US 12,449,538 B2
Ambiguity mitigation for FMCW lidar system
Diego F. Pierrottet, Poquoson, VA (US); Glenn D. Hines, Yorktown, VA (US); and Farzin Amzajerdian, Yorktown, VA (US)
Assigned to UNITED STATES OF AMERICA AS REPRESENTED BY THE ADMINISTRATOR OF NASA, Washington, DC (US)
Filed by UNITED STATES OF AMERICA AS REPRESENTED BY THE ADMINISTRATOR OF NASA, Washington, DC (US)
Filed on May 25, 2021, as Appl. No. 17/329,976.
Claims priority of provisional application 63/030,215, filed on May 26, 2020.
Prior Publication US 2021/0373157 A1, Dec. 2, 2021
Int. Cl. G01S 17/34 (2020.01); G01S 7/481 (2006.01); G01S 17/58 (2006.01); G01S 17/89 (2020.01)
CPC G01S 17/34 (2020.01) [G01S 7/4817 (2013.01); G01S 17/58 (2013.01); G01S 17/89 (2013.01)] 20 Claims
OG exemplary drawing
 
1. A frequency modulated continuous wave (FMCW) Doppler lidar system for use with a host vehicle, comprising:
a laser system configured to generate first, second, and third laser beams and first, second, and third local oscillator beams using a seed laser and a beam splitter;
a frequency modulator configured to generate a modulated three-section waveform using the first, second, and third laser beams and the first, second, and third local oscillator beams, the modulated three-section waveform having a Doppler frequency section, an up-ramp frequency section, and a down-ramp frequency section;
first, second, and third lenses configured to transmit the modulated three-section waveform toward a target-of-interest, and to receive respective first, second, and third return signals reflected from the target-of-interest;
a homodyne receiver configured to receive and mix the first, second, and third return signals with a respective one of the first, second, and third local oscillator beams to output a three-section return waveform having a Doppler intermediate frequency (IF) section, an up-ramp IF section, and a down-ramp IF section; and
a signal processing unit (SPU) coupled to the homodyne receiver and configured to estimate a sign of, and measure a respective magnitude and frequency of, the up-ramp IF section, the down-ramp IF section, and the Doppler IF section, to calculate a range to the target-of-interest and/or velocity of the host vehicle relative to the target-of-interest using the respective magnitude, frequency, and sign, and to control an operation of the host vehicle using the range and/or the velocity,
wherein the SPU, in response to one of the up-ramp IF section, the Doppler IF section, and the down-ramp IF section not being detected by the homodyne receiver, is configured to mitigate sign ambiguity by assigning a positive or negative sign to the undetected IF section based on respective slopes of the detected IF sections.