HL7800/HL8548/HL7688 don't always connect to the best cellular network

IoT Modules HL78
1

We are using the HL7800/HL8548/HL7688 modules with a SierraWireless SIM. However, all the HL modules have the same issue in that they don’t always connect to the best cellular network. How do we get the HL modules to connect to the best network.

For example, with the HL7800 we have two cellular providers nearby, both with LTE Band 28 (700MHz). The modem will connect to either of them.

Here is the good network (Vodafone NZ):

  • Tower is line-of-sight 100m away.
  • ppp connects and there are no issues. Near 0% packet loss.
  • Below is the output of the relevant AT commands.
AT+CSQ
+CSQ: 31,99

AT+KCELL=0
+KCELL: 1,5,35f010,86601,460,41216,88,28,2

AT+KBND?
+KBND: 0,00000000000008000000

AT+KSRAT?
+KSRAT: 0

The poor network (Spark NZ):

  • Tower is hidden but also about 100m away.
  • ppp may connect, when it does there a huge packet losses.
AT+CSQ
+CSQ: 14,7        - both values fluctuate a lot

AT+KCELL=0
+KCELL: 1,5,35f050,75479,460,41216,88,28,2

AT+KBND?
+KBND: 0,00000000000008000000

AT+KSRAT?
+KSRAT: 0

Once connected to the poor network the modem modules will not change to the better network. Even after a power cycle.

2

Hi simon,

Sierra Sim does not choose the best coverage operator, it chooses the best economic one.

At the first time, your device connected to Spark NZ then this operator was stored in the last registered PLMN list(LRPLMN list) which is in your sim. After power cycle, your device will try to register on the LRPLMN.

If you want to switch to Vodafone NZ, you can try this:

  1. Make your device deregister from network by unplugging antenna or issue AT+COPS=2
  2. Wait for about 5 mins
  3. Make your device register to network by plugging in antenna or issue AT+COPS=0

Thanks,

3

Hi Jerdung,

Sierra Sim does not choose the best coverage operator, it chooses the best economic one.

What’s your source for this information?

Is there anyway to clear the LRPLMN list?

4

Hi simon,

Sierra sim chooses the best network base on balancing of some factors and I’m pretty sure that signal strength is not the main factor. You can contact technical support for the information.

Sorry for my confusion, LRPLMN is not a list. When your device successfully registers to the network, PLMN will become LRPLMN after you issue a power cycle on your device.

Thanks,

5

Thanks. I’ve tried that a few times now and it seems to work.