U.S. patent application number 12/015326 was filed with the patent office on 2010-09-23 for method and apparatus for obtaining satellite trajectory data at a satellite positioning system receiver.
Invention is credited to Charles Abraham, Boaz Efroni Rotman.
Application Number | 20100238069 12/015326 |
Document ID | / |
Family ID | 36180215 |
Filed Date | 2010-09-23 |
United States Patent
Application |
20100238069 |
Kind Code |
A9 |
Rotman; Boaz Efroni ; et
al. |
September 23, 2010 |
METHOD AND APPARATUS FOR OBTAINING SATELLITE TRAJECTORY DATA AT A
SATELLITE POSITIONING SYSTEM RECEIVER
Abstract
Method and apparatus for locating position of a mobile receiver
is described. In one embodiment, satellite measurements are
obtained at the mobile receiver for a plurality of satellites in a
satellite positioning system constellation. Satellite trajectory
data is obtained at the mobile receiver from a server. Ephemeris
data is obtained at the mobile receiver from at least one satellite
of the plurality of satellites. Position is computed for the mobile
receiver using the satellite measurements, the satellite trajectory
data, and the ephemeris data.
Inventors: |
Rotman; Boaz Efroni;
(Cupertino, CA) ; Abraham; Charles; (Los Gatos,
CA) |
Correspondence
Address: |
MCANDREWS HELD & MALLOY, LTD
500 WEST MADISON STREET
SUITE 3400
CHICAGO
IL
60661
US
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Prior
Publication: |
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Document Identifier |
Publication Date |
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US 20080111739 A1 |
May 15, 2008 |
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Family ID: |
36180215 |
Appl. No.: |
12/015326 |
Filed: |
January 16, 2008 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10968345 |
Oct 19, 2004 |
7342533 |
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12015326 |
Jan 16, 2008 |
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10774309 |
Feb 6, 2004 |
7447253 |
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12015326 |
Jan 16, 2008 |
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10926791 |
Aug 26, 2004 |
7688260 |
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12015326 |
Jan 16, 2008 |
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10976191 |
Oct 28, 2004 |
7327310 |
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12015326 |
Jan 16, 2008 |
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Current U.S.
Class: |
342/357.42 ;
342/357.64 |
Current CPC
Class: |
G01S 19/258 20130101;
G01S 19/05 20130101 |
Class at
Publication: |
342/357.42 ;
342/357.64 |
International
Class: |
G01S 19/05 20100101
G01S019/05; G01S 19/24 20100101 G01S019/24 |
Claims
1. A method of locating position of a mobile receiver, comprising:
obtaining satellite measurements at said mobile receiver for a
plurality of satellites in a satellite positioning system
constellation; obtaining satellite trajectory data at said mobile
receiver from a server; obtaining ephemeris data at said mobile
receiver from at least one satellite of said plurality of
satellites; and computing position of said mobile receiver using
said satellite measurements, said satellite trajectory data, and
said ephemeris data.
2. The method of claim 1, wherein said satellite trajectory data is
obtained from said server at a first time, and wherein the method
further comprises: detecting connectivity between said mobile
receiver and said server at a second time; wherein said ephemeris
data is obtained from said at least one satellite in response to
absence of said connectivity at said second time.
3. The method of claim 1, wherein said satellite trajectory data is
obtained from said server at a first time and said ephemeris data
is obtained from said at least one satellite at a second time, and
wherein the method further comprises: determining whether a
combination of said satellite trajectory data and said ephemeris
data includes data for each of said plurality of satellites; and
obtaining additional satellite trajectory data at said mobile
receiver from said server in response to said combination ephemeris
data not including data for each of said plurality of
satellites.
4. The method of claim 1, wherein said satellite trajectory data is
obtained from said server at a first time and said ephemeris data
is obtained from said at least one satellite at a second time, and
wherein the method further comprises: processing a combination of
said satellite trajectory data and said ephemeris data to identify
missing data for said plurality of satellites; and obtaining said
missing data at said mobile receiver from said server.
5. The method of claim 1, wherein said satellite trajectory data
comprises ephemeris.
6. The method of claim 1, wherein said satellite trajectory data is
associated with a set of satellites in said satellite positioning
system constellation exclusive of said at least one satellite.
