U.S. patent application number 13/774342 was filed with the patent office on 2014-01-02 for crystal oscillator calibration.
This patent application is currently assigned to QUALCOMM Incorporated. The applicant listed for this patent is QUALCOMM INCORPORATED. Invention is credited to Vishal AGARWAL, Dominic Gerard FARMER, Daniel Fred FILIPOVIC, Sasidhar MOWA, Emilija Milorad SIMIC.
Application Number | 20140004887 13/774342 |
Document ID | / |
Family ID | 49778609 |
Filed Date | 2014-01-02 |
United States Patent
Application |
20140004887 |
Kind Code |
A1 |
FARMER; Dominic Gerard ; et
al. |
January 2, 2014 |
CRYSTAL OSCILLATOR CALIBRATION
Abstract
Systems and methods for temperature-calibration of an
uncompensated XO in a mobile device during mobile device operation.
The XO is temperature-calibrated based on assistance from wireless
signals, such as from satellite source, and optionally from
terrestrial sources such as WWAN, CDMA, etc. Based on one or more
received wireless signals received at a receiver, corresponding
frequency estimates of the XO are obtained and correlated with
corresponding operating temperatures in a processor. Based on one
or more samples of frequency estimates and associated temperatures,
the XO is temperature-calibrated in the processor wherein a
frequency-temperature (FT) model is formulated for the XO. The
frequency of the temperature-calibrated XO can be determined from
the FT model at any given temperature.
Inventors: |
FARMER; Dominic Gerard; (Los
Gatos, CA) ; AGARWAL; Vishal; (San Diego, CA)
; SIMIC; Emilija Milorad; (La Jolla, CA) ;
FILIPOVIC; Daniel Fred; (Solana Beach, CA) ; MOWA;
Sasidhar; (Superior, CO) |
|
Applicant: |
Name |
City |
State |
Country |
Type |
QUALCOMM INCORPORATED |
San Diego |
CA |
US |
|
|
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
49778609 |
Appl. No.: |
13/774342 |
Filed: |
February 22, 2013 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
61666307 |
Jun 29, 2012 |
|
|
|
Current U.S.
Class: |
455/456.6 ;
375/145; 375/149 |
Current CPC
Class: |
H04W 56/00 20130101;
H03L 1/022 20130101; G01S 19/235 20130101 |
Class at
Publication: |
455/456.6 ;
375/149; 375/145 |
International
Class: |
H03L 1/02 20060101
H03L001/02; G01S 19/23 20060101 G01S019/23 |
Claims
1. A method of temperature-calibrating an uncompensated crystal
oscillator (XO), in a mobile device during mobile device operation,
the method comprising: receiving a first set of wireless signals
comprising at least a first wireless signal of known frequency, at
a first temperature; estimating a first frequency of the XO at the
first temperature, based on at least the first wireless signal; and
temperature-calibrating the XO based on the first frequency and the
first temperature.
2. The method of claim 1, wherein the uncompensated XO comprises a
lack of built-in compensation for frequency variation of the XO
with variation in temperature or voltage.
3. The method of claim 1, wherein the first wireless signal is
transmitted by a first satellite.
4. The method of claim 3, wherein the first satellite comprises a
global navigation satellite systems (GNSS) satellite.
5. The method of claim 4, further comprising receiving GNSS
assistance information.
6. The method of claim 5, wherein the GNSS assistance information
further comprises a location of the mobile device.
7. The method of claim 5, wherein the GNSS assistance information
comprises GNSS Ephemeris information.
8. The method of claim 5, wherein the GNSS assistance information
comprises Almanac information.
9. The method of claim 5, further comprising determining a location
of the mobile device.
10. The method of claim 9, wherein determining the location is
based on at least one terrestrial signal.
11. The method of claim 9, wherein determining the location is
based on GNSS signals.
12. The method of claim 9, wherein the first set of wireless
signals further comprises at least a second wireless signal
transmitted by a second satellite and a third wireless signal
transmitted by a third satellite.
13. The method of claim 12, wherein estimating the first frequency
of the XO at the first temperature is further based on at least the
second and third wireless signals.
14. The method of claim 13, wherein estimating the first frequency
of the XO at the first temperature comprises obtaining the location
based on at least the first, second, and the third wireless
signals.
15. The method of claim 13, wherein estimating the first frequency
of the XO at the first temperature comprises: obtaining an
effective frequency of the first, second, and third wireless
signals, wherein the frequencies of the first, second, and third
wireless signals are offset by a first, second, and third Doppler
relative to the effective frequency; and deriving a first frequency
error of the XO based on the effective frequency.
16. The method of claim 12, wherein, estimating the first frequency
of the XO at the first temperature comprises: deriving a first
effective frequency from the first wireless signal, a second
effective frequency from the second wireless signal, and a third
effective frequency from the third wireless signal; determining a
derived effective frequency based on one or more of the first,
second, and third effective frequencies; determining a frequency
variation of a local oscillator on the mobile device, as a
difference in frequency between the derived effective frequency and
a frequency of the local oscillator, wherein the local oscillator
is sourced from the XO; normalizing the frequency variation of the
local oscillator based on an expected nominal frequency of the
local oscillator; determining a normalized frequency variation of
the XO as equal to the normalized frequency variation of the local
oscillator; and determining the first frequency based on the
normalized frequency variation of the XO and an expected nominal
frequency of the XO.
17. The method of claim 16, wherein the derived effective frequency
is based on the strongest of the first, second, and third effective
frequencies.
18. The method of claim 16, wherein the derived effective frequency
is based on a combination of the first, second, and third effective
frequencies.
19. The method of claim 18, wherein the combination is one of a
weighted average, a mean, a median, a least squares, or a
pre-specified mathematical fit of the first, second, and third
effective frequencies.
20. The method of claim 3, wherein a Doppler of the first wireless
signal transmitted by the first satellite is constant.
21. The method of claim 20, wherein the first satellite is
geostationary and the Doppler of the first wireless signal is
zero.
22. The method of claim 20, wherein the first satellite comprises a
satellite-based augmentation system (SBAS) satellite.
23. The method of claim 20, further comprising determining whether
the first wireless signal satisfies a pre-specified signal to noise
ratio (SNR).
24. The method of claim 20, further comprising determining whether
the first wireless signal passes a pre-specified error or parity
check.
25. The method of claim 3, wherein the mobile device is in motion,
and wherein estimating the first frequency of the XO at the first
temperature, based on at least the first wireless signal further
comprises estimating a difference between a measured Doppler of the
first wireless signal and a predicted Doppler of the first wireless
signal based on a speed of motion of the mobile device.
26. The method of claim 1, wherein temperature-calibrating the XO
comprises determining a relationship between frequency of the XO
and temperature, based on at least the first frequency and the
first temperature.
27. The method of claim 26, wherein the relationship is a
polynomial equation of the frequency of the XO and temperature with
a number of unknown coefficients based on an order of the
polynomial equation.
28. The method of claim 27 comprising reducing the number of
unknown coefficients based on specifications of the XO.
29. The method of claim 27 comprising reducing the number of
unknown coefficients based on precalibration of the XO during
manufacturing of the XO.
30. The method of claim 27 comprising reducing the number of
unknown coefficients based on constraining a variation in
temperature.
31. The method of claim 1, further comprising: receiving a second
set of wireless signals comprising at least one wireless signal of
known frequency at a second temperature; estimating a second
frequency of the XO at the second temperature, based on the second
set of wireless signals, wherein the second temperature is
different from the first temperature; and further
temperature-calibrating the XO based on the second frequency and
the second temperature.
32. The method of claim 31, wherein further temperature-calibrating
the XO comprises determining a relationship between frequency of
the XO and temperature, based on at least the first frequency and
the first temperature and on the second frequency and the second
temperature.
33. The method of claim 31, further comprising receiving a third
set of wireless signals comprising at least one wireless signal of
known frequency at a third temperature; estimating a third
frequency of the XO at the third temperature, based on the third
set of wireless signals, wherein the third temperature is different
from the first temperature and the second temperature; and further
temperature-calibrating the XO based on the third frequency and the
third temperature.
34. The method of claim 33, wherein further temperature-calibrating
the XO comprises determining a relationship between frequency of
the XO and temperature, based on at least the first frequency and
the first temperature, the second frequency and the second
temperature, and the third frequency and the third temperature.
35. A method of temperature-calibrating an uncompensated crystal
oscillator (XO) in a mobile device during mobile device operation,
the method comprising: receiving a first set of wireless signals
comprising at least a first wireless signal, from a signal source
of known frequency and known Doppler, at a first temperature,
wherein a plurality of satellite signals is unavailable; estimating
a first frequency of the XO at the first temperature, based on at
least the first wireless signal; and temperature-calibrating the XO
based on the first frequency and the first temperature.
36. The method of claim 35, wherein the signal source is a
satellite.
37. The method of claim 36, wherein the satellite is geo-stationary
with zero Doppler.
38. The method of claim 37, wherein the satellite is a satellite
based augmentation system (SBAS) satellite.
39. The method of claim 36, further comprising obtaining a location
of the mobile device from an approximate location using cell sector
center of a serving cell, from a trilateration of terrestrial
signals, from a positioning server, or from a base station Almanac
on the mobile device.
40. The method of claim 39, further comprising determining an
effective frequency of the first wireless signal based on Ephemeris
and time at the mobile device.
41. The method of claim 40, wherein, estimating the first frequency
of the XO at the first temperature comprises: determining a
frequency variation of a local oscillator on the mobile device, as
a difference in frequency between the effective frequency and a
frequency of the local oscillator, wherein the local oscillator is
sourced from the XO; normalizing the frequency variation of the
local oscillator based on an expected nominal frequency of the
local oscillator; determining a normalized frequency variation of
the XO as equal to the normalized frequency variation of the local
oscillator; and determining the first frequency based on the
normalized frequency variation of the XO and an expected nominal
frequency of the XO.
42. The method of claim 36, further comprising determining whether
the first wireless signal satisfies a pre-specified signal to noise
ratio (SNR).
43. The method of claim 36, further comprising determining whether
the first wireless signal passes a pre-specified error or parity
check.
44. The method of claim 35, comprising receiving the first set of
wireless signals from a calibrated terrestrial source.
45. The method of claim 44, wherein the calibrated terrestrial
source is one of a wireless wide area network (WWAN), code division
multiple access (CDMA) network, or long term evolution (LTE)
network.
46. A system comprising: a mobile device comprising an
uncompensated crystal oscillator (XO); means for receiving a first
set of wireless signals comprising at least a first wireless signal
of known frequency, at a first temperature; means for estimating a
first frequency of the XO at the first temperature, based on at
least the first wireless signal; and means for
temperature-calibrating the XO based on the first frequency and the
first temperature during operation of the mobile device.
47. The system of claim 46, wherein the uncompensated XO comprises
a lack of built-in compensation for frequency variation of the XO
with variation in temperature or voltage.
48. The system of claim 46, wherein the first wireless signal is
transmitted by a first satellite.
49. The system of claim 48, wherein the first satellite comprises a
GNSS satellite.
50. The system of claim 49, further comprising means for receiving
GNSS assistance information.
51. The system of claim 50, wherein the GNSS assistance information
further comprises a location of the mobile device.
52. The system of claim 50, wherein the GNSS assistance information
comprises GNSS Ephemeris information.
53. The system of claim 50, wherein the GNSS assistance information
comprises Almanac information.
54. The system of claim 50, further comprising means for
determining a location of the mobile device.
55. The system of claim 54, wherein the means determining the
location utilizes at least one terrestrial signal.
56. The system of claim 54, wherein the means for determining the
location utilizes GNSS signals.
57. The system of claim 54, wherein the first set of wireless
signals further comprises at least a second wireless signal
transmitted by a second satellite and a third wireless signal
transmitted by a third satellite.
58. The system of claim 57, wherein the means for estimating the
first frequency of the XO at the first temperature is further based
on at least the second and third wireless signals.
59. The system of claim 58, wherein the means for estimating the
first frequency of the XO at the first temperature comprises means
for obtaining the location based on at least the first, second, and
the third wireless signals.
60. The system of claim 58, wherein the means for estimating the
first frequency of the XO at the first temperature comprises: means
for obtaining an effective frequency of the first, second, and
third wireless signals, wherein the frequencies of the first,
second, and third wireless signals are offset by a first, second,
and third Doppler relative to the effective frequency; and means
for deriving a first frequency error of the XO based on the
effective frequency.
61. The system of claim 57, wherein, the means for estimating the
first frequency of the XO at the first temperature comprises: means
for deriving a first effective frequency from the first wireless
signal, a second effective frequency from the second wireless
signal, and a third effective frequency from the third wireless
signal; determining a derived effective frequency based on one or
more of the first, second, and third effective frequencies; means
for determining a frequency variation of a local oscillator on the
mobile device, as a difference in frequency between the derived
effective frequency and a frequency of the local oscillator,
wherein the local oscillator is sourced from the XO; means for
normalizing the frequency variation of the local oscillator based
on an expected nominal frequency of the local oscillator; means for
determining a normalized frequency variation of the XO as equal to
the normalized frequency variation of the local oscillator; and
means for determining the first frequency based on the normalized
frequency variation of the XO and an expected nominal frequency of
the XO.
