Implementation and Evaluation of the Reference Broadcast Infrastructure Synchronization Protocol

This paper describes reference broadcast infrastructure synchronization (RBIS), a clock synchronization protocol for IEEE 802.11 infrastructure wireless networks. The protocol is especially tailored for industrial and home automation networks, and inmany application contexts, it offers several advantages compared with other solutions targeted at similar purposes. RBIS has been conceived to rely on conventional Wi-Fi equipment and, in particular, on unmodified access points. It is based on the master/ slave approach and follows the receiver/receiver paradigm. An implementation of RBIS--carried out completely in software and based on timestamps taken at the interrupt handler level--has been developed, which achieves a synchronization error below 3 ?s. Then, a simple distributed hard real-time control application has been set up, which consists in two PCs running real-time application interface for Linux (RTAI) and connected through Wi-Fi. The actuation error, measured on the generation of synchronous pulses, is strictly below 13 ?s.