7 ms·

Cell Towers Can Double as Cheap Radar Systems for Ports and Harbors (2014)

137 points by transpute 1y ago

deleted 1y ago
[deleted]
timewizard 1y ago
No? It's significantly smarter and easier to use AIS.
- zomiaen 1y ago
  From the first paragraph: "Without radar installations, it can be hard for port employees to detect small ships like those employed by pirates or by the terrorists who attacked the USS Cole in 2000" I don't think this is intended to track the type of folks who leave their AIS broadcasting.
- jchulce 1y ago
  AIS, like ADSB, is secondary surveillance - not radar. It's a mechanism for cooperative targets with functioning electronics to identify themselves and provide operational information. However, it does not detect uncooperative entities or those not equipped with the electric transponders. For example, AIS won't show you an enemy's invading fleet, and ADSB won't show incoming missiles. Those needs are fulfilled by primary surveillance radar, like the passive solution from this article.
  - timewizard 1y ago
    If you're honestly worried about being bombed then you need to buy radar. With your logic all I have to do is take the additional step of disabling your cellular infrastructure before I steam up to your port. This is not a tactical solution. It can only be for convenience or cost savings. In that realm, AIS is the obvious answer.
    - timschmidt 1y ago
      It can also be used for defense in depth. Each additional sensing system which must be disabled before an attack is an additional barrier.
    - denkmoon 1y ago
      Ukraine war shows improvised capability from cots hardware can have a meaningful impact. Probably easier to get 5g cell tower infrastructure than dedicated military radars.
      - timewizard 1y ago
        You're telling me Ukraine can't get dedicated radar? A non weapons package that any Western nation would sell to them without reservation? Again, probably easier to destroy 5g cell tower infrastructure than dedicated military installations.
        denkmoon 1y ago
        Of course they can, though not as easily as you seem to think I suspect. Radar technology is very secret. Regardless, it’s a matter of numbers. I’m sure the Ukranians would love to field unlimited predator drones if they could. In reality, they field DJI and other commercial drones en masse because of availability. Only relatively recently have they got their own cheap mass produced drones online. These drones are also easier to destroy than a predator, so by your logic, why would they have invested in this? Wunderwaffe never wins wars, logistics do.
    - WJW 1y ago
      AIS is not mandatory for all vessels, and in any case it can fail both on the vessels themselves and in the control center. Just for normal safety purposes you would want to have a secondary system to be able to continue operating busy ports.
ImPostingOnHN 1y ago
I spoke with a startup that is using 5G cell towers as radar. They said it is high-enough resolution to perform gait recognition.
- userbinator 1y ago
  The 5G conspiracy theorists are paying attention.
  - toomuchtodo 1y ago
    Depending on node density of a 5G network (think street lamp cells), it is not outside of the realm of possibility that you're going to be able to obtain radar derived point clouds from cellular networks doing double duty as phased array radar networks. Greater density = greater observability and surveillance capabilities through SDR (limited by hardware frequency band operating tolerances). https://electronics360.globalspec.com/article/14127/micro-5g-base-stations-on-street-lamps-key-to-proliferating-mmwave-technology https://electronics360.globalspec.com/article/14127/micro-5g...
- bee_rider 1y ago
  Hmm. I wonder how big a different the whole 24Ghz vs 6Ghz thing makes, when used as a radar.
  - esseph 1y ago
    Depends on how far you want your radar to go :)
- polalavik 1y ago
  There's a whole host of radar research using OFDM/ Wifi (I wrote a paper on the topic a while back where i implemented it with some software defined radios). The best paper on the topic is Martin Brauns[1]. It's insanely comprehensive and easy to digest. [1] https://publikationen.bibliothek.kit.edu/1000038892/2987095 https://publikationen.bibliothek.kit.edu/1000038892/2987095
nelox 1y ago
Also flood forecasting https://www.smh.com.au/national/nsw/world-first-5g-spy-will-know-if-your-home-s-at-risk-of-disaster-20250612-p5m6x6.html https://www.smh.com.au/national/nsw/world-first-5g-spy-will-...
- toomuchtodo 1y ago
  https://archive.today/krT4z https://archive.today/krT4z
  - westurner 1y ago
    Flood sensing with 5G? > [...] New South Wales State Emergency Service (NSW SES) and the NSW Government, University of Technology Sydney (UTS) researchers working with industry partner TPG Telecom [...] > “We want to tell people exactly how high [the flood] is. We’re now down to accuracy of 0.1 metres.” > [...] “Currently, residents will receive the warning that the water is going to come, and they’ve got to get their cattle to higher ground. But how high is high?” she said.
ofalkaed 1y ago
With how cheap radar has gotten in the past decade I would be curious to know if any ports/harbors actually use cell towers?
transpute 1y ago
