FAQ on the basics of FMCW LiDAR: part 3

This alternative to time-of-flight LiDAR has unique complexities and distinct attributes.

Modeling and simulation

Q: What design analysis is done on an FMCW LiDAR system?
A: In a word: lots. Much of the analysis parallels or leverages what has been done for radar, as there are so many similarities in operating principles and the analytical equations.

One starting point is the link budget, as is done with any signal path or channel. A high-level simplified link budget is shown in Figure 1.

Figure 1. This graphical outline representation of some important link budget considerations of the FMCW photonic radar system only begins to show the complexity of reality. (Image: Frontiers Media SA)

More highly detailed budgets are then worked out at each point in the link, as seen in Figure 2.

Figure 2. This is a conceptual diagram of a photonic radar system under the influence of various atmospheric weather conditions at the ground level and solar background noise. (Image: Frontiers Media SA)

Q: What do more advanced and detailed models look like?
A: One MATLAB Simulink model is shown in Figure 3.

Figure 3. This MATLAB Simulink model for the system is only one of many needed perspectives, due to the electro-optical nature of the system. (Image: Semantic Scholar)

However, this model only tells part of the multifaceted story. The reason is that FMCW is a hybrid electro-optic system, so the modeling must accommodate electronic-only, optical-only, and integrated electro-optical components. This is a major challenge among many challenges in providing realistic and accurate modeling and simulation.

Which is better: FMCW or ToF LiDAR?

Q: What are some of the presumed advantages of FMCW over ToF LiDAR?
A: Proponents of FMCW make these points, but ToF advocates dispute them, or say the considerations are not clear-cut or still to be decided: FMCW proponents say it offers:

Improved range resolution, enabling the measurement and separation of multiple closely spaced surfaces.
Improved dynamic range, enabling the measurement of both bright and dim objects simultaneously.
Single-photon sensitivity, enabling small apertures, long-range operation, and the ability to penetrate obscurants.
Velocity sensitivity enables the ability to detect and quantify motion.

Q: What is a major point that ToF proponents claim is their strength and an FMCW weakness?
A: One of the claims is that FMCW does not work well at detecting lateral motion (across the image plane) since there is little or no Doppler shift. Note, there are many other legitimate performance points that ToF advocates raise as well, in addition to cost and complexity; some of the References call these out from the ToF-advocate side, and others do side-by-side comparisons – so you have a lot to consider and weigh!

The final part looks at today’s reality and the possible future(s).