U.S. patent application number 11/766089 was filed with the patent office on 2008-12-25 for methods for processing external correction messages, correcting position measurements of gnss receiver, and related apparatuses.
Invention is credited to Kung-Shuan Huang.
Application Number | 20080316092 11/766089 |
Document ID | / |
Family ID | 40135932 |
Filed Date | 2008-12-25 |
United States Patent
Application |
20080316092 |
Kind Code |
A1 |
Huang; Kung-Shuan |
December 25, 2008 |
METHODS FOR PROCESSING EXTERNAL CORRECTION MESSAGES, CORRECTING
POSITION MEASUREMENTS OF GNSS RECEIVER, AND RELATED APPARATUSES
Abstract
Methods and apparatuses for processing external correction
messages in a GNSS receiver are provided. One of the proposed
methods includes providing a first storage unit; receiving a
plurality of external correction messages from different data
sources, wherein a plurality of GNSS differential correction data
are carried by the plurality of external correction messages; and
storing a portion of the GNSS differential correction data in the
first storage unit without storing remaining GNSS differential
correction data in the GNSS receiver.
Inventors: |
Huang; Kung-Shuan; (Changhua
County, TW) |
Correspondence
Address: |
NORTH AMERICA INTELLECTUAL PROPERTY CORPORATION
P.O. BOX 506
MERRIFIELD
VA
22116
US
|
Family ID: |
40135932 |
Appl. No.: |
11/766089 |
Filed: |
June 20, 2007 |
Current U.S.
Class: |
342/357.24 |
Current CPC
Class: |
G01S 19/41 20130101 |
Class at
Publication: |
342/357.03 |
International
Class: |
G01S 5/14 20060101
G01S005/14; G01S 1/00 20060101 G01S001/00 |
Claims
1. A method for processing external correction messages in a GNSS
receiver, comprising: providing a first storage unit; receiving a
plurality of external correction messages from different data
sources, wherein a plurality of GNSS differential correction data
are carried by the plurality of external correction messages; and
storing a portion of the GNSS differential correction data in the
first storage unit without storing remaining GNSS differential
correction data in the GNSS receiver.
2. The method of claim 1, wherein the plurality of external
correction messages are selected from a group consisting of SBAS
messages, RTCM messages, and A-GPS messages.
3. The method of claim 1, wherein the step of storing the portion
of the GNSS differential correction data in the first storage unit
comprises: selecting a portion of the plurality of external
correction messages according to a programmable setting; extracting
GNSS differential correction data from the selected external
correction messages; and storing the GNSS differential correction
data extracted from the selected external correction messages in
the first storage unit while discarding GNSS differential
correction data carried by other external correction messages.
4. The method of claim 3, wherein the selected external correction
messages are derived from a predetermined data source.
5. The method of claim 1, wherein the step of storing the portion
of the GNSS differential correction data in the first storage unit
comprises: extracting the plurality of GNSS differential correction
data from the plurality of external correction messages; selecting
a portion of the plurality of GNSS differential correction data
according to a programmable setting; and storing the selected GNSS
differential correction data in the first storage unit while
discarding unselected GNSS differential correction data.
6. The method of claim 5, wherein the selected GNSS differential
correction data are derived from a predetermined data source.
7. The method of claim 1, wherein a capacity of the first storage
unit is merely sufficient to store GNSS differential correction
data derived from a predetermined data source, wherein the data
amount of the GNSS differential correction data derived from the
predetermined data source is greater than that derived from other
data sources.
8. A GNSS receiver, comprising: a first storage unit; a receiving
module for receiving a plurality of external correction messages
from different data sources, wherein a plurality of GNSS
differential correction data are carried by the plurality of
external correction messages; and a decision unit, coupled to the
receiving module and the first storage unit, for storing a portion
of the GNSS differential correction data in the first storage unit
without storing remaining GNSS differential correction data in the
GNSS receiver.
