why is my MC7455 suddenly camping on a weak signal?

[Jim S.]

I have a WE826/MC7455 setup on the AT&T iPad plan. My antenna is the 1DP1727X15, connected with two short pieces of LMR400. It's all set up inside my house for the moment, as I don't want to expend any time and money on an outdoor setup til I see if (1) AT&t is going to crack down on non-iPad users and (2) if it still works in the spring when the trees leaf out. (I'm surrounded by wooded hills and the signal is barely coming over them.)

Normally it connects to one of two towers that are about the same distance away in about the same direction, toward which my antenna is aimed. For the past few weeks, however, it's gone through periods of connecting to a tower which is about three times farther away and about 45 degrees off perpendicular to my antenna. This signal is, as expected, much weaker, so weak in fact that aiming the antenna squarely at it does nothing to increase the signal. (Remember, the signals from any direction are most likely scattering off of trees.) The speed is barely usable.

The first few times it did this, it corrected itself after a few hours. This time, it's been that way for two days. My first thought, obviously, was that my "local" towers were down. But they're not -- I have a phone on an AT&T MVNO and it gets as good a signal as ever, from the same towers as usual. The only thought I have is that my phone prefers Band 12, but the MC7455 prefers Band 2, so maybe my Band 2 signal from the nearer towers is down. I've not yet tried locking the modem to Band 12 to test this theory because my antenna isn't optimized for Band 12 (and Band 2 has more bandwidth in my area anyway.)

[swwifty]

OK, a few things here.

1. The 1DP1727X15 is only designed to work for 1700mhz to 2700mhz, as you said. It is optimized to work in that frequency range, that however does not mean it won't try and still connect to band 12 (Without getting into too much antenna theory and design, even though a antenna is specified to work on a specific range, it can still detect signals outside of that range, albeit much weaker). I would suggest locking your modem to band 2, so the antenna/modem combo will only try to use the proper range for the antenna. This might help your modem connect to the closer tower with the stronger band 2 signal, rather than the one further away. If I didn't lock my modem to band 2 only, it would still select band 12 (sometimes as a primary cell surprisingly, but mostly as a secondary cell for CA), even though my antennas are not even remotely optimized for that frequency.

2. Do you have any screenshots of your modem signal stats connected to the "proper" tower, and the further antenna?

3. Is it possible for you to temporarily test this setup outside? Chances are you will get a much much better signal strength outside. Especially on band 2. In my situation, band 2 inside the house (with my band 2 specific yagis) the best I could do was about 30-40mbps download with about 3-5mbps upload. Outside, I can do about 65-85mbps down (depending on cell load, and the weather) and about 15-20mbps up.

4. I'd recommend reading my detailed post on my setup, as it sounds like our situation/setup is similar: http://wirelessjoint.com/viewtopic.php?f=37&t=123&sid=8f0425eecfd330e0691ce1aff3ec82c0

5. Have you tried to use any RF mapping tools? It could give you a better idea of the situation and terrain you are facing. I prefer the ubiquiti calculator here: https://link.ubnt.com/. It doesn't do LTE frequency ranges, but it gives you a good idea. You can also look up the exact location of your towers in your area, if you are not aware (to put them into the calculator) check them out here: http://www.antennasearch.com/. If you feel comfortable, post your results here so we can all get an idea of what kind of link you have.

Lastly, please respond with the results of your various testing. Any information you have to report back here, will be helpful to others.

[Jim S.]

I did in fact lock the modem to band 2 last night. It seems to now stay on the closer towers 99% of the time, but still has jumped to the distant tower at least once.

(As an aside, I've also seen it pick up the distant tower on band 30, which in theory should have, relative to band 12 or even 2, almost no ability to penetrate trees, weather, or buildings! Also, my phone picks up band 2 rather than band 12 at work inside a large building. I can only guess that AT&T is pushing more power on the bands with less penetrating ability. I wonder if there is any hard data on this published anywhere...)

I haven't tested the setup outside with AT&T since the weather hasn't been very pleasant, but shortly after I bought it I tested it outside with Sprint and found that it did no better (on band 25, just above band 2) than inside. (It also performed no better than my Sprint hotspot, as I've seen other people complain about on this forum...)