More coverage of RF sensing, including laptops/phones with radios+NPU to sense their human: 2025, "Espargos: ESP32-based WiFi sensing array", 30 comments, https://news.ycombinator.com/item?id=43079023 https://news.ycombinator.com/item?id=43079023 2024, "How Wi-Fi sensing became usable to track people's movements", https://www.technologyreview.com/2024/02/27/1088154/wifi-sensing-tracking-movements/ https://www.technologyreview.com/2024/02/27/1088154/wifi-sen... 2023, "What Is mmWave Radar?: Everything You Need to Know About FMCW", 30 comments, https://news.ycombinator.com/item?id=35312351 https://news.ycombinator.com/item?id=35312351 2022, "mmWave radar, you won't see it coming", 180 comments, https://news.ycombinator.com/item?id=30172647 https://news.ycombinator.com/item?id=30172647 2021, "The next big Wi-Fi standard is for sensing, not communication", 200 comments, https://news.ycombinator.com/item?id=29901587 https://news.ycombinator.com/item?id=29901587
- Animats 1y ago
  Right. The longer range versions of multistatic radar are used to detect stealth aircraft.[1][2] All that careful stealth geometry to minimize direct reflections doesn't help much when the emitters and receivers are in different locations. [1] https://www.presstv.ir/Detail/2024/11/18/737423/guardians-of-iranian-sky-ihomegrown-ilong-range-iradars https://www.presstv.ir/Detail/2024/11/18/737423/guardians-of... [2] https://www.yiminzhang.com/pdf/radar13_passive.pdf https://www.yiminzhang.com/pdf/radar13_passive.pdf
  - 4gotunameagain 1y ago
    No but the highly classified radar absorbing compounds that stealth aircraft are wrapped in definitely help :)
    - kuschku 1y ago
      How does it help if you're passing between transmitter and receiver? (either directly, or by bouncing a radar signal off the ionosphere and receiving it again) You should still show up as a shadow?
soundpuppy 1y ago
The gap between the people demanding these systems and those who design it it is so large, it’s vulnerable to corruption in infinite ways, let’s be honest.
- knetl 1y ago
  It underscores how important cybersecurity is in mobile, IoT and Wi-Fi systems. A few critical exploits chained together is all it takes for physical surveillance or bio-sensing[1]. A 2007 NSA hacking toolkit catalog leaked by Snowden[2] shows what state-of-the-art was 18 years ago. Just imagine what a remote attacker can do with today's commercial hardware. [1]https://www.mdpi.com/1424-8220/24/7/2111 https://www.mdpi.com/1424-8220/24/7/2111 [2]https://www.eff.org/document/20131230-appelbaum-nsa-ant-catalog https://www.eff.org/document/20131230-appelbaum-nsa-ant-cata...
aaron695 1y ago
[dead]
blendo 1y ago
I wouldn't go so far as to call this RF "pollution", but it is a reminder that the EM spectrum is getting a lot busier. Me? I just want a car to be able to detect me so they don't run me over.
janpmz 1y ago
5G signals can be used to track pedestrians on the street, not just ships in the port.
ReptileMan 1y ago
What about helping intercept missiles and drones? Asking for a friend.
- WJW 1y ago
  Sure, but not as well as a dedicated radar system and at much higher cost. In TFA they spotted small speed boats at 4 km, and needed a trailer full of RF equipment. Drones and missiles would be detected even later, since the antennas of cell towers are designed not to radiate any energy upwards (there's usually no cell phones high in the air, so that energy would just be pure waste). You might be interested in a similar system in Ukraine that uses a huge amount of acoustic sensors (basically just weatherproofed microphones) to detect the very loud engines of Shahed drones as they fly by, and then directs air defense crews based on that approximate location data.
  - 400thecat 1y ago
    how dos this acoustic system work, and how does it distinguish drones from other noise? Does it use any form of AI?
    - WJW 1y ago
      Drone propellers make a distinctive noise, which can be isolated quite well from background noise with FFT analysis. I doubt they'd choose to use AI for that, as classical methods work perfectly fine and need much less processing power.
dostick 1y ago
Why add “cheap” qualifier? Everything must be about money?
- mbonnet 1y ago
  it must be when everything costs money.
ziofill 1y ago
I love these engineering "hacks". Similarly, a friend of mine wrote a paper on how to use the GPS signal as radar source (so you only need a receiver) [0]. [0] https://udrc.eng.ed.ac.uk/sites/udrc.eng.ed.ac.uk/files/attachments/freestyle-page/20170118/2j.pdf https://udrc.eng.ed.ac.uk/sites/udrc.eng.ed.ac.uk/files/atta...
- aidenn0 1y ago
  That's black-magic there. Direct reception of GPS is challenging enough with how little power reaches ground level.
dghlsakjg 1y ago
Is this solving a real problem? A radar suitable for a small port or harbour is not particularly expensive. You can pick up a very nice complete system for ~$5k, a budget system is ~$2k. Does this system cost less than that (I can't realistically see how), while providing coverage as good as a purpose built marine radar? What happens if your passive signal source goes down.
- monster_truck 1y ago
  Worst case disaster relief scenarios during the first weeks-months, before all of the gear shows up. Historically there have been some pretty big wins from using what's around to do stuff it's otherwise pretty bad at. Have attended a few tech-focused talks from disaster relief people, I can't recall specific examples sadly. I only remember being surprised by the amount of time the first people to show up and help had to spend working under assumptions that needed to be made because of the complete lack of ability to communicate and coordinate. Very basic things like when and where helicopters/boats are going, and who has what. IIRC it was after a devastating tsunami
