U.S. patent application number 11/567629 was filed with the patent office on 2007-08-30 for method and apparatus for maintaining integrity of long-term orbits in a remote receiver.
This patent application is currently assigned to GLOBAL LOCATE, INC.. Invention is credited to Matthew Riben, Frank van Diggelen.
Application Number | 20070200752 11/567629 |
Document ID | / |
Family ID | 39167410 |
Filed Date | 2007-08-30 |
United States Patent
Application |
20070200752 |
Kind Code |
A1 |
van Diggelen; Frank ; et
al. |
August 30, 2007 |
METHOD AND APPARATUS FOR MAINTAINING INTEGRITY OF LONG-TERM ORBITS
IN A REMOTE RECEIVER
Abstract
A method and apparatus for maintaining integrity of
long-term-orbit information used by a
Global-Navigation-Satellite-System or other positioning receiver is
described. The method comprises obtaining a predicted pseudorange
from a first set of long-term-orbit information possessed by a
positioning receiver; obtaining, at the positioning receiver from
at least one satellite, a measured pseudorange; determining
validity of the predicted pseudorange as a function of the
predicted pseudorange and the measured pseudorange; and excluding
from the long-term-orbit information at least a portion thereof
when the validity of the predicted pseudorange is deemed invalid.
Optionally, the method may comprise updating or otherwise
supplementing the long-term-orbit information with other orbit
information if the validity of the predicted pseudorange is deemed
invalid.
Inventors: |
van Diggelen; Frank; (San
Jose, CA) ; Riben; Matthew; (Cupertino, CA) |
Correspondence
Address: |
RAYMOND R. MOSER JR., ESQ.;MOSER IP LAW GROUP
1040 BROAD STREET
2ND FLOOR
SHREWSBURY
NJ
07702
US
|
Assignee: |
GLOBAL LOCATE, INC.
3190 S. Bascom, Suite 260
San Jose
CA
|
Family ID: |
39167410 |
Appl. No.: |
11/567629 |
Filed: |
December 6, 2006 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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11333787 |
Jan 17, 2006 |
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11567629 |
Dec 6, 2006 |
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09993335 |
Nov 6, 2001 |
7053824 |
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11333787 |
Jan 17, 2006 |
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09884874 |
Jun 19, 2001 |
6560534 |
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09993335 |
Nov 6, 2001 |
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09875809 |
Jun 6, 2001 |
6542820 |
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09884874 |
Jun 19, 2001 |
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11289959 |
Nov 30, 2005 |
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11567629 |
Dec 6, 2006 |
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10712807 |
Nov 13, 2003 |
6992617 |
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11289959 |
Nov 30, 2005 |
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Current U.S.
Class: |
342/357.31 ;
342/357.41; 342/357.42; 342/357.44; 342/357.48; 342/357.66;
342/385 |
Current CPC
Class: |
G01S 19/254 20130101;
G01S 19/27 20130101; G01S 19/05 20130101; G01S 19/20 20130101; G01S
19/258 20130101 |
Class at
Publication: |
342/357.01 ;
342/357.02; 342/385 |
International
Class: |
G01S 5/02 20060101
G01S005/02 |
Claims
1. A method, comprising: obtaining a predicted pseudorange from
long-term-orbit information possessed by a first receiver;
obtaining, at a second receiver from at least one satellite, a
measured pseudorange; determining validity of the predicted
pseudorange as a function of the predicted pseudorange and the
measured pseudorange; and excluding from the long-term orbit
information at least a portion of thereof when the validity of the
predicted pseudorange is deemed invalid.
2. The method of claim 1, wherein excluding at least a portion of
the long-term orbit information comprises: discarding long-term
orbit information associated with the at least one satellite from
which the measured pseudorange is obtained.
3. The method of claim 1, wherein determining validity of the
predicted pseudorange comprises: determining a difference between
the predicted pseudorange and the measured pseudorange, and wherein
excluding at least a portion of the long-term-orbit information
occurs when the difference satisfies a given threshold.
4. The method of claim 1, further comprising: performing the
functions of claim 1 periodically.
5. The method of claim 1, further comprising: supplementing the
long-term-orbit information with other orbit information when the
validity of the predicted pseudorange is deemed invalid.
6. The method of claim 5, wherein the other orbit information
comprises information selected from the group consisting of
broadcast ephemeris, and long-term-orbit information.
7. The method of claim 5, wherein supplementing the long-term-orbit
information with orbit information comprises: discarding the
long-term-orbit information in lieu of broadcast ephemeris.
8. The method of claim 5, wherein determining validity of the
predicted pseudorange comprises: determining a difference between
the predicted pseudorange and the measured pseudorange, and wherein
supplementing the long-term-orbit information with other orbit
information occurs when the difference satisfies a given
threshold.
9. The method of claim 5, further comprising: sending from the
first receiver a request for the other orbit information when the
validity of the predicted pseudorange is deemed invalid; and
receiving at the first receiver, in response to the request, the
other orbit information.
10. The method of claim 3, wherein the other orbit information is
more current than the long-term-orbit information.
11. The method of claim 5, wherein the other orbit information
comprises broadcast ephemeris obtained from the at least one
satellite.
12. The method of claim 5, wherein supplementing the
long-term-orbit information with the other orbit information
comprises: replacing all of the long-term-orbit information with
other long-term-orbit information.
13. The method of claim 1, wherein the first receiver is a remote
receiver, and wherein the second receiver is a reference
receiver.
14. The method of claim 1, wherein the first and second receivers
are the same receiver.
15. The method of claim 14, wherein the same receiver is a remote
receiver.
16. A method, comprising: (a) using long-term-orbit information to
determine, at a receiver, a first position of the receiver, wherein
the first position comprises at least one first location parameter;
(b) using satellite-navigation data transmitted from at least one
satellite to determine, at the receiver, a second position of the
receiver, wherein the second position comprises at least one second
location parameter; (c) determining a difference between (i) the at
least one first location parameter and (ii) the at least one second
location parameter; and (d) confirming that the long-term-orbit
information is valid when the difference satisfies a given
threshold.
17. The method of claim 16, wherein the at least one first location
parameter comprises a first parameter and a second parameter,
wherein the at least one second location parameter comprises a
third parameter and a fourth parameter; wherein the difference
comprises a first difference and a second difference; wherein the
first difference comprises a difference between the first and third
parameters, wherein the second difference comprises a difference
between the second and fourth parameters, and wherein confirming
that the long-term-orbit information is valid comprises confirming
that the first and second differences satisfy respective
thresholds.
18. The method of claim 17, wherein the first parameter is a first
altitude and the second parameter is any of first longitude and
first latitude, and wherein the third parameter is a second
altitude and the second parameter is any of a second longitude and
second latitude.
19. The method of claim 16, further comprising: performing (c) and
(d) responsive to a deviation between the first and second
positions.
20. The method of claim 16, wherein the at least one first location
parameter comprises any of a first longitude, first latitude, first
altitude and first common-mode error obtained from the
long-term-orbit information, and wherein the at least one second
location parameter comprises any of a second longitude, second
latitude, second altitude and second common-mode error obtained
from the satellite-navigation data transmitted from at least one
satellite.
21. The method of claim 20, wherein the at least one first location
parameter comprises a plurality of first locations parameters,
wherein the at least one second location parameter comprises a
plurality of second location parameters, and further comprising:
performing (c) and (d) using each of the pluralities of first and
second location parameters.
22. The method of claim 16, further comprising: excluding from the
long-term orbit information at least a portion of thereof when the
long-term orbit information is deemed invalid; obtaining other
orbit information from a device remotely located from the receiver;
and supplementing the long-term-orbit information with the other
orbit information when the validity of the predicted pseudorange is
deemed invalid.
23. The method of claim 22, wherein the other orbit information
comprises information selected from the group consisting of
broadcast ephemeris, and long-term-orbit information.
24. The method of claim 22, wherein supplementing the
long-term-orbit information with the other orbit information
comprises: replacing the long-term-orbit information with the other
orbit information.
25. The method of claim 24, further comprising: sending from the
receiver a request for the other orbit information when the
difference between satisfies the given threshold; and receiving at
the satellite-signal receiver, in response to the request, the
other orbit information.
26. The method of claim 22, wherein supplementing the
long-term-orbit information with the other orbit information
comprises: replacing the at least one first location parameter with
a third location parameter obtained from the other orbit
information when the difference satisfies a given threshold.