9. The GNSS receiver of claim 8, wherein the plurality of external
correction messages are selected from a group consisting of SBAS
messages, RTCM messages, and A-GPS messages.
10. The GNSS receiver of claim 8, wherein the decision unit selects
a portion of the plurality of external correction messages
according to a programmable setting; extracts GNSS differential
correction data from the selected external correction messages; and
stores the GNSS differential correction data extracted from the
selected external correction messages in the first storage unit
while discarding GNSS differential correction data carried by other
external correction messages.
11. The GNSS receiver of claim 10, wherein the external correction
messages selected by the decision unit are derived from a same data
source.
12. The GNSS receiver of claim 8, wherein the decision unit
extracts the plurality of GNSS differential correction data from
the plurality of external correction messages; selects a portion of
the plurality of GNSS differential correction data according to a
programmable setting; and stores the selected GNSS differential
correction data in the first storage unit while discarding
unselected GNSS differential correction data.
13. The GNSS receiver of claim 12, wherein the GNSS differential
correction data selected by the decision unit are derived from a
same data source.
14. The GNSS receiver of claim 8, wherein a capacity of the first
storage unit is merely sufficient to store GNSS differential
correction data derived from a predetermined data source, wherein
the data amount of the GNSS differential correction data derived
from the predetermined data source is greater than that derived
from other data sources.
15. The GNSS receiver of claim 8, further comprising: a computing
unit coupled to the first storage unit for modifying at least one
of a pseudo-range measurement and a Doppler measurement of the GNSS
receiver according to the GNSS differential correction data stored
in the first storage unit.
16. A method for correcting position measurements of a GNSS
receiver, comprising: providing a first storage unit; receiving a
plurality of external correction messages from different data
sources, wherein a plurality of GNSS differential correction data
are carried by the plurality of external correction messages;
storing a portion of the GNSS differential correction data in the
first storage unit without storing remaining GNSS differential
correction data in the GNSS receiver; and modifying at least one of
a pseudo-range measurement and a Doppler measurement of the GNSS
receiver according to the GNSS differential correction data stored
in the first storage unit.
17. The method of claim 16, wherein the plurality of external
correction messages are selected from a group consisting of SBAS
messages, RTCM messages, and A-GPS messages.
18. The method of claim 16, wherein the step of storing the portion
of the GNSS differential correction data in the first storage unit
comprises: selecting a portion of the plurality of external
correction messages according to a programmable setting; extracting
GNSS differential correction data from the selected external
correction messages; and storing the GNSS differential correction
data extracted from the selected external correction messages in
the first storage unit while discarding GNSS differential
correction data carried by other external correction messages.
19. The method of claim 18, wherein the selected external
correction messages are derived from a same data source.
20. The method of claim 16, wherein the step of storing the portion
of the GNSS differential correction data in the first storage unit
comprises: extracting the plurality of GNSS differential correction
data from the plurality of external correction messages; selecting
a portion of the plurality of GNSS differential correction data
according to a programmable setting; and storing the selected GNSS
differential correction data in the first storage unit while
discarding unselected GNSS differential correction data.
21. The method of claim 20, wherein the selected GNSS differential
correction data are derived from a same data source.
22. The method of claim 16, wherein a capacity of the first storage
unit is merely sufficient to store GNSS differential correction
data derived from a predetermined data source, wherein the data
amount of the GNSS differential correction data derived from the
predetermined data source is greater than that derived from the
other data sources.
23. A method for processing external correction messages in a GNSS
receiver, comprising: providing a first storage unit; receiving a
plurality of external correction messages from different data
sources, wherein a plurality of GNSS differential correction data
are carried by the plurality of external correction messages;
selecting a portion of the plurality of external correction
messages according to a programmable setting; extracting GNSS
differential correction data from the selected external correction
messages; and storing the GNSS differential correction data
extracted from the selected external correction messages in the
first storage unit while discarding GNSS differential correction
data carried by other external correction messages.
