5 ms·

What will happen if every single car has radar? Wouldn't they interfere? You're stuck in traffic and 300 nearby cars are blasting radars all over the place?

by dvh 2y ago

psunavy03 2y ago
There are various ways a radar (or any RF signal) can be designed to recognize its own signal from all the background noise. We don't worry about millions of cell phones or WiFi routers sharing bandwidth either.
- r2_pilot 2y ago
  Actually, in both cases, we do. Cell towers deliberately have different frequencies allocated from their neighboring towers, and Wi-Fi has multiple channels, several of which do not have any overlap.
  - psunavy03 2y ago
    When I said "we don't worry about it," I meant the problem has been acceptably mitigated.
    - mitthrowaway2 2y ago
      What that really means is that several talented people dedicated their entire careers to worrying about it!
- ssl-3 2y ago
  Neither of those examples answers the question. Co-channel Wifi interference is real. It really puts a damper on range and throughout compared to how it used to be. It is a largely unmitigated clusterfuck, as is the way with CSMA/CA once density increases enough. LTE interference isn't an important thing in practice, in part because because all participating devices have very tightly-controlled timings. It isn't a clusterfuck at all because of the mitigations in place, but it does require centralized coordination to be this way. Radars on cars don't have centralized coordination (do they?). What mechanism prevents their performance from degrading as wifi does?
  - r2_pilot 2y ago
    For your specific question, you can send a pulse train specific to the radar emitter, and you filter out anything that doesn't match your specific pulse train
    - ssl-3 2y ago
      How do I know that each of the pulses I sent out are the same ones I receive in reflection, in terms of frequency (remember, we have moving targets and therefore Doppler shift here), and amplitude? The reflections of my own pulses are pretty quiet compared to the pulses of, say, an oncoming vehicle's own radar transmissions. How do I discern those individually-received pulses from the very similar pulses that are being received from other transmitting vehicles? (Sure, their timings should be be different, and the pulses may be very brief. But they may also overlap rather significantly, and errors can be very bad here. We need some rather good certainty here -- however that certainty is accomplished.)
      - r2_pilot 2y ago
        Claude 3.5 Sonnet suggests the following for your questions : Distinguishing Radar Pulse Reflections To answer these questions, we need to consider several key aspects of radar technology and signal processing. Let's break it down: Identifying your own pulses: The main ways to distinguish your own reflected pulses from other sources are: a) Frequency: While there is Doppler shift due to moving targets, the shift is typically small compared to the carrier frequency. Modern radars use sophisticated signal processing to account for and measure this shift. b) Pulse coding: Radars often use unique pulse patterns or modulation schemes. This allows the receiver to correlate incoming signals with the known transmitted pattern, effectively filtering out other sources. c) Timing: The time delay between transmission and reception is used to calculate distance. Signals arriving at unexpected times can be filtered out. d) Direction: Using directional antennas or phased arrays, the radar system knows where it's transmitting and expects returns from that direction. Dealing with weak reflections and interference: a) High sensitivity receivers: Modern radar systems use very sensitive receivers to detect weak return signals. b) Signal processing: Advanced digital signal processing techniques can extract weak signals from noise and interfering sources. c) Frequency diversity: Some systems use multiple frequencies to improve detection and reduce interference. Discerning from other vehicle transmissions: a) Frequency allocation: Automotive radars typically operate in specific frequency bands. Within these bands, individual systems may use slightly different frequencies. b) Time diversity: The probability of pulse overlap decreases with shorter pulse durations. Many modern systems use very short pulses or continuous wave techniques. c) Spatial filtering: Directional antennas help focus on specific areas, reducing interference from other directions. d) Signal characteristics: Different radar systems may use distinct modulation schemes, pulse repetition frequencies, or other signal characteristics that can be used to differentiate them.
- mitthrowaway2 2y ago
  Nonetheless, even in the very best case, every other radar still increases the background noise floor that each radar has to distinguish its own signal above. It won't ruin the signal completely, but it will affect how much scan time or output power is needed, or the detection resolution it can attain.
  - interloxia 2y ago
    Cars use a lot of space and don't pack very tightly. Most of the time. Any idea what the range of influence on the noise floor is/will likely be?
kube-system 2y ago
> What will happen if every single car has radar? If you're on the road in a relatively affluent area where people drive late model cars, this is pretty close to already the case. Automakers have started making these systems standard on many/all of their models in the US for several years now. Toyota, for example, started rolling out these systems a decade ago, and have been standard on all US models since 2018. I'm not sure what these systems use in practice for interference mitigations, but there's a bunch of stuff that could be done, for instance, hopping between different frequencies.
curiousfab 2y ago
Typical FMCW radars transmit very short ramps (microseconds) at a very long (relatively) intervals (several ten milliseconds), i.e. a duty cycle of less than 0.1%. In order to create interference between two radars, the ramps have to overlap pretty exactly, within a few nanoseconds of each other. This is very unlikely to happen. Modern radars employ technologies to detect and/or avoid such collisions. Overall it is not really an issue, even with many radars in crowded spaces.
- abstrakraft 2y ago
  This is true for some earlier lofi radars, but as driver assistance and self-driving have developed, so have the requirements and capabilities of the radar systems. Newer systems generally have shorter PRIs for higher doppler bandwidth, and much higher duty cycles for more energy on target - the FCC limits power, so you've got to get energy from the time axis. Both of these things make the interference problem harder.
- aidenn0 2y ago
  How is it continuous wave if it has a non-unity duty cycle?
  - abstrakraft 2y ago
    In practice, the difference between pulsed radar and continuous wave radar is a continuum rather than a dichotomy. Historically, FMCW (frequency modulated continuous wave) had a high duty cycle (though not 100%, the ramp generators need finite time to reset (though you can alternate between up and downramps and get closer)). For some applications, though, requirements force you to short ramps and long PRIs, thus low duty cycles, but the name (FMCW) sticks.
kazinator 2y ago
I suspect radar like this needs only a tiny time slices to do its work. Say for example that it's only necessary to get updates about the moving object 100 times per second: every 10 ms. The radar pulse durations necessary to do the job can probably be measured in microseconds, though. A 10 ms separation between pulses measured in microseconds is a large amount of empty space.
deleted 2y ago
[deleted]
isopede 2y ago
Interference is a real problem with FMCW radars, either maliciously in the case of electronic warfare, or accidentally in the case you mentioned, with many radars in the same space using the same frequency band. Wifi and cell phones use time division or frequency division multiplexing techniques, but radars (at least current-gen) generally do not. There are mitigation techniques like randomization of chirp frequencies, choosing different idle times between frames, and signal processing techniques to try to detect interference and filter it out. In the general case, FMCW techniques will always have interference problems. This is one reason amongst many others that military radars do not use FMCW but instead coded pulse compression techniques.