There is one bit of data I've noticed with the setup that puzzles me. I had mainly been checking my signal stats with the status.html page available from the router's welcome page. When it's connected to the distant tower, with the much poorer throughput, the CSQ, RSRP, and RSRQ are all worse than the nearer towers, as expected. However, if I go to the modem debug screen and look at the output of at!gstatus, I see that the distant tower has a much higher and steadier SINR than the nearby towers! I'm assuming that the modem is abandoning the nearby towers when the SINR goes too low for too long (due to traffic, trees moving in the wind, or whatever) but I don't know why I'm getting much lower throughput with a much higher SINR. Do the towers perhaps broadcast two different modulation schemes simultaneously, a more complex one for high signal levels and a simpler one for low signal levels? That's the only explanation I can think of.

[swwifty]

I did in fact lock the modem to band 2 last night. It seems to now stay on the closer towers 99% of the time, but still has jumped to the distant tower at least once.

(As an aside, I've also seen it pick up the distant tower on band 30, which in theory should have, relative to band 12 or even 2, almost no ability to penetrate trees, weather, or buildings! Also, my phone picks up band 2 rather than band 12 at work inside a large building. I can only guess that AT&T is pushing more power on the bands with less penetrating ability. I wonder if there is any hard data on this published anywhere...)

I haven't tested the setup outside with AT&T since the weather hasn't been very pleasant, but shortly after I bought it I tested it outside with Sprint and found that it did no better (on band 25, just above band 2) than inside. (It also performed no better than my Sprint hotspot, as I've seen other people complain about on this forum...)

There is one bit of data I've noticed with the setup that puzzles me. I had mainly been checking my signal stats with the status.html page available from the router's welcome page. When it's connected to the distant tower, with the much poorer throughput, the CSQ, RSRP, and RSRQ are all worse than the nearer towers, as expected. However, if I go to the modem debug screen and look at the output of at!gstatus, I see that the distant tower has a much higher and steadier SINR than the nearby towers! I'm assuming that the modem is abandoning the nearby towers when the SINR goes too low for too long (due to traffic, trees moving in the wind, or whatever) but I don't know why I'm getting much lower throughput with a much higher SINR. Do the towers perhaps broadcast two different modulation schemes simultaneously, a more complex one for high signal levels and a simpler one for low signal levels? That's the only explanation I can think of.

Glad to hear locking bands seems to have helped.

I suspect that the reason you are detecting these higher frequency bands now, is because its winter. Leaves and trees make a big impact on signal propagation. Carriers have a lot of reasons to transmit with as low power as they can to you, to save money. LTE transmissions in both directions (downlink/uplink) use only the required transmit power needed to get the highest modulation rate (they are adaptive, you can see this in your signal stats by tx power).

I'd recommend testing your AT&T setup outside. RF conditions change dramatically sometimes from day to day, and you might be surprised what you find.

A few questions that can help clear this up.

1. How do you know for sure you are switching between various towers, and how did you correlate which ones are which? This is not as trivial as it seems. I had to drive to my tower (with my router/modem) to confirm that was the same one I was connecting to, via signal stats.

2. Can you provide lots of screenshots of your signal stats of the various situations you're describing? Also, try and run 'at!lteinfo' it will show you all the various cells in your area (that your antenna and modem detects) and can help narrow down how many cells your modem sees.

SINR in LTE also includes interference, and in LTE most of the interference is actually from other nearby cells (sometimes ones on the same tower). It's likely that this one with the higher SINR just has less interference from other nearby cells. Also, just because you have a higher SINR doesn't always mean you will get more throughput, cause one thing you do not know is how busy the tower is. RSRQ provides information on how busy a cell is. If it is higher than -10.6 than the cell is fully loaded. You can only take this measurement accurately when you are not transmitting from your modem, so be sure to not be surfing the web when you do this.

Lastly, LTE uses adaptive modulation rates, so your theory is some what correct. If you have a lower SINR you will get a lower modulation rate, to be sure your data makes it through, than with a higher SINR. Wifi does this as well. Below is an image to give you an idea.

[Jim S.]

I don't have time for a detailed reply, but I'm getting the tower information by taking the eNB ID from the status screen (I don't know what command to use to get this, it doesn't seem to show up in the gstatus output) and plugging it in on cellmapper.net. (The tower locations there are crowdsourced, I think, but generally accurate.)

[swwifty]

I don't have time for a detailed reply, but I'm getting the tower information by taking the eNB ID from the status screen (I don't know what command to use to get this, it doesn't seem to show up in the gstatus output) and plugging it in on cellmapper.net. (The tower locations there are crowdsourced, I think, but generally accurate.)

