The ubiquity of sensors has offered great opportunities to monitoring infrastructures to track the real-time state of observed environments. Monitoring systems rely on synchronous massive data to calculate the environment state. However, collecting and communicating massive data usually leads to expensive energy consumption due to high sampling frequency and communication cost for the sensors operation. Clamp-on wireless sensors are a flexible plug-and-play technology easy to deploy where sensors operate on integrated batteries. This paper introduces a highly accurate time synchronization protocol to coordinate the operation of individual clamp-on sensors deployed as an energyconstrained monitoring solution. While maintaining sensors highly synchronized, the proposed protocol reduces drastically data communication and energy consumption of the sensor network. To minimize the energy consumption further, we optimize the protocol behavior using a genetic algorithm. The protocol has been modeled in VDM for formal analysis, implemented and compared to a state of the art protocol.

Wireless sensor networks (WSN) are becoming a pervasive technology integrated in most of real-time monitoring infrastructures and industrial control applications. Timeliness accuracy, performance and energy efficiency are key metrics to consider when deploying such WSN systems. Timeliness accuracy amounts to time-stamp collected data at sensor level in order to calculate an integrated real-time state of the monitored environment. It is usually achieved on the expense of energy consumption of sensors. Namely, such metrics are conflicting in a way that improving one metric deteriorates the other metrics. This paper proposes an energy-efficient time synchronization protocol to enable a high accuracy calibration for time stamping sensors data. The rational behind the protocol is to ensure that data is correctly time-stamped and timerelevant in order to operate the control loop managing the energy of the smart building. Our experimental results on an actual case study show that our protocol outperforms the state of the art protocols in terms of both time accuracy and energy efficiency.