Systems and methods for efficient multi-return light detectors
Described herein are systems and methods that may efficiently detect multi-return light signals. A light detection and ranging system, such as a LIDAR system, may fire a laser beam that may hit multiple objects with a different distance in one line, causing multi-return light signals to be received by the system. Multi-return detectors may be able to analyze the peak magnitude of a plurality of peaks in the return signals and determine a multitude of peaks, such as the first peak, the last peak and the maximum peak. One embodiment to detect the multi-return light signals may be a multi-return recursive matched filter detector. This detector comprises a matched filter, peak detector, centroid calculation and a zeroing out function. Other embodiments may be based on a maximum finder that algorithmically selects the highest magnitude peaks from samples of the return signal and buffers for regions of interests peaks.
1. A multiple-return light signal detection method for a light detection and ranging (LIDAR) system, the method comprising:
receiving a multi-return signal having a plurality of peaks in a time period;
filtering the multi-return signal based at least in part, on a pulse shape of an emitted laser beam, to produce a filtered signal;
identifying a sequence of two or more peaks of the filtered signal in the time period;
selecting at least one peak from the sequence of two or more peaks;
identifying a number of samples centered around each of the at least one selected peak; and
determining, for each selected peak, a centroid of the selected peak based at least in part on the samples centered around the selected peak.
2. The method of claim 1 , wherein filtering the multi-return signal comprises convolving the multi-return signal with a signal having the pulse shape of the emitted laser beam.
3. The method of claim 1 , further comprising:
determining, for each selected peak, a time of arrival and an intensity saturation count based on a centroid of the selected peak.
4. The method of claim 1 , wherein identifying the sequence of two or more peaks of the filtered signal in the time period comprises identifying each peak of the filtered signal having a respective amplitude that exceeds a pre-set threshold value, and wherein a probability of false alarm depends on the pre-set threshold value.
5. The method of claim 1 , wherein filtering the multi-return signal is performed by a matched filter operating at a rate of 8 samples per clock.
6. The method of claim 1 , wherein the sequence of two or more peaks is identified based at least in part on mean and variance noise statistics.
7. The method of claim 1 , wherein the selected peak is at least one of a largest peak and a second largest peak.
8. The method of claim 1 , wherein the selected peak is at least one of a first arrived peak and a last arrived peak.
9. The method of claim 1 , wherein samples are identified around each of the two or more peaks in the sequence of two or more peaks.
10. A light detection and ranging (LIDAR) system, comprising:
a transmitter configured to emit a laser beam;
a light detector configured to receive a multi-return signal having a plurality of peaks in a time period;
a matched filter circuit configured to filter the multi-return signal based at least in part on a pulse shape of the emitted laser beam to produce a filtered signal; and
a peak filter circuit configured to:
identify a sequence of two or more peaks of the filtered signal in the time period;
select at least one peak from the sequence of two or more peaks; and
cause a buffer to store a number of samples centered around each of the at least one selected peaks; and
determine, for each selected peak, a centroid of the selected peak based at least in part on the samples centered around the selected peak.
11. The system of claim 10 , wherein filtering the multi-return signal comprises convolving the multi-return signal with a signal having the pulse shape of the emitted laser beam.
12. The system of claim 10 , wherein selecting at least one peak comprises:
determining a peak magnitude for each of the two or more peaks in the time period; and
selecting at least one peak from the two or more peaks based on a time of arrival.
13. The system of claim 10 , further configured to:
determine, for each selected peak, a time of arrival and an intensity saturation count based on a centroid of the selected peak.
14. The system of claim 13 , wherein the matched filter operates at a rate of 8 samples per clock.
15. The system of claim 10 , wherein the buffer stores 10 samples around the selected peak.
16. The system of claim 10 , wherein the sequence of two or more peaks is determined based at least in part on mean and variance noise statistics.
17. The system of claim 10 , wherein the selected peak is at least one of a largest peak and a second largest peak.
18. The system of claim 10 , wherein the selected peak is at least one of a first arrived peak and a last arrived peak.
19. The system of claim 10 , wherein, identifying the sequence of two or more peaks of the filtered signal in the time period comprises identifying each peak of the filtered signal having a respective amplitude that exceeds a pre-set threshold value, and wherein a probability of false alarm depends on the pre-set threshold value.
20. The system of claim 10 , wherein samples are stored around each of the two or more peaks in the sequence of two or more peaks.