A Unified Clock Synchronization Protocol for Infrastructure Wireless LANs

In the past decade, a number of solutions have appeared for industrial communication systems, which include both a wired backbone and a number of wireless extensions. Ethernet and Wi-Fi are two popular technologies that can be profitably adopted to set up this kind of networks. Although both of them feature very high throughput, the inability of Wi-Fi to tackle real-time constraints properly has undermined their joint adoption at the shop-floor in real-world plants. Clock synchronization protocols are able to decouple, to a good extent, timing accuracy--as measured at the application level-- from the intrinsic determinism of the underlying communication network. In this paper, a number of practical solutions are first described that achieve synchronized operation in infrastructure wireless LANs, and their features are compared. Then, a proposal is introduced that shows how they can be combined into a single, comprehensive solution.