27. A receiver comprising: memory operable to store executable
instructions and long-term-orbit information; a processor operable
to obtain from the memory the executable instructions and operable
to execute the executable instructions to: obtain a predicted
pseudorange from the long-term-orbit information; obtain a measured
pseudorange from at least one satellite; determine validity of the
predicted pseudorange as a function of the predicted pseudorange
and the measured pseudorange; and exclude from the long-term-orbit
information at least a portion thereof when deeming the validity of
the predicted pseudorange is deemed invalid.
28. The receiver of claim 27, wherein the executable instructions
to exclude at least a portion of the long-term orbit information
comprises: executable instructions to discard long-term orbit
information associated with the at least one satellite from which
the measured pseudorange is obtained.
29. The receiver of claim 27, further comprising: executable
instructions to supplement the long-term-orbit information with
other orbit information when the validity of the predicted
pseudorange is deemed invalid.
30. The receiver of claim 29, wherein the other orbit information
comprises information selected from the group consisting of
broadcast ephemeris, and long-term-orbit information.
31. The receiver of claim 29, wherein executable instructions to
supplement the long-term-orbit information comprise: executable
instructions to discard the long-term-orbit information in lieu of
broadcast ephemeris.
32. The receiver of claim 27, wherein the executable instructions
to determine validity of the predicted pseudorange comprises
executable instructions to determine a difference between the
predicted pseudorange and the measured pseudorange, and wherein the
processor is operable to execute the executable instructions to
exclude at least a portion of the long-term-orbit information when
the difference satisfies a given threshold.
33. The receiver of claim 27, further comprising: a transceiver for
sending from the receiver a request for the other orbit information
when the validity of the predicted pseudorange is deemed invalid;
and for receiving at the receiver, in response to the request, the
other orbit information.
34. A system comprising: a receiver comprising: a first memory
operable to store executable instructions and long-term-orbit
information; and a first processor operable to obtain from the
first memory the executable instructions and operable to execute
the executable instructions to: use long-term-orbit information to
determine, at the receiver, a first position of the receiver,
wherein the first position comprises at least one first location
parameter; use satellite-navigation data transmitted from at least
one satellite to determine, at the receiver, a second position of
the receiver, wherein the second position comprises at least one
second location parameter; determine a difference between (i) the
at least one first location parameter and (ii) the at least one
second location parameter; and confirm that the long-term-orbit
information is valid when the difference satisfies a given
threshold; and a server comprising: a second memory operable to
store executable instructions, the long-term-orbit information and
other orbit information; and a second processor operable to obtain
from the second memory the executable instructions and operable to
execute the executable instructions to: provide to the receiver the
long-term-orbit information; and provide to the receiver the other
orbit information.
35. The system of claim 35, wherein the first processor is further
operable to execute the executable instructions to: exclude from
the long-term orbit information at least a portion of thereof when
the long-term orbit information is deemed invalid; and supplement
the long-term-orbit information with the other orbit information
when the validity of the predicted pseudorange is deemed
invalid.
36. The system of claim 36, wherein the other orbit information
comprises information selected from the group consisting of
broadcast ephemeris, and long-term-orbit information.
37. The system of claim 36, wherein the executable instructions to
supplement the long-term-orbit information with the other orbit
information comprise: executable instructions to replace the
long-term-orbit information with the other orbit information.
38. The system of claim 35, wherein the first parameter is a first
altitude and the second parameter is any of first longitude and
first latitude, and wherein the third parameter is a second
altitude and the second parameter is any of a second longitude and
second latitude.
39. The system of claim 35, wherein the first processor is further
operable to execute the executable instructions to determine the
difference and to confirm that the long-term-orbit information is
valid responsive to a deviation between the first and second
positions.
40. The system of claim 35, wherein the first processor is further
operable to execute the executable instructions to supplement the
at least one first location parameter with a third location
parameter obtained from the orbit information when the difference
satisfies a given threshold.
41. A system comprising: a receiver comprising: a first memory
operable to store executable instructions and a first set of
long-term-orbit information; and a first processor operable to
obtain from the first memory the executable instructions and
operable to execute the executable instructions to: use the first
set of long-term-orbit information to determine, at the receiver, a
first position of the receiver, wherein the first position
comprises at least one first location parameter; use
satellite-navigation data transmitted from at least one satellite
to determine, at the receiver, a second position of the receiver,
wherein the second position comprises at least one second location
parameter; and a server comprising: a second memory operable to
store executable instructions, the long-term-orbit information and
first and second sets of long-term-other orbit information; and a
second processor operable to obtain from the second memory the
executable instructions and operable to execute the executable
instructions to: provide to the receiver the first set of set of
long-term-orbit information; determine a difference between (i) the
at least one first location parameter and (ii) the at least one
second location parameter; confirm that the first set of
long-term-orbit information is valid when the difference satisfies
a given threshold; and provide to the receiver the second set of
long-term-other orbit information.
42. A system comprising: a first receiver comprising: a first
memory operable to store executable instructions and
long-term-orbit information; and a first processor operable to
obtain from the first memory the executable instructions and
operable to execute the executable instructions to: obtain a
predicted pseudorange from the long-term-orbit information
possessed by the first receiver; a second satellite-signal receiver
comprising: a second memory operable to store executable
instructions; and a second processor operable to obtain from the
second memory the executable instructions and operable to execute
the executable instructions to: obtain, from at least one
satellite, a measured pseudorange; a server comprising: a third
memory operable to store executable instructions, the
long-term-orbit information and other orbit information; and a
third processor operable to obtain from the third memory the
executable instructions and operable to execute the executable
instructions to: determine validity of the predicted pseudorange as
a function of the predicted pseudorange and the measured
pseudorange; and send to the first receiver the other orbit
information when the validity of the predicted pseudorange is
deemed invalid.
43. The system of claim 42, wherein the executable instructions to
determine validity of the predicted pseudorange comprise:
executable instructions to determine a difference between the
predicted pseudorange and the measured pseudorange, and wherein the
executable instructions to send to the first receiver the second
set of long-term-other orbit information occurs when the difference
satisfies a given threshold.
44. The system of claim 42, wherein the first receiver is a remote
receiver, and wherein the second receiver is a reference
receiver.
45. The system of claim 42, wherein the first and second receivers
are the same receiver.
46. The system of claim 45, wherein the same receiver is a remote
receiver.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a continuation-in-part application of
co-pending U.S. patent application Ser. No. 11/333,787, filed Jan.
17, 2006 (Attorney Docket GLBL 022P2), which is a
continuation-in-part application of co-pending U.S. patent
application Ser. No. 09/993,335, filed Nov. 6, 2001, which is a
continuation-in-part of U.S. patent application Ser. No.
09/884,874, filed Jun. 19, 2001, now U.S. Pat. No. 6,560,534, which
is a continuation-in-part of U.S. patent application Ser. No.
09/875,809, filed Jun. 6, 2001, now U.S. Pat. No. 6,542,820.
[0002] This application is also a continuation-in-part application
of co-pending U.S. patent application Ser. No. 11/289,959, filed
Nov. 30, 2005, which is a continuation of U.S. patent application
Ser. No. 10/712,807, filed 13 Nov. 2003, now U.S. Pat. No.
6,992,617.
[0003] This application contains subject matter that is related to
U.S. patent application Ser. No. 09/715,860, filed Nov. 17, 2000,
now U.S. Pat. No. 6,417,801. Each of the aforementioned related
patents and/or patent applications is herein incorporated by
reference.
BACKGROUND OF THE INVENTION
[0004] 1. Field of the Invention
[0005] The present invention generally relates to position-location
systems, and more particularly, to monitoring the integrity of
satellite-navigation data for a Global-Navigation-Satellite
System.
[0006] 2. Description of the Related Art
[0007] A Global-Navigation-Satellite-System (GNSS) receiver needs
satellite-navigation data, such as satellite orbits and clock
models, to compute distances to each of several satellites, which
in turn, may be used to compute a position of the GNSS receiver.
The distances are formed by computing time delays between
transmission and reception of satellite signals broadcast from
satellites in view of the GNSS receiver and received by the GNSS
receiver on or near the surface of the earth. The time delays
multiplied by the speed of light yield the distances from the GNSS
receiver to each of the satellites that are in view.
[0008] In some current implementations, the type of
satellite-navigation data acquired by the GNSS receiver is
broadcast ephemeris data (or simply broadcast ephemeris) and
broadcast satellite time, which are obtained by decoding
satellite-navigation messages contained within the satellite
signals. This broadcast ephemeris includes standard satellite
orbits and clock models, and the broadcast satellite time is an
absolute time associated with the entire constellation of
satellites. The GNSS receiver uses the broadcast satellite time to
unambiguously determine exact time of broadcast (e.g., by time
tagging the transmission and reception) for each of the satellite
signals.
