Cooperative Relaying and Resource Allocation in Future-Generation Cellular Networks

Driven by the significant consumer demand for reliable and high data rate communications, the future-generation cellular systems are expected to employ cutting-edge techniques to improve the service provisioning at substantially reduced costs. Cooperative relaying is one of the primary techniques due to its ability to improve the spectrum utilization by taking advantage of the broadcast nature of wireless signals. This dissertation studies the physical layer cooperative relaying technique and resource allocation schemes in the cooperative cellular networks to improve the spectrum and energy efficiency from the perspectives of downlink transmission, uplink transmission and device-to-device transmission, respectively. For the downlink transmission, we consider an LTE-Advanced cooperative cellular network with the deployment of Type II in-band decode-and-forward relay stations (RSs) to enhance the cell-edge throughput and to extend the coverage area. This type of relays can better exploit the broadcast nature of wireless signals while improving the utilization of existing allocated spectral resources. For such a network, we propose joint orthogonal frequency division multiplexing (OFDM) subcarrier and power allocation schemes to optimize the downlink multi-user transmission efficiency. Firstly, an optimal power dividing method between eNB and RS is proposed to maximize the achievable rate on each subcarrier. Based on this result, we show that the optimal joint resource allocation scheme for maximizing the overall throughput is to allocate each subcarrier to the user with the best channel quality and to distribute power in a water-filling manner. Since the users' Quality of Service (QoS) provision is one of the major design objectives in cellular networks, we further formulate a lexicographical optimization problem to maximize the minimum rate of all users while improving the overall throughput. A sufficient condition for optimality is derived. Due to the complexity of searching for the optimal solution, we then propose an efficient, low-complexity suboptimal joint resource allocation algorithm, which outperforms the existing suboptimal algorithms that simplify the joint design into separate allocation. Both theoretical and numerical analyses demonstrate that our proposed scheme can drastically improve the fairness as well as the overall throughput. As the physical layer uplink transmission technology for LTE-Advanced cellular network is based on single carrier frequency division multiple access (SC-FDMA) with frequency domain equalization (FDE), this dissertation further studies the uplink achievable rate and power allocation to improve the uplink spectrum efficiency in the cellular network. Different from the downlink OFDM system, signals on all subcarriers in the SC-FDMA system are transmitted sequentially rather than in parallel, thus the user's achievable rate is not simply the summation of the rates on all allocated subcarriers. Moreover, each user equipment (UE) has its own transmission power constraint instead of a total power constraint at the base station in the downlink case. Therefore, the uplink resource allocation problem in the LTE-Advanced system is more challenging. To this end, we first derive the achievable rates of the SC-FDMA system with two commonly-used FDE techniques, zero-forcing (ZF) equalization and minimum mean square error (MMSE) equalization, based on the joint superposition coding for cooperative relaying. We then propose optimal power allocation schemes among subcarriers at both UE and RS to maximize the overall throughput of the system. Theoretical analysis and numerical results are provided to demonstrate a significant gain in the system throughput by our proposed power allocation schemes. Besides the physical layer technology, the trend of improving energy efficiency in future cellular networks also motivates the network operators to continuously bring improvements in the entire network infrastructure. Such techniques include efficient base station (BS) redesign, opportunistic transmission such as device-to-device and cognitive radio communications. In the third part of this dissertation, we explore the potentials of employing cooperative relaying in a green device-to-device communication underlaying cellular network to improve the energy efficiency and spectrum utilization of the system. As the green base station is powered by sustainable energy, the design objective is to enhance both sustainability and efficiency of the device-to-device communication. Specifically, we first propose optimal power adaptation schemes to maximize the network spectrum efficiency under two practical power constraints. We then take the dynamics of the charging and discharging processes of the energy buffer at the BS into consideration to ensure the network sustainability. To this end, the energy buffer is modeled as a G/D/1 queue where the input energy has a general distribution. Power allocation schemes are proposed based on the statistics of the energy buffer to further enhance the network efficiency and sustainability. Theoretical analysis and numerical results are presented to demonstrate that our proposed power allocation schemes can improve the network throughput while maintaining the network sustainability at a certain level. Our analyses developed in this dissertation indicate that the cooperative transmission based on cooperative relaying can significantly improve the spectrum efficiency and energy efficiency of the cellular network for downlink transmission, uplink transmission and device-to-device communication. Our proposed cooperative relaying technique and resource allocation schemes can provide efficient solutions to practical design and optimization of future-generation cellular networks

