Games on graphs with a public signal monitoring

We study pure Nash equilibria in games on graphs with an imperfect monitoring based on a public signal. In such games, deviations and players responsible for those deviations can be hard to detect and track. We propose a generic epistemic game abstraction, which conveniently allows to represent the knowledge of the players about these deviations, and give a characterization of Nash equilibria in terms of winning strategies in the abstraction. We then use the abstraction to develop algorithms for some payoff functions.Comment: 28 page

A Game-theoretic Approach To Uplink Power Control In Cdma Networks

Tez (Yüksek Lisans) -- İstanbul Teknik Üniversitesi, Fen Bilimleri Enstitüsü, 2011Thesis (M.Sc.) -- İstanbul Technical University, Institute of Science and Technology, 2011Kablosuz iletişim ağlarında temel kaynaklar olan bant genişliği (spektrum) ve güç sınırlıdır. Bu nedenle, bu kaynakların verimli kullanımı önem kazanmıştır. Bu yüzden DS-CDMA türü çoklu erişimin kullanıldığı sistemlerde telsiz kaynaklarının yönetiminde güç kontrolü önemli bir gerekliliktir. DS-CDMA sistemi girişim kısıtlı olduğundan dolayı, herhangi bir kullanıcı bencilce hareket ederek, kullanıcıdan erişim noktasına olan kendi iletim gücünü arttırarak, kendi servis kalitesini arttırılabilir. Ancak bu artış diğer kullanıcılara için istenmeyen girişime sebebiyet verir. Servis kalitesi, sinyal girişim oranına (SIR) bağlıdır ve yüksek SIR elde etmek için yüksek iletim gücüne ihtiyaç vardır, bununla beraber bit hata oranı (BER) düşmekte ve böylece daha yüksek bir veri aktarımı elde edilmektedir. Ayrıca, kullanıcının iletim gücünü arttırması, pil tüketimini hızlandırmakta bu da kullanıcının memnuniyetini azaltmaktadır. Bu sebeple, SIR ve iletim gücü değerlerinin mobil kullanıcılar için önem kazanmaya başlar ve kullanıcılar bir yandan yüksek SIR elde etmek isterken aynı zamanda düşük enerji tüketmek ister. Bu iki çelişen amaç arasında iyi bir denge kurmak, DS-CDMA ağlarında telsiz kaynaklarının yönetiminin bir parçası olan güç kontrolünün ana odak noktasıdır. Güç kontrolü çoğunlukla ortak kanal girişimini azaltmak ve SIR değerini garanti altına alarak daha iyi bir servis kalitesi elde etmek amacıyla kullanılır. Bu tez çalışmasında, kablosuz haberleşme şebekelerinde güç kontrolü için en genel yaklaşımlardan biri olan güç dengeleme veya diğer adıyla SIR dengeleme yaklaşımı incelenmiştir. Güç dengeleme algoritmaları basit ve çoğu dağıtık olarak gerçekleştirilmektedir ancak yakınsama açısından oldukça yavaş olması dezavantajdır. Son yıllarda, oyun teorisi alternatif bir yaklaşım olarak veri şebekelerinde güç kontrolü çalışmaları için kullanılmıştır. Bu tez çalışmasında, DS-CDMA sistemlerin yukarı yönde iletişimindeki güç kontrolü probleminin oyun teorisi yaklaşımıyla ele alınması incelenmiştir. Bu problem çok kullanıcılı ve kullanıcılar arasında herhangi bir işbirliğinin olmadığı ve her kullanıcının kendi kazancını maksimize etmeye çalıştığı N-oyunculu işbirliksiz bir oyun olarak modellenmiştir. Her kullanıcı için tanımlanan kazanç fonksiyonu, SIR ve iletim gücüne bağlı olarak kullanıcının tercihini gösterir. Her bir kullanıcı için enerji verimliliğine ve yüksek hizmet kalitesine teşvik edici kazanç fonksiyonları tanımlanmıştır. Kazanç fonksiyonuna bağlı olarak, belirtilen oyunda optimum çalışma noktası olarak ifade edilen bir adet “Nash dengesinin” var olduğu gösterilmiştir. Bunun yanında, yukarı yöndeki güç kontrolü için güç dengeleme algoritması ve oyun kuramı yaklaşımı uygulanmış ve güce karşılık gelen iterasyon sayısı baz alınarak analiz edilmiştir. Benzetim sonuçları karşılaştırılmış ve oyun kuramı yaklaşımının, güç dengeleme algoritmasından daha iyi sonuçlar verdiği gösterilmiştir.In wireless communication networks, fundamental resources that are bandwidth (spectrum) and power are limited. For this reason, efficient use of these resources becomes important. Therefore, power control is an essential requirement for radio resource management in the design of wireless systems, especially in direct-sequence code-division multiple-access (DS-CDMA) systems. Since DS-CDMA system is interference-limited, when a user acts selfishly to improve its quality-of-service (QoS) requirements by increasing its individual transmit power at the uplink that causes unnecessary interference to other users in the cell. QoS depends on the signal-to-interference ratio (SIR) and achieving a high SIR requires a high transmit power, though, resulting in a lower bit-error rate (BER) and thus higher throughput. Additionally, increasing the transmit power of a user expedites its battery drain, which reduces the satisfaction of the mobile user. Hence, SIR and transmit power become valuable commodities, thus a wireless user prefers to obtain high SIR and to consume low energy. Finding a good balance between two conflicting objectives is the main focus of the power control component of radio resource management in CDMA networks. Power control has mainly used to reduce co-channel interference and to guarantee SIR, resulting better QoS. In this thesis, one of the most common approaches to power control in wireless communication networks which is power balancing, also called SIR balancing is considered. Power balancing algorithms are simple and most of them can be implemented distributively, but have the disadvantage that convergence can be slow and it is guaranteed only if every mobile’s target SIR is feasible. In recent years, an alternative approach based on game theory has been used to study power control in data networks. In this thesis, the application of game theory for studying uplink power control in DS-CDMA network is considered. Power control problem is modeled as a N-person non-cooperative game in which each mobile user tries to maximize its own utility without any deal among the users. A utility function is defined for each user, which represents the user’s choice with respect to the SIR and the transmitter power. For a proper utility function, it is shown that there exists an optimum operating point referred to as a “Nash equilibrium” that is unique. Furthermore, power balancing algorithm and game theoretic approach to uplink power control were implemented and analyzed based on power versus number of iterations. A comparison of simulation results are carried out. The game theoretic power control algorithm was shown to give better results compared to SIR balancing power control algorithm.Yüksek LisansM.Sc

