Distributed Frequency-Locked Loops for Wireless Networks

The establishment of a common frequency reference in a distributed wireless network is a critical factor in enabling any degree of node cooperation in communication and sensing functions. In this paper we introduce Distributed Frequency-Locked Loops (D-FLL´s) to control the carrier frequencies of autonomous nodes with wireless communication capabilities. A novel frequency difference detector (FDD) is introduced allowing each node to estimate the frequency difference with respect to the ensemble of its neighbors. D-FLL´s are characterized in terms of stability and tracking accuracy when the synchronization network has a peer-to-peer (mutually coupled - MC) or hierarchical (master slave - MS) topology. In particular, synchronization error accumulates in MS architectures as the distance from the reference node increases. MC architectures, instead, trade slower convergence times for a smoother error distribution. Overall, D-FLL´s prove to be a robust and accurate technique for carrier frequency synchronization purposes that can be readily employed with any network architecture.