[0009] With knowledge of the exact time of broadcast of each of the
satellite signals, the GNSS receiver uses the broadcast ephemeris
to calculate a satellite position for each of the satellites (i.e.,
where each of the satellites was) when it broadcast its
corresponding satellite signals. The satellite positions along with
the distances to the each of the satellites allow the position of
the GNSS receiver to be determined.
[0010] By way of example, a Global Positioning System (GPS)
receiver (i.e., one possible embodiment of the GNSS receiver) may
receive from each orbiting GPS satellites in view of the GPS
receiver a number of GPS signals that are formed using unique
pseudo-random noise (PN) codes. These PN codes are commonly known
as C/A codes, and each is used by the GPS receiver to uniquely
identify which of the GPS satellites broadcast such the GPS
signals. The GPS receiver determines the aforementioned time delays
by comparing time shifts between or otherwise correlating sequences
of (i) the PN codes of the broadcast GPS signals received at the
GPS receiver and (ii) replicas of the PN codes locally generated by
the GPS receiver.
[0011] At very low signal levels, the GPS receiver may obtain the
PN codes of the broadcast GPS signals to provide unambiguous time
delays by processing, and essentially averaging, many frames of the
sequences of the PN codes. These time delays are called
"sub-millisecond pseudoranges" because they are known modulo of the
1 millisecond boundaries of these frames. By resolving the integer
number of milliseconds associated with each of the time delays to
each of the satellite, then true, unambiguous pseudoranges may be
determined. The process of resolving the unambiguous pseudoranges
is commonly known as "integer millisecond ambiguity
resolution."
[0012] A set of four pseudoranges together with knowledge of (i)
the absolute times of transmissions of the GPS signals, and (ii)
satellite positions at such absolute times is sufficient to solve
for the position of the GPS receiver. The absolute times of
transmission are used for determining the positions of the
satellites at the times of transmission, and hence, for determining
the position of the GPS receiver.
[0013] Each of the GPS satellites move at approximately 3.9 km/s,
and thus, the range of such satellite, as observed from the earth,
changes at a rate of at most .+-.800 m/s. Errors in absolute may
result in range errors of up to 0.8 m for each millisecond of
timing error. These range errors produce a similarly sized error in
the GPS receiver position. Hence, absolute time accuracy of 10 ms
is sufficient for position accuracy of approximately 10 m. Errors
in the absolute timing of much more than 10 ms result in large
position errors, and so, current and prior implementations have
typically required the absolute time to have a minimum accuracy of
approximately 10 milliseconds.
[0014] Downloading the broadcast ephemeris from one or more of the
satellites is always slow (i.e., no faster than 18 seconds given
that the GPS satellite-navigation message is 900 bits in length and
broadcast in a 50 bit-per-second (bps) data stream). When in
environments in which the GPS signals have very low signal
strengths, downloading the broadcast ephemeris is frequently
difficult and sometimes impossible. Response to these obstacles,
some prior and current GPS implementations make use of a
terrestrial wireless or wired communication medium for transmitting
the broadcast ephemeris to a GPS. These GPS implementations are
commonly known as "Assisted-Global-Positioning Systems" or, simply,
AGPSs.
[0015] Recently, the GNSS began using the AGPS (or an AGPS-like
system) to provide to the GNSS receiver other types of assistance
information along with or instead of the broadcast ephemeris. This
assistance information may include acquisition-assistance
information to assist in acquiring the satellite signals; one or
more types of the satellite-navigation data, including, for
example, long-term orbit and clock models (collectively LTO
information), and any other information that the may be used to
acquire the satellite signals and/or determine the position of the
GNSS receiver.
[0016] To be able to acquire the satellite signals and/or determine
the position of the GNSS receiver with appropriate accuracy, the
GNSS receiver uses the assistance data only while it is valid. The
assistance data (regardless of its type) is valid for a given
amount of time or "validity period." For example, the validity
period for acquisition-assistance information is generally several
minutes. The validity period for the broadcast ephemeris is a few
(i.e., 2-4) hours. The validity period for the LTO information is
any amount of time greater than the validity period for the
broadcast ephemeris, and may be a few days, a week or more.
[0017] When the validity period expires, the assistance data has to
be retired and replaced with "fresh" assistance data. Using the
assistance data after its validity period expires may prevent
acquisition of the satellites and/or cause a significant amount of
error in a computed position of the GNSS receiver. Similarly, the
satellite-navigation data, such as the ephemeris and the LTO
information, may become invalid despite having an unexpired
validity period.
[0018] For example, a clock within a given satellite may have
drifted outside the expected range or an orbit of a given satellite
may have changed beyond an expected range (i) between the time that
the assistance data is delivered and used by the GNSS receiver,
and/or (ii) during the validity period of the assistance data.
Using such assistance data may prevent acquisition of the
satellites and/or cause a significant amount of error in a computed
position of the GNSS receiver.
[0019] Therefore, there exists a need in the art for a method and
apparatus that monitors and maintains the integrity of assistance
data delivered to a GNSS receiver.
SUMMARY
[0020] A method and apparatus for maintaining integrity of
long-term-orbit information used by a GNSS or other positioning
receiver is described. The method may include obtaining a predicted
pseudorange from a first set of long-term-orbit information
possessed by a positioning receiver; obtaining, at the positioning
receiver from at least one satellite, a measured pseudorange;
determining validity of the predicted pseudorange as a function of
the predicted pseudorange and the measured pseudorange; and
excluding from the long-term-orbit information at least a portion
thereof when the validity of the predicted pseudorange is deemed
invalid. Optionally, the method may comprise updating or otherwise
supplementing the long-term-orbit information with other orbit
information if the validity of the predicted pseudorange is deemed
invalid.
BRIEF DESCRIPTION OF THE DRAWINGS
[0021] So that the manner in which the above recited features of
the present invention can be understood in detail, a more
particular description of the invention, briefly summarized above,
may be had by reference to embodiments, some of which are
illustrated in the appended drawings.
[0022] It is to be noted that the Figures in the appended drawings,
like the detailed description, are examples. And as such, the
Figures and the detailed description are not to be considered
limiting, and other equally effective examples are possible and
likely. Furthermore, like reference numerals in the Figures
indicate like elements, and wherein:
[0023] FIG. 1 is a block diagram depicting an example of a position
location system;
[0024] FIG. 2 is a block diagram depicting an example of a receiver
for use with a Global-Navigation-Satellite System;
[0025] FIG. 3 is a block diagram depicting an example of a server
for use with a Global-Navigation-Satellite System;
[0026] FIG. 4 is a flow diagram depicting an example of a process
for monitoring the integrity of assistance data in use by one or
more receivers of a Global-Navigation-Satellite System;
[0027] FIG. 5 is a flow diagram depicting an example of a process
for identifying unhealthy satellites;
[0028] FIG. 6 is a flow diagram depicting another example of a
process for identifying unhealthy satellites;
[0029] FIG. 7 is a flow diagram depicting yet another example of a
process for identifying unhealthy satellites;
[0030] FIG. 8 is a flow diagram depicting an example of a process
for obtaining from a server integrity data and/or fresh aiding
data;
[0031] FIG. 9 is a flow diagram depicting another example of a
process for identifying unhealthy satellites;
[0032] FIG. 10 is a flow diagram illustrating an example of a
process for obtaining and using fresh aiding data; and
[0033] FIG. 11 is a flow diagram illustrating another example of a
process for obtaining and using fresh aiding data.
DETAILED DESCRIPTION
[0034] FIG. 1 is a block diagram depicting an example of a Global
Navigation Satellite System ("GNSS") 100. The GNSS 100 includes a
plurality or constellation of satellites for transmitting satellite
signals, as represented satellites 105, a GNSS receiver 104 for
receiving the satellite signals, and a server 102. The satellites
105, the GNSS receiver 104, the server 102, the GNSS 100 as a
whole, and functions, procedures, components and other details
provided herein may be tailored for any GNSS, including, for
example, the Global Positioning System ("GPS"), GALILEO, GLONASS,
SBAS (Space Based Augmentation System), QZSS (Quazi-Zenith
Satellite System), LAAS (Local Area Augmentation System) or some
combination thereof.
[0035] The GNSS receiver 104 may be in communication with the
server 102 via a communication link. This communication link may be
formed, for example, by communicatively coupling one or more nodes
of a network, such as a wireless communication system 106 (e.g.,
cellular telephone network) and/or other type of network 108,
including a packet-data network, such as the Internet, a
circuit-switched network, such as a PSTN, or a convergence of
both.
