U.S. patent application number 10/438441 was filed with the patent office on 2003-11-20 for system and method for frequency management in a communications positioning device.
Invention is credited to Deck, Ronald H., Tawadrous, Sameh W., Voor, Thomas E..
Application Number | 20030214432 10/438441 |
Document ID | / |
Family ID | 29550020 |
Filed Date | 2003-11-20 |
United States Patent
Application |
20030214432 |
Kind Code |
A1 |
Tawadrous, Sameh W. ; et
al. |
November 20, 2003 |
System and method for frequency management in a communications
positioning device
Abstract
A frequency management scheme for a hybrid
communications/positioning device, such as a cellular/GPS or other
combined device, generates a local clock signal for the
communications portion of the device, using a crystal oscillator or
other part. The oscillator output may be corrected by way of an
automatic frequency control (AFC) circuit or software, to drive the
frequency of that clock signal to a high accuracy. The base
oscillator may be delivered to a phase locked loop to drive a
high-frequency clock for the cellular or other communications
portion of the hybrid device, which clock signal may also be
frequency-converted to drive a GPS or other positioning receiver.
The extraction of a base GPS clock from the radio frequency
reference eliminates the need for a second oscillator or
synthesizer for that portion of the hybrid device. In embodiments,
AFC tuning on the cellular clock may be omitted and the high
frequency clock signal divided down for delivery to the GPS or
other positioning receiver may be adjusted via a frequency
prescaler, or other module.
Inventors: |
Tawadrous, Sameh W.; (Coral
Springs, FL) ; Deck, Ronald H.; (Cooper City, FL)
; Voor, Thomas E.; (Lauderhill, FL) |
Correspondence
Address: |
Scott M. Garrett
Motorola, Inc.
Law Department
8000 West Sunrise Boulevard
Fort Lauderdale
FL
33322
US
|
Family ID: |
29550020 |
Appl. No.: |
10/438441 |
Filed: |
May 15, 2003 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60380832 |
May 17, 2002 |
|
|
|
Current U.S.
Class: |
342/357.31 |
Current CPC
Class: |
H03L 7/23 20130101; G01S
19/235 20130101; H03J 7/065 20130101; H03J 2200/11 20130101; H04B
1/403 20130101; H03L 7/183 20130101; H04B 1/3805 20130101 |
Class at
Publication: |
342/357.1 ;
342/357.15 |
International
Class: |
G01S 005/14 |
Claims
We claim:
1. A system for generating a frequency reference in a hybrid
communications device, comprising: a clock source in a
communications portion of the hybrid communications device, the
clock source generating a clock signal at a first frequency; a
frequency correction module, communicating with the clock source,
the frequency correction module generating a clock signal at a
corrected first frequency; a frequency converter, the frequency
converter communicating with the frequency correction module to
receive the clock signal at the corrected first frequency and
outputting a clock signal at a second frequency to operate a
positioning receiver portion of the hybrid communications device to
receive a wireless positioning signal.
2. A system according to claim 1, wherein the communications
portion comprises at least one of a cellular telephone, a two-way
pager and a network-enabled wireless communication device.
3. A system according to claim 1, wherein the clock source
comprises an oscillator.
4. A system according to claim 3, wherein the clock source
comprises a synthesizer.
5. A system according to claim 1, wherein the frequency correction
module comprises a temperature frequency control module.
6. A system according to claim 5, wherein the temperature frequency
control module comprises a temperature frequency control
algorithm.
7. A system according to claim 5, wherein the temperature frequency
control module comprises a temperature frequency control
circuit.
8. A system according to claim 1, wherein the frequency correction
module comprises an automatic frequency control module.
9. A system according to claim 8, wherein the automatic frequency
control module comprises an automatic frequency control
circuit.
10. A system according to claim 8, wherein the automatic frequency
control module comprises an automatic frequency control
algorithm.
11. A system according to claim 1, wherein the frequency correction
module operates on manufacturing tolerance data.
12. A system according to claim 1, wherein the frequency converter
comprises a frequency divider.
13. A system according to claim 1, wherein the positioning receiver
portion comprises a global positioning system receiver.
