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Author: Anh H. Nguyen
Publisher:
ISBN: 9781303814372
Category :
Languages : en
Pages : 148
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Book Description
In wireless communications, it is of utmost importance to exploit multi-user diversity and at the same time provide satisfactory quality of service for all users. However, these two goals often conflict with each other. On one hand, multiuser diversity is maximized by selecting the user with the best channel condition. On the other, ensuring fairness among users demands the allocation of network resources to those who do not necessarily have the best channel conditions. Whenever a user with a poorer channel condition is selected, there is a certain loss in the overall system throughput. The major objective of this thesis is to find scheduling algorithms that guarantee fairness with minimal performance tradeoff. First, we consider multi-user diversity in a multi-user MIMO system. When zero-forcing beam-forming transmission technique is used, the system needs to find a subset of users such that the transmission to these users results in the highest throughput. As the number of users grows, the complexity of the user subset selection increases exponentially. To address this issue, simple user-subset-selection algorithms have been developed that can perform well and are very close to the optimal ones found through an exhaustive search. Maximizing system throughput is a key factor in ensuring high network performance, but guaranteeing service provision to all users is no less important. To support fairness among users, cumulative distribution function (CDF) scheduling is utilized because of the its capability to precisely control allocation for each user. The CDF scheduling algorithm requires knowledge of the channel distribution among all users. However, the channel distribution or even an approximation of it is hard to obtain in real systems. In this dissertation, two classes of practical, CDF-based scheduling algorithms are developed. They are the non-parametric CDF scheduling (NPCS), used when the channel model is unknown, and the parametric CDF scheduling (PCS), used when the channel model is known. These algorithms are shown to frequently outperform the well-known Proportional Fair (PF) scheduling method, and may be viable alternatives to it. The performance of the developed scheduling technique is then carefully analyzed and verified through simulations under various channel models. In order to apply them in real systems, these algorithms are first proposed for continuous rate transmission. Modified versions are then developed for finite rate transmission and limited feedback resources. Lastly, we analyze throughput of heterogeneous relay OFDMA systems using CDF scheduling with partial feedback. The scheduling problem is even more challenging with the incorporation of relays because of the different coherent time on their two hops. The CDF scheduling algorithm is modified to satisfy short-term fairness among users. In addition, performance of different feedback schemes in a wideband multi-user system are compared. Among the considered schemes, thresholding feedback is numerically shown to have the lowest feedback requirement, given a certain probability of feedback availability.
Author: Anh H. Nguyen
Publisher:
ISBN: 9781303814372
Category :
Languages : en
Pages : 148
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Book Description
In wireless communications, it is of utmost importance to exploit multi-user diversity and at the same time provide satisfactory quality of service for all users. However, these two goals often conflict with each other. On one hand, multiuser diversity is maximized by selecting the user with the best channel condition. On the other, ensuring fairness among users demands the allocation of network resources to those who do not necessarily have the best channel conditions. Whenever a user with a poorer channel condition is selected, there is a certain loss in the overall system throughput. The major objective of this thesis is to find scheduling algorithms that guarantee fairness with minimal performance tradeoff. First, we consider multi-user diversity in a multi-user MIMO system. When zero-forcing beam-forming transmission technique is used, the system needs to find a subset of users such that the transmission to these users results in the highest throughput. As the number of users grows, the complexity of the user subset selection increases exponentially. To address this issue, simple user-subset-selection algorithms have been developed that can perform well and are very close to the optimal ones found through an exhaustive search. Maximizing system throughput is a key factor in ensuring high network performance, but guaranteeing service provision to all users is no less important. To support fairness among users, cumulative distribution function (CDF) scheduling is utilized because of the its capability to precisely control allocation for each user. The CDF scheduling algorithm requires knowledge of the channel distribution among all users. However, the channel distribution or even an approximation of it is hard to obtain in real systems. In this dissertation, two classes of practical, CDF-based scheduling algorithms are developed. They are the non-parametric CDF scheduling (NPCS), used when the channel model is unknown, and the parametric CDF scheduling (PCS), used when the channel model is known. These algorithms are shown to frequently outperform the well-known Proportional Fair (PF) scheduling method, and may be viable alternatives to it. The performance of the developed scheduling technique is then carefully analyzed and verified through simulations under various channel models. In order to apply them in real systems, these algorithms are first proposed for continuous rate transmission. Modified versions are then developed for finite rate transmission and limited feedback resources. Lastly, we analyze throughput of heterogeneous relay OFDMA systems using CDF scheduling with partial feedback. The scheduling problem is even more challenging with the incorporation of relays because of the different coherent time on their two hops. The CDF scheduling algorithm is modified to satisfy short-term fairness among users. In addition, performance of different feedback schemes in a wideband multi-user system are compared. Among the considered schemes, thresholding feedback is numerically shown to have the lowest feedback requirement, given a certain probability of feedback availability.
