THE PRICE OF NON-COOPERATION IN RESERVATION-BASED BANDWIDTH SHARING PROTOCOLS

ABSTRACTIn reservation-based bandwidth sharing protocols, the base station relies on the stations’ requests to allocate time slots to them. Like most  other protocols, reservation-based protocols were designed with the assumption that all stationsrespect the rules of the protocols. However, as mobile devices are becoming more intelligent andprogrammable, they can selfishly optimize their operations to obtain a larger share of commonbandwidth. Here, we study reservation-based bandwidth sharing protocols considering the existence of selfish stations through game-theoretic perspectives. We show that this game admits a Nash  equilibrium. Then, we prove the inefficiency of the Nash equilibrium. Game-theoretical analysis shows that local optimization in the bandwidth sharing problem with conflicted interests does not lead to any global optimization.Keywords. Nash equilibrium, Repeated game, Reservation-based

Network coding-aided MAC protocols for cooperative wireless networks

The introduction of third generation (3G) technologies has caused a vast proliferation of wireless devices and networks, generating an increasing demand for high level Quality of Service (QoS). The wide spread of mobile applications has further reinforced the user need for communication, motivating at the same time the concepts of user cooperation and data dissemination. However, this trend towards continuous exchange of information and ubiquitous connectivity is inherently restricted by the energy-greedy functionalities of high-end devices. These limitations, along with the pressure exerted on the Information and Communications Technology (ICT) industry towards energy awareness, have induced the design of novel energy efficient schemes and algorithms. In this context, the Medium Access Control (MAC) layer plays a key role, since it is mainly responsible for the channel access regulation, the transmission scheduling and the resource allocation, thus constituting an appropriate point to effectively address energy efficiency issues that arise due to the users overcrowding. This dissertation provides a contribution to the design, analysis and evaluation of novel MAC protocols for cooperative wireless networks. In our attempt to design energy efficient MAC schemes, we were extensively assisted by the introduction of new techniques, such as Network Coding (NC), that intrinsically bring considerable gains in system performance. The main thesis contributions are divided into two parts. The first part presents NCCARQ, a novel NC-aided Cooperative Automatic Repeat reQuest (ARQ) MAC protocol for wireless networks. NCCARQ introduces a new access paradigm for cooperative ARQ schemes, exploiting NC benefits in bidirectional communication among wireless users. The NCCARQ performance in terms of QoS and energy efficiency is assessed by means of analytical probabilistic models and extensive computer-based simulations, revealing the significant gains we can achieve compared to standardized MAC solutions. In addition, the impact of realistic wireless channel conditions on the MAC protocol operation further motivated us to study the NCCARQ performance in wireless links affected by correlated shadowing, showing that the channel correlation may adversely affect the distributed cooperation benefits. The second part of the thesis is dedicated to the investigation of MAC issues in wireless data dissemination scenarios. In particular, the existence of multiple source nodes in such scenarios generates conflicting situations, considering the selfish behavior of the wireless devices that want to maximize their battery lifetime. Bearing in mind the energy efficiency importance, we propose game theoretic medium access strategies, applying energy-based utility functions which inherently imply energy awareness. In addition, Random Linear NC (RLNC) techniques are adopted to eliminate the need of exchanging excessive control packets, while Analog NC (ANC) is employed to efface the impact of collisions throughout the communication. During the elaboration of this thesis, two general key conclusions have been extracted. First, there is a fundamental requirement for implementation of new MAC protocols in order to effectively deal with state-of-the-art techniques (e.g., NC), recently introduced to enhance both the performance and the energy efficiency of the network. Second, we highlight the importance of designing novel energy efficient MAC protocols, taking into account that traditional approaches - designed mainly to assist the collision avoidance in wireless networks - tend to be obsolete.La presente tesis doctoral contribuye al diseño, análisis y evaluación de nuevos protocolos MAC cooperativos para redes inalámbricas. La introducción de nuevas técnicas, tales como la codificación de red (NC), que intrínsecamente llevan un considerable aumento en el rendimiento del sistema, nos ayudó ampliamente durante el diseño de protocolos MAC energéticamente eficientes. Las principales contribuciones de esta tesis se dividen en dos partes. La primera parte presenta el NCCARQ, un protocolo cooperativo de retransmisión automática (ARQ), asistido por NC para redes inalámbricas. La segunda parte de la tesis se centra en el diseño de protocolos de capa MAC en escenarios inalámbricos de difusión de datos. Teniendo en cuenta la importancia de la eficiencia energética, se proponen técnicas de acceso al medio basadas en teoría de juegos dónde las funciones objetivo están motivadas por el consumo energético. Las soluciones propuestas son evaluadas por medio de modelos analíticos y simulaciones por ordenador

Distributed radio resource allocation in wireless heterogeneous networks

This dissertation studies the problem of resource allocation in the radio access network of heterogeneous small-cell networks (HetSNets). A HetSNet is constructed by introducing smallcells(SCs) to a geographical area that is served by a well-structured macrocell network. These SCs reuse the frequency bands of the macro-network and operate in the interference-limited region. Thus, complex radio resource allocation schemes are required to manage interference and improve spectral efficiency. Both centralized and distributed approaches have been suggested by researchers to solve this problem. This dissertation follows the distributed approach under the self-organizing networks (SONs) paradigm. In particular, it develops game-theoretic and learning-theoretic modeling, analysis, and algorithms. Even though SONs may perform subpar to a centralized optimal controller, they are highly scalable and fault-tolerant. There are many facets to the problem of wireless resource allocation. They vary by the application, solution, methodology, and resource type. Therefore, this thesis restricts the treatment to four subproblems that were chosen due to their significant impact on network performance and suitability to our interests and expertise. Game theory and mechanism design are the main tools used since they provide a sufficiently rich environment to model the SON problem. Firstly, this thesis takes into consideration the problem of uplink orthogonal channel access in a dense cluster of SCs that is deployed in a macrocell service area. Two variations of this problem are modeled as noncooperative Bayesian games and the existence of pure-Bayesian Nash symmetric equilibria are demonstrated. Secondly, this thesis presents the generalized satisfaction equilibrium (GSE) for games in satisfaction-form. Each wireless agent has a constraint to satisfy and the GSE is a mixed-strategy profile from which no unsatisfied agent can unilaterally deviate to satisfaction. The objective of the GSE is to propose an alternative equilibrium that is designed specifically to model wireless users. The existence of the GSE, its computational complexity, and its performance compared to the Nash equilibrium are discussed. Thirdly, this thesis introduces verification mechanisms for dynamic self-organization of Wireless access networks. The main focus of verification mechanisms is to replace monetary transfers that are prevalent in current research. In the wireless environment particular private information of the wireless agents, such as block error rate and application class, can be verified at the access points. This verification capability can be used to threaten false reports with backhaul throttling. The agents then learn the truthful equilibrium over time by observing the rewards and punishments. Finally, the problem of admission control in the interfering-multiple access channel with rate constraints is addressed. In the incomplete information setting, with compact convex channel power gains, the resulting Bayesian game possesses at least one pureBayesian Nash equilibrium in on-off threshold strategies. The above-summarized results of this thesis demonstrate that the HetSNets are amenable to self-organization, albeit with adapted incentives and equilibria to fit the wireless environment. Further research problems to expand these results are identified at the end of this document