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Observing my cellphone switch towers

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Re: Observing my cellphone switch towers

#31

Post by aembleton »

ganafagol wrote: post #18
rcarmo wrote: post #16

This is nicely done, and takes me back to when I worked in mobile network planning. Most people are blissfully unaware of how much radio chatter and constant adjustment is actually holding up their browsing session from second to second, with the UE negotiating the best possible terms (power, throughput, etc.) with adjacent cell towers before it decides (or is prompted) to hand-over to a new cell. Optimizing cell han…

Um, I'm pretty sure that there is not much of that handover stuff happening while browsing hacker news since that's likely in a low-velocity scenario, i.e., sitting on the toilet.

Might be sitting on the toilet in a train

Re: Observing my cellphone switch towers

#32

Post by rurban »

vbsteven wrote: post #20

On a related note, this same mechanism can be used as a fallback for GPS to determine device location. I have worked on an IoT device with builtin SIM in the personal alarm space. Often when a device is indoors no GPS fix can be found, but the GSM module can report all celltower ids in range with signal strengths. These can be used to triangulate the device location. Google has an API for this where you can pass celt…

I'm doing same right now. My cheap soc has no gps module, which would need too much power also, but I can trivially get the tac+cellid from the AT+CEREG command, which have to do anyway to check network connection (I have no roaming with NB-IoT). And from this you can externally get the lat/long gps values via the OpenCellID database. They protected queries, but you can get the source also as csv. Didn't know about the Google API, but it's trivial to build something like this by yourself.

In my case I don't even need the gps coords, the cellid is enough, as my devices travel on fixed lines through various countries. For cars or buses you would need it though.

Re: Observing my cellphone switch towers

#33

Post by elric »

ng55QPSK wrote: post #2

"There are no open source LTE stack to learn from" https://osmocom.org/projects

That website is not the greatest for finding out about the state of the projects, as in, is anyone using this? Are there any notable deployments?

Can someone shed some light on this?

Re: Observing my cellphone switch towers

#34

Post by aembleton »

ganafagol wrote: post #17

Would be great to have an app that shows a map with my position and the position of the current cell. And that could create such maps as in the article on-the-fly. Anybody knows of such an app?

Network cell info https://play.google.com/store/apps/details?id=com.wilysis.ce...

Re: Observing my cellphone switch towers

#35

Post by WJW »

ganafagol wrote: post #18
rcarmo wrote: post #16

This is nicely done, and takes me back to when I worked in mobile network planning. Most people are blissfully unaware of how much radio chatter and constant adjustment is actually holding up their browsing session from second to second, with the UE negotiating the best possible terms (power, throughput, etc.) with adjacent cell towers before it decides (or is prompted) to hand-over to a new cell. Optimizing cell han…

Um, I'm pretty sure that there is not much of that handover stuff happening while browsing hacker news since that's likely in a low-velocity scenario, i.e., sitting on the toilet.

It can also happen due to other phones in the tower area moving and needing more or less power, which might result in "the system" deciding to move your phone over to another tower to reduce congestion. Even if you are just sitting on the toilet.

Re: Observing my cellphone switch towers

#36

Post by kqr »

vbsteven wrote: post #20

On a related note, this same mechanism can be used as a fallback for GPS to determine device location. I have worked on an IoT device with builtin SIM in the personal alarm space. Often when a device is indoors no GPS fix can be found, but the GSM module can report all celltower ids in range with signal strengths. These can be used to triangulate the device location. Google has an API for this where you can pass celt…

> I assume this is one of the many things Google is doing with their fleet of Streetview cars.

...and Google services-enabled Android smartphones.

Source: I have used a single access points in many locations across the country in a relatively short period of time. When there's no GPS fix, Google always thinks I'm where I just was. (And there are no Streetview cars in some of these locations.)

Re: Observing my cellphone switch towers

#37

Post by londons_explore »

kqr wrote: post #36
vbsteven wrote: post #20

On a related note, this same mechanism can be used as a fallback for GPS to determine device location. I have worked on an IoT device with builtin SIM in the personal alarm space. Often when a device is indoors no GPS fix can be found, but the GSM module can report all celltower ids in range with signal strengths. These can be used to triangulate the device location. Google has an API for this where you can pass celt…

> I assume this is one of the many things Google is doing with their fleet of Streetview cars. ...and Google services-enabled Android smartphones. Source: I have used a single access points in many locations across the country in a relatively short period of time. When there's no GPS fix, Google always thinks I'm where I just was. (And there are no Streetview cars in some of these locations.)

If an access point moves more than a few times per year, it will be blacklisted from Googles location database as unreliable.

Re: Observing my cellphone switch towers

#38

Post by hansor »

It's quite hilarious seeing bunch of skilled and intelligent hackers being excited regrading process known as "Handover" :) It is well known, and well documented in every single book in subject...

Worth to mention that there are 3 types of handovers:

- Intra-relations: user can be switched between various cells at same tower.

- Intra-relations but with handover to lower technology (let's say when 4g is not available[too much traffic], so you will be dropped to let's say 3g or even 2g cell)

- External-relations: relations between cells on different towers.

As for towers:

- Not all operators allows for local roaming between various operators.

- Most towers have 3-5 sectors (pizza slices), but it's not that unusual to see OMNI antennas(single sector for 360 degrees).

Re: Observing my cellphone switch towers

#39

Post by hansor »

masklinn wrote: post #27
Balantio wrote: post #3

How do i do this myself now? I always have put my phone in air plane mode when i was in a train due to the modem consuming a lot more energy. I always assumed and still doe its due switching towers and less connecitivy which means using more power. Whenever people argue that public transport doesn't need wifi i would argue against it due to power usage and also for more accessablity of the internet in general.

> How do i do this myself now? As the essay notes, it's through TelephonyManager on Android. On iOS it used to be possible through CoreTelephony private APIs, but I think Apple cracked down on these a few years back and either removed them entirely or locked them down behind entitlements, as they were getting abused by analytics frameworks.

There are plenty of free android applications showing you your local cellular info with CID LAC, CI etc.

For example "Signal strength" APK. It's just matter of time until you will find one with logging and export ability. You can always write it down with pencil :)

Re: Observing my cellphone switch towers

#40

Post by kqr »

londons_explore wrote: post #37
kqr wrote: post #36

Earlier quoted context omitted.

> I assume this is one of the many things Google is doing with their fleet of Streetview cars. ...and Google services-enabled Android smartphones. Source: I have used a single access points in many locations across the country in a relatively short period of time. When there's no GPS fix, Google always thinks I'm where I just was. (And there are no Streetview cars in some of these locations.)

If an access point moves more than a few times per year, it will be blacklisted from Googles location database as unreliable.

This AP definitely moved a few times per year, so it must have skirted just below that threshold, then.
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