[AT&T, Rogers, Bell, Telus Samsung Galaxy S III] flexfulton:
4G Signal Strength and Network Handoff Problems

Hi Guys,

I know there has been a lot of telephony and RIL commits for our phones the last couple nights which has prompted discussion about network handoff improving and full radio loss for extended periods of time. I would like to just say that the issue I have been chasing for the last couple of weeks has NOT yet been fixed up until the latest nightly 06/04 and I would also like to make my issue a little more clear as some folks don’t quite seem to understand what I’m seeing or believing they are seeing the same thing when they are not. I flash every nightly as they come out and this is up to date as of the 06/04 release but all of my screen captures and debugging information has been recorded using RC3 unless indicated otherwise. Kernel has been stock CM kernel.

I know my posts are spread all over this forum now and the JIRA report is a lengthy one as I worked out all the details as to what was going on so I’d like to try and shore it up for you guys in one clear easy to understand post.

I do understand that not all people will see this if they are never in a location where the situation below exists for them. Some folks live in areas with great 4G signal and never frequent an area that allows for the signal to be present but extemely weak. I have heard from various people however that are experiencing what I am about to explain both on CM10.1 and other AOSP ROMS with a CM base. Whether the issue is a Google Issue, CM issue, the fact that our modems are technically outdated for the ROM base we are using or a combination remains to be seen.

Useful Information To Start Us Off

1. 4G = LTE

2. The closer your signal strength gets to 0dBm the better your signal is. -60dBm is usually considered great strength and it won't get much better than that while -120dBm is considered very poor.

3. To see the signal strength value as a number go to Settings/About Phone/Status

4. To see cell standby battery usage go to Settings/Battery/Cell Standby

5. To see a history of your most recent signal strength levels go to Settings/Battery/Click on the graph you see. This link shows what the different colours represent. http://xdaforums.com/showpost.php?p=26891039&postcount=14

6. If interested and you have the time, here is a good read about signal strength and how it’s calculated. http://rootzwiki.com/topic/36320-app2013-06-02-advanced-signal-status-v122/

The Location And Cell Network Types

1. 4G(LTE) signal at my work and at my house is full and strong when standing outside.

2. 4G signal when in my house and in my location of work is present but very weak (1 bar or less). This is expected as everyone should know that 4G cell service does not penetrate walls very well and my lab at work doesn’t have any windows and is a fairly solid structure.

3. I have a very strong 3G signal both outside AND inside at these two locations.

4. I think it’s safe to say that my carrier isn’t the issue based on these conditions as I am able to receive both 3G and 4G signal fully if the conditions are correct.

5. I also think it’s fair to say that the hardware side of things on my phone are fully functional as well as the APNs and Preferred Network Type is correct as I am able to receive both 4G and 3G cell phone signal. I have also been through the ringers on all of the available modems for my phone with no changes seen in this behavior.

The Problem(s)

#1

1. When inside the building I work in, my phone is desperate to hang onto a very weak 4G signal even though a full 3G signal is present.

2. 50% of the time it will show 1 bar signal strength and read approx -110 to -115 dBm. This is not a great signal but I still consider this strong enough to not make the jump over to the 3G network. See screen capture 1.

3. 50% of the time it will show 0 bar signal strength and read 0dBm 99asu. This is a bogus reading as technically 0dBm would be an AMAZING signal and is absolutely impossible to achieve on any cell phone. See screen capture 2. Captures 3 and 4 show a third party app reporting the signal strength correctly. By comparison I’ve turned on text for signal strength in the status bar which in another twist shows -1 instead of 0 seen in the phone status menu.

4. At 0 bars and a reading of 0dBm, the phone should actually be reporting a cell signal of approx -115 to -120dBm or worse which it obviously is not.

5. The phone should actually never see 0 bars or a 4G signal that bad as it severely increases battery drain as it tries to maintain that weak signal and transfer data over it.

6. Data still works at both -115 and 0dBm signal strength but the speeds are very different. -115 download is approx 20Mbps and at 0dBm download is 5Mbps.

