CDR: Bandwidth-Efficient Cross-Interface Downlink Relay Scheme for Low-Power Multihop Wireless Networks

Driven by emerging wireless applications, numerous smart objects will be deployed, forming things networks interconnected by the Internet of Things (IoT). Many of these networks follow the low-power multihop wireless network (LPMWN) paradigm due to the good scalability of the distributed schemes adopted by LPMWNs. Although distributed schemes may operate satisfactorily most of the time, they are often complex and costly to manage. To simplify network management, the LoRa (long range) wireless technology has been introduced into LPMWNs for centralized network control. Unfortunately, due to LoRa's inherent limitation that a downlink packet must be in response to a precedent uplink packet, the existing protocols typically require every node to periodically send an uplink packet to the gateway for downlink network command dissemination. This causes intensive uplink collisions and quickly depletes LoRa bandwidth, especially when the network is large. In light of these pitfalls, we propose a (cross-interface downlink relay (CDR)) scheme, which leverages the ZigBee communications that are already available in LPMWNs to relay LoRa downlink data traffic for bandwidth-efficient and delay-guaranteed data dissemination. CDR determines the optimal network topology for bandwidth-minimized data relay while adjusting system parameters to ensure each node's delay requirement under network dynamics. A prototype system is implemented by integrating LoRa and ZigBee into an IoT platform. Extensive outdoor experiments show that the bandwidth consumption of CDR is 39.3% lower than a state-of-the-art LoRa data dissemination protocol for ZigBee-based LPMWNs under a moderate data traffic and delay requirement. Besides, CDR improves energy efficiency and network lifetime significantly.