Question

Hi guys

I've just recently installed a RUTX50 on a ship, using four Omni 493 marine antennas by Poynting antennas. Plan attached

Anyway I was abit let down over the last few days as while the modem worked and recieved near excellent signal strength locking onto band 28 (modem was in auto) , I always had horrendous SINR, near zero. 

I played around with the antenna configurations however this did not fix the issue at all.

What I then did was disable LTE B28 forcing the modem to pick another frequency, LTE B3, as soon as I did this the signal strength dropped to -73 (from -47) but the SINR improved dramatically to around 18/20 and now my modem seems to be functioning very well.

Unfortunetly however, B28 seems to be the common band in most less populated areas and this includes offshore, so while it's disabled i'm missing out on alot of signal.

Can anyone explain to my why I might of had such poor signal to noise with B28? and will 5G low frequencys (when they are rolled out in area) likly have the same problems?

Why does the modem not select the best band by signal to noise? instead of only going off strength?

Any advise apperciated 

Comments

I have a funny feeling I might know what this issue is.

I believe the b28 telstra towers in Australia screaming at my modem, signal strength is super strong  but signal to noise is very poor.

Could it be that there is a bug between this band negotiating power level with the modem closer? Or could it be that there is an issue with the modem not switching to a less strong tower or band when the signal to noise is very poor?

Like I said the only way I have managed to resolve this issue is to disable B28 which is frustrating as I'm on a ship and B28 is the ideal frequency when further offshore, we are around 35km from the tower and the signal strength is still around 50 db when using this band but as mentioned signal to noise is terrible

When I disable B28 it roams to B3 plus a 5G band (duel) signal strength drops to 70/75 db (in this location) but signal to noise is greatly reduced sometimes showing "excellent" on the modem and download bandwidth is excellent, due to the weaker signal however upload is poorer. It's worth noting that while i have poor signal to noise pn b28 nearly everywhere I've tested so far and thus poor / slow download speed.. When uploading / transmitting, speeds are excellent.

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Thanks but we are not at the edge infact we always have excellent signal strength with b28.

I have heard of this happening to someone else in Australia using b28 with telstra.

Anyway i will just wait and see if things resolve themselves.

Thank you

And yes all cables are half inch low loss heliax runs are Max 9 meters all antenna are omni 493

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Not an answer, sorry, but a possibly similar issue.

I have an RUT950 and am currently at a remote location where there is a Telstra "small cell" 700MHz 4GX service within 100m and and another about 6km away. There are no other Telstra services that I can detect e.g. using manual band selection and disabling B28 results reports no signals. Apparently there is also an Optus small cell 700Mhz "4G+" and 900Mhz "3G" service here too. The RFNA map shows the next nearest service to be a Telstra small cell 19km away.

For reference, my iPhone 11 using LTE (WiFi disabled) running Speedtest consistently gets 50 to 75 Mbits/second download. The RUT950 reports RSSI=-65dBm (good) but RSRP around -100dBm (very bad) and SINR 0 to 2 dB (very bad). Some of the time Data connection state is Disconnected, and some of the time it is Connected at which time Speedtest gets around 5 - 10 Mbits/sec.

I am not using any external antennae on the RUT950 but the iPhone above is within one metre of it. Router is RUT950M02XXX. Internal modem is Quectel EC25-AU. Modem firmware is EC25AUFAR06A03M4G_01.001.01.001. RUT950 firmware versions RUT9_R_00.07.03.4_WEBUI, RUT9_R_00.07.04.1_WEBUI and RUT9_R_00.07.04.2_WEBUI give similar results.

So, to your point, if SINR really is as bad as zero, how does the iPhone manage 50 Mbits/sec?

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What I would love todo if it was possible is program the router to only use band 28 LTE when CA is available or on a tower that supports multiple bands / CA. Reason is while band 28 is great, my ship is a roaming structure and it keeps connecting to strong signal but low capacity small cells which only have limited throughput / capacity via band 28 meaning low speeds.  Disabling band 28 lte causes the router to connect to larger towers with multiple bands but the problem then is that theses larger towers also have excellent band 28 capacity, but because I've disabled this band to stop the router connecting to "small cells" i can no longer take advantage of that band via CA.

Any advise?

Answer 1

Hello,

As mentioned in your previous thread, the way modem selects the band and cell tower it connects to is determined by the it's firmware. You do have some degree of control on how the modem behaves through the WebUI, more can be achieved through interaction with AT commands via CLI/SSH.

There are no known bugs related to LTE connectivity. If 5G is of importance for you, be aware that there is a issue with the band n28, when it is used in 4x4 MIMO configuration. It has been reported here. It is being worked on from Quectel side, though current suggestion is to avoid using n28, by selecting all 5G bands manually, except for n28, if you intend to connect to 5G networks. 

However, it does not relate to 28 LTE band. I have tested it locally with several operators, band works as intended. The thing to understand about SINR is that it is a measure of the quality of the received signal relative to the level of interference and noise in the channel. Thus, despite there being an excellent RSSI in your area, it's effectiveness is reduced by, other signals operating in nearby frequencies, for example, interference from the same or adjacent frequency bands due to multiple users communicating in the same frequency band, or multiple cells using the same frequency band in the same area, some external electrical equipment or atmospheric disturbances. 

Best regards,

Comments

Thanks for your reply, however we are roaming around on a vessel and it appears to be the same issue on any of the telstra b28 frequencies and different towers via lte.

If I disconnect my external antennas and connect the smaller supplied ones, the signal strength decreases and so does the signal to noise issue.

Anyway I will leave this band disabled for the time being and hope that telstra 5G 850 mhz offers a solution in the near future.

Attached ia is a photo of antenna layout but please note I have disabled the radars etc to see if SINR improves and it had no impact what so ever negative or positive.

Upgrade, keep seem to attach photos even tho there under 2mb

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Could you also explain to me in the above scenario (N28 LTE poor download) why is it with very poor signal to noise, when performing a speed test the upload is excellent speeds? I guess signal to noise doesn't effect upload?

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It is difficult to tell the exact reason. It might turn out to be the device in the end, but something specific to your unit only, as I have not been able to replicate problems with band 28.

Such discrepancies as low download/high upload might point to physical layer issues, such as cables, connectors. Could you, for example, perform a speed test, switch port 0 and port 3 antennas, and try speed test again, to check, if the cable does not have any impact on the performance? What are cable lengths between antennas and the router? What is the cable type?

Also, since band 28 is an FDD band, it has separate frequency channels for uplink and downlink streams. In general, far more data is transmitted from base tower to users equipment than the other way around and if you are roaming around edges of tower coverage zones, is possible that interference becomes stronger the further you are from the tower you are connected to.

Low download may also be an indication of high tower load.

It would be interesting to compare another device's reception on band 28 at the same spots.

Best regards,