U.S. patent application number 09/766184 was filed with the patent office on 2001-10-11 for gps receiver utilizing a communication link.
Invention is credited to Krasner, Norman F..
Application Number | 20010028321 09/766184 |
Document ID | / |
Family ID | 27116694 |
Filed Date | 2001-10-11 |
United States Patent
Application |
20010028321 |
Kind Code |
A1 |
Krasner, Norman F. |
October 11, 2001 |
GPS receiver utilizing a communication link
Abstract
Methods and apparatuses for deriving an approximate Doppler for
a satellite positioning system (SPS) receiver from an approximate
location which is obtained from a cellular communication system
information source. In one embodiment, an approximate location of
the SPS receiver is derived from the information source and this
approximation location is used to determine approximate Dopplers to
a plurality of SPS satellites at a given time. The approximate
Dopplers are then used to reduce processing time in either
determining pseudoranges to the SPS satellites or acquiring signals
from the SPS satellites. In another aspect of the invention, a
reference signal is used to provide a local oscillator signal which
is used to acquire SPS signals in an SPS receiver. This reference
signal is extracted from a data signal modulated on a carrier
frequency. The data signal on the carrier frequency is transmitted
from, in one example, a wireless cell site which is communicating
with the SPS receiver which has a cellular based communication
receiver.
Inventors: |
Krasner, Norman F.; (San
Carlos, CA) |
Correspondence
Address: |
James C. Scheller, Jr.
BLAKELY, SOKOLOFF, TAYLOR & ZAFMAN LLP
Seventh Floor
12400 Wilshire Boulevard
Los Angeles
CA
90025-1026
US
|
Family ID: |
27116694 |
Appl. No.: |
09/766184 |
Filed: |
January 18, 2001 |
Related U.S. Patent Documents
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Application
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Filing Date |
Patent Number |
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09766184 |
Jan 18, 2001 |
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08842559 |
Apr 15, 1997 |
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6208290 |
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08842559 |
Apr 15, 1997 |
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08759523 |
Dec 4, 1996 |
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5841396 |
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08842559 |
Apr 15, 1997 |
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08612582 |
Mar 8, 1996 |
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5874914 |
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60005318 |
Oct 9, 1995 |
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Current U.S.
Class: |
342/357.64 |
Current CPC
Class: |
G01S 5/0045 20130101;
G01S 5/009 20130101; H03D 7/163 20130101; G01S 19/41 20130101; H03J
7/047 20130101; G01S 2205/008 20130101; G06F 2221/2111 20130101;
H03J 2200/11 20130101; G01S 19/256 20130101; H03J 1/0008 20130101;
G01S 19/254 20130101; G01S 19/06 20130101; G01S 19/071 20190801;
G01S 19/09 20130101; H01Q 1/273 20130101; G01S 19/258 20130101;
H04B 1/3805 20130101; H04B 1/00 20130101; G01S 19/235 20130101;
H04B 1/0007 20130101; G01S 5/0036 20130101; G01S 5/0054 20130101;
H01Q 21/28 20130101; H03J 7/06 20130101; G01S 19/11 20130101; G01S
19/252 20130101; H04B 1/28 20130101; H03J 7/04 20130101 |
Class at
Publication: |
342/357.1 |
International
Class: |
G01S 005/14 |
Claims
What is claimed is:
1. A method for reducing processing time in a satellite positioning
system (SPS) receiver having a cell based communication receiver,
said method comprising: determining an approximate location of said
SPS receiver from a cell based information source, said approximate
location being determined by at least one of a location of a
cellular service area which includes a cell site or a location of
said cell site; determining an approximate Doppler for at least one
SPS satellite relative to said SPS receiver, said approximate
Doppler being based on said approximate location; using said
approximate Doppler in said SPS receiver to reduce processing time
in one of either determining at least one pseudorange to said at
least one SPS satellite or acquiring signals from said at least one
SPS satellite.
2. A method as in claim 1 further comprising: transmitting said
approximate Doppler from said cell site to said cell based
communication receiver and wherein said cell site is capable of
communicating with said cell based communication receiver.
3. A method as in claim 2 wherein said approximate location is
determined by either a selected position in a general geographical
region defined by said cellular service area or said location of
said cell site which is located in a portion of said general
geographical region.
4. A method as in claim 2 further comprising: transmitting said at
least one pseudorange from said SPS receiver to a remote processing
station.
5. A method as in claim 4 wherein said transmitting step is through
said cell site.
6. A method as in claim 5 wherein said remote processing station is
located at said cell site.
7. A method as in claim 5 wherein said remote processing station is
coupled to a cellular switching center.
8. A method as in claim 7 wherein said approximate Doppler is
determined by said remote processing station.
9. A method as in claim 8 wherein said remote processing station
receives said approximate location from said cell site and provides
said approximate Doppler to said SPS receiver through said cell
site.
10. A method as in claim 8 wherein said remote processing station
receives a cell site identifier from said cell site and determines
said approximate location from said cell site identifier and
provides said approximate Doppler to said SPS receiver through said
cell site.
11. A method as in claim 10 wherein said remote processing station
comprises a storage device having a table which relates said cell
site identifier to said approximate location and wherein said
remote processing station has access to information specifying a
plurality of approximate Dopplers at a given time for said
approximate location.
12. A method as in claim 1 further comprising: transmitting said at
least one pseudorange from said SPS receiver to a remote processing
station through said cell site, and wherein said cell based
communication receiver is integrated in one enclosure with said SPS
receiver.
13. A method as in claim 12 wherein said remote processing station
is coupled to a cellular switching center which is coupled to a
plurality of cell sites, including said cell site.
14. A method of using a data processing station which is capable of
being coupled to at least one wireless cell site, said method
comprising: receiving a site information which determines an
approximate location, said approximate location being determined by
at least one of a location of a cellular service area which
includes said wireless cell site or a location of said wireless
cell site; determining an approximate Doppler for at least one SPS
satellite, said approximate Doppler being based on said approximate
location; transmitting said approximate Doppler to said wireless
cell site.
15. A method as in claim 14 further comprising: receiving at least
one pseudorange from said wireless cell site, said pseudorange
being provided by a satellite positioning system (SPS) receiver
having a cell based communication receiver which is capable of
communicating with said wireless cell site.
16. A method as in claim 15 further comprising: transmitting a
request for a position information from said SPS receiver, said
request being transmitted to said wireless cell site.
17. A method as in claim 16 wherein said step of transmitting a
request occurs after said step of transmitting said approximate
Doppler.
18. A method as in claim 15 wherein said data processing station is
capable of being coupled to a plurality of wireless cell sites.
19. A method as in claim 15 wherein said site information
identifies said wireless cell site and wherein said data processing
station determines said approximate location from said site
information.
20. A method as in claim 15 wherein said site information provides
said approximate location.
21. A method as in claim 15 wherein said data processing station
accesses a storage device which contains information specifying a
plurality of approximate Dopplers at a given time.
22. A method as in claim 15 wherein said approximate location and
said at least one pseudorange are used to calculate a position
information for said SPS receiver.
23. A data processing station comprising: a processor; a storage
device coupled to said processor; a transceiver coupled to said
processor, said transceiver for coupling said data processing
station to a wireless cell site, said storage device containing
information specifying at least one approximate Doppler at a given
time for an approximate location determined by at least one of a
location of a cellular service area which includes said wireless
cell site or a location of said wireless cell site, said
transceiver receiving a site information which determines said
approximate location, said processor determining an approximate
Doppler for at least one SPS satellite, said approximate Doppler
being based on said approximate location, and said transceiver
sending said approximate Doppler to said wireless cell site.
24. A data processing station as in claim 23 further comprising: a
source of SPS signals coupled to said processor, and wherein said
transceiver receives at least one pseudorange from said wireless
cell site and wherein said processor uses said SPS signals and said
at least one pseudorange to determine a position information for a
satellite position system (SPS) receiver which is capable of
communicating with said wireless cell site.
25. A data processing system as in claim 24 wherein said data
processing system is capable of being coupled to another data
processing system which issues a request to provide said position
information to said another data processing system.
26. A data processing system as in claim 25 wherein said data
processing system and said another data processing system are
coupled through the Internet.
27. A data processing system as in claim 24 wherein said source of
SPS signals comprises one or more SPS receivers.
28. A computer readable medium containing executable computer
program instructions which, when executed by a data processing
system, cause said data processing system to perform steps
comprising: receiving a site information which determines an
approximate location, said approximate location being determined by
at least one of a location of a cellular service area which
includes a wireless cell site which is capable of being coupled to
said data processing system or a location of said wireless cell
site; determining an approximate Doppler for at least one SPS
satellite, said approximate Doppler being based on said approximate
location; transmitting said approximate Doppler to said wireless
cell site.
29. A computer readable medium as in claim 28 wherein said steps
further comprise: receiving a source of SPS signals; receiving at
least one pseudorange from said wireless cell site; processing said
at least one pseudorange and said SPS signals to determine a
position information for an SPS receiver which provided said at
least one pseudorange.
30. A computer readable medium as in claim 29 wherein said
approximate location and said SPS signals and said at least one
pseudorange are processed to determine said position
information.
