Optimization of Discovery Period for Peer Device Discovery in Cellular-Assisted D2D Communication Systems

Abstract

One of the most important processes in cellular-assisted device-to-device (D2D) communications is device discovery, which decides whether two devices are located close to each other. The discovery process is performed by devices periodically transmitting discovery signals so that neighbor devices can receive them to recognize their proximate physical presence. While a fixed set of discovery parameters are used regardless of devices in most of the existing works, discovery periods are not necessarily the same for all devices, as they can be set differently depending on their channel conditions and operational environments, e.g., the mobile speeds. In this paper, we present an optimization framework to determine the discovery periods for individual devices in cellular-assisted D2D communication systems. We consider two different types of optimization problems, taking the different user velocities into account: minimizing the average number of undiscovered device pairs, and minimizing the number of discovery signal transmissions while maintaining the average number of undiscovered device pairs for each device less than a pre-specified threshold. We present analytical and simulation results to demonstrate that short discovery periods can be beneficial to high-mobility devices, while longer discovery periods are allowed for devices with lower velocities.