Abstract-Duty cycling is often used to reduce the energy consumption caused by idle listening in Wireless Sensor Networks (WSNs). Most studies on WSN protocols define a common duty cycle value throughout the network to achieve synchronization among the nodes. On the other hand, a few studies propose adaptation of the duty cycle according to uniform traffic conditions, which is beneficial assuming one-to-one traffic patterns that result in evenly distributed packet traffic. In this work, we consider the convergecast communication pattern commonly observed in WSNs. In convergecast communication, the packet traffic observed around the sink node is much higher than the traffic observed far from the sink, i.e., nodes with different distances to the sink node receive and must relay different amounts of traffic. Additionally, we utilize receiver-based protocols, which enable nodes to communicate with no synchronization or neighbor information, and hence do not require all nodes in the network to have the same duty cycle. In this paper, we model the expected energy consumption of nodes utilizing receiver-based protocols as a function of their duty cycle and their distance to the sink node. Using this analysis, we derive a closed-form formula for the duty cycle that minimizes the expected energy consumption at a given distance. Moreover, we propose an adaptation method for the derived distance-based duty cycle based on local observed traffic. Performance evaluations of the two proposed duty cycle assignment methods show that they greatly improve the energy efficiency without sacrificing packet delivery ratio or delay significantly.Index Terms-Receiver-based protocols, convergecast traffic, adaptive duty cycle, energy-efficiency, wireless sensor networks.

Abstract-Multicast routing protocols typically rely on the apriori creation of a multicast tree (or mesh), which requires the individual nodes to maintain state information. In sensor networks where traffic is bursty, with long periods of silence between the bursts of data, this multicast state maintenance adds a large amount of overhead for no benefit to the application. Thus, we have developed a stateless receiver-based multicast protocol that simply uses a list of the multicast members (e.g., sinks), embedded in packet headers, to enable receivers to decide the best way to forward the multicast traffic. This protocol, called RBMulticast (Receiver-Based Multicast), exploits the knowledge of the geographic locations of the nodes to remove the need for costly state maintenance (e.g., tree/mesh/neighbor table maintenance), making it ideally suited for sensor network multicast applications. RBMulticast was implemented in TinyOS and tested using a sensor network implementation as well as TOSSIM simulations. Both simulation and experimental results confirm that RBMulticast provides high success rates without the burden of state maintenance.

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Protocols for wireless sensor networks (WSNs) are very diverse. Reflecting this diversity, no single protocol architecture for WSNs dominates: programmers often modify the legacy-architecture to fit their set of protocols in the stack. However, there exists desirable goals for a sensor network architecture: modularity, flexibility and universality. At the same time, a WSN architecture should enable the protocols to achieve long network lifetimes for various applications. These are, in general, conflicting goals, with the former achieved using layered architectures and the latter obtained through cross-layer interactions. A good balance can be provided by architectures that enable layers to share common information, as these architectures allow for cross-layer protocol improvements, while preventing some of the short-comings of cross-layer designs. Confirming this observation, some architectures that enable information-sharing have been proposed in recent years. We survey these state-of-the-art information-sharing architectures for WSNs, and we introduce X-Lisa, a novel Cross-Layer Information-Sharing Architecture that provides many desirable properties such as flexibility and simplicity, and offers programmers a modular framework, simplifying cross-layer interactions.