We recently encountered problems with the Nimble Link NL-SW-LTE-S7588 (HL7588) using the A.2.13 version of the firmware where the MBIM USB interface (at+ksubcomp=2) would periodically disconnect from our linux base product when doing mobility testing in a car. Stationary testing on a desk were always successful (no radio unregistration, no USB disconnection overnight). We then saw that in the release notes of A.2.15 that this version introduced a fix for a potential baseband reset problem related to base station handovers with an opened data session, precisely what we were observing. Indeed, upgrading to A.2.15 seem to have fixed the USB reset problem we were seeing on the road. However, in our connection monitoring log we often now also see signal strength drop from 80 %+ to 0% within 5 seconds (obtained from ModemManager in our linux based product which is in return converted from AT+CSQ commands). The radio is still reported as registered and the IP connection is also reported as active but no data can be sent. Our tests are done in a dense urban place where LTE coverage is not an issue and a phone was used as a comparison device). This null signal strength stays like that for a couple of minutes (from 3 to 6 so far) and would jump back up to 80%+ again. This pattern is seen every 10-15 minutes or so when driving around in the city.
Is sudden signal drop like this a known problem with this radio/firmware ? Although it seems to recover at some point, data over our PDP context does not seem to get through during that time.
I would gladly attach a log from our ltemonitor script that shows the different timestamps and the registration/ip connection states overtime as well the signal strength but it seems new accounts can’t do that
Any ideas/support would be appreciated !
Thanks in advance