Device-to-Device Communication in Future Cellular Networks : Resource allocation and mode selection

Sammanfattning: The widespread use of smart devices and mobile applications is leading to a massive growth of wireless data traffic. Supporting the upcoming demands of data volume, communication rate, and system capacity requires reconsideration of the existing network architecture. Traditionally, users communicate through the base station via uplink/downlink paths. By allowing device-to-device (D2D) communication, that is, direct transmission between the users, we can enhance both efficiency and scalability of future networks. In this thesis, we address some of the challenges brought by the integration of D2D communication in cellular systems, and validate the potential of this technology by means of proper resource management solutions. Our main contributions lie in the context of mode selection, power control, and frequency/time resource allocation mechanisms. First, we investigate how the integration of D2D communication in dynamic Time Division Duplex systems can enhance the energy efficiency. We propose a joint optimization of mode selection, uplink/downlink transmission time, and power allocation to minimize the energy consumption. The optimization problem is formulated as a mixed-integer nonlinear programming problem, which is NP-hard in general. By exploiting the problem structure, we develop efficient (and for some scenarios, optimal) solutions. We complement the work with a heuristic scheme that achieves near-optimal solutions while respecting practical constraints in terms of execution times and signaling overhead. Second, we study the performance of several power control strategies applicable to D2D-enabled networks. In particular, we compare 3GPP LTE uplink power control with a distributed scheme based on utility maximization. Furthermore, to extend the application of well-known power control approaches to Rician-fading environments, we propose a power allocation scheme based on the concept of coherent-measure-of-risk. This approach allows to obtain a convex and efficiently solvable problem. Third, we study the subcarrier allocation problem in D2D-enabled networks. We maximize the total transmission rate by modeling the problem as a potential game. Nash equilibria of the game correspond to local optima of the objective function, which are found via better-response dynamic implemented with message passing approach. Finally, we propose two different applications of full-duplex technology for D2D communication. First, we present a practical mode selection algorithm that leverages only the existing control signaling to minimize the users' probability of outage. Second, we investigate how the combination of D2D relaying and full-duplex operations can improve the network coverage and the communication quality without additional infrastructure deployment.