14. A method for generating a frequency reference in a hybrid
communications device, comprising: generating a clock signal at a
first frequency in a communications portion of the hybrid
communications device; generating a clock signal at a corrected
first frequency based on the clock signal at the first frequency;
generating a clock signal at a second frequency based on the clock
signal at the corrected first frequency to operate a positioning
receiver portion of the hybrid communications device to receive a
wireless positioning signal.
15. A method according to claim 14, wherein the communications
portion comprises at least one of a cellular telephone, a two-way
pager and a network-enabled wireless communication device.
16. A method according to claim 14, wherein the step of generating
a clock signal at a first frequency comprises a step of exciting an
oscillator.
17. A method according to claim 16, wherein the step of generating
a clock signal at a first frequency comprises operating a
synthesizer.
18. A method according to claim 14, wherein the step of generating
a clock signal at a corrected first frequency comprises a step of
applying a temperature frequency control module.
19. A method according to claim 18, wherein the step of applying a
temperature frequency control module comprises a step of executing
a temperature frequency control algorithm.
20. A method according to claim 18, wherein the step of applying a
temperature frequency control module comprises a step of operating
a temperature frequency control circuit.
21. A method according to claim 14, wherein the step of generating
a clock signal at a corrected first frequency comprises operating
an automatic frequency control module.
22. A method according to claim 21, wherein the step of operating
an automatic frequency control module comprises a step of operating
an automatic frequency control circuit.
23. A method according to claim 21, wherein the step of operating
an automatic frequency control module comprises a step of executing
an automatic frequency control algorithm.
24. A method according to claim 14, wherein the step of generating
a clock signal at a corrected first frequency comprises a step of
operating on manufacturing tolerance data.
25. A method according to claim 14, wherein the step of generating
a clock signal at a second frequency comprises a step of operating
a frequency divider.
26. A method according to claim 14, wherein the positioning
receiver portion comprises a global positioning system
receiver.
27. A system for generating a frequency reference in a hybrid
communications device, comprising: a clock source in a
communications portion of the hybrid communications device, the
clock source generating a clock signal at a first frequency; a
frequency converter, the frequency converter communicating with the
clock source to receive the clock signal at the first frequency and
outputting a clock signal at a second frequency, the second
frequency being used to operate a positioning receiver portion of
the hybrid communications device to receive a wireless positioning
signal.
28. A system according to claim 27, wherein the communications
portion comprises at least one of a cellular telephone, a two-way
pager and a network-enabled wireless communication device.
29. A system according to claim 27, wherein the clock source
comprises an oscillator.
30. A system according to claim 29, wherein the clock source
comprises a synthesizer.
31. A system according to claim 27, wherein the frequency converter
comprises a frequency divider.
32. A system according to claim 27, wherein the frequency converter
comprises a prescaler.
33. A system according to claim 27, wherein the positioning
receiver portion comprises a global positioning system
receiver.
34. A method for generating a frequency reference in a hybrid
communications device, comprising: generating a clock signal at a
first frequency in a communications portion of the hybrid
communications device; generating a clock signal at a second
frequency based on the clock signal at the first frequency to
operate a positioning receiver portion of the hybrid communications
device to receive a wireless positioning signal.
35. A method according to claim 34, wherein the communications
portion comprises at least one of a cellular telephone, a two-way
pager and a network-enabled wireless communication device.
36. A method according to claim 34, wherein the step of generating
a clock signal at a first frequency comprises a step of exciting an
oscillator.
37. A method according to claim 36, wherein the step of generating
a clock signal at a first frequency comprises a step of operating a
synthesizer.
38. A method according to claim 34, wherein the step of generating
a clock signal at a second frequency comprises a step of dividing
the clock signal at the first frequency.
39. A method according to claim 38, wherein the step of generating
a clock signal at a second frequency comprises a step of operating
a prescaler.
40. A method according to claim 34, wherein the positioning
receiver portion comprises a global positioning system receiver.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This application relates to and claims priority from U.S.
Provisional Application Serial No. 60/380,832 filed May 17, 2002,
which application is incorporated by reference. This application is
also related to the subject matter of U.S. application Ser. No.
______ entitled "SYSTEM AND METHOD FOR FREQUENCY MANAGEMENT IN A
COMMUNICATIONS POSITIONING DEVICE", having a docket No. CM03713J
and filed of even date with this application, having the same
inventors as this application, being assigned to or under
obligation of assignment to the same entity as this application,
and which application is incorporated by reference in this
application.
