Systems and methods for efficient multi-return light detectors

Patent metadata

Field	Value
Publication number	US-10690773-B2
Application number	US-201715835374-A
Country	US
Kind code	B2
Filing date	Dec 7, 2017
Priority date	Dec 7, 2017
Publication date	Jun 23, 2020
Grant date	Jun 23, 2020

Abstract

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.

First claim

What is claimed is:

1. A Light Detection and Ranging (LIDAR) system comprising:
a transmitter that emits a laser beam having a signal with a plurality of pulses in a particular sequence;
a matched filter operable to receive a multi-return signal comprising N peaks in a time period;
wherein a matched filter value of the matched filter is equal to a value of the signal of the laser beam having the plurality of pulses in the particular sequence, and the matched filter convolves the signal of the laser beam with the multi-return signal;
a peak detector coupled to receive an output of the matched filter and operable to determine a first maximum peak of the multi-return signal in the time period;
a centroid calculation operable to derive a position of the first maximum peak of the multi-return signal in the time period; and
a zeroing out function that eliminates—the first maximum peak from the multi-return signal to allow the peak detector to determine a second maximum peak and the centroid calculation derive the position of the second maximum peak in the time period,
wherein, the peak detector, the centroid calculation and the zeroing out function determine subsequent maximum peaks until M peaks of the N peaks are detected in the multi-return signal in the time period,
wherein, the centroid calculation determines a first peak, a last peak and a maximum peak in the multi-return signal in the time period.

2. The LIDAR system of claim 1 , wherein each of the N peaks exceed a pre-set threshold.

3. The LIDAR system of claim 1 , wherein the peak detector comprises a threshold comparator, a buffer and a maximum finder, wherein the threshold comparator compares the output of the matched filter to a pre-set threshold and determines peak samples above the pre-set threshold, wherein the maximum finder determines a set of maximum peaks.

4. The LIDAR system of claim 3 , wherein the matched filter calculates a mean value and a RMS value of noise of the multi-return signal by excluding peak samples above a threshold of the peak detector.

5. The LIDAR system of claim 1 , wherein under conditions of additive white Gaussian noise, a value of the matched filter, h(t), is equal to a value of a signal s(t).

6. The LIDAR system of claim 1 , wherein if the M peaks are equal to the N peaks, then the N peaks are processed to determine a peak value for each of the N peaks.

7. The LIDAR system of claim 1 , wherein a maximum return is a first peak output from the LIDAR system.

8. The LIDAR system of claim 1 , wherein first M peaks of the N peaks define M maximum valid returns.

9. The LIDAR system of claim 1 , wherein if M peaks are sorted according to position, the first peak and the last peak corresponds to a first return and a last return, respectively.

10. The LIDAR system of claim 1 , wherein if the N peaks are sorted according to position, the first peak and the last peak correspond to a front peak and a back peak, respectively.

11. The LIDAR system of claim 1 , wherein a threshold of the peak detector is adjusted based on operating noise environment and a target error rate.

12. A Light Detection and Ranging (LIDAR) system comprising:
a transmitter that emits a laser beam having a signal with a plurality of pulses in a particular sequence;
a matched filter operable to filter a multi-return signal comprising a sequence of N peaks in a time period;
wherein a matched filter value of the matched filter is equal to a value of the signal of the laser beam having the plurality of pulses in the particular sequence, and the matched filter convolves the signal of the laser beam with the multi-return signal;
a peak detector coupled to receive an output of the matched filter and operable to determine peak magnitudes of each peak of the sequence of N peaks in the time period;
a maximum finder operable to select one or more maximum peaks from the sequence of N peaks in the time period;
a register operable to select one or more peaks based on a time of arrival; and
a buffer operable to generate a number of samples centered around each of the selected peaks.

13. The LIDAR system of claim 12 , wherein the one or more maximum peaks is a largest peak in the sequence of N peaks, and the one or more peaks based on the time of arrival is a last peak.

14. The LIDAR system of claim 12 , wherein the one or more maximum peaks are a largest peak and a second largest peak in the sequence of N peaks, and the one or more peaks based on the time of arrival is a last peak.

15. The LIDAR system of claim 12 , wherein the one or more maximum peaks are a largest peak and a second largest peak in the sequence of N peaks, and the one or more peaks based on the time of arrival are a first peak and a last peak.

16. The LIDAR system of claim 12 , wherein the one or more maximum peaks are a largest peak, a second largest peak, and K other peaks and the one or more peaks in the sequence of N peaks based on the time of arrival are a first peak and a last peak.

17. The LIDAR system of claim 12 , wherein a threshold derivation for the peak detector is utilized to achieve a certain probability of false alarm.

18. The LIDAR system of claim 12 , further comprising a centroid calculation operable to determine a time of arrival and an intensity saturation count for each of the selected peaks.

19. An apparatus comprising:
a transmitter that emits a laser beam having a signal with a plurality of pulses in a particular sequence;
a matched filter operable to filter a multi-return signal comprising a sequence of N peaks in a time period;
wherein a matched filter value of the matched filter is equal to a value of the signal of the laser beam having the plurality of pulses in the particular sequence, and the matched filter convolves the signal of the laser beam with the multi-return signal;
a peak detector coupled to receive an output of the matched filter and operable to determine peak magnitudes of each peak of the sequence of N peaks in the time period;
a maximum finder operable to select a largest peak from the sequence of N peaks in the time period;
a register operable to select a last peak from the sequence of N peaks in the time period;
a first buffer operable to select and store samples for regions of interest for the sequence of N peaks in the time period by generating X samples centered around the largest peak and generating Y samples centered around one or more other peaks; and
a second buffer operable to detect a peak hidden in a blinding spot immediately after the largest peak by zeroing out a contribution of a waveform of the largest peak utilizing the samples for the regions of interest for the sequence of N peaks in the time period.

20. The apparatus of claim 19 , further comprising a centroid calculation operable to determine a time of arrival, intensity saturation count for the largest peak, the last peak, and a peak in the blinding spot immediately after the largest peak.

Assignees

• Velodyne Lidar Inc

Inventors

• Gunnam Kiran Kumar
• Gao Kanke
• Barot Nitinkumar Sagarbhai
• Gopalan Anand
• Hall David S

Classifications

• G01S17/931

  of land vehicles · CPC title

• G01S7/4816

  of receivers alone · CPC title

• G01S17/42 Primary

  Simultaneous measurement of distance and other co-ordinates (indirect measurement G01S17/46) · CPC title

• G01S7/4861 Primary

  Circuits for detection, sampling, integration or read-out · CPC title

• G01S17/06

  Systems determining position data of a target · CPC title