userbinator
6 hours ago
A friend recently got a (carrier-supplied) phone and has been complaining about how it would often have no reception despite showing a good signal; taking mine to the same areas on the same carrier and doing a comparison, mine was indeed showing no bars on the signal indicator. The difference is, mine predates this stupidity, and I can also see the details in the MTK Engineer Mode app, which shows the actual signal strength --- it was around -140dBm when it was showing 0 bars.
The signal strength measurement is actually standardised: https://en.wikipedia.org/wiki/Mobile_phone_signal#ASU
dataflow
6 hours ago
> taking mine to the same areas on the same carrier and doing a comparison
Unfortunately I don't think it's that simple. I've seen one phone simultaneously show significantly different numbers of bars for two SIMs installed in it for the same exact network and operator. After a while they become similar... then differ again... etc.
I have no clue how to explain it yet, but what I do know is that it literally makes no sense with a naive model of how these work, whether you try to explain it as reception or deception.
objectcode
4 hours ago
The phone selects a RAT (radio access technology) and frequency for each SIM slot.
After selecting, each SIM slot is subject to inter freq / inter RAT reselection / handover.
Both are controlled by messages received from the tower (e.g. on 4GLTE, for reselection, System Information messages), though there is an additional constraint: what's supported by/enabled in the phone.
Perhaps one SIM slot was in the connected state and the other was in the idle state at one point. So the reselection logic applied for one and the handover logic applied for the other. There is for example a problem called ping pong handover. Once a phone is switched to a different frequency or RAT, the tower may have the phone be sort of stuck in the new frequency, until the conditions of the previous RAT or frequency improve substantially, in order to prevent the phone being like a ping pong ball between the two. This frees resources that would otherwise be spent on repeated handover-related messages.
Each frequency has its own signal strength (free space path loss, transmit power, one frequency might be on one tower and another might be on another, etc).
lukec11
5 hours ago
This is usually for a good reason - dual sim phones are almost always “DSDS”, or “Dual SIM Dual Standby”. The secondary SIM, because it doesn’t need to make a data connection, parks itself on the lowest-frequency (and therefore usually lowest-bandwidth) connection it can find. Meanwhile, your data-connected SIM is busy trying to stream a video or upload your photos, so it’s using a higher-frequency + higher bandwidth connection, resulting in a lower signal strength.
dataflow
5 hours ago
> Meanwhile, your data-connected SIM is busy trying to stream a video or upload your photos
You're making huge and incorrect assumptions here, no? This also happens when your phone is entirely idle... and it randomly changes if you sit still for some time...
hulitu
6 hours ago
> I have no clue how to explain it yet
Android is quiet lazy searching for towers.
userbinator
5 hours ago
I think it has more to do with the cellular modem itself, or precisely the firmware it's running; of which there is much more diversity on the Android side.
devmor
5 hours ago
As I read this comment on my iPhone 15, I have 1 bar of 5G signal on one esim and 3 bars of signal on the other.
This suggests that the issue is not related to Android.
brewdad
5 hours ago
When we visit downtown of our city, I get great data coverage. My wife, on a different model but same gen iPhone and same plan, gets nothing. Her phone shows three or four bars but her apps won't load anything.
No idea why, especially since I'm the one who installs ad blockers and such. Her phone is essentially stock.
toast0
3 hours ago
> My wife, on a different model but same gen iPhone and same plan, gets nothing.
Some generations, different Apple models have pretty different radios. Is there a difference in bands or ?
Yizahi
an hour ago
I highly recommend Network Cell Info Lite app for the network diag. It shows signal strength with all details for each of the SIM modules, shows on a map in real time where are the base station you are currently connected to, and other interesting statistics.