31. A method for providing a local oscillator signal in a mobile
satellite positioning system (SPS) receiver, said method
comprising: receiving a signal having a carrier frequency and a
data signal modulated on said carrier frequency; extracting a
reference signal from said data signal modulated on said carrier
frequency; using said reference signal to provide a local
oscillator signal to acquire SPS signals.
32. A method as in claim 31 wherein said data signal modulated on
said carrier frequency comprises a pseudorandom sequence.
33. A method as in claim 31 wherein said signal operates in either
a code division multiple access system or a time division multiple
access system.
34. A method as in claim 31 wherein said extracting step comprises
automatically locking to said data signal modulated on said carrier
frequency.
35. A method as in claim 31 wherein said using step comprises
comparing said reference signal to an oscillator signal generated
by a local oscillator in said SPS receiver.
36. A method as in claim 31 wherein said using step comprises
providing said reference signal to a frequency synthesizer and
producing said local oscillator signal from said reference signal
and said frequency synthesizer.
37. A method as in claim 35 wherein said oscillator signal is
calibrated by said reference signal to provide said local
oscillator signal.
38. A method as in claim 31 wherein said data signal modulated on
said carrier frequency is a digital signal.
39. A method for determining a position of a satellite positioning
system (SPS) receiver having a wireless cell based transmitter,
said method comprising: determining an approximate location of said
SPS receiver from a cell based information source, said approximate
location being determined by at least one of a location of a
cellular service area which includes a wireless cell site which is
capable of communicating with said cell based transmitter or a
location of said wireless cell site; receiving a source of SPS
signals; receiving a plurality of pseudorange data from said
wireless cell based transmitter, said plurality of pseudorange data
being determined by said SPS receiver; computing a position
information of said SPS receiver by using SPS signals, said
plurality of pseudoranges and said approximate location.
40. A method as in claim 39 further comprising: transmitting a
signal having a carrier frequency and a data signal modulated on
said carrier frequency, said SPS receiver using one of said carrier
frequency and said data signal to provide a local oscillator signal
which is used to acquire SPS signals.
41. A method as in claim 1 wherein said cell based communication
receiver determines said approximate location from a cellular
transmission from said cell site and wherein said cell based
communication receiver transmits said approximate location to a
remote processing station which determines said approximate Doppler
and causes said approximate Doppler to be transmitted from said
cell site to said cell based communication receiver.
42. A method as in claim 39 further comprising: determining an
approximate Doppler for at least one SPS satellite relative to said
SPS receiver, said approximate Doppler being based on said
approximate location; transmitting said approximate Doppler to said
SPS receiver through said wireless cell site.
43. A method as in claim 42 further comprising: transmitting a
signal having a carrier frequency and a data signal modulated on
said carrier frequency, said SPS receiver using one of said carrier
frequency and said data signal to provide a local oscillator signal
which is used to acquire SPS signals.
44. A method as in claim 15 further comprising: transmitting a
signal having a carrier frequency and a data signal modulated on
said carrier frequency, said SPS receiver using one of said carrier
frequency and said data signal to provide a local oscillator signal
which is used to acquire SPS signals.
45. A method for providing Doppler information to a satellite
positioning system (SPS) receiver, said method comprising:
determining a plurality of approximate Doppler data from an
approximate location based upon at least one of a location of a
wireless cell site or a location of a cellular service area which
includes said wireless cell site, said plurality of approximate
Doppler data for a corresponding plurality of satellites;
broadcasting said plurality of approximate Doppler data from a
wireless cellular transmitter of said wireless cell site to a
plurality of SPS receivers in a cell serviced by said wireless cell
site.
46. A method as in claim 45 further comprising: receiving at least
one pseudorange from said wireless cell site, said pseudorange
being provided by an SPS receiver having a cell based wireless
transmitter which communicates with said wireless cell site.
47. A method as in claim 46 further comprising: computing a
position information of said SPS receiver by using SPS signals from
a source of SPS signals and using said pseudorange and said
approximate location.
48. A method as in claim 46 further comprising: transmitting a
signal having a carrier frequency and a data signal modulated on
said carrier frequency, said SPS receiver using one of said carrier
frequency and said data signal to provide a local oscillator signal
which is used to acquire SPS signals.
49. A method for providing a satellite information to a satellite
positioning system (SPS) receiver, said method comprising:
determining an approximate location from a cell based information
source, said approximate location being based on at least one of a
location of a cellular service area which includes a wireless cell
site and a location of said wireless cell site, and determining a
plurality of satellite ephemeris data for a corresponding plurality
of satellites, which are in view of said approximate location;
transmitting said plurality of satellite ephemeris data from a
wireless cellular transmitter of said wireless cell site to an SPS
receiver in a cell serviced by said wireless cell site.
50. A method as in claim 49 wherein said transmitting step
comprises broadcasting said plurality of satellite ephemeris data
to a plurality of SPS receivers in said cell.
51. A method as in claim 49 further comprising: receiving a
plurality of pseudorange data from said SPS receiver, said
plurality of pseudorange data being determined by said SPS
receiver.
52. A method as in claim 51 further comprising: computing a
position information of said SPS receiver by using SPS signals from
a source of SPS signals and said plurality of pseudoranges.
53. A method as in claim 52 wherein said position information is
computed by also using said approximate location.
54. A method as in claim 52 further comprising: transmitting a
signal having a carrier frequency and a data signal modulated on
said carrier frequency, said SPS receiver using one of said carrier
frequency and said data signal to provide a local oscillator signal
which is used to acquire SPS signals.
55. A method as in claim 1 further comprising: transmitting said
approximate Doppler from said cell site to said cell based
communication receiver, wherein said approximate Doppler is
determined by a remote processing station which is coupled to said
cell site and which receives an identifier of at least one of said
cellular service area or said cell site from said cell based
communication receiver.
56. A method as in claim 55 wherein said remote processing station
determines said approximate Doppler from said identifier which is
transmitted by said cell based communication receiver to said
remote processing station.
57. A method as in claim 56 wherein said identifier is provided by
said cell site to said cell based communication receiver, and said
cell based communication receiver transmits said identifier through
said cell site to said remote processing station.
58. A method as in claim 56 wherein said cell based communication
receiver derives said identifier from a signal transmitted by said
cell site to said cell based communication receiver.
59. A method as in claim 58 wherein said signal is a pseudorandom
(PN) code which corresponds to said cell site.
60. A method as in claim 59 wherein said signal is transmitted in a
CDMA system.
61. A method as in claim 1 wherein said approximate Doppler is
determined at a remote processing station which causes said
approximate Doppler to be transmitted from said cell site to said
cell based communication receiver, and wherein said cell based
communication receiver causes said at least one pseudorange to be
transmitted to said remote processing station which determines a
position information for said SPS receiver using said at least one
pseudorange, and wherein said SPS receiver uses said approximate
Doppler without extracting satellite position data from SPS signals
from SPS satellites.
62. A method as in claim 1 further comprising: determining a
reference signal from a communication signal transmitted from said
cell site to said cell based communication receiver; using said
reference signal to provide a local oscillator signal which is used
to acquire SPS signals in said SPS receiver.
63. A method as in claim 62 wherein said reference signal is
determined from a data signal modulated on a carrier frequency of
said communication signal.
64. A method as in claim 62 wherein said reference signal is
determined from a carrier frequency of said communication
signal.
65. A combined mobile satellite positioning system (SPS) receiver
and a communication receiver, said SPS receiver and communication
receiver comprising: a first antenna which receives a communication
signal having a data signal modulated on a carrier frequency; a
data signal acquisition and tracking circuit coupled to said first
antenna, said acquisition and tracking circuit producing a
reference signal from the data signal; a frequency synthesizer
coupled to said acquisition and tracking circuit to receive said
reference signal, said frequency synthesizer providing a local
oscillator signal to acquire SPS signals in said SPS receiver.
66. A combined SPS receiver and communication receiver as in claim
65 further comprising: a voltage controlled oscillator (VCO) in
said acquisition and tracking circuit, said VCO providing said
reference signal; and wherein said data signal comprises a
pseudorandom sequence.
67. A combined SPS receiver and communication receiver as in claim
65 wherein said reference signal is generated by locking to said
data signal.
68. A method for determining a position information of a mobile
satellite positioning system (SPS) receiver having a cell based
communication receiver, said method comprising: receiving a
plurality of differential SPS correction data for a plurality of
different locations; selecting a first differential SPS correction
data for a first location from said plurality of differential SPS
correction data, said first differential SPS correction data being
selected based upon an approximate location which is determined
from a cell based information source by at least one of a location
of a cellular service area which includes a cell site or a location
of said cell site; receiving a plurality of pseudorange data from
said SPS receiver, said plurality of pseudorange data and said
first differential SPS correction data being used to determine said
position.
69. A method as in claim 68 further comprising: receiving satellite
ephemeris data which is used to determine said position.
70. A method as in claim 69 wherein said position is determined at
a data processing station which is capable of communicating with
said cell based communication receiver through a cell based
communication system which includes said cell site.
