Method and system for enhanced velocity resolution and signal to noise ratio in optical phase-encoded range detection
A system and method for enhanced velocity resolution and signal to noise ratio in optical phase-encoded range detection includes receiving an electrical signal generated by mixing a first optical signal and a second optical signal, wherein the first optical signal is generated by modulating an optical signal, wherein and the second optical signal is received in response to transmitting the first optical signal toward an object, and determining a Doppler frequency shift of the second optical signal, and generating a corrected electrical signal by adjusting the electrical signal based on the Doppler frequency shift, and determining a range to the object based on a cross correlation of the corrected electrical signal with a radio frequency (RF) signal that is associated with the first optical signal.
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;
transform the electrical signal into a frequency domain to generate a transformed electrical signal;
determine a Doppler frequency shift of the returned optical signal based on a cross spectrum of the transformed electrical signal;
determine, based on the Doppler frequency shift, movement information indicative of whether the object is moving closer to or further away from the autonomous vehicle control system; and
control the at least one of a steering system or a braking system based on the movement information.
2. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
determine the Doppler frequency shift of the returned optical signal based on a particular point in the cross spectrum of the transformed electrical signal.
3. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
generate the cross spectrum of the transformed electrical signal by processing the transformed electrical signal and a conjugate of a Fourier transform of a phase code.
4. The autonomous vehicle control system as recited in claim 3 , wherein the one or more processors are further configured to:
circular shift the phase code to align a direct current (DC) frequency to a Doppler frequency associated with the electrical signal.
5. The autonomous vehicle control system as recited in claim 3 , wherein the one or more processors are further configured to:
calculate a cross-correlation based on the electrical signal and the Fourier transform of the phase code.
6. The autonomous vehicle control system as recited in claim 5 , wherein the one or more processors are further configured to:
re-calculate the cross-correlation according to an internal associated with a transmission or reception of an optical signal.
7. The autonomous vehicle control system as recited in claim 3 , wherein the one or more processors are further configured to:
apply a Doppler compensated signal with at least one of a shifted version of the Fourier transform of the phase code, a scaled version of the Fourier transform of the phase code, or a phased version of the Fourier transform of the phase code.
8. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
adjust the electrical signal by removing the Doppler frequency shift from the electrical signal to generate an adjusted electrical signal; and
determine a range to the object based on the adjusted electrical signal.
9. The autonomous vehicle control system as recited in claim 1 , wherein the one or more processors are further configured to:
determine, based on the electrical signal, in-phase and quadrature components of the returned optical signal; and
determine a separation of the in-phase and quadrature components.
10. The autonomous vehicle control system as recited in claim 9 , wherein the one or more processors are further configured to:
determine a sign of the Doppler frequency shift based on the separation; and
determine the movement information indicative of whether the autonomous vehicle is moving closer to or further away from the autonomous vehicle control system based on the sign of the Doppler frequency shift.
11. 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;
transform the electrical signal into a frequency domain to generate a transformed electrical signal;
determine a Doppler frequency shift of the returned optical signal based on a cross spectrum of the transformed electrical signal; and
determine, based on the Doppler frequency shift, movement information indicative of whether the object is moving closer or further away from the autonomous vehicle control system.
12. 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;
transform the electrical signal into a frequency domain to generate a transformed electrical signal;
determine a Doppler frequency shift of the returned optical signal based on a cross spectrum of the transformed electrical signal;
determine, based on the Doppler frequency shift, movement information indicative of whether the object is moving closer or further away from the autonomous vehicle; and
control the at least one of the steering system or the braking system based on the movement information.
13. The autonomous vehicle as recited in claim 12 , wherein the one or more processors are further configured to:
determine the Doppler frequency shift of the returned optical signal based on a particular point in the cross spectrum of the transformed electrical signal.
14. The autonomous vehicle as recited in claim 12 , wherein the one or more processors are further configured to:
generate the cross spectrum of the transformed electrical signal by processing the transformed electrical signal and a conjugate of a Fourier transform of a phase code.
15. The autonomous vehicle as recited in claim 14 , wherein the one or more processors are further configured to:
circular shift the phase code to align a direct current (DC) frequency to a Doppler frequency associated with the electrical signal.
16. The autonomous vehicle as recited in claim 14 , wherein the one or more processors are further configured to:
calculate a cross-correlation based on the electrical signal and the Fourier transform of the phase code.
17. The autonomous vehicle as recited in claim 16 , wherein the one or more processors are further configured to:
re-calculate the cross-correlation according to an internal associated with a transmission or reception of an optical signal.
18. The autonomous vehicle as recited in claim 14 , wherein the one or more processors are further configured to:
apply a Doppler compensated signal with at least one of a shifted version of the Fourier transform of the phase code, a scaled version of the Fourier transform of the phase code, or a phased version of the Fourier transform of the phase code.
19. The autonomous vehicle as recited in claim 12 , wherein the one or more processors are further configured to:
adjust the electrical signal by removing the Doppler frequency shift from the electrical signal to generate an adjusted electrical signal; and
determine a range to the object based on the adjusted electrical signal.
20. The autonomous vehicle as recited in claim 12 , wherein the one or more processors are further configured to:
determine, based on the electrical signal, in-phase and quadrature components of the returned optical signal;
determine a separation of the in-phase and quadrature components; and
determine a sign of the Doppler frequency shift based on the separation.