What will happen if every single car has radar? Wouldn't they interfere? You're stuck in traffic and 300 nearby cars are blasting radars all over the place?

by dvh 2y ago

What will happen if every single car has radar? Wouldn't they interfere? You're stuck in traffic and 300 nearby cars are blasting radars all over the place?

psunavy03 2y ago

There are various ways a radar (or any RF signal) can be designed to recognize its own signal from all the background noise. We don't worry about millions of cell phones or WiFi routers sharing bandwidth either.

r2_pilot 2y ago
Actually, in both cases, we do. Cell towers deliberately have different frequencies allocated from their neighboring towers, and Wi-Fi has multiple channels, several of which do not have any overlap.
- psunavy03 2y ago
  When I said "we don't worry about it," I meant the problem has been acceptably mitigated.
  - mitthrowaway2 2y ago
    What that really means is that several talented people dedicated their entire careers to worrying about it!
ssl-3 2y ago
Neither of those examples answers the question. Co-channel Wifi interference is real. It really puts a damper on range and throughout compared to how it used to be. It is a largely unmitigated clusterfuck, as is the way with CSMA/CA once density increases enough. LTE interference isn't an important thing in practice, in part because because all participating devices have very tightly-controlled timings. It isn't a clusterfuck at all because of the mitigations in place, but it does require centralized coordination to be this way. Radars on cars don't have centralized coordination (do they?). What mechanism prevents their performance from degrading as wifi does?
- r2_pilot 2y ago
  For your specific question, you can send a pulse train specific to the radar emitter, and you filter out anything that doesn't match your specific pulse train
  - ssl-3 2y ago
    How do I know that each of the pulses I sent out are the same ones I receive in reflection, in terms of frequency (remember, we have moving targets and therefore Doppler shift here), and amplitude? The reflections of my own pulses are pretty quiet compared to the pulses of, say, an oncoming vehicle's own radar transmissions. How do I discern those individually-received pulses from the very similar pulses that are being received from other transmitting vehicles? (Sure, their timings should be be different, and the pulses may be very brief. But they may also overlap rather significantly, and errors can be very bad here. We need some rather good certainty here -- however that certainty is accomplished.)
    - r2_pilot 2y ago
      Claude 3.5 Sonnet suggests the following for your questions : Distinguishing Radar Pulse Reflections To answer these questions, we need to consider several key aspects of radar technology and signal processing. Let's break it down: Identifying your own pulses: The main ways to distinguish your own reflected pulses from other sources are: a) Frequency: While there is Doppler shift due to moving targets, the shift is typically small compared to the carrier frequency. Modern radars use sophisticated signal processing to account for and measure this shift. b) Pulse coding: Radars often use unique pulse patterns or modulation schemes. This allows the receiver to correlate incoming signals with the known transmitted pattern, effectively filtering out other sources. c) Timing: The time delay between transmission and reception is used to calculate distance. Signals arriving at unexpected times can be filtered out. d) Direction: Using directional antennas or phased arrays, the radar system knows where it's transmitting and expects returns from that direction. Dealing with weak reflections and interference: a) High sensitivity receivers: Modern radar systems use very sensitive receivers to detect weak return signals. b) Signal processing: Advanced digital signal processing techniques can extract weak signals from noise and interfering sources. c) Frequency diversity: Some systems use multiple frequencies to improve detection and reduce interference. Discerning from other vehicle transmissions: a) Frequency allocation: Automotive radars typically operate in specific frequency bands. Within these bands, individual systems may use slightly different frequencies. b) Time diversity: The probability of pulse overlap decreases with shorter pulse durations. Many modern systems use very short pulses or continuous wave techniques. c) Spatial filtering: Directional antennas help focus on specific areas, reducing interference from other directions. d) Signal characteristics: Different radar systems may use distinct modulation schemes, pulse repetition frequencies, or other signal characteristics that can be used to differentiate them.
