5 ms·

I'm sure this is being considered, but I'm curious what the strategy is for handling signal/laser interference in dense traffic situations, in the future when a

by sbr464 8y ago

I'm sure this is being considered, but I'm curious what the strategy is for handling signal/laser interference in dense traffic situations, in the future when all cars have 3d lidar installed. For example, assuming 3 lidar units on the front of each car, in a large intersection, say two lanes of cars turning in front of 4 lanes of cars pointed at them, waiting at a red light. That would be hundreds of potential reflection/collisions per second. The user manual for an older Hokuyo lidar with a single scanning plane (for example, mounted on a forklift to avoid hitting a wall) mentions to offset the mounting/angle slightly across the fleet to avoid interference.

taneq 8y ago
I've always wondered this about LIDAR. It's all peachy with one car wandering down the road on its own, but a busy freeway with half a dozen cars all busily scanning everything is a different situation. Not to mention issues with sun glare dazzling sensors etc. Nobody talks about it so maybe it's not an issue in practice, but my own experience with sensors of all sorts is that they're never as good as you'd hope they are.
deleted 8y ago
[deleted]
etrautmann 8y ago
current state of the art LIDAR systems have unbelievably tight windows in terms of space, time, frequency, and pulse coding which collectively allow for excellent background rejection. In practice, this actually isn't that much of an issue. Sunlight and retro reflectors are more difficult challenges to deal with than other LIDARS causing interference. More specifically, each detector is looking through a soda straw at a tiny spot in space, and rejecting anything that doesn't arrive within a narrow range of time, which also has to have the right light frequency and something like a pseudorandom code sequence which gets match filtered against itself. In practice, you'd have to send the right wavelength of light to the right 1cm circle in space, send it during just the right few hundred nanoseconds, send it with the right pulse sequence (which one could determine but would be unlikely to happen by chance). Even if it happens once, it would have to happen many times at the imaging rate of the sensor to cause major issues...
- vonmoltke 8y ago
  Is there an equivalent to the Skolnik books[1] for LIDAR? I keep applying radar principles to LIDAR, but it seems like the function is significantly different if it includes things like a "pseudorandom code sequence". [1] https://books.google.com/books/about/Radar_Handbook.html?id=s35UAAAAMAAJ&source=kp_book_description https://books.google.com/books/about/Radar_Handbook.html?id=...
  - al2o3cr 8y ago
    AFAIK Lidar is using a variant of the well-known radar technique of using pseudorandom noise modulation to avoid some of the gotchas with fixed-frequency pulses: https://apps.dtic.mil/dtic/tr/fulltext/u2/479308.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/479308.pdf
  - Junk_Collector 8y ago
    Skolnik's books are good but they are pretty old and focus mostly on the hardware/transmission of radar. The code sequencing is on the baseband signal processing side and is a direct result of IQ modulation being a thing in vector signal processing. Lots of modern radar designs use the same style of pseudo-random encoding to prevent interference between units. It's a major push in automotive radar right now (70GHz band) for instance. Think of it as encoding your mac address on each packet you transmit wirelessly so you can tell which signals come from which source.
    - vonmoltke 8y ago
      I don't recall such a scheme being used on either system I worked on. However, skimming the paper in your sibling's post it would be something done in the RF front end, which is probably why I never encountered it. The closest I got to the front end was pseudo-raw IQ from the pulses. It was also probably tied up in the anti-jamming measures, so it wouldn't get wide circulation on the programs.
      - Junk_Collector 8y ago
dbuder 8y ago
What about a malicious device for targeted and non targeted use, I mean you'd have to be really into tech to make a capable one, but none of those people using credit card scanners made their own.
Tomminn 8y ago
There's a trivial solution to this kind of problem. Frequency filtering. Essentially, you make sure that your light source beats at a peculiar frequency, and then you only look for signals in that beat with the same frequency. So you're only competing with LIDAR's beating at the same frequency. If you randomly select this frequency, you can have a lot of LIDAR's simultaneously operating without effecting one another.

by sbr464 8y ago

taneq 8y ago

I've always wondered this about LIDAR. It's all peachy with one car wandering down the road on its own, but a busy freeway with half a dozen cars all busily scanning everything is a different situation. Not to mention issues with sun glare dazzling sensors etc. Nobody talks about it so maybe it's not an issue in practice, but my own experience with sensors of all sorts is that they're never as good as you'd hope they are.

deleted 8y ago

[deleted]

etrautmann 8y ago

current state of the art LIDAR systems have unbelievably tight windows in terms of space, time, frequency, and pulse coding which collectively allow for excellent background rejection. In practice, this actually isn't that much of an issue. Sunlight and retro reflectors are more difficult challenges to deal with than other LIDARS causing interference. More specifically, each detector is looking through a soda straw at a tiny spot in space, and rejecting anything that doesn't arrive within a narrow range of time, which also has to have the right light frequency and something like a pseudorandom code sequence which gets match filtered against itself. In practice, you'd have to send the right wavelength of light to the right 1cm circle in space, send it during just the right few hundred nanoseconds, send it with the right pulse sequence (which one could determine but would be unlikely to happen by chance). Even if it happens once, it would have to happen many times at the imaging rate of the sensor to cause major issues...

vonmoltke 8y ago
Is there an equivalent to the Skolnik books[1] for LIDAR? I keep applying radar principles to LIDAR, but it seems like the function is significantly different if it includes things like a "pseudorandom code sequence". [1] https://books.google.com/books/about/Radar_Handbook.html?id=s35UAAAAMAAJ&source=kp_book_description https://books.google.com/books/about/Radar_Handbook.html?id=...
- al2o3cr 8y ago
  AFAIK Lidar is using a variant of the well-known radar technique of using pseudorandom noise modulation to avoid some of the gotchas with fixed-frequency pulses: https://apps.dtic.mil/dtic/tr/fulltext/u2/479308.pdf https://apps.dtic.mil/dtic/tr/fulltext/u2/479308.pdf
- Junk_Collector 8y ago
  Skolnik's books are good but they are pretty old and focus mostly on the hardware/transmission of radar. The code sequencing is on the baseband signal processing side and is a direct result of IQ modulation being a thing in vector signal processing. Lots of modern radar designs use the same style of pseudo-random encoding to prevent interference between units. It's a major push in automotive radar right now (70GHz band) for instance. Think of it as encoding your mac address on each packet you transmit wirelessly so you can tell which signals come from which source.
  - vonmoltke 8y ago
    I don't recall such a scheme being used on either system I worked on. However, skimming the paper in your sibling's post it would be something done in the RF front end, which is probably why I never encountered it. The closest I got to the front end was pseudo-raw IQ from the pulses. It was also probably tied up in the anti-jamming measures, so it wouldn't get wide circulation on the programs.
    - Junk_Collector 8y ago

dbuder 8y ago

What about a malicious device for targeted and non targeted use, I mean you'd have to be really into tech to make a capable one, but none of those people using credit card scanners made their own.

Tomminn 8y ago

There's a trivial solution to this kind of problem. Frequency filtering. Essentially, you make sure that your light source beats at a peculiar frequency, and then you only look for signals in that beat with the same frequency. So you're only competing with LIDAR's beating at the same frequency. If you randomly select this frequency, you can have a lot of LIDAR's simultaneously operating without effecting one another.