Abstract
Flooding service has been investigated extensively in wireless networks to efficiently disseminate network-wide commands, configurations, and code binaries. However, little work has been done on low-duty-cycle wireless sensor networks in which nodes stay asleep most of the time and wake up asynchronously. In this type of network, a broadcasting packet is rarely received by multiple nodes simultaneously, a unique constraining feature that makes existing solutions unsuitable. In this paper, we introduce Opportunistic Flooding, a novel design tailored for low-duty-cycle networks with unreliable wireless links and predetermined working schedules. Starting with an energy-optimal tree structure, probabilistic forwarding decisions are made at each sender based on the delay distribution of next-hop receivers. Only opportunistically early packets are forwarded via links outside the tree to reduce the flooding delay and redundancy in transmission. We further propose a forwarder selection method to alleviate the hidden terminal problem and a link-quality-based backoff method to resolve simultaneous forwarding operations. We show by extensive simulations and test-bed implementations that Opportunistic Flooding is close to the optimal performance achievable by oracle flooding designs. Compared with Improved Traditional Flooding, our design achieves significantly shorter flooding delay while consuming only 20-60% of the transmission energy.
Highlights
Wireless Sensor Networks have been used for many long-term applications such as military surveillance [11], infrastructure protection [44] and scientific exploration [33]
One could argue that traditional flooding methods could be adapted to low-duty-cycle networks by permitting (i) multiple transmissions of the same packet based on the neighbors’ active schedules and (ii) ARQ-based retransmission to deal with unreliable links, but this still has a number of problems
It can be proved that this tree structure is the energy-optimal one for flooding among all tree structures generated from the directed acyclic graph (DAG)
Summary
Wireless Sensor Networks have been used for many long-term applications such as military surveillance [11], infrastructure protection [44] and scientific exploration [33]. Sleep latency degrades the performance (e.g, delay and energy consumption) of various kinds of communication designs in low-duty-cycle networks. The combination of low-duty-cycle operation and unreliable links makes the problem of flooding different from that found in wired networks and always-awake wireless networks. This work introduces Opportunistic Flooding: a flooding method specially designed for low-duty-cycle wireless sensor networks. The key novelty of this work lies in the forwarding decision making, in which nodes forward a packet with a higher probability if the packet arrives opportunistically earlier. To the best of our knowledge, this is the first distributed flooding method designed for wireless sensor networks that considers the effect of both low-duty-cycle and unreliable wireless links.
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