On the Synchronization of Intermittently Powered Wireless Embedded   Systems
  Battery-free computational RFID platforms, such as WISP (Wireless Identification and Sensing Platform), are emerging intermittently powered devices designed for replacing existing battery-powered sensor networks. As their applications become increasingly complex, we anticipate that synchronization (among others) to appear as one of crucial building blocks for collaborative and coordinated actions. With this paper we aim at providing initial observations regarding the synchronization of intermittently powered systems. In particular, we design and implement the first and very initial synchronization protocol for the WISP platform that provides explicit synchronization among individual WISPs that reside inside the communication range of a common RFID reader. Evaluations in our testbed showed that with our mechanism a synchronization error of approximately 1.5 milliseconds can be ensured between the RFID reader and a WISP tag. 
Kas{\i}m Sinan Y{\i}ld{\i}r{\i}m, Henko Aantjes, Amjad Yousef Majid,   Przemys{\l}aw Pawe{\l}czak
cs.NI