Community discussions

MikroTik App
 
CJn3
just joined
Topic Author
Posts: 7
Joined: Wed Dec 29, 2021 6:45 pm

Chateau 5G - Unable to hold N3/N78 connection

Wed Dec 29, 2021 7:19 pm

Hello , trying to figure out an issue with 5G where I live, I live about 16 kilometers away from the serving mast from Three Ireland with direct line of sight. Ill link the thread below but basically with even more detail.

I have a netgear MR5200 + Mikrotik chateau 5G , and a samsung S20 + A52 5G and they all cannot connect to the 5G from home. The *#0011# SIM information readout on my S20 says : RACH_PROBLEM and the 5G symbol keeps flickering from outlined grey to white over and over.

I initially thought in the past the 5G symbol flickering from outlined 5G to full white was something to do with N78 band being unable to synchronise the uplink since I am 16km away. Three Ireland upgraded the site and deployed N3 here so I thought I should have no problem getting that but the same issue occurs. Regardless of where I select N3 only on the mikrotik 5G router or not. However the A22 5G has no problem getting 500 Mbps down and about 60-70 Mbps upload and it connects to both N78 and N3.

One thing to note is my S20 connects to N78 and N3 on every other site I've been to while travelling and also when I drive closer to my serving cell. It just seems to be unable to from home. I assume the routers would be able to as well.


The chateau 5G is modified for use with external antennas by using the u.fl to SMA cables. (Swapping A5 with A6 and connecting A0 and A1 to the ANT 2 and ANT 3 ports.) details of modification here:
https://confusedbird.com/thread-119.html

So I have 4 external antennas connected to the chateau 5G, so I have even better signal than the A22 5G has.


It will just keep failing to connect every few seconds... on the chateau 5G it is something similar. It will show N3 for a second or two then disappear and all the bands will aggregate differently. It will keep doing this in a loop every few seconds and will not hold onto the N3 connection. There is more than adequate signal.
I manage to catch a screenshot of when it briefly connected before losing it.

Image




I then tested my partners A22 5G phone connects no problem though with really good speed results, on both N78 and N3. I was really surprised about being able to connect to N78 since I am 16 km away.

The common thing between my devices is they all have a snapdragon X55 modem. and the A22 5G has a Mediatek Dimensity 700.

Why is the mediatek able to connect no problem whereas my other 4 devices all have this same issue. Is there a way to rectify this ? :(

The whole thread is here for anyone interested https://confusedbird.com/thread-136-pos ... ml#pid1377
 
CJn3
just joined
Topic Author
Posts: 7
Joined: Wed Dec 29, 2021 6:45 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sat Jan 01, 2022 5:59 pm

Further update:

The snapdragon X55 devices get stuck in an endless loop trying to register n78 NSA and N3 NSA . The MTK 700 device registers successfully with n78 NSA and N3 NSA - both at the same location 16km from the base station.
The X55 cannot at all, keeps dropping it in a loop

Image

I attached the screenshot of the commands quectel support said, and I used winbox through the router to print a log as I have no access to QXDM

The modem diagnostic log is linked below

https://forums.quectel.com/uploads/shor ... ZabA7T.zip
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11381
Joined: Thu Mar 03, 2016 10:23 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sat Jan 01, 2022 7:17 pm

Contrary to your beliefs, 5G signal you're receiving is poor ... and your screenshots say so (n3 band NR RSRP at -105dBm is marked as poor). The only reason it somehow works on one of your devices is that the interference is almost non existant (NR SINR at 26dB) which will change with more people using 5G in your area and with MNO adding 5G transmitters to other towers.
The reason for low signal level is distance - 16km for 3.5GHz is huge. It's far also for 1.8GHz (you can verify that if you lock Chateau to B3 ... see what RSRP value it comes up with, probably it'll be similar to n3 value or perhaps slightly lower). Your 4G signal is fair (not good even if the screenshot says so) because you're being served by a 750MHz cell. Don't ever look at RSSI value, it doesn't mean anything (it includes also noise etc.).
RACH stands for Random Access CHannel and is used for initial transmissions by mobile device. It is shared by all devices wanting to start communication (after successfull initial signalling communication, device gets assigned DCH - Dedicated CHannel). RACH problem means that device can't establish initial communication with cell due to any reason (and in your case it's likely caused by large signal attenuation between transmitter and receiver, a hunch supported by the fact that your S20 can work with same cell tower when in a little better radio conditions).

