New DUAL SIM finally works on my MI8 :-)

[Don Henry]

Over the last updates I always experienced severely weak and unreliable network coverage performance on my MI8, when both sim cards were active.
I checked both sim cards in different devices and they were working fine. Also, in the MI8 they are functioning alright, when only one is active.
So, to me it seems that in the MI8 the two cards are interfering and disturbing each other's network quality.
Please find attached a few screen shots. They were taken in the exact same position and after rebooting the phone.
It drives me mad, and in effect, I do not have a reliable phone.
I played around with the "preferred network type" (i.e. switching between 3G and 4G). When both cards are on 3G, they seem to at least have a stable signal, but only low quality.
Is this problem known? Are Xiaomi and/or you experts perhaps already working on a solution?
Cheers...Henry

 

[cobben]

I don't know about Mi8, but this might be a general problem on most/all newer "fullscreen" devices.

I found this in a Xiaomi weibo post on antenna design problems with the new Mix3, where they brag about having reduced the antenna area by 72%!:


"With the popularity of the full screen, the proportion of mobile phone screens has further increased, leaving less space for RF and antennas, and various manufacturers have racked their brains on balancing design and signal quality issues. Supporting more 4G network bands has further increased the difficulty of antenna design."

 

[Don Henry]

Thanx mate! That's interessting..

A smart phone (even a 'Phablet') still remains a cell phone, and the 'phone part' of the device should still work reliably, especially for emergency calls. Besides, without a stable network reception, users cannot reliably use the mobile data connections for their apps either...
My older devices did not have these 'design related' weaknesses.
So, are we doomed to carry around high-performance 'Nano-PCs' in our pockets, only to have no data connections outdoors when there are no wifi networks available?

Edit:
However, I still do not quite understand, why my (?) problems only occur, when both sim cards are active...
Hence, why manufacturing and promoting a dual sim device, when the dual sim operations are not working flawlessly?

 

[cobben]

Where do you have these problems, in a city with good signal quality, or out in the boondocks med poor signal quality?

 

[Don Henry]

... In a city with very strong signal quality of the network providers (Telefonica o2 & German Telekom D1).
We have mobile telephone masts all around us
I have actually tried a third sim card by Vodafone (D2). Again, according to the official network coverage map it's got excellent signal strength here in my neighborhood, but this one worked even worse in the MI8 in dual sim mode.
This card is now in an older phone working just fine...

What is really weird about this whole issue is that in one moment, I have both sim cards with full strength signals diplayed on the screen, and in the next moment 'splash' the better one is completely gone (D1 is allegedly considered to be the best network in Germany). Not moving the phone, just restarting it and the signal comes back in full strength (for a while at least)....

--> That's basically why I think it's an issue of the phone's general hardware design or the software versions.
(I did shortly try the stable version MIUI 10.0/10.1 STABLE RELEASE, but it did not improve the situation..)

 

[cobben]

In the same article on weibo, about the Mix3 construction, they indicate a similar AI based approach to improving network reception (thus allowing use of mediocre antennas?) as with the "AI camera":


"First, the full simulation simulator prediction
. . .
Second, custom smart antenna switching

Xiaomi MIX 3 can call Qualcomm Xiaolong 845 flagship processor to intelligently process signal data and determine which scene the user is using. The powerful AI computing capability of the Snapdragon 845 helps the Xiaomi MIX 3 to switch antennas more intelligently, thus ensuring signal strength.

Third, sensor-assisted detection

In addition, in order to better determine which usage scenario the mobile phone is in, Xiaomi MIX 3 will use sensors to detect how the user holds the mobile phone in actual use, and whether the slide is open or closed, and then transfer the data to the 845 processor processes it to enable the antenna that best fits the current scene."

 

[Don Henry]

LOL ... So I guess Xiaomi needs to improve their software for "the powerful AI computing capability of the Snapdragon 845 ... to switch antennas more intelligently, thus ensuring signal strength." ...

 

[cobben]

Who can say what is going on in "older" phones like your Mi8?;-)

Another problem you can have is when your operator has a poorly optimized network and tries to constantly switch your phone between 5 different LTE bands all the time.

I had that problem last spring for a while in Latvia, now it is gone.

 

[Don Henry]

Who can say what is going on in "older" phones like your Mi8?;-)

Another problem you can have is when your operator has a poorly optimized network and tries to constantly switch your phone between 5 different LTE bands all the time.

