Method and system for sidelobe suppression in phase encoded doppler LIDAR
A system and method for sidelobe suppression in phase-encoded Doppler LIDAR to support the operation of a vehicle includes determining a sequence code that is indicative of a sequence of phases for an optical signal; modulating an optical signal based on the sequence code to produce a phase-encoded optical signal; transmitting the phase-encoded optical signal to an environment; receiving, from the environment, a returned optical signal in response to transmitting the phase-encoded optical signal; generating, based on the returned optical signal, an electrical signal; and determine a Doppler frequency shift in the returned optical signal.
1. 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:
determine an m-sequence code that is indicative of a sequence of phases for an optical signal;
modulate an optical signal based on the m-sequence code to produce a phase-encoded optical signal;
transmit the phase-encoded optical signal to an environment;
receive, from the environment, a returned optical signal in response to transmitting the phase-encoded optical signal;
generate, based on the returned optical signal, an electrical signal; and
determine a Doppler frequency shift in the returned optical signal based on the electrical signal,
wherein the one or more processors determine the m-sequence code by selecting, from a plurality of m-sequence codes, the m-sequence code that causes an autocorrelation spur to occur at a predetermined lag of a maximum unambiguous range of the transmitted phase-encoded optical signal.
2. The LIDAR system as recited in claim 1 , wherein the one or more processors are further configured to:
step up or stepping down a clock signal relative to a clock signal for generating the electrical signal.
3. The LIDAR system as recited in claim 1 , wherein the m-sequence code has symbols of a first length and the electrical signal has samples of a second length, and wherein the one or more processors are further configured to:
sample the m-sequence code to generate a sampled signal; and
interpolate the sampled signal at the samples of the second length to generate the phase-encoded optical signal.
4. The LIDAR system as recited in claim 3 , wherein the one or more processors are further configured to:
up-sample the m-sequence code to generate the sampled signal.
5. The LIDAR system as recited in claim 3 , wherein the one or more processors are further configured to:
filter the sampled signal to generate a smoothed signal prior to interpolating the sampled signal.
6. The LIDAR system as recited in claim 1 , wherein the one or more processors are further configured to:
sample the m-sequence code to generate a sampled signal; and
semi-randomly insert symbols in the sampled signal to generate the phase-encoded optical signal.
7. The LIDAR system as recited in claim 1 , wherein the one or more processors are further configured to:
determine the Doppler frequency shift in the returned optical signal based on a power of two Fast Fourier Transform of the electrical signal.
8. The LIDAR system as recited in claim 1 , wherein the m-sequence code has symbols of a first length and the electrical signal has samples of a second length and wherein the one or more processors are further configured to:
pad the m-sequence code to generate the electrical signal with the samples of the second length.
9. The LIDAR system as recited in claim 1 , wherein the m-sequence code has symbols of a first length and the electrical signal has samples of a second length and wherein the one or more processors are further configured to:
detect the returned optical signal by interpolating the returned optical signal at the samples of the second length.
10. 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:
determine an m-sequence code that is indicative of a sequence of phases for an optical signal;
cause an optical signal to be modulated based on the m-sequence code to produce a phase-encoded optical signal;
cause an optical detector to receive a returned signal from an environment by causing the phase-encoded optical signal to be transmitted into the environment;
obtain an electrical signal from the optical detector in response to causing the optical detector to receive the returned signal from the environment;
determine a Doppler frequency shift in the returned optical signal based on the electrical signal; and
control operation of a vehicle using the Doppler frequency shift,
wherein the one or more processors determine the m-sequence code by selecting, from a plurality of m-sequence codes, the m-sequence code that causes an autocorrelation spur to occur at a predetermined lag of a maximum unambiguous range of the transmitted phase-encoded optical signal.
11. The autonomous vehicle control system as recited in claim 10 , wherein the one or more processors are further configured to:
step up or step down a clock signal relative to a clock signal for generating the digital electrical signal.
12. The autonomous vehicle control system as recited in claim 10 , wherein the m-sequence code has symbols of a first length and the electrical signal has samples of a second length, and wherein the one or more processors are further configured to:
sample the m-sequence code to generate a sampled signal; and
interpolate the sampled signal at the samples of the second length to generate the phase-encoded optical signal.
13. The autonomous vehicle control system as recited in claim 12 , wherein the one or more processors are further configured to:
filter the sampled signal to generate a smoothed signal prior to interpolating the sampled signal.
14. The autonomous vehicle control system as recited in claim 10 , wherein the one or more processors are further configured to:
sample the m-sequence code to generate a sampled signal; and
semi-randomly insert symbols in the sampled signal to generate the phase-encoded optical signal.
15. The autonomous vehicle control system as recited in claim 14 , wherein the one or more processors are further configured to:
up-sample the m-sequence code to generate the sampled signal.
16. The autonomous vehicle control system as recited in claim 10 , wherein the one or more processors are further configured to:
determine the Doppler frequency shift in the returned optical signal based on a power of two Fast Fourier Transform of the electrical signal.
17. The autonomous vehicle control system as recited in claim 10 , wherein the m-sequence code has symbols of a first length and the electrical signal has samples of a second length, and wherein the one or more processors are further configured to:
pad the m-sequence code to generate the electrical signal with the sample of the second length.
18. The autonomous vehicle control system as recited in claim 10 , wherein the m-sequence code has symbols of a first length and the electrical signal has samples of a second length, and wherein the one or more processors are further configured to:
detect the returned optical by interpolating the returned optical signal at the samples of the second length.
19. 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:
determine an m-sequence code that is indicative of a sequence of phases for an optical signal;
modulate an optical signal based on the m-sequence code to produce a phase-encoded optical signal;
transmit the phase-encoded optical signal to an environment;
receive, from the environment, a returned optical signal in response to transmitting the phase-encoded optical signal;
generate, based on the returned optical signal, an electrical signal;
determine a Doppler frequency shift in the returned optical signal based on the electrical signal; and
control the at least one of the steering system or the braking system using the Doppler frequency shift,
wherein the one or more processors determine the m-sequence code by selecting, from a plurality of m-sequence codes, the m-sequence code that causes an autocorrelation spur to occur at a predetermined lag of a maximum unambiguous range of the transmitted phase-encoded optical signal.
20. The autonomous vehicle as recited in claim 19 , wherein the m-sequence code has symbols of a first length and the electrical signal has samples of a second length.