Global navigation satellite system beam based attitude determination
Disclosed is a technique to estimate at least a portion of an attitude, such as an azimuth angle from true North, based on beam angles from a controlled reception pattern antenna (CRPA) to space vehicle locations. Other attitude information such as roll and/or pitch can also be estimated. The at least portion of the attitude can be provided with or without an additional sensor, such as a compass or magnetometer, an inertial measurement unit (IMU), or the like. An attitude estimate can be useful because oftentimes the attitude of an object can vary from its track or velocity direction.
1. An apparatus configured to determine at least one of a heading, roll, or pitch of an attitude of an object, the apparatus comprising:
a plurality of radio frequency (RF) downconverters configured to receive controlled reception pattern antenna (CRPA) signals and to downconvert the received signals, wherein the CRPA is attached to the object for which the heading, roll, or pitch is to be determined;
a beamformer configured to generate one or more antenna patterns for downconverted received signals corresponding to signals received by the CRPA, wherein the beamformer is configured to use downcoverted received signals in generating the one or more antenna patterns;
a processor configured:
to associate instances of observed signal strength of signals at various observed beam angles of the CRPA with physical locations of a plurality of space vehicles, wherein the plurality of space vehicles comprises sources of the signals; and
to determine the at least one of the heading, roll, or pitch of the object based at least partly on an orientation of the object with respect to the observed beam angles.
2. The apparatus of claim 1 , wherein the processor is configured to determine heading, roll, and pitch of the object to which the CRPA is attached, based at least partly on the orientation of the object with respect to the observed beam angles.
3. The apparatus of claim 1 , wherein the processor is configured to determine the heading of the object, to which the CRPA is attached, without use of a compass, magnetometer, or inertial measurement unit.
4. The apparatus of claim 1 , wherein the processor is configured to determine if a spoofer is present and to filter out directions to the spoofer from instances of observed signal strength at corresponding beam angles.
5. The apparatus of claim 1 , the apparatus further comprising:
a plurality of analog-to-digital converters (ADCs) configured to receive the downconverted received signals and to generate digital downconverted received signals;
wherein the beamformer comprises a digital beamformer configured to combine digital downconverted received signals in generating the one or more antenna patterns.
6. The apparatus of claim 1 , wherein the CRPA signals are received from between 3 and 7 antenna elements.
7. The apparatus of claim 1 , wherein the processor is further configured to determine the orientation of the object by conversion of the orientation from a first reference frame to a second reference frame, wherein the first reference frame is relative to beamforming angles and the second reference frame is global.
8. The apparatus of claim 1 , wherein the CRPA comprises a plurality of elements, wherein for a given CRPA element the apparatus is configured to a generate a digital IF signal downconverted from an L1 band and to a generate a digital IF signal downconverted from an L2 band.
9. The apparatus of claim 1 , wherein the observed signal strength is based on at least on a carrier to noise ratio versus antenna direction.
10. An electronically-implemented method of determining at least one of a heading, roll, or pitch of an attitude of an object, the method comprising:
downconverting received controlled reception pattern antenna (CRPA) radio frequency (RF) signals to generate downconverted received signals, wherein the CRPA is attached to the object for which the heading, roll, or pitch is to be determined;
generating, using a beamformer, one or more antenna patterns for downconverted received signals corresponding to signals received by the CRPA;
associating instances of observed signal strength of signals at various observed beam angles of the CRPA with physical locations of a plurality of space vehicles, wherein the plurality of space vehicles comprise sources of the signals; and
determining the at least one of the heading, roll, or pitch of the object based at least partly on an orientation of the object with respect to the observed beam angles.
11. The method of claim 10 , the method further comprising observing instances of radio frequency (RF) signal strength relative to a line of sight of a main lobe of an antenna pattern of the CRPA, wherein the main lobe is generated by the beamformer.
12. The method of claim 10 , wherein generating, using the beamformer, one or more antenna patterns for downconverted received signals corresponding to signals received by the CRPA, further comprises generating a main lobe of the one or more antenna patterns using a combination of downconverted received signals.
13. The method of claim 10 , the method further comprising:
electronically beam steering the CRPA in a plurality of beam angles to perform surveying;
observing signal strength for the plurality of steered beam angles; and
storing indications of the signal strength for the plurality of steered beam angles in non-transitory computer readable memory.
14. The method of claim 10 , the method further comprising:
determining a presence of a spoofer; and
filtering out directions to the spoofer from instances of observed signal strength at corresponding beam angles.
15. The method of claim 10 , wherein determining the at least one of the heading, roll, or pitch of the object based at least partly on the orientation of the object with respect to the observed beam angles further comprises determining heading, roll, and pitch of the object to which the CRPA is attached, based at least partly on the orientation of the object with respect to the observed beam angles.
16. The method of claim 10 , wherein determining the at least one of the heading, roll, or pitch of the object further comprises determining the heading of the object, to which the CRPA is attached, without use of a compass, magnetometer, or inertial measurement unit.
17. The method of claim 10 , wherein determining the orientation of the object further comprises conversion of the orientation from a first reference frame to a second reference frame.
18. The method of claim 10 , the method further comprising using global navigation satellite system (GNSS) data to calibrate drift of an inertial measurement unit.
19. The method of claim 10 , the method further comprising generating a position, velocity, and time (PVT) output relating to position, velocity, and time of the object using signals received via a nulled path.
20. The method of claim 10 , further comprising performing the method in a global positioning system (GPS) receiver.