[0036] For purposes of clarity, the system 100 is shown with only
one GNSS receiver 104 and only one server 102. It is to be
understood, however, that the system 100 may include and/or be
deployed with a plurality of GNSS receivers and servers, and that
each of these additional GNSS receivers and servers may communicate
with the server 102 (and/or the additional servers) via respective
communication links.
[0037] In the GNSS 100, a position of the GNSS receiver 102 may be
determined, computed or otherwise formed as a function of the
satellite signals received from the satellites 105. For example,
the GNSS receiver 104 may acquire satellite signals broadcast by a
one or more satellites in a constellation (shown collectively as
the "satellites 105"), and may measure pseudoranges to one or more
(and typically four) of the satellites 105 to locate its unknown
position ("receiver position"). When configured for GPS, the GNSS
receiver 104 may, for example, measure pseudoranges to a plurality
of GPS satellites in the GPS constellation.
[0038] To assist in the acquisition of satellite signals, the
computation of the receiver position, or both, the GNSS receiver
104 may receive from the server 102 assistance data, which is
formed from, contains, derived from and/or is associated with or
otherwise garnered from the satellite signals. The GNSS receiver
104, in turn, may (i) use the assistance data, including one or
more expected or predicted pseudoranges (hereinafter "predicted
pseudoranges"), to assist in acquisition of the satellite signals;
(ii) measure actual pseudoranges from the satellite signals
("measured pseudoranges"); and (iii) transmit the measured
pseudoranges to the server 102 over the communication link, e.g.,
the wireless communication system 106.
[0039] The server 102 may use the measured pseudoranges to solve
for the unknown position of the GNSS receiver 104 (i.e., the
"receiver position"). The receiver position may be thereafter
transmitted to the GNSS receiver 104 via the communication link, or
made available to a third-party requester 199 via another manner,
such as through the Internet.
[0040] As an alternative, the GNSS receiver 104 may use the
measured pseudoranges to compute its own position (i.e., the
receiver position) without transmitting the pseudoranges to the
server 102. In this case, the GNSS receiver 104 uses the assistance
data to assist in acquisition of the satellite signals and/or the
computation of the receiver position.
[0041] To generate the assistance data, the server 102 uses various
broadcasted measurements and information associated with the
constellation, including for example, broadcast ephemeris, code
phase measurements, carrier phase measurements; Doppler
measurements, and the like. As noted, the broadcasted measurements
and information may be obtained directly from the satellite signals
and/or by decoding one or more satellite-navigation messages that
are broadcast from the satellites 105.
[0042] Alternatively, the server 102 may have to obtain or receive
the various broadcasted measurements and information from an
external source. This external source may be any device that
obtains and distributes the broadcasted measurements and
information, and may be, for example, embodied as reference network
110; a satellite control station 112, such as a Master Control
Station ("MCS") in GPS; or other source of such information, such
as a data store communicatively coupled to the Internet.
[0043] The reference network 110 may include a plurality of
tracking stations; each of which may include a satellite-signal
receiver (also known as a reference receiver). The plurality of
tracking stations collect and distribute, in one form or another,
the broadcasted measurements and information from all the
satellites in the constellation. Alternatively, the reference
network 110 may include a one or more tracking stations that
collect and distribute, in one form or another, such measurements
and information (i) from a subset of all the satellites in the
constellation or (ii) for one or more particular regions of the
world. Each of the aforementioned tracking stations is typically at
a known location. Details of one or more examples of a system for
distributing broadcasted measurements and information, such as the
broadcast ephemeris, is described in U.S. Pat. No. 6,411,892,
issued Jun. 25, 2002, which is incorporated by reference herein in
its entirety. Included within such details are one or more examples
of a reference network and corresponding tracking stations.
[0044] The assistance information generated by the server 102 may
include (i) acquisition-assistance information to assist in
acquiring the satellite signals such as code phase measurements,
carrier phase measurements; Doppler measurements, and the like;
(ii) one or more types of the satellite-navigation data, including,
for example, broadcast ephemeris and/or long-term orbit and clock
models (collectively LTO information), and (iii) any other
information that the may be used to acquire the satellite signals
and/or determine the receiver position.
[0045] In addition, the satellite-navigation data may include one
or more of the predicted pseudoranges and/or a model of such
predicted pseudoranges ("pseudorange model"). Accordingly, the
server 102 may obtain and distribute the predicted pseudoranges
and/or the pseudorange model. Details of one or more examples of a
system for distributing and using predicted pseudoranges and/or a
pseudorange model to acquire satellite signals is described in U.S.
Pat. No. 6,453,237, issued Sep. 17, 2002, which is incorporated by
reference herein in its entirety.
[0046] When the assistance data includes broadcast ephemeris and/or
LTO information, such as an LTO model, the server 102 and/or the
external source may obtain the broadcast ephemeris from the
satellites 105 (directly or indirectly), process the broadcast
ephemeris (if at all), and distribute the broadcast ephemeris
and/or LTO information to the GNSS receiver 104. Details of one or
more examples of systems and methods for obtaining, processing,
distributing and/or using the broadcast ephemeris and LTO
information, such as an LTO model, are described in co-pending U.S.
patent application Ser. Nos. 11/333,787, filed Jan. 17, 2006; Ser.
No. 09/993,335, filed Nov. 6, 2001; and U.S. Pat. Nos. 6,560,534
and 6,542,820, which as noted above, are incorporated herein by
reference in their entirety.
[0047] As above, the assistance data (regardless of its type) is
valid for its "validity period," which may be a short, medium, or
long amount or duration of time. The validity period for
acquisition-assistance information is generally several minutes.
The validity period for the broadcast ephemeris is a few (i.e.,
2-4) hours. The validity period for the LTO information is any
amount of time greater than the validity period for the broadcast
ephemeris, and may be a few days, a week or more. The assistance
data may also become invalid unexpectedly during its validity
period. This typically occurs when a satellite orbit or satellite
clock is adjusted during the validity period of the assistance
data.
[0048] Regardless of the type, content and/or format of the
assistance data, if (or when) the broadcasted measurements and
information upon which a current version of the assistance data is
based becomes invalid ("invalid assistance data"), then the GNSS
receiver 104 might not be able to adequately, if at all, acquire
the satellite signals and/or compute the receiver position using
such current assistance data. If, however, the GNSS receiver 104 is
able to acquire the satellite signals and/or compute the receiver
position using the invalid assistance data then accuracy of the
receiver position is more likely than not to be severely degraded.
To detect and potentially compensate for such situation, the server
102 and/or the GNSS receiver 104 may monitor and adjust for
deficiencies in the integrity of the assistance data in use by the
GNSS receiver 104 ("current assistance data").
[0049] As described in detail below, the server 102 may obtain the
broadcasted measurements and information, and generate, using such
broadcasted measurements and information, integrity data for use
with the assistance data. Alternatively the GNSS receiver 104 may
obtain from the server 102 (usually responsive to one or more
requests from the GNSS receiver 104) more recent or "fresh"
assistance data when the GNSS receiver 104 determines that the
current assistance data lacks integrity or is no longer valid, as
described below with respect to FIGS. 8, 10 and 11, for example.
The GNSS receiver 104 may do so notwithstanding that the
broadcasted measurements and information upon which the current
assistance data is deemed valid.
[0050] Typically, the broadcasted measurements and information
obtained by the server 102 is more up to date than the current
assistance data. The integrity data produced by the server 102, in
turn, may reflect this condition, and as such, may be transmitted
to the GNSS receiver 104, accordingly.
[0051] FIG. 2 is a block diagram depicting an example of a GNSS
receiver 200 for a GNSS. The GNSS receiver 200 may be used as the
GNSS receiver 104 shown in FIG. 1. The GNSS receiver 200
illustratively comprises a satellite signal receiver 202, a
wireless transceiver 204, a processor 206, a memory 208, and
optionally, a modem 210 (or other communication port or device).
The combination of the satellite signal receiver 202, the wireless
transceiver 204, and memory 208 may be contained within a mobile
station, such as a cellular phone, pager, laptop computer,
personal-digital assistant (PDA) and like type wireless device
known in the art.
[0052] The satellite signal receiver 202 comprises circuitry to
facilitate receiving and processing satellite signals in a
well-known manner. Typically, the satellite signal receiver 202
comprises a radio frequency (RF) front end 203 coupled to a
baseband processor 205. The satellite signal receiver 202 acquires
the satellite signals via the RF front end 203 and uses the
baseband processor 205 to generate pseudorange measurements (i.e.,
clock errors plus distances between the GNSS receiver 200 and the
satellites 105). Any form of a positioning module is useful in this
role. Examples of the satellite signal receiver 202 may be found in
any of the GL20000, Hammerhead and Marlin available from Global
Locate Inc. of San Jose, Calif., or the SiRFStarIII available from
SiRF Technology Holdings Inc. of San Jose, Calif. An exemplary AGPS
receiver that may be used with the invention is described in U.S.