62. The system of claim 61, wherein the derived effective frequency
is based on the strongest of the first, second, and third effective
frequencies.
63. The system of claim 61, wherein the derived effective frequency
is based on a combination of the first, second, and third effective
frequencies.
64. The system of claim 63, wherein the combination is one of a
weighted average, a mean, a median, a least squares, or a
pre-specified mathematical fit of the first, second, and third
effective frequencies.
65. The system of claim 48, wherein a Doppler of the first wireless
signal transmitted by the first satellite is constant.
66. The system of claim 65, wherein the first satellite is
geostationary and the Doppler of the first wireless signal is
zero.
67. The system of claim 65, wherein the first satellite comprises a
satellite-based augmentation system (SBAS) satellite.
68. The system of claim 65, further comprising means for
determining whether the first wireless signal satisfies a
pre-specified signal to noise ratio (SNR).
69. The system of claim 65, further comprising means for
determining whether the first wireless signal passes a
pre-specified error or parity check.
70. The system of claim 48, wherein the mobile device is in motion,
and wherein the means for estimating the first frequency of the XO
at the first temperature, based on at least the first wireless
signal further comprises means for estimating a difference between
a measured Doppler of the first wireless signal and a predicted
Doppler of the first wireless signal based on a speed of motion of
the mobile device.
71. The system of claim 46, wherein the means for
temperature-calibrating the XO comprises means for determining a
relationship between frequency of the XO and temperature, based on
at least the first frequency and the first temperature.
72. The system of claim 71, wherein the relationship is a
polynomial equation of the frequency of the XO and temperature with
a number of unknown coefficients based on an order of the
polynomial equation.
73. The system of claim 72 comprising means for reducing the number
of unknown coefficients based on specifications of the XO.
74. The system of claim 72 comprising means for reducing the number
of unknown coefficients based on precalibration of the XO during
manufacturing of the XO.
75. The system of claim 72 comprising means for reducing the number
of unknown coefficients based on constraining a variation in
temperature.
76. The system of claim 46, further comprising: means for receiving
a second set of wireless signals comprising at least one wireless
signal of known frequency at a second temperature; means for
estimating a second frequency of the XO at the second temperature,
based on the second set of wireless signals, wherein the second
temperature is different from the first temperature; and means for
further temperature-calibrating the XO based on the second
frequency and the second temperature.
77. The system of claim 76, wherein the means for further
temperature-calibrating the XO comprises means for determining a
relationship between frequency of the XO and temperature, based on
at least the first frequency and the first temperature and on the
second frequency and the second temperature.
78. The system of claim 76, further comprising means for receiving
a third set of wireless signals comprising at least one wireless
signal of known frequency at a third temperature; means for
estimating a third frequency of the XO at the third temperature,
based on the third set of wireless signals, wherein the third
temperature is different from the first temperature and the second
temperature; and means for further temperature-calibrating the XO
based on the third frequency and the third temperature.
79. The system of claim 78, wherein the means for further
temperature-calibrating the XO comprises means for determining a
relationship between frequency of the XO and temperature, based on
at least the first frequency and the first temperature, the second
frequency and the second temperature, and the third frequency and
the third temperature.
80. A system comprising: a mobile device comprising an
uncompensated crystal oscillator (XO); means for receiving a first
set of wireless signals comprising at least a first wireless
signal, from a signal source of known frequency and known Doppler,
at a first temperature, wherein a plurality of satellite signals is
unavailable; means for estimating a first frequency of the XO at
the first temperature, based on at least the first wireless signal;
and means for temperature-calibrating the XO based on the first
frequency and the first temperature during operation of the mobile
device.
81. The system of claim 80, wherein the signal source is a
satellite.
82. The system of claim 81, wherein the satellite is geo-stationary
with zero Doppler.
83. The system of claim 82, wherein the satellite is a satellite
based augmentation system (SBAS) satellite.
84. The system of claim 81, further comprising means for obtaining
a location of the mobile device from an approximate location using
cell sector center of a serving cell, from a trilateration of
terrestrial signals, from a positioning server, or from a base
station Almanac on the device.
85. The system of claim 84, further comprising means for
determining an effective frequency of the first wireless signal
based on Ephemeris and time at the mobile device.
86. The system of claim 85, wherein, the means for estimating the
first frequency of the XO at the first temperature comprises: means
for determining a frequency variation of a local oscillator on the
mobile device, as a difference in frequency between the effective
frequency and a frequency of the local oscillator, wherein the
local oscillator is sourced from the XO; means for normalizing the
frequency variation of the local oscillator based on an expected
nominal frequency of the local oscillator; means for determining a
normalized frequency variation of the XO as equal to the normalized
frequency variation of the local oscillator; and means for
determining the first frequency based on the normalized frequency
variation of the XO and an expected nominal frequency of the
XO.
87. The system of claim 81, further comprising means for
determining whether the first wireless signal satisfies a
pre-specified signal to noise ratio (SNR).
88. The system of claim 81, further comprising means for
determining whether the first wireless signal passes a
pre-specified error or parity check.
89. The system of claim 80, comprising means for receiving the
first set of wireless signals from a calibrated terrestrial
source.
90. The system of claim 89, wherein the calibrated terrestrial
source is one of a wireless wide area network (WWAN), code division
multiple access (CDMA) network, or long term evolution (LTE)
network.
91. A mobile device comprising: an uncompensated crystal oscillator
(XO); a temperature sensor configured to provide a first
temperature; one or more receivers configured to receive a first
set of wireless signals comprising at least a first wireless signal
of known frequency, at the first temperature; and a processor
configured to estimate a first frequency of the XO at the first
temperature, based on at least the first wireless signal, and
temperature-calibrate the XO based on the first frequency and the
first temperature during operation of the mobile device.
92. The mobile device of claim 91, wherein the uncompensated XO
comprises a lack of built-in compensation for frequency variation
of the XO with variation in temperature or voltage.
93. The mobile device of claim 91, wherein the first wireless
signal is transmitted by a first satellite.
94. The mobile device of claim 93, wherein the first satellite
comprises a GNSS satellite.
95. The mobile device of claim 94, wherein at least one of the
receivers is further configured to receive GNSS assistance
information.
96. The mobile device of claim 95, wherein the GNSS assistance
information further comprises a location of the mobile device.
97. The mobile device of claim 95, wherein the GNSS assistance
information comprises GNSS Ephemeris information.
98. The mobile device of claim 95, wherein the GNSS assistance
information comprises Almanac information.
99. The mobile device of claim 5, wherein the processor is further
configured to determine a location of the mobile device.
100. The mobile device of claim 99, wherein the processor is
configured to determine the location based on at least one
terrestrial signal.
101. The mobile device of claim 99, wherein the processor is
configured to determine the location based on GNSS signals.
102. The mobile device of claim 99, wherein the first set of
wireless signals further comprises at least a second wireless
signal transmitted by a second satellite and a third wireless
signal transmitted by a third satellite.
103. The mobile device of claim 102, wherein the processor is
further configured to estimate the first frequency of the XO at the
first temperature based on at least the second and third wireless
signals.
104. The mobile device of claim 103, wherein the processor is
configured to estimate the first frequency of the XO at the first
temperature based on a location of the mobile device determined
from at least the first, second, and the third wireless
signals.
105. The mobile device of claim 103, wherein the processor is
configured to: estimate the first frequency of the XO at the first
temperature based on an effective frequency of the first, second,
and third wireless signals, wherein the frequencies of the first,
second, and third wireless signals are offset by a first, second,
and third Doppler relative to the effective frequency; and derive a
first frequency error of the XO based on the effective
frequency.
106. The mobile device of claim 102, further comprising at least
one local oscillator sourced from the XO, wherein the processor is
configured to derive a first effective frequency from the first
wireless signal, a second effective frequency from the second
wireless signal, and a third effective frequency from the third
wireless signal, and a derived effective frequency based on one or
more of the first, second, and third effective frequencies; a band
pass filter configured to determine a frequency variation of the at
least one local oscillator as a difference in frequency between the
derived effective frequency and a frequency of the local
oscillator; and the processor is further configured to normalize
the frequency variation of the local oscillator based on an
expected nominal frequency of the local oscillator, determine a
normalized frequency variation of the XO as equal to the normalized
frequency variation of the local oscillator, and determine the
first frequency based on the normalized frequency variation of the
XO and an expected nominal frequency of the XO.
107. The mobile device of claim 106, wherein the derived effective
frequency is based on the strongest of the first, second, and third
effective frequencies.
108. The mobile device of claim 106, wherein the derived effective
frequency is based on a combination of the first, second, and third
effective frequencies.
109. The mobile device of claim 108, wherein the combination is one
of a weighted average, a mean, a median, a least squares, or a
pre-specified mathematical fit of the first, second, and third
effective frequencies.
110. The mobile device of claim 93, wherein a Doppler of the first
wireless signal transmitted by the first satellite is constant.
111. The mobile device of claim 110, wherein the first satellite is
geostationary and the Doppler of the first wireless signal is
zero.
112. The mobile device of claim 110, wherein the first satellite
comprises a satellite-based augmentation system (SBAS)
satellite.
113. The mobile device of claim 10, wherein the processor is
further configured to determine whether the first wireless signal
satisfies a pre-specified signal to noise ratio (SNR).
114. The mobile device of claim 110, wherein the processor is
further configured to determine whether the first wireless signal
passes a pre-specified error or parity check.
115. The mobile device of claim 93, wherein the mobile device is in
motion, and wherein the processor is configured to estimate the
first frequency of the XO at the first temperature, based on a
difference between a measured Doppler of the first wireless signal
and a predicted Doppler of the first wireless signal based on a
speed of motion of the mobile device.
116. The mobile device of claim 91, wherein the
temperature-calibration of the XO comprises a relationship between
frequency of the XO and temperature, based on at least the first
frequency and the first temperature.
117. The mobile device of claim 116, wherein the relationship is a
polynomial equation of the frequency of the XO and temperature with
a number of unknown coefficients based on an order of the
polynomial equation.
118. The mobile device of claim 117, wherein the processor is
further configured to temperature-calibrate the XO using a reduced
number of unknown coefficients, wherein the reduced number of
unknown coefficients is based on specifications of the XO.
119. The mobile device of claim 118, wherein the reduced number of
unknown coefficients is based on precalibration of the XO during
manufacture of the XO.
120. The mobile device of claim 118, wherein the reduced number of
unknown coefficients is based on constraints in variation of
temperature.
121. The mobile device of claim 91, wherein, the one or more
receivers are further configured to receive a second set of
wireless signals comprising at least one wireless signal of known
frequency at a second temperature; the temperature sensor is
configured to provide a second temperature, wherein the second
temperature is different from the first temperature; and the
processor is further configured to estimate a second frequency of
the XO at the second temperature, based on the second set of
wireless signals and further temperature-calibrate the XO based on
the second frequency and the second temperature.
122. The mobile device of claim 121, wherein the further
temperature-calibration of the XO comprises a relationship between
frequency of the XO and temperature, based on at least the first
frequency and the first temperature and on the second frequency and
the second temperature.
123. The mobile device of claim 121, wherein the one or more
receivers are further configured to receive a third set of wireless
signals comprising at least one wireless signal of known frequency
at a third temperature; the temperature sensor is configured to
provide a third temperature, wherein the third temperature is
different from the first temperature and the second temperature;
and the processor is further configured to estimate a third
frequency of the XO at the third temperature, based on the third
set of wireless signals and further temperature-calibrate the XO
based on the third frequency and the third temperature.
124. The mobile device of claim 123, wherein the further
temperature-calibration of the XO comprises a relationship between
frequency of the XO and temperature, based on at least the first
frequency and the first temperature, the second frequency and the
second temperature, and the third frequency and the third
temperature.
125. A mobile device comprising: an uncompensated crystal
oscillator (XO); a temperature configured to provide a first
temperature; one or more receivers configured to receive a first
set of wireless signals comprising at least a first wireless
signal, from a signal source of known frequency and known Doppler,
at the first temperature, wherein a plurality of satellite signals
is unavailable; and a processor configured to estimate a first
frequency of the XO at the first temperature, based on at least the
first wireless signal and temperature-calibrate the XO based on the
first frequency and the first temperature.
126. The mobile device of claim 125, wherein the signal source is a
satellite.
127. The mobile device of claim 126, wherein the satellite is
geo-stationary with zero Doppler.
128. The mobile device of claim 127, wherein the satellite is a
satellite based augmentation system (SBAS) satellite.
129. The mobile device of claim 126, wherein the processor is
further configured to obtain a location of the mobile device from
an approximate location using cell sector center of a serving cell,
from a trilateration of terrestrial signals, from a positioning
server, or from a base station Almanac on the mobile device.
130. The mobile device of claim 129, wherein the processor is
further configured to determine an effective frequency of the first
wireless signal based on Ephemeris and time at the mobile
device.
131. The mobile device of claim 130, further comprising a local
oscillator sourced from the XO and a band pass filter configured to
determine a frequency variation of the local oscillator as a
difference in frequency between the effective frequency and a
frequency of the local oscillator, and wherein the processor is
further configured to normalize the frequency variation of the
local oscillator based on an expected nominal frequency of the
local oscillator, determine a normalized frequency variation of the
XO as equal to the normalized frequency variation of the local
oscillator, and determine the first frequency based on the
normalized frequency variation of the XO and an expected nominal
frequency of the XO.
