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Author: Justin Foo
Publisher:
ISBN:
Category : Internetworking (Telecommunication)
Languages : en
Pages : 70
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Book Description
In a wireless network, owing to the time-varying nature of wireless channels, different mobile users typically experience peaks and troughs in channel quality at different times. This diversity in channel quality is known as multiuser diversity. With the aid of rate adaptation, multiuser diversity can be exploited by allowing the mobile user with the best channel to use the channel resource. However, in order to achieve this in most practical systems, the mobile users in the network must feed back their channel state information (CSI) to the transmitting user. In large networks, this feedback overhead can outweigh the multiuser diversity gain. In this thesis dissertation, a centralised wireless medium access control (MAC) scheme, namely Multiuser Diversity with Capture (MDC), is discussed as a solution to obviate the overhead problem. MDC explicitly employs the capture effect in radio receivers to reduce network overhead by allowing multiple mobile stations (MSs) with channels better than a nominal response threshold to simultaneously compete for the wireless channel. Owing to the capture effect, the base station (BS) can determine which MS has the best channel. In comparison with the Medium Access Diversity (MAD) scheme in the literature, the proposed MDC possesses the strong merit that the feedback overhead is independent of the number of MSs in the network. Several aspects of the MDC scheme are investigated in detail. An application of the MDC scheme based on the physical layer and parts of the MAC layer of the IEEE 802.11a standard is considered. A general analytical framework for the goodput performance of MDC is derived. Using this framework, the exact closed form solution for the expected goodput of MDC with rate adaptation over Rayleigh fading channels is calculated. The fairness performance of MDC in networks where some MSs experience better average channel conditions than others is also addressed. MSs with low average channel states tend to use the channel less often in MDC than MSs with high average channel states. This issue is tackled with Fairer Multiuser Diversity with Capture (FMDC), a variant of the MDC scheme designed to share the channel resource more equitably across all of the MSs in the network. In FMDC, instead of using the network-wide response threshold to decide whether to compete for the channel, each MS only competes for the channel when their channel state is greater than a threshold factor multiplied by their average channel state. Finally, the problem of adaptive optimisation of the response threshold for MDC and the threshold factor for FMDC is also considered. In the proposed solution, the response threshold and the threshold factor are adapted heuristically according to the estimated goodput performance of the system. The adaptive heuristic has importance in practical systems because the BS usually does not know the characteristics of the time varying channels of the MSs in the network.
Author: Justin Foo
Publisher:
ISBN:
Category : Internetworking (Telecommunication)
Languages : en
Pages : 70
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Book Description
In a wireless network, owing to the time-varying nature of wireless channels, different mobile users typically experience peaks and troughs in channel quality at different times. This diversity in channel quality is known as multiuser diversity. With the aid of rate adaptation, multiuser diversity can be exploited by allowing the mobile user with the best channel to use the channel resource. However, in order to achieve this in most practical systems, the mobile users in the network must feed back their channel state information (CSI) to the transmitting user. In large networks, this feedback overhead can outweigh the multiuser diversity gain. In this thesis dissertation, a centralised wireless medium access control (MAC) scheme, namely Multiuser Diversity with Capture (MDC), is discussed as a solution to obviate the overhead problem. MDC explicitly employs the capture effect in radio receivers to reduce network overhead by allowing multiple mobile stations (MSs) with channels better than a nominal response threshold to simultaneously compete for the wireless channel. Owing to the capture effect, the base station (BS) can determine which MS has the best channel. In comparison with the Medium Access Diversity (MAD) scheme in the literature, the proposed MDC possesses the strong merit that the feedback overhead is independent of the number of MSs in the network. Several aspects of the MDC scheme are investigated in detail. An application of the MDC scheme based on the physical layer and parts of the MAC layer of the IEEE 802.11a standard is considered. A general analytical framework for the goodput performance of MDC is derived. Using this framework, the exact closed form solution for the expected goodput of MDC with rate adaptation over Rayleigh fading channels is calculated. The fairness performance of MDC in networks where some MSs experience better average channel conditions than others is also addressed. MSs with low average channel states tend to use the channel less often in MDC than MSs with high average channel states. This issue is tackled with Fairer Multiuser Diversity with Capture (FMDC), a variant of the MDC scheme designed to share the channel resource more equitably across all of the MSs in the network. In FMDC, instead of using the network-wide response threshold to decide whether to compete for the channel, each MS only competes for the channel when their channel state is greater than a threshold factor multiplied by their average channel state. Finally, the problem of adaptive optimisation of the response threshold for MDC and the threshold factor for FMDC is also considered. In the proposed solution, the response threshold and the threshold factor are adapted heuristically according to the estimated goodput performance of the system. The adaptive heuristic has importance in practical systems because the BS usually does not know the characteristics of the time varying channels of the MSs in the network.
