Method and system for enhanced velocity resolution and signal to noise ratio in optical phase-encoded range detection
An autonomous vehicle control system may include one or more processors configured to receive an electrical signal generated based on a returned optical signal that is reflected from an object. The one or more processors may determine a Doppler frequency shift of the returned optical signal over a first duration of the electrical signal. The one or more processors may generate a corrected electrical signal based on the Doppler frequency shift. The one or more processors may determine a range to the object based on the corrected electrical signal over a second duration that is shorter than the first duration. The one or more processors may control at least one of a steering system or a braking system based on the range.
1. An autonomous vehicle control system comprising: one or more processors; and one or more computer-readable storage mediums storing instructions which, when executed by the one or more processors, cause the one or more processors to:
receive an electrical signal generated based on a returned optical signal that is reflected from an object;
determine a Doppler frequency shift of the returned optical signal over a first duration of the electrical signal;
generate a corrected electrical signal based on the Doppler frequency shift;
determine a range to the object based on the corrected electrical signal over a second duration that is shorter than the first duration; and
control at least one of a steering system or a braking system based on the range.
2. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
generate a first optical signal by modulating a code that indicates a sequence of phases for a phase encoded signal with reference to an optical signal; and
transmit the first optical signal to the object.
3. The autonomous vehicle control system as recited in claim 2 , wherein the first duration is an integer multiple greater than 1 of a duration of the code.
4. The autonomous vehicle control system as recited in claim 2 , wherein the second duration is equal to or substantially equal to a duration of the code.
5. The autonomous vehicle control system as recited in claim 2 , wherein the one or more processors are further configured to:
determine the range to the object based on a cross correlation, over the second duration, between the corrected electrical signal and a radio frequency (RF) signal that is associated with the first optical signal.
6. The autonomous vehicle control system as recited in claim 5 , wherein the one or more processors are further configured to:
determine the cross correlation, over the second duration, between (i) a first Fourier transform of the RF signal that is associated with the first optical signal and (ii) a second Fourier transform of the corrected electrical signal.
7. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
determine a spectrum over the first duration of the electrical signal; and
determine the Doppler frequency shift based on the spectrum.
8. The autonomous vehicle control system as recited in claim 1 , wherein the spectrum is a cross spectrum of an in-phase component of the electrical signal and a quadrature component of the electrical signal.
9. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
determine the first duration based on at least one of a speed of a vehicle relative to a surface external to the vehicle, a location of the vehicle relative to the surface external to the vehicle, and a scan angle relative to the surface external to the vehicle.
10. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
control the at least one of the steering system or the braking system based on the range and a sign of the Doppler frequency shift.
11. The autonomous vehicle as recited in claim 1 , wherein the one or more processors are further configured to:
generate a first optical signal by modulating a code that indicates a sequence of phases for a phase encoded signal with reference to an optical signal; and
transmit the first optical signal to the object.
12. The autonomous vehicle as recited in claim 11 , wherein the first duration is an integer multiple greater than 1 of a duration of the code.
13. The autonomous vehicle as recited in claim 11 , wherein the second duration is equal to or substantially equal to a duration of the code.
14. The autonomous vehicle as recited in claim 11 , wherein the one or more processors are further configured to:
determine the range to the object based on a cross correlation, over the second duration, between the corrected electrical signal and a radio frequency (RF) signal that is associated with the first optical signal.
15. The autonomous vehicle as recited in claim 14 , wherein the one or more processors are further configured to:
determine the cross correlation, over the second duration, between (i) a first Fourier transform of the RF signal that is associated with the first optical signal and (ii) a second Fourier transform of the corrected electrical signal.
16. A light detection and ranging (LIDAR) system, the LIDAR system comprising:
one or more processors; and one or more computer-readable storage mediums storing instructions which, when executed by the one or more processors, cause the one or more processors to:
receive an electrical signal generated based on a returned optical signal that is reflected from an object;
determine a Doppler frequency shift of the returned optical signal over a first duration of the electrical signal;
generate a corrected electrical signal based on the Doppler frequency shift; and
determine a range to the object based on the corrected electrical signal over a second duration that is shorter than the first duration.
17. An autonomous vehicle comprising:
at least one of a steering system or a braking system; and
a vehicle controller comprising one or more processors configured to:
receive an electrical signal generated based on a returned optical signal that is reflected from an object;
determine a Doppler frequency shift of the returned optical signal over a first duration of the electrical signal;
generate a corrected electrical signal based on the Doppler frequency shift;
determine a range to the object based on the corrected electrical signal over a second duration that is shorter than the first duration; and
control the at least one of the steering system or the braking system based on the range.
18. The autonomous vehicle as recited in claim 17 , wherein the one or more processors are further configured to:
determine a spectrum over the first duration of the electrical signal; and
determine the Doppler frequency shift based on the spectrum.
19. The autonomous vehicle as recited in claim 17 , wherein the one or more processors are further configured to: determine the first duration based on at least one of a speed of a vehicle relative to a surface external to the vehicle, a location of the vehicle relative to the surface external to the vehicle, and a scan angle relative to the surface external to the vehicle.
20. The autonomous vehicle as recited in claim 17 , wherein the one or more processors are further configured to:
control the at least one of the steering system or the braking system based on the range and a sign of the Doppler frequency shift.