7. The method of claim 6, wherein said satellite trajectory data is
obtained at a first time and said ephemeris data is obtained at a
second time, and wherein said at least one satellite is not in view
of said mobile receiver at said first time.
8. The method of claim 1, wherein said step of obtaining said
ephemeris data comprises: detecting at least one satellite signal
broadcast by said at least one satellite; and decoding said at
least one satellite signal to obtain said ephemeris data.
9. A mobile receiver, comprising: a wireless transceiver for
obtaining satellite trajectory data from a server; a satellite
signal receiver for obtaining satellite measurements for a
plurality of satellites in a satellite positioning system
constellation and obtaining ephemeris data from at least one
satellite of said plurality of satellites; and a processor for
computing position of said mobile receiver using said satellite
measurements, said satellite trajectory data, and said ephemeris
data.
10. The mobile receiver of claim 9, further comprising: means for
detecting connectivity between said mobile receiver and said
server; wherein said satellite signal receiver is configured to
obtain said ephemeris data from said at least one satellite in
response to absence of said connectivity at said second time.
11. The mobile receiver of claim 9, further comprising: means for
determining whether a combination of said satellite trajectory data
and said ephemeris data includes data for each of said plurality of
satellites; wherein said wireless transceiver is configured to
obtain additional satellite trajectory data from said server in
response to said combination ephemeris data not including data for
each of said plurality of satellites.
12. The mobile receiver of claim 9, wherein said processor is
configured to process a combination of said satellite trajectory
data and said ephemeris data to identify missing data for said
plurality of satellites, and wherein said wireless transceiver is
configured to obtain said missing data from said server.
13. The mobile receiver of claim 9, wherein said satellite
trajectory data comprises ephemeris.
14. The mobile receiver of claim 9, wherein said satellite
trajectory data is associated with a set of satellites in said
satellite positioning system constellation exclusive of said at
least one satellite.
15. The mobile receiver of claim 9, wherein said satellite signal
receiver is configured to: detect at least one satellite signal
broadcast by said at least one satellite; and decode said at least
one satellite signal to obtain said ephemeris data.
16. Apparatus for locating position of a mobile receiver,
comprising: means for obtaining satellite measurements at said
mobile receiver for a plurality of satellites in a satellite
positioning system constellation; means for obtaining satellite
trajectory data at said mobile receiver from a server; means for
obtaining ephemeris data at said mobile receiver from at least one
satellite of said plurality of satellites; and means for computing
position of said mobile receiver using said satellite measurements,
said satellite trajectory data, and said ephemeris data.
17. The apparatus of claim 16, wherein said satellite trajectory
data is obtained from said server at a first time, and wherein the
apparatus further comprises: means for detecting connectivity
between said mobile receiver and said server at a second time;
wherein said ephemeris data is obtained from said at least one
satellite in response to absence of said connectivity at said
second time.
18. The apparatus of claim 16, wherein said satellite trajectory
data is obtained from said server at a first time and said
ephemeris data is obtained from said at least one satellite at a
second time, and wherein the apparatus further comprises: means for
determining whether a combination of said satellite trajectory data
and said ephemeris data includes data for each of said plurality of
satellites; and means for obtaining additional satellite trajectory
data at said mobile receiver from said server in response to said
combination ephemeris data not including data for each of said
plurality of satellites.
19. The apparatus of claim 16, wherein said satellite trajectory
data is obtained from said server at a first time and said
ephemeris data is obtained from said at least one satellite at a
second time, and wherein the apparatus further comprises: means for
processing a combination of said satellite trajectory data and said
ephemeris data to identify missing data for said plurality of
satellites; and means for obtaining said missing data at said
mobile receiver from said server.
20. The apparatus of claim 16, wherein said satellite trajectory
data comprises ephemeris.
21. The apparatus of claim 16, wherein said satellite trajectory
data is associated with a set of satellites in said satellite
positioning system constellation exclusive of said at least one
satellite.
22. The apparatus of claim 21, wherein said satellite trajectory
data is obtained at a first time and said ephemeris data is
obtained at a second time, and wherein said at least one satellite
is not in view of said mobile receiver at said first time.
