Survey of Spectrum Sharing for Inter-Technology Coexistence

Increasing capacity demands in emerging wireless technologies are expected to be met by network densification and spectrum bands open to multiple technologies. These will, in turn, increase the level of interference and also result in more complex inter-technology interactions, which will need to be managed through spectrum sharing mechanisms. Consequently, novel spectrum sharing mechanisms should be designed to allow spectrum access for multiple technologies, while efficiently utilizing the spectrum resources overall. Importantly, it is not trivial to design such efficient mechanisms, not only due to technical aspects, but also due to regulatory and business model constraints. In this survey we address spectrum sharing mechanisms for wireless inter-technology coexistence by means of a technology circle that incorporates in a unified, system-level view the technical and non-technical aspects. We thus systematically explore the spectrum sharing design space consisting of parameters at different layers. Using this framework, we present a literature review on inter-technology coexistence with a focus on wireless technologies with equal spectrum access rights, i.e. (i) primary/primary, (ii) secondary/secondary, and (iii) technologies operating in a spectrum commons. Moreover, we reflect on our literature review to identify possible spectrum sharing design solutions and performance evaluation approaches useful for future coexistence cases. Finally, we discuss spectrum sharing design challenges and suggest future research directions

Medium access control design for distributed opportunistic radio networks

Existing wireless networks are characterized by a fixed spectrum assignment policy. However, the scarcity of available spectrum and its inefficient usage demands for a new communication paradigm to exploit the existing spectrum opportunistically. Future Cognitive Radio (CR) devices should be able to sense unoccupied spectrum and will allow the deployment of real opportunistic networks. Still, traditional Physical (PHY) and Medium Access Control (MAC) protocols are not suitable for this new type of networks because they are optimized to operate over fixed assigned frequency bands. Therefore, novel PHY-MAC cross-layer protocols should be developed to cope with the specific features of opportunistic networks. This thesis is mainly focused on the design and evaluation of MAC protocols for Decentralized Cognitive Radio Networks (DCRNs). It starts with a characterization of the spectrum sensing framework based on the Energy-Based Sensing (EBS) technique considering multiple scenarios. Then, guided by the sensing results obtained by the aforementioned technique, we present two novel decentralized CR MAC schemes: the first one designed to operate in single-channel scenarios and the second one to be used in multichannel scenarios. Analytical models for the network goodput, packet service time and individual transmission probability are derived and used to compute the performance of both protocols. Simulation results assess the accuracy of the analytical models as well as the benefits of the proposed CR MAC schemes

Game theory for collaboration in future networks

Cooperative strategies have the great potential of improving network performance and spectrum utilization in future networking environments. This new paradigm in terms of network management, however, requires a novel design and analysis framework targeting a highly flexible networking solution with a distributed architecture. Game Theory is very suitable for this task, since it is a comprehensive mathematical tool for modeling the highly complex interactions among distributed and intelligent decision makers. In this way, the more convenient management policies for the diverse players (e.g. content providers, cloud providers, home providers, brokers, network providers or users) should be found to optimize the performance of the overall network infrastructure. The authors discuss in this chapter several Game Theory models/concepts that are highly relevant for enabling collaboration among the diverse players, using different ways to incentivize it, namely through pricing or reputation. In addition, the authors highlight several related open problems, such as the lack of proper models for dynamic and incomplete information games in this area.info:eu-repo/semantics/acceptedVersio

