Communications: directive radio wave systems and devices (e.g. – Directive – Including a satellite
Reexamination Certificate
1999-06-30
2001-01-30
Issing, Gregory C. (Department: 3662)
Communications: directive radio wave systems and devices (e.g.,
Directive
Including a satellite
C342S357490
Reexamination Certificate
active
06181274
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to radio navigation receivers, and in particular to satellite navigation receivers (e.g., a GPS receiver) for precise relative positioning in real time.
Satellite navigation receivers such as GPS and GLONASS are all-weather, worldwide, continuous coverage, satellite-based radio navigation systems. These receivers measure time delays and decode messages from satellites within view of the receivers to determine the information necessary to complete position and time bias calculations. For a detailed discussion see “
The Global Positioning System and Inertial Navigation
”, J. Farrell and M. Barth, McGraw-Hill, 1999.
The quality of the position estimates available to the users of GPS/GLONASS can vary widely. The position errors for different users can range from centimeters to tens of meters. The performance specifications for civil use of the GPS system are given in terms of 95th and 99.99th percentile points of the error in the estimate of all users (i.e., civilian and military). These specifications for the horizontal error are 100 meters and 300 meters respectively for civilian use. Additional resources are required to obtain position estimates of better quality. Real-time position estimates with errors no worse than a few meters can be obtained if the user subscribes to a commercial service broadcasting differential corrections to be applied to the measurements. Actually, in coastal areas such corrections are available for free from the U.S. Coast Guard, which broadcasts them on maritime radio beacons. All the user needs is a radio beacon receiver and a differential-ready GPS receiver.
To get position estimates with centimeter(cm)-level accuracy requires a different approach. Until now, requirements for such accuracy have typically been limited to the geodetic community (e.g., studying plate tectonics), since achieving this level of accuracy has generally required minutes or hours of computation. As is known, GPS carrier phase measurements can provide cm-level positioning accuracy if the integer ambiguities are resolved correctly, and the process of integer ambiguity resolution is often referred to as initialization.
The approach commonly used for initialization (static and kinematic), is to filter measurements from multiple epochs until the floating estimates of the integer ambiguities appear to converge to integer values. With dual-frequency GPS measurements, the wide-lane formulation accelerates this process, but it still takes several minutes. The approach offers robustness in terms of overcoming measurement errors over short stretches. However, this approach is impractical for navigation where a user is unlikely to have the luxury of waiting for minutes for the integer ambiguity to be resolved.
Therefore, there is a need for system that can provide a robust navigation receiver capable of providing centimeter-level accuracy in real-time.
SUMMARY OF THE PRESENT INVENTION
Briefly, according to the present invention, a navigation receiver system provides real-time precise (cm-level) relative positioning in cooperation with an associated carrier phase receiver. The navigation receiver system and the associated carrier phase receiver both sample signals during a single epoch, and the associated carrier phase receiver processes the received signals to provide and transmit first carrier phase measurement data to the navigation receiver system. The navigation receiver system comprises a data link receiver that receives the first carrier phase measurement data from the associated carrier phase receiver, and a carrier phase receiver that receives carrier phase signals during the sampling epoch, and processes the carrier phase signals to provide a second carrier phase measurement data. The navigation system receiver also includes a processing unit that receives the first carrier phase measurement data and the second carrier phase measurement data and computes carrier phase difference measurements. The processing unit applies a local-minima search (LMS) technique to the carrier phase difference measurements to resolve carrier phase integer ambiguities within a subspace of local minima, wherein the resolved carrier phase integers are subsequently used to determine a precise relative position of the navigation receiver system with respect to the associated carrier phase receiver.
According another aspect of the present invention, a high accuracy navigation system includes a navigation receiver system and an associated carrier phase receiver, wherein the navigation system receiver provides real-time precise relative positioning in cooperation with the associated carrier phase receiver. The navigation receiver system and the associated carrier phase receiver both sample signals during a single epoch, and the associated carrier phase receiver processes the received signals to provide and transmit first carrier phase measurement data. The navigation receiver system comprises a data link receiver that receives the first carrier phase measurement data from the associated carrier phase receiver, and a carrier phase receiver that receives carrier phase signals during the sampling epoch, and processes the carrier phase signals to provide a second carrier phase measurement data. The navigation system receiver also includes a processing unit that receives the first carrier phase measurement data and the second carrier phase measurement data and computes carrier phase difference measurements. The processing unit applies a local-minima search technique to the carrier phase difference measurements to resolve carrier phase integer ambiguities within a subspace of local minima, wherein the resolved carrier phase integers are subsequently used to determine a precise relative position of the navigation receiver system with respect to the associated carrier phase receiver.
The processing unit reads the two sets of carrier phase measurements, forms difference combinations, uses a numerical method to find integer solutions that are local minima of a cost function associated with the difference combinations. The processing unit compares the cost function value for each of the local minima and selects the one with the smallest value (i.e., a global minimum), and uses the resulting resolved integers in conjunction with the two sets of carrier phase measurements to compute the relative position.
The local-minima search (LMS) technique is a deterministic method for resolving carrier phase ambiguities. The geometry of the carrier phase ambiguity resolution problem leads to the realization that the subspace of integer solutions that are local minima of a least squares cost function comprise a three dimensional subspace of the full ambiguity space. The combination of an analytical expression for the subspace of local minima, and a numerical method for computing elements of that subspace, results in an efficient, deterministic method for resolving carrier phase ambiguities.
Relative position is the position of the navigation receiver system relative to the associated carrier phase receiver. If the precise coordinates of the associated carrier receiver are known, then the precise coordinates of the navigation receiver system can also be determined. However, the associated carrier receiver may also be mobile and therefore the relative position is from a mobile position.
Advantageously, the present invention provides high precision, real-time position data from a signal time epoch. That is, the present invention resolves the integer ambiguities in carrier phase measurements with a single snap shot of the measurements. In addition, the system recovers very quickly following signal interruption.
These and other objects, features and advantages of the present invention will become more apparent in light of the following detailed description of preferred embodiments thereof, as illustrated in the accompanying drawings.
REFERENCES:
patent: 5442363 (1995-08-01), Remondi
patent: 5991691 (1999-11-01), Johnson
Park, Chansik et al, “Efficient Technique To Fix GPS Carr
Burke Brian P.
Misra Pratap N.
Pratt Michael M.
Issing Gregory C.
Massachusetts Institute of Technology
Samuels, Gauthier & Stevens, LLP.
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