Download or read book Low complexity and Power efficient Wireless Cooperative Relay Networks with Enhanced Reliability written by Gi Wan Choi and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: In recent years, global mobile data traffic has been increasing exponentially as mobile devices pervade our daily lives. To cope with the ever growing demands for higher data rates and seamless connectivity, one solution is to drastically increase the number of macro base stations in the conventional cellular architecture. However, this results in high deployment costs. Deploying low-power nodes such as relays that do not require a wired backhaul connection within a macrocell is one of cost-effective ways to extend high data rate coverage range. Relays are typically deployed to increase signal strength in poor coverage areas or to eliminate dead spots. But more importantly, relays provide a natural diversity, called cooperative diversity. In addition to a direct signal from a base station, extra copies of the same signal are forwarded from relays. Utilizing this diversity at the destination can yield significant performance enhancements. Thus, cooperative relay strategies need to be considered to enable high data rate coverage in a cost-effective manner. In this dissertation, we consider a simple single-relay network and present low-complexity and power-efficient cooperative relay designs that can achieve low error rate. We first study decode-and-forward (DF) relay networks with a single antenna at each node, where the relay decodes the received signal and forwards the re-encoded information to the destination. In DF relay scheme, decoding at the relay is not perfect and the error-propagation phenomenon is a detrimental problem, preventing the destination from collecting the cooperative diversity. To enable cooperative diversity in DF relay networks, we adopt link-adaptive power-scaling relay strategies where the relay scales the transmission power of the re-encoded signal based on the reliability of the source-relay link. We generalize power-profile designs and analyze the diversity order enabled by the general power-profile designs. We provide necessary and sufficient conditions for the designs to enable full cooperative diversity at the destination. In the second part of this dissertation, we extend the power-scaling relay strategy to DF multi-input multi-output (MIMO) relay networks, where multiple antennas are adopted at each node, and show that full cooperative diversity can also be achieved here. To collect spatial diversity provided by multiple antennas without using maximum-likelihood equalizers (MLEs) or near-ML detectors which exhibit high complexity, channel-controlled automatic repeat request (CC-ARQ) scheme is developed for DF MIMO relay networks to enable spatial diversity with linear equalizers (LEs) maintaining low-complexity. We also show that joint cooperative and spatial diversity can be achieved at the destination when the power-scaling strategy and the CC-ARQ with LEs are combined. Finally, amplify-and-forward (AF) MIMO relay designs, where the relay simply amplifies the received signal and forwards it to the destination, are studied with consideration of peak-power constraints at the relay. One practical concern for AF relaying is that the output signal at the relay may suffer from large peak-to-average power ratio (PAR), which may cause nonlinear distortion and/or saturation in the transmitted signal due to the limited linear range of power amplifiers. Thus, we first investigate peak-power constrained power-scaling strategies and find a sufficient condition to enable joint cooperative and spatial diversity at the destination. Based on this study, we propose simple and practical AF MIMO relay designs with peak-power constraint at the relay. CC-ARQ is also applied to AF MIMO relay networks to reduce the decoding complexity.

Download or read book Reliable Communications for Short Range Wireless Systems written by Ismail Guvenc and published by Cambridge University Press. This book was released on 2011-03-24 with total page 427 pages. Available in PDF, EPUB and Kindle. Book excerpt: Ensuring reliable communication is an important concern in short-range wireless communication systems with stringent quality of service requirements. Key characteristics of these systems, including data rate, communication range, channel profiles, network topologies and power efficiency, are very different from those in long-range systems. This comprehensive book classifies short-range wireless technologies as high and low data rate systems. It addresses major factors affecting reliability at different layers of the protocol stack, detailing the best ways to enhance the capacity and performance of short-range wireless systems. Particular emphasis is placed on reliable channel estimation, state-of-the-art interference mitigation techniques and cooperative communications for improved reliability. The book also provides detailed coverage of related international standards including UWB, ZigBee, and 60 GHz communications. With a balanced treatment of theoretical and practical aspects of short-range wireless communications and with a focus on reliability, this is an ideal resource for practitioners and researchers in wireless communications.