24. The method of claim 23, wherein the plurality of external
correction messages are selected from a group consisting of SBAS
messages, RTCM messages, and A-GPS messages.
25. The method of claim 23, wherein the selected external
correction messages are derived from a predetermined data
source.
26. The method of claim 23, wherein a capacity of the first storage
unit is merely sufficient to store GNSS differential correction
data derived from a predetermined data source, wherein the data
amount of the GNSS differential correction data derived from the
predetermined data source is greater than that derived from other
data sources.
27. A method for processing external correction messages in a GNSS
receiver, comprising: providing a first storage unit; receiving a
plurality of external correction messages from different data
sources, wherein a plurality of GNSS differential correction data
are carried by the plurality of external correction messages;
extracting the plurality of GNSS differential correction data from
the plurality of external correction messages; selecting a portion
of the plurality of GNSS differential correction data according to
a programmable setting; and storing the selected GNSS differential
correction data in the first storage unit while discarding
unselected GNSS differential correction data.
28. The method of claim 27, wherein the selected GNSS differential
correction data are derived from a predetermined data source.
29. The method of claim 27, wherein a capacity of the first storage
unit is merely sufficient to store GNSS differential correction
data derived from a predetermined data source, wherein the data
amount of the GNSS differential correction data derived from the
predetermined data source is greater than that derived from other
data sources.
30. The method of claim 27, wherein the plurality of external
correction messages are selected from a group consisting of SBAS
messages, RTCM messages, and A-GPS messages.
31. A GNSS receiver, comprising: a first storage unit; a receiving
module for receiving a plurality of external correction messages
from different data sources, wherein a plurality of GNSS
differential correction data are carried by the plurality of
external correction messages; and a decision unit, coupled to the
receiving module and the first storage unit, for storing a portion
of the GNSS differential correction data in the first storage unit
without storing remaining GNSS differential correction data in the
GNSS receiver; wherein the decision unit selects a portion of the
plurality of external correction messages according to a
programmable setting; extracts GNSS differential correction data
from the selected external correction messages; and stores the GNSS
differential correction data extracted from the selected external
correction messages in the first storage unit while discarding GNSS
differential correction data carried by other external correction
messages.
32. The GNSS receiver of claim 31, wherein the external correction
messages selected by the decision unit are derived from a same data
source.
33. The GNSS receiver of claim 31, wherein the plurality of
external correction messages are selected from a group consisting
of SBAS messages, RTCM messages, and A-GPS messages.
34. The GNSS receiver of claim 31, wherein a capacity of the first
storage unit is merely sufficient to store GNSS differential
correction data derived from a predetermined data source, wherein
the data amount of the GNSS differential correction data derived
from the predetermined data source is greater than that derived
from other data sources.
35. The GNSS receiver of claim 31, further comprising: a computing
unit coupled to the first storage unit for modifying at least one
of a pseudo-range measurement and a Doppler measurement of the GNSS
receiver according to the GNSS differential correction data stored
in the first storage unit.
36. A GNSS receiver, comprising: a first storage unit; a receiving
module for receiving a plurality of external correction messages
from different data sources, wherein a plurality of GNSS
differential correction data are carried by the plurality of
external correction messages; and a decision unit, coupled to the
receiving module and the first storage unit, for storing a portion
of the GNSS differential correction data in the first storage unit
without storing remaining GNSS differential correction data in the
GNSS receiver; wherein the decision unit extracts the plurality of
GNSS differential correction data from the plurality of external
correction messages; selects a portion of the plurality of GNSS
differential correction data according to a programmable setting;
and stores the selected GNSS differential correction data in the
first storage unit while discarding unselected GNSS differential
correction data.
37. The GNSS receiver of claim 36, wherein the GNSS differential
correction data selected by the decision unit are derived from a
same data source.
38. The GNSS receiver of claim 36, wherein the plurality of
external correction messages are selected from a group consisting
of SBAS messages, RTCM messages, and A-GPS messages.
