Attitude determination utilizing an inertial measurement unit and a plurality of satellite transmitters

Claim 3

The method of claim 1 wherein the phase function is a double-differenced phase and the range function is a double-differenced range, a double-differenced phase being the difference in the single-differenced phases for two satellite transmitters, a single-differenced phase for a satellite transmitter being the difference in phase of the signals received from the satellite transmitter at two antennas, a double-differenced range being the difference in the single-differenced ranges for the satellite transmitters, a single-differenced range for a satellite transmitter being the difference in ranges of the satellite transmitter to two antennas.

Claim 4

The method of claim 1 wherein the first set of one or more quality requirements is comprised of: the quality measure for the candidate heading is greater than a threshold value.

Claim 5

The method of claim 1 wherein the quality measure is the reciprocal of the sum of the squares of range function residuals over all satellite transmitter groups, a range function residual being the difference in values of the computed range function and the measured range function.

Claim 6

The method of claim 1 further comprising the following steps: eliminating particular candidate headings from further consideration under certain conditions, the conditions being that a second set of one or more quality requirements is specified and the refined headings associated with the particular candidate headings fail to satisfy the second set of quality requirements; discarding the data associated with a candidate heading for prior method intervals under certain conditions, the conditions being that a third set of one or more quality requirements is specified and the refined headings associated with the candidate heading fail to satisfy the third set of quality requirements; declaring a candidate heading associated with a refined heading to be the correct candidate heading under certain conditions, the conditions being that a fourth set of one or more quality requirements is specified and the refined heading satisfies the fourth set of quality requirements, the range function residuals being made available to the Kalman process, a range function residual being the difference in values of a computed range function and the corresponding measured range function associated with the refined heading associated with the correct candidate heading.

Claim 7

The method of claim 5 wherein the second set of one or more quality requirements is comprised of: the quality measure for a refined heading is greater than a threshold value.

Claim 8

The method of claim 5 wherein the third set of one or more quality requirements is comprised of: the quality measure for a refined heading for a method interval is greater than a threshold value.

Claim 9

The method of claim 5 wherein the third set of one or more quality requirements is comprised of: the values of the integer function for the candidate heading associated with a refined heading are the same for the present and previous method intervals.

Claim 10

The method of claim 5 wherein the third set of one or more quality requirements is comprised of: the ratio of the smaller value to the larger value of a quality measure for refined headings associated with the same candidate heading for present and previous method intervals is greater than a threshold value.

Claim 11

The method of claim 5 wherein the third set of one or more quality requirements is comprised of: the difference between the IMU heading change and a refined heading change from the previous method interval to the present method interval is less than a threshold value.

Claim 12

The method of claim 5 wherein the third set of one or more quality requirements is comprised of: the difference in refined headings associated with the same candidate heading for present and previous method intervals is less than a threshold value.

Claim 13

The method of claim 5 wherein the third set of one or more quality requirements is comprised of: the values of a quality measure for refined headings associated with the same candidate heading for present and previous method intervals are greater than a threshold value.

Claim 14

The method of claim 5 wherein the fourth set of one or more quality requirements is comprised of: the quality measure of each of the refined headings associated with the correct candiate heading for one or more specified evaluation intervals is the highest of all refined headings for the same evaluation interval.

Claim 15

The method of claim 5 wherein the fourth set of one or more quality requirements is comprised of: the quality measure of each of the refined headings associated with the correct candidate heading for one or more specified evaluation intervals is greater than a threshold value.

Claim 16

The method of claim 5 wherein the fourth set of one or more quality requirements is comprised of: the quality measure of each of the refined headings associated with the correct candidate heading for one or more specified evaluation intervals having the second-highest quality measures is less than a threshold value.

Claim 17

The method of claim 5 wherein the fourth set of one or more quality requirements is comprised of: the number of degrees of freedom accumulated over a specified number of method intervals is greater than a threshold value.

Claim 18

The method of claim 5 wherein the fourth set of one or more quality requirements is comprised of: for the correct candidate heading, the difference between the change in each of the associated refined headings for one or more specified evaluation intervals from the previous method interval to the present method interval and the corresponding IMU heading change is less than a threshold value.

Claim 19

The method of claim 5 wherein the fourth set of one or more quality requirement is comprised of: the ratio of the smaller to the larger of the quality measures of the refined headings associated with the correct candidate heading for evaluation intervals of different lengths is greater than a threshold value.

Claim 20

The method of claim 5 wherein the fourth set of one or more quality requirement is comprised of: the change of each of the refined headings associated with the correct candidate heading for one or more specified evaluation intervals from the previous method interval to the present method interval is less than a threshold value.

Claim 21

Apparatus for practicing the method of claim 1.

Claim 22

Apparatus for practicing the method of claim 5.