I had that problem last spring for a while in Latvia, now it is gone.

Finally SOLVED

I completely stripped and wiped my MI8, flashed the original Xiaomi Global ROM (which didn't really work that well due to the Anti Roll Back protection. It booted up and launched MIUI, but then complained about the file system being not encrypted and only offering "reset phone".)
Then I installed the latest TWRP 3.2.3.1110 via fastboot-adb and afterwards flashed the latest eu.community beta rom (8.11.15).
Now, the two damn sim cards are working super nicely along each other in dual sim mode.
AWESOME !!!!

 

[cobben]

Finally SOLVED

I completely stripped and wiped my MI8, flashed the original Xiaomi Global ROM (which didn't really work that well due to the Anti Roll Back protection.
Then I installed the latest TWRP 3.2.3.1110 via fastboot-adb and then flashed the latest eu.community beta rom (8.11.15).
Now, the two damn sim cards are working super nicely along each other in dual sim mode.
AWESOME !!!!

I think there are different modem/firmware partions, or whatever it is called, for the official Chinese resp. Global MIUI versions.

The EU roms do not replace these partitions, as they are recovery roms, only fastboot roms replace them.

Thus for a Chinese device, you would have to first fastboot flash an official Xiaomi Global rom to get the correct modem/radio stuff, before flashing the EU ROM.

Or flash only the needed Global firmware partitions, obtainable separately from yshalsager on XDA.

I think we need to ask the staff here if this is correct thinking. @Igor Eisberg ?

 

[Don Henry]

... The problems returned :-(

I found yshalgar firmware on XDA here:
https://github.com/XiaomiFirmwareUpdater/firmware_xiaomi_dipper/releases/tag/weekly-16.11.2018.

But I am to much an amateur to succeed in installing them via TWRP.
What do I have to do in TWRP in order to get the firmware updated?

 

[cobben]

... The problems returned :-(

I found yshalgar firmware on XDA here:ems - y
https://github.com/XiaomiFirmwareUpdater/firmware_xiaomi_dipper/releases/tag/weekly-16.11.2018.
t.
But I am to much an amateur to succeed in installing them via TWRP.
What do I have to do in TWRP in order to get the firmware updated?

I have never done this, have just been keeping track of what can be done.
His firmwares are normally used by folk flashing other AOSP custom roms, which explicitly require you to flash firmware, I think.

But there is no reason why his firmwares could not be used together with EU roms, I believe.
I have just not had any reason to dig into this matter further, as I have not had any such problems -yet.

 

[Don Henry]

Cheers Cobben!

I'll see what I can find in Google

 

[Don Henry]

Very Interesting and absolutely supporting the idea, that only a firmware update is providing a stable dual sim card functionality for the Mi8 'global version'.

After trying these two firmware versions (with the current beta rom version xiaomi.eu_multi_MI8_8.11.15_v10-9.zip):
- fw_dipper_miui_MI8Global_8.11.15_308ad20336_9.0.zip
- fw_dipper_miui_MI8_8.11.15_72d3139c34_9.0.zip
this morning, it turns out that the first (MI8Global) is the one that solves the issue more reliably!

P.S. Installing the firmware.zip file via TWRP works the same, easy way we flash a rom.zip on an unlocked MI8.
(....I must have accidentally done something wrong in my first attempt.)

 

[cobben]

Very Interesting and absolutely supporting the idea, that only a firmware update is providing a stable dual sim card functionality for the Mi8 'global version'.

After trying these two firmware versions (with the current beta rom version xiaomi.eu_multi_MI8_8.11.15_v10-9.zip):
- fw_dipper_miui_MI8Global_8.11.15_308ad20336_9.0.zip
- fw_dipper_miui_MI8_8.11.15_72d3139c34_9.0.zip
this morning, it turns out that the first (MI8Global) is the one that solves the issue more reliably!


P.S. Installing the firmware.zip file via TWRP works the same, easy way we flash a rom.zip on an unlocked MI8.
(....I must have accidentally done something wrong in my first attempt.)

Now the question is, how do the firmware files/partitions overlap the ones in the EU Rrom

I.e., should one flash the EU rom first, and then the firmware rom, or the opposite?

 

[Don Henry]

Very good question, indeed.
Is any developer ready to answer it?

BTW, at this moment fw_dipper_miui_MI8_8.11.15_72d3139c34_9.0.zip seems to offer the more stable netork coverage ... WEIRD !!