ToF vs. FMCW
At their core, both ToF and FMCW lidar technologies measure distance to create detailed 3D maps of the surrounding environment. However, their underlying methodologies differ significantly.
ToF Lidar: This technology emits short light pulses and calculates the distance to an object based on the time it takes for the light to return. As a well-established technology, ToF is widely recognized and understood. For a primer on ToF, check out The Basics of Lidar..
FMCW Lidar: FMCW uses a continuous light beam with frequency modulation, analyzing the frequency shift between emitted and reflected light to calculate both distance and velocity simultaneously. Though this technology has existed for decades, its adoption is growing, especially for autonomous vehicles. Companies adopting FMCW tout numerous advantages. For more details, read What is FMCW Lidar?.
Benefits of FMCW
In Clement Kong’s article, The battle of LiDAR sensor technologies: FMCW vs. ToF, he identifies key advantages of FMCW over ToF:
– Higher optical power
– Reduced susceptibility to blooming
– Improved range
– Potential for lower costs through integration
Kong explains that FMCW can sustain higher peak power without compromising measurement accuracy, making it ideal for precision-demanding applications like autonomous driving and factory automation. He also notes that ToF is prone to blooming — a phenomenon where bright objects, such as traffic signs or reflective clothing, overwhelm sensors. Additionally, ToF’s range is constrained by power limitations for eye safety, with increased power exacerbating blooming issues.
FMCW, Kong argues, offers better long-range performance and resilience in reflective environments, such as construction zones. Moreover, FMCW’s potential for integration into a system-on-chip (SoC) could drastically reduce production costs, making it a more economical choice in the future.
Benefits of ToF
AEye counters these claims in their recent post, arguing that ToF holds several advantages over FMCW:
– Superior range
– Lower susceptibility to interference
– Scalability of FMCW remains uncertain
Regarding range, AEye asserts, “Although recent articles claim FMCW has superior range, we haven’t seen an FMCW system that matches the range of advanced ToF systems while offering comparable field of view (FOV), overall range swath, and point density.”
They also identify interference from sidelobes as a critical issue for FMCW. According to AEye, FMCW’s reliance on window-based sidelobe rejection can lead to inaccuracies, particularly in complex environments. “To provide context, a 10μs FMCW pulse spreads light radially across 1.5km range. Any objects within this range extent will be caught in the FFT (time) sidelobes. Even a shorter 1μs FMCW pulse can be corrupted by high intensity clutter 150m away. The first sidelobe of a Rectangular Window FFT is well known to be –13dB, far above the levels needed for a consistently good point cloud. (Unless no object in the shot differs in intensity by any other range point in a shot by more than about 13dB, something that is unlikely in operational road conditions).”
Finally, AEye raises concerns about the cost of FMCW manufacturing, noting that the specialized components required may hinder its ability to achieve widespread affordability.
The Road Ahead
As the competition between FMCW and ToF technologies heats up, companies are vying for market share, particularly in the autonomous vehicle sector. Both sides bring compelling arguments, especially regarding range and interference — two areas of ongoing disagreement. We’ll continue to monitor and report on developments in this evolving battle of lidar technologies. We had Sabbir Rangwala of Forbes Magazine write a full analysis of FMCW vs. ToF LiDAR, read it here – Analysis of FMCW vs. ToF LiDAR.