71. A method as in claim 70 wherein said SPS receiver provides a
site information to said data processing station which uses said
site information to determine said approximate location.
72. A method as in claim 71 further comprising: determining an
approximate Doppler for at least one SPS satellite relative to said
SPS receiver, said approximate Doppler being based on said
approximate location; transmitting said approximate Doppler to said
SPS receiver; using said approximate Doppler in said SPS
receiver.
73. A method as in claim 70 further comprising: determining an
approximate Doppler for at least one SPS satellite relative to said
SPS receiver, said approximate Doppler being based on said
approximate location; transmitting said approximate Doppler to said
SPS receiver; using said approximate Doppler in said SPS
receiver.
74. A method for determining Doppler information in a satellite
positioning system (SPS) receiver having a cell based communication
receiver, said method comprising: receiving, at said SPS receiver,
satellite almanac information for a plurality of SPS satellites in
view of said SPS receiver; determining an approximate location of
said SPS receiver, said approximate location being determined by at
least one of a location of a cellular service area which includes a
cell site or a location of said cell site; using said satellite
almanac information and said approximate location to determine an
approximate Doppler for at least one of said SPS satellites.
Description
RELATED APPLICATIONS
[0001] This application is a continuation-in-part of U.S. patent
application Ser. No. 08/759,523, filed on Dec. 4, 1996 by Norman F.
Krasner and a continuation-in-part of U.S. patent application Ser.
No. 08/612,582, filed on Mar. 8, 1996 by Norman F. Krasner.
[0002] This application is also related to and hereby claims the
benefit of the filing date of a provisional patent application by
the same inventor, Norman F. Krasner, which application is entitled
Low Power, Sensitive Pseudorange Measurement Apparatus and Method
for Global Positioning Satellites Systems, Ser. No. 60/005,318,
filed Oct. 9, 1995.
BACKGROUND OF THE INVENTION
[0003] 1. Field of the Invention
[0004] The present invention relates to receivers capable of
determining position information of satellites and, in particular,
relates to such receivers which find application in satellite
positioning systems (SPS) such as the U.S. global positioning
satellite (GPS) systems.
[0005] 2. Background Art
[0006] GPS receivers normally determine their position by computing
relative times of arrival of signals transmitted simultaneously
from a multiplicity of GPS (or NAVSTAR) satellites. These
satellites transmit, as part of their message, both satellite
positioning data as well as data on clock timing, so-called
"ephemeris" data. The process of searching for and acquiring GPS
signals, reading the ephemeris data for a multiplicity of
satellites and computing the location of the receiver from this
data is time consuming, often requiring several minutes. In many
cases, this lengthy processing time is unacceptable and,
furthermore, greatly limits battery life in micro-miniaturized
portable applications.
[0007] Another limitation of current GPS receivers is that their
operation is limited to situations in which multiple satellites are
clearly in view, without obstructions, and where a good quality
antenna is properly positioned to receive such signals. As such,
they normally are unusable in portable, body mounted applications;
in areas where there is significant foliage or building blockage;
and in in-building applications.
[0008] There are two principal functions of GPS receiving systems:
(1) computation of the pseudoranges to the various GPS satellites,
and (2) computation of the position of the receiving platform using
these pseudoranges and satellite timing and ephemeris data. The
pseudoranges are simply the time delays measured between the
received signal from each satellite and a local clock. The
satellite ephemeris and timing data is extracted from the GPS
signal once it is acquired and tracked. As stated above, collecting
this information normally takes a relatively long time (30 seconds
to several minutes) and must be accomplished with a good received
signal level in order to achieve low error rates.
[0009] Virtually all known GPS receivers utilize correlation
methods to compute pseudoranges. These correlation methods are
performed in real time, often with hardware correlators. GPS
signals contain high rate repetitive signals called pseudorandom
(PN) sequences. The codes available for civilian applications are
called C/A codes, and have a binary phase-reversal rate, or
"chipping" rate, of 1.023 MHz and a repetition period of 1023 chips
for a code period of 1 msec. The code sequences belong to a family
known as Gold codes. Each GPS satellite broadcasts a signal with a
unique Gold code.
[0010] For a signal received from a given GPS satellite, following
a downconversion process to baseband, a correlation receiver
multiplies the received signal by a stored replica of the
appropriate Gold code contained within its local memory, and then
integrates, or lowpass filters, the product in order to obtain an
indication of the presence of the signal. This process is termed a
"correlation" operation. By sequentially adjusting the relative
timing of this stored replica relative to the received signal, and
observing the correlation output, the receiver can determine the
time delay between the received signal and a local clock. The
initial determination of the presence of such an output is termed
"acquisition." Once acquisition occurs, the process enters the
"tracking" phase in which the timing of the local reference is
adjusted in small amounts in order to maintain a high correlation
output. The correlation output during the tracking phase may be
viewed as the GPS signal with the pseudorandom code removed, or, in
common terminology, "despread." This signal is narrow band, with
bandwidth commensurate with a 50 bit per second binary phase shift
keyed data signal which is superimposed on the GPS waveform.
[0011] The correlation acquisition process is very time consuming,
especially if received signals are weak. To improve acquisition
time, many GPS receivers utilize a multiplicity of correlators (up
to 12 typically) which allows a parallel search for correlation
peaks.
[0012] Another approach to improve acquisition time is described in
U.S. Pat. No. 4,445,118, referred to as the "Taylor patent." This
approach uses the transmission of Doppler information from a
control basestation to a remote GPS receiver unit in order to aid
in GPS signal acquisition. While this approach does improve
acquisition time, the Doppler information is transmitted from a
basestation to a mobile GPS receiver by a point to point
transmission system, and there is no indication of how this Doppler
information is obtained.
[0013] An approach for improving the accuracy of the position
determination by a remote GPS receiver unit is also described in
the Taylor patent. In the Taylor patent, a stable frequency
reference is transmitted to a remote GPS receiver unit from a
basestation in order to eliminate a source of error due to a poor
quality local oscillator at the remote GPS receiver unit. This
method uses a special frequency shift keyed (FSK) signal that must
be situated in frequency very close to the GPS signal frequency. As
shown in FIG. 4 of the Taylor patent, the special FSK signal is
about 20 MHz below the 1575 MHz GPS signal which is also received
by the receiver in order to demodulate the GPS satellite signals
from the GPS satellites so as to extract satellite position data
Moreover, the approach described in the Taylor patent uses a common
mode rejection mechanism in which any error in the local oscillator
(shown as L.O. 52) of the receiver will appear in both the GPS
channel and the reference channel and hence be canceled out. There
is no attempt to detect or measure this error. This approach is
sometimes referred to as a homodyne operation. While this approach
provides some advantages, it requires that the two channels be
closely matched, including closely matched in frequency. Moreover,
this approach requires that both frequencies remain fixed, so
frequency hopping or frequency tuning (channelization) techniques
are not compatible with this approach.
SUMMARY OF THE INVENTION
[0014] In one aspect of the present invention, a method is
described for reducing processing time due to Doppler error in a
satellite positioning system (SPS) receiver having a cell based
communication receiver. The method includes determining an
approximate location of the SPS receiver from a cell based
information source. This approximate location is determined by
using at least one of a location of a cellular service area which
includes a cell site which is capable of communicating with the
cell based communication receiver or a location of the cell site
itself. The method further includes determining an approximate
Doppler for at least one SPS satellite relative to the SPS
receiver, where the approximate Doppler is based upon the
approximate location. This approximate Doppler is used in the SPS
receiver to reduce processing time in either determining at least
one pseudorange to the at least one SPS satellite, or in acquiring
signals from the at least one SPS satellite.
[0015] An exemplary embodiment of this method is a cellular
telephone which includes a GPS receiver. The cellular telephone
operates by communicating with cell sites, each of which are
connected to a cellular switching center. A database, which
represents a cellular based information source, may be maintained
at the cellular switching center or at the cell site or at a remote
processing station, which may be termed a "server," may be used to
determine an approximate location of the cellular telephone based
upon the cell site (or cellular service area) with which the
cellular telephone is communicating. This approximate location may
then be used to derive an approximate Doppler relative to the
various SPS satellites which are transmitting SPS signals to the
GPS receiver in the cellular telephone. This approximate Doppler is
then transmitted in one embodiment from the cell site to the
cellular telephone, and is then used in the GPS receiver in order
to reduce processing time due to Doppler induced effects in the GPS
receiver.
[0016] A further embodiment of this aspect of the present invention
is a data processing station which includes a processor and a
storage device coupled to the processor, and a transceiver coupled
to the processor. The transceiver is for coupling the data
processing station to a wireless cell site. The storage device
contains information specifying at least one approximate Doppler at
a given time for an approximate location which is determined by at
least one of a location of a cellular service area which includes
the wireless cell site or a location of the wireless cell site
itself. The transceiver receives a site information which
determines the approximate location, and the processor determines
an approximate Doppler for at least one SPS satellite which is in
view of said approximate location. The approximate Doppler is based
upon the approximate location. The transceiver sends this
approximate Doppler to the wireless cell site which then transmits
the approximate Doppler to a cell based communication receiver
which is coupled to an SPS receiver.