Author: Hang Li
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
For multi-user wireless communications, information theory has demonstrated that system performance can be significantly improved by exploiting multi-user diversity, where the channel is always scheduled to the user with the best instantaneous channel gain. For achieving the benefit of multi-user diversity, conventionally, all users' channel state information (CSI) must be available at the Base Station (BS), thereby inducing enormous system overhead. In a wireless communication system with a large number of users, the overhead induced by polling CSIs may overshadow the multiuser diversity gain. The first part of this dissertation (Chapters 2 and 3) proposes a user identification approach (UIDA) to handle the overhead issue in a generic wireless network exploiting multiuser diversity, and demonstrates two user identification (UID) design methods and application in the orthogonal frequency-division multiplexing (OFDM) system and the multiple-input multiple-output OFDM (MIMO-OFDM) system. Then, we present a theoretical upper bound of the throughput of the system with the UIDA over general channels. In addition, a modified UIDA is proposed to effectively trade off throughput and fairness performances. In comparison with Medium Access Diversity and Multiuser Diversity with Capture (two alternative approaches in the literature for exploiting multiuser diversity), the proposed UIDA achieves better throughput performance when there are a reasonably large number of users. Following the above work, a simplified UIDA for multiuser diversity with enhanced throughput is proposed in Chapter 3 to reduce the overhead further by allowing a small degree of outage to occur. In view of the opportunistic feedback protocol proposed in the literature, the second part of this dissertation (Chapters 4-6) analyses the system performances further by considering the following conditions, respectively: (1) The capture effect and the effect of the overhead on system throughput, (2) Fairness and capacity performances for maximum throughput (MT) or proportional fair (PF) scheduling [Signal-to-noise ratios (SNRs) with independent but not necessarily identical distributions], (3) The finite-length queuing effect. Our work investigates and improves the system performances of the opportunistic feedback protocol in a practical wireless environment. In the third part of this dissertation (Chapter 7), a cluster-based feedback protocol is proposed for multiuser orthogonal frequency-division multiple access (OFDMA) systems, where the capture effect is employed in each cluster to reduce the enormous system overhead induced by polling CSIs. This work in Chapter 7 is an extension of our previous protocol (Multiuser Diversity with Capture). Our previous protocol is a special case of the proposed one, i.e., the number of clusters is 1. The proposed one additionally exploits multiuser diversity in the frequency domain, thereby achieving better throughput with the increase of the number of clusters.
Author: Savo Glisic
Publisher: John Wiley & Sons
ISBN: 9780470745731
Category : Technology & Engineering
Languages : en
Pages : 892
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Book Description
With 40% new material the new edition of Advanced Wireless Networks provides a comprehensive representation of the key issues in 4G wireless networks. Focussing on cognitive, cooperative and opportunistic paradigms to provide further increase in network efficiency, the book explores and addresses issues in wireless internet, mobile cellular and WLAN, as well as sensor, ad hoc, bio-inspired, active and cognitive networks. It examines the problem of cross-layer optimisation and network information theory as well as adaptability and reconfigurability in wireless networks. This book is an integral description of future wireless networks and the interconnection between their elements. The information is presented in a logical order within each chapter making it ideal for all levels of reader including researchers involved in modelling and analysis of future networks as well as engineers working in the area. Each chapter starts with introductory material and gradually includes more sophisticated models and mathematical tools concluding with a comprehensive list of references. Fully updated throughout with five new chapters on Opportunistic Communications; Relaying and Mesh Networks; Topology Control; Network Optimization; and Cognitive Radio Resource Management Unifies the latest research on cognitive, cooperative and opportunistic paradigms in wireless communications Provides efficient analytical tools for network analysis Discusses security issues, an essential element of working with wireless networks Supports advanced university and training courses in the field Companion website containing extra appendix on Queuing theory
Author: Frank H. P. Fitzek
Publisher: Springer Science & Business Media
ISBN: 1402047118
Category : Technology & Engineering
Languages : en
Pages : 679
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Book Description
Cooperation in Wireless Networks: Principles and Applications covers the underlying principles of cooperative techniques as well as several applications demonstrating the use of such techniques in practical systems. The book is written in a collaborative manner by several authors from Asia, America, and Europe. This book puts into one volume a comprehensive and technically rich appraisal of the wireless communications scene from a cooperation point of view.
Author: Christina Comaniciu
Publisher: Springer Science & Business Media
ISBN: 0387277501
Category : Technology & Engineering
Languages : en
Pages : 214
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Book Description
Cross-layer design seeks to enhance the capacity of wireless networks significantly through the joint optimization of multiple layers in the network, primarily the physical (PHY) and medium access control (MAC) layers. Although there are advantages of such design in wireline networks as well, this approach is particularly advantageous for wireless networks due to the properties (such as mobility and interference) that strongly affect performance and design of higher layer protocols. This unique monograph is concerned with the issue of cross-layer design in wireless networks, and more particularly with the impact of node-level multiuser detection on such design. It provides an introduction to this vibrant and active research area insufficiently covered in existing literature, presenting some of the principal methods developed and results obtained to date. Accompanied by numerous illustrations, the text is an excellent reference for engineers, researchers and students working in communication networks.