132. The mobile device of claim 126, wherein the processor is
further configured to determine whether the first wireless signal
satisfies a pre-specified signal to noise ratio (SNR).
133. The mobile device of claim 126, wherein the processor is
further configured to determine whether the first wireless signal
passes a pre-specified error or parity check.
134. The mobile device of claim 125, wherein the one or more
receivers are configured to receive the first set of wireless
signals from a calibrated terrestrial source.
135. The mobile device of claim 134, wherein the calibrated
terrestrial source is one of a wireless wide area network (WWAN),
code division multiple access (CDMA) network, or long term
evolution (LTE) network.
136. A mobile device comprising: an uncompensated crystal
oscillator (XO); a temperature sensor configured to provide a first
temperature; one or more receivers configured to receive a first
set of wireless signals comprising at least a first wireless signal
of known frequency, at a first temperature; a processor; and a
non-transitory computer-readable storage medium comprising code,
which, when executed by the processor, causes the processor to
perform operations for temperature-calibrating a crystal oscillator
(XO), the non-transitory computer-readable storage medium
comprising: code for estimating a first frequency of the XO at the
first temperature, based on at least the first wireless signal;
code for determining unknown coefficients of a polynomial equation
comprising a relationship between frequency of the XO and
temperature based on at least the first frequency and the first
temperature.
Description
CLAIM OF PRIORITY UNDER 35 U.S.C. .sctn.119
[0001] The present application for patent claims the benefit of
U.S. Provisional Application No. 61/666,307, entitled "GNSS BASED
CRYSTAL OSCILLATOR CALIBRATION" filed Jun. 29, 2012, assigned to
the assignee hereof, and expressly incorporated herein by
reference.
FIELD OF DISCLOSURE
[0002] Disclosed embodiments are directed to field calibration of
an XO, and more particularly, for temperature-calibration of an
uncompensated XO using assistance from one or more wireless signals
of known frequency, including satellite signals, and optionally,
terrestrial signals. The uncompensated XO does not comprise
built-in compensation for frequency variation with variation in
temperature or voltage.
BACKGROUND
[0003] Global navigation satellite systems (GNSS) are well known in
applications related to tracking and positioning. GNSS systems such
as global positioning systems (GPS) are satellite-based systems
used for pinpointing a precise location of a GNSS receiver or
object capable of tracking satellite signals. With advances in GNSS
technology, it is possible to locate and track movements of an
object on the globe.
[0004] GNSS systems operate by configuring a GNSS satellite to
transmit certain signals which may include pre-established codes.
These signals are based on a GNSS time or satellite time derived
from an atomic clock or satellite clock present in the satellite.
The transmitted signals may include a time stamp indicating the
time at which they were transmitted. A GNSS receiver, which may be
integrated in a handheld device, is timed by a local clock located
at the receiver end. Ideally, this local clock is synchronized to
the satellite clock (also known as the GNSS time). The device
comprising the GNSS receiver is configured to estimate the GNSS
time based on the satellite signals in order to synchronize their
local clocks to the GNSS time. Once the local clocks are accurately
synchronized, the device is configured to calculate the propagation
time for the satellite signals to reach the receiver, based on a
difference between the time at which the signals were received, and
the time at which they were transmitted. This propagation time is
an indication of the distance between the satellite and the device,
keeping in mind that factors such as atmospheric conditions may
affect the propagation time.
[0005] In order to pinpoint the location of the device, the device
performs the above process to calculate the distance to two or more
other satellites (if altitude and/or local time of the device is
known, the location can be determined with a total of three
satellites, otherwise, a total of four satellites may be needed).
Using the distances to the satellites, it is theoretically possible
to "trilaterate" the position of the device. However, practical
applications diverge from theoretical expectations due to several
sources of inaccuracies inherent in GNSS based positioning.
[0006] One source of inaccuracy relates to synchronization of the
local clock. In modern devices comprising GNSS receivers, time is
typically maintained via a temperature-compensated crystal
oscillator (TCXO), to maintain the frequency stability required for
GNSS operation across varying device temperatures. Even small
errors in frequency may result in large positional errors in
position estimation. Thus, the TCXO and/or a voltage controlled
temperature compensated crystal oscillator (VCTCXO) have been used
in the art to maintain nearly constant frequency across fluctuating
temperature and voltage. While the TCXO and VCTCXO may also
experience some fluctuation in frequency with fluctuations in
temperature and voltage, the frequency variations in an XO, i.e., a
crystal oscillator without such temperature or voltage
compensation, is much larger. Accordingly, the XO has historically
not been used because of the large frequency variations across
temperature and voltage that may prolong GNSS searches or cause
them to fail.
SUMMARY
[0007] Exemplary embodiments of the invention are directed to
systems and methods for calibration of an XO, and more
particularly, for temperature-calibration of an uncompensated XO,
in order to overcome frequency variation of the XO. In several
exemplary aspects, temperature-calibration of the XO includes
determining an accurate relationship between frequency and
temperature of the XO using assistance from one or more signal
sources.
[0008] For example, an exemplary embodiment is directed to a method
of temperature-calibrating an uncompensated crystal oscillator
(XO), in a mobile device during mobile device operation, the method
comprising: receiving a first set of wireless signals comprising at
least a first wireless signal of known frequency, at a first
temperature, estimating a first frequency of the XO at the first
temperature, based on at least the first wireless signal, and
temperature-calibrating the XO based on the first frequency and the
first temperature.
[0009] Another exemplary embodiment is directed to a method of
temperature-calibrating an uncompensated crystal oscillator (XO) in
a mobile device during mobile device operation, the method
comprising: receiving a first set of wireless signals comprising at
least a first wireless signal, from a signal source of known
frequency and known Doppler, at a first temperature, wherein a
plurality of satellite signals is unavailable, estimating a first
frequency of the XO at the first temperature, based on at least the
first wireless signal, and temperature-calibrating the XO based on
the first frequency and the first temperature.
[0010] Another exemplary embodiment is directed to a system
comprising: a mobile device comprising an uncompensated crystal
oscillator (XO), means for receiving a first set of wireless
signals comprising at least a first wireless signal of known
frequency, at a first temperature, means for estimating a first
frequency of the XO at the first temperature, based on at least the
first wireless signal, and means for temperature-calibrating the XO
based on the first frequency and the first temperature during
operation of the mobile device.
[0011] Another exemplary embodiment is directed to a system
comprising: a mobile device comprising an uncompensated crystal
oscillator (XO), means for receiving a first set of wireless
signals comprising at least a first wireless signal, from a signal
source of known frequency and known Doppler, at a first
temperature, wherein a plurality of satellite signals is
unavailable, means for estimating a first frequency of the XO at
the first temperature, based on at least the first wireless signal,
and means for temperature-calibrating the XO based on the first
frequency and the first temperature during operation of the mobile
device.
[0012] Another exemplary embodiment is directed to a mobile device
comprising: an uncompensated crystal oscillator (XO), a temperature
sensor configured to provide a first temperature, one or more
receivers configured to receive a first set of wireless signals
comprising at least a first wireless signal of known frequency, at
the first temperature, and a processor configured to estimate a
first frequency of the XO at the first temperature, based on at
least the first wireless signal, and temperature-calibrate the XO
based on the first frequency and the first temperature during
operation of the mobile device.
[0013] Another exemplary embodiment is directed to a mobile device
comprising: an uncompensated crystal oscillator (XO), a temperature
configured to provide a first temperature, one or more receivers
configured to receive a first set of wireless signals comprising at
least a first wireless signal, from a signal source of known
frequency and known Doppler, at the first temperature, wherein a
plurality of satellite signals is unavailable, and a processor
configured to estimate a first frequency of the XO at the first
temperature, based on at least the first wireless signal and
temperature-calibrate the XO based on the first frequency and the
first temperature.
[0014] Yet another exemplary embodiment is directed to a mobile
device comprising: an uncompensated crystal oscillator (XO), a
temperature sensor configured to provide a first temperature, one
or more receivers configured to receive a first set of wireless
signals comprising at least a first wireless signal of known
frequency, at a first temperature, a processor, and a
non-transitory computer-readable storage medium comprising code,
which, when executed by the processor, causes the processor to
perform operations for temperature-calibrating a crystal oscillator
(XO), the non-transitory computer-readable storage medium
comprising: code for estimating a first frequency of the XO at the
first temperature, based on at least the first wireless signal,
code for determining unknown coefficients of a polynomial equation
comprising a relationship between frequency of the XO and
temperature based on at least the first frequency and the first
temperature.
BRIEF DESCRIPTION OF THE DRAWINGS
[0015] The accompanying drawings are presented to aid in the
description of embodiments of the invention and are provided solely
for illustration of the embodiments and not limitation thereof.
[0016] FIG. 1 is a graphical illustration of XO frequency as a
function of temperature.
[0017] FIGS. 2A-B illustrate exemplary devices configured for XO
temperature-calibration based on received wireless signals
according to exemplary embodiments.
[0018] FIGS. 3A-C depict flow chart illustrations of exemplary
methods of temperature-calibrating an XO based on one or more sets
of received wireless signals.
[0019] FIG. 4 illustrates an exemplary wireless device configured
for XO temperature-calibration based on received wireless signals
according to exemplary embodiments.
DETAILED DESCRIPTION
[0020] Aspects of the invention are disclosed in the following
description and related drawings directed to specific embodiments
of the invention. Alternate embodiments may be devised without
departing from the scope of the invention. Additionally, well-known
elements of the invention may not be described in detail or may be
omitted so as to not obscure the relevant details of the
invention.
[0021] The word "exemplary" is used herein to mean "serving as an
example, instance, or illustration." Any embodiment described
herein as "exemplary" is not necessarily to be construed as
preferred or advantageous over other embodiments. Likewise, the
term "embodiments of the invention" does not require that all
embodiments of the invention include the discussed feature,
advantage or mode of operation.
[0022] The terminology used herein is for the purpose of describing
particular embodiments only and is not intended to be limiting of
embodiments of the invention. As used herein, the singular forms
"a", "an" and "the" are intended to include the plural forms as
well, unless the context clearly indicates otherwise. It will be
further understood that the terms "comprises", "comprising,",
"includes" and/or "including", when used herein, specify the
presence of stated features, integers, steps, operations, elements,
and/or components, but do not preclude the presence or addition of
one or more other features, integers, steps, operations, elements,
components, and/or groups thereof.
[0023] Further, many embodiments are described in terms of
sequences of actions to be performed by, for example, elements of a
computing device. It will be recognized that various actions
described herein can be performed by specific circuits (e.g.,
application specific integrated circuits (ASICs)), by program
instructions being executed by one or more processors, or by a
combination of both. Additionally, these sequence of actions
described herein can be considered to be embodied entirely within
any form of computer readable storage medium having stored therein
a corresponding set of computer instructions that upon execution
would cause an associated processor to perform the functionality
described herein. Thus, the various aspects of the invention may be
embodied in a number of different forms, all of which have been
contemplated to be within the scope of the claimed subject matter.
In addition, for each of the embodiments described herein, the
corresponding form of any such embodiments may be described herein
as, for example, "logic configured to" perform the described
action.
[0024] Embodiments described herein may generally pertain to a
crystal oscillator (XO) in a device configured for GNSS or GPS
applications. More particularly, an exemplary XO is
"uncompensated," which refers herein to an XO which lacks built-in
temperature or voltage compensation (or in other words, an XO which
comprises a lack of built-in compensation) to account for frequency
variation, in contrast to the aforementioned TCXO and VCTCXO, which
have temperature and/or voltage compensation on the TCXO and/or
VCTCXO device. The description of embodiments may simply make
reference to an XO, and it will be understood hereinafter that such
a reference will pertain to an uncompensated XO, unless otherwise
specified. Therefore, exemplary embodiments may be configured to
overcome the problem associated with large frequency variation in
the XO by calibrating the XO. As used herein, the term
"calibration," or more specifically, "temperature-calibration,"
pertains to a relationship between frequency and temperature (also
known as a "frequency-temperature relationship" or "FT
relationship" or "FT model" or "FT curve") of the XO, formulated to
a high degree of accuracy, whereby the frequency of the XO can be
determined from the formulated relationship at any given
temperature. While in some cases, the more general term,
"calibration," may be used, it will be understood that
"calibration" refers to "temperature-calibration" as it pertains to
the exemplary embodiments, wherein temperature-calibration
generally means determination of an FT relationship or FT model for
the XO.
[0025] Moreover, temperature-calibration of the XO in exemplary
embodiments may also be distinguished from precalibration of the XO
during manufacture or in factory settings. Precalibration,
factory-based calibration, or hereinafter, "factory-calibration,"
as used herein, pertains to calibration of the XO in factory
settings before it is placed in the field or under operational
conditions. Factory-calibration is limited to the frequency offset
at nominal temperature. Calibrating each XO across a broad range of
temperatures in the factory is time and cost prohibitive.