[0017] Another aspect of the present invention relates to a method
for providing a local oscillator signal in a mobile satellite
positioning system receiver. The method includes receiving a signal
having a carrier frequency and a data signal modulated on the
carrier frequency, extracting a reference signal from the data
signal modulated on the carrier frequency, and using the reference
signal to provide a local oscillator signal to acquire SPS signals
from SPS satellites.
[0018] Another embodiment according to this aspect of the present
invention, is a combined SPS receiver and communication system. The
communication system includes an acquisition and tracking circuitry
which is coupled to an antenna to receive the communication
signals. This acquisition and tracking circuitry acquires and
tracks the data signal which is modulated onto a carrier frequency
and provides a reference signal from the data signal modulated on
the carrier frequency. The reference signal is then provided to a
phaselock loop or to a frequency synthesizer in order to generate a
local oscillator signal which is used to acquire SPS signals in the
SPS receiver.
[0019] In another aspect of the present invention, a method for
determining a position of an SPS receiver having a wireless cell
based transmitter is described. This method includes determining an
approximate location of the SPS receiver from a cell based
information source. The approximate location is determined by at
least one of a location of a cellular service area which includes a
wireless cell site which is capable of communicating with the cell
based transmitter or a location of the wireless cell site. The SPS
receiver receives a source of SPS signals and determines a
plurality of pseudorange data and transmits this plurality of
pseudorange data to the wireless cell site. Then a position of the
SPS receiver is computed by using the SPS signals, the plurality of
pseudoranges and the approximate location. In this method, the
approximate location is used to facilitate convergence of the
position calculation.
[0020] In another aspect of the present invention, a method for
providing Doppler information to an SPS receiver is described. In
this method, a plurality of approximate Doppler data from an
approximate location is determined. This approximate location is
based upon at least one of a location of a wireless cell site or a
location of a cellular service area which includes the wireless
cell site. The plurality of approximate Doppler data is for a
corresponding plurality of satellites. The method further includes
broadcasting the plurality of approximate Doppler data from a
wireless cell transmitter of the wireless cell site to a plurality
of SPS receivers in a cell serviced by the wireless cell site.
Typically, at least in one embodiment, the cell site would then
receive a plurality of pseudoranges and would forward these
pseudoranges to a remote processing station in which the position
of the SPS receiver is computed using the SPS signals and the
pseudoranges.
[0021] In yet another aspect of the present invention, a method for
providing satellite information to an SPS receiver is described.
This method includes determining an approximate location from a
cellular based information source and determining a plurality of
satellite ephemeris data for a corresponding plurality of
satellites which are in view of the approximate location. The
method further includes transmitting the plurality of satellite
ephemeris data from a wireless cellular transmitter of the wireless
cell site to an SPS receiver in a cell serviced by the wireless
cell site.
[0022] In yet another aspect of the present invention the
approximate location, which is derived from a cell based
information source, is used to select a particular set of
differential GPS correction data.
[0023] Various embodiments of apparatuses which can perform the
various methods described above are also described herein.
BRIEF DESCRIPTION OF THE DRAWINGS
[0024] The present invention is illustrated by way of example and
not limitation in the figures of the accompanying drawings in which
like references indicate similar elements.
[0025] FIG. 1 illustrates a cellular communication system having a
plurality of cells each of which is serviced by a cell site, and
each of which is coupled to a cellular switching center.
[0026] FIG. 2 represents a generalized flowchart according to one
embodiment of the present invention.
[0027] FIG. 3A shows a flowchart illustrating one particular
implementation of the present invention in which cellular based
information is used to obtain approximate Doppler information.
[0028] FIG. 3B is a flowchart showing another particular
implementation of the present invention in which cellular based
information is used to derive approximate Doppler information.
[0029] FIG. 3C is a flowchart showing another particular
implementation of the present invention wherein the mobile receiver
extracts the approximate location from the cellular communication
signal.
[0030] FIG. 4A shows another flowchart of another particular
implementation of the present invention in which a cellular based
information source is used to derive approximate Doppler
information.
[0031] FIG. 4B illustrates another implementation according to the
present invention in which a cellular based information source is
used to derive approximate Doppler information.
[0032] FIG. 5 shows an exemplary representation of a cellular based
information source which provides an association between sets of
Doppler information at given times relative to cellular service
areas and/or cellular cell sites.
[0033] FIG. 6 illustrates an implementation of a basestation system
according to one embodiment of the present invention.
[0034] FIG. 7A illustrates an example of a combined SPS receiver
and communication system according to one embodiment of the present
invention.
[0035] FIG. 7B illustrates another embodiment of an SPS receiver
with an integrated communication system according to one embodiment
of the present invention.
[0036] FIG. 8 is a flowchart showing a method of broadcasting
approximate Doppler information according to one embodiment of the
present invention.
[0037] FIG. 9 is a flowchart illustrating a method according to one
embodiment of the present invention in which a plurality of
satellite ephemeris data which is appropriate for a particular
cellular location, is transmitted from a wireless cellular
transmitter site.
[0038] FIG. 10A shows an example of a combined communication
receiver and SPS receiver in which a data signal which is modulated
on a carrier frequency of a communication signal is used to provide
a reference signal which in turn is used to provide a local
oscillator signal which is used to acquire SPS signals in the SPS
receiver.
[0039] FIG. 10B shows another embodiment of the present invention
in which data signals modulated on a communication signal are used
to derive a local oscillator signal which is used to acquire SPS
signals in an SPS receiver.
[0040] FIG. 11A illustrates a generalized method of the present
invention in which a reference signal is extracted from a data
signal that is modulated on a carrier frequency of a communication
signal in order to provide a local oscillator signal to acquire SPS
signals.
[0041] FIG. 11B shows a particular implementation of the method
shown in FIG. 11A.
DETAILED DESCRIPTION
[0042] The present invention primarily relates to apparatuses and
methods for computing the position of a mobile object by using a
communication link. In one embodiment, this communication link is
used to determine an approximate Doppler to thereby reduce
processing time due to Doppler induced error in a satellite
positioning system (SPS) receiver. In another embodiment, the
communication link is used to provide a data signal from which a
reference signal is extracted. This reference signal is used to
provide a local oscillator signal in the SPS receiver to acquire
SPS signals.
[0043] One aspect of the present invention relates to a cellular
based communication system which includes a cellular based
information source that is used to provide approximate Doppler
information in response to the determination of approximate
location. FIG. 1 shows an example of a cellular based communication
system 10 which includes a plurality of cell sites, each of which
is designed to service a particular geographical region or
location. Examples of such cellular based communication systems are
well known in the art. See, for example, U.S. Pat. No. 5,519,760
which describes a cellular network-based location system. The
cellular based communication system 10 includes two cells 12 and 14
both of which are defined to be within a cellular service area 11.
In addition, the system 10 includes cells 18 and 20. It will be
appreciated that a plurality of other cells with corresponding cell
sites and/or cellular service areas may also be included in the
system 10 and coupled to one or more cellular switching centers,
such as the cellular switching center 24 and cellular switching
center 24b.
[0044] Within each cell, such as cell 12, there is a wireless cell
or cellular site such as cell site 13 which includes an antenna 13a
which is designed to communicate through a wireless communication
medium with a communication receiver which may be a combined mobile
GPS receiver and communication system such as the receiver 16 shown
in FIG. 1. An example of such a combined system is shown in FIG. 7A
and may include both a GPS antenna 377 and a communication system
antenna 379. It will be appreciated that alternative embodiments
may employ a single antenna or more than two antennas.
[0045] Each cell site is coupled to a cellular switching center. In
FIG. 1, cell sites 13, 15, and 19 are coupled to switching center
24 through connections 13b, 15b and 19b respectively and cell site
21 is coupled to a different switching center 24b through
connection 21b. These connections are typically wire line
connections between the respective cell site and the cellular
switching centers 24 and 24b. Each cell site includes an antenna
for communicating with communication systems serviced by the cell
site. It will be appreciated that a communication system within one
cell, such as the receiver 22 shown in cell 4, may in fact
communicate with the cell site 19 in cell 18 due to blockage (or
other reasons why cell site 21 cannot communicate with the receiver
22).
[0046] In a typical embodiment of the present invention, the mobile
GPS receiver 16 includes a cellular based communication system
which is integrated with the GPS receiver, such that both the GPS
receiver and the communication system are enclosed in the same
housing. One example of this is a cellular telephone having an
integrated GPS receiver which shares common circuitry with the
cellular based telephone transceiver, such as that shown in FIG.
7B. When this combined system is used for cellular telephone
communications, transmissions occur between the receiver 16 and the
cell site 13. Transmissions from the receiver 16 to the cell site
13 are then propagated over the connection 13b to the cellular
switching center 24 and then to either another cellular telephone
in a cell serviced by the cellular switching center 24, or through
a connection 30 (typically wired) to another telephone through the
land based telephone system/network 28. It will be appreciated that
the term wired includes fiber-optic and other non-wireless
connections such as copper cabling, etc. Transmissions from the
other telephone which is communicating with the receiver 16 are
conveyed from the cellular switching center 24 through the
connection 13b and the cell site 13 back to the receiver 16 in the
conventional manner.