The other problem is Tx power of your devices ... cell transmits with tens of watts (even in excess of a hundred watts) while user devices are limited to around 0.2 W ... that's almost 1000-times the difference (or 30 dB). And yet for duplex communication cell needs to hear your device. Could be your A22 has a slightly better transmitter and cell can just hear it...

Which all means you'll need some expertise (and luck) to get your 5G gear (in general) to work reliably with that cell tower 16km away.
 
CJn3
just joined
Topic Author
Posts: 7
Joined: Wed Dec 29, 2021 6:45 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sat Jan 01, 2022 10:05 pm

Image
Around -93 RSRP on B3 and -97 on B1.

The 5G RSRP on this cell improves whenever data is being downloaded so that N3 signal is only showing up for a split second and dropping again. The lowest I've saw that N3 reading matches what you see on B3 above for a split second. Problem is it won't hold the N3 connection longer than 2 or 3 seconds.

On the A22 it's able to connect to N78 as well as N3 which I didn't think would work at all for multiple reasons) RSRP value at around -113 (N78) and whenever I initiate something like a speed test it'll improve to about -98 during downloads. Same happens on the chateau whenever I connect to a cell I'm close to when I brought it testing.
Even when I drive much closer to the cell, the RSRP is about what I get at home unless I drive right up to it and then I'll get an RSRP in the -80s.

I managed to get this speed result with just holding the A22 phone in my hand , I'd love to be able to get this using my chateau 5G, max I get is around 350/40 Mbps when the cell is quiet. Even if the signal is weak in the grand scheme of things, the A22 phone pulls great results. The download speed wasn't much better when I tested close to the mast, but there was a bigger improvement in upload.

Image
I just don't understand how the A22 can perform so well whereas the other X55 modem devices refuse to connect. I will try to get a hold of more devices to see if it's just the snapdragon series.
Is -93 RSRP on N3 a strong enough signal for use though , no? I'm not an expert by any means, just trying to figure out the most likely scenario here.
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11381
Joined: Thu Mar 03, 2016 10:23 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sat Jan 01, 2022 10:21 pm

OK, what we need to do is to improve signal strength redeived by chateau, -80 dBm close to cell tower foesn't sound right. A question: which exactly antennae are you using for 4G/5G and how exactly are they placed and connected to Chateau? Antenna type matters, antenna placement matters, antenna cable length matters, antenna connectors matter ...
 
CJn3
just joined
Topic Author
Posts: 7
Joined: Wed Dec 29, 2021 6:45 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sat Jan 01, 2022 10:29 pm

Yeah, at the moment , I have 2x LPDA-92's from Poynting. 12M of cable. My cable loss is only about -2 dBm as I tested plugging the chateau 5G outside without my SMA cable extension. The same flickering and dropping of connection occurs.

So I get about -91 RSRP on B3 without the 12m of cable.
And -93 RSRP on B3 with. I tried to purchase low loss cable from poynting to try reduce the signal loss.

My goal for the chateau 5G is just to get N3 to work , N78 would be a bonus , but I understand the cable loss is even worse with higher bands too. I would get 5CA if N3 was able to connect. So that would be more than good enough for me :D

One thing to note, a few months ago when 5G was deployed there , I managed to get -88 RSRP on N78 on my S20 16km away by taping my phone to the LNB area of a 80 CM offset parabolic dish and pointing it directly at the tower ( wish I could use this for the chateau but it catches too much wind :D ) the RACH_PROBLEM still occured, flickering 5G symbol constantly dropping the connection even with a strong signal for this distance ... which is what made me think it was something to do with physical distance , uplink sychronisation since it's a TDD band. But this doesn't explain the issue on N3 which shouldn't theoretically have this problem right?