Therefore, factory-calibration is generally insufficient for
reliable operation of the device during operation or in field
conditions. Therefore, embodiments are directed to
field-calibration, or more specifically, temperature-calibration in
the field, of the XO, which pertains to temperature-calibrating the
XO during operation of the device comprising the XO, after the
device has left the factory, is integrated into a mobile device,
and is put in use, for example, by the end user of the mobile
device. Accordingly, it will be understood that the term
"calibration" as used herein, refers to field-calibration, and more
specifically, temperature-calibration in the field, during
operation of the device, and excludes any precalibration that may
exist in the XO.
[0026] With the above definitions in mind, exemplary embodiments
are directed to temperature-calibration (i.e.,
temperature-calibration in the field) of the XO using one or more
wireless signals of known frequency. As described herein, "wireless
signals" (or sometimes, more generally, signals received by an
exemplary receiver, or "received signals") include satellite
signals from satellite sources such as GNSS. Additionally, and
optionally, in some aspects, wireless signals may also include
terrestrial signals from terrestrial sources (or more particularly,
"calibrated terrestrial sources" which have known frequency with
negligible frequency variation) such as, some wireless wide area
networks (WWAN) such as code division multiple access (CDMA), and
some long term evolution (LTE) networks. In general, when compared
to terrestrial signals, temperature-calibration performed using
satellite signals may have beneficial aspects based on relative
imperviousness to user motion. In more detail, when the device is
in motion, for example, transported by a user on a freeway, large
variations in "Doppler," or shift in frequency, are introduced in
terrestrial signals, say when the device approaches or moves away
from a base station. On the other hand, the impact of user motion
is significantly smaller on the Doppler of satellite signals, due
to the large distances between the device and the satellites, as
well as, the speed of motion of the satellites when compared to the
distances traversed by the device and the velocity of the device.
Therefore, temperature-calibration can be performed using satellite
signals, even when the device is in motion. Moreover, due to the
above beneficial aspects of satellite signals, a smaller
temperature range (e.g., within a variation of 2.5.degree. C.), at
which frequencies are sampled, may be sufficient to
temperature-calibrate the XO. However, it is possible to augment,
or replace, satellite signal based temperature-calibration of an
exemplary XO with terrestrial signals, in scenarios where
terrestrial signals are available and temperature-calibration based
on the terrestrial signals is feasible. In general, a common aspect
of the wireless signals--both satellite signals and terrestrial
signals--is that these wireless signals have known frequency. As
used herein, "known frequency" of a wireless signal, particularly
in the case of satellite signals, is intended to mean that
frequency of the wireless signal is predetermined or determinable,
from additional information (referred to herein as "GNSS assistance
information"), such as, but not limited to, GNSS Ephemeris and/or
Almanac or velocity of the device. As one of ordinary skill in the
art would recognize, Almanac provides a course position and time
and Ephemeris provides a fine position and time for each satellite.
If Ephemeris is available, Almanac may not be necessary. On the
other hand, if only Almanac is available, Doppler may be estimated
with the Almanac information in some cases. Each satellite
broadcasts its own Ephemeris (for that satellite only) and Almanac
for all of the satellites. Location servers typically have
Ephemeris for all visible satellites and Almanac available for
download.
[0027] For calibrated terrestrial sources, the known frequency can
be obtained in a more straightforward manner, for example, based on
the WWAN or CDMA transmission frequency. However, it will be
understood that one or more of the wireless signals of known
frequency may have an associated "Doppler" or shift from the known
frequency, based on factors such as, speed or relative speed of the
signal source. This Doppler would optimally be accounted for, for
example, by taking multiple samples across a longer period of time,
in order to determine whether there is a variation in velocity, and
by determining a nominal frequency. As seen from the above, in some
cases, the Doppler of a wireless signal of known frequency can be
constant and of a known value. However, in some other cases, the
Doppler may vary. The variation in Doppler sometimes may be known
or determinable, however, in some cases, the Doppler variation may
not be known and further, may not be easily determinable or
predictable. The wireless signals of known frequency (or
hereinafter, simply, "wireless signals") may be used to derive
frequency estimates of the XO at the device. If the Doppler of the
one or more wireless signals used in obtaining the frequency
estimates is unknown, then a plurality of wireless signals may be
used to determine and offset the Doppler values. On the other hand,
a known Doppler source (e.g., a Doppler-true or zero Doppler
source, such as a geostationary source) can also be used in the
temperature-calibration process where a single known Doppler source
would suffice (wherein a plurality would not be needed for
offsetting the Doppler in calculations of frequency estimates). In
either case, frequency estimates are obtained at various operating
temperatures and associated with the operating temperatures to form
sample points comprising frequency estimates and operating
temperatures. Based on the implementation, the number of such
sample points required to temperature-calibrate the XO or form the
FT model may vary.
[0028] In exemplary embodiments, signals from one or more
satellites sources are used to derive a frequency estimate at a
given operating temperature. The minimum number of satellite
sources required to obtain the frequency estimate of the XO may be
dependent on various scenarios. In general, three satellites may be
sufficient to obtain the location or position of the device with an
assumed altitude. With a fourth satellite, the altitude of the
device can also be solved for. In some cases, location can also be
obtained through other means, such as, via a cell sector center or
the location of a terrestrial transmitter. In these cases, one
satellite signal and known Ephemeris, or a terrestrial transmission
of known and reliable frequency, may suffice for obtaining the
frequency estimate of the XO. Note that in embodiments which only
utilize terrestrial wireless signals of known frequency, Ephemeris,
time, and location are not required. In cases where only satellite
or GNSS signals are relied upon, the GNSS location fix or position
fix can provide a location that may be used, along with GNSS
Ephemeris information, to determine the frequency of the XO.
Obtaining a position fix for the device can essentially compensate
for the Doppler of the various received satellite signals, due to
the motion of the GNSS satellites, and therefore, the actual
frequency of the received satellite signals can be known. The
actual frequency can be correlated to the frequency of the XO, and
correspondingly the variation in the frequency of the XO from an
expected nominal XO frequency can be calculated and associated with
the temperature at which the above operation is performed. In some
cases, if the altitude of the device is known, then satellite
signals from three satellite sources are sufficient to obtain the
fix, and therefore for estimating frequency and
temperature-calibration of the XO. Similarly, knowing an
approximate location of the device can also bring down the minimum
number of satellites required for temperature-calibration. An
approximate location may be obtained through various means. In one
example, relying on terrestrial sources, a cell sector center for a
serving cell can be used to obtain an approximate location. If
Ephemeris and Almanac are known, they may be used, in conjunction
with the location of the mobile device, to determine the Doppler
shift for at least one satellite signal and, consequently, the
actual frequency of the received signal may be determined to
estimate the frequency of the XO. Thus, the minimum number of
signal sources may vary for different embodiments, but once the
device has searched for, and locked on to the minimum number of
signal sources based on particular situations and criteria,
wireless signal(s) can be received from these signal sources, and
frequency estimates for the XO can be derived from the received
wireless signals.
[0029] In some embodiments temperature-calibration of the XO can be
based on wireless signals received from at most one signal source.
These embodiments may pertain to situations wherein a minimum
plurality of satellite sources (e.g., three or four, depending on
the scenarios described previously) required for a GNSS fix and/or
terrestrial sources which can provide a GNSS fix are unavailable
and/or situations wherein power levels of GNSS signals is low,
requiring a longer, more time consuming search. As used herein, the
term "unavailable," as it pertains to signal sources, refers to
lack of availability of signals from the signal source at the
device comprising the XO. For example, a signal source may be
unavailable with respect to the device when it is not in the line
of sight or plain view of the device, when signals from the signal
source are prevented from reaching the device due to any reason,
such as distance or obstructions, or when the device cannot easily
receive signals from the signal source for any reason, including
lack of capability for reception (e.g., the device may not be
configured for WWAN and thus not be capable of receiving signals
from a calibrated terrestrial source such as WWAN), or where the
amount of time or power required to receive the signals is
prohibitively high. Accordingly, for temperature-calibrating the XO
according to these embodiments, the device may first search for
signal sources and determine whether a minimum number of satellite
sources and/or calibrated terrestrial sources for obtaining a GNSS
fix are available (keeping in mind that in some aspects a specific
search may not be required, as the device can be configured to rely
on information, obtained for example, from a user, or other
configuration information, in order to determine or assume that a
minimum number of satellite sources and/or calibrated terrestrial
sources for obtaining a GNSS fix are unavailable). Thereafter, the
device may nevertheless be configured to temperature-calibrate the
XO based on assistance from a single or at most one signal source
when the at most one signal source has a "known Doppler." As used
herein, the term "known Doppler" can refer to a signal source whose
Doppler is known or can be precisely determined. In one example,
the known Doppler can be zero. A zero Doppler source is also known
as a Doppler-true or Doppler-accurate source. Doppler-true sources
can be geo-stationary, which guarantees that their Doppler is 0 Hz
at all times. Doppler-true sources can also include stationary
terrestrial sources. A satellite based augmentation system (SBAS)
is an example of a Doppler-true source which can be utilized in
this embodiment. Another example of a known Doppler is a non-zero
Doppler source, such as a GNSS satellite vehicle whose position and
velocity are known (e.g., based on Satellite Ephemeris and/or
Almanac), which may be utilized in these embodiments when at least
a coarse location of the device is known, and further at least a
coarse time at the device is known. When feasible (e.g., when a
SBAS vehicle or other stationary signal source of known frequency
is available), the temperature-calibration of the XO based on a
single known Doppler source can beneficially reduce search time and
computation time associated with the XO temperature-calibration in
these embodiments. In the case where the single known Doppler
signal source is a satellite source (e.g., SBAS vehicle), the
device may obtain a position estimate for the device from a
positioning determining entity (PDE) (e.g. as known in the art for
CDMA systems), or more generally, a positioning server or location
server, which covers other air interfaces. The position estimate or
location of the device can also be obtained from an approximate
location derived from terrestrial signals (e.g. using cell sector
center of the serving cell or trilaterating terrestrial signals,
wherein looking up the cell sector location can be done using a
positioning server or on device 100 if it has a base station
Almanac), location derived from a positioning server or a
positioning determining entity (PDE) or a location server Once the
location is known, using Ephemeris and time, the received wireless
signal can be used to determine an effective frequency of the
satellite constellation. This effective frequency derived from the
received wireless signal can be compared with the frequency of the
local oscillator, in order to obtain the frequency estimate for the
XO. In cases where the known Doppler signal source is not a
satellite source (e.g., if the signal source is a calibrated
terrestrial source such as WWAN or other fixed frequency source of
known frequency), and if the device is stationary, then the known
fixed frequency is treated as the effective frequency which is
compared with the frequency of the local oscillator in order to
obtain the frequency estimate for the XO.
[0030] A detailed description of the configuration and operation of
devices according to the above exemplary embodiments will now be
provided with reference to the figures.
[0031] With reference to FIG. 1, the formulation of the
frequency-temperature (FT) relationship (also known as, FT curve or
FT model) for the XO will be discussed in detail. More
particularly, the formulation of the FT model pertains to field
calibration of the XO, e.g., during mobile device operation related
to GNSS-based positioning applications of an exemplary mobile
device. The FT model can be expressed as a polynomial equation or
function, wherein frequency is expressed as an n.sup.th degree
polynomial function of temperature. At least some of the parameters
or coefficients of this polynomial equation are unknown quantities
for an XO and accordingly, an objective of the XO
temperature-calibration can comprise determining or refining the
coefficients of the FT model for the XO. In general, the number of
coefficients will vary proportionally with the value of "n" or the
degree of the polynomial. However, in exemplary embodiments,
certain constraints can be imposed to make reasonable assumptions
regarding the value of one or more coefficients, such that the
number of coefficients that are unknown, and need to be determined,
may be reduced. The unknown coefficients are determined using the
aforementioned samples of frequency estimates of the XO at
associated temperatures. The number of samples required for the
temperature-calibration of the XO will vary based on the number of
coefficients that need to be determined. Accordingly, by reducing
the number of unknown coefficients, the temperature-calibration of
the XO can be performed with fewer samples, which correspondingly
leads to advantages in terms of increased speed and efficiency of
the temperature-calibration process.
[0032] In FIG. 1, FT curves FT1 and FT2 are based on a third degree
(i.e., n=3) polynomial equation for exemplary XOs. Each of these FT
curves can be represented by the third order polynomial equation:
f(T)=c.sub.3(T-T.sub.0).sup.3+c.sub.2(T-T.sub.0).sup.2+c.sub.1(T-T.sub.0)-
.sup.1+c.sub.0, where f(T) is the function of frequency f of the XO
with variation in temperature T, T.sub.0 is a constant, typically,
room temperature (e.g., 30.degree. C.), and c.sub.0-c.sub.3 are the
parameters or coefficients to be determined to
temperature-calibrate the XO. The elements c.sub.0-c.sub.3 are the
parameters of the polynomial equation, which are to be determined
in an exemplary process. Once the coefficients are determined with
a high degree of precision, FT curves such as FT1/FT2 can be
plotted, and frequency of the corresponding XO can be read or
determined from the FT curve for any given temperature. While the
discussion herein will pertain to third degree polynomial equations
for exemplary FT curves, it will be understood that the embodiments
may be easily extended to polynomial equations of any degree (e.g.,
n=4, 5, etc.), or for that matter, any mathematical expression or
function of any order or degree for representing the FT model for
exemplary XO temperature-calibration, without departing from the
scope of this disclosure.
