Preserving Temporal Relationships of Events for Wireless Sensor Actor Networks

In this paper, we present the performance evaluation of an algorithm for preserving temporal relationships of events in Wireless Sensor Actor Networks (WSANs). The algorithm consists of two modules, which deal with the problems of temporal event ordering and time synchronization. These two problems are approached as a whole as they complement each other: in order to temporally order the events, the nodes must be synchronized. The goal of the proposed event ordering algorithm for WSANs is to reduce the overhead in terms of energy dissipation and delay. We also propose a tunable time synchronization algorithm employing a hybrid synchronization scheme suited for clustered topology. The proposed algorithm utilizes the message exchange necessary for event ordering and routing for synchronization purposes by piggybacking messages with synchronization pulses and replies to reduce the communication cost of synchronization. Simulation experiments showed that the event ordering algorithm is capable of reducing the overhead when compared to previously proposed algorithms. The synchronization algorithm demonstrated that the combination of synchronization techniques was well suited for the communication mode utilized in a clustered topology. The approach of piggybacking synchronization pulses and replies resulted in a considerable gain, which we demonstrated in the number of messages that were piggybacked for synchronization purposes.