Wireless powered D2D communications underlying cellular networks: design and performance of the extended coverage

Because of the short battery life of user equipments (UEs), and the requirements for better quality of service have been more demanding, energy efficiency (EE) has emerged to be important in device-to-device (D2D) communications. In this paper, we consider a scenario, in which D2D UEs in a half-duplex decode-and-forward cognitive D2D communication underlying a traditional cellular network harvest energy and communicate with each other by using the spectrum allocated by the base station (BS). In order to develop a practical design, we achieve the optimal time switching (TS) ratio for energy harvesting. Besides that, we derive closed-form expressions for outage probability, sum-bit error rate, average EE and instantaneous rate by considering the scenario when installing the BS near UEs or far from the UEs. Two communication types are enabled by TS-based protocol. Our numerical and simulation results prove that the data rate of the D2D communication can be significantly enhanced.Web of Science58439939

Outage performance analysis of non-orthogonal multiple access with time-switching energy harvesting

In recent years, although non-orthogonal multiple access (NOMA) has shown its potentials thanks to its ability to enhance the performance of future wireless communication networks, a number of issues emerge related to the improvement of NOMA systems. In this work, we consider a half-duplex (HD) relaying cooperative NOMA network using decode-and-forward (DF) transmission mode with energy harvesting (Ell) capacity, where we assume the NOMA destination (D) is able to receive two data symbols in two continuous time slots which leads to the higher transmission rate than traditional relaying networks. To analyse EH, we deploy time-switching (TS) architecture to comprehensively study the optimal transmission time and outage performance at D. In particular, we are going to obtain closed-form expressions for outage probability (OP) with optimal TS ratio for both data symbols with both exact and approximate forms. The given simulation results show that the placement of the relay (R) plays an important role in the system performance.Web of Science253918

Large Scale Geometry of Surfaces in 3-Manifolds

A compact, orientable, irreducible 3-manifold M with empty or toroidal boundary is called geometric if its interior admits a geometric structure in the sense of Thurston. The manifold M is called non-geometric if it is not geometric. Coarse geometry of an immersed surface in a geometric 3-manifold is relatively well-understood by previous work of Hass, Bonahon-Thurston. In this dissertation, we study the coarse geometry of an immersed surface in a non-geometric 3- manifold. The first chapter of this dissertation is a joint work with my advisor, Chris Hruska. We answer a question of Daniel Wise about distortion of a horizontal surface subgroup in a graph manifold. We show that the surface subgroup is quadratically distorted in the fundamental group of the graph manifold whenever the surface is virtually embedded (i.e., separable) and is exponentially distorted when the surface is not virtually embedded. The second chapter of this dissertation generalizes the previous work of the author and Hruska to surface subgroups in non-geometric 3-manifold groups. We show that the only possibility of the distortion is linear, quadratic, exponential, and double exponential. We also establish a strong connection between the distortion and the separability of surface subgroups in non-geometric 3-manifold groups. The final chapter of the dissertation makes a progress in understanding the structure of the group of quasi-isometries of a closed graph manifold which is mysterious