I forgot to mention , the cell tower that serves me is unique compared to most, as it's on an island , so the closest I got to it was right at the waterside , probably a kilometer across the water to the island where it is. So that's why it's not a stronger signal I guess. But I do have direct line of sight at home as I am up high on the hill
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11381
Joined: Thu Mar 03, 2016 10:23 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sun Jan 02, 2022 12:56 am

The antenbae you've got are decent. They should be pointing at the cell tower, they should ideally be mohnted at least half a metre apart snd ideally they should be at angle of 90° longitudinally (dipoles of one antenna horizontal and vertical on the other antenna). Cable loss of 2dB is not too bad. Try to find micro location which gives most space around direct line of sight ... in radio also a cone around it attributes to signal strength, meaning that obstacle close to LOS degrades signal ... at the same time obstacle just blocking LOS (from one side) doesn't entirely kill the signal. With higher frequency this cone becomes extremely narrow though.

OK, RSRP of -80dBm at distance of one kilometre sounds quite right. You're right, there are some (settable) limits of maximum mobile station distance from cell tower. I don't know what are these distances in 5G, they are higher than 14km for 4G. And that limit is there on FDD as well. You might want to ask your MNO if they had any restrictions about that (but I wouldn't hold my breathe while waiting for an answer). But then physical distance is the same for your A22 as well but it somehow works.
Hmm... the limit is not really about physical distance (cell doesn't know where mobile device really is), it's about delay. Part of delay is speed of light ... and there's processing delay on mobile device. So could be that 5G chip in A22 is a bit faster which would allow for longer physical distances ...

I guess it's obvious I've no idea what else to try :wink:
 
CJn3
just joined
Topic Author
Posts: 7
Joined: Wed Dec 29, 2021 6:45 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sun Jan 02, 2022 1:37 am

Yeah that's the thing I'm afraid of , if it has a slower processor , would mean I'm not able to overcome a hardware limitation like that :(
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11381
Joined: Thu Mar 03, 2016 10:23 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sun Jan 02, 2022 12:19 pm

Yeah that's the thing I'm afraid of , if it has a slower processor , would mean I'm not able to overcome a hardware limitation like that :(

Sometimes modem firmware upgrade reduces processing delay allowing modem's better performance. I wouldn't seriously count on it though.

However, you may be able to replace the built-in 5G modem with something better in future ... even now there are several options, not sure which you're using now. Most often modems supporting highest throughputs (CAT20 on the list) support lower throughputs better as well because they have higher processing speed needed for their top speed.
 
CJn3
just joined
Topic Author
Posts: 7
Joined: Wed Dec 29, 2021 6:45 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Sun Jan 02, 2022 7:23 pm

Is there any you'd recommend for this? I'd be interesting in experimenting with something like this, is there any resources on how one could do such modification? :D
 
User avatar
mkx
Forum Guru
Forum Guru
Posts: 11381
Joined: Thu Mar 03, 2016 10:23 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Mon Jan 03, 2022 8:21 pm

I don't have any experience with MT-compatible 5G modems, so I can't give any recommendation.
 
CJn3
just joined
Topic Author
Posts: 7
Joined: Wed Dec 29, 2021 6:45 pm

Re: Chateau 5G - Unable to hold N3/N78 connection

Thu Jan 06, 2022 2:43 pm

Working with mikrotik support at the minute along with my ISP to see if they can shed any light on it, support reckon it's weird behaviour they haven't seen before, hopefully it's a fixable thing. Will post any updates I get that may rectify the issue. But any other theories are welcome :D

Who is online

Users browsing this forum: Ahrefs [Bot], pe1chl and 21 guests