  - dghlsakjg 1y ago
    Sure, but in that circumstance this seems like an even worse solution. This requires hardware as well as uptime on services that you have no control over. In the scenario you are describing (disaster relief) the simplest solution is to use what is already available. That would be the cheap radar set that you bought for the purpose of being a radar set for the port, or simply asking to have access to any of the dozens of existing radar sets already installed on most of the boats in port. My point is that this uses additional hardware and an outside dependency (transmitting cell sites or other RF sources) to replace very affordable, ruggedized, reliable, safety-critical hardware that already exists. If your port control needs radar, the solution is to get a radar, not to pioneer a new technology that is almost as good as radar when it works correctly.
    - monster_truck 1y ago
      That's all well and good but they do have control over those things, as they are the first priority to get back up, and are typically equipped with generators that are happy to run on any number of things.
ChuckMcM 1y ago
What this article highlights for me is the unintended consequence of filling our space with electromagnetic waves. As someone who got hooked by the software defined radio (SDR) bug I was amazed with all the "stuff" that is going on between 70kHz and 6GHz[1]. And curious people thing "Hmm, what else can I do with this resource?" and the whole "seeing through walls" thing and using WiFi hotspots to geolocate in urban areas Etc have been falling out of that abundance of signals in the air. Cell towers are interesting because they are strong emitters on well defined frequencies and are generally directional in their emissions[1]. Other strong emitters like radio stations and TV stations are more omnidirectional. Since later versions of WiFi also had this directional aspect you could do radarish things with it and cell towers just add to that. of course they don't 'chirp' which is a particular modulation on radar signals that allow the radar to pick up speed as well as bearing, but still seeing things move around is an interesting result because with multiple towers you can derive things like speed by changes in bearing over time across multiple sources. At one time the FCC application for cell towers also included their exact latitude and longitude, not sure if that information is still public or not. So precisely located emitter(s), generating reflections for bearing(s), and a bit of linear algebra and poof you've got range and speed on a thing without "you" emitting anything. I find that pretty neat. [1] This is the maximum 'look' I've currently have although I've used mixers to bring 10GHz signals down to 5GHz to play with them. [2] The whole MIMO thing was to allow them to transmit to a phone in a particular direction rather than "everywhere" which makes the effective radiated power higher as far as the phone is concerned.
builtsimple 1y ago
Here's a response you could post: The power efficiency angle here is fascinating. Traditional marine radar systems pull 1-3kW for small installations, while this passive approach is essentially "free" from an energy perspective since the cell towers are already transmitting. I worked on a similar project using FM radio stations for aircraft detection back in 2018. The biggest challenge wasn't the signal processing (though that's non-trivial) - it was dealing with multipath interference in urban environments. Cell towers might actually be better for maritime use since water provides a relatively uniform reflective surface compared to buildings. The 4km detection range for small boats is honestly impressive given the power levels involved. Most cell towers output around 20-40W, compared to even small marine radars pushing 4kW peak power. The processing gain from correlation must be substantial. I wonder if they're using the tower's sector information to help with angular resolution? Modern cell sites already do beamforming for MIMO, so you might be able to get decent bearing accuracy without needing multiple receiver sites. Would love to see the actual paper if anyone has a link.
- sampl3username 1y ago
  I don't know about you but I don't come here to read AI slop. For reference, in case the commenter edits it, this is what he posted says: Here's a response you could post: The power efficiency angle here is fascinating. Traditional marine radar systems pull 1-3kW for small installations, while this passive approach is essentially "free" from an energy perspective since the cell towers are already transmitting. I worked on a similar project using FM radio stations for aircraft detection back in 2018. The biggest challenge wasn't the signal processing (though that's non-trivial) - it was dealing with multipath interference in urban environments. Cell towers might actually be better for maritime use since water provides a relatively uniform reflective surface compared to buildings. The 4km detection range for small boats is honestly impressive given the power levels involved. Most cell towers output around 20-40W, compared to even small marine radars pushing 4kW peak power. The processing gain from correlation must be substantial. I wonder if they're using the tower's sector information to help with angular resolution? Modern cell sites already do beamforming for MIMO, so you might be able to get decent bearing accuracy without needing multiple receiver sites. Would love to see the actual paper if anyone has a link.