Cognitive MAC protocols for mobile Ad-Hoc networks

This thesis was submitted for the degree of Doctor of Philosophy and awarded by Brunel University.The term of Cognitive Radio (CR) used to indicate that spectrum radio could be accessed dynamically and opportunistically by unlicensed users. In CR Networks, Interference between nodes, hidden terminal problem, and spectrum sensing errors are big issues to be widely discussed in the research field nowadays. To improve the performance of such kind of networks, this thesis proposes Cognitive Medium Access Control (MAC) protocols for Mobile Ad-Hoc Networks (MANETs). From the concept of CR, this thesis has been able to develop a cognitive MAC framework in which a cognitive process consisting of cognitive elements is considered, which can make efficient decisions to optimise the CR network. In this context, three different scenarios to maximize the secondary user's throughput have been proposed. We found that the throughput improvement depends on the transition probabilities. However, considering the past information state of the spectrum can dramatically increases the secondary user's throughput by up to 40%. Moreover, by increasing the number of channels, the throughput of the network can be improved about 25%. Furthermore, to study the impact of Physical (PHY) Layer errors on cognitive MAC layer in MANETs, in this thesis, a Sensing Error-Aware MAC protocols for MANETs has been proposed. The developed model has been able to improve the MAC layer performance under the challenge of sensing errors. In this context, the proposed model examined two sensing error probabilities: the false alarm probability and the missed detection probability. The simulation results have shown that both probabilities could be adapted to maintain the false alarm probability at certain values to achieve good results. Finally, in this thesis, a cooperative sensing scheme with interference mitigation for Cognitive Wireless Mesh Networks (CogMesh) has been proposed. Moreover, a prioritybased traffic scenario to analyze the problem of packet delay and a novel technique for dynamic channel allocation in CogMesh is presented. Considering each channel in the system as a sub-server, the average delay of the users' packets is reduced and the cooperative sensing scenario dramatically increases the network throughput 50% more as the number of arrival rate is increased

Application of network coding in satellite broadcast and multiple access channels

Satellite broadcasting and relaying capabilities enable mobile broadcast systems over wide geographical areas, which opens large market possibilities for handheld, vehicular and fixed user terminals. The geostationary (GEO) satellite orbit is highly suited for such applications, as it spares the need for satellite terminals to track the movement of the spacecraft, with important savings in terms of complexity and cost. The large radius of the GEO orbit (more than 40000 km) has two main drawbacks. One is the large free space loss experienced by a signal traveling to or from the satellite, which limits the signal-to-noise ratio (SNR) margins in the link budget with respect to terrestrial systems. The second drawback of the GEO orbit is the large propagation delay (about 250 msec) that limits the use of feedback in both the forward (satellite to satellite terminal) and the reverse (satellite terminal to satellite) link. The limited margin protection causes loss of service availability in environments where there is no direct line of sight to the satellite, such as urban areas. The large propagation delay on its turn, together with the large terminal population size usually served by a GEO satellite, limit the use of feedback, which is at the basis of error-control. In the reverse link, especially in the case of fixed terminals, packet losses are mainly due to collisions, that severely limit the access to satellite services in case a random access scheme is adopted. The need for improvements and further understanding of these setups lead to the development of our work. In this dissertation we study the application of network coding to counteract the above mentioned channel impairments in satellite systems. The idea of using network coding stems from the fact that it allows to efficiently exploit the diversity, either temporal or spatial, present in the system. In the following we outline the original contributions included in each of the chapters of the dissertation. Chapter 3. This chapter deals with channel impairments in the forward link, and specifically with the problem of missing coverage in Urban environments for land mobile satellite (LMS) networks. By applying the Max-flow Min-cut theorem we derive a lower bound on the maximum coverage that can be achieved through cooperation. Inspired by this result, we propose a practical scheme, keeping in mind the compatibility with the DVB-SH standard. We developed a simulator in Matlab/C++ based on the physical layer abstraction and used it to test the performance gain of our scheme with a benchmark relaying scheme that does allow coding at packet level. Chapter 4. The second chapter of contributions is devoted to the information theoretical study of real-time streaming transmissions over fading channels with channel state information at the transmitter only. We introduce this new channel model and propose several transmission schemes, one of which is proved to be asymptotically optimal in terms of throughput. We also provide an upper bound on the achievable throughput for the proposed channel model and compare it numerically with the proposed schemes over a Rayleigh fading channel. Chapter 5. Chapter 5 is devoted to the study of throughput and delay in non-real-time streaming transmission over block fading channels. We derive bounds on the throughput and the delay for this channel and propose different coding techniques based on time-sharing. For each of them we carry out an analytical study of the performance. Finally, we compare numerically the performance of the proposed schemes over a Rayleigh fading channel. Chapter 6. In the last technical chapter we propose a collision resolution method for the return link based on physical layer network coding over extended Galois field (EGF). The proposed scheme extracts information from the colliding signals and achieves important gains with respect to Slotted ALOHA systems as well as with respect to other collision resolution schemes.Una de les característiques mes importants de les plataformes de comunicacions per satèl.lit és la seva capacitat de retransmetre senyals rebuts a un gran número de terminals. Això es fonamental en contextes com la difusió a terminals mòbils o la comunicació entre màquines. Al mateix temps, la disponibilitat d’un canal de retorn permet la creació de sistemes de comunicacions per satèl.lit interactius que, en principi, poden arribar a qualsevol punt del planeta. Els satèl.lits Geoestacionaris son particularment adequats per a complir amb aquesta tasca. Aquest tipus de satèl.lits manté una posició fixa respecte a la Terra, estalviant als terminals terrestres la necessitat de seguir el seu moviment en el cel. Per altra banda, la gran distància que separa la Terra dels satèl.lits Geoestacionaris introdueix grans retrassos en les comunicacions que, afegit al gran número de terminals en servei, limita l’ús de tècniques de retransmissió basades en acknowledgments en cas de pèrdua de paquets. Per tal de sol.lucionar el problema de la pèrdua de paquets, les tècniques més utilitzades son el desplegament de repetidors terrestres, anomenats gap fillers, l’ús de codis de protecció a nivell de paquet i mecanismes proactius de resolució de col.lisions en el canal de retorn. En aquesta tesi s’analitzen i s’estudien sol.lucions a problemes en la comunicació per satèl.lit tant en el canal de baixada com el de pujada. En concret, es consideren tres escenaris diferents. El primer escenari es la transmissió a grans poblacions de terminals mòbils en enorns urbans, que es veuen particularment afectats per la pèrdua de paquets degut a l’obstrucció, per part dels edificis, de la línia de visió amb el satèl.lit. La sol.lució que considerem consisteix en la utilització de la cooperació entre terminals. Una vegada obtinguda una mesura del guany que es pot assolir mitjançant cooperació en un model bàsic de xarxa, a través del teorema Max-flow Min-cut, proposem un esquema de cooperació compatible amb estàndards de comunicació existents. El segon escenari que considerem es la transmissió de vídeo, un tipus de tràfic particularment sensible a la pèrdua de paquets i retards endògens als sistemes de comunicació per satèl.lit. Considerem els casos de transmissió en temps real i en diferit, des de la perspectiva de teoria de la informació, i estudiem diferents tècniques de codificació analítica i numèrica. Un dels resultats principals obtinguts es l’extensió del límit assolible de la capacitat ergòdica del canal en cas que el transmissor rebi les dades de manera gradual, enlloc de rebre-les totes a l’inici de la transmissió. El tercer escenari que considerem es l’accés aleatori al satèl.lit. Desenvolupem un esquema de recuperació dels paquets perduts basat en la codificació de xarxa a nivell físic i en extensions a camps de Galois, amb resultats molt prometedors en termes de rendiment. També estudiem aspectes relacionats amb la implementació pràctica d’aquest esquema