Author: Adibi, Sasan
Publisher: IGI Global
ISBN: 1615206752
Category : Business & Economics
Languages : en
Pages : 836
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Book Description
Fourth-Generation Wireless Networks: Applications and Innovations presents a comprehensive collection of recent findings in access technologies useful in the architecture of wireless networks.
Author: Stefanos Vatsikas
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Book Description
The fundamental principle of multiuser diversity states that it is possible to achieve a significant received energy gain in a multi user wireless communication system if channel resources are divided between users in an adaptive, dynamic and intelligent fashion. When every channel resource block is assigned to the user with the best channel quality at any time or frequency bin, the system-wide sum rate achieved can be significantly increased. There is a risk, though, that users with a weaker channel quality might starve for resources, as this approach prioritizes the stronger users. Therefore, it is of utmost important that some type of fairness control mechanism is used at the same time. Most of the work published in the relevant literature assumes that a central controller dictates the resource allocation process. Such an approach induces various costs though; all users have to transmit their channel quality information to the central controller and then the allocation decisions have to be fed back to them. In an inherently fast-varying wireless channel this generates a lot of overheads and makes the whole allocation process less efficient. In an attempt to minimize this cost and to remove the need for the existence of a central controller, this PhD work investigates the use of game theoretic concepts to achieve distributed resource allocation. Coalition formation is a game theoretic concept that allows individual entities to cooper- ate and perform a task more efficiently. By allowing users to form disjoint coalitions in a distributed fashion, this work tackles the problem of cooperative distributed resource allocation. Using the Nash Bargaining Solution as a means for enabling intra-coalition cooperation, individual users are able to exchange resource blocks and harvest the bene- fits of multiuser diversity, in a fashion that maintains a level of fairness similar to that of Proportional Fairness. For the purposes of this work, three different schedulers for resource allocation were de- veloped and are presented in this thesis. Two of them are based on the aforementioned game theoretic concepts, while the third is a hybrid between the Greedy scheduler and the game theoretic approach. Simulation results are presented and comparison to the widely adopted Proportional Fair scheduler is made. Additionally, the trade-offs between sum rate performance, fairness, complexity and overheads are investigated and the protocol used for the allocation process is presented.
Author: Guowang Miao
Publisher: Cambridge University Press
ISBN: 1107039886
Category : Computers
Languages : en
Pages : 387
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Book Description
Provides the fundamental principles and practical tools needed to design next-generation wireless networks that are both energy- and spectrum-efficient.
Author: Hongyi Wu
Publisher: Nova Publishers
ISBN: 9781600219443
Category : Computers
Languages : en
Pages : 662
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Book Description
Wireless technologies and applications are becoming one of the fastest growing and most promising areas in recent years. To accommodate data transmission by multiple stations sharing the scarce wireless bandwidth, a medium access control (MAC) protocol plays a crucial role in scheduling packet transmission fairly and efficiently. The emerging wireless networks, such as ad-hoc networks, sensor networks or mesh networks, are mostly multi-hop based and in distributed manner, which brings a lot of problems and challenges in designing fine-tuned MAC protocols tailored for modern wireless network. In this book, the authors give complete and in-depth overviews to the classic medium access control algorithms and the related protocols, as well as their applications in various wireless data networks especially the most successful Wireless Local Area Networks (WLAN). The book consists of three major parts. Part I of this book, including Chapters 1-7, is emphasising on the fundamentals of medium access control algorithms and protocols. Chapter 1 provides an introduction to the wireless networks, such as overview of wireless networks, problems and challenges of the wireless networks, and the classifications of MAC protocols as well as the performance metrics. Chapter 2 introduces important collision resolution algorithms applied in medium access controls, for example, the splitting algorithm and the backoff algorithm. Chapter 3 reviews the hybrid access control algorithms that combine both contention and allocation schemes. A series of important collision avoidance schemes are introduced in Chapters 4-7 respectively, with a specific design goal covered in each chapter. Chapter 4 focuses on the multi-channel MAC protocols for collision avoidance; Chapter 5 introduces the concepts of power control and power management in medium access control and how they can be applied in MAC protocol design; Chapter 6 presents how to provide Quality-of- Service (QoS) to multimedia wireless networks, in either centralised or distributed manner; and Chapter 7 explains how the smart antennas can be applied in the medium access control to provide high channel throughput and low packet collision.
Author: Tuá̂n Đõ̂
Publisher:
ISBN:
Category : Technology
Languages : en
Pages :
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Book Description
Improving Spectrum Sensing Performance by Exploiting Multiuser Diversity.