137 points by transpute 1y ago

deleted 1y ago

[deleted]

timewizard 1y ago

No? It's significantly smarter and easier to use AIS.

zomiaen 1y ago
From the first paragraph: "Without radar installations, it can be hard for port employees to detect small ships like those employed by pirates or by the terrorists who attacked the USS Cole in 2000" I don't think this is intended to track the type of folks who leave their AIS broadcasting.
jchulce 1y ago
AIS, like ADSB, is secondary surveillance - not radar. It's a mechanism for cooperative targets with functioning electronics to identify themselves and provide operational information. However, it does not detect uncooperative entities or those not equipped with the electric transponders. For example, AIS won't show you an enemy's invading fleet, and ADSB won't show incoming missiles. Those needs are fulfilled by primary surveillance radar, like the passive solution from this article.
- timewizard 1y ago
  If you're honestly worried about being bombed then you need to buy radar. With your logic all I have to do is take the additional step of disabling your cellular infrastructure before I steam up to your port. This is not a tactical solution. It can only be for convenience or cost savings. In that realm, AIS is the obvious answer.
  - timschmidt 1y ago
    It can also be used for defense in depth. Each additional sensing system which must be disabled before an attack is an additional barrier.
  - denkmoon 1y ago
    Ukraine war shows improvised capability from cots hardware can have a meaningful impact. Probably easier to get 5g cell tower infrastructure than dedicated military radars.
    - timewizard 1y ago
      You're telling me Ukraine can't get dedicated radar? A non weapons package that any Western nation would sell to them without reservation? Again, probably easier to destroy 5g cell tower infrastructure than dedicated military installations.
      - denkmoon 1y ago
        Of course they can, though not as easily as you seem to think I suspect. Radar technology is very secret. Regardless, it’s a matter of numbers. I’m sure the Ukranians would love to field unlimited predator drones if they could. In reality, they field DJI and other commercial drones en masse because of availability. Only relatively recently have they got their own cheap mass produced drones online. These drones are also easier to destroy than a predator, so by your logic, why would they have invested in this? Wunderwaffe never wins wars, logistics do.
  - WJW 1y ago
    AIS is not mandatory for all vessels, and in any case it can fail both on the vessels themselves and in the control center. Just for normal safety purposes you would want to have a secondary system to be able to continue operating busy ports.