Author: Mehri Mehrjoo
Publisher:
ISBN:
Category :
Languages : en
Pages : 117
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Book Description
Orthogonal frequency division multiple access (OFDMA) is becoming a widely deployed mechanism in broadband wireless networks due to its capability to combat the channel impairments and support high data rate. Besides, dealing with small units of spectrum, named sub-carriers, instead of whole spectrum, results in enhanced flexibility and efficiency of the resource allocation for OFDMA networks. Resource allocation and scheduling in the downlink of OFDMA networks supporting heterogeneous traffic will be considered in this thesis. The purpose of resource allocation is to allocate sub-carriers and power to users to meet their service requirements while maintaining fairness among users and maximizes resource utilization. To achieve these objectives, utility-based resource allocation schemes along with some state-of-the-art resource allocation paradigms such as power control, adaptive modulation and coding, sub-carrier assignment, and scheduling are adopted. On one hand, a utility-based resource allocation scheme improves resource utilization by allocating enough resources based on users' quality of service (QoS) satisfaction. On the other hand, resource allocation based on utilities is not trivial when users demand different traffic types with convex and nonconvex utilities.
Author: Amila Tharaperiya Gamage
Publisher: Springer
ISBN: 3319642685
Category : Technology & Engineering
Languages : en
Pages : 116
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Book Description
This book provides an in-depth discussion on how to efficiently manage resources of heterogeneous wireless networks and how to design resource allocation algorithms to suit real world conditions. Efficiently managing resources of the networks is more crucial now, than ever before, to meet users’ rapidly increasing demand for higher data rates, better quality-of-service (QoS) and seamless coverage. Some of the techniques that can be incorporated within heterogeneous wireless networks to achieve this objective are interworking of the networks, user multi-homing and device-to-device (D2D) communication. Designing resource allocation algorithms to suit real world conditions is also important, as the algorithms should be deployable and perform well in real networks. For example, two of the conditions considered in this book are resource allocation intervals of different networks are different and small cell base stations have limited computational capacity. To address the first condition, resource allocation algorithms for interworking systems are designed to allocate resources of different networks at different time-scales. To address the second condition, resource allocation algorithms are designed to be able to run at cloud computing servers. More of such conditions, algorithms designed to suit these conditions, modeling techniques for various networks and performance analysis of the algorithms are discussed in the book. This book concludes with a discussion on the future research directions on the related fields of study. Advanced-level students focused on communication and networking will use this book as a study guide. Researchers and experts in the fields of networking, converged networks, small-cell networks, resource management, and interference management, as well as consultants working in network planning and optimization and managers, executives and network architects working in the networking industry will also find this book useful as a reference.
