3G SIM5320 support for MQTT

Question

Looking for feedback from others who have been using the SIM53xx series modules for IoT solutions over the 3G network. I have an MQTT broker on the internet to collect data for a fleet tracking system being developed. There is a lot of information about this type of solution with 2G connections but as 2G is being phased out I don't have choice but use 3G as the newer NB1 / CAT M1, sigfox etc. solutions aren't available on the small Pacific island this solution is targeted to and LoRa doesn't have sufficient range (the island isn't that small!).

After a lot of research it seems the SIM5320 is the most applicable solution (reasonable cost, popular, small, has GPS features) and there is also a whitepaper that states extensions to the AT command set has extensions for MQTT session setup, pub/sub etc. Perfect for my application, however it is only referred to in an isolated whitepaper simcom mqtt 3g and there is no other references to it in other simcom documentation or on the net.

Before I go out and purchase a couple for testing, can anyone confirm if the MQTT extensions actually exist and if they are reliable?

Also any feedback on reliability / support for simcom modules would be appreciated as I'm new to IoT over 3G.

Answer 1

I used the SIM5320 in a product and none of the modules I bought have the MQTT functionality so you must implement the MQTT protocol in a external processor or MCU. Maybe you have to request a different firmware at the moment of purchase.

About the reliability, I think that the modem functionality is reliable enough, I sometimes find that the modem gets stuck (could be linux driver or modem firmware) and a hard reset makes everything work again, no data loss.

I think that the GPS works fine most of the time, sometimes it stops sending useful NMEA sentences, it just sends a propietary one ($PSTIS*61), sometimes it losses the fix and its unable to recover by itself and I have to reset the module (a lot of the times it doesn't work) and sometimes it gives wrong fixes, about 1000 km wrong but this can be filtered in software.

The GPS part of these modems lack configuration options and commands, you can't change the fix rate, you can't make a cold start without first disabling the GPS and this is problematic because if you have no fix the GPS can refuse to be disabled with the excuse to be downloading ephemeris data for faster next startup.

I think your best option would be to try the SIM5360, as it has two serial ports, one for modem/GPS and one exclusive for GPS and also supports GLONASS. The SIM5320 has only one serial port and only supports GPS.

Anyway I would include in the design an optional independent GPS module (u-blox, simcom, etc). I think that using a SIMCOM 3g module and a independent GPS module is still cheaper than using a 3g modem from other manufacturer (at least for small scale).

About the support, they seem to not offer direct support, however the distributor I bought from offered plenty of support free of charge, they asked me for logs, pass me tools for the operating system I was using and answered very technical questions.