Applications of Repeated Games in Wireless Networks: A Survey

A repeated game is an effective tool to model interactions and conflicts for players aiming to achieve their objectives in a long-term basis. Contrary to static noncooperative games that model an interaction among players in only one period, in repeated games, interactions of players repeat for multiple periods; and thus the players become aware of other players' past behaviors and their future benefits, and will adapt their behavior accordingly. In wireless networks, conflicts among wireless nodes can lead to selfish behaviors, resulting in poor network performances and detrimental individual payoffs. In this paper, we survey the applications of repeated games in different wireless networks. The main goal is to demonstrate the use of repeated games to encourage wireless nodes to cooperate, thereby improving network performances and avoiding network disruption due to selfish behaviors. Furthermore, various problems in wireless networks and variations of repeated game models together with the corresponding solutions are discussed in this survey. Finally, we outline some open issues and future research directions.Comment: 32 pages, 15 figures, 5 tables, 168 reference

Thirty Years of Machine Learning: The Road to Pareto-Optimal Wireless Networks

Future wireless networks have a substantial potential in terms of supporting a broad range of complex compelling applications both in military and civilian fields, where the users are able to enjoy high-rate, low-latency, low-cost and reliable information services. Achieving this ambitious goal requires new radio techniques for adaptive learning and intelligent decision making because of the complex heterogeneous nature of the network structures and wireless services. Machine learning (ML) algorithms have great success in supporting big data analytics, efficient parameter estimation and interactive decision making. Hence, in this article, we review the thirty-year history of ML by elaborating on supervised learning, unsupervised learning, reinforcement learning and deep learning. Furthermore, we investigate their employment in the compelling applications of wireless networks, including heterogeneous networks (HetNets), cognitive radios (CR), Internet of things (IoT), machine to machine networks (M2M), and so on. This article aims for assisting the readers in clarifying the motivation and methodology of the various ML algorithms, so as to invoke them for hitherto unexplored services as well as scenarios of future wireless networks.Comment: 46 pages, 22 fig

Markov Decision Processes with Applications in Wireless Sensor Networks: A Survey

Wireless sensor networks (WSNs) consist of autonomous and resource-limited devices. The devices cooperate to monitor one or more physical phenomena within an area of interest. WSNs operate as stochastic systems because of randomness in the monitored environments. For long service time and low maintenance cost, WSNs require adaptive and robust methods to address data exchange, topology formulation, resource and power optimization, sensing coverage and object detection, and security challenges. In these problems, sensor nodes are to make optimized decisions from a set of accessible strategies to achieve design goals. This survey reviews numerous applications of the Markov decision process (MDP) framework, a powerful decision-making tool to develop adaptive algorithms and protocols for WSNs. Furthermore, various solution methods are discussed and compared to serve as a guide for using MDPs in WSNs

