Synchronizing Transmission Schedules of Partitioned Ad Hoc Networks

We present a new protocol for synchronizing terminals in wireless ad hoc networks which communicate using transmission schedules. Synchronization between terminals is required in these networks to support reliable time-slotted transmissions and, in some cases, periodic network control phases. A common global time reference, such as a beacon from a base station or a GPS time signal, may not be available to all terminals at all times. Distributed terminal initialization and clock drift may lead to a situation in which several groups of terminals are locally synchronized, but lack a common global synchronization. We introduce a distributed protocol designed to respond to and correct synchronization differences between groups of terminals. When a synchronization difference is detected, the protocol first attempts to resolve the synchronization ambiguity, i.e. determine which synchronization is correct. The protocol then provides an orderly process of silencing and resynchronizing portions of the network so that terminals may adopt a common synchronization. The basic properties of the protocol are analyzed and verified through simulation.