LTE-M Connection Issue

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mark0412's picture
mark0412
Junior(0)

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
jflynn129
Moderator(2)

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.

/Jim

mark0412's picture
mark0412
Junior(0)

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.

 

jflynn129's picture
jflynn129
Moderator(2)

were you able to resolve this issue?

jflynn129's picture
jflynn129
Moderator(2)

No response

mark0412's picture
mark0412
Junior(0)

Checked the SIM should be OK. However, network registration still keeps working only for few hours for some days. When it worked, I was able to access internet with data transaction.

Therefore I suspect the LTE-M signal is not stable in my testing area. Could you advise is -100dBm RSRP enough for modem to get register?

 

jflynn129's picture
jflynn129
Moderator(2)

I'm not sure about signal strength, but because it works sometimes and doesn't other, I strongly suspect it is a singal strength issue as you seem to have already determined.

PeterF's picture
PeterF
Moderator(15)

In my experience you can anticipate network connection issues if the reported signal strength is only -100 dBm. I suggest you attempt to improve the received signal strength... Make sure the SMA connector is tightened, try repositioning and/or reorienting the antenna, preferably the location of your testing is not in a basement or behind metal cabinets, etc!