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I have a strange issue with sim7600 minipcie Module.Data roaming is not stable.Let me explane exactly issue: we have 3 devices:

A- SIM7600(minipcie) + Openwrt base on Mediatek

B- Huawei E5172, CPE modem

C- Huawei Y9 2019, Cell Phone

ISP SIM CARD originally should work on PLMN 44444 and data roaming destination is 55555.(PLMN numbers is fake). Data Roaming network is on FDD band 3 or 1, so all devices support this bands.

1- At first I tested E5172 and successfully registered on roaming and data passed easily.I'm sure ISP didn't add IMEI's E5172 on their networks and didn't lock My SIM card to special IMEI or Modem.You can see a screenshot of web page after ping 8.8.8.8

Huawei E5172 Connection

2- 2nd step was test with Huawei Y9 - I set APN correctly in setting page and also active Roaming, but for a while (less than 1 minutes) Roaming sign appeared and cell phone was trying to connect, but it was filed and disconnected.During trying connection data can't pass. You cans see some screenshot here.

Huawei Y9 Trying Roaming 2

Huawei Y9 Roaming Field

3- 3rd I tested on SIM7600 and Openwrt exactly have same issue with Huawei Y9. But openwrt can get IP address for shot time but can't pass data.I tested some AT command like AT+CREG? for a shor time report 0,6 and it is mean data roaming but after a seconds report 0,3 and it is mean registering denied. Also I tested AT+COPS=1,2,"55555", unfortunately not effected. You can see some screenshot here.

Creg Report

Openwrt get IP

Openwrt Disconnect

CPSI Report

Base on this info please help and tell me your ideas

Thanks experts.

Amir Farahani
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1 Answers1

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After a lot of searching and make contact with SIMCOM, finally, I found Issue. I have answered this question because some peoples can use this experience in the future. This answer isn't only for this issue and may use in another issue.

1- Debugging tools for Qualcomm are QXDM and QPST both of them need to Qualcomm Licence, my Chinese friend help me to register these tools on my PC.

2-By QXDM and QPST you can understand what happens exactly, even if you can't debugging, these tools let you collect and send logs to company and they find the issue.

3- NV parameters are very important values on any LTE module. They are complex and need enough experience. Nv parameters make behavior for your LTE module my issue solve by change NV but SIMCOM helps me to change it.NV parameters could change by QXDM but fortunately, SIMCOM has the option you can change it by AT command, like this:

AT+CNV=/nv/item_files/modem/mmode/ue_usage_setting,0,00,1

Please before change NV parameters consult with SIMCOM or other LTE module maker

4-Reason of issue: GSM rejects my SIMcard on roaming, because of main(home) provider support only LTE so it could not connect to Roaming Network.

Thanks, Mr.Guo of SIMCOM also Mr.Ning in other company to help me solve this issue.

Amir Farahani
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