39. The GNSS receiver of claim 36, wherein a capacity of the first
storage unit is merely sufficient to store GNSS differential
correction data derived from a predetermined data source, wherein
the data amount of the GNSS differential correction data derived
from the predetermined data source is greater than that derived
from other data sources.
40. The GNSS receiver of claim 36, further comprising: a computing
unit coupled to the first storage unit for modifying at least one
of a pseudo-range measurement and a Doppler measurement of the GNSS
receiver according to the GNSS differential correction data stored
in the first storage unit.
Description
BACKGROUND
[0001] The present invention relates to global navigation satellite
systems (GNSS), and more particularly, to methods for processing
external correction messages, correcting position measurements of a
GNSS receiver, and related apparatuses.
[0002] The global navigation satellite systems (GNSS), such as
Global Position System (GPS), Galileo, or GLONASS, are widely used
in many applications. A GNSS receiver can determine its position by
receiving and analyzing coded signals transmitted from a plurality
of orbiting satellites. The GNSS receiver computes the difference
between the time a satellite transmits its signal and the time that
the GNSS receiver receives the signal. The GNSS receiver then
calculates its distance, or "pseudo-range," from the satellite in
accordance with the time difference. Using the pseudo-ranges from
at least four satellites, the GNSS receiver can determine its
three-dimensional position (i.e., latitude, longitude, and
altitude).
[0003] Unfortunately, the GNSS receiver has potential position
errors due primarily to a variety of unintended sources, such as
ionosphere and troposphere delays, receiver clock error, satellite
orbit drift (a.k.a. ephemeris errors), etc. Most of the errors are
"common errors" that are experienced by all the GNSS receivers in a
local area.
[0004] To improve the accuracy of position measurement of the GNSS
receiver, differential global positioning systems (DGPS) were
developed. Conventional DGPS uses a stationary GNSS receiver at a
known location as a reference station. The reference station
measures satellite signal error by comparing its known position
with the position measurement derived from the received satellite
signals, and then transmits GNSS differential correction
information (e.g., timing error measurements) to GNSS receivers
within the area covered by the reference station. The GNSS
differential correction information is applied to the position
calculations of the GNSS receivers so that the GNSS receivers can
get a more accurate position measurement.
[0005] A well-known example of DGPS is the Radio Technical
Commission for Maritime (RTCM) Service provided by the U.S. Coast
Guard. Generally, the GNSS receiver can receive GNSS differential
correction data carried by the RTCM messages from a beacon,
Internet, or through an RS232 cable.
[0006] The Satellite Based Augmentation System (SBAS) is another
source of GNSS differential correction data. There are several
types of SBAS, such as the Wide Area Augmentation System (WAAS) of
North America, the Canada-Wide DGPS Correction Service (CDGPS) of
Canada, the Multi-Functional Satellite Augmentation System (MSAS)
of Japan, and the European Geostationary Navigation Overlay Service
(EGNOS) of Europe. The SBAS satellites broadcast SBAS messages
containing GNSS differential correction data to GNSS receivers
within the coverage area of the SBAS satellites. The GNSS receivers
with SBAS capabilities are capable of using the GNSS differential
correction data carried by the SBAS messages to correct the GNSS
satellite signal errors.
[0007] In addition to the RTCM and SBAS, some cellular
communication systems (e.g., GSM) can also be utilized as a source
of GNSS differential correction data. For example, a GSM base
station can directly transmit A-GPS messages containing GNSS
differential correction data to GNSS receivers with A-GPS
capabilities through a wireless network.
[0008] As described previously, there are many sources of GNSS
differential correction data. However, the data format and contents
are different from each other. If a GNSS receiver wants to support
multiple types of the GNSS differential correction data,
considerable amounts of memory are required, thereby significantly
increasing the hardware cost.
SUMMARY OF THE INVENTION
[0009] It is therefore an objective of the present disclosure to
provide methods and apparatuses for processing external correction
messages to reduce the memory requirement, and associated methods
and apparatuses for correcting position measurements of a GNSS
receiver.