Author: Ian C. Wong
Publisher: Springer Science & Business Media
ISBN: 0387749454
Category : Technology & Engineering
Languages : en
Pages : 126
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Book Description
This book proposes a unified algorithmic framework based on dual optimization techniques that have complexities that are linear in the number of subcarriers and users, and that achieve negligible optimality gaps in standards-based numerical simulations. Adaptive algorithms based on stochastic approximation techniques are also proposed, which are shown to achieve similar performance with even much lower complexity. All the algorithms proposed are clearly presented in concise block diagrams allowing the reader to implement these algorithms in the software of their choice. This book is an accessible reference for researchers and industry practitioners alike.
Author: Jagadish Ghimire
Publisher:
ISBN:
Category :
Languages : en
Pages : 147
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Book Description
Heterogeneous networking paradigm addresses the ever growing need for capacity and coverage in wireless networks by deploying numerous low power base stations overlaying the existing macro cellular coverage. Heterogeneous cellular networks encompass many deployment scenarios, with different backhauling techniques (wired versus wireless backhauling), different transmission coordination mechanisms and resource allocation schemes, different types of links operating at different bands and air-interface technologies, and different user association schemes. Studying these deployment scenarios and configurations, and understanding the interplay between different processes is challenging. In the first part of the thesis, we present a flow-based optimization framework that allows us to obtain the throughput performance of a heterogeneous network when the network processes are optimized jointly. This is done under a given system ``snapshot'', where the system parameters like the channel gains and the number of users are fixed and assumed known. Our framework allows us to configure the network parameters to allocate optimal throughputs to these flows in a fair manner. This is an offline-static model and thus is intended to be used at the engineering and planning phase to compare many potential configurations and decide which ones to study further. Using the above-mentioned formulation, we have been able to study a large set of deployment scenarios and different choices of resource allocation, transmission coordination, and user association schemes. This has allowed us to provide a number of important engineering insights on the throughput performance of different scenarios and their configurations. The second part of our thesis focuses on understanding the impact of backhaul infrastructure's capacity limitation on the radio resource management algorithms like user scheduling and user association. Most existing studies assume an ideal backhaul. This assumption, however, needs to be revisited as backhaul considerations are critical in heterogeneous networks due to the economic considerations. In this study, we formulate a global $\alpha$-fair user scheduling problem under backhaul limitations, and show how this limitation has a fundamental impact on user scheduling. Using results from convex optimization, we characterize the solution of optimal backhaul-aware user scheduling and show that simple heuristics can be used to obtain good throughput performance with relatively low complexity/overhead. We also study the related problem of user association under backhaul-limitations. This study is a departure from our ``snapshot'' approach. We discuss several important design considerations for an online user association scheme. We present a relatively simple backhaul-unaware user association scheme and show that it is very efficient as long as the network has fine-tuned the resource allocation.
Author: Jennifer Elizabeth Price
Publisher:
ISBN: 9780549051879
Category :
Languages : en
Pages : 157
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Book Description
The contributions of this research lie in four main areas: (i) distributed and adaptive rate assignments for CDMA 1xEVDO-type systems, (ii) cross-layer optimal rate assignments for hybrid wired/wireless CDMA networks, (iii) leveraging downlink for socially optimal and incentive compatible uplink rate allocation in cellular networks, and (iv) capacity-achieving rate assignments in unicast networks that employ network coding. In each of these problems, I address issues related to modeling, analysis, implementation, and validation.
Author: Sławomir Stańczak
Publisher: Springer Science & Business Media
ISBN: 3540462481
Category : Computers
Languages : en
Pages : 200
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Book Description
The wireless industry is in the midst of a fundamental shift from providing voice-only services to offering customers an array of multimedia services, including a wide variety of audio, video and data communications capabilities. Future wireless networks will be integrated into every aspect of daily life, and therefore could affect our life in a magnitude similar to that of the Internet and cellular phones. This monograph demonstrates that these emerging applications and directions require fundamental understanding on how to design and control wireless networks that lies far beyond what the currently existing theory can provide. It is shown that mathematics is the key technology to cope with central technical problems in the design of wireless networks since the complexity of the problem simply precludes the use of engineering common sense alone to identify good solutions. The main objective of this book is to provide tools for better understanding the fundamental tradeoffs and interdependencies in wireless networks, with the goal of designing resource allocation strategies that exploit these interdependencies to achieve significant performance gains. The book consists of three largely independent parts: theory, applications and appendices. The latter contain foundational apects to make the book more understandable to readers who are not familiar with some basic concepts and results from linear algebra and convex analysis.
