LTE-M Connection Issue

mark0412's picture

I am developing LTE-M application with IMS2 HDK from Avnet and using SIM Card from IoT Starter Kit.
I got connection problem. Sometimes it cannot get register to the network for whole day, but it sometimes works for few hours. When it can register, signal stength is good (AT+CSQ -> +CSQ: 19,99). Therefore, it is not likely caused by signal coverage issue.

Could I get technical advise here?

Thanks a lot for your help.


jflynn129's picture

If it is sometimes connecting but sometimes not, it would indicate that there is no HW issue (if there was, I would never connect) plus you indicate that there is a good signal strengh indication. Assuming that nothing is changing except time (e.g., you aren't running new SW each time), I suspect there may be an AT&T issue in that the SIM is having problems getting autherization/authentication.  Can you check with AT&T and ensure that the SIM card is properly enabled and no issue exists with it.  

On the other hand, if the SW you are running is changing and sometimes it works and sometimes it doesnt, it may be a SW issue and posting details about what is running would be helpful.


mark0412's picture

Thanks for your advice. I am checking with AT&T about the SIM issue.

For more information, the testing setup is typing AT-Command on Tera Term to control the IMS2 HDK through on board USB to UART connections.

When it can get register, <+CEREG: 1,"3CA4","035F9D0F",7> will respond automatically without typing any AT command to it. When it is not work, only <+CEREG: 4> response shown.

However, when it is not work, I type <AT+COPS=?> to check operators, it can still be able to scan for base station with response

<+COPS: (1,"AT&T","AT&T","310410",7)(1,"AT&T","313100","313100",7),,(0,1,2,3,4),(0,1,2) OK>

And if check with <AT+BGLTEPLMN=?>, which provides RSPR info, it responds

<+BGLTEPLMN: (1,"AT&T","AT&T","310410",7,-10060)(1,"AT&T","313100","313100",7,-10060),,(0,1,2)>

Is -100dBm RSRP enough for modem to get register? I am suspecting that the LTE signal is not stable in my testing area.