Recent advances in micro-electromechanical systems (MEMS) technology have led to the development of small, low-cost, and low-power sensors. Wireless sensor networks (WSNs) consist of large populations of wirelessly connected nodes, capable of computation, communication, and sensing. In such networks, data from each sensor is agglomerated using data fusion to form a single meaningful result, which makes time synchronization between sensors highly desirable. Hence, time synchronization is a crucial component of WSNs, but achieving synchronization in WSNs, which combine stringent precision requirements with severe resource constraints, is particularly challenging. Instead of time synchronization between just the sender and receiver or within a local group of sensor nodes, some applications require the sensor nodes to maintain a similar time within a certain tolerance throughout the lifetime of the network. This paper surveys and evaluates that time-diffusion synchronization protocols based on a variety of factors like precision, accuracy, cost, and complexity.
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