Claim 23

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: 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.

Claim 24

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: 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.

Claim 25

The apparatus of claim 22 wherein the phase function is a double-differenced phase and the range function is a double-differenced range, a double-differenced phase being the difference in the single-differenced phases for two satellite transmitters, a single-differenced phase for a satellite transmitter being the difference in phase of the signals received from the satellite transmitter at two antennas, a double-differenced range being the difference in the single-differenced ranges for the satellite transmitters, a single-differenced range for a satellite transmitter being the difference in ranges of the satellite transmitter to two antennas.

Claim 26

The apparatus of claim 22 wherein the first set of one or more quality requirements is comprised of: the quality measure for the candidate heading is greater than a threshold value.

Claim 27

The apparatus of claim 22 wherein the quality measure is the reciprocal of the sum of the squares of range function residuals over all satellite transmitter groups, a range function residual being the difference in values of the computed range function and the measured range function.

Claim 28

The apparatus of claim 22 further comprising the following steps: a means for eliminating particular candidate headings from further consideration under certain conditions, the conditions being that a second set of one or more quality requirements is specified and the refined headings associated with the particular candidate headings fail to satisfy the second set of quality requirements; a means for discarding the data associated with a candidate heading for prior method intervals under certain conditions, the conditions being that a third set of one or more quality requirements is specified and the refined headings associated with the candidate heading fail to satisfy the third set of quality requirements; a means for declaring a candidate heading associated with a refined heading to be the correct candidate heading under certain conditions, the conditions being that a fourth set of one or more quality requirements is specified and the refined heading satisfies the fourth set of quality requirements, the range function residuals being made available to the Kalman process, a range function residual being the difference in values of a computed range function and the corresponding measured range function associated with the refined heading associated with the correct candidate heading.

Claim 29

The apparatus of claim 26 wherein the second set of one or more quality requirements is comprised of: the quality measure for a refined heading is greater than a threshold value.

Claim 30

The apparatus of claim 26 wherein the third set of one or more quality requirements is comprised of: the quality measure for a refined heading for a method interval is greater than a threshold value.

Claim 31

The apparatus of claim 26 wherein the third set of one or more quality requirements is comprised of: the values of the integer function for the candidate heading associated with a refined heading are the same for the present and previous method intervals.

Claim 32

The apparatus of claim 26 wherein the third set of one or more quality requirements is comprised of: the ratio of the smaller value to the larger value of a quality measure for refined headings associated with the same candidate heading for present and previous method intervals is greater than a threshold value.

Claim 33

The apparatus of claim 26 wherein the third set of one or more quality requirements is comprised of: the difference between the IMU heading change and a refined heading change from the previous method interval to the present method interval is less than a threshold value.

Claim 34

The apparatus of claim 26 wherein the third set of one or more quality requirements is comprised of: the difference in refined headings associated with the same candidate heading for present and previous method intervals is less than a threshold value.

Claim 35

The apparatus of claim 26 wherein the third set of one or more quality requirements is comprised of: the values of a quality measure for refined headings associated with the same candidate heading for present and previous method intervals are greater than a threshold value.

Claim 36

The apparatus of claim 26 wherein the fourth set of one or more quality requirements is comprised of: the quality measure of each of the refined headings associated with the correct candiate heading for one or more specified evaluation intervals is the highest of all refined headings for the same evaluation interval.

Claim 37

The apparatus of claim 26 wherein the fourth set of one or more quality requirements is comprised of: the quality measure of each of the refined headings associated with the correct candidate heading for one or more specified evaluation intervals is greater than a threshold value.

Claim 38

The apparatus of claim 26 wherein the fourth set of one or more quality requirements is comprised of: the quality measure of each of the refined headings associated with the correct candidate heading for one or more specified evaluation intervals having the second-highest quality measures is less than a threshold value.

Claim 39

The apparatus of claim 26 wherein the fourth set of one or more quality requirements is comprised of: the number of degrees of freedom accumulated over a specified number of method intervals is greater than a threshold value.

Claim 40

The apparatus of claim 26 wherein the fourth set of one or more quality requirements is comprised of: for the correct candidate heading, the difference between the change in each of the associated refined headings for one or more specified evaluation intervals from the previous method interval to the present method interval and the corresponding IMU heading change is less than a threshold value.

Claim 41

The apparatus of claim 26 wherein the fourth set of one or more quality requirement is comprised of: the ratio of the smaller to the larger of the quality measures of the refined headings associated with the correct candidate heading for evaluation intervals of different lengths is greater than a threshold value.

Claim 42

The apparatus of claim 26 wherein the fourth set of one or more quality requirement is comprised of: the change of each of the refined headings associated with the correct candidate heading for one or more specified evaluation intervals from the previous method interval to the present method interval is less than a threshold value.