mitthrowaway2 2y ago
Nonetheless, even in the very best case, every other radar still increases the background noise floor that each radar has to distinguish its own signal above. It won't ruin the signal completely, but it will affect how much scan time or output power is needed, or the detection resolution it can attain.
- interloxia 2y ago
  Cars use a lot of space and don't pack very tightly. Most of the time. Any idea what the range of influence on the noise floor is/will likely be?

kube-system 2y ago

> What will happen if every single car has radar? If you're on the road in a relatively affluent area where people drive late model cars, this is pretty close to already the case. Automakers have started making these systems standard on many/all of their models in the US for several years now. Toyota, for example, started rolling out these systems a decade ago, and have been standard on all US models since 2018. I'm not sure what these systems use in practice for interference mitigations, but there's a bunch of stuff that could be done, for instance, hopping between different frequencies.

curiousfab 2y ago

Typical FMCW radars transmit very short ramps (microseconds) at a very long (relatively) intervals (several ten milliseconds), i.e. a duty cycle of less than 0.1%. In order to create interference between two radars, the ramps have to overlap pretty exactly, within a few nanoseconds of each other. This is very unlikely to happen. Modern radars employ technologies to detect and/or avoid such collisions. Overall it is not really an issue, even with many radars in crowded spaces.

abstrakraft 2y ago
This is true for some earlier lofi radars, but as driver assistance and self-driving have developed, so have the requirements and capabilities of the radar systems. Newer systems generally have shorter PRIs for higher doppler bandwidth, and much higher duty cycles for more energy on target - the FCC limits power, so you've got to get energy from the time axis. Both of these things make the interference problem harder.
aidenn0 2y ago
How is it continuous wave if it has a non-unity duty cycle?
- abstrakraft 2y ago
  In practice, the difference between pulsed radar and continuous wave radar is a continuum rather than a dichotomy. Historically, FMCW (frequency modulated continuous wave) had a high duty cycle (though not 100%, the ramp generators need finite time to reset (though you can alternate between up and downramps and get closer)). For some applications, though, requirements force you to short ramps and long PRIs, thus low duty cycles, but the name (FMCW) sticks.

kazinator 2y ago

I suspect radar like this needs only a tiny time slices to do its work. Say for example that it's only necessary to get updates about the moving object 100 times per second: every 10 ms. The radar pulse durations necessary to do the job can probably be measured in microseconds, though. A 10 ms separation between pulses measured in microseconds is a large amount of empty space.

deleted 2y ago

[deleted]

isopede 2y ago

Interference is a real problem with FMCW radars, either maliciously in the case of electronic warfare, or accidentally in the case you mentioned, with many radars in the same space using the same frequency band. Wifi and cell phones use time division or frequency division multiplexing techniques, but radars (at least current-gen) generally do not. There are mitigation techniques like randomization of chirp frequencies, choosing different idle times between frames, and signal processing techniques to try to detect interference and filter it out. In the general case, FMCW techniques will always have interference problems. This is one reason amongst many others that military radars do not use FMCW but instead coded pulse compression techniques.