FMCW – Frequency Modulated Continuous Wave Lidar

It certainly sounds more complicated than Time of Flight (ToF), but Frequency Modulated Continuous Wave (FMCW) lidar has a number of important advantages over ToF, like being able to measure the velocity of objects in a scene and having the sensor not be affected by bright light sources such as the Sun.

picture of Aeva FMCW Lidar

Aeva FMCW Lidar

Two veterans of the yet-to-be-taken-public, Apple driverless car project have left the mother-ship and gone off on their own to form Aeva. They are pushing FMCW (more on that below) as the differentiator among the myriad of autonomous vehicle start-ups jockeying for position in over-hyped, VC-driven Silicon Valley.

This market is in a classic bubble. How does one know a bubble when you see one? It’s simple. When your reason for buying something at an inflated price is that it will be worth more tomorrow, then my friend you are in a bubble.

O.K. let’s be sure we have a basic understanding of FMCW since that may be something you can actually make use of in the future. As opposed to ToF which sends out a brief laser pulse and then waits for its return, FMCW transmits a continuous laser beam with a prescribed, continuous change in the frequency.

Because the frequency is changing at a constant rate, there’s a frequency difference between the outgoing and the incoming beams that’s directly proportional to the distance that the returning beam traveled before bouncing back. Combining beams with two slightly different frequencies produces a beat frequency that gives a precise estimate of the frequency difference—and hence a precise distance measurement.

In addition to the advantages mentioned above, the fact that the frequencies are precisely known there is little chance of interference from other FMCW sensors in the area. I have not even seen this topic mentioned by the ToF’ers.

Seems like that is a major advantage, along with the ability to not be affected by glare and potentially the biggest item of all, the ability to measure the velocity of moving objects in the path of the vehicle.

I am not convinced that the ability to measure velocity is a must-have, but as long as the software can make efficient use of the information I would probably say why not. What do you think?

For us Built Environment, 3D laser scanning and lidar folks the bubble is tremendous news. It reminds me of how photogrammetry reaped the rewards of the huge investments being made in digital cameras for the consumer market. The same thing is happening with the cost and capability of lidar sensors and technology.

Strobe and Blackmore previously reviewed by Lidar News, both claim they are able to measure velocity.

For more information click here.

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