Attitude determination utilizing an inertial measurement unit and a plurality of satellite transmitters
First Claim
1. A method for obtaining observables for input to a Kalman filter process which determines the roll, pitch, and heading of a platform, the method utilizing an inertial measurement unit (IMU) attached to the platform and an associated processor, a plurality of signal receiving antennas attached to the platform, and a plurality of satellite transmitters, the platform having a reference point to which the IMU is referenced, the antennas having known locations relative to the platform reference point, the method being repeatedly executed at time intervals called method intervals, the Kalman filter process supplying roll, pitch, and heading corrections to the IMU and its associated processor at time intervals called Kalman filter intervals, a Kalman filter interval being a multiple of the method interval, the method comprising the following steps:
- determining the value of a phase function for each of a plurality of satellite transmitter groups, a satellite transmitter group consisting of one or more satellite transmitters, a phase function being a function of the phases of the signals received from the satellite transmitters in a satellite transmitter group at the plurality of antennas;
obtaining pitch, roll, and heading of the platform from the IMU and its associated processor, the heading being called the IMU heading;
determining the value of a computed range function for each satellite transmitter group and for each of a plurality of candidate headings, a range function being a function of the ranges of the satellite transmitters in a satellite transmitter group to the plurality of antennas, the ranges for the computed range function being determined from ranges calculated from the locations of the satellite transmitters, the location of the platform reference point, the locations of the antennas relative to the platform reference point, the pitch and roll of the platform, and a candidate heading, the plurality of candidate headings spanning the range of headings from the IMU heading minus a first value to the IMU heading plus a second value;
determining the value of an integer function for each satellite transmitter group and for each candidate heading, the integer function being the difference in the computed range function and the phase function rounded to the nearest integer;
determining the value of a measured range function for each satellite-transmitter group and for each candidate heading, a measured range function being the sum of the phase function and the integer function;
eliminating candidate headings from further consideration under certain conditions, the conditions being that a first set of one or more quality requirements is specified and the candidate headings fail to satisfy the first set of quality requirements;
determining a refined candidate heading for each of one or more evaluation intervals for each of the remaining candidate headings utilizing the values of the measured range function for the satellite transmitter groups obtained during each of the one or more evaluation intervals, an evaluation interval including the present method interval and zero or more prior method intervals, a refined candidate heading being the heading for which a quality measure is highest.
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Abstract
The invention is a method for obtaining observables for input to a Kalman filter process which determines the attitude (roll, pitch, and heading) of a platform. The invention utilizes an inertial measurement unit (IMU) attached to the platform and an associated processor, a plurality of signal receiving antennas attached to the platform, and a plurality of satellite transmitters. The heading of the platform as determined by the IMU and its associated processor by themselves can be significantly in error. A comparison of the values of an attitude-sensitive function of the ranges from the platform antennas to different groupings of satellite transmitters obtained first by using IMU data and second by using the measured phases of the satellite-transmitter signals received at the platform antennas, a very accurate value for the range function is obtained. This accurate value of the range function is used in a Kalman filter process to obtain very accurate values for platform attitude.
109 Citations
40 Claims
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1. A method for obtaining observables for input to a Kalman filter process which determines the roll, pitch, and heading of a platform, the method utilizing an inertial measurement unit (IMU) attached to the platform and an associated processor, a plurality of signal receiving antennas attached to the platform, and a plurality of satellite transmitters, the platform having a reference point to which the IMU is referenced, the antennas having known locations relative to the platform reference point, the method being repeatedly executed at time intervals called method intervals, the Kalman filter process supplying roll, pitch, and heading corrections to the IMU and its associated processor at time intervals called Kalman filter intervals, a Kalman filter interval being a multiple of the method interval, the method comprising the following steps:
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determining the value of a phase function for each of a plurality of satellite transmitter groups, a satellite transmitter group consisting of one or more satellite transmitters, a phase function being a function of the phases of the signals received from the satellite transmitters in a satellite transmitter group at the plurality of antennas; obtaining pitch, roll, and heading of the platform from the IMU and its associated processor, the heading being called the IMU heading; determining the value of a computed range function for each satellite transmitter group and for each of a plurality of candidate headings, a range function being a function of the ranges of the satellite transmitters in a satellite transmitter group to the plurality of antennas, the ranges for the computed range function being determined from ranges calculated from the locations of the satellite transmitters, the location of the platform reference point, the locations of the antennas relative to the platform reference point, the pitch and roll of the platform, and a candidate heading, the plurality of candidate headings spanning the range of headings from the IMU heading minus a first value to the IMU heading plus a second value; determining the value of an integer function for each satellite transmitter group and for each candidate heading, the integer function being the difference in the computed range function and the phase function rounded to the nearest integer; determining the value of a measured range function for each satellite-transmitter group and for each candidate heading, a measured range function being the sum of the phase function and the integer function; eliminating candidate headings from further consideration under certain conditions, the conditions being that a first set of one or more quality requirements is specified and the candidate headings fail to satisfy the first set of quality requirements; determining a refined candidate heading for each of one or more evaluation intervals for each of the remaining candidate headings utilizing the values of the measured range function for the satellite transmitter groups obtained during each of the one or more evaluation intervals, an evaluation interval including the present method interval and zero or more prior method intervals, a refined candidate heading being the heading for which a quality measure is highest. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21)
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22. Apparatus for obtaining observables for input to a Kalman filter process which determines the roll, pitch, and heading of a platform, the method utilizing an inertial measurement unit (IMU) attached to the platform and an associated processor, a plurality of signal receiving antennas attached to the platform, and a plurality of satellite transmitters, the platform having a reference point to which the IMU is referenced, the antennas having known locations relative to the platform reference point, the method being repeatedly executed at time intervals called method intervals, the Kalman filter process supplying roll, pitch, and heading corrections to the IMU and its associated processor at time intervals called Kalman filter intervals, a Kalman filter interval being a multiple of the method interval, the apparatus comprising:
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a means for determining the value of a phase function for each of a plurality of satellite transmitter groups, a satellite transmitter group consisting of one or more satellite transmitters, a phase function being a function of the phases of the signals received from the satellite transmitters in a satellite transmitter group at the plurality of antennas; a means for obtaining pitch, roll, and heading of the platform from the IMU and its associated processor, the heading being called the IMU heading; a processor for determining the value of a computed range function for each satellite transmitter group and for each of a plurality of candidate headings, a range function being a function of the ranges of the satellite transmitters in a satellite transmitter group to the plurality of antennas, the ranges for the computed range function being determined from ranges calculated from the locations of the satellite transmitters, the location of the platform reference point, the locations of the antennas relative to the platform reference point, the pitch and roll of the platform, and a candidate heading, the plurality of candidate headings spanning the range of headings from the IMU heading minus a first value to the IMU heading plus a second value; a means for determining the value of an integer function for each satellite transmitter group and for each candidate heading, the integer function being the difference in the computed range function and the phase function rounded to the nearest integer; a means for determining the value of a measured range function for each satellite transmitter group and for each candidate heading, a measured range function being the sum of the phase function and the integer function; a means for eliminating candidate headings from further consideration under certain conditions, the conditions being that a first set of one or more quality requirements is specified and the candidate headings fail to satisfy the first set of quality requirements; a means for determining a refined candidate heading for each of one or more evaluation intervals for each of the remaining candidate headings utilizing the values of the measured range function for the satellite transmitter groups obtained during each of the one or more evaluation intervals, an evaluation interval including the present method interval and zero or more prior method intervals, a refined candidate heading being the heading for which a quality measure is highest. - View Dependent Claims (23, 24, 25, 26, 27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38, 39, 40)
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Specification