Transmission Timing Control Using ACK Signal in LoRaWAN

Long range wide area network (LoRaWAN) enables low-power and long-range communication suitable for wireless sensor networks (WSNs). Since LoRaWAN is a decentralized network, packet collision may occur if multiple nodes send data packets simultaneously. It is necessary to adjust the node's transmission interval properly to avoid such packet collisions. This paper proposes a transmission interval control strategy that takes advantage of an acknowledgment (ACK) signal from a gateway (GW) to each node. Instead of transmitting a controlling signal, the GW selects one of two receiving windows for ACK packet transmission to indicate 0 or 1. Thus, it does not incur any overhead. The proposed method adaptively changes the transmission interval of each LoRaWAN node by utilizing the ACK signal returned from the GW. The proposed method uses a simple prediction method that is computationally simple and can provide good properties even when there are constraints on the systems associated with observing gentle changes, such as environmental monitoring. Computer simulation results show that the proposed method can reduce the number of transmitted packets while achieving the same observation accuracy level as conventional methods.