Adaptive synchronization reference selection for out-of-coverage Proximity Services (ProSe)

Proximity services (ProSe) is a Long Term Evolution Advanced (LTE-A) feature that allows User Equipments (UEs) to communicate without the need of routing the data throughout the network. In this paper, we studied the synchronization protocol used by ProSe-enabled UEs in out- of-coverage scenarios. In particular, we studied the triggering frequency of the distributed Synchronization Reference (SyncRef) selection algorithm used in these scenarios. We showed the disadvantage of using a periodic algorithm, and we developed an adaptive algorithm that triggers the process when suitable depending on the conditions of each UE. We evaluated the algorithm performance using our ns-3 ProSe implementation, and considering the protocol and requirements specified in the LTE-A standard. The results show that fast convergence time to a synchronized state can be achieved using the adaptive algorithm.