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B41 not preferred??


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I am using a galaxy note 5 in Buffalo, NY market. It seems that band 41 was recently added to my home tower. I used to only get extremely slow band 25. Now however I have been picking up band 41 from the tower (I can tell because signal check reports the sAme pci) but it doesn't seem to be preferred. How does this phone decide what band to go to? Is it based on snr? Oddly enough when I am outside the phone stays on band 25 (which is still <1mb), it only switches to 41 if I go INSIDE.

 

I am baffled by this so I have been watching signal check closely. When outside I get -70dbm on band 25, the SNR is also very high, >20. As I travel inside my apartment then signal and Snr get worse on b25, the phone then switches randomly between b25 and b41, and I have noticed the SNR will be better than the b25 was when the phone decides to switch to 41(as I travelled inside and the signal worsened). When I go from inside to outside, the phone switches from b41 to b25 permanently. As I watch the numbers on signal check, I notice that the snr does not exceed 15 or so on b41, even when I get outaide, right before the phone switches to b25. Outside the b25 snr is >20. I have watched the phone for almost 10 minutes and even with airplane mode toggles it will NOT connect to b41 at all outside.

 

Is it possible the phone is choosing b25 due to the better snr? I have never seen this happen before. It is frustrating because the b25 is so slow! While the 41 is giving me 40mbps +. Yet the phone still does not seem to prefer b41 the way it usually does everywhere else. Again the pci remains the same between the band switches and I know there's only 1 tower that would provide this kind of signal to me so I believe I am on the same sector. It is also strange because only this 1 sector is broadcasting b41 at all and the other sides of the tower are not...

 

Has anyone seen anything like this happen before? Should I report it?

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The phone is pretty much juts a pawn in this scenario, relaying on direction from the site. However, the phone does have to tell the site what bands it supports, but this is not an easy thing for the user to manipulate. Personally I would think you would want users to attach to the bands in the following order based on congestion and RF conditions.

  1. B41
  2. B25
  3. B26

This has to do with capacity and coverage. B41 coverage is smallest, but has the highest capacity. B26 is used in cases where the other two bands are not favorable, usually for RF reasons, but it could also be because B26 is less utilized (usually only in extreme congestion cases on B41 and B25).

 

I would suspect your site is just not optimized. I also think if the B25 and B41 PCIs are the same its a relatively safe assumption those signals are coming from the same sector on your nearby site.

 

There are two modes for handover. Idle and active. Idle mode occurs when you do not have an active RRC connection. Phones will lose their active connections due to inactivity to free up resources and save battery life. They are still "connected" to the serving LTE carrier (what you see in signal check/debug screens), just not active. Active mode occurs when you are transferring data, and for a short time afterwards, which is configured at the site. You can see your connection state at the top of the signal check screen and in the debug screen.

 

The Spark icon seems to be an indicator of connection state as well. It is greyed out when the connection is idle, white while the connection is active, and spinning while transferring data. This may be specific to my LG G3.

 

In idle mode the serving LTE carrier will tell the phone which bands to prefer (cell re-selection priority) and how to measure for them. The phone will then act on this information accordingly.

 

In active mode, the serving LTE carrier will tell the phone what to measure, and it will also have a list of neighbors (cell relations). When certain signal level criteria are met (events A3, A4 or A5 generally which could be based on RSRP or RSRQ) the phone will generate measurements reports and then the serving LTE cell will decide what to do about mobility.

 

Basically mobility is based on conditions dictated by the site, and then measured for by the phone. It can be based on signal level (more common from my experience) or signal quality.

 

It might be worth it to call Sprint about this. They are setting up a lot of B41 sites and TDD is new to many market engineers. I would mention that B41 is difficult to connect to despite very slows B25 speeds when outside. Also mention that toggling airplane mode in the main beam of the sector does not get you on B41 (as long as you are sure you are in the main beam, B25 SNR can be a clue). This could be congestion or RF condition based, but probably is just an optimization problem.

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The phone is pretty much juts a pawn in this scenario, relaying on direction from the site....

Excellent explanation. Great post!

 

 

Sent from OnePlus 2 using Tapatalk

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No band 26 for us : (. Maybe it is not fully launched yet on this tower because I don't know why it would only broadcast from 1 sector. I cannot pick up any B41 on the other 2 sectors. I guess I will just wait a bit and see if it is resolved.

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No band 26 for us : (. Maybe it is not fully launched yet on this tower because I don't know why it would only broadcast from 1 sector. I cannot pick up any B41 on the other 2 sectors. I guess I will just wait a bit and see if it is resolved.

 

Close to the Canadian border, you can run into many odd sector configurations -- so as to avoid cross border interference.  That is a possibility in this case.

 

AJ

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My note 5 has problem connecting band 41 some sites and others very quick. Some times takes 10 mins switch band 41, phone loves band 26.

Just depends on the area. My note 5 loves band 25 and is only on band 26 inside or far from the site as it should. I have noticed some sites the note 5 takes a while to connect to band 41 but I have only examined 2 band 41 sites because they are the closest to me with in 30 mile radius.

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Seems to be working normally now and is Connecting to B41 on all 3 sectors. woohoo. Getting around 20mbps down on B41 and about 5mbps on B25, much improved from the unusable B25 before. Has taken load off a neighboring B25 only tower as well so it is also somewhat useable. Still no Carrier aggregation though. Idk why they wouldn't just turn everything on at the same time. We still have several towers (in dense areas) that don't even have B41, and I only know of 2 that have Carrier aggregation turned on. 

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