FIELD OF THE INVENTION
[0002] The invention relates to the field of communications, and
more particularly to techniques for generating and managing
precision frequency sources in cellular telephones or other
communications devices having a positioning capability, such as
Global Positioning System (GPS) or other location service.
BACKGROUND OF THE INVENTION
[0003] GPS receivers can be characterized by performance criteria
such as acquisition and tracking time, which reflect the amount of
processing necessary to detect and lock on to GPS satellite signals
and hence the amount of time needed to begin accurately reporting a
user's position. The acquisition, tracking, sensitivity and other
performance parameters of GPS receivers can be affected by a
variety of factors. Those factors include the precision with which
frequency references for radio frequency detection and other
purposes can be generated and managed within the device. L1 GPS
signals used for civilian coarse acquisition (C/A) purposes are
broadcast at 1.575 GHz from the associated NAVSTAR satellites.
Russian GLONASS satellites broadcast in a similar frequency
range.
[0004] Handheld, vehicle-mounted, stationary and other GPS and
other positioning receivers require frequency stability in their
clocks generally in the range of a few parts per million or less to
accurately derive Doppler and other data from those signals, and
therefore triangulate a precise receiver position within a
reasonable acquisition time.
[0005] Recently, market trends have developed toward GPS
functionality combined with other communications services. Various
wireless devices, such as cellular telephones, digital pagers,
wireless personal digital assistants, 802.11a and other clients may
all be combined with GPS location receivers for various
applications.
[0006] However, the accuracy of reference clocks generally employed
in cellular telephones and other communications devices may
generally not be as great as that needed for useful GPS service,
which as noted may require extended accuracy to within at least a
few parts per million, down to tenths of 1 part per million or less
for increased tracking performance. Cellular telephones on the
other hand may contain uncompensated oscillators accurate to within
only perhaps five to tens of parts per million, depending on
implementation. Cellular devices may tolerate higher frequency
variability in part because handsets or other devices may be able
to derive a stable frequency reference from a base station or the
wireless network, itself.
[0007] In the case of a GPS receiver combined with a cellular
telephone for caller location service as mandated by the Federal
Communications Commission, a cellular telephone's local crystal
oscillator, tuned to 16.8 MHz or another base frequency, may for
instance have a frequency variance of .+-.30 ppm or more or less. A
cellular handset's internal clock may therefore not be sufficient
to drive GPS circuitry in a combined device for useful GPS
operation by itself. Temperature compensation circuits operating on
ordinary crystal oscillators may improve the frequency reference to
perhaps .+-.5 ppm or so, although those types of parts may add to
the cost of a relatively low-cost mobile device. Solutions such as
supplying two corrected reference oscillators, one for GPS and one
for cellular or other communications service at different
frequencies, for instance, would not be likely to be economical in
a combined device. Other problems exist.
SUMMARY OF THE INVENTION
[0008] The invention overcoming these and other problems in the art
relates in one regard to a system and method for frequency
management in a combined communications/positioning system, in
which a stable base reference may be extracted for GPS purposes
from a high-frequency reference used to drive the demodulation of
signals on the communications side of the device. The invention in
one regard thus allows both cellular and GPS circuits to be
controlled from one source, without a need for a second oscillator
in the GPS receiver portion of the device. According to the
invention in one regard, the GPS circuitry may be driven by a
signal from a phase locked loop generating a radio local oscillator
for demodulation, downconversion or other communications
operations, divided down to an appropriate base GPS frequency. The
base oscillator driving the communications portion of the combined
device may be corrected using for instance software temperature
correction, hardware temperature correction, measurement of
frequency bias at time of manufacture, automatic frequency control
(AFC) or other techniques to establish accuracy in the
communications portion of the device to .+-.5 ppm or more or less.
The GPS receiver component may consequently be driven with
corresponding accuracy and therefore need not have a local
oscillator of its own, while still achieving sufficient GPS
performance at comparatively low cost.
BRIEF DESCRIPTION OF THE DRAWINGS
[0009] The invention will be described with reference to the
accompanying drawings, in which like elements are referenced with
like numbers, and in which:
[0010] FIG. 1 illustrates a frequency management architecture,
according to an embodiment of the invention.