23. The apparatus of claim 16, wherein said means for obtaining
said ephemeris data comprises: means for detecting at least one
satellite signal broadcast by said at least one satellite; and
means for decoding said at least one satellite signal to obtain
said ephemeris data.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application is a continuation of U.S. patent
application Ser. No. 10/968,345 filed Oct. 19, 2004, which is
incorporated by reference herein in its entirety.
BACKGROUND OF THE INVENTION FIELD OF THE INVENTION
[0002] Embodiments of the present invention generally relate to
satellite position location systems. More particularly, the
invention relates to a method and apparatus for obtaining satellite
trajectory data at a satellite positioning system receiver.
DESCRIPTION OF THE RELATED ART
[0003] Global Positioning System (GPS) receivers use measurements
from several satellites to compute position. GPS receivers normally
determine their position by computing time delays between
transmission and reception of signals transmitted from satellites
and received by the receiver on or near the surface of the earth.
The time delays multiplied by the speed of light provide the
distance from the receiver to each of the satellites that are in
view of the receiver.
[0004] More specifically, each GPS signal available for commercial
use utilizes a direct sequence spreading signal defined by a unique
pseudo-random noise (PN) code (referred to as the coarse
acquisition (C/A) code) having a 1.023 MHz spread rate. Each PN
code bi-phase modulates a 1575.42 MHz carrier signal (referred to
as the L1 carrier) and uniquely identifies a particular satellite.
The PN code sequence length is 1023 chips, corresponding to a one
millisecond time period. One cycle of 1023 chips is called a PN
frame or epoch.
[0005] GPS receivers determine the time delays between transmission
and reception of the signals by comparing time shifts between the
received PN code signal sequence and internally generated PN signal
sequences. These measured time delays are referred to as
"sub-millisecond pseudoranges", since they are known modulo the 1
millisecond PN frame boundaries. By resolving the integer number of
milliseconds associated with each delay to each satellite, then one
has true, unambiguous, pseudoranges. A set of four pseudoranges
together with a knowledge of absolute times of transmission of the
GPS signals and satellite positions in relation to these absolute
times is sufficient to solve for the position of the GPS receiver.
The absolute times of transmission (or reception) are needed in
order to determine the positions of the GPS satellites at the times
of transmission and hence to compute the position of the GPS
receiver.
[0006] Accordingly, each of the GPS satellites broadcasts a model
of satellite orbit and clock data known as the satellite navigation
message. The satellite navigation message is a 50 bit-per-second
(bps) data stream that is modulo-2 added to the PN code with bit
boundaries aligned with the beginning of a PN frame. There are
exactly 20 PN frames per data bit period (20 milliseconds). The
satellite navigation message includes satellite-positioning data,
known as "ephemeris" data, which identifies the satellites and
their orbits, as well as absolute time information (also referred
to herein as "GPS time" or "time-of-day") associated with the
satellite signal. The absolute time information is in the form of a
second of the week signal, referred to as time-of-week (TOW). This
absolute time signal allows the receiver to unambiguously determine
a time tag for when each received signal was transmitted by each
satellite.
[0007] In some GPS applications, the signal strengths of the
satellite signals are so low that either the received signals
cannot be processed, or the time required to process the signals is
excessive. As such, to improve the signal processing, a GPS
receiver may receive assistance data from a network to assist in
satellite signal acquisition and/or processing. For example, the
GPS receiver may be integrated within a cellular telephone and may
receive the assistance data from a server using a wireless
communication network. This technique of providing assistance data
to a remote mobile receiver has become known as "Assisted-GPS" or
A-GPS. In some A-GPS systems, the assistance data received from the
network comprises ephemeris data for satellites in-view of the GPS
receiver. Conventionally, the GPS receiver polls the network every
15 to 30 minutes for updated ephemeris to allow for inclusion of
newly risen satellites in the navigation solution.
[0008] Presently, if the connection between the GPS receiver and
the network is lost (e.g., the receiver roams out of the service
area of the network or communications between the network and the
receiver are blocked by obstructions), the GPS receiver cannot
obtain updated ephemeris from the network. As such, the GPS
receiver must wait until the network connection is re-established
before obtaining updated ephemeris. As a result, the GPS receiver
may not have sufficient ephemeris data to compute position during
the time that the network connection is lost.
[0009] Accordingly, there exists a need in the art for a method and
apparatus capable of locating position of a mobile receiver when
unable to receive satellite trajectory data from a network.