Author: Xue Chen
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
Device-to-Device communications have the great potential to bring significant performance boost to the conventional heterogeneous network by reusing cellular resources. In cellular networks, Device-to-Device communication is defined as two user equipments in a close range communicating directly with each other without going through the base station, thus offloading cellular traffic from cellular networks. In addition to improve network spectral efficiency, D2D communication can also improve energy efficiency and user experience. However, the co-existence of D2D communication on the same spectrum with cellular users can cause severe interference to the primary cellular users. Thus the performance of cellular users must be assured when supporting underlay D2D users. In this work, we have investigated cross-layer optimization, resource allocation and interference management schemes to improve user experience, system spectral efficiency and energy efficiency for D2D communication underlaying heterogeneous networks. By exploiting frequency reuse and multi-user diversity, this research work aims to design wireless system level algorithms to utilize the spectrum and energy resources efficiently in the next generation wireless heterogeneous network.
Author: Ahmed Ragab Elsherif
Publisher:
ISBN: 9781321362435
Category :
Languages : en
Pages :
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Book Description
Recent studies have shown that a large percentage of cellular voice and data traffic originate from indoor usage. The concept of heterogeneous networks (HetNets) consisting of traditional macrocells and newly envisioned small cells has been proposed to solve the indoor coverage problem and to offload some traffic from traditional macrocells. The heterogeneity in HetNets refers mainly tocoverage where, unlike macrocells, small cells are low power short range base stations that can be deployed by network operators or end users. The main challenge of the deployment of HetNets is theinter- and intra-tier interference when sharing the same spectrum. In this work, we study HetNet deployments in various scenarios and propose several algorithms for interference management and resource allocation in those scenarios. In the first part of the dissertation, we study HetNets operating in licensed cellular band. We study the two popular deployment scenarios of public/home femtocells and enterprise femtocells. For public/home femtocells, the main challenge we study is the inter-tier interference between femtocell base station (FBS) and macrocell user equipment (MUE) in downlink. We propose a spatial domain approach for interference management through MIMO precoding and develop three time-frequency domain approaches for interference management through resource allocation. The main theme of our work is to exploit the already-available feedback information in existing cellular systems for interference management and resource allocation in HetNets. On the other hand, in enterprise femtocell deployments such as shopping malls, stadiums, or corporate premises, the major challenge is intra-tier interference among femtocells. For enterprise environments, we present a partially centralized architecture for interference management among femtocells through graph coloring followed by local resource allocation for HUEs associated with each femtocell with consideration of fairness. Next, we present the concept of dual-access-technology small cells with both licensed and unlicensed band interfaces which represents another dimension of heterogeneity that can be thought of as vertical heterogeneity. The use of dual-access-technology small cells is motivated by the widespread WiFi hotspots and the common inclusion of WiFi interface in most cellular user terminals. For dual-access-technology small cells, we study public/home small cells as well as enterprise femtocells. We formulate an optimization problem that jointly allocates resources over both licensed and unlicensed bands with the goal of maximizing sum rate of small cell user equipments with fairness constraints together with controlling inter- or intra-tier interference to neighboring macrocell or femtocell users, respectively. An important feature that our proposed solution furtherconsiders is the Quality of Service (QoS) requirements of different users traffic types to be distributed over licensed and/or unlicensed bands.
Author: Slawomir Stanczak
Publisher: Springer
ISBN: 9783540872269
Category :
Languages : en
Pages : 456
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Book Description
