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hacknix
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R11e-LTE6 cell selection

Sun Jun 21, 2020 11:07 pm

Hi,

I've been working with a device in a remote location that has an R11e-LTE6 modem installed. I am noticing some oddities in the way cells are selected and I wondered if anyone has any insight as to how the modem/firmware chooses the cell and if this can be modified in any way.

What I am seeing is that cells seem to be chosen that has a good RSSI and RSRP, despite the RSRQ and SINR figures being sub-optimal. This is causing remote cells with a high power TX to be chosen, even though they are on a very congested band and offer lower quality connection. I'm seeing, for example RSRQ of -19.5 dB and SINR of -16 dB being chosen over a connection that has RSRQ -11dB and SINR 2dB. I know these signals are still pretty marginal, but it's a remote location some 12km from the nearest cell. We're sometimes working with cells up to 25km away. I suspect that the modem/firmware is only considering the RSSI and RSRP figures and not RSRQ and SINR. Unfortunately, each set of figures seem to be giving an opposite view as to which cells are strongest. the RSRQ and SNR seem to be more accurate, as you would expect.

I have tried to use cell locking to lock the primary to the band I want (B3@20Mhz - earfcn 1501) and to a specific cell which offers much better performance and doesn't trigger almost constant handoffs. However, if the connection is lost temporarily (for example due to rain fade), the IP link doesn't come up again even though info shows the modem connected to the cell. I think the modem just hangs, but only when cell lock is on. If I remove the locking, the modem recovers fine every time but the connection is not stable and doesn't perform right as it is constantly selecting a primary on band B20@10Mhz on remote and congested cells with a high noise floor.

Any thoughts or experiences on this would be greatly appreciated.
 
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krafg
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Re: R11e-LTE6 cell selection

Sun Jun 21, 2020 11:11 pm

If you want to know my network, you can find it here.

Telegram: @krafgrgi

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hacknix
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Re: R11e-LTE6 cell selection

Sun Jun 21, 2020 11:21 pm

Thanks for the link to the manual. I have read it and I have had cell lock working, it's just whenever I use it, the modem does not recover from temporarily lost connection correctly so it makes it impossible for me to use as I lose my connection to the device and have to get in via backup satellite link to reset the interface. (By enable/disabling the lte interface). After doing this, it connects as normal. I have read elsewhere that there was a bug that caused something similar to this in older firmware versions, but I am running the latest available firmware.

So I think these questions still stand:

Is there a way of manipulating how cells are selected?

Is anyone else having issues using cell lock when the signal fades?

Is this a known bug in the firmware?
 
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krafg
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Re: R11e-LTE6 cell selection

Sun Jun 21, 2020 11:30 pm

You can do a script that restart your LTE interface when connection is lost.

If you believe that it is a bug, I suggest to contact directly with MikroTik support sending RIF file.

Regards.
If you want to know my network, you can find it here.

Telegram: @krafgrgi

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SiB
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Re: R11e-LTE6 cell selection

Mon Jun 22, 2020 9:47 am

it's just whenever I use it, the modem does not recover from temporarily lost connection correctly so it makes it impossible for me to use as I lose my connection to the device and ...
Looks like second person who have the same problem like I, check this:
viewtopic.php?f=21&t=154848&hilit=freez#p765554
MTCNA + MTCRE + MTCINE | ~600 users at ~150 RouterBoards in EMEA | Telegram: @SiB_PL | Buy me a caffe
WinBox Tip: F6 works as ALT+TAB | Gliffy.com - free network schematic | prnt.sc - free ScreenShot software
 
hacknix
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Re: R11e-LTE6 cell selection

Mon Jun 22, 2020 12:42 pm

Thanks SiB.

I am reading that thread now ..
 
mkx
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Re: R11e-LTE6 cell selection

Tue Jun 23, 2020 2:20 pm

I've been working with a device in a remote location that has an R11e-LTE6 modem installed. I am noticing some oddities in the way cells are selected and I wondered if anyone has any insight as to how the modem/firmware chooses the cell and if this can be modified in any way.

What I am seeing is that cells seem to be chosen that has a good RSSI and RSRP, despite the RSRQ and SINR figures being sub-optimal.

Unlike WiFi in LTE device has to strictly follow network's commands (which is actually source of good mobility). The only way device can affect that process is via measurement reports. Cell lock actually works by not reporting other measured signals back to network and network can't order device to use other cells.

Next: native quantities, measured by devices in LTE, are RSSI, RSRP and RSRQ ... SINR is devised from primary quantities and is only illustrative. Then: RSSI is a fairly meaningless quantity, it actually indicates level of total power in given spectrum and doesn't matter if that energy comes from serving cell, other cells of the same network, other unrelated LTE cells or is plain noise. RSRP is actually "purified" measurement of serving cell's signal strength and RSRQ is sort of signal/noise for that same cell. Networks tend to move devices from cell to cells to maximize RSRP and RSRQ, but there are other strategies in the play as well (some vendors prefer to push devices to high-capacity cells working on higher frequencies even though particular device might work better with other lower-capacity cell). Strategies are virtue of each individual MNO ...and there is no magic button for MNO engineers to automagically come up with greatest settings for everybody.
BR,
Metod
 
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krafg
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Re: R11e-LTE6 cell selection

Tue Jun 23, 2020 11:47 pm

In my opinion, I think that is better to work with high frequencies, but no too much signal strength, I get better results (More speed).

If I get excellent link between my device and the cell tower, but 100 - 200kbps speed because the cell tower have poor throughput capacity or cell tower is saturated, it not serves much.

In my case it occurs a lot with towers that works with Band 28 (700 Mhz). Normally, 3G is better and sometimes 2G also.

Regards.
If you want to know my network, you can find it here.

Telegram: @krafgrgi

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