SUMMARY OF THE INVENTION
[0010] Method and apparatus for locating position of a mobile
receiver is described. In one embodiment, satellite measurements
are obtained at the mobile receiver for a plurality of satellites
in a satellite positioning system constellation. Satellite
trajectory data is obtained at the mobile receiver from a server.
Ephemeris data is obtained at the mobile receiver from at least one
satellite of the plurality of satellites. Position is computed for
the mobile receiver using the satellite measurements, the satellite
trajectory data, and the ephemeris data.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] 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. It is to be noted, however,
that the appended drawings illustrate only typical embodiments of
this invention and are therefore not to be considered limiting of
its scope, for the invention may admit to other equally effective
embodiments.
[0012] FIG. 1 is a block diagram depicting an exemplary embodiment
of a position location system;
[0013] FIG. 2 is a flow diagram depicting an exemplary embodiment
of a method of obtaining satellite trajectory data at a mobile
receiver in accordance with the invention;
[0014] FIG. 3 is a flow diagram depicting another exemplary
embodiment of a method for obtaining satellite trajectory data at a
mobile receiver in accordance with the invention;
[0015] FIG. 4 is a flow diagram depicting yet another exemplary
embodiment of a method for obtaining satellite trajectory data at a
mobile receiver in accordance with the invention; and
[0016] FIG. 5 is a data flow diagram depicting an exemplary
embodiment of a method for computing position of a mobile receiver
in accordance with the invention.
[0017] To facilitate understanding, identical reference numerals
have been used, wherever possible, to designate identical elements
that are common to the figures.
DETAILED DESCRIPTION
[0018] A method and apparatus for locating position of a mobile
receiver in a satellite position location system is described.
Those skilled in the art will appreciate that the invention may be
used with various types of mobile or wireless devices that are
"location-enabled," such as cellular telephones, pagers, laptop
computers, personal digital assistants (PDAs), and like type
wireless devices known in the art. Generally, a location-enabled
mobile device is facilitated by including in the device the
capability of processing satellite positioning system (SPS)
satellite signals.
[0019] FIG. 1 is a block diagram depicting an exemplary embodiment
of a position location system 100. The system 100 comprises a
mobile receiver 102 in communication with a server 108 via a
wireless communication network 110. For example, the server 108 may
be disposed in a serving mobile location center (SMLC) of the
wireless communication network 110. The wireless communication
network 110 may comprise a cellular communication network having a
plurality of base stations or cell sites. The mobile receiver 102
is configured to receive satellite signals from a plurality of
satellites 112 in a constellation of satellites. The mobile
receiver 102 processes the received signals to produce satellite
measurement data (e.g., pseudoranges, Doppler measurements) with
respect to the satellites 112.
[0020] The mobile receiver 102 is configured to request and receive
satellite trajectory data from the server 108 (e.g., ephemeris data
or other satellite orbit model). The mobile receiver 102 may
receive the satellite trajectory data via the wireless
communication network 110 or from a network 109, such as the
Internet. Such a configuration is referred to as a mobile station
based or "MS-based" mode. The mobile receiver 102 is also
configured to obtain satellite navigation data directly from the
satellites 112 (e.g., ephemeris data). Notably, the GPS receiver
104 may decode satellite signals to recover the satellite
navigation data using a well known decoding process. Such a
configuration is referred to as an "autonomous" mode.
[0021] In one embodiment of the invention, if the mobile receiver
102 is not capable of communication with the server 108 at a given
moment, the mobile receiver 102 may transition from obtaining
satellite trajectory data from the server 108 to obtaining
ephemeris directly from the satellites 112. That is, the mobile
receiver 102 may transition from MS-based mode to autonomous mode.
For example, the mobile receiver 102 may update satellite
trajectory data obtained from the server 108 with ephemeris
obtained directly from the satellites 112 to allow for inclusion of
newly risen satellites (i.e., satellites that were not in view of
the mobile receiver 102 at the time the server 108 sent the
satellite trajectory data and thus were not accounted for by the
server 108). The mobile receiver 102 may then compute position
using a combination of satellite trajectory data obtained from the
server 108 and ephemeris obtained directly from the satellites
112.
