Multipath calibration in GPS pseudorange measurements
First Claim
1. In a global positioning system comprising a GPS receiver, a first satellite having a first trajectory, and a second satellite having a second trajectory that intersects the first trajectory in an azimuth vs. elevation plot at a cross-over point, a method for multipath calibration of pseudorange measurements comprising the steps of:
- receiving a first signal at the receiver from the first satellite, where a portion of the first signal is received when the first satellite is at the cross-over point;
receiving a second signal at the receiver from the second satellite, where a portion of the second signal is received when the second satellite is at the cross-over point; and
determining a first calibrated pseudorange multipath signal and a second calibrated pseudorange multipath signal by correlating the portion of the first signal with the portion of the second signal, whereby the relative mean multipath bias between the first signal and the second signal is eliminated.
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Accused Products
Abstract
Novel techniques are disclosed for eliminating multipath errors, including mean bias errors, in pseudorange measurements made by conventional global positioning system receivers. By correlating the multipath signals of different satellites at their cross-over points in the sky, multipath mean bias errors are effectively eliminated. By then taking advantage of the geometrical dependence of multipath, a linear combination of spherical harmonics are fit to the satellite multipath data to create a hemispherical model of the multipath. This calibration model can then be used to compensate for multipath in subsequent measurements and thereby obtain GPS positioning to centimeter accuracy.
62 Citations
13 Claims
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1. In a global positioning system comprising a GPS receiver, a first satellite having a first trajectory, and a second satellite having a second trajectory that intersects the first trajectory in an azimuth vs. elevation plot at a cross-over point, a method for multipath calibration of pseudorange measurements comprising the steps of:
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receiving a first signal at the receiver from the first satellite, where a portion of the first signal is received when the first satellite is at the cross-over point; receiving a second signal at the receiver from the second satellite, where a portion of the second signal is received when the second satellite is at the cross-over point; and determining a first calibrated pseudorange multipath signal and a second calibrated pseudorange multipath signal by correlating the portion of the first signal with the portion of the second signal, whereby the relative mean multipath bias between the first signal and the second signal is eliminated. - View Dependent Claims (2, 3, 4, 5)
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- 6. A method for reducing multipath errors in pseudorange signals received at a GPS receiver from a plurality of satellites, the method comprising adjusting each of the pseudorange signals by each of a corresponding plurality of calibrated multipath signals, the calibrated multipath signals indicating the multipath as a function of direction relative to an antenna of the receiver.
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11. A method for calibrating multipath in GPS pseudorange measurements at a receiver, the method comprising:
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measuring a set of multipath signals arriving at an antenna connected to the receiver, the antenna being surrounded by a cylinder tapered outward toward the top that reflects GPS signals arriving at an elevation angle below a predetermined threshold; and fitting a calibration function to the set of multipath signals, the calibration function giving the multipath as a function of elevation angle. - View Dependent Claims (12, 13)
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Specification