Pat. No. 6,453,237. The pseudoranges measurements may be coupled to
the wireless transceiver 204 through the processor 206.
[0053] The processor 206 comprises a central processing unit
("CPU") 212, an input/output ("I/O") interface 214, support
circuits 218, and at least one bus or serial communication link
216. The CPU 210 may be one or more well-known processors or
microprocessors. The support circuits 216 comprise well known
circuits that facilitate operation of the CPU 212. The support
circuits 216 may comprise at least one of cache, power supplies,
clock circuits, and the like.
[0054] The bus or serial communication link 218 provides for
transmissions of digital information, including information
relating to determining the receiver position, among the CPU 212,
support circuits 216, memory 208, I/O interface 214, and other
portions of the GNSS receiver 200 (not shown).
[0055] The I/O interface 214 provides an interface to control the
transmissions of digital information to and from the GNSS receiver
200. The I/O interface 214 may interface with one or more I/O
devices, such as the modem 210, a keyboard, touch screen, and/or
other device.
[0056] The transceiver 204 may be used to communicate with the
wireless communication system 106 and/or the other type of network
108. Using the transceiver 204, the GNSS receiver 200 may obtain
from an external source, such as the server 102, assistance
information to assist in acquiring and processing the satellite
signals.
[0057] Examples of a combination of a satellite-signal receiver and
a transceiver, and an assistance server are provided in
commonly-assigned U.S. Pat. Nos. 6,411,892; 6,429,814; 6,587,789;
6,590,530; 6,703,972; 6,704,651; and 6,813,560; U.S. patent
application Ser. No. 09/993,335, filed Nov. 6, 2001; Ser. No.
10/349,493, filed Jan. 22, 2003; Ser. No. 10/359,468, filed on Feb.
5, 2003; Ser. No. 10/692,292, filed Oct. 23, 2003; Ser. No.
10/719,890, filed Nov. 21, 2003; Ser. No. 10/926,792, filed Aug.
26, 2004; Ser. No. 10/884,424, filed on Jul. 1, 2004; Ser. No.
10/912,516, filed Aug. 5, 2004; Ser. No. 10/932,557, filed on Sep.
1, 2004; Ser. No. 10/968,345, filed on Oct. 19, 2004; Ser. No.
11/077,380, filed on Mar. 3, 2005; Ser. No. 11/206,615, filed on
Aug. 18, 2005; Ser. No. 11/261,413, filed on Oct. 28, 2005; and
U.S. Provisional Patent Application Ser. No. 60/760,140, filed on
Jan. 19, 2006; all of which are incorporated herein by reference in
their entirety.
[0058] The wireless transceiver 204 may transmit, using its antenna
220, the measured pseudoranges for computing the receiver position
at a server, such as server 102. Alternatively the measured
pseudoranges may be stored within the memory 208 and later used by
the GNSS receiver 200 to compute the receiver position. For
example, the GNSS receiver 200 may perform processing to compute
the receiver position using the pseudoranges that are generated by
the satellite signal receiver 202. That is, the GNSS receiver 200
may use its processor 206, which is capable of performing functions
other than the computation of receiver position, to (i) load from
the memory 208 (or obtain directly from the satellite signal
receiver 202) the pseudoranges that are generated by the satellite
signal receiver 202, and (ii) compute the receiver position using
these measured pseudoranges.
[0059] The memory 208 may be embodied as random access memory, read
only memory, an erasable programmable read only memory and
variations thereof, content addressable memory and variations
thereof, flash memory, disk drive storage, removable storage, hard
disc storage etc., and any combination thereof. The memory 208 may
be loaded with and store the current assistance data 222, which can
be used to assist in the acquisition of satellite signals or the
computation of position or both. The current assistance data 222
may be received from the server 102 via the communication link
using the wireless transceiver 204 or via the other type computer
network 108 (e.g., Internet) using the modem 210 (or other
communication port or device that connects the device to a computer
network).
[0060] In addition, the memory 208 may be loaded with and store
executable instructions or other code (e.g., software) for some or
all of the process or function described herein. These executable
instructions may include, for example, assistance-data-maintenance
software 228 for performing some or all of the processes 800, 1000
and 100 illustrated in FIGS. 8, 10 and 11 (below).
[0061] Referring now to FIG. 3, a block diagram depicting an
example of a server 300 for a GNSS is shown. The server 300 may be
used as the server 102 shown in FIG. 1. The server 300
illustratively comprises a central processing unit (CPU) 302,
input/output (I/O) circuits 304, support circuits 306, a memory
308, and a server clock 310.
[0062] The server 300 may include or be coupled to a device
database 312. The support circuits 306 comprise well-known circuits
that facilitate operation of the CPU 202, such as clock circuits,
cache, power supplies, and the like. The server clock 310 may be
used to provide a time tag to indicate the time-of-arrival of
measured pseudoranges transmitted by a GNSS receiver, such as GNSS
receiver 104 and/or 200.
[0063] The memory 308 may be embodied as random access memory, read
only memory, an erasable programmable read only memory and
variations thereof, content addressable memory and variations
thereof, flash memory, disk drive storage, removable storage, hard
disc storage etc., and any combination thereof. The memory 308 may
be loaded with and store executable instructions or other code
(e.g., software) for any process or function described herein.
These executable instructions may include, for example,
integrity-monitoring software 320 for performing process 400
illustrated in FIG. 4 (below), satellite-health-monitoring software
322 for performing any of the processes 500, 600, 700 and 900
illustrated in FIGS. 5, 6, 7 and 9 (below);
assistance-data-maintenance software 324 for performing some or all
of the process 800 illustrated in FIG. 8 (below).
[0064] The server 300 via its I/O circuits 304 may receive the
broadcasted measurements and information (e.g., ephemeris, code
phase measurements, carrier phase measurements, Doppler
measurements, etc.) from the external source (e.g., reference
network, satellite control station, Internet). The server 300 may
use the broadcasted measurements and information to generate or
compute the current assistance data and/or one or more previous or
future versions of the assistance data.
[0065] To monitor the integrity of the current assistance data, the
server 300 keeps track of the type of assistance data distributed
to each of a plurality of remote receivers (not shown), a time of
delivery of the current assistance data, and a time of expiration
of the current assistance data. In one embodiment, this information
may be stored in a table 350 within a device database 312. The
table 350 may have entries (e.g., three are shown) defined by, for
example, a remote device ID, the time-of-day that the current
assistance data was delivered to each of the remote devices listed
in the table, the type of assistance data delivered, and the
expiration time of the aiding data.
[0066] For example, an entry 352 indicates that (i) acquisition
assistance information was delivered, at time t1, to one of the
remote devices having an ID of "1," and (ii) the acquisition
assistance data is set to expire 10 minutes from time t1. An entry
354 indicates that (i) broadcast ephemeris was delivered, at time
t2, to one of the remote devices having an ID of "2," and (ii) the
broadcast ephemeris data is set to expire four hours from time t2.
An entry 356 indicates that (i) LTO information was delivered, at
time t3, to a device having an ID of "3," and (ii) the LTO
information is set to expire two days from time t3.
[0067] The server 300 monitors the integrity of the current
assistance data in use by the remote devices identified in the
device database 312, and responsively, produces integrity data 314.
The integrity data 314 may be stored in the memory 308 and
transmitted to one or more remote devices, as described below.
[0068] FIG. 4 is a flow diagram depicting an example of a process
400 for monitoring the integrity of current assistance data used by
one or more GNSS receivers of a GNSS. The process 400 may be
executed by a server of a GNSS, such as the server 300, to monitor
the integrity of the current assistance data in use by the GNSS
receivers.
[0069] The process 400 begins at step 402 where unhealthy
satellites associated with current assistance data used by GNSS
receivers are identified. As described by way of example, any of
the example processes 500, 600, 700, and 900 (below) may be used to
identify unhealthy satellites.
[0070] At optional step 403, a period of outage is determined for
each of the identified unhealthy satellites. For example, a period
of outage for each of the identified unhealthy satellites may be
obtained from outage notification data generated by a satellite
control station, as discussed below with respect to the process 900
of FIG. 9.
[0071] At step 404, integrity data is generated. This integrity
data includes an identity of each of the unhealthy satellites and a
corresponding period of outage, if known. If outage periods are
unknown, then the integrity data may include no period of outage or
the period of outage may be set to a pre-defined value or to a
value based on the particular type of aiding data in use.