[0033] In some embodiments, the device comprising the XO can be
configured to receive wireless signals from one or more satellite
sources and additionally, in some cases, from one or more
calibrated terrestrial sources. Based on these received wireless
signals, a GNSS location can be obtained, if needed, and a
frequency error in the XO can be computed, based upon at least one
frequency reference. Using the nominal/expected frequency of
operation of the XO and the computed frequency error in the XO, a
frequency estimate, say a first frequency estimate, of the XO can
be obtained. A reading of the temperature, say a first temperature,
of the device is also obtained at the time when the frequency
estimate is obtained, and a first sample comprising the first
frequency estimate and the first temperature is formed. This
process is repeated at a second, different temperature to obtain
second sample comprising a second frequency estimate and a second
temperature. In some cases, as low as two samples may be
sufficient, based on certain constraints and assumptions pertaining
to the coefficients c.sub.0-c.sub.3. In other cases, the process is
repeated at other different temperatures to determine additional
corresponding frequency estimates to refine the coefficient
estimates.
[0034] In an illustrative example, the coefficients may be
determined based on certain specifications related to the XO, which
may be available, for example from a vendor or manufacturer of the
XO. The coefficients may also be determined based on knowledge of
operating conditions and expected range of variation in temperature
of the device. It will be understood that the below discussion
pertaining to determination of coefficients for the FT model of an
exemplary XO are only illustrative, and they may be based on
specific implementations and operating conditions. Accordingly, in
one implementation, the coefficient c.sub.0 may be a constant, and
can be assumed to be of value zero (or precalibrated at a nominal
temperature during manufacturing with a non-zero constant or known
value), which reduces the number of unknown coefficients to three,
i.e., c.sub.1-c.sub.3. This constant c.sub.0 may be referred to as
a DC offset in the art. In yet another optional implementation, the
temperature variation of T from T.sub.0 may be known in advance or
may be constrained to be very small, and therefore, the
contribution of the third order term, i.e.,
c.sub.3(T-T.sub.0).sup.3, to the polynomial function of f(T), may
be negligible, and therefore c.sub.3 may be assumed to be zero.
This could reduce the number of unknown coefficients to two, i.e.,
c.sub.1 and c.sub.2. Obtaining two sample points comprising first
and second frequency estimates at corresponding first and second
temperatures would then be sufficient to determine c.sub.1 and
c.sub.2 and thus temperature-calibrate the XO.
[0035] Some specifications for the XO may also define the maximum
range of acceptable error in the coefficients for the XO, which may
determine the number of samples needed to obtain the coefficients
to the specified degree of error. For example, acceptable error in
c.sub.0 may be specified to fall within the range of .+-.2 parts
per million (ppm), and therefore setting c.sub.0 to "0," as
described above would satisfy this requirement. The contribution of
the term c.sub.1(T-T.sub.0/to the polynomial function f(T) may be
significant in many cases, and therefore c.sub.1 may need to be
determined to a high degree of accuracy, or in other words, finely
temperature-calibrated in the field. Some specifications may limit
the error in c.sub.1 to fall in the range of, -0.10 ppm/.degree. C.
to -0.40 ppm/.degree. C., for example. Some embodiments herein can
achieve c.sub.1 to within -0.10 ppm/.degree. C. based on exemplary
techniques to satisfy such stringent requirements. As previously
discussed, a higher tolerance may be acceptable for error in the
coefficient c.sub.3 and sometimes, factory precalibration of
c.sub.3 may be sufficient. Some specifications may require error in
c.sub.3 to fall within a relatively relaxed range of 8.5e-5
ppm/.degree. C. to 11.5e-5 ppm/t, and therefore, using factory
precalibration values or even assuming c.sub.3 to be zero may
satisfy the error requirements in the specification.
[0036] In the illustrations of FIG. 1, for FT curve FT1, the
coefficients are, c.sub.1=-0.1 and c.sub.3=11.5e-5, and for FT
curve FT2, c.sub.1=-0.4 and c.sub.3=8.5e-5. In these examples, it
can be seen that the total range of XO frequency, with an
uncertainty in c.sub.0 contained within an upper limit of 2
ppm/.degree. C., can be up to .+-.20 ppm for a temperature
variation between 30.degree. C. and 90.degree. C. Viewing FT1 and
FT2, it can be observed that as this temperature range is widened,
for example, between -40.degree. C. and 100.degree. C., the
uncertainty in XO frequency can be as high as .+-.34 ppm.
Accordingly, some embodiments are configured to
temperature-calibrate the XO by choosing the constraints and
assumptions based on operating conditions such as the temperature
range pertaining to the device operation.
[0037] With reference now to FIG. 2A, a simplified schematic of an
exemplary device 100 configured for XO field calibration according
to exemplary embodiments is illustrated. It will be noted that
device 100 may be a mobile device or handheld device and may
further comprise one or more components as known to one skilled in
the art, but which are not illustrated in FIG. 2A for the sake of
clarity (although FIGS. 2B and 4 provide other exemplary
embodiments directed to devices similar to device 100, which
illustrate certain other components which may be included in the
exemplary devices). Device 100 may comprise receiver 102, which may
be configured to receive wireless signals from various sources such
as, one or more signal sources 110a-n. In one non-limiting example,
one or more of signal sources 110a-n may be satellite or GNSS
sources capable of providing GNSS fixes. Additionally and
optionally, one or more signal sources 110a-n may also be
calibrated terrestrial sources, such as WWAN or CDMA, which can
augment the temperature-calibration process, although it will be
recalled that such features pertaining to calibrated terrestrial
sources are purely optional and not required in the various
embodiments. As described further in later sections, one of the
signal sources 110a-n can also be a stationary satellite signal
source such as an SBAS satellite, wherein temperature-calibration
can be performed using a single SBAS satellite. Receiver 102 may be
driven by clock 104 which can be sourced from XO 106. Temperature
sensor 114 may be included in device 100 to sense temperature of XO
106 and provide XO manager 108 with operating temperature
associated with XO 106. Temperature sensor 114 may be a discrete
block on device 100 as illustrated, or in some embodiments, a
thermistor, such as temperature sensor 114, may be integrated into
one of the other blocks. Moreover, while temperature sensor 114 may
be configured to measure temperature directly at XO 106 in some
embodiments, it is also possible to configure a similar
device/sensor to representatively measure or sense the required
temperature on a printed circuit (PC) board or at a pin or lead
external to an integrated circuit on which device 100 is
integrated. XO manager 108 may be configured to obtain frequency
estimates for XO 106 based on signals received by receiver 102. XO
manager 108 may be further configured to associate operating
temperatures provided by temperature sensor 114, and perform
operations related to temperature-calibration of XO 106 according
to the above-described techniques. While XO manager 108 is
designated as a separate block in this illustration, the
functionality and logic associated with XO manager 108 may be
integrated in any processor, such as a digital signal processor or
a general purpose processor, in device 100.
[0038] In FIG. 2A, one local oscillator, local oscillator 112, is
illustrated as included in receiver 102. However, it will be
understood that in the various embodiments described herein, one or
more other local oscillators may be present in one or more other
blocks. For example (as will be further described with reference to
FIG. 4), an exemplary mobile device may comprise one or more
receivers or transceivers configured for reception of satellite
signals and one or more receivers or transceivers configured for
other wireless signals such as WWAN signals. Accordingly, in some
embodiments, each of those receivers and/or transceivers may have
one or more local oscillators. However, exemplary techniques
described below with reference generally to local oscillator 112,
can be easily extended to any other local oscillator which may be
present in the device, based on the source of the particular
wireless signal under consideration.
[0039] In one exemplary embodiment, receiver 102, along with one or
more components not specifically illustrated in device 100, may
search for a minimum number of wireless signal sources 110a-n to
obtain a GNSS fix (keeping in mind, that in some embodiments, for
example, device 400 of FIG. 4, separate receivers/transceivers and
accompanying local oscillators may be configured for different
types of wireless signals, such as satellite signals and WWAN
signals). As previously explained, this minimum number of wireless
signal sources 110a-n may be as low as one (e.g., when the Doppler
of the signal source is known, such as in the case of an SBAS
satellite), or may be three or four, depending on whether
additional information, such as Ephemeris, Almanac, position of
device 100, time at device 100, etc. are known. If the required
minimum number of signal sources 110a-n is found, then device 100
locks on to these signal sources 110a-n to receive wireless signals
from them through receiver 102. A position fix or GNSS fix is
obtained using these received wireless signals, for example, at XO
manager 108. The GNSS fix may provide information such as the
location of device 100 and a frequency error of local oscillator
112. Using the GNSS fix, a frequency error of XO 106 can be
calculated, using which, a first frequency of the XO can be
estimated.
[0040] In one example, a first set of wireless signals comprising
at least, three wireless signals, say, a first, second, and a third
wireless signal, may be received by receiver 102, at an associated
first temperature. The first, second, and third wireless signals
may be from a first, second, and a third satellite respectively,
such that a position fix or GNSS fix for device 100 may be obtained
from at least the three wireless signals (e.g., by a process of
trilateration). It will be recalled that wireless signals from
three satellites may be sufficient to calculate location of the
device comprising the XO if altitude of the device is known, but if
altitude is unknown, then wireless signals from at least four
satellites may be needed. Determining the location can also be
based on additional information or GNSS assistance which may be
derived from signal sources, such as calibrated terrestrial sources
(e.g., WWAN, CDMA, etc.). Once location is determined based on the
wireless signals, using Ephemeris and time, the frequency of the
wireless signals can be determined. Using a received wireless
signal(s), the Doppler(s) of the wireless signals may be
determined, allowing the frequency of the received wireless signal
to be determined, which then allows deriving an effective frequency
of zero Doppler (from a stationary source) or known Doppler (from a
moving source or source moving relative to the receiver) from the
wireless signal(s).
[0041] The Doppler of the wireless signals received from a
satellite source can be determined through the use of Ephemeris or
Almanac information and a known location, such as the location
determined through a GNSS fix or a terrestrial estimate (such as
the location of a visible terrestrial transceiver). Ephemeris
information, when used in conjunction with a known location of the
device can be used to predict the location, velocity, and heading
of a GNSS satellite relative to the device and thus calculate the
Doppler shift. Once the Doppler shift is known, the impact of the
Doppler shift can be removed from the received signal frequency to
determine the effective frequency of the wireless signal. If
multiple wireless signals are used to determine a reference
frequency at a given temperature (such as the nominal GNSS
frequency, the effective frequency of the satellite constellation,
or the frequency offset at that temperature), multiple frequency
estimates derived from the multiple wireless signals may be
combined into a single frequency estimate which can be utilized as
the derived effective frequency. If Ephemeris and location are
known, wireless signals received from a single satellite can be
used to derive the effective frequency of the satellite signal.
Note that the satellites in a given GNSS constellation generally
broadcast at the same effective frequencies. Similarly, a single
terrestrial wireless signal of known frequency can be used to
derive the effective frequency of the terrestrial signal source.
Effective frequency can also be derived from multiple wireless
signals when Ephemeris for each GNSS satellite and location of the
mobile device are known. The effective frequencies, as derived from
the multiple wireless signals, can be combined in several ways to
obtain a "derived effective frequency," which can be based on the
effective frequency derived from one or more of the multiple
wireless signals. For example, a first effective frequency can be
derived from a first wireless signal, a second effective frequency
from a second wireless signal, and a third effective frequency from
a third wireless signal, wherein the derived effective frequency
can be based on one or more of the first, second, and third
effective frequencies. However, it will be kept in mind that while
sometimes it may be possible to derive an effective frequency (e.g.
first, second, and third effective frequencies) from each of the
received wireless signals, in some cases the effective frequency
may be obtained from fewer than all of the received wireless
signals (e.g., only one wireless signal in some cases). In some
embodiments, multiple satellite signals may be required to
determine an initial location. In other embodiments, location can
be determined via a previously saved location, or via terrestrial
wireless signals, such as by utilizing a cell sector center derived
either locally on the device or on a location server by looking up
the serving cell in a base station Almanac, or by trilaterating a
position based on terrestrial signals. In any case, in embodiments
utilizing GNSS signals, once a location is determined, not all of
the wireless signals may be required for the purposes of estimating
the frequency of the XO at a given temperature. In embodiments
utilizing terrestrial signals, only one wireless signal is
sufficient for estimating the frequency of the XO at a given
temperature. For example, in one embodiment, once the location is
determined, the effective frequency (e.g. first effective
frequency) may be derived from the strongest signal and may be used
as the derived effective frequency based on all of the received
wireless signals. In another embodiment, frequencies (or effective
frequencies when Ephemeris and location are known) may be derived
from multiple wireless signals (e.g., first, second, and third
effective frequencies), which may be combined as stated above to
obtain an overall effective frequency, or derived effective
frequency, of the multiple signals. For GNSS signals, the derived
effective frequency is an estimate of the frequency of the GNSS
satellite signals, which is typically shared among the satellites
in the GNSS constellation. The combination can be based on schemes
such as a weighted average obtained by weighting and averaging the
signal frequencies such that the effective frequency derived from
the strongest or several of the strongest of the received signals
is/are weighted more heavily and the effective frequency derived
from the weaker signals are afforded less weight. In another
embodiment, the effective frequency may be derived from the
frequency of the strongest of the received signals while also
utilizing the frequency from each of the other received signals,
which are weaker. Other combination mechanisms for obtaining the
derived effective frequency of the multiple signals can include a
mean, a median, a geometric mean, a least squares fit, or other
pre-specified mathematical fit of the effective frequencies derived
from the multiple wireless signals, such as, the first, second, and
third effective frequencies. By using Ephemeris to determine
predicted Doppler offset for each of the one or more signals
(wherein multiple signals may be combined to obtain a derived
effective frequency), the respective Doppler shift of the signals
can be corrected for to obtain each effective frequency prior to
calculating the derived effective frequency. Once the Doppler of
the received wireless signals is accounted for, the derived
effective frequency can be obtained, which may be used to estimate
a frequency error, say first frequency error, of XO 106 (a further
detailed process for estimating the frequency error from the
effective frequency of known or zero Doppler derived from a
received wireless signal will be provided in the following
sections).
