METHODS AND APPARATUS FOR DETERMINING PHASE AMBIGUITIES IN RANGING AND NAVIGATION SYSTEMS
First Claim
1. A method of determining a value of an integer ambiguity of a carrier-based pseudorange measurement at a time epoch, wherein the integer ambiguity indicates an integer number of carrier wavelengths that the carrier-based pseudorange measurement is offset from an absolute pseudorange, the method comprising:
- (a) measuring the absolute pseudorange at the time epoch based on a received signal, thereby forming an absolute pseudorange measurement;
(b) measuring a carrier-based pseudorange at the time epoch based on a carrier phase of the received signal, thereby forming the carrier-based pseudorange measurement;
(c) estimating a probability that each of a plurality of candidate integer ambiguity values is a correct value of the integer ambiguity at the time epoch based on the absolute pseudorange measurement and the carrier-based pseudorange measurement, thereby determining which of the candidate integer ambiguity values is the most likely integer ambiguity value to be the correct value; and
(d) selecting the most likely integer ambiguity value as the value of the integer ambiguity at the time epoch.
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Abstract
An improved technique for determining the integer value of phase ambiguities (integer ambiguities) of pseudorange measurements based on the carrier phase of received navigation signals provides more accurate ranging and position determination in navigation and ranging systems. A Bayesian methodology is employed to estimate the probability that each of a group of candidate integer ambiguity values is the correct value of the integer ambiguity at each pseudorange measurement time epoch. The candidate having the highest probability is selected as the value of the integer ambiguity, and the selected value is used to estimate the pseudorange and geographic position at each time epoch. The probability estimates are computed based on factors including: the code-based and carrier-based pseudorange measurements, the estimated variability of these measurements, integer ambiguity probabilities computed at the preceding time epoch, and the probability of a cycle slip from the preceding time epoch to the present time epoch.
44 Citations
25 Claims
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1. A method of determining a value of an integer ambiguity of a carrier-based pseudorange measurement at a time epoch, wherein the integer ambiguity indicates an integer number of carrier wavelengths that the carrier-based pseudorange measurement is offset from an absolute pseudorange, the method comprising:
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(a) measuring the absolute pseudorange at the time epoch based on a received signal, thereby forming an absolute pseudorange measurement;
(b) measuring a carrier-based pseudorange at the time epoch based on a carrier phase of the received signal, thereby forming the carrier-based pseudorange measurement;
(c) estimating a probability that each of a plurality of candidate integer ambiguity values is a correct value of the integer ambiguity at the time epoch based on the absolute pseudorange measurement and the carrier-based pseudorange measurement, thereby determining which of the candidate integer ambiguity values is the most likely integer ambiguity value to be the correct value; and
(d) selecting the most likely integer ambiguity value as the value of the integer ambiguity at the time epoch. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13)
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14. A method of detecting a cycle slip in a carrier-based pseudorange measurement, indicated by a change in a value of an integer ambiguity which indicates an integer number of carrier wavelengths from which the carrier-based pseudorange measurement is offset from an absolute pseudorange, the method comprising:
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(a) measuring the absolute pseudorange at a time epoch based on a received signal, thereby forming an absolute pseudorange measurement;
(b) measuring a carrier-based pseudorange at the time epoch based on a carrier phase of the received signal, thereby forming the carrier-based pseudorange measurement;
(c) estimating a probability that each of a plurality of candidate integer ambiguity values is a correct value of the integer ambiguity at the time epoch based on the absolute pseudorange measurement and the carrier-based pseudorange measurement, thereby determining which of the candidate integer ambiguity values is the most likely integer ambiguity value to be the correct value; and
(d) determining that a cycle slip has occurred in response to the most likely integer ambiguity value at the time epoch being different from a value of the integer ambiguity at a preceding time epoch.
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15. An apparatus for determining geographic position based on pseudorange measurements, comprising:
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a receiver configured to receive navigation signals from a plurality of sources, wherein, for each navigation signal, said receiver generates an absolute pseudorange measurement and a carrier-based pseudorange measurement based on a carrier phase of the navigation signal, the carrier-based pseudorange measurement being offset from the absolute pseudorange by an integer ambiguity which is an integer number of carrier wavelengths; and
a processor configured to estimate, for each carrier-based pseudorange measurement, a probability that each of a plurality of candidate integer ambiguity values is a correct value of the integer ambiguity based on the absolute pseudorange measurement and the carrier-based pseudorange measurement, and selecting a most likely of the candidate integer ambiguity values as the value of the integer ambiguity, said processor estimating the pseudorange for each navigation signal based on the carrier-based pseudorange measurement and the value of the integer ambiguity corresponding to the navigation signal, and computing the geographic position of the apparatus from pseudoranges estimated from the navigation signals. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24)
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25. An apparatus for determining geographic position based on pseudorange measurements, comprising:
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means for receiving navigation signals from a plurality of sources generating an absolute pseudorange measurement and a carrier-based pseudorange measurement based on a carrier phase of each of the navigation signals, the carrier-based pseudorange measurement being offset from the absolute pseudorange by an integer ambiguity which is an integer number of carrier wavelengths;
means for estimating, for each carrier-based pseudorange measurement, a probability that each of a plurality of candidate integer ambiguity values is a correct value of the integer ambiguity based on the absolute pseudorange measurement and the carrier-based pseudorange measurement, and for selecting a most likely of the candidate integer ambiguity values as the value of the integer ambiguity; and
means for estimating the pseudorange for each navigation signal based on the carrier-based pseudorange measurement and the value of the integer ambiguity corresponding to the navigation signal, and for computing the geographic position of the apparatus from pseudoranges estimated from the navigation signals.
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Specification