Feed-forward control of free space optical communication system based on inertial measurement unit
Embodiments relate to a free space optical (FSO) communications system with a feed-forward control path. A data-encoded FSO beam is transmitted from a local terminal to a remote terminal. The local terminal directs a propagation direction of the FSO beam by a beam steering unit. To reduce pointing errors between the terminals, the FSO communications system includes a feed-forward control path. The control path includes an inertial measurement unit (IMU) that outputs motion data indicative of motion of the local terminal, for example if the local terminal is mounted to a tower that sways. The control path also includes a controller that receives the motion data from the IMU and generates feed-forward control signals for the beam steering unit. The control signals compensate for an effect of the motion of the local terminal on the propagation direction of the FSO beam.
1. A free space optical (FSO) communications system comprising:
an FSO communications terminal comprising a beam steering unit that adjusts a propagation direction of a data-encoded optical beam towards a remote FSO communications terminal; and
a feed-forward control path comprising:
an inertial measurement unit (IMU) that outputs motion data that is indicative of motion of the FSO communications terminal; and
a controller that receives the motion data from the IMU and generates and provides feed-forward control signals to the beam steering unit, wherein the feed-forward control signals compensate for an effect of the motion of the FSO communications terminal on the propagation direction of the data-encoded optical beam,
wherein, responsive to the controller receiving a threshold amount of motion data, the controller generates the feed-forward control signals by fitting the threshold amount of motion data to a motion model.
2. The FSO communications system of claim 1 , wherein the IMU measures rotation of the FSO communications terminal about two axes.
3. The FSO communications system of claim 1 , wherein the IMU measures translation of the FSO communications terminal along two dimensions.
4. The FSO communications system of claim 1 , wherein the IMU comprises one or more cameras and a processor that determines motion data based on video data from the one or more cameras.
5. The FSO communications system of claim 1 , wherein the IMU comprises two gyroscopes and/or accelerometers and/or cameras that measure rates and/or accelerations and/or displacement angles along two dimensions.
6. The FSO communications system of claim 1 , wherein the controller is a digital controller.
7. The FSO communications system of claim 1 , wherein the controller is an analog controller.
8. The FSO communications system of claim 1 , wherein the controller is a stateless controller.
9. The FSO communications system of claim 1 , wherein the motion model is a parameterized motion model.
10. The FSO communications system of claim 1 , wherein the controller is an analog circuit or analog computer.
11. The FSO communications system of claim 1 , further comprising:
a feed-back control path from the remote FSO communications terminal to the beam steering unit, the feed-back control path providing feed-back control signals to the beam steering unit based on a strength of the data-encoded optical beam received at the remote FSO communications terminal, wherein the motion data and the feed-back control signals are weighted based on availability and accuracy.
12. The FSO communications system of claim 1 , wherein the FSO communications terminal receives a data-encoded optical beam from the remote FSO communications terminal, the received data-encoded optical beam encoding motion data from an IMU of the remote FSO communications terminal; and the controller further generates and provides control signals to the beam steering unit based on the motion data encoded in the received optical beam.
13. The FSO communications system of claim 1 , wherein the beam steering unit includes a steering mirror.
14. The FSO communications system of claim 1 , wherein the FSO communications terminal and the IMU are mounted to a stationary but flexible object and the motion data is indicative of swaying of the object.
15. The FSO communications system of claim 1 , wherein the FSO communications terminal and the IMU are mounted to a vehicle and the motion data is indicative of movement of the vehicle.
16. The FSO communications system of claim 1 , wherein the IMU is mounted outside the FSO communications terminal.
17. The FSO communications system of claim 1 , wherein the IMU is mounted inside the FSO communications terminal.
18. The FSO communications system of claim 1 , wherein a controller generates and provides feed-forward control signals to the beam steering unit at least 100 times per second.
19. A free space optical (FSO) communications system comprising:
an FSO communications terminal comprising a beam steering unit that adjusts a propagation direction of a data-encoded optical beam towards a remote FSO communications terminal;
a feed-forward control path comprising:
an inertial measurement unit (IMU) that outputs motion data that is indicative of motion of the FSO communications terminal; and
a controller that receives the motion data from the IMU and generates and provides feed-forward control signals to the beam steering unit, wherein the feed-forward control signals compensate for an effect of the motion of the FSO communications terminal on the propagation direction of the data-encoded optical beam, and
a feed-back control path from the remote FSO communications terminal to the beam steering unit, the feed-back control path providing feed-back control signals to the beam steering unit based on a strength of the data-encoded optical beam received at the remote FSO communications terminal, wherein a bandwidth of the feed-forward control path is at least twice a bandwidth of the feed-back control path.