[0011] FIG. 2 illustrates a flowchart of frequency management
processing, according to an embodiment of the invention.
[0012] FIG. 3 illustrates a frequency management architecture,
according to an embodiment of the invention.
[0013] FIG. 4 illustrates a frequency management architecture,
according to an embodiment of the invention.
DETAILED DESCRIPTION OF EMBODIMENTS
[0014] An architecture in which a frequency management system
according to the invention may be implemented is illustrated in
FIG. 1, in which a combined communications/positioning device
incorporates both GPS receiver 124 and a communications transceiver
120. The communications transceiver 120 of the combined device may
be or include for instance a portable radio, cellular telephone,
two-way or other pager, wireless modem, wireless personal digital
assistant or other device that receives or transmits a radio,
optical or other wireless communications signal.
[0015] The combined communications/positioning device as
illustrated may contain a base oscillator 102 to provide a
frequency reference to ultimately drive the communications
transceiver 120. In embodiments base oscillator 102 may be a
free-running, uncompensated reference part. The base frequency of
the base oscillator 102 may be set to values compatible with
cellular or other operation at 800/900 MHz, 1900 MHz or other
frequency ranges. The base oscillator 102 may for example be set to
16.8 MHz or other frequencies which may be multiplied to carrier
ranges. An uncompensated crystal oscillator such as may be used to
implement base oscillator 102 may by itself typically exhibit, for
instance, a frequency deviation of .+-.30 ppm or more or less.
[0016] In embodiments the output of base oscillator 102 may be
processed or corrected using hardware, software or other techniques
to improve frequency stability. Techniques to control base
oscillator 102 may include, for instance, the use of factory
measurement data 104 to compensate for detected frequency bias or
offset in the manufactured part, and other artifacts. Factory
measurement data 104 may in one regard be stored in the combined
device and used to re-center the frequency of base oscillator 102
during operation, via software or otherwise. Other adjustments are
possible.
[0017] In embodiments, base oscillator 102 may likewise be
controlled for frequency drift or other artifacts associated with
varying temperature, using temperature frequency control module
106. Temperature frequency control module 106 may in embodiments be
implemented using hardware, software, firmware, or combinations of
the same to correct base oscillator 102.
[0018] Temperature frequency control module 106 may, for instance,
in embodiments be combined in the base oscillator 102 using
hardware components such as a temperature-controlled crystal
oscillator (TCXO) or other hardware-corrected oscillator or
reference part. A hardware TXCO may for instance exhibit a
frequency accuracy of .+-.5 ppm or more or less, depending on
manufacturing, design or other factors.
[0019] In embodiments, temperature frequency control module 106 may
be implemented using software control such as a temperature
frequency control (TFC) or other algorithm, to sense and adjust
frequency settings based for instance on temperature, power and
other parameters.
[0020] The output of the base oscillator 102 may in embodiments be
processed to further increase the accuracy of the frequency
reference. As illustrated in FIG. 1, the frequency tracking control
module 108 may apply correction to the base oscillator 102 to
increase the accuracy of the frequency output. In embodiments, the
frequency tracking control module 108 may be implemented in
hardware, software, firmware or combinations of the same.
[0021] In embodiments, the frequency tracking control module 108
may be implemented in hardware, such as an automatic frequency
control (AFC) circuit, of the superheterodyne, direct conversion or
other type locking to a cellular or other carrier.
[0022] In embodiments, the frequency tracking control module 108
may be implemented in software algorithms, with correction instead
for instance applied to a synthesizer or other associated part by
programming logic or otherwise to achieve enhanced frequency
precision.
[0023] In cellular or other communications networks, the accuracy
of the frequency reference corrected by frequency tracking control
module 108 may for instance reach .+-.0.2 ppm or more or less, in
part because cellular or other base stations may maintain accurate
cesium or other clock references which may be broadcast over their
communications channels. Frequency tracking control module 108 as
illustrated may for instance communicate with and receive input
from communications transceiver 120 to perform frequency tracking,
by negative feedback or other techniques.
