On the scalability of IEEE 802.11 ad-hoc-mode timing synchronization function

The IEEE 802.11 standards support the peer-to-peer mode Independent Basic Service Set (IBSS), which is an ad hoc network with all its stations within each other’s transmission range. In an IBSS, it is important that all stations are synchronized to a common clock. Synchronization is essential for the MAC layer power management. Also, if frequency hopping spread spectrum is used in the physical layer, synchronization is needed to ensure that all stations “hop” at the same time. This paper evaluates the synchronization mechanism as specified in the IEEE 802.11 standards. Through rigorous analysis, it is shown that when the number of stations in an IBSS is not very small, there is a non-negligible probability that stations may get out of synchronization. The more stations, the higher probability of asynchronism. In this sense, the current IEEE 802.11 synchronization algorithm does not scale; it cannot support a large -scale IBSS. To alleviate the asynchronism problem, this paper proposes a simple remedy to the 802.11 algorithm. The resulting algorithm enjoys many nice properties—it is compatible, scalable, effective, mobility-friendly and simple. We are able to exceed the industry expectation of time accuracy (maximum clock offset under 12 mus) without any change of beacon format.