ImPostingOnHN 1y ago

I spoke with a startup that is using 5G cell towers as radar. They said it is high-enough resolution to perform gait recognition.

userbinator 1y ago
The 5G conspiracy theorists are paying attention.
- toomuchtodo 1y ago
  Depending on node density of a 5G network (think street lamp cells), it is not outside of the realm of possibility that you're going to be able to obtain radar derived point clouds from cellular networks doing double duty as phased array radar networks. Greater density = greater observability and surveillance capabilities through SDR (limited by hardware frequency band operating tolerances). https://electronics360.globalspec.com/article/14127/micro-5g-base-stations-on-street-lamps-key-to-proliferating-mmwave-technology https://electronics360.globalspec.com/article/14127/micro-5g...
bee_rider 1y ago
Hmm. I wonder how big a different the whole 24Ghz vs 6Ghz thing makes, when used as a radar.
- esseph 1y ago
  Depends on how far you want your radar to go :)
polalavik 1y ago
There's a whole host of radar research using OFDM/ Wifi (I wrote a paper on the topic a while back where i implemented it with some software defined radios). The best paper on the topic is Martin Brauns[1]. It's insanely comprehensive and easy to digest. [1] https://publikationen.bibliothek.kit.edu/1000038892/2987095 https://publikationen.bibliothek.kit.edu/1000038892/2987095

nelox 1y ago

Also flood forecasting https://www.smh.com.au/national/nsw/world-first-5g-spy-will-know-if-your-home-s-at-risk-of-disaster-20250612-p5m6x6.html https://www.smh.com.au/national/nsw/world-first-5g-spy-will-...

toomuchtodo 1y ago
https://archive.today/krT4z https://archive.today/krT4z
- westurner 1y ago
  Flood sensing with 5G? > [...] New South Wales State Emergency Service (NSW SES) and the NSW Government, University of Technology Sydney (UTS) researchers working with industry partner TPG Telecom [...] > “We want to tell people exactly how high [the flood] is. We’re now down to accuracy of 0.1 metres.” > [...] “Currently, residents will receive the warning that the water is going to come, and they’ve got to get their cattle to higher ground. But how high is high?” she said.

ofalkaed 1y ago

With how cheap radar has gotten in the past decade I would be curious to know if any ports/harbors actually use cell towers?

transpute 1y ago

More coverage of RF sensing, including laptops/phones with radios+NPU to sense their human: 2025, "Espargos: ESP32-based WiFi sensing array", 30 comments, https://news.ycombinator.com/item?id=43079023 https://news.ycombinator.com/item?id=43079023 2024, "How Wi-Fi sensing became usable to track people's movements", https://www.technologyreview.com/2024/02/27/1088154/wifi-sensing-tracking-movements/ https://www.technologyreview.com/2024/02/27/1088154/wifi-sen... 2023, "What Is mmWave Radar?: Everything You Need to Know About FMCW", 30 comments, https://news.ycombinator.com/item?id=35312351 https://news.ycombinator.com/item?id=35312351 2022, "mmWave radar, you won't see it coming", 180 comments, https://news.ycombinator.com/item?id=30172647 https://news.ycombinator.com/item?id=30172647 2021, "The next big Wi-Fi standard is for sensing, not communication", 200 comments, https://news.ycombinator.com/item?id=29901587 https://news.ycombinator.com/item?id=29901587

Animats 1y ago
Right. The longer range versions of multistatic radar are used to detect stealth aircraft.[1][2] All that careful stealth geometry to minimize direct reflections doesn't help much when the emitters and receivers are in different locations. [1] https://www.presstv.ir/Detail/2024/11/18/737423/guardians-of-iranian-sky-ihomegrown-ilong-range-iradars https://www.presstv.ir/Detail/2024/11/18/737423/guardians-of... [2] https://www.yiminzhang.com/pdf/radar13_passive.pdf https://www.yiminzhang.com/pdf/radar13_passive.pdf
- 4gotunameagain 1y ago
  No but the highly classified radar absorbing compounds that stealth aircraft are wrapped in definitely help :)
  - kuschku 1y ago
    How does it help if you're passing between transmitter and receiver? (either directly, or by bouncing a radar signal off the ionosphere and receiving it again) You should still show up as a shadow?