[0010] An exemplary embodiment of a method for processing external
correction messages in a GNSS receiver is disclosed comprising:
providing a first storage unit; receiving a plurality of external
correction messages from different data sources, wherein a
plurality of GNSS differential correction data are carried by the
plurality of external correction messages; and storing a portion of
the GNSS differential correction data in the first storage unit
without storing remaining GNSS differential correction data in the
GNSS receiver.
[0011] An exemplary embodiment of a GNSS receiver is disclosed
comprising: a first storage unit; a receiving module for receiving
a plurality of external correction messages from different data
sources, wherein a plurality of GNSS differential correction data
are carried by the plurality of external correction messages; and a
decision unit, coupled to the receiving module and the first
storage unit, for storing a portion of the GNSS differential
correction data in the first storage unit without storing remaining
GNSS differential correction data in the GNSS receiver.
[0012] An exemplary embodiment of a method for correcting position
measurements of a GNSS receiver is disclosed comprising: providing
a first storage unit; receiving a plurality of external correction
messages from different data sources, wherein a plurality of GNSS
differential correction data are carried by the plurality of
external correction messages; storing a portion of the GNSS
differential correction data in the first storage unit without
storing remaining GNSS differential correction data in the GNSS
receiver; and modifying at least one of a pseudo-range measurement
and a Doppler measurement of the GNSS receiver according to the
GNSS differential correction data stored in the first storage
unit.
[0013] These and other objectives of the present invention will no
doubt become obvious to those of ordinary skill in the art after
reading the following detailed description of the preferred
embodiment that is illustrated in the various figures and
drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0014] FIG. 1 is a simplified block diagram of a global navigation
satellite system (GNSS) receiver according to an exemplary
embodiment.
[0015] FIG. 2 is a flowchart illustrating a method for processing
the external correction messages in the GNSS receiver of FIG. 1
according to a first embodiment of the present invention.
[0016] FIG. 3 is a flowchart illustrating a method for processing
the external correction messages in the GNSS receiver of FIG. 1
according to a second embodiment of the present invention.
DETAILED DESCRIPTION
[0017] Certain terms are used throughout the description and
following claims to refer to particular components. As one skilled
in the art will appreciate, electronic equipment manufacturers may
refer to a component by different names. This document does not
intend to distinguish between components that differ in name but
not in function. In the following description and in the claims,
the terms "include" and "comprise" are used in an open-ended
fashion, and thus should be interpreted to mean "include, but not
limited to . . . ". Also, the term "couple" is intended to mean
either an indirect or direct electrical connection. Accordingly, if
one device is coupled to another device, that connection may be
through a direct electrical connection, or through an indirect
electrical connection via other devices and connections.
[0018] Please refer to FIG. 1, which shows a simplified block
diagram of a global navigation satellite system (GNSS) receiver 100
(e.g., a GPS receiver) according to an exemplary embodiment. The
GNSS receiver 100 comprises a receiving module 110, a decision unit
120, a first storage unit 130, a second storage unit 140, and a
computing unit 150. The first and second storage units 130 and 140
may be separate memory devices or different sections of a same
memory module. The receiving module 110 is arranged for receiving
GNSS signals from a plurality of observable GNSS satellites (such
as GPS satellites) denoted as 102, and for receiving a plurality of
external correction messages transmitted from different data
sources, such as a SBAS satellite 104, an RTCM message source 106,
and a cellular phone base station 108 shown in FIG. 1. As in the
foregoing descriptions, GNSS differential correction data are
carried by the external correction messages.
[0019] Note that the term "external correction message" as used
herein encompasses various signals or data transmitted from a data
source to the GNSS receiver 100. The term "GNSS differential
correction data" as used herein encompasses various signals or
information for improving the accuracy of position measurements of
the GNSS receiver 100. Additionally, the external correction
messages derived from different data sources are usually different
in terms of format and/or contents.
