System and method for generating repeatable PPM waveforms

Patent metadata

Field	Value
Publication number	US-11630206-B2
Application number	US-202016863858-A
Country	US
Kind code	B2
Filing date	Apr 30, 2020
Priority date	Apr 30, 2020
Publication date	Apr 18, 2023
Grant date	Apr 18, 2023

Abstract

Lidar and method for generating repeatable PPM waveforms to determine a range to a target include: a processor for a) creating a modulation pool, based on a maximum nominal PRF and a specified final PPM code length of N; b) obtaining a seed code; c) eliminating bad modulation levels from the modulation pool to generate a good modulation pool, d) selecting a modulation level from the good modulation pool; e) concatenating the selected modulation level to the seed code to generate an i-element modulation sequence; f) repeating steps c to e N times to generate an N-element modulation sequence; g) selecting a PRF less than the maximum nominal PRF; and h) generating a repeatable PPM waveform by applying the N-element modulation sequence to the selected PRF.

First claim

What is claimed is:

1. A method for generating repeatable Pulse Position Modulated (PPM) waveforms in a lidar, the method comprising:
a) creating a modulation pool, based on a maximum nominal pulse repetition frequency (PRF) and a specified final PPM code length of N, wherein N is an integer greater than 1;
b) obtaining a seed code;
c) eliminating bad modulation levels from the modulation pool to generate a good modulation pool;
d) selecting a modulation level from the good modulation pool;
e) concatenating the selected modulation level to the seed code to generate an i-element modulation sequence, wherein i is an integer index greater than 1;
f) repeating steps c to e N times to generate an N-element modulation sequence;
g) selecting a PRF less than the maximum nominal PRF;
h) generating a concatenated repeatable base PPM waveform by applying the N-element modulation sequence to the selected PRF; and
i) transmitting the concatenated repeatable base PPM waveform by the lidar toward a target to determine a range to the target, wherein
eliminating bad modulation levels comprises: discarding modulation levels that cause a baud collision between any pair of code elements in the base PPM waveform;

discarding modulation levels that cause a baud collision between any pair of code elements in the base PPM waveform and a concatenated code formed by concatenating the base PPM waveform to itself; and discarding modulation levels that lie equidistant between the elements in the base PPM waveform, and code elements in the concatenated code.

2. The method of claim 1 , further comprising concatenating the base PPM waveform to itself before or during transmission.

3. The method of claim 1 , wherein the modulation level is selected using a selection function.

4. The method of claim 3 , wherein the selection function selects a modulation level via random sampling of the good modulation pool.

5. The method of claim 3 , wherein the selection function computes a best available next PPM code element.

6. The method of claim 3 , wherein the selection function is optimized to generate longer PPM codes.

7. The method of claim 3 , wherein the selection function chooses a new modulation level from the good modulation pool such that the new modulation level maximizes the minimum distance between its own position and position of modulation levels that have been removed from the modulation pool.

8. The method of claim 1 , further comprising receiving a waveform reflected from the target to determine the range to the target.

9. The method of claim 1 , wherein the bad modulation levels are determined from the following formula:

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Assignees

• Raytheon Co

Inventors

• Greenberg Adam Hodge
• Marcus Eran

Classifications

• G01S17/89

  for mapping or imaging · CPC title

• G01S7/484 Primary

  Transmitters · CPC title

• G01S17/10 Primary

  using transmission of interrupted, pulse-modulated waves (determination of distance by phase measurements G01S17/32) · CPC title

• G01S7/4811

  common to transmitter and receiver · CPC title

• G01S7/489

  Gain of receiver varied automatically during pulse-recurrence period · CPC title