Cross-Layered Synchronization Protocol for Wireless Sensor Networks

The aircraft industry has a conception cycle based on a massive use of Computer Assisted Design in order to allow more complex plane designs, and cheaper development costs compared to multiple prototyping steps. Among the many processes necessary to validate calculated aerodynamic models, real time pressure measurements are made on the wings during test flights. Such measurements are currently performed using wired sensors, with all the cost and weight problems it causes. Advances in wireless sensor network performances and improvement of attainable bit rates allow research on such measurement systems using Wireless Sensor Networks (WSNs). However, current WSN synchronization protocols do not reach performances required for a reliable correlation of data collected by all the sensors. In this paper, we present a solution to overcome this difficulty to reach sub-microsecond synchronization based on cross-layered design. Specific algorithms are implanted into the MAC and physical layers and form a cross-layered synchronization protocol for deterministic Wireless Sensor Networks named WiDeCS (Wireless Deterministic Clock Synchronization). This protocol propagates master time reference to nodes of a cluster tree network. WiDeCS Cross layered scheme is possible thanks to flag signals in the physical layer. These signals capture precise dates of transmission and reception. Hardware level simulations show a synchronization precision of 100 ns. In this paper, the sources of variable delays in WSN network interfaces are detailed, and the effect of cross-layered WiDeCS scheme on the knowledge of different delays is explained.