Carrier-based differential-position determination using multi-frequency pseudolites
View Patent ↗Apparatus and methods for resolving integer ambiguities in position determination. An embodiment of the invention includes a reference system, augmented with multi-frequency pseudolites using a carrier phase differential GPS implementation, and a mobile system. In one embodiment, the components of the reference system includes one or more multi-frequency pseudolites, one or more multi-frequency reference receivers, a data link standing alone or built into the pseudolites, and the associated antennae for each of these elements. The components of the reference system may be stationary. The mobile system may include a multi-frequency receiver and its associated antennae. Because the mobile systems may passively receive information, an unlimited number of mobile systems may be included in any given embodiment of the invention. A multi-frequency pseudolite uses a single frequency source to synthesize all of the multiple carrier frequencies and all of the multiple base band signals modulated onto carrier frequencies for transmission.
1. A positioning system comprising a plurality of pseudolite transmitters and a receiver system:
each transmitter capable of transmitting a plurality of direct-sequence spread spectrum signals, each signal including a carrier frequency signal and a direct-sequence spreading code modulating said carrier signal at a code chipping rate; and
the receiver system capable of:
a) receiving a direct-sequence spread spectrum signal selected from said plurality of signals;
b) determining a plurality of measurements including:
a carrier phase measurement of each said carrier frequency signal; and a code phase measurement of each said spreading code; and
c) calculating a range between the transmitter and the receiver system from said measurements
wherein said range is determinable using a mathematical function of:
a first relationship between
a first integer wavelength corresponding to said first carrier phase measurement and
a first statistical property of said first code phase measurement, and a second relationship between
a second integer wavelength corresponding to said second carrier phase measurement and
a second statistical property of said second code phase measurement.
2. The positioning system of claim 1 , wherein said mathematical function is a product of said first relationship and said second relationship.
3. A transmittable signal plan for a ranging system based on electromagnetic radiation, the signal plan comprising:
a first carrier frequency signal;
a second carrier frequency signal;
a first direct-sequence spreading code modulating said first carrier signal at a first code chipping rate; and
a second direct sequence-spreading code modulating said second carrier signal at a second code chipping rate;
wherein a reception of said signal plan in one measurement period can be used to determine a plurality of measurements including:
a first carrier phase measurement of said first carrier frequency signal;
a second carrier phase measurement of said second carrier frequency signal;
a first code phase measurement of said first spreading code; and
a second code phase measurement of said second spreading code; and
wherein said range is determinable using a mathematical function of:
a first probabilistic relationship between a first integer wavelength corresponding to said first carrier phase measurement and a first statistical property of said first code phase measurement, and
a second probabilistic relationship between a second integer wavelength corresponding to said second carrier phase measurement and a second statistical property of said second code phase measurement.
4. The transmittable signal plan of claim 3 , wherein said mathematical function is a product of said first probabilistic relationship and said second probabilistic relationship.
5. The transmittable signal plan of claim 3 , wherein said first and second probabilistic relationship provides at least 50% probability that a difference between an actual range and said range estimate is accurate to within the lesser of a first half wavelength corresponding to said first carrier phase measurement and a second half wavelength corresponding to said second carrier phase measurement.
6. The transmittable signal plan of claim 3 , wherein said range is determinable with an accuracy to within a tolerance corresponding to a length of the shortest wavelength selected from:
a first wavelength corresponding to said first carrier phase measurement; and a second wavelength corresponding to said second carrier phase measurement
when said probabilistic relationship represents maximum likelihood outcome and is used to determine:
a first number of wavelengths corresponding to said first carrier phase measurement; and
a second number of wavelengths corresponding to said second carrier phase measurement.