Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
2000-09-22
2001-07-24
Blum, Theodore M. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S174000, C701S214000
Reexamination Certificate
active
06266007
ABSTRACT:
FIELD OF THE INVENTION
The current invention is in the field of the calibration systems, and more specifically, in the field of code group delay calibration systems.
DESCRIPTION OF THE BACKGROUND ART
In the available art related to calibration systems, one kind of errors (that should be calibrated for) is caused by code group delay.
Indeed, code phase (also known as pseudo-range) measurements are now commonly processed successfully in GPS receivers to provide high accuracy position, velocity and time measurements, e. g. in differential and surveying applications. Numerous error sources in these measurements have been revealed and techniques have been developed to minimize or completely eliminate these errors. The U.S. Pat. No. 5,526,291, issued to Lennen, discloses how to solve the error in code and carrier phase caused by different receiver designs reacting differently to the same satellite signal because the different receiver types use different filtering, amplification and other components. Lennen et al. in the U.S. Pat. No. 5,515,057, describes how errors in the code and carrier phase measurement caused by electrical asymmetries in the antenna element could be solved.
One important kind of the code phase error is caused by the group delay characteristics within a GPS/GLONASS receiver. The group delay code phase errors caused by variations in the group delay across the received bandwidth are due to the specific characteristics of filters, amplifiers and other active components in a GPS/GLONASS receiver design. For instance, it is desirable for a GPS/GLONASS receiver to include the specific filter and amplifier components that would allow for the substantial filtering of out of band signals to prevent possible jamming. The code phase errors caused by the group delay characteristics within a satellite receiver are more pronounced in a GLONASS receiver than in a GPS receiver.
The technique that would allow the satellite receiver to maintain the active components with the specific desirable characteristics (like antijamming capabilities) while allowing the group delay code phase errors to be removed as an error source from the pseudo range measurements was disclosed by Gary Lennen in the U.S. Pat. No. 5,949,372, entitled “Signal Injection for Calibration of Pseudo-Range Errors in Satellite Positioning System Receivers”. The '372 patent is specifically referred to in the present patent application and is incorporated herein in its entirety.
However, the Calibration Signal Generator disclosed in the '372 patent is an independently important circuit. Indeed, the Calibration Signal Generator can be used in a number of different applications, where there is a need to remove the delay group errors caused by the propagation of the received signal within the Narrow Band Receiver circuit.
SUMMARY OF THE INVENTION
To address the shortcomings of the available art, the present invention provides a method and a system for removing the delay group errors caused by propagation of the received signal within a Narrow Band Receiver circuit.
One aspect of the present invention is directed to an apparatus for calibrating in real time a Narrow Band Receiver for a code group delay in signals generated by a Narrow Band Transmitter.
In one embodiment of the present invention, the apparatus comprises: a Broad Band Receiver configured to receive signals generated by the Narrow Band Transmitter; and a Calibration Signal Generator circuit connected to the Broad band Receiver. The Calibration Signal Generator is configured to generate a calibration signal that is substantially free from the code group delay errors and intermodulation errors, and that is substantially similar to the signals generated by the Narrow Band Transmitter. The Calibration Signal Generator circuit is linked to the Narrow Band Receiver in order to transmit to the Narrow Band Receiver the calibration signal that is used to calibrate in real time the Narrow Band Receiver for the code group delay in signals generated by the Narrow Band Transmitter. In alternative embodiment, the Transmitter comprises a satellite Transmitter, the Narrow Band Receiver comprises a satellite Narrow Band Receiver including a Receiver Antenna, and the Calibration Signal Generator is configured to generate the calibration signal in order to calibrate the satellite signals for errors caused by variations in the group delay of the satellite signals across the received bandwidth in the satellite Narrow Band Receiver.
In one embodiment, the Narrow Band Satellite Receiver receives the satellite signals from the GPS system including a plurality of GPS satellites and from the GLONASS system including a plurality of GLONASS satellites, and wherein the GPS system generates L
1
GPS
and L
2
GPS
signals, wherein the GLONASS system generates L
1
GLONASS
and L
2
GLONASS
signals.
In one embodiment, the Calibration circuit further includes: a Calibration Signal Generator circuit configured to generate the calibration signal; and a Directional Coupler circuit connected to the Calibration Signal Generator circuit in order to receive the calibration signal and connected to the Narrow Band Satellite Receiver circuit in order to receive the satellite signals. The Directional Coupler is configured to combine the satellite signals with the calibration signal in order to generate a combined signal and in order to inject the combined signal into the Narrow Band Satellite Receiver circuit.
In one embodiment, the Calibration circuit further includes the Calibration Signal Generator circuit further comprising: a Calibration Signal Synthesizer configured to generate a code clock signal C
clk
—
GLONASS
, a code clock signal C
clk
—
GPS
, a local oscillator signal LO
L1
—
GLONASS
, a local oscillator signal LO
L2
—
GLONASS
, a local oscillator signal LO
L1
—
GPS
, and a local oscillator signal LO
L2
—
GPS
. The code clock signal C
clk
—
GLONASS
, the code clock signal C
clk
—
GPS
, the local oscillator signal LO
L1
—
GLONASS
, the local oscillator signal LO
L2
—
GLONASS
, the local oscillator signal LO
L1
—
GPS
, and the local oscillator signal LO
L2
—
GPS
are locked to a single calibration clock frequency signal.
In one embodiment, the Calibration circuit further includes a Calibration Code Generator configured to generate a local code C
GLONASS
and a local code C
GPS
; a Mixer configured to frequency translate the local code C
GLONASS
signal using the LO
L1
—
GLONASS
signal into an L
1
_GLONASS signal, the local code C
GLONASS
signal using the LO
L2
—
GLONASS
signal into an L
2
_GLONASS signal, the local code C
GPS
signal using the LO
L1
—
GPS
signal into an L
1
_GPS signal, and the local code C
GPS
signal using the LO
L2
—
GPS
signal into an L
2
_GPS signal; an RF Switch block configured to pass the L
1
_GLONASS signal, the L
2
_GLONASS signal, the L
1
_GPS signal, or the L
2
_GPS; and an Attenuator block configured to generate a calibration signal C
RF
—
GLONASS
—
L1
, a calibration signal C
RF
—
GLONASS
—
L2
, a calibration signal C
RF
—
GPS
—
L1
, or a calibration signal C
RF
—
GPS
—
L2
.
Another aspect of the present invention is directed to a method of generating a calibration signal for calibrating in real time a Narrow Band Receiver for code group delay in a signal generated by a Narrow Band Transmitter. In one embodiment, the method comprises the following steps: determining characteristics of the signal generated by the Narrow Band Transmitter; generating the calibration signal substantially similar to the signal generated by the Transmitter using a Calibration Signal Generator circuit; and transmitting the calibration signal to the Narrow Band Receiver in order to calibrate the Narrow Band Receiver for errors caused by variations in the code group delay signals across the received bandwidth.
The present invention also includes a method of generating a calibration signal for calibrating in real time a satellite Receiver for pseudo-range errors caused by variations in the code group delay of the received satellite signals across the received bandwidth. T
Blum Theodore M.
Tankhilevich Boris G.
Trimble Navigation LTD
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