İşbirlikçi bilişsel radyo sistemleri için kodlama ve kod çözme teknikleri, erişilebilir veri hızları ve kaynak tahsisi

İşbirlikli iletişim ve bilişsel radyo, yeni nesil kablosuz haberleşme ağlarında kapasite ve iletişim kalitesinin artırımı için kilit tekniklerdir. Bu tekniklerin her ikisi de, çevrelerinin farkında olan ve bu farkındalığı gönderim stratejilerini belirlerken kullanabilen akıllı düğümlere dayalı olduğundan, yeni nesil protokollerin tasarımında bir arada ele alınmaları son derece doğaldır. Bu projenin temel amacı, kablosuz ağlarda bu iki tekniği bir arada kullanabilen yeni işbirliği stratejileri geliştirmek, ve bunlar ile elde edilebilecek veri hızlarını özkaynakların verimli tahsisi ile eniyilemektir. Projede, iki kullanıcı - tek alıcılı, üç kullanıcı - tek alıcılı, çok kullanıcı - tek alıcılı ve çok kullanıcı - çok alıcılı olmak üzere dört farklı işbirlikli çoklu erişim modeli ele alınmıştır. Bunların ilk üçünde, birincil kullanıcılara belirli veri hızı garantileri sağlanırken, ikincil kullanıcıların ya da tüm sistemin veri hızlarını eniyileyen güç tahsisi algoritmaları geliştirilmiştir. Çok kullanıcı - tek alıcılı sistemde, birincil ve ikincil kullanıcılar arası işbirliği çiftler halinde modellendiğinden, ayrıca en iyi işbirlikçi ortak seçimi de ele alınmıştır. Çok kullanıcı – çok alıcılı hücresel sistem modelinde ise, kullanıcıların hem işbirlikçi ortak, hem de alıcı seçimini güç tahsisi ile birlikte veri hızlarını en büyükleyecek şekilde seçebilecekleri bir kaynak tahsisi algoritması geliştirilmiş, hücre kenarındaki kullanıcılar arasında işbirliğini ve alıcı seçimini mümkün kılmak amacıyla özgün bir zıt kısmi frekans tekrarı modeli önerilmiştir. Ele alınan tüm problemlerde, veri hızlarının aynı miktarda kaynak kullanılmasına karşın yardımlaşma sayesinde kayda değer biçimde artırılabildiği gösterilmiştir. Sonuç olarak, proje kapsamında bilgi kuramsal yaklaşımlarla elde edilen temel sonuçlar bilişsel radyo ile işbirlikli iletişimin kablosuz ağlarda bir arada ele alınmasının faydasına ve gerekliliğine işaret etmektedir.Cooperative communication and cognitive radio are key techniques for increasing the capacity and quality of service of the next generation wireless communication networks. Both of these techniques rely on intelligent nodes, which are aware of their surroundings, and are capable of using this awareness to determine their transmit strategies. Therefore, it is quite natural to consider the joint use of these techniques in the design of next generation communication protocols. The main goal of this project is to develop new cooperation strategies capable of combining cognition and cooperation in wireless networks, and to optimize the rates achievable by these strategies via efficient utilization of the available resources. In this project, we consider four different cooperative multiple access models: two user - single receiver; three user - single receiver, multi user - single receiver and multi user – multi receiver models. The first three models aim to optimize either the rates of the secondary users, or the sum rate of the system, under hard single user rate guarantees for primary users, via power control. In the multi user - single receiver model, the cooperation among the primary and secondary users is modeled as pairwise cooperation, hence, in this scenario, we also solve the optimal partnering problem. In the multi user - multi receiver cellular model, we obtain the jointly optimal power allocation, receiver selection and cooperating partner selection policies that maximize the sum rate of the system. In order to facilitate cooperation among the cell edge users, and receiver selection, we propose a novel complementary fractional frequency reuse scheme, directly tailored for cognitive cooperation. In all of the problems that were considered, it was shown that despite the same amount of total resources being used, the achievable rates can be increased significantly, thanks to cooperation. In conclusion, the fundamental results obtained in this project, based on information theoretic approaches, point to the usefulness, and the necessity of joint consideration of cognition and cooperation in wireless networks.TÜBİTA

