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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 c

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?

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?