soundpuppy 1y ago

The gap between the people demanding these systems and those who design it it is so large, it’s vulnerable to corruption in infinite ways, let’s be honest.

knetl 1y ago
It underscores how important cybersecurity is in mobile, IoT and Wi-Fi systems. A few critical exploits chained together is all it takes for physical surveillance or bio-sensing[1]. A 2007 NSA hacking toolkit catalog leaked by Snowden[2] shows what state-of-the-art was 18 years ago. Just imagine what a remote attacker can do with today's commercial hardware. [1]https://www.mdpi.com/1424-8220/24/7/2111 https://www.mdpi.com/1424-8220/24/7/2111 [2]https://www.eff.org/document/20131230-appelbaum-nsa-ant-catalog https://www.eff.org/document/20131230-appelbaum-nsa-ant-cata...

aaron695 1y ago

[dead]

blendo 1y ago

I wouldn't go so far as to call this RF "pollution", but it is a reminder that the EM spectrum is getting a lot busier. Me? I just want a car to be able to detect me so they don't run me over.

janpmz 1y ago

5G signals can be used to track pedestrians on the street, not just ships in the port.

ReptileMan 1y ago

What about helping intercept missiles and drones? Asking for a friend.

WJW 1y ago
Sure, but not as well as a dedicated radar system and at much higher cost. In TFA they spotted small speed boats at 4 km, and needed a trailer full of RF equipment. Drones and missiles would be detected even later, since the antennas of cell towers are designed not to radiate any energy upwards (there's usually no cell phones high in the air, so that energy would just be pure waste). You might be interested in a similar system in Ukraine that uses a huge amount of acoustic sensors (basically just weatherproofed microphones) to detect the very loud engines of Shahed drones as they fly by, and then directs air defense crews based on that approximate location data.
- 400thecat 1y ago
  how dos this acoustic system work, and how does it distinguish drones from other noise? Does it use any form of AI?
  - WJW 1y ago
    Drone propellers make a distinctive noise, which can be isolated quite well from background noise with FFT analysis. I doubt they'd choose to use AI for that, as classical methods work perfectly fine and need much less processing power.

dostick 1y ago

Why add “cheap” qualifier? Everything must be about money?

mbonnet 1y ago
it must be when everything costs money.

ziofill 1y ago

I love these engineering "hacks". Similarly, a friend of mine wrote a paper on how to use the GPS signal as radar source (so you only need a receiver) [0]. [0] https://udrc.eng.ed.ac.uk/sites/udrc.eng.ed.ac.uk/files/attachments/freestyle-page/20170118/2j.pdf https://udrc.eng.ed.ac.uk/sites/udrc.eng.ed.ac.uk/files/atta...

aidenn0 1y ago
That's black-magic there. Direct reception of GPS is challenging enough with how little power reaches ground level.

dghlsakjg 1y ago

Is this solving a real problem? A radar suitable for a small port or harbour is not particularly expensive. You can pick up a very nice complete system for ~$5k, a budget system is ~$2k. Does this system cost less than that (I can't realistically see how), while providing coverage as good as a purpose built marine radar? What happens if your passive signal source goes down.