[0020] For example, the SBAS satellite 104 may be a WAAS satellite,
a MSAS satellite, an EGNOS satellite, or any other satellite that
continuously broadcasts SBAS messages carrying GNSS differential
correction data from space. In case of the WAAS satellite, the GNSS
differential correction data carried by the WAAS messages include
message types 1 through 7, 10, 18, and 24 through 26. Note that the
number of the SBAS satellite is not limited to one as illustrated
in FIG. 1.
[0021] In practice, the RTCM message source 106 may be an RTCM
beacon for broadcasting RTCM messages carrying GNSS differential
correction data (such as message types 1, 2, and 9) on a particular
radio frequency, but this is merely an example rather than a
restriction of the practical implementations. For example, since
the RTCM messages can be retrieved form the Internet, the RTCM
message source 106 may be an access point and the receiving module
110 can retrieve the RTCM messages on the Internet from the access
point by adopting wireless means. Alternatively, the receiving
module 110 may be coupled to a mobile device (e.g. a laptop
computer, a cellular phone, etc.) that capable of retrieving the
RTCM messages from the Internet using wireless means. In this case,
the receiving module 110 can receive the RTCM messages from the
mobile device through a RS232 cable or other communication
interfaces, so the mobile device can be regarded as an RTCM message
source for the GNSS receiver 100.
[0022] In addition, the cellular phone base station 108 shown in
FIG. 1 may be a GSM base station or a base station of any other
cellular communication system that capable of transmitting A-GPS
messages containing GNSS differential correction data to the GNSS
receiver 100 through a wireless network.
[0023] The aforementioned SBAS messages, RTCM messages, and A-GPS
messages are merely some examples of the external correction
messages rather than restrictions of the practical implementations.
In other words, the external message sources are not limited to
those illustrated in FIG. 1.
[0024] In operations, the receiving module 110 receives GNSS
signals from each observable GNSS satellite 102. The decision unit
120 stores GNSS data carried by the received GNSS signals in the
second storage unit 140. Then, the computing unit 150 calculates
position measurements (such as a pseudo-range measurement and a
Doppler measurement) for the GNSS receiver 100 according to the
GNSS data stored in the second storage unit 140. The way to
calculate a position measurement for the GNSS receiver 100
according to the GNSS signals is well known in the art, and further
details are omitted herein for brevity. Hereinafter, the operations
of processing the external correction messages will be explained in
detail with reference to FIG. 2 and FIG. 3.
[0025] FIG. 2 is a flowchart 200 illustrating a method for
processing the external correction messages in the GNSS receiver
100 according to a first embodiment of the present invention. Steps
of the flowchart 200 are described below.
[0026] In step 210, the receiving module 110 receives a plurality
of external correction messages from different sources, wherein
GNSS differential correction data of different types are carried by
the plurality of external correction messages. In this embodiment,
the receiving module 110 receives SBAS messages, RTCM messages, and
A-GPS messages from the SBAS satellite 104, the RTCM message source
106, and the cellular phone base station 108, respectively. In
practice, the implementations of the receiving module 110 may vary
with the formats and number of the external correction messages to
be supported by the GNSS receiver 100.
[0027] Although there are many data sources of GNSS differential
correction data, and the data format and contents are different
from each other. Nevertheless, some GNSS differential correction
data derived from different data sources have common
functionalities, such as to correct the pseudo-range measurement
and/or the Doppler measurement of the GNSS receiver 100.
Accordingly, if the GNSS differential correction data derived from
a data source is stored in the first storage unit 130, then
remaining GNSS differential correction data derived from other data
sources that have the same functionalities can be discarded to
reduce the memory requirement.
[0028] Therefore, in step 220, the decision unit 120 selects a
portion of the plurality of external correction messages according
to a programmable setting (not shown). Preferably, the decision
unit 120 selects external correction messages that are derived from
a predetermined data source according to the programmable setting
in step 220. In practice, a user of the GNSS receiver 100 is
allowed to switch/select the source of GNSS differential correction
data by changing the programmable setting.