Download or read book Cooperative Diversity Techniques for High throughput Wireless Relay Networks written by Quoc-Tuan Vien and published by . This book was released on 2013 with total page pages. Available in PDF, EPUB and Kindle. Book excerpt: Relay communications has attracted a growing interest in wireless communications with application to various enhanced technologies. This thesis considers a number of issues related to data throughput in various wireless relay network models. Particularly, new implementations of network coding (NC) and space-time coding (STC) techniques are investigated to offer various means of achieving high-throughput relay communications. Firstly, this thesis investigates different practical automatic repeat request (ARQ) retransmission protocols based on NC for two-way wireless relay networks to improve throughput efficiency. Two improved NC-based ARQ schemes are designed based on go-back-N and selective-repeat (SR) protocols. Addressing ARQ issues in multisource multidestination relay networks, a new NC-based ARQ protocol is proposed and two packet-combination algorithms are developed for retransmissions at relay and sources to significantly improve the throughput. In relation to the concept of channel quality indicator (CQI) reporting in two-way relay networks, two new efficient CQI reporting schemes are designed based on NC to improve the system throughput by allowing two terminals to simultaneously estimate the CQI of the distant terminal-relay link without incurring additional overhead. The transmission time for CQI feedback at the relays is reduced by half while the increase in complexity and the loss of performance are shown to be negligible. Furthermore, a low-complexity relay selection scheme is suggested to reduce the relay searching complexity. For the acknowledgment (ACK) process, this thesis proposes a new block ACK scheme based on NC to significantly reduce the ACK overheads and therefore produce an enhanced throughput. The proposed scheme is also shown to improve the reliability of block ACK transmission and reduce the number of data retransmissions for a higher system throughput. Additionally, this thesis presents a new cooperative retransmission scheme based on relay cooperation and NC to considerably reduce the number of retransmission packets and im- prove the reliability of retransmissions for a more power efficient and higher throughput system with non-overlapped retransmissions. Moreover, two relay selection schemes are recommended to determine the optimised number of relays for the retransmission. Finally, with respect to cognitive wireless relay networks (CWRNs), this thesis proposes a new cooperative spectrum sensing (CSS) scheme to improve the spectrum sensing performance and design a new CSS scheme based on NC for three-hop CWRNs to improve system throughput. Furthermore, a new distributed space-time-frequency block code (DSTFBC) is designed for a two- hop nonregenerative CWRN over frequency-selective fading channels. The proposed DSTFBC design achieves higher data rate, spatial diversity gain, and decoupling detection of data blocks at all destination nodes with a low-complexity receiver structure.

Download or read book Energy Efficient Cooperative Wireless Communication and Networks written by Zhengguo Sheng and published by CRC Press. This book was released on 2014-11-11 with total page 216 pages. Available in PDF, EPUB and Kindle. Book excerpt: Compared with conventional communications, cooperative communication allows multiple users in a wireless network to coordinate their packet transmissions and share each other's resources, thus achieving high-performance gain and better service coverage and reliability. Energy Efficient Cooperative Wireless Communication and Networks provides a comp