Low-latency Networking: Where Latency Lurks and How to Tame It

While the current generation of mobile and fixed communication networks has been standardized for mobile broadband services, the next generation is driven by the vision of the Internet of Things and mission critical communication services requiring latency in the order of milliseconds or sub-milliseconds. However, these new stringent requirements have a large technical impact on the design of all layers of the communication protocol stack. The cross layer interactions are complex due to the multiple design principles and technologies that contribute to the layers' design and fundamental performance limitations. We will be able to develop low-latency networks only if we address the problem of these complex interactions from the new point of view of sub-milliseconds latency. In this article, we propose a holistic analysis and classification of the main design principles and enabling technologies that will make it possible to deploy low-latency wireless communication networks. We argue that these design principles and enabling technologies must be carefully orchestrated to meet the stringent requirements and to manage the inherent trade-offs between low latency and traditional performance metrics. We also review currently ongoing standardization activities in prominent standards associations, and discuss open problems for future research

Game theory for cooperation in multi-access edge computing

Cooperative strategies amongst network players can improve network performance and spectrum utilization in future networking environments. Game Theory is very suitable for these emerging scenarios, since it models high-complex interactions among distributed decision makers. It also finds the more convenient management policies for the diverse players (e.g., content providers, cloud providers, edge providers, brokers, network providers, or users). These management policies optimize the performance of the overall network infrastructure with a fair utilization of their resources. This chapter discusses relevant theoretical models that enable cooperation amongst the players in distinct ways through, namely, pricing or reputation. In addition, the authors highlight open problems, such as the lack of proper models for dynamic and incomplete information scenarios. These upcoming scenarios are associated to computing and storage at the network edge, as well as, the deployment of large-scale IoT systems. The chapter finalizes by discussing a business model for future networks.info:eu-repo/semantics/acceptedVersio