[0022] In another embodiment of the invention, the mobile receiver
102 is configured to initially attempt to obtain ephemeris directly
from the satellites 112 (i.e., the mobile receiver 102 is
initialized in autonomous mode). If sufficient ephemeris cannot be
obtained directly from the satellites 112, the mobile receiver 102
then transitions to obtaining satellite trajectory data from the
server 108 (i.e., the mobile receiver 102 transitions to MS-based
mode). In this manner, the mobile receiver 102 only communicates
with the server 108 if sufficient satellite orbit data cannot be
obtained from the satellites 112, which minimizes network
traffic.
[0023] The mobile receiver 102 illustratively comprises a GPS
receiver 104, a wireless transceiver 106, a processor 122, support
circuits 124, an input/output (I/O) interface 150, and a memory
120. The GPS receiver 104 receives satellite signals from the
satellites 112 using an antenna 116. The GPS receiver 104 may
comprise a conventional A-GPS receiver. An exemplary A-GPS receiver
is described in commonly-assigned U.S. Pat. No. 6,453,237, issued
Sep. 17, 2002, which is incorporated by reference herein in its
entirety. The wireless transceiver 106 receives wireless signals
from the wireless communication network 110 via an antenna 118. The
GPS receiver 104 and the wireless transceiver 106 may be controlled
by the processor 122.
[0024] The processor 122 may comprise a microprocessor,
instruction-set processor (e.g., a microcontroller), or like type
processing element known in the art. The processor 122 is coupled
to the memory 120 and the support circuits 124. The memory 120 may
be random access memory, read only memory, removable storage, hard
disc storage, or any combination of such memory devices. The memory
120 may be used to store satellite trajectory data 139 received
from the server 108 and/or the satellites 112. Various processes
and methods described herein may be implemented via software 140
stored in the memory 120 for execution by the processor 122.
Alternatively, such processes and methods may be implemented using
dedicated hardware, such as an application specific integrated
circuit (ASIC), or a combination of hardware and software. The
support circuits 124 include conventional cache, power supplies,
clock circuits, data registers, I/O circuitry, and the like to
facilitate operation of the mobile receiver 102. The I/O interface
150 may comprise a modem or like-type communication interface for
communicating with the network 109.
[0025] Satellite navigation data, such as ephemeris for at least
the satellites 112, may be collected by a network of tracking
stations ("reference network 114"). The reference network 114 may
include several tracking stations that collect satellite navigation
data from all the satellites in the constellation, or a few
tracking stations, or a single tracking station that only collects
satellite navigation data for a particular region of the world. An
exemplary system for collecting and distributing ephemeris is
described in commonly-assigned U.S. Pat. No. 6,411,892, issued Jun.
25, 2002, which is incorporated by reference herein in its
entirety. The reference network 114 may provide the collected
satellite navigation data to the server 108.
[0026] The server 108 illustratively comprises an input/output
(I/O) interface 128, a central processing unit (CPU) 126, support
circuits 130, and a memory 134. The CPU 126 is coupled to the
memory 134 and the support circuits 130. The memory 134 may be
random access memory, read only memory, removable storage, hard
disc storage, or any combination of such memory devices. The
support circuits 130 include conventional cache, power supplies,
clock circuits, data registers, I/O interfaces, and the like to
facilitate operation of the server 108. The I/O interface 128 is
configured to receive satellite navigation data from the reference
network 114 and is configured for communication with the wireless
communication network 110. In addition, the I/O interface 128 may
be in communication with the network 109.
[0027] The server 108 may use the satellite navigation data from
the reference network 114 to provide assistance data to the mobile
receiver 102. The assistance data comprises satellite trajectory
data (e.g., ephemeris, Almanac, and/or some other orbit model).
Upon request, the server 108 may transmit satellite trajectory data
to the mobile receiver 102 via the wireless communication network
110. Alternatively, the mobile receiver 102 may receive satellite
trajectory data via the network 109. Notably, the satellite
trajectory data may comprise a long term satellite trajectory
model, as described in commonly-assigned U.S. Pat. No. 6,560,534,
issued May 6, 2003, which is incorporated by reference herein in
its entirety.
