GNSS ultra-short baseline heading determination system and method

• US 8,130,142 B2
• Filed: 09/21/2009
• Issued: 03/06/2012
• Est. Priority Date: 09/21/2009
• Status: Active Grant

• Current Assignee: Appareo Systems LLC (AGCO Corporation)
• Original Assignee: Appareo Systems LLC (AGCO Corporation)
• Inventors: Zietz, John M., Weinmann, Robert V., Allen, Robert M.
• Primary Examiner(s): LIU, HARRY K
• Application Number:
  US12/563,893
• Publication Number:
  US 20110068975A1
• Time in Patent Office: 897 Days
• Field of Search: 342/357.36
• US Class Current: 342/357.36
• CPC Class Codes: A61B 2018/206 the laser light passing along a liquid-filled conduit
• CPC Class Codes: G01C 21/165 combined with non-inertial navigation instruments
• CPC Class Codes: G01S 19/35 Constructional details or hardware or software details of the signal processing chain
• CPC Class Codes: G01S 19/55 Carrier phase ambiguity resolution; Floating ambiguity; LAMBDA [Least-squares AMBiguity Decorrelation Adjustment] method

Abstract

A heading determination system comprises an inertial measurement unit (IMU) coupled with at least two GNSS receivers, each receiver paired with and receiving signals from a corresponding GNSS antenna, wherein the GNSS antennas are separated by an ultra-short baseline. The heading determination system receives signals broadcast by a plurality of GNSS satellites and calculates the phase difference in the signal seen among the separate GNSS antennas. Using this phase difference information, derived from comparing the signals received from a plurality of GNSS satellites, along with attitude data generated by the IMU, the heading determination system calculates a highly-accurate heading solution. A method is provided for determining a heading of a system including an IMU coupled with at least two GNSS receivers, with each receiver being paired with and receiving signals from a corresponding GNSS antenna and the antennas being separated by an ultra-short baseline.

Claims

1. A heading determination system comprising:

an inertial measurement unit (IMU) adapted for detecting a magnitude and a direction of movement of the system about an axis of rotation and providing an output signal corresponding to said movement magnitude and direction;

a first GNSS receiver and a first GNSS antenna mounted on a first side of a mobile object;

a second GNSS receiver and a second GNSS antenna mounted on a second and opposite side of said mobile object;

wherein the baseline separation between the first GNSS antenna and the second GNSS antenna is variable and determined by the width and shape of the mobile object upon which it is mounted;

a means for calculating the baseline separation between the first GNSS antenna and the second GNSS antenna in real time; and

a processor connected to said IMU and said receivers, wherein the processor receives output data from the IMU and GNSS receivers and uses said output data in combination with the calculated baseline separation to calculate a heading of the heading determination system.

2. The heading determination system of claim 1, further comprising a data recorder, wherein the data recorder is capable of storing the data received by and calculated by the heading determination system for eventual retrieval, analysis and playback.

3. The heading determination system of claim 1, wherein the means for calculating the baseline separation is a plurality of accelerometers, wherein the acceleration due to gravity can be measured by the accelerometers and used to determine the current configuration and orientation of each component of the heading determination system.

4. The heading determination system of claim 1, wherein the heading determination system is in a fixed configuration mounted to a vehicle.

5. The heading determination system of claim 1, wherein said processor is configurable to receive and process signals from external sensors including, but not limited to, an outside air temperature (OAT) sensor, a rotor torque sensor as used on helicopters, pitot static sensors, and/or one or more operator switches.

6. The heading determination system of claim 1, wherein there are three major phases of defined USBL algorithms required to derive an accurate heading solution, including:

a preparation phase;

an analysis phase; and

a validation phase.

7. The heading determination system of claim 6 wherein the preparation phase comprises:

timing and synchronizing data acquired from the GNSS and IMU systems to eliminate time delays and synch data;

interpolating GNSS receiver signals based on timestamps of position recordings to allow for the data of one receiver to be interpolated off of a second receiver'"'"'s data;

selecting the best GNSS satellites for USBL calculations to allow for the highest quality position data using an algorithm and ranking system which uses factors such as satellite elevation, recent cycle slips, satellite health, signal-to-noise ratio, and other relevant satellite quality factors; and

determining the usability of the data obtained from the satellites based on the actual data received.

