Comment by BatteryMountain
5 hours ago
Here's another one for you: today I found out that my dual-sim android phone has a single radio that is shared between the two sims. So when you are on a call, the 4G/5G doesn't work on the other sim, likewise, sometimes the the voice sim is unavailable while the other sim engaged with 4G/5G things... which is just stupid. Can't they just add two radios/chips (like many wifi AP's....)? So the whole setup on a consumer phone is actually quite unreliable because of reusing a single radio. I thought it was my buggy code, but nope, just the radio being shared and the mobile operator seeing the sim as offline. Crazy.
I can't speak to your specific setup, but if the two SIMs use different carriers then they will often need to use different frequencies. A phone could in theory use twice as many radios, but the emitted power limits would be the same, so you'd have reduced range or throughout for each (plus additional size, weight and power for the second radio). Access points have different SWaP budgets than phones.
When I travel, I try to use an eSIM that uses a network my home provider partners with. This seems to improve the chance that voice and data over LTE or 5G NR work simultaneously.
An additional radio would raise the price of your phone for at least another 200 or 300 dollars. Try to enable VoLTE if available for your operator. That makes the phone use the LTE connection for voice and don't drop the Internet connection while you talk.
You can get an additional phone with a screen, 5g radio, ram and everything for $150. An additional radio should not raise the price for another 300.
I assume for something like a phone these things are non-linear. going from 2 PCIe lanes (nand, radios) to 3 (another radio) may cause an SOC to jump from entry-level to mid-level, larger PCB and increased layer count, more antenna for simultaneous use, etc. so its not just the cost of the chip but all the secondary effects.
Dual SIM Dual Active phones are under £100 in the UK, I imagine under $100 in the US.
Dual SIM Dual Standby (two or more SIMs, one radio) is cheaper, less battery, less space, and usually good enough. It's literally a few dollars, not 200-300.
Seems like I forgot to specify "5G" (those radios tend to be expensive) as the original poster was asking for an additional 4G/5G radio.
DSDA in 5G is rare, and I can't reliably find a phone that can do it in EU or US (I can find higher end chipsets that can do it, but phone vendors don't seem to follow through with it). Usually it's 4G+5G or 4G+4G.
The chips cost under $100 even for top tier modems from Qualcomm.
Voice is normally done using VoLTE now.
Yep, although (at least in my experience) it's not enabled by default. I also learnt about VoWiFi (also called "WiFi Calling") that allows you using WiFi for calling, including when you're abroad or you don't even have phone signal.
Support for VoWiFi is a bit weird. Some operators don't allow it outside of your region (for example, the EU), some others will allow it and even bill you as if it were a local call made from your country.
Also, although it's in theory made only for working through WiFi, seems like if you have a second SIM or eSIM with a data plan (for example, a travel SIM local for the country you're on vacations) and some combination of phone and/or operators, it can use the second SIM as the data provider for WiFi Calling.
For the major US carriers, since they shut down 3G, VoLTE is the only way calls work. Which meant that a non-VoLTE-but-4G-capable device can no longer make 911 calls.
I was using a Samsung S5 running LineageOS for a while with Google voice for calls, but the no 911 thing is one of the main reasons I finally moved to a different phone. The S5 supports VoLTE but only with stock firmware.
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Not for everyone in many places. Many carriers still only allow VoLTE for a limited alow-list of phone models. Any customers of those with less popular models still gets dropped to 3G calls.
> Can't they just add two radios/chips
no. Too expensive.
Ironically, the cheapest phones available all tend to have Dual SIM Dual Active, usually because (in Europe at least) many have a second SIM card specifically for international calls.
So yes, it's "too expensive" because it's higher than $0, but it's not "too expensive" as in it would cost a lot.