[0028] FIG. 2 is a flow diagram depicting an exemplary embodiment
of a method 200 for obtaining satellite trajectory data at a mobile
receiver in accordance with the invention. Aspects of the method
200 may be understood with simultaneous reference to FIG. 1. The
method 200 begins at step 202, where the mobile receiver 102
initially obtains satellite trajectory data from the server 108
(e.g., the mobile receiver 102 is configured to operate in a MS
based mode). The mobile receiver 102 may use the satellite
trajectory data along with satellite measurement data to compute
position.
[0029] At step 204, a determination is made as to whether the
satellite trajectory data should be updated. The satellite
trajectory data may be updated upon occurrence of various
conditions. For example, the satellite trajectory data obtained at
step 202 is valid for a particular period of time (e.g., broadcast
ephemeris data is valid for two to four hours). The satellite
trajectory data should be updated if the associated validity period
has expired. In another example, the satellite trajectory data
obtained at step 202 corresponds to a particular set of satellites
in the constellation (e.g., satellites in-view of the mobile
receiver 102 at the time the satellite trajectory data was sent by
the server 108). If the mobile receiver 102 is receiving satellite
signals from satellites not accounted for in the current satellite
trajectory data, then the satellite trajectory data should be
updated to account for the new satellites (e.g., satellites that
were previously below the horizon, but are now in view). In yet
another example, the satellite trajectory data may be updated
periodically in accordance with a pre-defined schedule (e.g., every
15 to 30 minutes).
[0030] If the satellite trajectory data should be updated, the
method 200 proceeds to step 206. Otherwise, step 204 is repeated
until the satellite trajectory data should be updated. At step 206,
a determination is made as to whether a connection between the
mobile receiver 102 and the server 108 can be established. If so,
the method 200 proceeds to step 208. Otherwise, the method 200
proceeds to step 210. At step 208, the mobile receiver 102 requests
updated satellite trajectory data from the server 108. The method
200 then returns to step 204.
[0031] At step 210, the mobile receiver obtains ephemeris from one
or more in-view satellites. For example, the mobile receiver 102
may decode satellite signals to obtain ephemeris data for one or
more satellites. The ephemeris data may be used to update the
satellite trajectory data. For example, the mobile receiver 102 may
obtain ephemeris from newly risen satellites that were not in view
at the time the most recent satellite trajectory data was obtained
from the server 108. The mobile receiver 102 may also obtain
ephemeris data for particular satellites to replace expired
portions of the most recent satellite trajectory data obtained from
the server 108. The mobile receiver 102 may then compute its
position using a combination of ephemeris received from satellites
and satellite trajectory data received from the server 108 (e.g.,
ephemeris data). The method 200 then returns to step 204.
[0032] In this manner, the mobile receiver 102 may continue to
compute position when updated satellite orbit data is required
despite a lack of connectivity to the server 108. In addition, if
connectivity is lost, the mobile receiver 102 is able to utilize
any valid satellite trajectory data previously obtained from the
server 108 in combination with any recently obtained ephemeris data
acquired directly from the satellites to compute position
("enhanced autonomous mode"). If connectivity is absent for a long
enough period such that the most recently obtained satellite
trajectory data from the server 108 is completely invalid, then the
mobile receiver 102 must obtain all of the required ephemeris data
directly from the satellites ("full autonomous mode").
[0033] FIG. 3 is a flow diagram depicting another exemplary
embodiment of a method 300 for obtaining satellite trajectory data
at a mobile receiver in accordance with the invention. Aspects of
the method 300 may be understood with reference to FIG. 1. The
method 300 begins at step 302, where the mobile receiver 102
initially obtains satellite trajectory data from the server 108
(e.g., the mobile receiver 102 is configured to operate in a MS
based mode). The mobile receiver 102 may use the initial satellite
trajectory data along with satellite measurement data to compute
position.
[0034] At step 304, a determination is made as to whether the
satellite trajectory data should be updated. The satellite
trajectory data may be updated upon occurrence of various
conditions, such as those described above with respect to the
method 200 of FIG. 2. Notably, new the mobile receiver 102 may be
in view of new satellites not accounted for in the initial
satellite trajectory data. For example, the mobile receiver 102 may
detect new satellites using Almanac data. As is well known in the
art, the Almanac provides coarse satellite trajectory data that is
valid for two months. The mobile receiver 102 may use the Almanac
as a basis for deciding which satellites are currently in view. If
one or more satellites are currently in-view for which there is no
satellite trajectory-data; the mobile-receiver 102 attempts to
obtain ephemeris directly from such new satellites. In another
embodiment of the invention, the may detect the presence of the PN
codes for new satellites. That is, if the GPS receiver 104 detects
PN codes of satellites for which there is no satellite trajectory
data, the mobile receiver 102 may attempt to obtain ephemeris data
directly from such new satellites.