[0024] The frequency tracking control module 108 as illustrated may
be applied to a phase locked loop 110 to drive operating
frequencies for cellular or other communications or other
operations. The phase locked loop 110 may include a phase
comparator 112, to compare the phase of the base oscillator 102
with the phase of a high-frequency oscillator 116. High-frequency
oscillator 116 may for instance be implemented as a voltage
controlled high-frequency oscillator (VCO) generating frequencies,
for instance, in the 800/900 MHz, 1900 MHz or other ranges for
cellular or other operation. A loop filter 114 may low-pass filter
the output of the phase comparator 112 to remove higher frequency
artifacts or other noise.
[0025] The output of the loop filter 114 may in turn drive the
high-frequency oscillator 116 to operating frequencies, which
through the return provided by loop divider 118 completes a closed
feedback loop to phase comparator 112. The phase of the
high-frequency oscillator 116 is thereby locked to the phase of the
base oscillator 102, so that the phase angle between them remains
zero or approximately zero, or at a fixed or approximately fixed
separation during operation.
[0026] The clock reference of the high-frequency oscillator 116
forms an output of the phase locked loop 110, which may in turn
drive communications transceiver 120 to demodulate, downconvert and
receive the wireless signals broadcast to the communications
device, or perform other communications operations. In the
embodiment illustrated in FIG. 1, each of the factory measurement
data 104, temperature frequency control module 106 and frequency
tracking control module 108 may likewise be in communication with
loop divider 118 of phase locked loop 110, to correlate the
adjustment of the output of phase locked loop 110 used to drive
communications transceiver 120. For instance, in embodiments
comparatively fine or other adjustments may be made to the ratio of
loop divider 118, according to inputs from those corrective data or
modules.
[0027] According to embodiments of the invention, the output of the
phase locked loop 110 may also be used to drive GPS receiver 124
within the combined device. The GPS receiver 124 may consequently
acquire and track GPS signals without the added costs of
incorporating an additional local oscillator as well as associated
automatic frequency control (AFC) or other signal processing
circuitry or software to enhance the frequency reference for that
portion of the combined device.
[0028] According to the embodiment illustrated in FIG. 1, a
frequency reference output from phase locked loop 110 may be
communicated to the GPS receiver 124 from the communications or
other circuitry, without requiring a local oscillator apparatus in
the GPS receiver 124. In this embodiment, the frequency reference
derived from base oscillator 102 may for instance be divided by GPS
divider 122 to a desired GPS frequency. GPS divider 122 as
illustrated may likewise communicate with and receive input from
the frequency tracking control module 108, to refine divider ratios
or other adjust processing parameters. The output of GPS divider
122 may be communicated via filter 128 to remove noise, isolate
demodulation frequencies or perform other signal conditioning. In
embodiments the frequency division may for instance be performed
using GPS divider 122 as a separate part, by an auxiliary
synthesizer prescaler contained as part of a synthesizer or other
part, or by other parts or software.
[0029] Since the accuracy of the output of the GPS divider 122 may
track the accuracy of the base oscillator 102 treated by
temperature, AFC, phase locked loop or other correction, this
downconversion process may provide a reference signal to the GPS
receiver 124 having an accuracy in embodiments of .+-.5 ppm to 0.2
ppm or more or less. This may eliminate any necessity to introduce
a separate oscillator or a step-up phase locked loop in the GPS
receiver 124 itself, reducing cost and increasing reliability in
the resulting device.
[0030] Processing according to the invention in one regard is
illustrated in FIG. 2. In step 202, processing begins. In step 204,
base oscillator 102 may generate a 16.8 MHz or other clock
reference signal, for communications or other purposes. In step
206, offset correction, if used, may be applied to center or
otherwise correct the output of base oscillator 102, based on
factory measurement data 104 or other data. In step 208,
temperature correction using temperature frequency control module
106, if used, may be applied to correct the output of base
oscillator 102 to increase frequency accuracy or stability, for
instance using software, circuitry, or other techniques.
[0031] In step 210, the output of the base oscillator 102 may be
transmitted to the phase locked loop 110. In step 212, the phase
locked loop 110 may lock the phase of high-frequency oscillator 116
to the phase of base oscillator 102. In step 214, the output of
phase locked loop 110 may drive communications transceiver 120, for
instance for cellular or other operation.
