Improving time synchronization protocols in wireless sensor networks

Abstract

As the world moves towards greater ubiquity of wireless sensor networks, the need for lightweight, resilient time synchronization protocols is apparent. Wireless nodes' internal clocks are subject to drift over time due to manufacturing imperfections and environmental changes. Such drift can be detrimental for many systems, especially for those where accurate data timestamping is required. Time synchronization protocols introduce a means by which two or more nodes can wirelessly synchronize their internal clocks. We have implemented and compared two existing time synchronization protocols, Reference Broadcast Synchronization (RBS) and Simple Synchronization Protocol (SISP), on Atmel ATMega328p based microcontroller platforms with IEEE 802.15.4 Xbee radio modules. We have found that SISP is able to achieve much higher synchronization performance than RBS. Our goal, however, is to improve upon current time synchronization protocols even further. Thus, we have developed a new protocol, the Sticking Heartbeat Aperture Resynchronization Protocol (SHARP), that aims to reduce synchronization error and resolve shortcomings of existing protocols. We show that SHARP exhibits a higher level of synchronization than SISP, while requiring significantly fewer messages. Additionally, to assist in developing accurate time synchronization protocols, we have performed message transmission / reception latency measurement experiments on the Xbee radios using a logic analyzer. Latency was found to be consistent across test runs, exhibiting a low standard deviation under 100µs. Such latency was also found to strongly follow a Gaussian distribution. These results will be useful in a future implementation of SHARP.