[0042] XO 106 may be configured for a nominal or reference
frequency, such as 19.2 MHz. A first frequency error can be an
offset of the effective frequency from the reference frequency.
Therefore, using the first frequency error and the reference
frequency, a first frequency estimate of XO 106 can be obtained.
Temperature sensor 114 can supply the first temperature at which
the first frequency estimate is obtained in this manner from the
three wireless signals. XO manager 108 can then form a first sample
comprising the first frequency estimate and the first temperature.
The process of temperature-calibrating the XO can be started with
this first sample comprising the first frequency and the first
temperature.
[0043] In some examples, the process of temperature-calibration can
be completed with the first sample, (e.g., in a case where the
degree n of the polynomial equation is low enough that one sample
point can sufficiently complete the temperature-calibration
process, or in a case where the factory precalibration or
assumptions made for the coefficients make it possible to complete
the temperature-calibration with just one sample point). However,
if for example, the temperature-calibration is not completed with
the first sample, (e.g., not all of the coefficients of the
polynomial equation have been determined with required or desired
precision), the process can comprise further
temperature-calibrating the XO. As described herein, "further
temperature-calibrating" comprises proceeding with or refining the
temperature-calibration (i.e., determining the coefficients of the
FT model) with additional sample points. Additional sample points
may be obtained, for example, from a second frequency obtained
using a second set of at least one wireless signal, third frequency
obtained using a third set of at least one wireless signal, etc.,
at respective second temperature, third temperature, etc. The
number of samples may be based on the number of unknown
coefficients which need to be determined for the FT model
pertaining to XO 106. If the FT model is a third order polynomial
and c.sub.0 is a DC value of zero as previously explained, then
three such samples may be needed to obtain the remaining unknown
coefficients c.sub.1-c.sub.3 (keeping in mind that c.sub.3 may be
constrained to be zero in some cases, and thereby reducing the
number of samples to two).
[0044] In one embodiment, the temperature-calibration of the XO can
be performed using a single signal source of known Doppler, for
example, in situations where the minimum number of signal sources
110a-n, as above, may not be available, or where device 100 is
configured to attempt temperature-calibration with a single source
of known Doppler first, if such a source is available. For example,
when receiver 102, along with one or more components not
specifically illustrated in device 100, searches for a minimum
number of wireless signals from signal sources 110a-n to obtain a
GNSS fix, it may be determined that this minimum number of signal
sources is unavailable (e.g., first, second, and third wireless
signals from first, second, and third satellites, as above, may not
be available) and device 100 may search for a signal source with
known Doppler, and if one is available, then, in this embodiment,
device 100 may be configured to temperature-calibrate XO 106 based
on a single signal source of known Doppler. In other embodiments,
the mobile device may be configured to attempt
temperature-calibration with a single signal source of known
Doppler first, and if that single signal source of known Doppler is
not available, then attempt temperature-calibration with multiple
sources. If receiver 102 receives a first set of wireless signals
which comprises a first wireless signal from a first satellite or
signal source of known Doppler, the temperature-calibration may be
performed based on the first wireless signal from that signal
source of known Doppler. In other embodiments, if an approximate
location of the device is known, the device may default to using a
single GNSS signal source of known frequency in conjunction with
satellite Ephemeris information and may skip a search for
additional GNSS signal sources. In another embodiment, a
terrestrial source of known frequency is sufficient to
temperature-calibrate the XO and a location is not required. As
previously explained, a known frequency signal source may be either
a Doppler-true source such as a geostationary source (e.g., SBAS or
terrestrial transmitter), or a non-zero Doppler source such as a
GNSS or other satellite vehicle of known position (e.g., a position
that may be determined utilizing Ephemeris and/or extended Almanac
or other Ephemeris-related source of information), when at least a
coarse position and time at device 100 is known. Accordingly, the
term "known Doppler" as used herein, can indicate a constant known
value such as zero or a determinable quantity.
[0045] The process of frequency estimation of the XO will now be
provided, with reference to a case where the Doppler of the
received wireless signal is a constant known value or determinable
quantity. It will be recalled that once the wireless signal of
known Doppler (including wireless signals with zero Doppler) is
received, the frequency estimation process herein is similar in
many aspects to the case where the effective frequency is
determined from frequencies derived from a minimum number (e.g.,
three) of wireless signals, such as the first, second, and third
wireless signals from respective first, second, and third
satellites (wherein these satellites are utilized to calculate a
location of the device and wherein the frequency estimates received
from each of these satellites may be combined, or selected between,
in order to optimize the frequency estimate). With continuing
reference to FIG. 2A, receiver 102 may be configured to search for
and receive signals from, say, signal source 110a which is of known
Doppler. Local oscillator 112 may be any generic local oscillator
configured to oscillate at a nominal frequency such as a GPS L1
center frequency or a GPS L1 carrier frequency. Similarly, for a
terrestrial wireless signal from a terrestrial source or calibrated
terrestrial source, local oscillator 112 may be configured to
oscillate at the expected nominal frequency of the terrestrial
source, such as the standard frequency of the terrestrial wireless
signal. Local oscillator 112 may be sourced from XO 106, such that
a variation of frequency in XO 106 is proportionally reflected as a
frequency variation in local oscillator 112. In one numerical
example, local oscillator 112 may be configured for a nominal
frequency of 1575.42 MHz, which will be recognized by the skilled
person as a GPS L1 center or carrier frequency, or other known
frequency. Further, as previously mentioned, XO 106 may be
configured for a typical or reference frequency of 19.2 MHz.
[0046] In one example, signal source 110a is a Doppler-true source
(e.g., a geo-stationary source, such as a SBAS satellite vehicle
(SV), wherein the Doppler of received signals at receiver 102 from
the Doppler-true source is zero). In an illustrative example,
frequency variation of XO 106 is initially assumed to be an
unknown, say ".delta.f" parts per million (ppm). Accordingly, the
frequency variation ".delta.F" in ppm of local oscillator 112,
which is sourced from XO 106 (i.e., is a multiple of the frequency
of XO 106) will also be equal to .delta.f ppm. Thus, frequency
variation of local oscillator 112 can be first calculated, based on
signals obtained from the Doppler-true signal source 110a, in order
to determine the value of .delta.f. Once the frequency variation
.delta.f of XO 106 is known, the frequency of XO 106 can be
estimated based on frequency variation .delta.f and the expected
reference frequency of XO 106. In this numerical example, since
local oscillator 112 is configured to oscillate at the expected
nominal frequency of the signal source, e.g., 1575.42 MHz, which
corresponds to that of the Doppler-true signal (because there is
zero Doppler or variation from the nominal frequency), a comparison
of the frequency of the received signal at receiver 102 with the
frequency of local oscillator 112 can reveal the frequency
uncertainty of local oscillator 112. This is because the
Doppler-true signal from signal source 110 is assumed to not have
any frequency uncertainty of its own, and therefore, the frequency
of the Doppler-true signal can be predicted as zero in the
calculations pertaining to XO temperature-calibration. A band pass
filter, as is known in the art (not specifically illustrated, but
may be present in one of the illustrated blocks, such as, within XO
manager 108), can be used to reveal the difference, ".DELTA.F"
between the measured nominal frequency of local oscillator 112 and
the predicted true Doppler (i.e., zero) of the received signal from
signal source 110a. In other words, .DELTA.F provides the frequency
uncertainty or the amount the frequency of local oscillator 112
deviates from the precise nominal frequency of the received signal
at 1575.42 MHz. This value of .DELTA.F can then be normalized by
dividing .DELTA.F with the nominal frequency 1575.42 MHz in order
to obtain the frequency variation of local oscillator 112 as
.delta.F ppm. As previously discussed, the frequency variation
.delta.f of XO 106 and therefore, the absolute variation .DELTA.f
of XO 106 from the expected reference frequency of 19.2 MHz can now
be calculated. Accordingly, the frequency of XO 106 can be
estimated with a high degree of precision, as, say, the first
frequency estimate, and associated with the first temperature,
which will be supplied by temperature sensor 114. In this manner, a
first sample comprising the first frequency estimate and the first
temperature can be formed, and the process of
temperature-calibration or determination of coefficients of the FT
model for XO 106 can be started with the first sample point. The
above process can be repeated at different operating temperatures
to obtain further such samples comprising frequency estimates and
associated temperatures (e.g., a second frequency estimate at a
second temperature, and a third frequency estimate at a third
temperature, etc.) to further temperature-calibrate XO 106 or to
determine the coefficients of the FT model for XO 106 with higher
precision.
[0047] In another example, one of the signal sources, say signal
source 110n may be determined to be a known Doppler source, whose
Doppler is a non-zero value. The Doppler of such a source can be
determined or predicted or "known" according to when its position
is known. Position of signal source 110n can be obtained in several
ways which have been previously described. For example, position of
a GNSS signal source can be determined based on satellite
Ephemeris, assuming that a coarse location and GNSS time is
available. The position or location of device 100 may be available
from a prior location fix or it may need to be determined, for
example, through trilateration of GNSS or terrestrial signals or
through cell sector center of the serving cell. GNSS time may be
available from a terrestrial network source or may be determined
directly from the GNSS satellite signals. With regard to location
of device 100, while in this embodiment, device 100 is preferably
stationary for purposes of temperature-calibration using signals
from a signal source 110n of known position, it is possible to
extend exemplary techniques to cases where device 100 is in motion,
but position, as well as, relative Doppler of device 100 is
precisely known. For example, a GNSS fix can be utilized to
determine velocity and heading of device 100 which may be used to
determine a resultant or combined Doppler due to motion of device
100 and of signal source 110n. With regard to determining a local
time at device 100, a clock on device 100, such as clock 104 may
need to have at least a coarse correlation to GNSS time, and/or in
some cases, uncertainty in the local clock must be very low.
Moreover, in some cases, temperature-calibration of XO 106 may be
improved by imposing threshold requirements for quality of the
wireless signals received from signal source 110n. For example,
embodiments may require the received signals from the GNSS
satellite vehicle (SV) to satisfy a pre-specified signal to noise
ratio (SNR) and/or pass pre-specified error/parity checks, in order
to utilize the received wireless signals for XO
temperature-calibration. Imposing such requirements or standards on
the strength and accuracy of the received signals can improve
efficiency and accuracy in the temperature-calibration process.
[0048] Accordingly, when the position of signal source 110n is
known (and Ephemeris, in the case of satellite sources), the
position of device 100 is known, a coarse time at device 100 is
known, and signals received from signal source 110n meet
pre-specified quality standards, the Doppler of signal source 110
can be known (i.e., predicted or determined to high degree of
accuracy). Using the known non-zero Doppler value, the process of
temperature-calibration of XO 106 is substantially similar to the
process of temperature-calibration of XO 106 outlined above for the
case of a Doppler-true source, with only minor variations, notably,
to replace the previously used zero Doppler value with the known
non-zero Doppler value (say, .DELTA.S) in the calculations. The
remaining detailed aspects of the calculations pertaining to
temperature-calibration of XO 106 will not be repeated herein, for
the sake of brevity.
[0049] In some cases, as an alternative to using GNSS Ephemeris,
extended terrestrial receiver assistance (EXTRA) assistance (or
other time-extended ephemeris information) may be used instead of
the most recent GNSS Ephemeris information. For example, device 100
is in motion, EXTRA assistance, such as extended Almanac
corrections, may be available, wherein, once receiver 102 becomes
capable of tracking a signal source 110a-n comprising a GNSS SV, a
difference in measured speed and expected speed of device 100, can
be obtained. This difference can be translated to a bias in
frequency of XO 106. For example, if the received signal from the
GNSS SV has strong carrier to noise ratio (C/N.sub.0), and the
speed and heading (or vector speed) of device 100 can be measured
with high confidence, the received GNSS signal can be used for
obtaining an estimated frequency uncertainty (e.g., .DELTA.F) of
local oscillator 112. More specifically, the frequency estimate may
be based on a difference between a measured Doppler of the received
signal from the GNSS SV and a predicted Doppler based on the vector
speed or speed and heading of device 100 (e.g., a prediction based
on an expected GPS L1 center frequency and the speed).