I tried to use that site before, but there was literally zero information for my location, heh.

The only way I could be sure was to drive to the tower with my setup, and confirm the cell id, but more importantly the PCI (Physical Cell Identifier) which can be found with the 'at!lteinfo' command. The PCI is unique across a wide geographical range, so you can be positive you are correlating properly.

When you get more time, post up some of the signal status and lte info from those AT commands.

Happy holidays!

[oma215]

Hi can any one tell me how to lock my we826-t to band 2 I also have the AT&T plan

[swwifty]

Hi can any one tell me how to lock my we826-t to band 2 I also have the AT&T plan

Run the following AT commands against your modem

Code: Select all

AT!ENTERCND="A710"
AT!BAND=10,"B2 (1900)",0,0000000000000002
AT!BAND=10
AT!RESET

To unlock just do:

AT!ENTERCND="A710"
AT!BAND=00
AT!RESET

[oma215]

ok thank I will try this and see if there is any difference.

[oma215]

also, do I need to unplog the power to reset it or not.

[oma215]

HI I did try it but discconnecting and reconnecting. I made a mistike when I was coping the code for band 2 a coped all the zeros but not the 2.

[oma215]

HI I did try it but disconnecting and reconnecting. I made a mistake when I was coping the code for band 2 a coped all the zeros but not the 2. then I unlocked it but Its disconnecting and connecting while on channel 12.

[oma215]

HI I did change it but it kept disconnecting over and over and the speed was super slow like not even 1 mps. what am I suppose to do because I get about 20 mps in my ZTE hotspot? what can I do to boost my speed with this router?

[Jim S.]

You shouldn't need to unplug the power, but every time I've changed bands I've had to reset the router, not the modem, to reestablish internet traffic even though the modem was connected to the tower. No idea why. I originally thought it was a Sprint thing but it happens with AT&T too.

[swwifty]

You shouldn't need to unplug the power, but every time I've changed bands I've had to reset the router, not the modem, to reestablish internet traffic even though the modem was connected to the tower. No idea why. I originally thought it was a Sprint thing but it happens with AT&T too.

That's odd, I don't have that issue if I issue a at!reset.

Any more updates Jim on your tower connectivity issues?

[Jim S.]

Since I set it to not use band 30 it's been behaving as expected. Only problem is that I'm over the 22-gig mark and getting deprioritized a lot til my next month starts. The previous month I was also over 22 gig early and didn't notice it at all. I suppose a bunch of people got new phones for Christmas...

Someday when I'm home alone I'm going to plug the modem into a long extension cord (to avoid the ridiculous boot and connection time) and look for spots in the house with more signal strength. I probably won't bother trying it outside until I see how it behaves when the trees are well-sprouted.

[swwifty]

Since I set it to not use band 30 it's been behaving as expected. Only problem is that I'm over the 22-gig mark and getting deprioritized a lot til my next month starts. The previous month I was also over 22 gig early and didn't notice it at all. I suppose a bunch of people got new phones for Christmas...

Someday when I'm home alone I'm going to plug the modem into a long extension cord (to avoid the ridiculous boot and connection time) and look for spots in the house with more signal strength. I probably won't bother trying it outside until I see how it behaves when the trees are well-sprouted.

oh, I thought you locked it to band 2 instead of band 30.

Yeah, I noticed a lot more congestion around the holidays (I was deprioritized as well)

[Ziggy1]

Just want to say thanks for this thread, I was having the same issue it kept connecting to a slow cell, after restarting or reconnecting it would get on the right cell, sometimes, I used the lock commands above and so far so good!!

I had to power cycle it to work.

Code: Select all

AT!ENTERCND="A710"
AT!BAND=10,"B2 (1900)",0,0000000000000002
AT!BAND=10
AT!RESET

To unlock just do:

Code: Select all

AT!ENTERCND="A710"
AT!BAND=00
AT!RESET

[LilAkka]

I think I might be having a similar issue. How did you know what band to lock to?

[BillA]

I think I might be having a similar issue. How did you know what band to lock to?

You can use a Samsung phone in test mode to find all your local live channels, or just take a look at the table below and test each band one by one on you particular carrier.

US LTE Bands (Frequencies)
*Primary bands
ATT = *2, 4, 5, 12, 14, 17, 29, 30, 46, 66
TMO = 2, *4, 5, 12, 46, 66, 71
VZW = 2, 4, 5, *13, 66
SPR = *25, 26, 41