LAUSR

As public safety migrates from existing digital land mobile radio networks to fourth generation (4G) long-term evolution (LTE), a novel feature in the latter is the enablement of direct communications between devices. In this article, we examine the performance of the LTE device-to-device direct discovery process in out-of-coverage scenarios (Mode 2). We model individual discovery periods as a slotted random access protocol with half-duplex user equipment (UE). We outline a simulation framework using the open-source network simulator 3 (ns-3) and evaluate the discovery process’s performance as a function of the size of the resource pool, UE density, and the transmission probability. We establish that there exists an optimal transmission probability that minimizes discovery time for a given network configuration. However, because a UE cannot know the number of neighbors when it goes off-network, we develop a method to allow UEs to learn the optimal transmission probability during discovery. We compare our algorithm’s performance to the 3rd Generation Partnership Project standards prescribed method and others to demonstrate its superiority.