[0072] For example, the period of outage may be set to any time
between two to four hours when the current assistance data is based
on or uses the broadcast ephemeris. Alternatively, the period of
outage may be set to a time greater than such validity period when
the current assistance data is based on or uses the LTO
information.
[0073] The integrity data may then be transmitted to the GNSS
receivers that are using the current assistance data. In one
embodiment, at step 406, the integrity data may be transmitted to
affected GNSS receivers in response to identified unhealthy
satellites. That is, if any satellites were identified as being
unhealthy, the integrity data is transmitted to the GNSS receivers
having current assistance data that is affected by such unhealthy
satellites. Thus, the integrity data is only sent when unhealthy
satellites are identified and only sent to the GNSS receivers
affected by such identified unhealthy satellites. In another
embodiment, at step 405, the integrity data may be transmitted to
some or all of the GNSS receivers in response to unhealthy
satellites being identified.
[0074] In another embodiment, at step 408, the integrity data is
transmitted to GNSS receivers in accordance with a pre-defined
transmission schedule. For example, the integrity data may be
periodically broadcast to some or all of the GNSS receivers using
the current assistance data; whether or not unhealthy satellites
have been identified. In yet another embodiment, at step 410, the
integrity data may be transmitted to one or more of the GNSS
receivers in response to requests from such GNSS receivers.
[0075] FIG. 5 is a flow diagram depicting an example of a process
500 for identifying unhealthy satellites. The process 500 begins at
step 502, where a current set of the broadcasted measurements and
information is obtained. This current set of measurements and
information may be received over the communication link from a
reference network, a satellite control station and/or other source
of information.
[0076] At step 504, satellite orbit data, satellite clock data or
both (hereinafter generally referred to as "orbit/clock data") is
extracted from the current set of the measurements and information.
At step 506, the orbit/clock data is compared with orbit/clock data
of one or more sets of the current assistance data being used by
GNSS receivers so as to identify discrepancies. Such discrepancies
may arise, for example, from a change in one or more of the
satellites' orbits or a drift in one or more of the satellites'
clocks since the time the current assistance data was generated.
These discrepancies manifest may themselves as differences between
the orbit/clock data extracted from the current set of the
measurements and information and orbit/clock data underlying or
otherwise part of the current assistance data.
[0077] At step 508, a determination is made as to whether any
identified discrepancies exceed a pre-defined threshold. If, for
example, one or more of the satellites' orbits change beyond a
corresponding pre-defined threshold, and/or if one or more of the
satellites' clocks drifted outside a corresponding pre-defined
threshold, then the process 500 proceeds to step 510. Otherwise,
the process 500 ends at step 512. At step 510, the affected
satellites associated with the identified discrepancies are flagged
as being unhealthy.
[0078] FIG. 6 is a flow diagram depicting another example of a
process 600 for identifying unhealthy satellites. The process 600
begins at step 602, where a current set of the broadcasted
measurements and information is obtained. This current set of
measurements and information may be received over the communication
link from a reference network, a satellite control station, and/or
other source of information.
[0079] At step 604, satellite health data is extracted from the
current set of measurements and information. As described above,
the broadcast ephemeris from each of the satellites contains
precise satellite orbit and time model information for such
satellite. In addition, the broadcast ephemeris may contain an
indication of satellite health ("health status").
[0080] In GPS, for example, changes in ephemeris are announced by
the MCS by changing the health status in the broadcast ephemeris.
At step 606, the satellite health data is analyzed to identify the
presence of unhealthy satellites.
[0081] FIG. 7 is a flow diagram depicting yet another example of a
process 700 for identifying unhealthy satellites. The process 700
begins at step 702, where satellite signals are received at one or
more tracking stations having known positions.
[0082] At step 704, positions of each of the tracking stations are
computed using one or more sets of current assistance data being
used by the GNSS receivers. At step 706, these positions ("computed
positions") are compared to the known positions of the tracking
stations. If, for example, a given set of the current assistance
data that is used to compute one or more of the computed positions
of the tracking stations is invalid due to an unhealthy satellite,
then these computed positions will be in error (and/or be
identified as having discrepancies).
[0083] Thus, at step 708, a determination is made as to whether any
or each of the computed positions exceeds the respective known
positions by a pre-defined threshold. If so, the process 700
proceeds to step 710. Otherwise, the process 700 ends at step 712.
At step 710, the affected satellites associated with the identified
discrepancies are flagged as being unhealthy.
[0084] FIG. 8 is a flow diagram depicting an example of a process
800 for obtaining (e.g., requesting and receiving) from a server
integrity data and/or fresh assistance data. The process 800 begins
at step 802, where measured pseudoranges are measured from between
a GNSS receiver, such as the GNSS receiver 104 or 200, and one or
more (and typically four) of a plurality of satellites,
respectively.
[0085] At step 804, a computed position of the GNSS receiver is
computed using the measured pseudoranges and the current assistance
data. At step 806, a validity of the computed position is
estimated.
[0086] The validity of the computed position may be estimated in
any number of various ways. For example, the validity of the
computed position may be estimated using a-posteriori residuals,
which may be formed as a function of the measured pseudoranges.
After formation, these a-posteriori residuals may be analyzed to
identify, which, if any, of the measured pseudoranges are
erroneous. If any of the measured pseudoranges are identified to be
erroneous, then the validity of the computed position may be
estimated as being invalid.
[0087] Other techniques may be used for estimating the validity of
the computed position. For example, the validity of the computed
position may be estimated as a function of the computed position
with an a-priori position. The a-priori position may be obtained,
formed or otherwise garnered from the current assistance data
(including any broadcast ephemeris and/or LTO information).
[0088] If, for example, a difference between the computed position
and the a-priori position satisfies a particular threshold, then
the validity may be estimated as invalid. Alternatively, if the
difference does not satisfy the particular threshold, then the
validity may be estimated as valid.
[0089] The particular threshold may be statically set to
accommodate for or, alternatively, dynamically set to adjust for
one or more of myriad of conditions, including, for example, an
actual location of the GNSS receiver, a time since last obtaining
the current assistance data, basis and/or type of the current
assistance data (e.g., whether the current assistance data includes
broadcast ephemeris and/or LTO information), etc. The particular
threshold may include one or more thresholds, and may be applied as
one or more boundaries to the difference. The boundaries may
function as one or more upper bounds, one or more lower bounds or
some combination thereof.
[0090] As another alternative, the validity of the computed
position may be estimated as a function of one or more a-priori
pseudorange residuals. That is, the computed position may be
estimated as a function of a comparison between respective
predicted and measured pseudoranges. The predicted pseudorange may
be based on the a-priori position and time, and/or other
satellite-tracking data. The a-priori position and time, and/or any
other satellite-tracking data may be garnered from or be part of
the current assistance data, including the LTO information, or
alternatively, from the broadcast ephemeris garnered from the
satellite signals.
[0091] Like above, when one or more of the a-priori pseudorange
residuals satisfy respective thresholds, the validity may be
estimated as invalid. Alternatively, when the a-priori pseudorange
residuals do not satisfy respective particular thresholds, the
validity may be estimated as valid.
[0092] Each of these respective thresholds may be statically set to
accommodate for or, alternatively, dynamically set to adjust for
one or more of a myriad of conditions, including, for example, an
actual location of the GNSS receiver, a time since last obtaining
the current assistance data, basis and/or type of the current
assistance data (e.g., whether including broadcast ephemeris and/or
LTO information), etc. Each of the particular thresholds may
include one or more thresholds, and may be applied as boundaries to
the a-priori pseudorange residuals. These boundaries may function
as one or more upper bounds, one or more lower bounds or some
combination thereof.
[0093] Other examples for estimating the validity of the computed
position may use variations and/or combinations of the foregoing,
including, for example, comparing computed and predicted altitudes,
times, etc.
[0094] At step 808, a determination is made as to whether the
computed position is valid. This determination may be made as a
function of estimating the validity of the computed position as
described above. If the computed position is valid, then the
process 800 may return to step 802, at which point the process 800
may be repeated. Otherwise, at least a portion of the current
assistance data may be marked to prevent use, removed, deleted or
otherwise excluded from the current assistance data ("excluded
assistance data") and then the process 800 proceeds to (i) step 810
or, as alternatives, to (ii) step 814 or (iii) step 818. The
excluded assistance data may be, for example, the current
assistance data associated with satellite or satellites from which
the measured pseudorange is determined.
