Abstract

Time synchronization is important for any distributed system. In particular, wireless sensor networks make extensive use of synchronized time in many contexts (e.g. for data fusion, TDMA schedules, synchronized sleep periods, etc.). Existing time synchronization methods were not designed with wireless sensor networks in mind, and need to be extended or redesigned. Our solution centers around the development of a deterministic time synchronization method relevant for wireless sensor networks. The proposed solution features minimal complexity in network bandwidth, storage and processing and can achieve good accuracy. Highly relevant for sensor networks, it also provides tight, deterministic bounds on both the offsets and clock drifts. A method to synchronize the entire network in preparation for data fusion is presented. A real implementation of a wireless ad-hoc network is used to evaluate the performance of the proposed approach.

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Abstract-Wireless sensor networks are considered the sensing technology of the future. Large numbers of untethered sensor nodes can he used for tracking small animals and targets, environmental monitoring, enforcing security perimeters, etc. A major prohlem for many sensor network applications is determining the mvst efficient way of conserving the energy of the power source. Some networks use batteries, while others suggest different methods of gathering energy (e.g., solar cells). Regardless of the powering method, energy conservation is of prime importance for sensor networks. The hest way to cvnserve energy is to turn the sensor nodes off; however, since an inactive sensor node is no longer part of the network, the network can become disconnected. This creates a fundamental trade-off. In this paper, we propose a deterministic, schednlebased energy conservation scheme. In the proposed approach, time-synchronized sensors form on-vff schedules that enable the sensors to he awake only when necessary. The schednle establishment is fuUy distributed and thus appropriate for large selwr networks. The performance of the proposed approach is evaluated through the use of simulations.