[0047] The remote data processing system 26 (which may be referred
to in some embodiments as a GPS server) is included in the system
10 and is used when, in some embodiments, a mobile GPS receiver
within a particular cell is used to determine the position of the
receiver using GPS signals received by the GPS receiver. The GPS
server 26 may be coupled to the land based telephone system/network
28 through a connection 27 and it may also be optionally coupled to
the cellular switching center 24 through the connection 25 and also
optionally coupled to center 24b through the connection 25b. It
will be appreciated that connections 25 and 27 are typically wired
connections although they may be wireless. Also shown as an
optional component of the system 10 is a query terminal 29 which
may consist of another computer system which is coupled through the
network 28 to the GPS server. This query terminal 29 may send a
request for the position of a particular GPS receiver in one of the
cells to the GPS server 26 which then initiates a conversation with
a particular GPS receiver through the cellular switching center in
order to determine the position of the GPS receiver and report that
position back to the query terminal 29.
[0048] It should be noted that a cellular based communication
system is a communication system which has more than one
transmitter, each of which serves a different geographical area,
which is predefined at any instant in time. Typically, each
transmitter is a wireless transmitter which serves a cell which has
a geographical radius of less than 20 miles, although the area
covered depends on the particular cellular system. There are
numerous types of cellular communication systems, such as cellular
telephones, PCS (personal communication system), SMR (specialized
mobile radio), one way and two-way pager systems, RAM, ARDIS, and
wireless packet data systems. Typically the predefined different
geographical areas are referred to as cells and a plurality of
cells are grouped together into a cellular service area such as the
cellular service area 11 shown in FIG. 1 and these plurality of
cells are coupled to one or more cellular switching centers which
provide connections to land based telephone systems and/or
networks. Service areas are often used for billing purposes. Hence,
it may be the case that cells in more than one service area are
connected to one switching center. For example, in FIG. 1, cells 1
and 2 are in service area 11, and cell 3 is in service area 18, but
all three are connected to switching center 24. Alternatively it is
sometimes the case that cells within one service area are connected
to different switching centers, especially in dense population
areas. In general, a service area is defined as a collection of
cells within close geographical proximity to one another. Another
class of cellular systems that fits the above description is
satellite based, wherein the cellular basestations are satellites
that typically orbit the earth. In these systems, the cell sectors
and service areas move as a function of time. Examples of such
systems include Iridium, Globalstar, Orbcomm and Odyssey.
[0049] FIG. 2 shows a generalized example of the present invention
in which approximate Doppler information is derived from
approximate position information from a cellular based information
source. The method begins in step 40 in which an approximate
position of the cell site (and consequently objects within the cell
serviced by the cell site) is determined from a cellular based
information source. Alternatively, the approximate position may
represent a position within the cellular service area which
includes the cell site. In step 42, approximate Dopplers to a
plurality of satellites in view of the approximate position is
determined. Then in step 44, the approximate Dopplers are used in a
mobile SPS receiver in order to reduce processing time due to
Doppler induced effects in determining the position of the SPS
receiver. The approximate Dopplers are typically used to determine
pseudoranges or may be used to acquire SPS signals from in view
satellites. An example of the use of approximate Doppler is
described in co-pending U.S. patent application Ser. No.
08/612,669, filed Mar. 8, 1996, now U.S. Pat. No. ______, which is
hereby incorporated herein by reference. The use of Doppler
information in a mobile SPS receiver to reduce processing time due
to Doppler induced error and to also reduce error in determining
the position of the SPS receiver is also described in co-pending
U.S. patent application Ser. No. 08/759,523, which was filed Dec.
4, 1996, and which is hereby incorporated herein by reference. It
is noted that for most of those embodiments where the mobile SPS
receiver transmits a pseudorange to a server (for the position
calculation to be completed by the server), the Doppler is
transmitted to the SPS receiver (or used in the SPS receiver) and
used in the SPS receiver without extracting satellite position
information from SPS signals. In other words, in this case the SPS
receiver will not receive and demodulate SPS signals (from SPS
satellites) for the purpose of extracting satellite position
information (such as ephemeris) from the SPS signals from the SPS
satellites. It is also noted here that without Doppler information
the SPS receiver must search over a wide range of carrier
frequencies, which may take a very long time.
[0050] FIG. 3A illustrates one particular implementation of the
present invention in which a cellular based information source is
used to obtain a plurality of approximate Doppler information to a
corresponding plurality of satellites in view of the approximate
location. This particular implementation, in one embodiment, may
involve the use of a "911" panic call from a cellular telephone
which will then cause the cellular based system to determine the
location of the cellular telephone. Thus, the cellular telephone
itself initiates the communication with the cell site as indicated
in step 50. The cellular based communication system which includes
the SPS receiver (in this case a cellular telephone with a GPS
receiver) transmits a position request to the cellular cell site.
In one embodiment, the cell site determines the cell site location
or the cell site identity or obtains either of these from the
cellular switching center or determines the cellular service area
which contains the cell site. This is shown as step 52 in FIG.
3A.
[0051] As an alternative to this step 52, a cellular telephone may
determine from the communication signals transmitted from the
cellular site the cellular site's location or identity or the
cellular service area This will be possible in those cellular
communication systems in which the mobile cellular based
communication system can detect a data signal in the cellular
transmission which identifies the cell site or the cellular service
area which contains the cell site. An example of this type of
communication system is the IS-95 North American Standard code
division multiple access system (CDMA). In IS-95 the cell site
transmission includes the cell site identity as well as its
latitude and longitude. Alternatively, the cell site may be
identified by the particular spreading sequence transmitted by the
cell site (there are 512 possibilities in IS-95). This alternative
is described further below with FIG. 3C. In the case where the
mobile cellular based communication system determines the cell site
identity or service area identity from the communication signal,
then step 52 is not necessary.
[0052] Returning to FIG. 3A, step 54 is performed by having the
cell site transmit the cell site location or cell site identity or
the cellular service area identity to the mobile cellular based
communication system. In step 56, the mobile cellular based
communication system then transmits the cellular site location or
identity or cellular service area which contains the cell site to
an SPS server, such as the server 26 shown in FIG. 1 through the
cell site.
[0053] In step 58, the SPS server determines a plurality of
approximate Dopplers to a 5 corresponding plurality of satellites
in view of the approximate location from either the cell site
location or from the cell site identity or from the cellular
service area identity. These Dopplers may be determined from
satellite position and velocity information supplied by GPS
satellites in the Almanac or ephemeris portions of data messages
transmitted within the GPS signals, as is well known in the art.
The GPS signals may be received by a receiver at the SPS server or
by a receiver remote to it. Typically, the SPS server will also
determine the time of day in order to time stamp the approximate
Doppler at the approximate location. Alternatively, if the
approximate Doppler is provided from a source of approximate
Dopplers to the SPS server, and this source of information already
takes into account the time of day, then the SPS server need not
determine the time of day. Then in step 60, the SPS server
transmits the approximate Dopplers to the mobile cellular based
communication system through the cell site which is communicating
with the cellular based communication system. In step 62, the
cellular based communication system uses the approximate Dopplers
for its SPS receiver in order to reduce processing time in
determining the position of the SPS receiver. Typically, at least
in some embodiments, the position calculation is performed at the
SPS server after the server receives pseudorange data from the GPS
receiver through the cell site and cellular switching center.
[0054] It is noted that Doppler may include a Doppler value plus
rate of change of Doppler vs. time and/or other mathematical fits
of Doppler vs. time. Transmitting such fits to the mobile SPS
allows the mobile to compute Doppler accurately for much longer
periods (e.g. 1/2 hour) than would otherwise be possible.
[0055] It will be appreciated that an alternative implementation of
the method shown in FIG. 3A may include the use of a lookup table
(or other storage or computation device) in the mobile cellular
based communication system to determine the approximate location
(from the cell site identity or cellular service area identity)
which is then sent to the SPS server in order to receive an
approximate Doppler information from the SPS server. As a further
alternative to this method, the approximate location determined in
the cellular based communication system from a lookup table or
other memory or computation device may be used to determine an
approximate Doppler which is stored in a memory or derived from
satellite almanac information which is periodically received from
SPS satellites or sent to it from the SPS server as previously
described. This memory would associate the approximate location
with the corresponding approximate Dopplers in a manner similar to
that shown in FIG. 5.
[0056] FIG. 3B shows another implementation of the present
invention in which a cellular based information source is used to
obtain approximate Doppler information which is used in an SPS
receiver. This particular implementation of FIG. 3B may also be
considered to be a "911" panic circumstance wherein the mobile
cellular based communication system, such as a cellular telephone
having an integrated SPS receiver, initiates the process by
transmitting a position request. Thus, the process of FIG. 3B
begins in step 70 in which a cellular based communication system
transmits a position request to a cellular cell site. Then in step
72, the cellular cell site determines the cell site location or the
cell site identity or the cellular service area identity.
