Device-to-device (D2D) communications underlaying a cellular infrastructure takes advantage of the physical proximity of communicating devices and increasing resource utilisation. However, adopting D2D communications in complex scenarios poses substantial challenges for the resource allocation design. Meanwhile, matching theory has emerged as a promising framework for wireless resource allocation which can overcome some limitations of game theory and optimisation. This thesis focuses on the resource allocation optimisation for D2D communications based on matching theory. First, resource allocation policy is designed for D2D communications underlaying cellular networks. A novel spectrum allocation algorithm based on many-to-many matching is proposed to improve system sum rate. Additionally, considering the quality-of-service (QoS) requirements and priorities of di erent applications, a context-aware resource allocation algorithm based on many-to-one matching is proposed, which is capable of providing remarkable performance enhancement in terms of improved data rate, decreased packet error rate (PER) and reduced delay. Second, to improve resource utilisation, joint subchannel and power allocation problem for D2D communications with non-orthogonal multiple access (NOMA) is studied. For the subchannel allocation, a novel algorithm based on the many-to-one matching is proposed for obtaining a suboptimal solution. Since the power allocation problem is non-convex, sequential convex programming is adopted to transform the original power allocation problem to a convex one. The proposed algorithm is shown to enhance the network sum rate and number of accessed users. Third, driven by the trend of heterogeneity of cells, the resource allocation problem for NOMA-enhanced D2D communications in heterogeneous networks (HetNets) is investigated. In such a scenario, the proposed resource allocation algorithm is able to closely approach the optimal solution within a limited number of iterations and achieves higher sum rate compared to traditional HetNets schemes. Thorough theoretical analysis is conducted in the development of all proposed algorithms, and performance of proposed algorithm is evaluated via comprehensive simulations. This thesis concludes that matching theory based resource allocation for D2D communications achieves near-optimal performance with acceptable complexity. In addition, the application of D2D communications in NOMA and HetNets can improve system performance in terms of sum rate and users connectivity.

Device-to-Device (D2D) communication is one of the technologies for next generation communication system. Unlike traditional cellular network, D2D allows proximity users to communicate directly with each other without routing the data through a base station. The main aim of this study is to improve the overall energy efficiency (EE) of D2D communications overlaying cellular system. To reduce the complexity of joint EE optimization, we decompose the main EE problem into two subproblems; resource efficiency (RE) optimization in the first stage and EE optimization for D2D pairs in the second stage. Firstly, we propose an alternative two-stage RE-EE scheme for a single cellular user equipment (CUE) and a D2D pair utilizing uplink spectrum. Later, we extend this work for multiple CUEs and D2D pairs by considering the downlink orthogonal frequency division multiple access (OFDMA). By exploiting a range of optimization tools including the Bisection method, interior point algorithm, fractional programming, Dinkelbach approach, Lagrange dual decomposition, difference of convex functions, and concave-convex procedure, the original non-convex problems are solved and we present iterative two-stage RE-EE solutions. Simulation results demonstrate that the proposed two-stage scheme for uplink scenario outperforms the cellular mode and dedicated mode of communications and the performance is close to the global optimal solution. The results also show that the proposed schemes for downlink resource sharing provide improved system EE performance with significant gain on EE for D2D users compared to a two-stage EE-EE solution, which is obtained numerically. Furthermore, the RE and EE optimization for non-orthogonal multiple access (NOMA) are considered to study the effect of users' access to the whole spectrum. The results indicate that the proposed RE scheme for NOMA with D2D communications achieves higher system EE compared to the OFDMA based schemes.

In this thesis, we proposed the use of device-to-device (D2D) communications for extending the coverage area of active base stations, for public safety communications with partial coverage. A 3GPP standard compliant D2D system level simulator is developed for HetNets and public safety scenarios and used to evaluate the performance of D2D discovery and communications underlying cellular networks. For D2D discovery, the benefits of time-domain inter-cell interference coordi- nation (ICIC) approaches by using almost blank subframes were evaluated. Also, the use of multi-hop is proposed to improve, even further, the performance of the D2D discovery process. Finally, the possibility of using multi-hop D2D communications for extending the coverage area of active base stations was evaluated. Improvements in energy and spectral efficiency, when compared with the case of direct UE-eNB communi- cations, were demonstrated. Moreover, UE power control techniques were applied to reduce the effects of interference from neighboring D2D links.