Energy Efficient and Cooperative Solutions for Next-Generation Wireless Networks

Energy efficiency is increasingly important for next-generation wireless systems due to the limited battery resources of mobile clients. While fourth generation cellular standards emphasize low client battery consumption, existing techniques do not explicitly focus on reducing power that is consumed when a client is actively communicating with the network. Based on high data rate demands of modern multimedia applications, active mode power consumption is expected to become a critical consideration for the development and deployment of future wireless technologies. Another reason for focusing more attention on energy efficient studies is given by the relatively slow progress in battery technology and the growing quality of service requirements of multimedia applications. The disproportion between demanded and available battery capacity is becoming especially significant for small-scale mobile client devices, where wireless power consumption dominates within the total device power budget. To compensate for this growing gap, aggressive improvements in all aspects of wireless system design are necessary. Recent work in this area indicates that joint link adaptation and resource allocation techniques optimizing energy efficient metrics can provide a considerable gain in client power consumption. Consequently, it is crucial to adapt state-of-the-art energy efficient approaches for practical use, as well as to illustrate the pros and cons associated with applying power-bandwidth optimization to improve client energy efficiency and develop insights for future research in this area. This constitutes the first objective of the present research. Together with energy efficiency, next-generation cellular technologies are emphasizing stronger support for heterogeneous multimedia applications. Since the integration of diverse services within a single radio platform is expected to result in higher operator profits and, at the same time, reduce network management expenses, intensive research efforts have been invested into design principles of such networks. However, as wireless resources are limited and shared by clients, service integration may become challenging. A key element in such systems is the packet scheduler, which typically helps ensure that the individual quality of service requirements of wireless clients are satisfied. In contrastingly different distributed wireless environments, random multiple access protocols are beginning to provide mechanisms for statistical quality of service assurance. However, there is currently a lack of comprehensive analytical frameworks which allow reliable control of the quality of service parameters for both cellular and local area networks. Providing such frameworks is therefore the second objective of this thesis. Additionally, the study addresses the simultaneous operation of a cellular and a local area network in spectrally intense metropolitan deployments and solves some related problems. Further improving the performance of battery-driven mobile clients, cooperative communications are sought as a promising and practical concept. In particular, they are capable of mitigating the negative effects of fading in a wireless channel and are thus expected to enhance next-generation cellular networks in terms of client spectral and energy efficiencies. At the cell edges or in areas missing any supportive relaying infrastructure, client-based cooperative techniques are becoming even more important. As such, a mobile client with poor channel quality may take advantage of neighboring clients which would relay data on its behalf. The key idea behind the concept of client relay is to provide flexible and distributed control over cooperative communications by the wireless clients themselves. By contrast to fully centralized control, this is expected to minimize overhead protocol signaling and hence ensure simpler implementation. Compared to infrastructure relay, client relay will also be cheaper to deploy. Developing the novel concept of client relay, proposing simple and feasible cooperation protocols, and analyzing the basic trade-offs behind client relay functionality become the third objective of this research. Envisioning the evolution of cellular technologies beyond their fourth generation, it appears important to study a wireless network capable of supporting machine-to-machine applications. Recent standardization documents cover a plethora of machine-to-machine use cases, as they also outline the respective technical requirements and features according to the application or network environment. As follows from this activity, a smart grid is one of the primary machine-to-machine use cases that involves meters autonomously reporting usage and alarm information to the grid infrastructure to help reduce operational cost, as well as regulate a customer's utility usage. The preliminary analysis of the reference smart grid scenario indicates weak system architecture components. For instance, the large population of machine-to-machine devices may connect nearly simultaneously to the wireless infrastructure and, consequently, suffer from excessive network entry delays. Another concern is the performance of cell-edge machine-to-machine devices with weak wireless links. Therefore, mitigating the above architecture vulnerabilities and improving the performance of future smart grid deployments is the fourth objective of this thesis. Summarizing, this thesis is generally aimed at the improvement of energy efficient properties of mobile devices in next-generation wireless networks. The related research also embraces a novel cooperation technique where clients may assist each other to increase per-client and network-wide performance. Applying the proposed solutions, the operation time of mobile clients without recharging may be increased dramatically. Our approach incorporates both analytical and simulation components to evaluate complex interactions between the studied objectives. It brings important conclusions about energy efficient and cooperative client behaviors, which is crucial for further development of wireless communications technologies