[0032] In step 216, the communications transceiver 120 may register
or communicate with a cellular base station or other remote or
other transceiver. In step 218, an AFC or other frequency tracking
control may be performed on base oscillator 102, for instance by
software, circuitry or other techniques.
[0033] In step 220, the output of phase locked loop 110 may be
communicated to GPS divider 122, for instance to divide the
incoming reference signal down to base frequencies which may be
used to drive GPS operation, such as, for example, 24.5535 MHz or
other frequencies.
[0034] In step 222, GPS divider 122 may generate an output
reference signal according to the divide ratio, which in
embodiments may be programmable or dynamically adjusted according
to communications or other conditions. In other embodiments, the
divide ratio may be hardwired, or be flashed or otherwise be set to
remain relatively static.
[0035] In step 224, the output of GPS divider 122 may drive GPS
receiver 124 for instance via filter 128 for radio frequency
demodulation or other operations. In step 226, processing may end,
repeat, or return to a prior processing point.
[0036] In an embodiment of the invention illustrated in FIG. 3, the
output of base oscillator 102 may be communicated to the phase
locked loop 110 omitting any frequency tracking control module, if
that correction is not needed to achieve satisfactory accuracy in
given implementations. In such embodiments, the divide ratio of the
GPS divider 122 may in cases be dynamically or otherwise adjusted,
for instance in fine increments, to tune the resulting GPS
frequency reference delivered to GPS receiver 124 without the
benefit of an AFC or other circuit or algorithm. In this case,
other compensation, such as that performed or effected by factory
measurement data 104 and temperature frequency control module 106,
may still be performed on base oscillator 102 as well as
communicated to loop divider 118 or other parts of phase locked
loop 110. Other types of correction or compensation to base
oscillator 102, such as correction using factory measurement data
104 or other data, may also be applied, alone or in conjunction
with temperature control or other techniques.
[0037] As noted, in this embodiment the divide ratio of the GPS
divider 122 may for instance be adjusted to alter the clock
reference delivered to the GPS receiver 124 by comparatively fine,
or in implementations more or less coarse, amounts. The divide
ratio may illustratively be an integer N, but floating point and
other divide ratios are possible. The omission of frequency
tracking correction or other types of compensation on base
oscillator 102 in embodiments may depend, in part, on factors such
as the frequency range of the communications transceiver 120, the
detected offset of the base oscillator 102 during manufacture, the
numerical precision of the divide ratio effected by GPS divider
122, or other factors.
[0038] In an embodiment illustrated in FIG. 4, the phase locked
loop 110 may drive a synthesizer 126 or other part to generate
other desired frequencies for cellular or other operation, rather
than drive the communications transceiver 120 directly. According
to this embodiment, the frequency reference may be programmed or
scaled according to design needs, such as for instance for
multi-band operation for cellular handsets, or other
implementations. Likewise, in embodiments the GPS divider 122 may
in turn drive a synthesizer or other part to generate desired
frequency ranges, rather than drive GPS receiver 124 directly.
Other combinations are possible.
[0039] The foregoing description of the invention is illustrative,
and variations in configuration and implementation will occur to
persons skilled in the art. For instance, while the phase locked
loop 110 locking high-frequency oscillator 116 to base oscillator
102 has been generally described in terms of a negative feedback
topology including a comparator, loop filter, high-frequency
oscillator and feedback divider, in embodiments the phase locking
function may be implemented in other circuit configurations, by
software algorithms, or other combinations of hardware and
software.
[0040] Further, while the communications transceiver 120 and
related circuitry has generally been described in terms of a
cellular telephone equipped with positioning capability, other
communications receivers or transceivers may be used. For instance,
in embodiments a passive communications receiver rather than a
two-way communications transceiver 120 may be implemented. Other
receivers, transceivers, modems or other communications components
may be used. For instance, in embodiments satellite-based
communications receivers or transceivers, data links or other
wired, wireless, optical and other interfaces or channels may be
used. Likewise again, while the invention has generally been
described in terms of a GPS device as the positioning receiver,
other positioning systems or a combination of positioning systems
may be used. Furthermore, while the invention has generally been
described in terms of a pair of communications and positioning
receivers, modems or elements, in embodiments three or more
communications, positioning or other receivers, modems or other
communications devices may be employed. The invention is
accordingly intended to be limited only by the following
claims.
* * * * *