With the increasing demand for wireless communications, radio resource management (RRM) plays an important role in future wireless networks in order to provide higher data rates and better quality of services, given the limited amount of available radio resources. Although some specific features of wireless communication networks cause challenges to effective and efficient RRM, they bring opportunities that help improv- ing network performance and resource utilization. In this thesis, we focus on RRM issues related to the broadcast/multicast nature in wireless communication networks. The work is divided into two parts. In the first part, we exploit how to take advantage of the broadcast nature of wire- less transmissions in RRM by opportunistically applying two-way relaying (or network coding) and traditional one-way relaying. Different objectives are considered, includ- ing maximizing total packet transmission throughput (Chapter 2), minimizing costs related to transmission power and delay (Chapter 3), and minimizing packet transmis- sion delay subject to maximum and average transmission power limits (Chapter 4). While designing these scheduling schemes, the random traffic and channel conditions are also taken into consideration. Our results show that the proposed opportunis- tic scheduling schemes can indeed take good advantage of the broadcast feature at the relay nodes and achieve much higher throughput and, in some scenarios, provide close-to-optimum QoS performance. The second part (Chapter 5) of the thesis deals with the issue of efficient resource management in multicast communications, where we study channel sharing and power allocations for multicast device-to-divice (D2D) communication groups underlaying a cellular network. In such a scenario, D2D multicasting together with the mutual inter- ference between cellular and D2D communications, makes the interference conditions and power allocations a very complicated issue. Different approaches are proposed that allow each D2D group to share the cellular channels and allocate transmission power to each D2D and cellular transmitter, so that the sum throughput of D2D and cellular users is maximized. Our results indicate that it is possible to achieve close-to-optimum throughput performance in such a network. / Dissertation / Doctor of Philosophy (PhD)

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Cette thèse étudie les communications directes entre les mobiles, appelées communications D2D, en tant que technique prometteuse pour améliorer les futurs réseaux cellulaires. Cette technologie permet une communication directe entre deux terminaux mobiles sans passer par la station de base. La modélisation, l'évaluation et l'optimisation des différents aspects des communications D2D constituent les objectifs fondamentaux de cette thèse et sont réalisés principalement à l'aide des outils mathématiques suivants: la théorie des files d'attente, l'optimisation de Lyapunov et les processus de décision markovien partiellement observable POMDP. Les résultats de cette étude sont présentés en trois parties. Dans la première partie, nous étudions un schéma de sélection entre mode cellulaire et mode D2D. Nous dérivons les régions de stabilité des scénarios suivants: réseaux cellulaires purs et réseaux cellulaires où les communications D2D sont activées. Une comparaison entre ces deux scénarios conduit à l'élaboration d'un algorithme de sélection entre le mode cellulaire et le mode D2D qui permet d'améliorer la capacité du réseau. Dans la deuxième partie, nous développons un algorithme d'allocation de ressources des communications D2D. Les utilisateurs D2D sont en mesure d'estimer leur propre qualité de canal, cependant la station de base a besoin de recevoir des messages de signalisation pour acquérir cette information. Sur la base de cette connaissance disponibles au niveau des utilisateurs D2D, une approche d'allocation des ressources est proposée afin d'améliorer l'efficacité énergétique des communications D2D. La version distribuée de cet algorithme s'avère plus performante que celle centralisée. Dans le schéma distribué des collisions peuvent se produire durant la transmission de l'état des canaux D2D ; ainsi un algorithme de réduction des collisions est élaboré. En outre, la mise en œuvre des algorithmes centralisé et distribué dans un réseau cellulaire, type LTE, est décrite en détails. Dans la troisième partie, nous étudions une politique de sélection des relais D2D mobiles. La mobilité des relais représente un des principaux défis que rencontre toute stratégie de sélection de relais. Le problème est modélisé par un processus contraint de décision markovien partiellement observable qui prend en compte le dynamisme des relais et vise à trouver la politique de sélection de relais qui optimise la performance du réseau cellulaire sous des contraintes de coût. / This thesis considers Device-to-Device (D2D) communications as a promising technique for enhancing future cellular networks. Modeling, evaluating and optimizing D2D features are the fundamental goals of this thesis and are mainly achieved using the following mathematical tools: queuing theory, Lyapunov optimization and Partially Observed Markov Decision Process (POMDP). The findings of this study are presented in three parts. In the first part, we investigate a D2D mode selection scheme. We derive the queuing stability regions of both scenarios: pure cellular networks and D2D-enabled cellular networks. Comparing both scenarios leads us to elaborate a D2D vs cellular mode selection design that improves the capacity of the network. In the second part, we develop a D2D resource allocation algorithm. We observe that D2D users are able to estimate their local Channel State Information (CSI), however the base station needs some signaling exchange to acquire this information. Based on the D2D users' knowledge of their local CSI, we provide an energy efficient resource allocation framework that shows how distributed scheduling outperforms centralized one. In the distributed approach, collisions may occur between the different CSI reporting; thus, we propose a collision reduction algorithm. Moreover, we give a detailed description on how both centralized and distributed algorithms can be implemented in practice. In the third part, we propose a mobile relay selection policy in a D2D relay-aided network. Relays' mobility appears as a crucial challenge for defining the strategy of selecting the optimal D2D relays. The problem is formulated as a constrained POMDP which captures the dynamism of the relays and aims to find the optimal relay selection policy that maximizes the performance of the network under cost constraints.