8. The heading determination system of claim 6 wherein the analysis phase comprises:

determining the USBL baseline length, either from hard-coded data or using pre-programmed algorithms based on the physical components allowing for a flexible USBL baseline length;

compensating for tilt effects using data received from the inertial measurement unit to determine the pitch and roll of the system and applying this information to positional equations for precise position determination;

resolving the integer ambiguity inherent in a USBL GNSS system with multiple antennas; and

determining the heading of the mobile entity using double difference phase measurements, baseline length, and satellite elevations and azimuths.

9. The method of claim 6 wherein the validation phase comprises:

comparing the new solution to historic data to check whether the determined heading is reasonable;

cross-comparing redundant data sources using other sources such as magnetic compasses or other secondary positioning systems; and

final validation of the solution.

10. A system for determining the heading of an entity, comprising:

an inertial measurement unit (IMU) adapted for detecting a magnitude and a direction of movement of the system about an axis of rotation and providing an output signal corresponding to said movement magnitude and direction;

at least two GNSS receivers each providing an output comprising GNSS ranging signals;

at least two GNSS antennas each attached to a respective GNSS receiver;

each GNSS antenna having a baseline separation from every other GNSS antenna that is no more than 0.5 meters;

a processor connected to said IMU and said receivers, wherein the processor receives output data from the IMU and GNSS receivers and uses said output data to calculate a heading of the heading determination system;

a data recorder, wherein the data recorder is capable of storing the data received by and calculated by the heading determination system for eventual retrieval, analysis and playback;

a three-phase process of defined USBL algorithms required to derive an accurate heading solution, including a preparation phase, an analysis phase, and a validation phase;

said preparation phase comprising;

a) timing and synchronizing data acquired from the GNSS and IMU systems to eliminate time delays and synch data;

b) interpolating GNSS receiver signals based on timestamps of position recordings to allow for the data of one receiver to be interpolated off of a second receiver'"'"'s data;

c) selecting the best GNSS satellites for USBL calculations to allow for the highest quality position data using an algorithm and ranking system which uses factors such as satellite elevation, recent cycle slips, satellite health, signal-to-noise ratio, and other relevant satellite quality factors; and

d) determining the usability of the data obtained from the satellites based on the actual data received;

said analysis phase comprising;

a) determining the USBL baseline length, either from hard-coded data or using pre-programmed algorithms based on the physical components allowing for a flexible USBL baseline length;

b) compensating for tilt effects using data received from the inertial measurement unit to determine the pitch and roll of the system and applying this information to positional equations for precise position determination;

c) resolving the integer ambiguity inhering in a USBL GNSS system with multiple antennas; and

d) determining the heading of the mobile entity using double difference phase measurements, baseline length, and satellite elevations and azimuths;

said validation phase comprising;

a) comparing the new solution to historic data to check whether the determined heading is reasonable;

b) cross-comparing redundant data sources using other sources such as magnetic compasses or other secondary positioning systems; and

c) final validation of the solution.

11. The heading determination system of claim 10, which is adapted for to be worn on a human head and includes:

a first GNSS receiver and a first GNSS antenna mounted on a first side of the head;

a second GNSS receiver and a second GNSS antenna mounted on a second and opposite side of the head;

the baseline separation between the first GNSS antenna and the second GNSS antenna being variable and determined by the width and shape of the head upon which it is being worn, but in no case more than 0.5 meters; and

wherein the means for calculating the baseline separation is a plurality of accelerometers, wherein the acceleration due to gravity can be measured by the accelerometers and used to determine the current configuration and orientation of each component of the heading determination system.

12. The heading determination system of claim 10, wherein the heading determination system is in a fixed configuration mounted to a vehicle.

13. A method for determining a navigational heading comprising the steps of:

placing at least two GNSS receivers on an object;

connecting a GNSS antenna to each GNSS receiver;

mounting each GNSS antenna to the object such that each GNSS antenna is separated from every other GNSS antenna by a distance not to exceed 0.5 meters, wherein the separation between GNSS antennas is variable and determined by the width and shape of the object upon which the GNSS antennas are mounted;

providing a means for calculating the baseline separation among the GNSS antennas in real time;

placing an inertial measurement unit (IMU) on the object; and

placing a processor on the object, wherein the processor calculates the difference in phase of a GNSS satellite signal as it was received by at least two GNSS receivers, wherein the processor combines the calculated phase difference and the calculated baseline separation with data received from the IMU to determine the heading of the object.

