In this paper, we consider a distributed power control scheme that can maximize overall capacity of an interference-limited wireless system in which the same radio resource is spatially reused among different transmitter-receiver pairs. This power control scheme employs a gradient-descent method in each transmitter, which adapts its own transmit power to co-channel interference dynamically to maximize the total weighted sum rate (WSR) of the system over a given interval. The key contribution in this paper is to propose a common feedback channel, over which a backward physical signal is accumulated for computing the gradient of the transmit power in each transmitter, thereby significantly reducing signaling overhead for the distributed power control. We show that the proposed power control scheme can achieve almost 95% of its theoretical upper WSR bound, while outperforming the non-power-controlled system by roughly 63% on average.

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.