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Author: Hang Li
Publisher:
ISBN:
Category :
Languages : en
Pages :
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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: 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: Alessandro Bazzi
Publisher: IntechOpen
ISBN: 9789533070919
Category : Technology & Engineering
Languages : en
Pages : 722
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Book Description
In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks.
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: Alessandro Bazzi
Publisher: BoD – Books on Demand
ISBN: 9533070919
Category : Technology & Engineering
Languages : en
Pages : 724
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Book Description
In the last decades the restless evolution of information and communication technologies (ICT) brought to a deep transformation of our habits. The growth of the Internet and the advances in hardware and software implementations modified our way to communicate and to share information. In this book, an overview of the major issues faced today by researchers in the field of radio communications is given through 35 high quality chapters written by specialists working in universities and research centers all over the world. Various aspects will be deeply discussed: channel modeling, beamforming, multiple antennas, cooperative networks, opportunistic scheduling, advanced admission control, handover management, systems performance assessment, routing issues in mobility conditions, localization, web security. Advanced techniques for the radio resource management will be discussed both in single and multiple radio technologies; either in infrastructure, mesh or ad hoc networks.
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: Yahya S. Al-Harthi
Publisher:
ISBN:
Category :
Languages : en
Pages : 280
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Author: Shahab Sanayei
Publisher:
ISBN:
Category : Electrical engineering
Languages : en
Pages : 28
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Book Description
Opportunistic methods solve dynamic resource allocation problems by choosing only one (or a few) out of many allocation options at each point in time, thus solving the problem in sub-optimal, but efficient ways. This work explores several opportunistic methods in wireless communications and provides an analytic framework for such problems under limited feedback. An instance of opportunistic communication is antenna selection, a low-cost, low-complexity MIMO (multiple-input multiple-output) method that uses, at each point in time, the best of available antennas. We consider capacity-maximizing antenna selection algorithms, and explore their asymptotic performance at high- and low-SNR, as well as scaling laws with the number of antennas. We propose fast algorithms for joint transmit-receive antenna selection. We analyze the capacity and diversity of antenna selection algorithms under the so-called keyhole condition. In a multi-user network, opportunistic scheduling effectively captures multi-user diversity in the downlink, however, existing techniques require substantial channel state information, per user, at the base station. We propose a simple scheduling algorithm to achieve the multiuser diversity advantage with only minimal feedback requirement and prove its desirable properties in terms of the sum-rate capacity. Using this novel approach, we propose a beamforming scheme with limited-rate feedback in multiuser MIMO systems and show its superior performance over the known methods. Finally we extend our scheduling method to multiuser OFDM networks where reduction of feedback overhead is a crucial issue.
Author: Sofoklis Kyriazakos
Publisher: CRC Press
ISBN: 1000795160
Category : Science
Languages : en
Pages : 377
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Book Description
Mobile and wireless communications are moving towards a new era that will be characterized by the seamless collaboration of heterogeneous systems, the need for high speed communications while on the move and for advanced services with quality guarantees. Recent market research studies show that most of the traffic in the future wireless networks will be produced by mobile multimedia services which are expected to proliferate by the year 2010. On the other hand mobile and wireless communications technology is becoming more and more important in developing countries where people demand fast deployment and low cost for broadband wireless internet services.The objective of this volume is to gather research and development on topics shaping the fourth generation (4G) in mobile and wireless communications and reveal the key trends and enabling technologies for 4G. We envisage 4G wireless communication systems as IP based solution providing integrated services (voice, data, multimedia) regardless of time and end-users? location. 4G technologies will manifest the benefits of the wireless and wired technologies convergence, through enabling a wide range of innovative (both indoor and outdoor) applications. 4G applications will feature premium quality, high security and an affordable cost. The vision, though fantastic, is associated with a host of technical and technological challenges.A great deal of the latter are discussed in the articles of this volume, which aims at providing insights on the research issues and solutions that are directly associated with leading edge 4G technologies and services.Taking into account recent developments in the world of wireless communications we have given emphasis to cover all these technologies and aspects that are considered as cornerstones for achieving the goals set for 4G and that will further boost research and development of next-generation mobile communications.
Author:
Publisher:
ISBN:
Category : Telecommunication
Languages : en
Pages : 760
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Author: Xiangping Qin
Publisher:
ISBN:
Category :
Languages : en
Pages :
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Finally, a model of channel with memory is considered. Both the Aloha-based and splitting-based protocol to this model and performances are analyzed.
