Since I own dual band wifi routers and android devices I've been having various issues with WiFi, all started after the first upgrade from KitKat to Lollipop 5.1.x in both my two Z3c and my C5 ultra single Sim. But my wife with other brand android devices had the same issue.
Now, the good news are that this thread is more informative than a complaint, and also more of a solution rather than a bug report... However it's a bug report too.
Here is the thing, I use Bluetooth and wifi a lot, using my car stereo Bluetooth connection for phone calls and streaming, SWR10 and SmartWatch 2 or Pebble Time or Moto 360 (I rotate them, the Sony Sw2 it's still beautiful) plus some times connecting also my Bluetooth headset and computer and or wireless keyboard.. So yeah, you got the point.. Busy Bluetooth.
So why Bluetooth is related to WiFi? I'll arrive to it in a few.
So the issue with the wifi have been for me a big deal however I've always blamed at first the Bluetooth stack rather than wifi's. What was happening in both my xperia devices is that when I was at home, randomly, the Bluetooth was starting to fail. First the sw10 disconnecting and reconnecting, then all the others.. Finally also wifi stop to work and only solution is rebooting the device otherwise no wifi and no Bluetooth at all.
Four weeks ago after more than one year of repeated issues I started to play with my at&t router and decided to set it up like I always advise, two different ssids and different passwords. One for the 5ghz and one for the regular one.
Week 1: connected only on the 5ghz, Bluetooth crashing regularly, after few minutes of usage, and then also the wifi... Crashed. No Internet, no Bluetooth. Terrible battery life of both Bluetooth device and handset.
Week 2: connected to the regular wifi, no crash whatsoever... Phone and Bluetooth devices battery life improved.
Week 3: 5ghz again... Typical disconnect dance, then sudden death of Bluetooth and wifi. Worst battery life ever.
Finally I switched to the regular wifi and both phones are connecting regularly and battery life vastly improved.
So what's the point of this thread... After KitKat and especially when using Lollipop 5.1 (not lollipop 5.0) There are issues in android for what concern WiFi and Bluetooth. I've read on internet about possible buffer overflows and troubles of maintaining connections, I haven't been too willing to read technical docs and white papers about the issue but the empirical method made clear that the issue is in the advanced dual band wifi and especially when using the 5ghz.
Regular dual band rooter setting allow mixed connections on what available, meaning that devices can connect to whatever available, the can be the 2.4ghz or 5ghz band. Unfortunately it's not something that you can foresee, so if then the device connect to the 5ghz the problem start.
It's not an Xperia only problem, but apparently all android devices suffer of this problem. At least all the ones that are on 5.1 rather than 5.1.1 and recent builds and devices with dual band wifi.
Poor Bluetooth connection and problems as well wifi disconnecting repeatedly can be fixed: Solution is to set up dual band routers to use just the 2.4ghz band or to set up the 5ghz to be standalone and avoid to connect said devices to it.
Again, it's not an Xperia fault but android 5.1/5.1.1 one. Hopefully Marshmallow and N (nutella) will fix it. In the meantime I found peace of mind, not irritating Bluetooth disconnection and no loss of wifi. Once I'll receive M or N to the C5 or the Z3c (which I am purposely delaying, at next notification I'll download it) I'll check if the issue in the wifi and Bluetooth stack is fixed. If it's fixed then I'll enjoy the dual band features. In the meantime.. 2.4ghz it's not that bad.
Thanks for reading this, hopefully it will help someone.