[0095] At step 810, the GNSS receiver obtains from the server,
usually in response to one or more requests thereto, the integrity
data. After receipt, the GNSS receiver may use the integrity data
to determine whether the current assistance data possessed thereby
is still valid, as shown in step 812. If the current assistance
data is not valid, then the GNSS receiver may use the integrity
data to update or otherwise supplement the current assistance data
(including, for example, replacing or otherwise modifying the
excluded assistance data). Alternatively, the GNSS receiver may
transition to step 814 to obtain fresh assistance data. If, on the
other hand, the current assistance data is valid, then the process
800 transitions to step 802, at which point the process 800 may be
repeated.
[0096] At step 814, the GNSS receiver obtains from the server,
usually in response to one or more requests thereto, the fresh
assistance data. This fresh assistance data may be formed from and
include acquisition-assistance information
("fresh-acquisition-assistance information") and/or
satellite-navigation data ("fresh-satellite-navigation data") that
is more recent than the acquisition-assistance information and/or
the satellite-navigation data of the current assistance data.
[0097] The fresh-acquisition-assistance information, in turn, may
include information for acquiring the satellites, which may include
at least one of code phase measurements, carrier phase
measurements; Doppler measurements, and the like that are garnered
from one or more satellite navigation messages broadcast from at
least one of the satellites in the constellation. The
fresh-satellite-navigation data may include broadcast ephemeris,
one or more of the predicted pseudoranges, a pseudorange model, LTO
information etc. that are more recent than such parameters of the
current assistance data.
[0098] After obtaining the fresh assistance data, the GNSS receiver
may use some or all of the fresh assistance data to update or
otherwise supplement the current assistance data (including, for
example, replacing or otherwise modifying the excluded assistance
data), as shown in step 816. For example, the GNSS receiver may
replace one or more of the predicted pseudoranges of the current
assistance data with respective predicted pseudoranges of the fresh
assistance data.
[0099] If, for instance, the current assistance data is formed from
the LTO information, such as the LTO model, then the GNSS receiver
may replace one or more of the predicted pseudoranges of the
current assistance data with respective predicted pseudoranges of
the fresh assistance data, which may be also formed from LTO
information, such as an LTO model.
[0100] Alternatively, the GNSS receiver may replace all of the
current assistance data with some or all of the fresh assistance
data. If, like above, the current assistance data is formed from
LTO information, then the GNSS receiver may replace all of the
current assistance data with some or all the fresh assistance data,
which may also be formed from LTO information. The GNSS receiver
may replace all of the current assistance data as such
notwithstanding that only a portion of, e.g., only one of the
predicted pseudoranges, is estimated (step 808) or determined (step
812) invalid.
[0101] As noted above with respect to step 808, process 800 may
transition from step 808 to step 818 as an alternative. At step
818, the GNSS receiver may decode and then use broadcast ephemeris
obtained directly from the satellite-navigation messages contained
within satellite signals received at the GNSS receiver to update or
otherwise supplement the current assistance data (including, for
example, replacing or otherwise modifying the excluded assistance
data). The GNSS receiver may appropriately do so when (i)
attenuation of the satellite signals allows for successful decoding
of the broadcast ephemeris, and/or (ii) the GNSS receiver is unable
to obtain the integrity data and/or fresh assistance data from the
server. With respect to the latter, the GNSS receiver may not be
able to obtain the integrity data and/or fresh assistance data
because, for example, it lacks, cannot maintain or looses
connectivity with the server.
[0102] After updating or supplementing the current assistance data
with the fresh assistance data, the process 800 may transition to
step 802, at which point the process 800 may be repeated. The
process 800 may be repeated periodically, in continuous fashion, or
upon being triggered as a result a condition, such as detecting an
error in the receiver position or a satellite position. The 800 may
be repeated for other reasons as well.
[0103] In addition, the GNSS receiver may obtain the integrity data
and/or the fresh assistance data without making a request for such
data. For example, the integrity data and/or the fresh assistance
data may be obtained from messages broadcasted from the server.
[0104] Additionally, the process 800 may transition to step 814
from step 812. This may occur when the a current set of the
broadcasted measurements and information and the current assistance
data are both based on common information, yet between the time of
computing the receiver position and obtaining the current
assistance data, the actual positions of the satellites changed.
While such changes may be reflected in the
fresh-acquisition-assistance information and/or
fresh-satellite-navigation data at the server, the integrity data
sent to or at the GNSS receiver may not yet reflect such
change.
[0105] Moreover, the integrity data may not yet reflect the changes
or the time for triggering replacement may not be reached because
the current assistance data is formed from LTO information, such as
an LTO model. For instance, the server may not check and/or compute
the integrity data for the current assistance data because its
validity period has not expired or is not close to expiring. Other
possibilities for this are likely as well.
[0106] FIG. 9 is a flow diagram depicting another example of a
process 900 for identifying unhealthy satellites in accordance with
the invention. The process 900 begins at step 902, where outage
notification data generated by a satellite control station is
received. For example, the outage notification data may be received
directly from the satellite control station, or via some other
source, such as over the Internet. For example, in GPS, the
satellite constellation is monitored by stations around the world
under control of a Master Control Station (MCS). The MCS announces
satellite outages that are either planned for the future, or
unplanned and immediate, by providing Notice Advisories to Navstar
Users (NANUs) via the Internet.
[0107] At step 904, the outage notification data is parsed to
identify unhealthy satellites. At step 906, a period of outage for
each identified unhealthy satellite is determined. For example, a
period of outage for an identified unhealthy satellite may be
obtained from NANUs. By using outage notification data, the
invention ensures that current assistance data in use by GNSS
receivers always reflects the most current integrity status of the
GPS constellation, regardless of whether the changes in integrity
were planned for the future, or unplanned and immediate.
[0108] FIG. 10 is a flow diagram illustrating an example of a
process 1000 for obtaining and using fresh assistance data. For
convenience, the process 1000 is described herein with respect to
the architecture shown in FIGS. 1 and 2.
[0109] The process 1000 begins at termination block 1002, after the
GNSS receiver 104 (i) obtains from the server 102 the current
assistance data, which includes LTO information, such as an LTO
model, and (ii) acquires the satellite signals from one or more
(and typically four) of a plurality of satellites. For convenience,
the current assistance data is referred to as "current LTO
information" with respect to process 1000.
[0110] After termination block 1002, the process 1000 transitions
to process block 1004. At process block 1004, the current LTO
information is used to determine a predicted position of the GNSS
receiver 104 ("predicted-position fix"). The predicted-position fix
may be determined, for example, by the GNSS receiver 104 and/or the
server 102. The GNSS receiver 104 and/or server 102 may do so, for
instance, by applying the current LTO information and measured
pseudoranges to a first recursive or other type filter, and
detecting the predicted-position fix from an output of the first
filter. The predicted-position fix may include one or more
respective location parameters, including, for example, latitude,
longitude, altitude and/or a common-mode error.
[0111] To facilitate determining the predicted-position fix at the
server 102, the server 102 may obtain the measured pseudoranges and
current LTO information from the GNSS receiver 104. Alternatively,
the server 102 may determine the predicted-position fix using the
measured pseudoranges obtained from the GNSS receiver 104 and the
current LTO information known by the server 102 to be in use by the
GNSS receiver 104. After process block 1004, the process 1000
transitions to process block 1006.
[0112] At process block 1006, broadcast ephemeris obtained from
satellites signals is used to determine a measured position of the
GNSS receiver 104 ("measured-position fix"). The measured-position
fix may be determined by the GNSS receiver 104 and/or one or more
of the tracking stations of the reference network 110. The GNSS
receiver 104 and/or the tracking stations may do so, for instance,
by applying the broadcast ephemeris obtained from signals of the
satellites (garnered directly from the satellites or indirectly
from the server 102) and measured pseudoranges to a second
recursive or other type filter, and detecting the measured-position
fix from an output of the second filter. The measured-position fix,
like the first position fix, may include one or more respective
location parameters, including, for example, latitude, longitude,
altitude and/or a common-mode error. After process block 1006, the
process 1000 transitions to process block 1008.
[0113] At process block 1008, validity of at least one of the
predicted location parameters is determined as a function of such
predicted location parameter ("first-location parameter") and a
respective one of the measured location parameters
("second-location parameter"). The validity may be determined, for
example, by the GNSS receiver 104 and/or the server 102. The GNSS
receiver 104 and/or server 102 may do so, for instance, by forming
a difference between the first and second location parameters, and
then determining if the difference satisfies a given threshold. If,
for example, the difference satisfies the given threshold, then the
validity of the first-location parameter may be deemed valid,
otherwise, the validity of the first-location parameter may be
deemed invalid.