[0050] Accordingly, it is seen that exemplary embodiments can
accomplish temperature-calibration of XO 106 using only one signal
source with known Doppler (of zero or non-zero value). For example,
some embodiments may perform XO temperature-calibration with a
single signal source, for example, in situations where a required
minimum number of satellite sources or calibrated terrestrial
sources for obtaining a GNSS fix are unavailable. Moreover, some
embodiments may optionally determine (e.g., based on a signal
search) whether a calibrated terrestrial source or a plurality of
GNSS satellite signals for XO temperature-calibration are
unavailable, prior to selecting and performing exemplary
above-described operations pertaining to XO temperature-calibration
using only one signal source with known Doppler.
[0051] Referring now to FIG. 2B, another exemplary device 200, for
XO temperature-calibration using received wireless signals is
illustrated. More particularly, device 200 is illustrated with
components and logic elements which may be used for
temperature-calibration of the XO using received GNSS signals
(while it will be understood that this depiction is only exemplary,
and does not limit alternative implementations which may rely on
one or more of the other types of wireless signals which have been
described herein for use in XO temperature-calibration). As seen,
device 200 is shown with several additional components or blocks,
in comparison to the depiction of device 100. The function of these
additional components will be described in an exemplary
configuration of device 200. In device 200, GNSS receiver 202 may
be configured to receive GNSS signal 203, for example, from a GNSS
satellite vehicle (e.g., signal sources 110a-n of FIG. 2A). GNSS
receiver 202 may include a local GNSS clock generator 214 which may
comprise a local oscillator sourced from an XO in device 200 (the
local oscillator and XO are not explicitly shown in this
depiction). The received GNSS signal 203 may pass through GNSS
baseband processor (BP) & GPS accumulator (GACC) 204 and GNSS
correlation processor (CP) & GACC 206 which may be configured
to accumulate energy from searching for GNSS satellite signals, for
a selected time period corresponding to a measurement duration.
Measurement engine (ME) 208 can comprise measurement controller
(MC) 212, channel controller 216 and adder 218. Overall, ME 208 can
be configured to compile a report of all GNSS SV measurements 209
and transfer it to position engine (PE) 210. PE 210 may use
measurements 209 to compute location information for device 200. If
PE 210 is successful in calculating the location information, it
may further provide clock frequency bias 211 to measurement
controller (MC) 212, which may be applicable at a point in time
corresponding to a middle of the measurement duration. Clock
frequency bias 211 may relate to a variation in clock frequency or
representatively, a variation in frequency of the local oscillator
from its expected frequency (e.g., .DELTA.F from the above
embodiment related to device 100). XO frequency error 219 (e.g.,
.DELTA.f from above), can be obtained from ME 208 using MC 212 and
adder 218. XO frequency at a given temperature can be calculated by
ME 208 based on XO frequency error 219 and an XO frequency estimate
provided by XO frequency estimation block 220. Also note that a
communications transceiver, such as transceiver 440, for example,
may similarly receive terrestrial wireless signals for XO
temperature-calibration, as is discussed relative to FIG. 4.
[0052] In more detail, GNSS receiver 202 may be configured to use
XO frequency error 219 to apply any correction as needed to front
end rotators configured in GNSS BP & GACC 204. XO frequency
error 219 is passed on to XO manager 228. XO manager 228 may
comprise XO field calibration block 230 configured to solve the FT
polynomial equation pertaining to the XO using received values of
XO frequency error 219 and associating them with operating
temperature received from XO & power management integrated
circuit (PMIC) temperature block 234. In other embodiments, the
thermistor or other temperature sensor 114 may be discrete or
integrated into other integrated circuits. As a result of solving
the FT polynomial, coefficients (e.g., c.sub.0-c.sub.3 as discussed
above) can be obtained and stored in the block, XO coefficients
232. It will be understood that thermistors used in the XO &
PMIC temperature block 234 can pertain to one or more XOs and can
comprise any other thermistor that impact error or temperature of
the XOs. Additionally, XO & PMIC temperature block 234 may be
further configured to provide temperature information to both XO
thermal frequency estimation block 224 (located in XO frequency
estimation block 220). In some embodiments, XO
temperature-calibration can optionally and additionally integrate
assistance from calibrated terrestrial sources, although it will be
understood that such optional assistance from calibrated
terrestrial sources is not required, and exemplary embodiments are
configured to perform XO temperature-calibration even in situations
where such assistance is unavailable, unviable, and/or undesired.
Accordingly, total frequency estimation block 222 may take into
account, an input from an optional WWAN frequency assistance block
226 in some embodiments. Another input may be derived from XO
thermal frequency estimation block 224.
[0053] In this manner, exemplary embodiments may implement
functionality of the various above-described blocks of device 200
in order to temperature-calibrate the XO using GNSS signal 203. In
some embodiments, device 200, for example, with the use of ME 208,
may be selective on the received signals which are used for XO
temperature-calibration. For example, selection criteria may be
applied to ensure quality of received GNSS signal 203 prior to
basing frequency estimation for XO temperature-calibration based on
the received GNSS signal 203. One such selection criterion can
involve assigning a pre-specified maximum tolerable error in clock
frequency based on the received GNSS signal 203. For example, if
the error in clock frequency based on a received GNSS signal 203 is
above a maximum tolerable error, such as, 3 ms, the received GNSS
signal 203 may not be used for assistance to derive frequency
estimates. Conditions may also be imposed on other aspects, such as
a maximum tolerable position error, for example, as derived from PE
210. In some embodiments, if a horizontal estimate of position
error (HEPE) is greater than a predetermined threshold, such as 50
m, then, XO temperature-calibration may not be performed under such
conditions. Similar other conditions or criteria may be imposed to
ensure quality of XO temperature-calibration.
[0054] It will be appreciated that embodiments include various
methods for performing the processes, functions and/or algorithms
disclosed herein. For example, as illustrated in FIG. 3A, a first
embodiment can include a method of temperature-calibrating an
uncompensated crystal oscillator ("XO," e.g., XO 106), in a mobile
device (e.g. device 100) during mobile device operation (i.e.,
field calibration), the method comprising: receiving a first set of
wireless signals comprising at least a first wireless signal of
known frequency, at a first temperature (e.g., one or more wireless
signals received by receiver 102 from signal source 110a, wherein
signal source 110a may be a satellite with known frequency, such as
the GPS L1 frequency, and further, in some cases, a satellite with
known Doppler, such as zero Doppler when the satellite is an SBAS
or geo-stationary satellite or a terrestrial source of known
frequency)--Block 302; estimating a first frequency of the XO
(e.g., by determining a frequency variation .DELTA.F of local
oscillator 112 sourced from XO 106 as a difference in frequency
between the frequency of the first wireless signal (i.e., GPS L1
frequency) and the frequency of the local oscillator F, normalizing
the frequency variation of the local oscillator based on an
expected nominal frequency of the local oscillator (e.g., GPS L1
frequency or a terrestrial wireless signal's carrier frequency),
determining a normalized frequency of the XO (.delta.f) as equal to
the normalized frequency of the local oscillator (.delta.F), and
determining the first frequency (f) based on the normalized
frequency of the XO and an expected nominal frequency of the XO
(e.g., 19.2 MHz) at the first temperature (e.g. supplied by
temperature sensor 114), based on at least the first wireless
signal--Block 304; and temperature-calibrating the XO based on the
first frequency and the first temperature (e.g., by starting the
process of formulating the FT model or polynomial equation for XO
106, for example, using logic or means in XO manager 108, using a
first sample point comprising the first frequency and the first
temperature)--Block 306. A frequency tolerance or maximum frequency
error at a given temperature can be pre-specified for the
temperature-calibration, in order to determine whether the
temperature-calibration process is completed, or in other words,
whether frequency error has been determined within the
pre-specified tolerance for that temperature.
[0055] Accordingly, if the temperature-calibration is complete at
Block 308 (i.e., if frequency error of XO 106 meets a pre-specified
tolerance), then the temperature-calibration process can end in
Block 310. However, if for example, the temperature-calibration is
not completed at Block 308 (i.e., if the frequency error of XO 106
falls outside the pre-specified tolerance), the method can comprise
further temperature-calibrating XO 106 by repeating the methods of
Blocks 302 and 304, for estimating a second frequency at a second
temperature based on, for example, a second set of wireless signals
comprising at least one wireless signal of known frequency; and
maybe continuing on to further temperature-calibrating the XO by
estimating a third frequency at a third temperature based on, for
example, a third set of wireless signals comprising at least one
wireless signal of known frequency, and so on. It will be
understood that the various temperatures, i.e., the first, second,
and third temperature above, are different from each other, in
order to achieve useful frequency-temperature samples. Moreover,
the temperature-calibration can be improved if the various
temperatures are not too close to each other, and there is a
minimum gap or separation between the temperatures. The value of
the minimum gap may depend on the particular XO and desired or
pre-specified tolerance in frequency error. For three samples of
first, second, and third frequencies at respective first, second,
and third temperatures, the temperature-calibration of the XO by
the above process can be based on at least the first, second, and
third frequency and corresponding first, second, and third
temperatures. Moreover, it will also be understood that the three
samples can be based on the first, second, and third set of
wireless signals, wherein each set of wireless signals can comprise
at least one wireless signal from one satellite (e.g., an SBAS or
Doppler-true satellite source, see FIG. 3C) or one terrestrial
source, or three or more wireless signals from three or more
satellites (see FIG. 3B). For an exemplary third order polynomial
equation with three unknown coefficients (e.g., c.sub.0=0), at
least three such samples may be needed in some cases, while keeping
in mind that fewer or greater samples may be required based on the
order or degree of the polynomial function, data available from
precalibration, assumptions made based on operating conditions or
specifications of the XO obtained from the vendor, etc. Once the
relationship (e.g., polynomial relationship, or any other
relationship, without departing from the scope of this disclosure),
between frequency and temperature has been expressed in terms of
the polynomial equation, i.e., once XO 106 has been
temperature-calibrated, a fourth frequency can be determined from
the polynomial equation at any given temperature (e.g., a fourth
temperature).
[0056] With reference now to FIG. 3B, an embodiment similar to FIG.
3A is depicted, wherein temperature-calibration of the XO is based
on wireless signals received from three or more satellites. It will
be recalled that wireless signals from three satellites may be
sufficient to calculate location of the device (e.g., device 100
comprising XO 106) if altitude of the device is known, but if
altitude is unknown, then wireless signals from at least four
satellites may be needed. Once location is determined based on the
wireless signals, using Ephemeris and time, the frequency of the
wireless signals can be determined. Sometimes it may be possible to
determine the frequency of all of the received wireless signals,
but sometimes it may only be possible to determine the frequency of
less than all of the received wireless signals (e.g., only one
wireless signal in some cases). In any case, once the location is
determined, not all of the wireless signals may be required for the
purposes of estimating the frequency of the XO at a given
temperature. For example, once the location is determined, only the
effective frequency derived from the strongest signal may be used
as the derived effective frequency of all the received wireless
signals. In other examples, effective frequencies derived from the
multiple signals may be combined, using schemes such as weighting
signals such that effective frequency derived from the one or more
of the strongest of the received signals is weighted more heavily
and the effective frequencies derived from the weaker signals are
afforded less weight. Other combination mechanisms such as a mean,
median, least squares fit, etc. may also be used. Accordingly, if
more than one such frequency (or effective frequency, when
Ephemeris and location are known) is obtained, the multiple
frequencies (or effective frequencies) may be combined by any
suitable manner. By using Ephemeris to determine predicted Doppler
offset for each of the multiple signals being combined, the
respective Doppler shift can be offset from the respective
effective frequencies or from the derived effective frequency. Once
the Doppler of the received wireless signals is accounted for, the
effective frequency can be derived, which may correspond to the GPS
L1 frequency or other nominal frequency of the received wireless
signals. The effective frequency (or derived effective frequency)
is compared to the frequency of a local oscillator (e.g., local
oscillator 112 in receiver 102 of device 100, which has been set to
the nominal frequency). The comparison can be performed using a
band pass filter, and the frequency deviation ".DELTA.F" of the
local oscillator from the nominal frequency can be obtained, using
the frequency variation .delta.f of the XO, and the estimated
frequency of the XO at the given temperature can be obtained. More
particularly, the above process is depicted in FIG. 3B as a method
of temperature-calibrating an uncompensated crystal oscillator
("XO," e.g., XO 106), in a mobile device (e.g., device 100) during
mobile device operation (i.e. field calibration), the method
comprising: receiving a first set of wireless signals comprising at
least a first wireless signal from a first satellite, a second
wireless signal from a second satellite, and a third wireless
signal from a third satellite, at a first temperature--Block 312;
estimating a first frequency of the XO at the first temperature,
based on at least the first, second, and the third wireless signals
(e.g., by combining the wireless signals as described above to
obtain an effective frequency, or when Ephemeris and location are
known, deriving an effective frequency of the satellite
constellation from a single satellite signal, and thereby deriving
a first frequency error of the XO to obtain the first
frequency)--Block 314; and temperature-calibrating the XO based on
the first frequency and the first temperature (e.g., by starting
the process of formulating the FT model or polynomial equation for
XO 106, for example, using logic or means in XO manager 108, using
a first sample point comprising the first frequency and the first
temperature)--Block 316.
