I use the PANS and i connect my Gateways (Raspberry Pi3+ DWM1001) with the wi-fi network and all work fine.
if the environment in which I install the system does not provide a wifi connection I want to connect my gateways to send data using 3G-LTE USB dongle, is it possible?
technically it is possible as soon as the 3G-LTE USB dongle would provide a network interface.
The Gateway (DWM Proxy) is connected to the MQTT Broker via TCP. So if the MQTT Broker is on reliable internet it should work. If the MQTT Broker is on the Raspberry Pi, then the same should apply for the incoming connection.
If you test it please share the results.