[0029] In step 230, the decision unit 120 extracts GNSS
differential correction data from the selected external correction
messages.
[0030] Then, the decision unit 120 performs step 240 to store the
GNSS differential correction data extracted from the selected
external correction messages in the first storage unit 130 while
discarding GNSS differential correction data carried by the other
external correction messages. In a preferred embodiment, the first
storage unit 130 is designed to have a capacity that is merely
sufficient to store GNSS differential correction data derived from
a predetermined data source, wherein the data amount of the GNSS
differential correction data derived from the predetermined data
source is greater than that derived from the other data sources.
For example, suppose that the SBAS satellite 104 is a WAAS
satellite, the first storage unit 130 may be designed to have a
capacity that is merely sufficient to store GNSS differential
correction data derived from the WAAS satellite 104. Since the data
amount of the GNSS differential correction data transmitted from
the WAAS satellite 104 is greater than that of the GNSS
differential correction data transmitted from the RTCM message
source 106 or the cellular phone base station 108, the first
storage unit 130 can instead be used to store GNSS differential
correction data derived from the RTCM message source 106 or the
cellular phone base station 108.
[0031] In one aspect, the decision unit 120 functions as a memory
controller and the first storage unit 130 functions as a shared
memory.
[0032] When the GNSS differential correction data extracted from
the selected external correction messages are stored in the first
storage unit 130, the computing unit 150 of the GNSS receiver 100
modifies at least one of the pseudo-range measurement and the
Doppler measurement according to the GNSS differential correction
data stored in the first storage unit 130.
[0033] Please note that the executing order of the steps in the
flowchart 200 is merely an example rather than a restriction of the
practical implementations.
[0034] For example, FIG. 3 shows a flowchart 300 illustrating a
method for processing the external correction messages in the GNSS
receiver 100 according to a second embodiment of the present
invention. Steps of the flowchart 300 are described below.
[0035] In step 310, the receiving module 110 receives a plurality
of external correction messages from different sources, wherein a
plurality of GNSS differential correction data of different types
are carried by the plurality of external correction messages.
Similar to the previous embodiment, the receiving module 110
receives SBAS messages, RTCM messages, and A-GPS messages from the
SBAS satellite 104, the RTCM message source 106, and the cellular
phone base station 108, respectively.
[0036] In step 320, the decision unit 120 extracts the plurality of
GNSS differential correction data from the received SBAS messages,
RTCM messages, and A-GPS messages.
[0037] In step 330, the decision unit 120 selects a portion of the
plurality of GNSS differential correction data according to a
programmable setting (not shown). Preferably, the decision unit 120
selects GNSS differential correction data that are derived from a
predetermined data source (such as the SBAS satellite 104) in step
330. Similarly, the user of the GNSS receiver 100 is allowed to
switch/select the source of GNSS differential correction data by
changing the programmable setting.
[0038] In step 340, the decision unit 120 then stores the selected
GNSS differential correction data in the first storage unit 130
while discarding the unselected GNSS differential correction
data.
[0039] Once the selected GNSS differential correction data are
stored in the first storage unit 130, the computing unit 150
modifies at least one of the pseudo-range measurement and the
Doppler measurement according to the GNSS differential correction
data stored in the first storage unit 130.
[0040] In practice, the decision unit 120 and the computing unit
150 can be realized by a same component, such as a
microprocessor.
[0041] In contrast to the prior art, the disclosed GNSS receiver
100 and related methods can significantly reduce memory
requirements while allowing the GNSS receiver 100 to support
different data sources of GNSS differential correction data.
[0042] Those skilled in the art will readily observe that numerous
modifications and alterations of the device and method may be made
while retaining the teachings of the invention. Accordingly, the
above disclosure should be construed as limited only by the metes
and bounds of the appended claims.
* * * * *