Impact of timing on the Proximity Services (ProSe) synchronization function
Samantha M. Gamboa Quintiliani, Fernando J. Cintron, David W. Griffith, Richard A. Rouil
Long Term Evolution Advanced (LTE-A) introduces a new feature called Proximity Services (ProSe), which enables device-to-device (D2D) communication between User Equipment (UE) and the capability to operate out-of-network. In order to establish a D2D communication link, the UEs need to be synchronized. In out-of-network scenarios, the synchronization is performed in a distributed manner by the UEs. In this paper, we study problems associated with the simultaneous execution of the synchronization procedure by LTE-A D2D-enabled UEs operating out-of-network. In particular, we focus on detection and convergence problems resulting from the half-duplex constraint and periodic scheduling. We show that if two transmitter UEs are acting as synchronization references and they perform the procedure too close in time, convergence to a synchronized state is not possible. Moreover, the periodic triggering of the procedure will make the problematic condition persistent in time. We propose an effective algorithm that prevent these problems, or resolve them in a reasonable time. We consider the protocol and requirements specified in the LTE-A standard, and we evaluate the performance of the proposed algorithm using system level simulations.
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