Alternatively, this information could be obtained from the cellular
switching center if such information is not locally maintained at
the cell site. Then at step 74, the cell site sends a cell site
location or a cell site identity or a cellular service area
identity to an SPS receiver usually through a cellular switching
center. The cell site may also send the phone number or identifier
of the cellular based communication system in order to allow the
SPS server to directly communicate and identify the particular
mobile cellular based communication system which initiated the
position request in step 70. In step 76, the SPS server determines
the approximate Doppler from at least one of the cell site location
or cell site identity or service area identity or location. Then in
step 78 the SPS server sends the approximate Doppler to the
cellular based communication system. This transmission usually
occurs through the cellular switching center and the cell site. For
example, as shown in FIG. 1, the SPS server 26 may transmit the
approximate Doppler information through the cellular switching
center 24 and the cell site 13 to the receiver 16, and the
switching center 24 may receive this transmission through the land
based telephone system/network 28 or may occur through the optional
direct connection 25. The cellular based communication system in
step 80 then uses the approximate Doppler for its SPS receiver in
order to determine pseudoranges to at least one SPS satellite or in
order to acquire signals from at least one SPS satellite.
[0057] A further, more specific embodiment of the invention is
shown in FIG. 3C. In this example, the mobile cellular based
communication system begins a cellular transmission, in step 82, to
a cell site. From the ensuing cell site transmissions, in step 84,
the cell site location (e.g. latitude and longitude) or cell site
identity (or perhaps the cell service area) is determined. In
systems conforming to the IS-95 CDMA standard, the latitude and
longitude of the cell site is transmitted from the cell site as
part of the cellular transmissions from the site. In CDMA, there is
also a unique cell site identifier which may be sent to the mobile
cellular based communication system. Then, this information is
transmitted, in step 86, to the SPS server which determines (in
step 88) the approximate Dopplers and transmits these Dopplers
(step 90) to the cellular based communication system.
[0058] FIG. 4A shows another method of the present invention in
which a cellular based information source is used to obtain
approximate location from which approximate Doppler information for
the approximate location is obtained and used by an SPS receiver.
The method of FIG. 4A involves one in which the position operation
is initiated by the SPS server or by some other system rather than
by the mobile cellular based communication system which includes an
SPS receiver, such as the receiver 16 shown in FIG. 1. The method
of FIG. 4A begins in step 300 in which the SPS server requests a
position fix from a specific mobile cellular based communication
system which includes an SPS receiver. Typically, the specific
cellular based communication system will be specified by a phone
number or other identifier. The position request is normally
transmitted in step 302 through a cellular switching center to a
plurality of cell sites. As shown in FIG. 1, the GPS server 26
would transmit the position request either directly through the
connection 25 or connection 25b or through the connection 27 and
the network 28 to the cellular switching center 24 which would then
cause the position request to be transmitted to the cell sites 13,
15, 19, and 21. In step 304, the cell sites transmit the position
request and perhaps the cell site identity or cell site location or
service area identity or location which contains the cell site to
the specific mobile cellular based communication system. Again, it
may be the case that the cell site transmission inherently contains
cell site location and/or identity, as in the aforementioned IS-95
CDMA standard; hence, no special action is required of the cell
site in such situations. In step 306, the specific cellular based
communication system responds to a cell site which communicates
with the specific system. This response may include sending the
cell site identification or cell site location or service area
identity or location which contains the cell site to the SPS server
through the cell site. In step 308, the SPS server receives
information specifying the specific cellular based communication
system and at least one of the cellular site identification, or
cell site location, or the service area identification or location.
The SPS server then determines a plurality of approximate Dopplers
to a corresponding plurality of satellites in view of the cell site
which is communicating with the specific mobile cellular based
communication system from at least one of the cell site
identification or cell site location or service area identification
or location. Typically, the time of the day will also be used to
determine the approximate Doppler if a database having this
information is not available to the SPS server. In step 310, the
SPS server transmits approximate Dopplers to the cellular based
communication system typically through the cell site. Then in step
312, the cellular based communication system uses the approximate
Dopplers for its SPS receiver.
[0059] FIG. 4B shows yet another implementation of a method
according to the present invention in which a cellular based
information source is used to obtain an approximate location which
is then used to derive approximate Dopplers for use in an SPS
receiver which is in communication with cell sites or a cell site
in a cellular based communication system. The method of FIG. 4B
begins in step 320 in which the SPS server requests a position fix
from a specific mobile cellular based communication system which
includes an SPS receiver. Typically, this mobile cellular based
communication system is specified by a phone number or other
identifier. In step 322, the position request is normally
transmitted through a cellular switching center to a plurality of
cell sites. For example, as shown in FIG. 1, the SPS server 26 may
transmit the position request directly to the cellular switching
center 24 through the communication link 25 or indirectly through
the link 27, the network 28, and the link 30. Then the cellular
switching center 24 will convey the position request to various
cell sites. It will be appreciated that the position request
asserted by the SPS server in step 320 may actually initiate from a
query terminal 29 which may be a computer system operated by a user
who desires to know the location of a particular mobile cellular
based communication system, such as the mobile GPS receiver 16, or
the mobile receiver 17 as shown in FIG. 1. It will be appreciated
that an alternative of the method of FIG. 3C may also be used in
the situation of FIG. 4A where the SPS server (or some other
system) requests the position of the mobile SPS receiver.
[0060] In step 324, the cell sites having received the position
request, transmit the position request and perhaps also transmit
the cellular site identification or cellular site location or
service area location or identification which contains the cell
site to the specific mobile cellular based communication system. In
step 326, the specific mobile cellular based communication system
responds to a particular cell site which communicates with the
specific system. This response may include an acknowledgment signal
(or the optionally transmitted information such as cell site
identity) which is returned to the cell site which then sends the
cell site identification or cell site location or service area
identification or location through the cellular switching center to
the SPS server. In step 328, the SPS server receives the
information which specifies the specific mobile cellular based
communication system and also receives at least one of the cell
site identification or cell site location or service area
identification or location. Then the SPS server determines a
plurality of approximate Dopplers to a corresponding plurality of
satellites in view of the cell site (or approximate location) from
one of the provided information such as the cellular site
identification or the cellular site location or the cellular
service area identification or location. Typically, the SPS server
will also determine the time of day which is used to select the
particular set of Dopplers for the approximate location at the
given time of day. In step 330, the SPS server transmits the
approximate Doppler information to the cellular based communication
system through the cellular switching center and the particular
cell site which is in communication with the specific mobile
cellular based communication system. In step 332, the mobile
cellular based communication system uses the approximate Dopplers
for its SPS receiver in the manner described herein.
[0061] FIG. 5 shows an example of a cellular based information
source which in one embodiment may be maintained at an SPS server
such as the GPS server 26 shown in FIG. 1. Alternatively, this
information source may be maintained at a cellular switching center
such as the cellular switching center 24 of FIG. 1 or at each cell
site, such as cell site 13 shown in FIG. 1. Typically, however,
this information source is maintained and routinely updated at the
SPS server which is coupled to the cellular switching center. The
information source may maintain the data in various formats and it
will be appreciated that the format shown in FIG. 5 illustrates
only one example of this format. Typically, each set of Doppler
information at a particular time, such as Doppler set A1 at time T1
will include a corresponding location or identification for a cell
site or a service area. For example, in the case of Doppler sets A1
and A2 there is a corresponding identification of the cellular
service area A as well as the latitude and longitude for this
service area. It will be appreciated that typically this latitude
and longitude will be an "average" location which is generally
centrally located within the geographical region of the cellular
service area. However, other possible approximations may be
utilized particularly where the cellular service area includes
terrains which are not used. As shown in FIG. 5, the cellular based
information source includes a column specifying the cellular
service area, column 325a, and a column 325b specifying a cellular
site identification or number. Note that for cellular service area
A there is no specification of the cell site identification or
location and thus the approximate location is based upon a location
for the cellular service area and thus the approximate Dopplers A1
and A2 are based upon this location depending on the particular
time of day designated by the times T1 and T2. The column 325c
includes a specification of the latitude and longitude for the
particular location of the service area, and column 325d includes a
specification of the latitude and longitude for the location of the
particular cell site within the cellular service area.
[0062] FIG. 6 shows an example of an SPS server 350 of the present
invention, which includes 6 elements. These elements are the data
processing unit 351, which may be a computer system, the modem or
other interface 352, the modem or other interface 353, the modem or
other interface 354, the mass storage device 355, and optionally a
GPS receiver 356. This SPS server 530 may be coupled to three
different networks shown as networks 360, 362, and 364. In
particular, the network 360 includes the cellular switching center
or centers and/or the land based phone system switches or the cell
sites. An example of this network is shown in FIG. 1 wherein the
GPS server 26 represents the SPS server 350 of FIG. 6. Thus the
network 360 may be considered to include the cellular switching
centers 24 and 24b and the land based telephone system/network 28
and the cellular service area 11 as well as cells 18 ad 20. The
network 364 may be considered to include the query terminal 29 of
FIG. 1 as well as other computer systems which are coupled to the
GPS server 26 and which may be used to query the GPS server 26 in
order to obtain position information from the mobile SPS receivers
located in the various cells of the cellular based communication
system.