Modeling and Analysis of Cognitive Radio Ad Hoc Networks

Eine Welt ohne drahtlose Ad-Hoc Netzwerke ist heute kaum noch vorstellbar.Auf Grund der geringen Kosten und des minimalen Installationsaufwands werden gegenwärtig immer mehr Geräte in immer mehr Anwendungsfeldern eingesetzt. Da die meisten dieser Netzwerke im lizenzfreien ISM-Band operieren, ist dieses heute stark ausgelastet und weist kaum noch freie Kapazitäten auf. Aktuelle Studien der Federal Communication Commission (FCC) belegen allerdings, dass große Teile (bis zu 70%) der lizenzbehafteten Frequenzen ungenutzt sind. Dieser Umstand zeigt, dass das Problem weniger die generelle Knappheit an freien Frequenzen ist, sondern vielmehr in der ineffizienten Verteilung bzw.Nutzung der verfügbaren Resourcen zu suchen ist. Das Hauptaugenmerk der vorliegenden Dissertation liegt in der Verbesserung der Spektrumsauslastung, um dadurch die weitere Entwicklung von drahtlosen Ad-Hoc Netzwerken zu ermöglichen.In dieser Arbeit wird ein neues Spektrum-Management-Konzept mit dem Namen Opportunistic Spectrum Access with Backup channel (OSAB) entwickelt und vorgestellt. Das hierbei zugrunde liegende Konzept gestattet Secondary Users (SUs)dynamisch und flexibel auf Frequenzen unlizenzierter als auch lizensierterFrequenzbänder zu zugreifen, wenn diese vom Primary User (PU) gerade nicht genutzt werden - es also keine Interferenzen geben kann.Da der Zugriff auf das Frequenzspektrum heute existierender Systeme noch sehr unflexibel ist, soll dieser in Zukunft durch Cognitive Radios (CR)weit flexibler und dynamischer gestaltet werden können. Bei der Entstehung von OSAB wurden speziell die unterschiedlichen Eigenschaften verschiedener Frequenzbänder berücksichtigt.Der Hauptvorteil von lizenzbehafteten Bändern ist, dass diese in hoher Anzahl verfügbar sind. Der Hauptvorteil von lizenzfreien Frequenzen ergibt sich hingegen aus der Gleichstellung aller Nutzer. Sobald ein SU einmal einen Kanal belegt hat, kann er nicht mehr aus selbigem verdrängt werden.Kommuniziert OSAB in lizenzierten Bändern, so wird stets ein Backup Channel (BC)vorgehalten um auf das plötzliche Auftreten des PUs reagieren zu können.Das vorgeschlagene Konzept wurde in dieser Arbeit außerdem einer intensiven Analyse mittel Markov-Ketten unterzogen. Die dabei erzielten Ergebnisse zeigen,dass OSAB den Paketverlust und die erwartete Anzahl an Spektrum-Hand-Offs um 60% bzw. 17% reduzieren kann.Um den Nutzen und die Vorteile von OSAB praktisch unter Beweis zu stellen, wurde in der vorliegenden Arbeit weiterhin das MAC-Protokoll SWITCH (opportunisticSpectrum access WITh backup CHannel) entwickelt.SWITCH ist ein dezentrales, asynchrones, verbindungsbasiertes MAC-Protokoll, welchesdurch das Backup-Channel-Konzept in der Lage ist, effektiv auf das plötzliche Eintreffen von PUs zu reagieren.Jeder SU ist dabei mit zwei Transceivern ausgestattet, wobei einer davon stets für die Kommunikation auf dem gemeinsam genutzten Kontroll-Kanal (Common Control Channel) verantwortlich ist. Der zweite Transceiver ist so ausgelegt, dass dieser periodisch alle ungenutzten Kanäle absucht und dynamisch auf diese zugreifen kann. Um den Zustand eines Kanals (belegt/nicht belegt) korrekt erkennen zu können wird in dieser Arbeit eine einfache aber effektive Form des kooperativen Sensings genutzt. Die Performanz des Protokolls wurde mit Hilfe von Simulationen evaluiert. Die Ergebnisse zeigen, dass SWITCH im Vergleich zu anderen CR-MAC-Protokollen eine Verbesserung des Durchsatzes von bemerkenswerten 91,7% erzielen konnte. Zusammenfassend kann gesagt werden, dass die vorgeschlagenen Beiträge einen Schritt hin zu einer effektiveren Nutzung der verfügbaren Funkressourcen und zur Erhöhung der Kapazität von drahtlosen Ad-Hoc Netzwerken darstellen.Wireless ad hoc networks are becoming more ubiquitous in terms of devices, application areas, etc. due to their low cost and minimal deployment effort. Since all these networks operate in the unlicensed band, the problems of congestion and spectrum scarcity have arisen. On the other hand, a recent study by Federal Communications Commission (FCC) has revealed that swathes of licensed bands, measured by 70%, are unutilized. This highlights that the actual problem is not the scarcity of spectrum but inefficient allocation policies and usage. Therefore, this dissertation is focused on improving spectrum utilization and efficiency to tackle the spectrum scarcity problem and support further wireless ad hoc networks.This thesis proposes a new spectrum management concept called opportunistic spectrum access with backup channel (OSAB). The proposed concept provides secondary users (SUs) (e.g. ad hoc users) with the ability to adaptively and dynamically exploit channels from both licensed and unlicensed bands without interfering the legacy users of licensed bands, i.e. the so called primary users (PUs). Since existing radio systems offer very limited flexibility, cognitive radios (CR), which can sense and adapt to radio environments, are exploited to support such a dynamic concept. For the development of OSAB, the channels' characteristics from each band are taken into consideration. The main advantage of licensed channels is their availability in significant numbers, whereas, the main advantage of unlicensed channels is that all users have the same rights to channel access and thus no preemption occurs once a user obtains a channel. In addition, OSAB uses a backup channel (BC) to handle the appearance of PUs and thus facilitates SU communication. The proposed concept is extensively evaluated using a Markov chain model and compared to existing spectrum management approaches such as opportunistic spectrum access (OSA). The results indicate that OSAB decreases the dropping probability and the expected number of spectrum handoffs for SUs compared to OSA by 60% and 17% respectively.In order to apply OSAB practically, we develop a MAC protocol that reacts efficiently to sudden appearance of PUs. The new protocol is named opportunistic Spectrum access WITh backup CHannel (SWITCH) protocol. SWITCH is a decentralized, asynchronous, and contention-based MAC protocol. The BC's concept makes SWITCH extremely robust to the appearance of PUs. Each SU is equipped with two transceivers, one is tuned to a common control channel for the negotiation purpose with other SUs while the other is designed specifically to periodically sense and dynamically use the identified unused channels. To obtain the channel state accurately, we propose an efficient spectrum sensing strategy. This strategy is based on cooperative spectrum sensing among SUs. The performance of proposed protocol is evaluated through simulations. The results show that SWITCH accomplishes a remarkable 91.7% throughput gain over other CR-MAC protocolsTo conclude, the proposed contributions are a step forward towards efficient use of available radio resources and improve the spectrum capacity for wireless ad hoc networks