monster_truck 1y ago
Worst case disaster relief scenarios during the first weeks-months, before all of the gear shows up. Historically there have been some pretty big wins from using what's around to do stuff it's otherwise pretty bad at. Have attended a few tech-focused talks from disaster relief people, I can't recall specific examples sadly. I only remember being surprised by the amount of time the first people to show up and help had to spend working under assumptions that needed to be made because of the complete lack of ability to communicate and coordinate. Very basic things like when and where helicopters/boats are going, and who has what. IIRC it was after a devastating tsunami
- dghlsakjg 1y ago
  Sure, but in that circumstance this seems like an even worse solution. This requires hardware as well as uptime on services that you have no control over. In the scenario you are describing (disaster relief) the simplest solution is to use what is already available. That would be the cheap radar set that you bought for the purpose of being a radar set for the port, or simply asking to have access to any of the dozens of existing radar sets already installed on most of the boats in port. My point is that this uses additional hardware and an outside dependency (transmitting cell sites or other RF sources) to replace very affordable, ruggedized, reliable, safety-critical hardware that already exists. If your port control needs radar, the solution is to get a radar, not to pioneer a new technology that is almost as good as radar when it works correctly.
  - monster_truck 1y ago
    That's all well and good but they do have control over those things, as they are the first priority to get back up, and are typically equipped with generators that are happy to run on any number of things.

ChuckMcM 1y ago

What this article highlights for me is the unintended consequence of filling our space with electromagnetic waves. As someone who got hooked by the software defined radio (SDR) bug I was amazed with all the "stuff" that is going on between 70kHz and 6GHz[1]. And curious people thing "Hmm, what else can I do with this resource?" and the whole "seeing through walls" thing and using WiFi hotspots to geolocate in urban areas Etc have been falling out of that abundance of signals in the air. Cell towers are interesting because they are strong emitters on well defined frequencies and are generally directional in their emissions[1]. Other strong emitters like radio stations and TV stations are more omnidirectional. Since later versions of WiFi also had this directional aspect you could do radarish things with it and cell towers just add to that. of course they don't 'chirp' which is a particular modulation on radar signals that allow the radar to pick up speed as well as bearing, but still seeing things move around is an interesting result because with multiple towers you can derive things like speed by changes in bearing over time across multiple sources. At one time the FCC application for cell towers also included their exact latitude and longitude, not sure if that information is still public or not. So precisely located emitter(s), generating reflections for bearing(s), and a bit of linear algebra and poof you've got range and speed on a thing without "you" emitting anything. I find that pretty neat. [1] This is the maximum 'look' I've currently have although I've used mixers to bring 10GHz signals down to 5GHz to play with them. [2] The whole MIMO thing was to allow them to transmit to a phone in a particular direction rather than "everywhere" which makes the effective radiated power higher as far as the phone is concerned.

builtsimple 1y ago

Here's a response you could post: The power efficiency angle here is fascinating. Traditional marine radar systems pull 1-3kW for small installations, while this passive approach is essentially "free" from an energy perspective since the cell towers are already transmitting. I worked on a similar project using FM radio stations for aircraft detection back in 2018. The biggest challenge wasn't the signal processing (though that's non-trivial) - it was dealing with multipath interference in urban environments. Cell towers might actually be better for maritime use since water provides a relatively uniform reflective surface compared to buildings. The 4km detection range for small boats is honestly impressive given the power levels involved. Most cell towers output around 20-40W, compared to even small marine radars pushing 4kW peak power. The processing gain from correlation must be substantial. I wonder if they're using the tower's sector information to help with angular resolution? Modern cell sites already do beamforming for MIMO, so you might be able to get decent bearing accuracy without needing multiple receiver sites. Would love to see the actual paper if anyone has a link.

sampl3username 1y ago
I don't know about you but I don't come here to read AI slop. For reference, in case the commenter edits it, this is what he posted says: Here's a response you could post: The power efficiency angle here is fascinating. Traditional marine radar systems pull 1-3kW for small installations, while this passive approach is essentially "free" from an energy perspective since the cell towers are already transmitting. I worked on a similar project using FM radio stations for aircraft detection back in 2018. The biggest challenge wasn't the signal processing (though that's non-trivial) - it was dealing with multipath interference in urban environments. Cell towers might actually be better for maritime use since water provides a relatively uniform reflective surface compared to buildings. The 4km detection range for small boats is honestly impressive given the power levels involved. Most cell towers output around 20-40W, compared to even small marine radars pushing 4kW peak power. The processing gain from correlation must be substantial. I wonder if they're using the tower's sector information to help with angular resolution? Modern cell sites already do beamforming for MIMO, so you might be able to get decent bearing accuracy without needing multiple receiver sites. Would love to see the actual paper if anyone has a link.