Sécurité collaborative pour l internet des objets

Cette thèse aborde des nouveaux défis de sécurité dans l'Internet des Objets (IdO). La transition actuelle de l'Internet classique vers l'Internet des Objets conduit à de nombreux changements dans les modèles de communications sous-jacents. La nature hétérogène des communications de l IdO et le déséquilibre entre les capacités des entités communicantes qui le constituent rendent difficile l'établissement de connexions sécurisées de bout en bout. Contrairement aux nœuds de l Internet traditionnel, la plupart des composants de l'Internet des Objets sont en effet caractérisés par de faibles capacités en termes d'énergie et de puissance calcul. Par conséquent, ils ne sont pas en mesure de supporter des systèmes de sécurité complexes. En particulier, la mise en place d'un canal de communication sécurisé de bout en bout nécessite l établissement d'une clé secrète commune entre les deux nœuds souhaitant communiquer, qui sera négociée en s'appuyant sur un protocole d'échange de clés tels que le Transport Layer Security (TLS) Handshake ou l Internet Key Exchange (IKE). Or, une utilisation directe de ces protocoles pour établir des connexions sécurisées entre deux entités de l IdO peut être difficile en raison de l'écart technologique entre celles-ci et des incohérences qui en résultent sur le plan des primitives cryptographiques supportées. Le sujet de l'adaptation des protocoles de sécurité existants pour répondre à ces nouveaux défis a récemment été soulevé dans la communauté scientifique. Cependant, les premières solutions proposées n'ont pas réussi à répondre aux besoins des nœuds à ressources limitées. Dans cette thèse, nous proposons de nouvelles approches collaboratives pour l'établissement de clés, dans le but de réduire les exigences des protocoles de sécurité existants, afin que ceux-ci puissent être mis en œuvre par des nœuds à ressources limitées. Nous avons particulièrement retenu les protocoles TLS Handshake, IKE et HIP BEX comme les meilleurs candidats correspondant aux exigences de sécurité de bout en bout pour l'IdO. Puis nous les avons modifiés de sorte que le nœud contraint en énergie puisse déléguer les opérations cryptographiques couteuses à un ensemble de nœuds au voisinage, tirant ainsi avantage de l'hétérogénéité spatiale qui caractérise l IdO. Nous avons entrepris des vérifications formelles de sécurité et des analyses de performance qui prouvent la sureté et l'efficacité énergétique des protocoles collaboratifs proposés. Dans une deuxième partie, nous avons porté notre attention sur une classe d attaques internes que la collaboration entre les nœuds peut induire et que les mécanismes cryptographiques classiques, tels que la signature et le chiffrement, s'avèrent impuissants à contrer. Cela nous a amené à introduire la notion de confiance au sein d'un groupe collaboratif. Le niveau de fiabilité d'un nœud est évalué par un mécanisme de sécurité dédié, connu sous le nom de système de gestion de confiance. Ce système est lui aussi instancié sur une base collaborative, dans laquelle plusieurs nœuds partagent leurs témoignages respectifs au sujet de la fiabilité des autres nœuds. En nous appuyant sur une analyse approfondie des systèmes de gestion de confiance existants et des contraintes de l IoD, nous avons conçu un système de gestion de confiance efficace pour nos protocoles collaboratifs. Cette efficacité a été évaluée en tenant compte de la façon dont le système de gestion de la confiance répond aux exigences spécifiques à nos approches proposées pour l'établissement de clés dans le contexte de l'IdO. Les résultats des analyses de performance que nous avons menées démontrent le bon fonctionnement du système proposé et une efficacité accrue par rapport à la littératureThis thesis addresses new security challenges in the Internet of Things (IoT). The current transition from legacy Internet to Internet of Things leads to multiple changes in its communication paradigms. Wireless sensor networks (WSNs) initiated this transition by introducing unattended wireless topologies, mostly made of resource constrained nodes, in which radio spectrum therefore ceased to be the only resource worthy of optimization. Today's Machine to Machine (M2M) and Internet of Things architectures further accentuated this trend, not only by involving wider architectures but also by adding heterogeneity, resource capabilities inconstancy and autonomy to once uniform and deterministic systems. The heterogeneous nature of IoT communications and imbalance in resources capabilities between IoT entities make it challenging to provide the required end-to-end secured connections. Unlike Internet servers, most of IoT components are characterized by low capabilities in terms of both energy and computing resources, and thus, are unable to support complex security schemes. The setup of a secure end-to-end communication channel requires the establishment of a common secret key between both peers, which would be negotiated relying on standard security key exchange protocols such as Transport Layer Security (TLS) Handshake or Internet Key Exchange (IKE). Nevertheless, a direct use of existing key establishment protocols to initiate connections between two IoT entities may be impractical because of the technological gap between them and the resulting inconsistencies in their cryptographic primitives. The issue of adapting existing security protocols to fulfil these new challenges has recently been raised in the international research community but the first proposed solutions failed to satisfy the needs of resource-constrained nodes. In this thesis, we propose novel collaborative approaches for key establishment designed to reduce the requirements of existing security protocols, in order to be supported by resource-constrained devices. We particularly retained TLS handshake, Internet key Exchange and HIP BEX protocols as the best keying candidates fitting the end-to-end security requirements of the IoT. Then we redesigned them so that the constrained peer may delegate its heavy cryptographic load to less constrained nodes in neighbourhood exploiting the spatial heterogeneity of IoT nodes. Formal security verifications and performance analyses were also conducted to ensure the security effectiveness and energy efficiency of our collaborative protocols. However, allowing collaboration between nodes may open the way to a new class of threats, known as internal attacks that conventional cryptographic mechanisms fail to deal with. This introduces the concept of trustworthiness within a collaborative group. The trustworthiness level of a node has to be assessed by a dedicated security mechanism known as a trust management system. This system aims to track nodes behaviours to detect untrustworthy elements and select reliable ones for collaborative services assistance. In turn, a trust management system is instantiated on a collaborative basis, wherein multiple nodes share their evidences about one another's trustworthiness. Based on an extensive analysis of prior trust management systems, we have identified a set of best practices that provided us guidance to design an effective trust management system for our collaborative keying protocols. This effectiveness was assessed by considering how the trust management system could fulfil specific requirements of our proposed approaches for key establishment in the context of the IoT. Performance analysis results show the proper functioning and effectiveness of the proposed system as compared with its counterparts that exist in the literatureEVRY-INT (912282302) / SudocSudocFranceF