[0035] If no update is necessary, the step 304 is repeated.
Otherwise, the method 300 proceeds to step 306. At step 306, the
mobile receiver 102 attempts to obtain ephemeris data from one or
more satellites to update the initial satellite trajectory data
(e.g., obtain ephemeris for the newly detected satellites). At step
308, a determination is made as to whether ephemeris has been
obtained from the satellite(s). If so, the method 300 returns to
step 304. If not, the method 300 proceeds to step 310. Notably, the
mobile receiver may attempt to obtain ephemeris from the
satellite(s) for a predefined period of time. If ephemeris has not
been obtained from the satellites after the time period elapses,
the method proceeds to step 310.
[0036] At step 310, the mobile receiver 102 requests satellite
trajectory data from the server 108. The mobile receiver 102 may
request data from the server 108 for only the new satellites, or
may request a completely updated set of satellite trajectory data
for all currently in-view satellites. The method 300 then returns
to step 304. The mobile receiver 102 thus minimizes communication
with the server 108 (e.g., minimizes air-time usage) by first
attempting to update the initial satellite trajectory data using
ephemeris directly from the satellites before getting such an
update from the server.
[0037] FIG. 4 is a flow diagram depicting yet another exemplary
embodiment of a method 400 for obtaining satellite trajectory data
at a mobile receiver in accordance with the invention. Aspects of
the method 400 may be understood with reference to FIG. 1. The
method 400 begins at step 401. At step 402, the mobile receiver 102
attempts to obtain ephemeris data from satellites in view of the
mobile receiver 102. At step 404, a determination is made as to
whether sufficient ephemeris has been obtained to compute position
of the mobile receiver 102. In one embodiment, the mobile receiver
102 has "sufficient" ephemeris data if ephemeris has been obtained
from each satellite for which measurements are being used in a
position calculation. For example, the mobile receiver 102 may use
measurements from four in-view satellites and thus would require
ephemeris from those four satellites. As understood by those
skilled in the art, the mobile receiver 102 may generally require
measurements to one or more satellites, depending on the number of
position and time variables that need to be computed. Notably, some
of the variables (e.g., x, y, z position variables and common-mode
bias and time-of-day variables) may be known or fixed a-priori
(e.g., the z or altitude position variable may be fixed using a
terrain model).
[0038] If, at step 404, sufficient ephemeris has been obtained, the
method 400 ends at step 499. Otherwise, the method 400 proceeds to
step 406. At step 406, the mobile receiver 102 requests satellite
trajectory data from the server 108. In one embodiment, the mobile
receiver 102 only requests satellite trajectory data for the
in-view satellites for which such information is missing. In this
manner, communication time between the mobile receiver 102 and the
server 108 is reduced. The method 400 ends at step 499.
[0039] FIG. 5 is a data flow diagram depicting an exemplary
embodiment of a method 500 for computing position of a mobile
receiver in accordance with the invention. Aspects of the method
500 may be understood with reference to FIG. 1. Satellite
measurement data 506 and satellite tracking data 502 are input to a
position computation process 508 to produce position data 510. The
position computation process 508 implements a conventional
navigation solution. The satellite tracking data 502 is updated via
the update process 504. In one embodiment, the satellite tracking
data is initially obtained from the server 108 and the update
process 504 is implemented using the method 200 or the method 300
described above with respect to FIGS. 2 and 3, respectively. In
another embodiment, the satellite tracking data is obtained and
updated using the method 400 described above with respect to FIG.
4.
[0040] 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, the
European GALILEO system, combinations of these systems with one
another, and combinations of these systems and other satellites
providing similar signals, such as the wide area augmentation
system (WAAS) and SBAS that provide GPS-like signals. The term
"GPS" used herein includes such alternative satellite positioning
systems, including the Russian GLONASS system, the European GALILEO
system, the WAAS system, and the SBAS system, as well as
combinations thereof.
[0041] While the foregoing is directed to 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.
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