[0114] The given threshold may be statically set to accommodate for
or, alternatively, dynamically set to adjust for one or more of
myriad of conditions, including, for example, an actual location of
the GNSS receiver 104, a time since last obtaining the current LTO
information, basis and/or type of the current LTO information, etc.
The particular threshold may include one or more thresholds, and
may be applied as boundaries to the difference. These boundaries
may function as one or more upper bounds, one or more lower bounds
or some combination thereof.
[0115] The same functions may be performed for one or more of the
remaining predicted location parameters, as desired. Alternatively,
the same functions may be performed for each of the remaining
predicted location parameters unless one of them is deemed
invalid.
[0116] To facilitate determining the validity at the server 102,
the server 102 may have to obtain the predicted-position fix from
the GNSS receiver 104. Using the predicted-position fix, the server
102 can obtain the first-location parameter. Similarly, the server
102 may have to obtain the measured-position fix from the GNSS
receiver 104 or the tracking stations, depending of course, on
which determined the measured-position fix. Using the
measured-position fix, the server 102 can obtain the
second-location parameter.
[0117] To facilitate determining the validity at the GNSS receiver
104, the GNSS receiver 104 may have to obtain the
predicted-position fix from the server 102. Using the
predicted-position fix, the GNSS receiver 104 can obtain the
first-location parameter. As shown in decision block 1010, if the
GNSS receiver 104 and/or the server 102 determine that the
predicted location parameters are valid, then the process returns
to termination block 1002 to repeat the process 1000 as
desired.
[0118] If, on the other hand, any of the predicted location
parameters are deemed invalid, then the GNSS receiver 104 may
exclude (e.g., mark to prevent use, remove, delete, etc.) at least
a portion of the current LTO information from the current LTO
information ("excluded LTO information"). The excluded LTO
information may be, for example, the current LTO information
associated with satellite or satellites from which the measured
pseudoranges are determined.
[0119] In addition, the GNSS receiver 104 may obtain fresh
assistance data or "fresh LTO information" from the server 102, as
shown in process block 1012. The GNSS receiver 104 may obtain the
fresh LTO information from the server 102 with or without a request
from the GNSS receiver 104 for such fresh LTO information.
[0120] After obtaining the fresh LTO information, the GNSS receiver
104 may update or otherwise supplement, as noted above with respect
to FIG. 8, some or all of the current LTO information with the
fresh LTO information, as shown in process block 1014. This may
include replacing one or more of the predicted location parameters.
As above, the GNSS receiver 104 may update or otherwise supplement
some or all of the current LTO information with the fresh LTO
information notwithstanding that some or all of the current LTO
information (and location parameters thereof) is estimated or
determined invalid.
[0121] After process block 1014, the process 1000 transitions to
termination block 1016, at which point the process 1000 ends.
Alternatively, the process 1000 may be repeated periodically, in
continuous fashion, or upon being triggered as a result of a
condition, such as an error in receiver or satellite position.
[0122] FIG. 11 is a flow diagram illustrating an example of a
process 1100 for obtaining and using fresh assistance data. For
convenience, the process 1100 is described herein with respect to
the architecture shown in FIGS. 1 and 2.
[0123] The process 1100 begins at termination block 1102, after the
GNSS receiver 104 (i) obtains from the server 102 the current
assistance data, which includes LTO information, such as an LTO
model, and (ii) acquires the satellite signals from one or more
(and typically four) of a plurality of satellites. For convenience,
the current assistance data is referred to as "current LTO
information" with respect to process 1100.
[0124] After termination block 1102, the process 1100 transitions
to process block 1104. At process block 1104, broadcast ephemeris
obtained from satellites signals is used to determine a measured
position of the GNSS receiver 104 ("measured-position fix"). The
measured-position fix may be determined, for example, by the GNSS
receiver 104 and/or one or more of the tracking stations of the
reference network 110. The GNSS receiver 104 and/or the tracking
stations may do so, for instance, by applying the broadcast
ephemeris (garnered directly from the satellites or indirectly from
the server 102) and measured pseudoranges to a second recursive or
other type filter, and detecting the measured-position fix from an
output of the second filter. The measured-position fix may include
one or more respective location parameters, including, for example,
latitude, longitude, altitude and/or a common-mode error.
[0125] At process block 1106, the current LTO information is used
to generate, for each of the location parameters, a respective
parameter threshold. These parameter thresholds may be generated,
for example, by the GNSS receiver 104 and/or the server 102. To
facilitate generating the parameter thresholds, the GNSS receiver
104 and the server 102 may have to obtain the measured-position fix
from the other.
[0126] The parameter thresholds may be statically set to
accommodate for or, alternatively, dynamically set to adjust for
one or more of myriad of conditions, including, for example, an
actual location of the GNSS receiver 104, a time since last
obtaining the current LTO information, basis and/or type of the
current LTO information, etc. Each of the parameter thresholds may
include one or more thresholds, and may be applied as boundaries to
the location parameters. The boundaries may function as one or more
upper bounds, one or more lower bounds or some combination
thereof.
[0127] After process block 1106, the process 1100 transitions to
process block 1108. At process block 1108, validity of the current
assistance data as a function of at least one of the parameter
thresholds and a respective one of the measured location parameters
is determined. The validity of the current assistance data may be
determined, for example, by the GNSS receiver 104 and/or the server
102. The GNSS receiver 104 and/or the server 102 may do so, for
instance, by determining if such measured location parameter
satisfies its respective parameter threshold. If the measured
location parameter satisfies its respective parameter threshold,
then the validity of the measured location parameter may be deemed
valid. Otherwise, the validity of the measured location parameter
may be deemed invalid.
[0128] The process block 1108 may be performed for one or more of
the remaining measured location parameters, as desired.
Alternatively, the same functions may be performed for each of the
remaining measured location parameters unless one of them is deemed
invalid. To facilitate determining the validity of the current LTO
information, the GNSS receiver 104 and the server 102 may have to
obtain from the other the respective parameter thresholds and
measured location parameters, depending of course, on which
maintains such parameter thresholds and measured location
parameters.
[0129] As shown in decision block 1110, if the GNSS receiver 104
determines that the measured location parameters are valid, then
the process returns to termination block 1102 to repeat the process
1100 as desired. If, on the other hand, any of the predicted
location parameters are deemed invalid, then the GNSS receiver 104
may exclude (e.g., mark to prevent use, remove, delete, etc.) at
least a portion of the current LTO information from the current LTO
information ("excluded LTO information"). The excluded LTO
information may be, for example, the current LTO information
associated with satellite or satellites from which the measured
pseudoranges are determined.
[0130] In addition, the GNSS receiver 104 may obtain from the
server 102 fresh assistance data or "fresh LTO information", as
shown in process block 1112. The GNSS receiver 104 may obtain the
fresh LTO information from the server 102 with or without a request
from the GNSS receiver 104.
[0131] After obtaining the fresh LTO information, the GNSS receiver
104 may update or otherwise supplement, as noted above with respect
to FIG. 8, some or all of the current LTO information with the
fresh LTO information, as shown in process block 1114. This may
include replacing one or more of the predicted location parameters.
As above, the GNSS receiver 104 may update or otherwise supplement
some or all of the current LTO information with the fresh LTO
information notwithstanding that some or all of the current LTO
information (and location parameters thereof) is determined
invalid.
[0132] After process block 1114, the process 1100 transitions to
termination block 1116, at which point the process 1100 ends.
Alternatively, the process 1100 may be repeated periodically, in
continuous fashion, or upon being triggered as a result of a
condition, such as an error in receiver or satellite position.
[0133] Although the foregoing has been described with reference to
GPS satellites, it will be appreciated that the teachings are
equally applicable to positioning systems that utilize pseudolites
or a combination of satellites and pseudolites. Pseudolites are
ground-based transmitters that broadcast a PN code (similar to the
GPS signal) that may be modulated on an L-band carrier signal,
generally synchronized with GPS time. The term "satellite", as used
herein, is intended to include pseudolites or equivalents of
pseudolites, and the term "GPS signals", as used herein, is
intended to include GPS-like signals from pseudolites or
equivalents of pseudolites.
[0134] Moreover, in the preceding discussion, the invention has
been described with reference to application upon the United States
Global Positioning System (GPS). It should be evident, however,
that these methods are equally applicable to similar satellite
systems, and in particular, the Russian Glonass system and the
European Galileo system. The term "GPS" used herein includes such
alternative Global-Navigation-Satellite Systems (GNSS), including
the Russian Glonass system and the European Galileo system.
[0135] While the foregoing is directed to illustrative embodiments
of the present invention, other and further embodiments of the
invention may be devised without departing from the basic scope
thereof, and the scope thereof is determined by the claims that
follow.
* * * * *