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The low-energy characteristics of Wireless Sensor Networks pose a great design challenge for MAC protocol design. The cluster-based scheme is a promising solution. Recent studies have proposed different cluster-based MAC protocols. We propose an intracluster communication bit-map-assisted (BMA) MAC protocol. BMA is intended for event-driven applications. The scheduling of BMA can change dynamically according to the unpredictable variations of sensor networks. In terms of energy efficiency, BMA reduces energy consumption due to idle listening and collisions. In this study, we develop two different analytic energy models for BMA, conventional Time Division Multiple Access (TDMA) and energy efficient TDMA (E-TDMA) when used as intra-cluster MAC schemes. Simulation experiments are constructed to validate the analytic models. Both analytic and simulation results show that in terms of energy efficiency, BMA performance heavily depends on the sensor node traffic offer load, the number of sensor nodes within a cluster, the data packet size and, in some cases, the number of sessions per round. BMA is superior for the cases of low and medium traffic loads, relatively few sensor nodes per cluster, and relatively large data packet sizes. In addition, BMA outperforms the TDMAbased MAC schemes in terms of average packet latency.

Abstract. Expressiveness and matching efficiency are two key design goals of publish/subscribe systems. In this paper, we introduce the Semantic Web technologies into the publish/subscribe system and propose an ontology-based publish/subscribe (OPS) system. The system can make use of the semantic of events to match events with subscriptions, and can support events with complex data structure (such as graph structure). An efficient matching algorithm is proposed for the OPS system, which can match events with subscriptions in a speed much higher than conventional graph matching algorithms. Therefore, the main contribution of our work is that it greatly improves the expressiveness of the publish/subscribe system without the sacrifice of matching efficiency.

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