4 ms·

Sorry, I know very little about this stuff, but how does LIDAR avoid interference with other cars emitting LIDAR?

brians 9y ago
Coded pulses: rather than emitting a uniform beam, they emit a pulse and listen for that back. You can think of it a little like a bar code, a sequence of short and long, on and off. Then select for that on receive.
- rubicon33 9y ago
  what happens if another source uses the same pattern?
  - DaiPlusPlus 9y ago
    LIDAR units could cycle through randomly-generated patterns for each pulse - if they can be made unpredictable then it would be impossible for someone to confuse a LIDAR unit by copying its pulses. Assuming it's a time-of-flight LIDAR then the time required for an attacker to read a pulse and send back their own signal would be greater than the time of the original signal to return - and if the sending LIDAR has a sufficiently short timeout then even an attacker using Vanta-black to absorb all of the victim's lasers still won't be able to respond quickly enough.
Judgmentality 9y ago
Nobody likes to talk about it, but they don't. It turns out there are some clever tricks you can do if you control all the cars, but if not you have to get competitors to agree to some protocols.
- CamperBob2 9y ago
  What's wrong with modulating the beam with a PRN code that's unique to each vehicle?
  - Judgmentality 9y ago
    There are a couple difficulties with this. For starters, in order to make lidar eye safe, it has to use incredibly short pulses of light. You're saying we need to take that single pulse and replace it with enough of them that it has a unique fingerprint - realistically it will have at least 5x the energy. Add in signal degradation and a safety buffer and you likely need at least 10x the energy to uniquely identify sensors. Suddenly the invisible lidar is visible and dangerous for regular use. Of course this only applies to the visible spectrum - Luminar is actually unique in using a 1500nm laser. In addition to the above, it just makes everything a lot more complicated and expensive when everybody is racing to make it cheaper.
keerthiko 9y ago
Much the same way two routers broadcasting different WiFi networks in the same space and received by two different computers don't really interfere with each other. It's all just EM stuff, you can apply standard EM communication protocols like modulation. However standards will still be necessary, it can indeed be messed with.
- Piskvorrr 9y ago
  Haha. Not much, except clobbering each other. This is not too probable with two routers, but with a dozen, all trying to work at 2412 MHz ("channel 1"), the SNR tends towards 0.
Symmetry 9y ago
Lidars are highly directional and have low duty cycles so even when large numbers are present the amount of interference is small. So you do have to model a certain amount of noise in your lidar returns but you have to do that anyways due to things like sun reflecting off of shiny surfaces. Noisy sensors have been a fact in autonomous robots for as long as there have been autonomous robots and there are a variety of standard techniques for coping.

Coded pulses: rather than emitting a uniform beam, they emit a pulse and listen for that back. You can think of it a little like a bar code, a sequence of short and long, on and off. Then select for that on receive.

rubicon33 9y ago
what happens if another source uses the same pattern?
- DaiPlusPlus 9y ago
  LIDAR units could cycle through randomly-generated patterns for each pulse - if they can be made unpredictable then it would be impossible for someone to confuse a LIDAR unit by copying its pulses. Assuming it's a time-of-flight LIDAR then the time required for an attacker to read a pulse and send back their own signal would be greater than the time of the original signal to return - and if the sending LIDAR has a sufficiently short timeout then even an attacker using Vanta-black to absorb all of the victim's lasers still won't be able to respond quickly enough.

Judgmentality 9y ago

Nobody likes to talk about it, but they don't. It turns out there are some clever tricks you can do if you control all the cars, but if not you have to get competitors to agree to some protocols.

CamperBob2 9y ago
What's wrong with modulating the beam with a PRN code that's unique to each vehicle?
- Judgmentality 9y ago
  There are a couple difficulties with this. For starters, in order to make lidar eye safe, it has to use incredibly short pulses of light. You're saying we need to take that single pulse and replace it with enough of them that it has a unique fingerprint - realistically it will have at least 5x the energy. Add in signal degradation and a safety buffer and you likely need at least 10x the energy to uniquely identify sensors. Suddenly the invisible lidar is visible and dangerous for regular use. Of course this only applies to the visible spectrum - Luminar is actually unique in using a 1500nm laser. In addition to the above, it just makes everything a lot more complicated and expensive when everybody is racing to make it cheaper.

keerthiko 9y ago

Much the same way two routers broadcasting different WiFi networks in the same space and received by two different computers don't really interfere with each other. It's all just EM stuff, you can apply standard EM communication protocols like modulation. However standards will still be necessary, it can indeed be messed with.

Piskvorrr 9y ago
Haha. Not much, except clobbering each other. This is not too probable with two routers, but with a dozen, all trying to work at 2412 MHz ("channel 1"), the SNR tends towards 0.

Symmetry 9y ago

Lidars are highly directional and have low duty cycles so even when large numbers are present the amount of interference is small. So you do have to model a certain amount of noise in your lidar returns but you have to do that anyways due to things like sun reflecting off of shiny surfaces. Noisy sensors have been a fact in autonomous robots for as long as there have been autonomous robots and there are a variety of standard techniques for coping.