[0063] The network 362, which is not shown in FIG. 1, is a network
of GPS receivers which provide differential correction GPS
information and which provide GPS signal data (e.g. ephemeris) to
the data processing unit. The provision of GPS signals from this
network 362 may not be necessary when the GPS receiver 356 is
provided at the SPS server 350. If the server serves a very large
geographical area, however, a local receiver 356 will not be able
to observe all GPS satellites that are in view of mobile SPS
receivers throughout this area.
[0064] As shown in FIG. 6, the mass storage 355 in one embodiment
will include storage for software for performing the GPS position
calculations after receiving pseudoranges from the mobile GPS
receivers, such as the receiver 16, through the cell site and
cellular switching center and the modem or other interface 353. The
mass storage 355 also includes storage for the cell based
information source, such as the information source shown in FIG.
5.
[0065] It will be appreciated that the data processing unit 351 may
be a conventional digital computer system, and the optional GPS
receiver 356 may be a conventional GPS receiver which provides an
output having Doppler and/or other satellite data such as satellite
ephemeris data which is provided as an input to the data processing
unit. It will be appreciated that the satellite ephemeris data is
used in a conventional manner with the pseudoranges obtained from
the mobile GPS receiver in order to compute the position
information (e.g. latitude, longitude and optionally altitude) for
the mobile GPS receiver. The interfaces 352, 353, and 354 may each
be a modem or other suitable interface for coupling the data
processing unit to other computer systems in the case of the
network 364 and to cellular based communication systems in the case
of modem 353 and the network 360. Similarly, the modem or other
interface 354 provides a connection between the GPS signal source
which may be a network of GPS receivers providing location
appropriate differential correction GPS information. It will be
appreciated that this network 362 includes a dispersed collection
of GPS receivers dispersed over a geographical region and that the
differential correction GPS information obtained from a receiver
near the cell site or cellular service area which is communicating
with the mobile GPS receiver through the cellular based
communication system will provide differential correction GPS
information which is appropriate for the approximate location of
the SPS receiver.
[0066] FIG. 7A shows a generalized combined GPS and communication
transceiver system. The system 375 includes a GPS receiver 376
having a GPS antenna 377 and a communication transceiver 378 having
a communication antenna 379. The GPS receiver 376 is coupled to the
communication transceiver 378 through the connection 380 shown in
FIG. 7A. In normal operation, the communication system transceiver
378 receives approximate Doppler information through the antenna
379 and provides this approximate Doppler information over the link
380 to the GPS receiver 376 which performs the pseudorange
determination by receiving the GPS signals from the GPS satellites
through the GPS antenna 377. Various embodiments for the combined
system 375 are known in the art and have been described in the
above referenced co-pending applications.
[0067] FIG. 7B shows a particular example of an integrated GPS and
communication system having shared circuitry between the two
systems. This particular example of a combined GPS and
communication system has been described in co-pending application
Ser. No. 08/652,833, which was filed May 23, 1996, and is hereby
incorporated herein by reference. The system 375 of FIG. 7A or the
system shown in FIG. 7B, as well as numerous alternative
communication systems having SPS receivers, may be employed with
the methods of the present invention to operate in cellular based
communication systems.
[0068] Another aspect of the present invention is shown in FIG. 8
which relates to the broadcasting of a plurality of approximate
Doppler data from a wireless cellular transmitter. This method
utilizes a location from the cellular based network to determine a
plurality of approximate Doppler data. The method begins in step
501 in which a plurality of approximate Doppler data is determined
from an approximate location. This location is based typically on
at least one of a location of a wireless cell site or a location of
a cellular service area which includes the wireless cell site. This
approximate location represents the approximate location of an SPS
receiver in the cell site or the cellular service area It will be
appreciated that the location of a fixed wireless cell site is
known; however, the approximate location referred to here is the
approximate location of the SPS receiver based upon the location of
the wireless cell site or the cellular service area In step 503,
the plurality of approximate Doppler data is broadcast from a
wireless cellular transmitter to a plurality of SPS receivers which
are serviced by the wireless cell site. In step 505, the wireless
cell site receives a plurality of pseudoranges from an SPS
receiver. Typically, this information is forwarded to a GPS server
which combines the plurality of pseudoranges with the ephemeris
data in order to determine the position of the SPS receiver.
Typically, as shown in step 507, the plurality of pseudoranges is
used with the approximate location in order to determine the
position of the SPS receiver. The approximate location allows the
position calculations performed by the SPS server to converge
quickly to a position solution.
[0069] FIG. 9 illustrates another aspect of the present invention
which relates to a method for transmitting location appropriate
satellite ephemeris data from a wireless cell site, for which
location appropriate satellite ephemeris data has been determined
based upon a location from a cell based information source. The
location represents an approximate location of an SPS receiver in
the cell or cellular service area which is communicating with the
SPS receiver. The location is determined in step 530 from a cell
based information source. This location is based on at least one of
a location of a cellular service area or a location of a wireless
cell site in the cellular service area and again represents the
approximate location of the SPS receiver being serviced by the
wireless cell site. In step 532, a plurality of satellite ephemeris
data is determined for a corresponding plurality of satellites
which are in view of the location determined in step 530. Then, in
step 534, the plurality of satellite ephemeris data is transmitted
from the wireless cell site to an SPS receiver in the cellular
service area. In this manner, an SPS receiver may use the ephemeris
data along with pseudoranges determined at the SPS receiver in
order to calculate the position of the SPS receiver rather than the
circumstance where a remote processing station such as the GPS
server 26 performs the position calculation. The method of FIG. 9
may alternatively be used in a way in which the satellite ephemeris
data is used to calculate Doppler at the SPS receiver and the SPS
receiver uses the approximate Doppler information to reduce
processing time in determining pseudoranges at the SPS receiver;
these pseudoranges are transmitted back to a GPS server which
combines the satellite ephemeris data with the pseudoranges to
determine a position information for the SPS receiver.
[0070] Another aspect of the present invention will now be
described by referring to FIGS. 10A and 10B as well as FIGS. 11A
and 11B. According to this aspect, methods and apparatuses are
described for synchronizing a GPS local oscillator by means of
synchronizing to cellular telephone signal modulation in the case
of at least one embodiment.
[0071] Rapid signal acquisition of GPS signals by GPS receivers is
aided by knowledge of the carrier frequency of these signals. The
ideal carrier frequency, without Doppler and other effects is
1575.42 MHz. Satellite and GPS receiver location and motion result
in a signal shift by up to approximately .+-.4 kHz. In addition,
the stability of the local oscillator of the GPS receiver may
contribute significant frequency errors. For example, a very stable
temperature controlled crystal oscillator has stability of 1 part
per million over a wide temperature range, which contributes to
frequency error of up to .+-.1.6 kHz. Higher stability oscillators
are available; however, such oscillators are expensive and high in
power consumption. An alternative method for producing a stable
local oscillator in the GPS receiver, when such a receiver is
connected to a cellular telephone or other cellular communication
device, such as a pager or data modem, is described here.
[0072] Most cellular communications signals, and especially digital
types, are modulated onto carriers with high stability. A cellular
receiver can phase or frequency lock to such a carrier and hence
provide within the receiver a local oscillator with similarly high
stability. This oscillator can be used as a reference in a
frequency synthesizer to produce the stable local oscillator of the
GPS signal. This approach has been previously described in
co-pending U.S. patent applications Ser. No. 08/612,582, filed Mar.
8, 1996, and Ser. No. 08/759,523 , filed Dec. 4, 1996. This method
is referred to as the "carrier synchronization method" in the
following discussion.
[0073] A problem with this carrier synchronization method is that
cellular communication signals often utilize carrier frequencies
that vary from transmission to transmission. Furthermore, some of
these signals, also vary their carrier frequency within one
transmission, so-called frequency hopping; an example of this is
the GSM digital cellular standard widely utilize in Europe. These
frequency variations may add complexity to the synchronization
approach described above, based upon the signal's carrier
frequency. In addition, the carrier synchronization method may
involve significant modification to a cellular receiver's frequency
synthesis circuits, which may incur high costs and/or performance
limitations.
[0074] An alternative to the carrier synchronization method, which
is the subject of an aspect of the current invention, is the
"modulation synchronization method." In this method, a stable
frequency is derived from the received cellular signal after its
carrier has been removed. Most digital cellular systems employ high
stable modulation rates in order to allow the transmission of
digital data in a shared or "multiplexed" condition with other
transmissions. One example of this is the aforementioned GSM signal
which transmits signals in time slot bursts lasting 0.577
milliseconds and having a data rate of approximately 270.83 kHz
(more precisely 13/48.times.1 MHz). The data within each such burst
is transmitted using Gaussian minimum shift keying (GMSK), which is
a form of frequency shift keying. A second example is the code
division multiple access (CDMA) digital cellular standard for North
America, IS-95 which utilizes spread spectrum signaling. In this
system a high rate phase shift keyed "spreading sequence" is
modulated onto a carrier at a rate 1.2288 MHz. This rate is very
stable and the timing of the symbols, or "chips", making up the
signal is linked to the very stable Global Positioning System. In
both of these examples, a local oscillator in the GPS receiver may
be phase or frequency locked to one of these modulation rates, thus
providing high stability to the local oscillator.
