Various protocols have been proposed in the area of wireless sensor networks in order to achieve network-wide time synchronization. A large number of proposed protocols in the literature employ a message passing mechanism to make sensor node clocks tick in unison. In this paper, we first classify Message Passing based Time Synchronization (MPTS) protocols and then analyze them based on different metrics. The classification is based on the following three criteria: structure formation of the network affected by the synchronization protocol, frequency of synchronization process (synchronization interval), and synchronization message overhead. Proposed protocols are analyzed and evaluated from different perspectives based on available data. A comparison table of the reviewed protocols is presented according to the evaluation metrics. Finally, some potential methods will be proposed to improve the synchronization process.

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Since wireless sensor nodes are battery powered, the emphasis was on reducing the energy consumption of the sensor nodes. However, with the increase in real-time traffic requirements in wireless sensor nodes, network performance metrics are increasingly important. Nonetheless, most existing network performance studies were done via simulation, with few experimental studies performed on testbeds using ad hoc methodologies. This paper proposes a structured experimental methodology for evaluating the delay, throughput, and packet loss performance of wireless sensor networks, while addressing practical issues related to the use of an experimental approach. A global clock synchronization technique, in addition to insertion of timestamps in the network packets was proposed for more accurate measurement of the network delay. Several different physical topologies such as single cluster, chain, and cluster tree topologies were defined as standard test topologies. The EMLMAC protocol was used to demonstrate the viability of the proposed structured experimental methodology. Based on the proposed experimental approach, the measured throughput forEMLMAC for the single cluster two-hop and three-hop chain topologies differed by 1.02%, 6.75% and 13.91% respectively from the simulation results. This indicates that an experimental approach is essential for verifying the actual performance of a wireless sensor network.

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