i have exactly the same problem, total loss of network for about a min randomly.mine is an early t-mobile uk s2. i flashed 4.0.3 iml74k.xwlp7 a few months ago and it was fine, a firmware upgrade was available through kies which was 4.0.4 and it all seemed fine for a day then this random loss of network. i have had to re flash back to 4.0.3 using odin and it's fine now, samsung needs to sort this out!

 

If I remember correctly jaliy, you are on the GT-i9100 with the XEU, UK, firmware. Quite a few Canadians have requested a different modem on the, "All Things Root", forum in an effort to improve their signal and it seems that the XXKG6 and UGLD3 modems work well in Canada.

However, I know that you are un-rooted and therefore constrained to the modem that comes with the UK firmware.

Therefore, I can only suggest doing a manual signal/network provider search and re-registering your phone with your network to see if this improves your signal...

1. Settings > Wireless and network > More > Mobile networks > Network operators.

2. Let the screen populate with all the available carriers.

3. Select a carrier that is not your own. You will be told, after trying to connect, not allowed or No way Jose.

4. Repeat this with one or two other non carriers.

5. Finally, select your own carrier, Automatic, and reconnect your phone again.

This procedure should ensure that your phone locks on to the strongest signal for your carrier.

I normally give a modem 1 or 2 days to, "bed", in before deciding if it is any good or not.

To check your signal strength, go to...

Settings > About phone > Status > Signal strength

Here you will see 2 results..

-dBm. The lower the -dBm, the better. For instance, -65dBm is better than -83dBm.

asu. asu, or, "Arbitrary Strength Unit", is also important to signal strength and, unlike -dBm, the higher the value, the better.

At home at the moment, indoors, my signal strength is showing as -83dBm and 16asu.

For more information on network signal strengths and how they are calculated, see, here.

 

Only amongst Canadians on XEU, UK, firmware, it would seem, if xda developers forum and the All Things Root section of this forum are anything to go by.

 

Not my area of expertise old boy, As I neither have the Canadian, "M", variant or live in Canada... however, in my wanderings through xda and on here, I have come across a number of requests from people who either own the SGSII, GT-i9100, on XEU firmware, or who have the "M", variant and have rooted and flashed a non, "M", variant firmware to it, and are requesting a modem that is more compliant with the Canadian networks, Bell, Virgin, Sasktel, Rogers, because of signal problems. Those who are rooted, I can help, as I now know that certain modems work better, from reports I have received and read, in Canada.

 

The issue I'm talking about has been there from day one of the SGSII, non, "M", variant, being available in Canada. There will, of course, be newer modems in Android 4.0.4 to make them more compliant and signal, not to mention battery, friendly with UK/European networks, which the XEU firmware is designed to operate on, this is why the, "M", Canadian variant has a different modem.

The bottom line is that the XEU, UK, modem was not designed with the Canadian networks in mind but rather the European ones. This is why the Galaxy S2, "M", variant was brought out for sale in Canada with it's own firmware and, more importantly, its own optimised modem. Certainly, people who have flashed modems more suited to the Canadian networks onto their non, "M", phones have reported less, signal outage, calls dropped and better battery performance. If you were to come to the UK you would get a great signal with your modem.

I'm afraid that unless you are rooted or willing to flash a Canadian firmware, both of which will void your warranty if you still have one, there is nothing you can do about it

 

Here are two screenshots that should explain the difference between the Canadian and UK modems.

Both screenshots are for the signal strength, indoors, on the Vodafone, UK, network and taken within 15 min's of one another.

The first is for the UK optimised modem and shows -87dBm 13asu. This was using HSDPA.

The second is for the Canadian optimised, "M", variant phone on my UK network and shows -103dBm 5asu. Could only get UMTS.

In other words, the Canadian modem is not as compatible with the UK network as the UK modem is. It is showing -16dBm and 8asu weaker.

That is why there is an, "M", variant of the SGSII for Canada.

UK modem on UK network



Canadian modem on UK network

 

Type into your dial pad... *#1234#

and give the four lines of information shown there.

PDA:

PHONE:

CSC:

Build info:

 

So, you are running XEU firmware which is the Samsung CSC code for the unbranded, UK. See post #2, here.

Therefore, you only have to look at your own screen to see a UK modem on a Canadian network.

 

Please post a screenshot showing your Status which gives both dBm + asu and HSDPA/UMTS.

 

What is your asu?



Don't forget to turn off your Wi-Fi on the phone before taking readings.

 

Do you ever get H for HSDPA showing?

(see my first screenshot above)

 

So, you are getting -90dBm 11 asu and HSDPA 15

If this is your average signal then that's not too bad. However, if you are, as you say in post #1, getting signal drops all the time that might indicate that either you have dead zones, which is down to your network providers signal, or your modem is either dropping the signal or not switching between different cell towers efficiently. This means that not only is your signal being dropped but also your battery is being drained as your phone will be constantly searching for, and connecting to, your carriers signal.