[0075] Advantages of the modulation synchronization method include
(A) the modulation rate is independent of the carrier frequency of
the transmission, and (B) providing this modulation rate to the GPS
receiver often requires little change to the cellular receiver's
frequency synthesis circuits. In many cases it is expected that
these advantages will lead to lower costs than the carrier
synchronization method, although the lower frequency of the
modulation rate may make it more susceptible to various sources of
noise and jitter.
[0076] Two examples of the modulation synchronization method will
be provided here to show embodiments of the current invention. FIG.
10A shows an apparatus which may employ the method applied to the
situation for the IS-95 CDMA cellular standard. A signal from the
cell basestation (e.g. cell site 13) is received by the antenna
101, converted to an appropriate IF via RF to IF converter 102 and
sent to PN acquisition and tracking circuit or subsystem 103, all
of which are a part of the cell phone receiver 120. The PN
acquisition circuit acquires and tracks the CDMA pseudorandom
sequence (frequency and phase) that is modulated onto the carrier
at a rate of 1.2288 MHz. In a typical implementation this tracking
is done using a voltage controlled, or tunable, oscillator 104
which drives a PN generator. This VCO 104 may be implemented in
analog or digital form. Often this oscillator is adjusted in
frequency to be twice that of the received PN rate; this permits
continuous tracking of the PN signal. In FIG. 1, the VCO 104 is run
at twice the PN, or chip, rate, i.e. 2.4567 MHz. It is well-known
in the art that utilizing a clock rate at twice (or a multiple
thereof of) the received chip rate enables construction of a good
quality tracking system utilizing an early/late PN tracking
loop.
[0077] As mentioned the received CDMA signal has a highly stable PN
modulation, locked to GPS time (except under certain outage
conditions). Hence, the supplied 2.4567 MHz clock from the PN
acquisition circuit will normally have very good long term
stability.
[0078] Its short term stability, or phase noise, is primarily a
function of the quality of the tracking loop described above. This
clock may be provided to a phaselock loop circuit 121 whose purpose
is to phase and frequency lock a second oscillator 109 to this
clock. This second oscillator has frequency 4.096 MHz and is used
as the frequency reference for the GPS receiver frequency
synthesizer 112. This frequency is a multiple of 1.024 MHz, which
may be used in GPS systems and is described in detail in co-pending
patent application Ser. No. 08/612,669, referred to above (filed on
Mar. 8, 1996). The PN VCO frequency 2.4576 MHz when divided by 3
equals 819.2 kHz, which is identical to the GPS reference frequency
4.096 MHz divided by 5. Hence use of two dividers 105 and 106 in
the phaselock loop 121 together with a conventional phase detector
107 and loop filter 108 enable the phaselocking of oscillator 109
to 104 in a conventional manner. This circuitry is very simple and
inexpensive to construct, especially in integrated circuit
form.
[0079] The phaselocked oscillator 109 is used as a reference for
GPS frequency synthesizer 112 which produces local oscillators for
a GPS RF to IF converter 111 and sample clock for the GPS signal
processor 113. In particular a 4.096 MHz sample clock is suitable
for processing the GPS signals, as explained in the above
referenced patent application Ser. No. 08/612,669, filed Mar. 8,
1996.
[0080] The application of this invention to the GSM signaling
format is similar to the CDMA, except that the primary symbol
modulation rate of GSM, namely 270.833 kHz does not have suitable
common factors with the abovementioned GPS receiver reference
frequency 4.096 MHz. However, alternative GPS receiver
implementations may be utilized which do have good common factors.
For example some GPS receivers utilize a 10 MHz reference
oscillator. Since 270.833 kHz times 48/13 equals 1 MHz, it is easy
to phaselock a 10 MHz reference oscillator to the GSM symbol rate
by an approach similar to FIG. 10A.
[0081] However, even if a 4.096 MHz reference is utilized by the
GPS, it is still possible to slightly modify the system of FIG. 10A
to accommodate this situation. This is illustrated in FIG. 10B.
Here the VCO 204 in the communication receiver 220 is locked to 8
times the TDMA symbol rate by the acquisition and tracking circuit
203. The VCO output from VCO 204 is supplied to a direct digital
frequency synthesizer 221a (DDS), sometimes referred to as a
numerically controlled oscillator (NCO). This device, well-known in
the art, consists of a digital phase accumulator, a sine lookup
table to generate digital samples of a sinusoid, and a D/A
converter and lowpass filter to create an analog signal from the
digital samples. In the example of FIG. 10B, the DDS is programmed
to frequency 0.23631 as a fraction of the input frequency 2.167
MHz, so that a 512 kHz output is produced. The frequency
synthesizer 212 can utilize the 512 kHz reference of FIG. 10B in a
manner similar to the 4.096 MHz of FIG. 10A, since the latter is a
multiple of the former. A disadvantage of the DDS is some
applications is that it may be more costly than a standard analog
phaselock loop; however, in some cases this cost, which is
dominated by the cost of the aforementioned D/A converter, may be
reduced by using a single bit D/A converter. This requires a
judicious choice of the exact programmed frequency of the DDS so
that resulting spurs are outside the loop bandwidth of the
frequency synthesizer 212 which is phaselocked to this
reference.
[0082] FIG. 11A illustrates a generalized method performed
according to the present invention by the systems shown in either
FIGS. 10A or 10B. In step 602, the communication signal is
received. This communication signal has a data signal modulated on
a carrier frequency. A reference signal is extracted from the data
signal in step 604. This reference signal in the examples of FIGS.
10A and 10B is the output from the VCO in the transition and
tracking circuitry of the communication receiver. This reference
signal is used in step 606 to provide a local oscillator signal to
acquire the SPS signals. The examples of FIGS. 10A and 10B
illustrate two examples in which the reference signal may be used.
In one case, the reference signal is used in a phaselock loop to
generate another clock output which is used as a reference for a
frequency synthesizer which drives the RF to IF converter as shown
in FIG. 10A. FIG. 11B shows a more specific implementation of the
present invention in one embodiment. In this embodiment, the data
signal which is modulated onto the carrier frequency is acquired
and tracked. A first local oscillator signal is generated which is
corrected by the tracked data signal. The first local oscillator
signal is then used to generate a second local oscillator signal
which is used to acquire the GPS signals from GPS satellites.
[0083] It will be appreciated that the Doppler information which is
transmitted to an SPS receiver according to the present invention
may include not only approximate Dopplers relative to each
satellite in view of the SPS receiver, but also the rate of change
for each approximate Doppler. The approximate Doppler information
may alternatively be expressed in the form of quadratic equations
or more sophisticated mathematical representations which may be
valid for approximately one-half hour from the time in which they
were originally determined.
[0084] Approximate Doppler may be computed by computing the range
from the remote to the satellites of interest at times separated by
an appropriate interval (e.g. 1 second). This is done utilizing the
supplied Almanac data and the approximate user position (e.g.,
based upon the fixed location of the cell site in a cellular phone
system). The difference in these ranges is a range rate, which can
be divided by the speed of light to yield a Doppler expressed in
seconds per second (or another suitable set of units such as
nanoseconds per second).
[0085] Although the methods and apparatus of the present invention
have been described with reference to GPS satellites, it will be
appreciated that the teachings are equally applicable to
positioning systems which utilize pseudolites or a combination of
satellites and pseudolites. Pseudolites are ground based
transmitters which broadcast a PN code (similar to a GPS signal)
modulated on an L-band carrier signal, generally synchronized with
GPS time. Each transmitter may be assigned a unique PN code so as
to permit identification by a remote receiver. Pseudolites are
useful in situations where GPS signals from an orbiting satellite
might be unavailable, such as tunnels, mines, buildings or other
enclosed areas. The term "satellite", as used herein, is intended
to include pseudolite 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.
[0086] In the preceding discussion the invention has been described
with reference to application upon the United States Global
Positioning Satellite (GPS) system. It should evident, however,
that these methods are equally applicable to similar satellite
positioning systems, and in, particular, the Russian Glonass
system. The Glonass system primarily differs from GPS system in
that the emissions from different satellites are differentiated
from one another by utilizing slightly different carrier
frequencies, rather than utilizing different pseudorandom codes. In
this situation substantially all the circuitry and algorithms
described previously are applicable with the exception that when
processing a new satellite's emission a different exponential
multiplier corresponding to the different carrier frequencies is
used to preprocess the data. The term "GPS" used herein includes
such alternative satellite positioning systems, including the
Russian Glonass system.
[0087] It will be appreciated that the various aspects of the
present invention may be used in GPS mobile units having
architectures such as those described in U.S. patent application
Ser. No. 08/652,833, filed May 23, 1996 by Norman F. Krasner, which
application is hereby incorporated herein by reference.
[0088] In the foregoing specification, the invention has been
described with reference to specific exemplary embodiments thereof.
It will, however, be evident that various modifications and changes
may be made thereto without departing from the broader spirit and
scope of the invention as set forth in the appended claims. The
specification and drawings are, accordingly, to be regarded in an
illustrative rather than a restrictive sense.
* * * * *