FMCW Lidar Architectures: Classification, Simulation, and Performance Assessment
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Heath, Kamri J.
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Abstract
Lidar, first developed in the 1960s, uses laser light to measure distance. Initially used for rangefinders and altimeters, lidar's role expanded with advancements in hardware and real-time data processing, making it a vital tool in fields like autonomous vehicles, archaeology, and forestry. Unlike radar, which generates a sparser dataset, lidar produces dense point clouds for detailed 3D mapping. While lidar offers higher spatial resolution, it struggles in adverse weather conditions.
There are different types of lidar, including pulsed, Amplitude-Modulated Continuous-Wave (AMCW), and Frequency-Modulated Continuous-Wave (FMCW) lidar. FMCW lidar modulates a continuous laser beam’s frequency to calculate distance, offering advantages such as simultaneous velocity and range measurements, better range resolution, and higher immunity to ambient light.
This thesis develops a comprehensive classification of FMCW lidar architectures, analyzing 186 relevant papers to address inconsistencies in naming conventions and definitions within the field. The findings categorize systems by key architectural distinctions, such as homodyne versus heterodyne configurations, modulation schemes (SSB vs. DSB), and demodulation methods (IQ vs. non-IQ). For example, heterodyne systems involve significant differences in frequency and phase between the local oscillator (LO) and received signal, requiring an intermediate frequency, while homodyne systems have nearly identical LO and received signals, allowing direct mixing in the baseband.
The thesis also presents a lidar simulator based on one of the most prominent FMCW lidar architectures identified in the survey, which reflects a DSB Homodyne Non-IQ architecture. This simulator adds realistic features such as band-limited noise, an amplifier, an Analog-to-Digital Converter (ADC), and most notably, speckle noise. It evaluates simulation performance based on theoretical expectations of metrics like probability of detection, probability of false alarm, and signal-to-noise ratio.
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2024-12-08
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Thesis (Masters Degree)