Efficient joint call admission control and bandwidth management schemes for QoS provisioning in heterogeneous wireless networks

Includes abstract.Includes bibliographical references (leaves 150-157).Next generation wireless network (NGWN) will be heterogeneous where different radio access technologies (RATs) coexist. This coexistence of different RATs necessitates joint radio resource management (JRRM) for enhanced QoS provisioning and efficient radio resource utilization. Joint call admission control (JCAC) algorithm is one of the joint radio resource management algorithms. The basic functions of a JCAC algorithm are to decide whether or not an incoming call can be accepted into a heterogeneous wireless network, and to determine which of the available RATs is most suitable to admit the incoming call. The objective of a JCAC algorithm is to guarantee the QoS requirements of all accepted calls and at the same time make the best use of the available radio resources. Traditional call admission control algorithms designed for homogeneous wireless networks do not provide a single solution to address the heterogeneous architecture, which characterizes NGWN. Consequently, there is need to develop JCAC algorithms for heterogeneous wireless networks. The thesis proposes three JCAC schemes for improving QoS and radio resource utilization, which are of primary concerns, in heterogeneous wireless networks. The first scheme combines adaptive bandwidth management and joint call admission control. The objectives of the first scheme are to enhance average system utilization, guarantee QoS requirements of all accepted calls, and reduce new call blocking probability and handoff call dropping probability in heterogeneous wireless networks. The scheme consists of three components namely: joint call admission controller, bandwidth reservation unit, and bandwidth adaptation unit. Using Markov decision process, an analytical model is developed to evaluate the performance of the proposed scheme considering three performance metrics, which are new call blocking probability, handoff call dropping probability, and system utilization. Numerical results show that the proposed scheme improves system utilization and reduces both new call blocking probability and handoff call dropping probability. The second proposed JCAC scheme minimizes call blocking probability by determining the optimal call allocation policy among the available RATs. The scheme measures the arrival rates of different classes of calls into the heterogeneous wireless network. Using linear programming technique, the JCAC scheme determines the call allocation policy that minimizes call-blocking probability in the heterogeneous network. Numerical results show that the proposed scheme reduces call-blocking probability in the heterogeneous wireless network

Game Theory in Communications:a Study of Two Scenarios

Multi-user communication theory typically studies the fundamental limits of communication systems, and considers communication schemes that approach or even achieve these limits. The functioning of many such schemes assumes that users always cooperate, even when it is not in their own best interest. In practice, this assumption need not be fulfilled, as rational communication participants are often only interested in maximizing their own communication experience, and may behave in an undesirable manner from the system's point of view. Thus, communication systems may operate differently than intended if the behavior of individual participants is not taken into account. In this thesis, we study how users make decisions in wireless settings, by considering their preferences and how they interact with each other. We investigate whether the outcomes of their decisions are desirable, and, if not, what can be done to improve them. In particular, we focus on two related issues. The first is the decision-making of communication users in the absence of any central authority, which we consider in the context of the Gaussian multiple access channel. The second is the pricing of wireless resources, which we consider in the context of the competition of wireless service providers for users who are not contractually tied to any provider, but free to choose the one offering the best tradeoff of parameters. In the first part of the thesis, we model the interaction of self-interested users in a Gaussian multiple access channel using non-cooperative game theory. We demonstrate that the lack of infrastructure leads to an inefficient outcome for users who interact only once, specifically due to the lack of coordination between users. Using evolutionary game theory, we show that this inefficient outcome would also arise as a result of repeated interaction of many individuals over time. On the other hand, if the users correlate their decoding schedule with the outcome of some publicly observed (pseudo) random variable, the resulting outcome is efficient. This shows that sometimes it takes very little intervention on the part of the system planner to make sure that users choose a desirable operating point. In the second part of the thesis, we consider the competition of wireless service providers for users who are free to choose their service provider based on their channel parameters and the resource price. We model this situation as a two-stage game where the providers announce unit resource prices in the first stage and the users choose how much resource they want to purchase from each provider in the second stage. Under fairly general conditions, we show that the competitive interaction of users and providers results in socially optimal resource allocation. We also provide a decentralized primal-dual algorithm and prove its convergence to the socially optimal outcome