FerryLink: Combating Link Degradation for Practical LPWAN Deployments

Abstract

Low-Power Wide-Area Networks (LPWANs) have been shown as a promising technique to provide long-range low-power communication for large-scale IoT devices. In this paper, however, we show the poor performance of LoRa network due to its link diversity in macro- and micro- scope through one-month measurements in an area of $2.2\ km\times 1.5\ km$. We present FerryLink, which exploits such link diversity and leverages peer nodes to ferry data of weak links, to combat performance degradation. Traditional arts (e.g., building multi-hop networks) are inefficient or too heavyweight for the current star-topology-based LoRa network. FerryLink thus proposes a novel ferry mechanism combining RSSI sampling and Channel Activity detection(CAD) to suit multiple orthogonal transmission parameters of LoRa. To reduce energy overhead, FerryLink leverages convention windows for coarse-grained transmission synchronization between two coupled nodes. Finally, FerryLink utilizes the orthogonality of uplink and downlink signals to avoid data redundancy due to the ferry mechanism, maintaining comparable capacity with original LPWANs. We build FerryLink on top of LoRaWANwith commercial off-the-shelf hardware. The extensive evaluation results show that FerryLink effectively improves the packet delivery rate (PDR) of LoRa nodes (to over 95%), achieves 2x less energy overhead, and increases communication range by 50% compared with the original LoRaWAN.