14. The method for determining a navigational heading of claim 13, wherein the object is selected from the group:

aircraft, airplane, helicopter, ground vehicle, automobile, robot, drone, equipment, weapon, tool or human being.

15. The method for determining a navigational heading of claim 13, wherein there are three major phases of defined USBL algorithms required to derive an accurate heading solution, including:

a preparation phase;

an analysis phase; and

a validation phase.

16. The method of claim 15 wherein the preparation phase comprises the additional steps of:

a first step of timing and synchronizing data acquired from the GNSS and IMU systems to eliminate time delays and synch data;

a second step of interpolating GNSS receiver signals based on timestamps of position recordings to allow for the data of one receiver to be interpolated off of a second receiver'"'"'s data;

a third step of selecting the best GNSS satellites for USBL calculations to allow for the highest quality position data using an algorithm and ranking system which uses factors such as satellite elevation, recent cycle slips, satellite health, signal-to-noise ratio, and other relevant satellite quality factors; and

a fourth step of determining the usability of the data obtained from the satellites based on the actual data received.

17. The method of claim 15 wherein the analysis phase comprises the additional steps of:

a first step of determining the USBL baseline length, either from hard-coded data or using pre-programmed algorithms based on the physical components allowing for a flexible USBL baseline length;

a second step of compensating for tilt effects using data received from the inertial measurement unit to determine the pitch and roll of the system and applying this information to positional equations for precise position determination;

a third step of resolving the integer ambiguity inhering in a USBL GNSS system with multiple antennas; and

a fourth step of determining the heading of the mobile entity using double difference phase measurements, baseline length, and satellite elevations and azimuths.

18. The method of claim 15 wherein the validation phase comprises the additional steps of:

a first step of comparing the new solution to historic data to check whether the determined heading is reasonable;

a second step of cross-comparing redundant data sources using other sources such as magnetic compasses or other secondary positioning systems; and

a third step of final validation of the solution.

19. A method for determining a navigational heading comprising the steps of:

placing at least two GNSS receivers on an object;

connecting a GNSS antenna to each GNSS receiver;

mounting each GNSS antenna to the object such that each GNSS antenna is separated from every other GNSS antenna by a distance not to exceed 0.5 meters;

placing an inertial measurement unit (IMU) on the object;

placing a processor on the object, wherein the processor calculates the difference in phase of a GNSS satellite signal as it was received by at least two GNSS receivers, wherein the processor combines the calculated phase difference with data received from the IMU to determine the heading of the object;

following three major phases of defined USBL algorithms required to derive an accurate heading solution, including a preparation phase, an analysis phase, and a validation phase;

said preparation further comprising a first step of timing and synchronizing data acquired from the GNSS and IMU systems to eliminate time delays and synch data, a second step of interpolating GNSS receiver signals based on timestamps of position recordings to allow for the data of one receiver to be interpolated off of a second receiver'"'"'s data, a third step of selecting the best GNSS satellites for USBL calculations to allow for the highest quality position data using an algorithm and ranking system which uses factors such as satellite elevation, recent cycle slips, satellite health, signal-to-noise ratio, and other relevant satellite quality factors, and a fourth step of determining the usability of the data obtained from the satellites based on the actual data received;

said analysis phase further comprising a first step of determining the USBL baseline length, either from hard-coded data or using pre-programmed algorithms based on the physical components allowing for a flexible USBL baseline length, a second step of compensating for tilt effects using data received from the inertial measurement unit to determine the pitch and roll of the system and applying this information to positional equations for precise position determination, a third step of resolving the integer ambiguity inhering in a USBL GNSS system with multiple antennas, and a fourth step of determining the heading of the mobile entity using double difference phase measurements, baseline length, and satellite elevations and azimuths; and

said validation phase further comprising a first step of comparing the new solution to historic data to check whether the determined heading is reasonable, a second step of cross-comparing redundant data sources using other sources such as magnetic compasses or other secondary positioning systems, and a third step of final validation of the solution.