Transmission of messages between a terminal, a gateway and a server using a relay in an LPWAN communication system

An LPWAN communication system includes server equipment, at least one gateway and at least one relay. Each gateway communicates with terminals using a Class A communication mode, wherein any response intended for a terminal uses a reception window defined with respect to a transmission time of an original message by said terminal. Each relay is seen as a terminal by each gateway, and communicates with terminals in accordance with a Class A′ communication mode, defined as follows: the relay transmits beacons at regular intervals and listens out to terminals only during timeslots defined with respect to said beacons. In this Class A′ communication mode, the relay propagates any response toward a terminal using at least one other reception window defined with respect to a transmission time of an original message by said terminal.