Resource Allocation for Cooperative Relaying

The delay-limited capacity of the half-duplex relay channel is analyzed for several cooperative protocols under a long-term average total transmit power constraint. It is assumed that the source and the relay have access to partial channel state information in the form of channel amplitudes. Nonorthogonal amplify-and-forward (NAF), compress-and-forward (CF) and opportunistic decode-and-forward (ODF) protocols are compared with optimal resource allocation, i.e., at each channel state, the source and the relay transmit with the minimum total power allocation required to achieve the target rate. A hybrid opportunistic protocol is proposed in which CF or ODF with optimal resource allocation is chosen at each channel state. Numerical results demonstrate that, while the hybrid protocol offers the best delay-limited capacity, ODF follows the hybrid scheme closely for a wide range of relay locations and average power constraints. We also consider various low complexity protocols such as fixed time allocation and the estimate-andforward (EF) protocol in order to analyze the trade-off between the system complexity and delay-limited capacity

Resource allocation for cooperative relaying

The delay-limited capacity of the half-duplex relay channel is analyzed for several cooperative protocols under a long-term average total transmit power constraint. It is assumed that the source and the relay have access to partial channel state information in the form of channel amplitudes. Nonorthogonal amplify-and-forward (NAF), compress-and-forward (CF) and opportunistic decode-and-forward (ODF) protocols are compared with optimal resource allocation, i.e., at each channel state, the source and the relay transmit with the minimum total power allocation required to achieve the target rate. A hybrid opportunistic protocol is proposed in which CF or ODF with optimal resource allocation is chosen at each channel state. Numerical results demonstrate that, while the hybrid protocol offers the best delay-limited capacity, ODF follows the hybrid scheme closely for a wide range of relay locations and average power constraints. We also consider various low complexity protocols such as fixed time allocation and the estimate-andforward (EF) protocol in order to analyze the trade-off between the system complexity and delay-limited capacity. © 2008 IEEE