Optimization of Spectrum Allocation in Cognitive Radio and Dynamic Spectrum Access Networks

Spectrum has become a treasured commodity. However, many licensed frequency bands exclusively assigned to the primary license holders (also called primary users) remain relatively unused or under-utilized for most of the time. Allowing other users (also called secondary users) without a license to operate in these bands with no interference becomes a promising way to satisfy the fast growing needs for frequency spectrum resources. A cognitive radio adapts to the environment it operates in by sensing the spectrum and quickly decides on appropriate frequency bands and transmission parameters to use in order to achieve certain performance goals. One of the most important issues in cognitive radio networks (CRNs) is intelligent channel allocation which will improve the performance of the network and spectrum utilization. The objective of this dissertation is to address the channel allocation optimization problem in cognitive radio and DSA networks under both centralized architecture and distributed architecture. By centralized architecture we mean the cognitive radio and DSA networks are infrastructure based. That is, there is a centralized device which collects all information from other cognitive radios and produces a channel allocation scheme. Then each secondary user follows the spectrum allocation and accesses the corresponding piece of spectrum. By distributed architecture we mean that each secondary user inside the cognitive radio and DSA networks makes its own decision based on local information on the spectrum usage. Each secondary user only considers the spectrum usage around itself. We studied three common objectives of the channel allocation optimization problem, including maximum network throughput (MNT), max-min fairness (MMF), and proportional fairness (PF). Given different optimization objectives, we developed mathematical models in terms of linear programing and non-linear programing formulations, under the centralized architecture. We also designed a unified framework with different heuristic algorithms for different optimization objectives and the best results from different algorithms can be automatically chosen without manual intervention. We also conducted additional work on spectrum allocation under distributed architecture. First, we studied the channel availability prediction problem. Since there is a lot of usable statistic information on spectrum usage from national and regional agencies, we presented a Bayesian inference based prediction method, which utilizes prior information to make better prediction on channel availability. Finally a distributed channel allocation algorithm is designed based on the channel prediction results. We illustrated that the interaction behavior between different secondary users can be modeled as a game, in which the secondary users are denoted as players and the channels are denoted as resources. We proved that our distributed spectrum allocation algorithm can achieve to Nash Equilibrium, and is Pareto optimal

Radio network management in cognitive LTE-Femtocell Systems

This thesis was submitted for the award of Doctor of Philosophy and was awarded by Brunel University London.There is a strong uptake of femtocell deployment as small cell application platforms in the upcoming LTE networks. In such two-tier networks of LTEfemtocell base stations, a large portion of the assigned spectrum is used sporadically leading to underutilisation of valuable frequency resources. Novel spectrum access techniques are necessary to solve these current spectrum inefficiency problems. Therefore, spectrum management solutions should have the features to improve spectrum access in both temporal and spatial manner. Cognitive Radio (CR) with the Dynamic Spectrum Access (DSA) is considered to be the key technology in this research in order to increase the spectrum efficiency. This is an effective solution to allow a group of Secondary Users (SUs) to share the radio spectrum initially allocated to the Primary User (PUs) at no interference. The core aim of this thesis is to develop new cognitive LTE-femtocell systems that offer a 4G vision, to facilitate the radio network management in order to increase the network capacity and further improve spectrum access probabilities. In this thesis, a new spectrum management model for cognitive radio networks is considered to enable a seamless integration of multi-access technology with existing networks. This involves the design of efficient resource allocation algorithms that are able to respond to the rapid changes in the dynamic wireless environment and primary users activities. Throughout this thesis a variety of network upgraded functions are developed using application simulation scenarios. Therefore, the proposed algorithms, mechanisms, methods, and system models are not restricted in the considered networks, but rather have a wider applicability to be used in other technologies. This thesis mainly investigates three aspects of research issues relating to the efficient management of cognitive networks: First, novel spectrum resource management modules are proposed to maximise the spectrum access by rapidly detecting the available transmission opportunities. Secondly, a developed pilot power controlling algorithm is introduced to minimise the power consumption by considering mobile position and application requirements. Also, there is investigation on the impact of deploying different numbers of femtocell base stations in LTE domain to identify the optimum cell size for future networks. Finally, a novel call admission control mechanism for mobility management is proposed to support seamless handover between LTE and femtocell domains. This is performed by assigning high speed mobile users to the LTE system to avoid unnecessary handovers. The proposed solutions were examined by simulation and numerical analysis to show the strength of cognitive femtocell deployment for the required applications. The results show that the new system design based on cognitive radio configuration enable an efficient resource management in terms of spectrum allocation, adaptive pilot power control, and mobile handover. The proposed framework and algorithms offer a novel spectrum management for self organised LTE-femtocell architecture. Eventually, this research shows that certain architectures fulfilling spectrum management requirements are implementable in practice and display good performance in dynamic wireless environments which recommends the consideration of CR systems in LTE and femtocell networks

