hckrnws

The coolest hack in here is definitely the way that the 4G base station can be (mostly uniquely) identified after the RF signal for a packet is run through an envelope detector through a low-pass filter, as opposed to the normal (and higher-power) method of using a high-frequency oscillator and a demodulation chain.

How are they able to achieve sub-100 meter accuracy? I might be missing something, but In my experience, collecting the cellular parameters is the easy part. The challenge is knowing where the cells actually are. You can ask Google's geolocation API, but that typically returns a fix with ~1000 meter accuracy if it returns a fix at all. These databases are curated based on GPS+cellular information from millions of phones. There is no global source of truth.

If only base stations included location information in their transmissions...

FTA: Our localization approach combines open-source databases (OpenCellID [47], Mozilla Location Services [66], and CellMapper [12]) for PCI-to-coordinate mapping of cell towers with a trilateration technique based on relative signal strengths.

That doesn't really answer the question. Those services basically work the same way as Google's geolocation API, but they're somehow able to magically get better accuracy.

Google's cellular geolocation implementation is probably unmaintained & all their focus is on WiFi+GPS+Fusion via SLAM.

Your assertion seems to be that Google's location service must be the best, and there's no way a trivial method can outperform it.

Have you considered that google might just perform poorly compared to other methods?

Interesting.

CellMapper, at least, is not even a little bit open source. It doesn't even have an API.

This leads me to wonder what other details that FA provides which might have been fabricated from thin air.

If someone is focusing on extracting data for a small area, they can manually browse the CellMapper data. An API isn’t required for that—it’s a matter of accessing and analyzing what’s already available through the platform.

Does that make it "open source"?

Kinda, yeah. It's open source in the "intelligence" sense of the phrase because it's openly available information (like OSINT), but it's not freely usable.

Where I am (Australia) all the cellular base stations are licensed, and you can find the licence details including accurate lat/long online:

https://web.acma.gov.au/rrl/site_proximity.main_page

I had 2 questions: 1. what about data transmissions 2. what about using this on containers in the open seas?

The first questions is at least partly answered in the document, copied below. However, you still need a collection infrastructure to make this useful.

> Communicating locations: Localization trackers often need a communication module to periodically update location to a server or nearby hub. Standalone GPS trackers (e.g., [35] and [95]) often use cellular or satellite communications to do so. LiTEfoot can incorporate an NB-IoT module for relaying location data. Using a low-power NB-IoT transmitter [96], which consumes 76 mW to transmit a 140 kb packet in eDRX mode, the system can intermittently send updates hourly, daily, or monthly depending on the application. This enables LiTEfoot to operate for approximately 10 years on a coin cell. The same antenna frontend can be shared between LiTEfoot and the communication unit, maintaining a compact form factor while providing flexible communication capabilities.

There are many cheap ultra low power microcontrollers that can keep a time clock going and a small amount (say 32KB) of ram. 30 years on a coin cell. Pair that with a Bluetooth low energy transceiver to automatically transfer the data when the home base is in range (or any number of base stations). Like at a port in your example.

Cute idea, works only in a very narrow range of scenarios, namely: dense urban without strong near-CW interferers: It has a sensitivity of -70dBm, so it misses >50dB of the bottom dynamic range, present typically in urban indoor and also in non-urban areas. And it get saturated by any strong signal, so it will fail near FM stations, microwave links, and any other transmitter with near-constant signal. This type of wideband non-rf-filtered design usually has too many failure modes in real-world tests to become an actual useful product.

Cool. I want this for my cats, my kids, my keys and everything else.

But I wonder: if millions of this are deployed, would this weaken cellular signals (by drawing power from it)?

The interaction of EM waves and their behavior is a long and complex topic to address here, however, keep in mind that the signal is sent out into void - what happens after emitting does not concern the emitter. Think of it as rain falling down, or water from the sprinkler. If you catch the droplets you ll cast a "shadow". Completely surrounding the emitter might create "Faraday" cage of sorts. However in reality in the droplet analogy, the EM waves curve around the buckets and leave the shadow. The reception of EM waves is a wave-cancellation process, but thats a deep rabbit hole..

Do you currently have tracker tags on those things? If not, why not? Multi-year lifetimes are already available with Tile (3 years), AirTag (>1 year), and Samsung's SmartTag 2 (700 days), using BLE detection instead of 4G detection.

Millions of these would not degrade signal. A random bit of metal (like a quarter, as shown for scale) in between you an a 4G tower should have the same effect as one of these devices. They are detecting existing 4G signal, not using it for energy harvesting.

> Do you currently have tracker tags on those things?

Yes. I have AirTags on my fur babbies, but if I were to need to use them I'd be hoping they came within range of a device to pick them up. Then, in FindMy app, I could see where the had been, but not where they are now to go get them. I would hope a system like this could give me a much more current location. Hopefully, I'll never need any of this.

Thanks. I miss-read it and thought it's energy harvesting from celular.

I already have some trackers on important stuff (like keys and school bag of kids if they loose it in the bus). But for other use cases it's either too large (cats) or makes no sense to have too many because then I'd have to replace a battery every few weeks ("everything else").

> replace a battery every few weeks

make it easy on yourself and change them all on the same day like a clock reset day like the recommendation for your smoke detectors. bite the bullet and change change some early to get them on the same schedule. it's worth it for sanity

I got a newish RF cat tracker lately and really like it: https://tabcat.com/

It's not app or Bluetooth based (has an included detector) and it works pretty well. Battery is supposed to last a few months. It easily fits on a cat collar and doesn't bother mine at all. I've been looking for something like this for years and someone finally made one!

Relevant Don't Get Distracted (2017) https://news.ycombinator.com/item?id=42388354