Data processing: vehicles – navigation – and relative location – Navigation – Employing position determining equipment
Reexamination Certificate
1999-09-02
2001-10-30
Nguyen, Tan (Department: 3661)
Data processing: vehicles, navigation, and relative location
Navigation
Employing position determining equipment
C701S215000, C342S357490, C342S357490
Reexamination Certificate
active
06311127
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates to satellite navigation systems. More particularly, the present invention relates to satellite navigation systems which implement measurement quality monitoring and Fault Detection and Exclusion (FDE) to enhance accuracy and integrity of positioning for safety-critical applications.
BACKGROUND OF THE INVENTION
Global navigational satellite systems (GNSS) are known and include the global positioning system (GPS) and the Russian global orbiting navigational satellite system (GLONASS). GNSS-based navigational systems are used for navigation and positioning applications. In the GPS navigational system, GPS receivers receive satellite positioning signals from a set of up to 32 satellites deployed in 12-hour orbits about earth and dispersed in six orbital planes at an altitude of 10,900 nautical miles. Each GPS satellite continuously transmits two spread spectrum, L-band signals: an L
1
signal having a frequency f
L1
of 1575.42 MHz, and an L
2
signal having a frequency f
L2
of 1227.6 MHz. The L
1
signal from each satellite is modulated by two pseudo-random codes, the coarse acquisition (C/A) code and the P-code. The P-code is normally encrypted, with the encrypted version of the P-code referred to as the Y-code. The L
2
signal from each satellite is modulated by the Y-code. The C/A code is available for non-military uses, while the P-code (Y-code) is reserved for military uses.
GPS navigational systems determine positions by timing how long it takes the coded radio GPS signal to reach the receiver from a particular satellite (e.g., the travel time). The receiver generates a set of codes identical to those codes (e.g., the Y-code or the C/A-code) transmitted by the satellites. To calculate the travel time, the receiver determines how far it has to shift its own codes to match the codes transmitted by the satellites. The determined travel times for each satellite are multiplied by the speed of light to determine the distances from the satellites to the receiver. By receiving GPS signals from four or more satellites, a receiver unit can accurately determine its position in three dimensions (e.g., longitude, latitude, and altitude). A conventional GPS receiver typically utilizes the fourth satellite to accommodate a timing offset between the clocks in the receiver and the clocks in the satellites. Additional satellite measurements can be used to improve the position solution.
Safety-critical satellite navigation systems require highly accurate and reliable measurement information. In safety-of-life applications such as precision aircraft landing, the equipment must be designed to ensure that it is extremely unlikely that it provides misleading navigation data (i.e., the system must function with high integrity). Noise in the code ranging (pseudorange) measurements degrades accuracy and can cause disagreements between redundant navigation sources (false alarms). Common methods to reduce ranging measurement error, such as complementary filtering of code and carrier measurements (carrier smoothing), require continuous carrier tracking, which can be difficult to maintain in interference and jamming environments. Enhancements in integrity, accuracy and carrier continuity are needed in safety-critical applications.
SUMMARY OF THE INVENTION
Satellite navigation systems and receivers of the present invention include an antenna adapted to receive satellite signals transmitted from a plurality of satellites. Radio frequency circuitry coupled to the antenna is adapted to convert the satellite signals into intermediate signals. Multiple (two or more) signal processors coupled to the radio frequency circuitry are adapted to implement similar or identical signal processing algorithms on the received satellite signals to provide redundant ranging information (i.e., code and carrier measurements). One or more navigation processors coupled to the signal processors process the ranging information and provide positioning data outputs.
The navigation processor of the present invention implements novel smoothing filter functions that combine the redundant ranging data in a manner which enhances the positional accuracy as compared to conventional smoothing filters that do not process redundant information. In parallel, the navigation processor implements unique fault-detection filter functions on the redundant ranging information to detect and exclude poor-quality ranging measurements and to detect faults in the individual signal processors that would otherwise cause misleading information to be output by the navigation processor. The characteristic response of the fault-detection filter functions are matched to the response of the smoothing filter functions, ensuring that signal processing faults are detected and before the smoothed data exhibits excessive errors.
REFERENCES:
patent: 5999126 (1999-12-01), Ito
McCall Daryl L.
Stratton D. Alexander
Thuringer Daniel J.
Donnelly Arthur D.
Eppele Kyle
Jensen Nathan O.
Nguyen Tan
Rockwell Collins
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