7. The phone should have switched over to 3G before it ever reported a signal that poor. It should be noted that my phone will eventually switch to the 3G network but not after an extended period of time sitting at 0dBm no bars.

#2

1. When sitting a 0dBm or no bars 4G, the phone starts showing a percentage of “Time Without Signal” even though I never see an empty triangle indicating that my phone as lost signal to my carrier. To back this up the Mobile Network Signal line in the battery history graph does not show any red blocks which would again indicate a full connection loss to my carrier.

2. Something is causing my phone to think it has no connection to the carrier which in reality it does. An easy way for me to see this to make sure I’m not missing anything is to charge my phone fully to reset the battery stats and then watch my phone while at 1 bar and 0 bar 4G connection. I can see the % of time without signal increasing without any red showing up in the line graph or without my bars turning into an empty no connection to network at all triangle. See captures 5 and 6.

3. By comparison, turning on Airplane Mode will also increase the % of time without signal. This however will show up as black in the line graph and the phone knows it shouldn’t have a connection.

4. So why is my phone thinking it has no connection to the network when in reality I do have a working data connection albeit a poor one and one that is reporting its strength wrong and with a bogus number at that?

Additional Debug Information As To Why And How (This Is Only My Theory)

1. I reverted back to stock; which is JB 4.1, to have a look at what was happening. My phone reported the 4G signal strength correctly (at least down until -115dBm) before seamlessly switching over to the 3G network as I entered a location where I normally receive 0 bars 4G. Back upstairs and outside and it seamlessly switched back to the 4G network.

2. CM10 which was based on JB 4.1 appears to also work correctly and show signal strength correctly.

3. CM10.1 M1 release was based on JB 4.2.1 This release was a bit odd in itself. It seems that 4G signal strength reporting was borked completely showing infinitely large dBm numbers at all time. As a result it was hard to see exactly what was going on with network handoff but my general impression was that it was better but not as great as the 4.1 releases. See screen capture 7.

4. CM10.1 M2, M3, RC1, RC2, RC3 and RC4 which is based off of JB 4.2.2 is back to correctly reporting the 4G signal strength but as I’ve discussed above, the 4G no bars and reporting of 0dBm is present. Every one of these installs was a clean flash for debug purposes.

5. As we can see from the information above, the JB 4.2.2 releases seem to be the reason for the incorrect reporting and lingering on the 4G network and super weak unacceptable signal strength.

6. In an article found here http://www.networkworld.com/community/blog/why-android-422-important-update there is discussion about the 4.2.2 release of JB and how it is supposed to IMPROVE network handoff between WIFI/3G/4G networks. We are obviously not seeing this.

7. I suspect that one potential reasons for the issue that we are seeing is because we have yet to see an official 4.2.2 release for our phone meaning we don’t have a modem optimized to play nicely with JB4.2.2 and its new network handoff improvements. We are trying to use an outdated modem with a new ROM and they aren’t working together very well.

8. So I believe that as a result of my phone not correctly handing off to the 3G network; when a very weak incorrectly reporting 4G signal is present, it is causing my phone to work extra hard to maintain that signal thus burning through extra battery trying to maintain that connection. What I would like to see is if CM can get this fixed, sorted out or improved up.

I also uploaded my catlogs in case anyone wants to take a look and for the purpose of keeping the entire story with this post.

So as you can see from the above information, my phone is set up correctly, my cell provider isn’t the issue, the cell towers in my area are functioning correctly and no form of wiping, clean flashing or reverting back to stock will help with this issue.

I hope this is a little more clear for you guys. I know I’ve spouted out a lot of information in the past that was likely hard to follow so I hope this e-mail; albeit long, is a little easier to follow, understand what I’m seeing and help you understand if it’s what you are seeing. If it is please log on JIRA and vote for this issue to help it get some attention. https://jira.cyanogenmod.org/browse/CYAN-1209

Thank you for your time.