[HL7692] Unreachable when low CSQ

I have made a product with the HL7692 that works fine when we test it.

However when we move it in the field, where the overall signal quality is worse of LTE. We notice that the device is sometimes not reachable.
We think it’s caused by the fact that the signal quality is to low and the bit error rate is to high. However the CSQ is good enough to keep the module registered to the network.

The CSQ is always around 0-1 and the LTE band used is 99% of the time LTE Band 3 (1800 MHz). Sometimes the band changes to LTE Band 20 (800 MHz) which has a CSQ of around 10-12

My questions:

  1. Why does the HL7692 keeps switching to band 3, while band 20 has a much better signal quality? Can I’ve influence on this pattern without completely disabling band 3?
  2. Can I’ve influence on the receiving/transmitting strength of the module?

NOTE with unreachable I mean, a tcp client was unable to setup a connection with the module within an acceptable time. Probably caused by to many packets lost/…

If you fixed to band 20, does it improve for the signal and the tcp connection? Please provide your full AT logs. Thank you.

Missed connection 1:
Band 3
CSQ: 0 rxqual: 5

Missed connection 2:
Band 3
CSQ: 1 rxqual: 4
XCSQ: 1 RSRQ: 17

Missed connection 3:
Band 20
CSQ: 11 rxqual: 4
XCSQ: 11 RSRQ: 15

It seems to be unrelated to signal quality/band after all. I still find it strange that my tcp client sometimes cannot conenct, and that not even one of the SYN packets (first one + retransmissions), arrive at the module

  1. I have network registration
  2. I have a data call open
  3. I have a PPP connection op
  4. I have a tcp server listening to incoming connections

Note that this test only fails when I execute it in an area with less signal strength, then the area where we develop the product

Hi roel0,

If possible please share your OK and NG logs with timestamp.

Note that due to the retransmission mechanism of TCP/IP protocol, in the worst case, it may take 6-8 minute until timeout.