[0057] With reference to FIG. 3C, yet another embodiment similar to
that of FIG. 3A is depicted, wherein temperature-calibration of the
XO is based on wireless signals received from a single signal
source. In the case where the single signal source is a satellite
source (e.g., SBAS vehicle), the device comprising the XO (e.g.,
device 100 comprising XO 106) may obtain a location or position
estimate for the device from, for example, using an approximate
location derived from terrestrial signals (e.g. using cell sector
center of the serving cell or trilaterating terrestrial signals),
or location derived from a positioning server. Once the location is
known, using Ephemeris and time, the received wireless signal can
be used to determine the effective frequency for comparison with
the frequency of the local oscillator, in order to obtain the
frequency estimate for the XO, as described in the case of FIG. 3B
above. In cases where the signal source is not a satellite source
(e.g. if the signal source is a WWAN or other fixed frequency
source of known frequency), and if the device is stationary, then
the known fixed frequency is treated as the effective frequency
which is compared with the frequency of the local oscillator in
order to obtain the frequency estimate for the XO. More
particularly, the above process is depicted in FIG. 3C as a method
of temperature-calibrating an uncompensated crystal oscillator
("XO," e.g., XO 106), in a mobile device (e.g., device 100) during
mobile device operation (i.e., field calibration), the method
comprising: receiving a first set of wireless signals comprising at
least a first wireless signal of known Doppler (e.g., from a signal
source such as a SBAS satellite or geostationary source of
zero-Doppler, or a known Doppler source or a terrestrial signal
source), at a first temperature--Block 322; estimating a first
frequency of the XO at the first temperature, based on the first
wireless signal (e.g., by determining the location of device 100
based on the processes described above, based on whether the signal
source is a satellite source or a terrestrial source, and once the
location is known, using Ephemeris and time, the received wireless
signal can be used to determine the effective frequency for
comparison with the frequency of the local oscillator, in order to
obtain the frequency estimate for the XO)--Block 324; and
temperature-calibrating the XO based on the first frequency and the
first temperature (e.g., by starting the process of formulating the
FT model or polynomial equation for XO 106, for example, using
logic or means in XO manager 108, using a first sample point
comprising the first frequency and the first temperature)--Block
326. Also note, in embodiments that utilize a terrestrial signal
source of known frequency, Ephemeris, time and location are not
required.
[0058] Those of skill in the art will appreciate that information
and signals may be represented using any of a variety of different
technologies and techniques. For example, data, instructions,
commands, information, signals, bits, symbols, and chips that may
be referenced throughout the above description may be represented
by voltages, currents, electromagnetic waves, magnetic fields or
particles, optical fields or particles, or any combination
thereof.
[0059] Further, those of skill in the art will appreciate that the
various illustrative logical blocks, modules, circuits, and
algorithm steps described in connection with the embodiments
disclosed herein may be implemented as electronic hardware,
computer software, or combinations of both. To clearly illustrate
this interchangeability of hardware and software, various
illustrative components, blocks, modules, circuits, and steps have
been described above generally in terms of their functionality.
Whether such functionality is implemented as hardware or software
depends upon the particular application and design constraints
imposed on the overall system. Skilled artisans may implement the
described functionality in varying ways for each particular
application, but such implementation decisions should not be
interpreted as causing a departure from the scope of the present
invention.
[0060] The methods, sequences and/or algorithms described in
connection with the embodiments disclosed herein may be embodied
directly in hardware, in a software module executed by a processor,
or in a combination of the two. A software module may reside in RAM
memory, flash memory, ROM memory, EPROM memory, EEPROM memory,
registers, hard disk, a removable disk, a CD-ROM, or any other form
of storage medium known in the art. An exemplary storage medium is
coupled to the processor such that the processor can read
information from, and write information to, the storage medium. In
the alternative, the storage medium may be integral to the
processor.
[0061] With reference now to FIG. 4, another exemplary device 400,
for GNSS-based XO temperature-calibration is illustrated. As seen,
device 400 is shown with several additional components or blocks,
in comparison to the depiction of device 100 in FIG. 2A. In some
embodiments, device 400 is implemented as a wireless communication
system. Device 400 includes digital signal processor (DSP) 464 and
a general purpose processor, depicted as processor 465. The
above-described functions and methods related to XO
temperature-calibration can be performed in DSP 464 or processor
465 or any combination of the processing elements thereof.
Accordingly, in some embodiments, processor 465 may be configured
to perform operations described with regard to XO manager 108, but
it will be understood that some of the operations related to XO
temperature-calibration can be performed in DSP 464, and moreover,
these operations can be implemented in any suitable combination of
hardware and software. Both DSP 464 and processor 465 may be
coupled to clock 104 driven by XO 106 as previously described and
to memory 432. Instructions related to related to a coder/decoder
(CODEC) (e.g., an audio and/or voice CODEC) can be stored in memory
432. Speaker 436 and microphone 438 can be coupled to audio
controller 434, which can be coupled to processor 465 and/or to DSP
464. Display controller 426 can be coupled to DSP 464, processor
465, and to display 428. Other components, such as transceiver 440
(which may be part of a modem) and receiver 441 are also
illustrated.
[0062] Transceiver 440 can be coupled to wireless antenna 442,
which may be configured to receive wireless communication signals
from a terrestrial source such as WWAN or CDMA. These signals can
be used to receive wireless signals from a terrestrial signal
source of known frequency to be used in XO temperature-calibration.
Receiver 441 can be coupled to a satellite or GNSS antenna 443,
which may be configured to receive wireless signals such as
satellite signals from a satellite or GNSS satellite, which, in
embodiments utilizing GNSS satellite signals may also require
knowledge of Ephemeris, time and location to be used in XO
temperature-calibration. In some embodiments, both receiver 441 and
transceiver 440 may include respective local oscillators 112 and
113, which may be sourced from XO 106. Temperature sensor 114 is
also illustrated, and may be coupled to clock 104 and processor
465. Either local oscillator 112 or 113 may be used for XO
temperature-calibration, depending on whether a GNSS satellite
signal source, or other satellite signal source, or a terrestrial
signal source is utilized. Local oscillator 112 would be used for
XO temperature-calibration when one or more satellite signal source
are utilized for XO temperature-calibration. Local oscillator 113
would be used for XO temperature-calibration if a terrestrial
source of known frequency is utilized for XO temperature
calibration. Additionally, band pass filter (BPF) 467 is also
illustrated as a functional block with processor 465, but it will
be understood that placement of BPF 467 in device 400 is not
restricted, and thus functionality of BPF 467 according to
exemplary embodiments, can be implemented anywhere within device
400. Exemplary functionality of BPF 467 can include logic/means for
comparing a frequency of local oscillator 112 and/or 113 with a
frequency of a signal received from receiver 441 and/or transceiver
440 respectively and logic/means for determining a frequency
variation of local oscillator 112/113 based on the comparison. In a
particular embodiment, DSP 464, processor 465, display controller
426, memory 432, audio controller 434, transceiver 440, receiver
441, clock 104, and temperature sensor 114 are included in a
system-in-package or system-on-chip device 422.
[0063] In a particular embodiment, input device 430 and power
supply 444 are coupled to the system-on-chip device 422. Moreover,
in a particular embodiment, as illustrated in FIG. 4, display 428,
input device 430, speaker 436, microphone 438, wireless antenna
442, GNSS antenna 443, and power supply 444 are external to the
system-on-chip device 422. However, each of display 428, input
device 430, speaker 436, microphone 438, wireless antenna 442, GNSS
antenna 443, and power supply 444 can be coupled to a component of
the system-on-chip device 422, such as an interface or a
controller.
[0064] In one embodiment, one or both of DSP 464 and processor 465,
in conjunction with one or more remaining components illustrated in
FIG. 4, can include logic/means to perform the method of
temperature-calibrating an uncompensated XO (e.g., XO 106) in
device 400 during operation of device 400 (i.e., field calibration)
as discussed, for example in Blocks 302-310 of FIG. 3A (or
similarly, with regard to Blocks 312-316 of FIG. 3B or Blocks
322-326 of FIG. 3C). For example, one or more of transceiver 440,
wireless antenna 442, receiver 441 and GNSS antenna 443 can include
logic/means for receiving a first set of wireless signals
comprising at least a first wireless signal of known frequency
(e.g., from a first satellite), and similarly, logic/means for
further receiving at least second and third wireless signals of
known frequencies. DSP 464 and/or processor 465 (illustrated as
comprising XO manager 108) in conjunction with input from
temperature sensor 114, can include logic/means for estimating a
first frequency of the XO at a first temperature, based on at least
the first wireless signal, and temperature-calibrating the XO based
on the first frequency at the first temperature. DSP 464 and/or
processor 465 can similarly, further comprise logic/means for
estimating a second frequency at a second temperature, based on a
second set of wireless signals comprising at least one wireless
signal of known frequency, estimating a third frequency at a third
temperature, based on a third set of wireless signals comprising at
least one wireless signal of known frequency, and further
temperature-calibrating the XO based at least on the first, second,
and third frequency and corresponding first, second, and third
temperature. DSP 464 and/or processor 465 may be configured to
estimate the first frequency of the XO at the first temperature
based on an effective frequency of the first, second, and third
wireless signals, wherein the frequencies of the first, second, and
third wireless signals are offset by a first, second, and third
Doppler relative to the effective frequency and derive a first
frequency error of the XO based on the effective frequency. As
previously described, the band pass filter BPF 467 may be
configured to determine a frequency variation of local oscillator
112/113 as a difference in frequency between the effective
frequency and a frequency of the local oscillator and the processor
is further configured to normalize the frequency variation of the
local oscillator based on an expected nominal frequency of the
local oscillator, determine a normalized frequency variation of XO
106 as equal to the normalized frequency variation of the local
oscillator 112/113, and determine the first frequency based on the
normalized frequency variation of XO 106 and an expected nominal
frequency of XO 106. It will be recalled that the effective
frequency can be, for example, equal to the strongest one of the
first, second, and third wireless signals, or can be based on a
combination of the first, second, and third wireless signals,
wherein the combination is one of a weighted average, a mean, a
median, a least squares, or a pre-specified mathematical fit of the
first, second, and third wireless signals.
[0065] In some cases, the signal source can be a signal source of
known Doppler, such as a geostationary source or a SBAS vehicle of
zero Doppler or a terrestrial source of known frequency such as a
wireless base station. At most one such signal source of known
Doppler may be available in some cases, where a plurality of
satellite signal sources, or calibrated terrestrial sources, are
unavailable. In such cases, DSP 464 and/or processor 465 may be
further configured to determine whether the wireless signal
received from such signal sources satisfies a pre-specified signal
to noise ratio (SNR) and/or passes a pre-specified error or parity
check. If device 400 is in motion, and a satellite signal is relied
upon, DSP 464 and/or processor 465 may be further configured to
estimate the first frequency of XO 106 at the first temperature,
based on a difference between a measured Doppler of the satellite
signal and a predicted Doppler of the satellite signal based on a
speed of motion of the mobile device. Temperature-calibration of XO
106 can comprise a relationship between frequency of the XO and
temperature, based on at least the first frequency and the first
temperature, wherein the relationship is a polynomial equation
(e.g., of third order) of the frequency of the XO and temperature
with a number (e.g., four) of unknown coefficients based on an
order of the polynomial equation. DSP 464 and/or processor 465 may
be able to perform temperature-calibration of XO 106 using a
reduced number of unknown coefficients, wherein the reduced number
can be based on constraints and/or assumptions, such as obtained
from vendor specifications of XO 106, precalibration of XO 106
during manufacture or in the factory, and/or constraining variation
in temperature.
[0066] Moreover, one or more of transceiver 440, wireless antenna
442, receiver 441 and GNSS antenna 443 can also be configured to
receive GNSS assistance information such as location of device 400,
GNSS Ephemeris and/or Almanac information. DSP 464 and/or processor
465 can also be configured to determine the location of device 400,
for example, from the above GNSS assistance or based on a
terrestrial signal or signals (e.g. using cell sector center of the
serving cell or the location of a wireless transceiver sending
signals received by the device 400 or by trilaterating terrestrial
and/or GNSS signals) and/or by using a positioning server.
[0067] It should be noted that although FIG. 4 depicts a wireless
communications device, DSP 464, processor 465, and memory 432 may
also be integrated into a set-top box, a music player, a video
player, an entertainment unit, a navigation device, a
communications device, a personal digital assistant (PDA), a fixed
location data unit, or a computer. Moreover, such a device may also
be integrated in a semiconductor die.
[0068] Accordingly, an embodiment of the invention can include a
computer readable media embodying a temperature-calibrating an
uncompensated crystal oscillator (XO), in a mobile device during
mobile device operation (i.e., field calibration). Accordingly, the
invention is not limited to illustrated examples and any means for
performing the functionality described herein are included in
embodiments of the invention.
[0069] While the foregoing disclosure shows illustrative
embodiments of the invention, it should be noted that various
changes and modifications could be made herein without departing
from the scope of the invention as defined by the appended claims.
The functions, steps and/or actions of the method claims in
accordance with the embodiments of the invention described herein
need not be performed in any particular order. Furthermore,
although elements of the invention may be described or claimed in
the singular, the plural is contemplated unless limitation to the
singular is explicitly stated.
* * * * *