embodied therein, for example, an electrical, optical,
acoustical, or other form of propagated signal (e.g., carrier
waves, infrared signals, digital signals, etc.). Program code
embodied on a machine-readable medium may be transmitted using any
suitable medium, including, but not limited to, wireline, wireless,
optical fiber cable, RF, or other communications medium.
[0072] Computer program code for carrying out operations of the
embodiments may be written in any combination of one or more
programming languages, including an object oriented programming
language such as Java, Smalltalk, C++ or the like and conventional
procedural programming languages, such as the "C" programming
language or similar programming languages. The program code may
execute entirely on a user's computer, partly on the user's
computer, as a stand-alone software package, partly on the user's
computer and partly on a remote computer or entirely on the remote
computer or server. In the latter scenario, the remote computer may
be connected to the user's computer through any type of network,
including a local area network (LAN), a personal area network
(PAN), or a wide area network (WAN), or the connection may be made
to an external computer (for example, through the Internet using an
Internet Service Provider).
[0073] FIG. 7 is a block diagram of one embodiment of an electronic
device 700 including a mechanism for indoor positioning using
pressure sensors. In some implementations, the electronic device
700 may be a dedicated user navigation device (e.g., a portable GPS
system) configured to determine the location of the user navigation
device and routing directions to a destination. In another
implementation, the electronic device 700 may be an electronic
device, such as a laptop, a netbook, a mobile phone, a personal
digital assistant (PDA), or other portable electronic systems,
which includes a navigation module or a navigation unit. The
electronic device 700 includes a processor unit 702 (possibly
including multiple processors, multiple cores, multiple nodes,
and/or implementing multi-threading, etc.). The electronic device
700 includes a memory unit 706. The memory unit 706 may be system
memory (e.g., one or more of cache, SRAM, DRAM, zero capacitor RAM,
Twin Transistor RAM, eDRAM, EDO RAM, DDR RAM, EEPROM, NRAM, RRAM,
SONOS, PRAM, etc.) or any one or more of the above already
described possible realizations of machine-readable media. The
electronic device 700 also includes a bus 710 (e.g., PCI, ISA,
PCI-Express, HyperTransport.RTM., InfiniBand.RTM., NuBus, AHB, AXI,
etc.), and network interfaces 704 that include at least one
wireless network interface (e.g., a WLAN interface, a
Bluetooth.RTM. interface, a WiMAX interface, a ZigBee.RTM.
interface, a Wireless USB interface, etc.).
[0074] The electronic device 700 also includes a navigation unit
720 comprising a location calculation unit 708 coupled to a routing
unit 712. In some implementations, the electronic device 700 can
also comprise a pressure sensor (not shown) coupled to the location
calculation unit 708. In another implementation, the location
calculator 708 may interface with an external pressure sensor to
determine the pressure at the electronic device 700. The location
calculation unit 708 can implement functionality to determine an
altitude and horizontal position of the electronic device 700 based
on reference pressure and altitude information received from access
points, and based on pressure measured at the electronic device
700, as described above with reference to FIGS. 1, 3-5. The routing
unit 712 can implement functionality to determine routing
directions to a destination, as described with reference to FIGS.
4-5. It is noted that, in some implementations, the location
calculation unit 708 and/or the routing unit 712 can be implemented
on a common chip or integrated circuit, on separate chips and then
coupled together, etc.
[0075] Any one of these functionalities may be partially (or
entirely) implemented in hardware and/or on the processor unit 702.
For example, the functionality may be implemented with an
application specific integrated circuit, in logic implemented in
the processor unit 702, in a co-processor on a peripheral device or
card, etc. Further, realizations may include fewer or additional
components not illustrated in FIG. 7 (e.g., video cards, audio
cards, additional network interfaces, peripheral devices, etc.).
The processor unit 702, the memory unit 706, and the network
interfaces 706 are coupled to the bus 710. Although illustrated as
being coupled to the bus 710, the memory unit 706 may be coupled to
the processor unit 702.
[0076] FIG. 8 is a block diagram of one embodiment of an access
point 800 including a mechanism for enabling indoor positioning of
a navigation device. In some implementations, the access point 800
may be a fixed access point. In another implementation, the access
point 800 may be a mobile access point. Furthermore, in some
implementations, the access point 800 may be a standalone access
point, an access point implemented within another electronic
device, etc. The access point 800 includes a processor unit 802
(possibly including multiple processors, multiple cores, multiple
nodes, and/or implementing multi-threading, etc.). The access point
800 includes a memory unit 806. The memory unit 806 may be system
memory (e.g., one or more of cache, SRAM, DRAM, zero capacitor RAM,
Twin Transistor RAM, eDRAM, EDO RAM, DDR RAM, EEPROM, NRAM, RRAM,
SONOS, PRAM, etc.) or any one or more of the above already
described possible realizations of machine-readable media. The
access point 800 also includes a bus 810 (e.g., PCI, ISA,
PCI-Express, HyperTransport.RTM., InfiniBand.RTM., NuBus, AHB, AXI,
etc.), and network interfaces 804 that include at least one
wireless network interface (e.g., a WLAN interface, a
Bluetooth.RTM. interface, a WiMAX interface, a ZigBee.RTM.
interface, a Wireless USB interface, etc.).
[0077] The access point 800 also includes an access point
positioning unit 808 coupled to the bus 810. In some
implementations, the access point 800 can also comprise a pressure
sensor (not shown) coupled to the access point positioning unit
808. In another implementation, the access point positioning unit
808 may interface with an external pressure sensor to determine the
pressure at the access point 800. The access point positioning unit
808 implements functionality to determine access point location
information associated with the access point 800, as described with
reference to FIGS. 1-3. Any one of these functionalities may be
partially (or entirely) implemented in hardware and/or on the
processor unit 802. For example, the functionality may be
implemented with an application specific integrated circuit, in
logic implemented in the processor unit 802, in a co-processor on a
peripheral device or card, etc. Further, realizations may include
fewer or additional components not illustrated in FIG. 8 (e.g.,
video cards, audio cards, additional network interfaces, peripheral
devices, etc.). The processor unit 802, the memory unit 806, and
the network interfaces 806 are coupled to the bus 810. Although
illustrated as being coupled to the bus 810, the memory unit 806
may be coupled to the processor unit 802.
[0078] While the embodiments are described with reference to
various implementations and exploitations, it will be understood
that these embodiments are illustrative and that the scope of the
inventive subject matter is not limited to them. In general,
techniques for indoor positioning using pressure sensors as
described herein may be implemented with facilities consistent with
any hardware system or hardware systems. Many variations,
modifications, additions, and improvements are possible.
[0079] Plural instances may be provided for components, operations,
or structures described herein as a single instance. Finally,
boundaries between various components, operations, and data stores
are somewhat arbitrary, and particular operations are illustrated
in the context of specific illustrative configurations. Other
allocations of functionality are envisioned and may fall within the
scope of the inventive subject matter. In general, structures and
functionality presented as separate components in the exemplary
configurations may be implemented as a combined structure or
component. Similarly, structures and functionality presented as a
single component may be implemented as separate components. These
and other variations, modifications, additions, and improvements
may fall within the scope of the inventive subject matter.
* * * * *