A novel MAC Protocol for Cognitive Radio Networks

In Partial Fulfilment of the Requirements for the Degree Doctor of Philosophy from the University of BedfordshireThe scarcity of bandwidth in the radio spectrum has become more vital since the demand for wireless applications has increased. Most of the spectrum bands have been allocated although many studies have shown that these bands are significantly underutilized most of the time. The problem of unavailability of spectrum bands and the inefficiency in their utilization have been smartly addressed by the cognitive radio (CR) technology which is an opportunistic network that senses the environment, observes the network changes, and then uses knowledge gained from the prior interaction with the network to make intelligent decisions by dynamically adapting transmission characteristics. In this thesis, recent research and survey about the advances in theory and applications of cognitive radio technology has been reviewed. The thesis starts with the essential background on cognitive radio techniques and systems and discusses those characteristics of CR technology, such as standards, applications and challenges that all can help make software radio more personal. It then presents advanced level material by extensively reviewing the work done so far in the area of cognitive radio networks and more specifically in medium access control (MAC) protocol of CR. The list of references will be useful to both researchers and practitioners in this area. Also, it can be adopted as a graduate-level textbook for an advanced course on wireless communication networks. The development of new technologies such as Wi-Fi, cellular phones, Bluetooth, TV broadcasts and satellite has created immense demand for radio spectrum which is a limited natural resource ranging from 30KHz to 300GHz. For every wireless application, some portion of the radio spectrum needs to be purchased, and the Federal Communication Commission (FCC) allocates the spectrum for some fee for such services. This static allocation of the radio spectrum has led to various problems such as saturation in some bands, scarcity, and lack of radio resources to new wireless applications. Most of the frequencies in the radio spectrum have been allocated although many studies have shown that the allocated bands are not being used efficiently. The CR technology is one of the effective solutions to the shortage of spectrum and the inefficiency of its utilization. In this thesis, a detailed investigation on issues related to the protocol design for cognitive radio networks with particular emphasis on the MAC layer is presented. A novel Dynamic and Decentralized and Hybrid MAC (DDH-MAC) protocol that lies between the CR MAC protocol families of globally available common control channel (GCCC) and local control channel (non-GCCC). First, a multi-access channel MAC protocol, which integrates the best features of both GCCC and non-GCCC, is proposed. Second, an enhancement to the protocol is proposed by enabling it to access more than one control channel at the same time. The cognitive users/secondary users (SUs) always have access to one control channel and they can identify and exploit the vacant channels by dynamically switching across the different control channels. Third, rapid and efficient exchange of CR control information has been proposed to reduce delays due to the opportunistic nature of CR. We have calculated the pre-transmission time for CR and investigate how this time can have a significant effect on nodes holding a delay sensitive data. Fourth, an analytical model, including a Markov chain model, has been proposed. This analytical model will rigorously analyse the performance of our proposed DDH-MAC protocol in terms of aggregate throughput, access delay, and spectrum opportunities in both the saturated and non-saturated networks. Fifth, we develop a simulation model for the DDH-MAC protocol using OPNET Modeler and investigate its performance for queuing delays, bit error rates, backoff slots and throughput. It could be observed from both the numerical and simulation results that when compared with existing CR MAC protocols our proposed MAC protocol can significantly improve the spectrum utilization efficiency of wireless networks. Finally, we optimize the performance of our proposed MAC protocol by incorporating multi-level security and making it energy efficient