Download or read book Design and Performance Analysis of Efficient Cooperative Wireless Communication Systems written by Essam Saleh Altubaishi and published by . This book was released on 2012 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooperative communication has recently become a key technology for modern wireless networks such as 3GPP long-term evolution and WiMAX, because in such networks the transmission rate, the communication reliability, and coverage problems could be improved in a cost-effective manner. This, however, faces many design challenges. First, cooperative transmission typically involves a relaying phase which requires extra resources. This may cause a reduction in the spectral efficiency. Second, extra control signaling increases the complexity of operation, which may limit practical implementation. In addition, a wireless channel is time-varying, mainly due to the multipath propagation. As a result, a careful design of efficient cooperative communication systems is required, not only to enhance the spectral efficiency and maintain the quality-of-service (QoS), but also to be practical. In this dissertation, we aim to address the challenges imposed by cooperative communication and wireless transmission, and design the efficient and distributed systems which can be practically implemented in existing wireless systems. The research work is divided into two main topics: 1) adaptive cooperative wireless systems with variable-rate transmission, and 2) cooperative wireless systems with a power consumption constraint. The first topic investigates how the spectral efficiency of cooperative wireless communication systems can be improved while maintaining the QoS in terms of bit error rate and outage probability. The spectral efficiency enhancement is achieved by using three techniques: adaptivity over the relay node (i.e., relay node is active or not), adaptivity over the modulation mode, and relay selection. Based on that, we propose several adaptive cooperative schemes for both the decode-and-forward (DF) and amplify-and-forward (AF) protocols. To evaluate these schemes, we provide performance analysis in terms of average spectral efficiency, average bit error rate (ABER), and outage probability over Rayleigh fading channels. We start with the single-relay cooperative system using DF protocol, in which two adaptive cooperative schemes with variable-rate transmission are proposed. The first scheme, called the minimum error rate scheme (MERS), aims to exploit the transmit diversity to improve the bit error rate. By trading the multiplexing gain against the diversity gain, we propose the second scheme, called the maximum spectral efficiency scheme (MSES), in which cooperative transmission is avoided whenever it is not beneficial. The MERS improves the ABER significantly and achieves equal or better average spectral efficiency compared to the fixed (i.e., non-adaptive) relaying scheme. In contrast, the MSES provides the best average spectral efficiency due to its ability to not only adapt to the channel variation but also to switch between cooperative and non-cooperative transmissions. To further increase the spectral efficiency, we then propose the third scheme, called variable-rate based relay selection (VRRS) scheme, in which a relay node is selected from among the available relay nodes, based on a predefined criterion. Furthermore, we propose two AF adaptive cooperative schemes, mainly to enhance the spectral efficiency. In the first scheme, we introduce a generalized switching policy (GSP) for a single-relay cooperative wireless system that exploits the variable-rate transmission and useful cooperative regions. The second scheme, called the AF efficient relay selection (AFERS) scheme, extends the GSP to also consider the relay selection technique. Analytical and simulation results verify that the AFERS scheme not only outperforms conventional direct transmission in terms of the average spectral efficiency, but also the AF fixed relaying and the outage-based AF adaptive cooperative scheme. The second topic investigates the fair power consumption of the relay nodes for AF cooperative wireless communication systems. The fairness is defined as to achieve equal power consumption over the relay nodes. We focus on how the relay selection process can be controlled in a distributed manner so that the power consumption of the relay nodes can be included in relay selection. We first introduce a simple closed-form expression for the weight coefficient used in order to achieve the considered fairness that depends only on the local average channel conditions of the relay path. We then derive closed-form expressions of the weighted outage probability and ABER and show that our proposed strategy not only has less complexity than the conventional centralized one but also provides better accuracy in distributing the total consumed power equally among the relay nodes without affecting the performance.

Download or read book Performance Analysis of Amplify and Forward Wireless Relay Networks written by Muhammad Khalil and published by . This book was released on 2017 with total page 284 pages. Available in PDF, EPUB and Kindle. Book excerpt: Wireless relay technology plays an important role in the next-generation mobile and wireless networks. It has been proposed as a cost effective solution to addressing a growing demand for high data rates and low power consumption. In the relay communication model, a source communicates to a destination through a wireless node(s) called a relay. There are two main relaying techniques: Decode-and-Forward (DF) and Amplify-and-Forward (AF). AF is the focus of this thesis. The AF relay networks provide considerable performance improvement in link reliability, Spectral Efficiency (SE), Energy Efficiency (EE) and Bit Error Rate (BER) performance. They also offer a low-complexity solution for practical relay networks that have critical energy constraints, as they enable the received signal to be amplified without the decoding process at the relays. This thesis proposes new methods of reducing the energy consumption and evaluating the error performance of AF relay networks, when the relay is either one-way (unidirectional) or two-way (bidirectional). The analysis is commenced by formulating the actual Signals-to-Noise Ratio (SNR) level, which corresponds to a low SNR level, in order to calculate the Exact Bit Error Rate (EBER) performance. Then, the approximated SNR, which refers to a high SNR level, is expressed and adopted to evaluate the Asymptotic Bit Error Rate (ABER). Another SNR level is presented in this work and defined as an optimal SNR level, which is obtained by optimal balancing of the SE and EE. The optimal SNR level allows evaluation of the ABER and the EBER of AF relay networks under optimal SNR conditions. Accordingly, a unifying BER evaluation at low, high, and optimal levels of AF relay networks is provided in this study. This thesis focuses on a high SNR level to derive an effective method for evaluating the ABER and EBER, whether in optimal or sub-optimal AF relay networks. The effectiveness of such a BER evaluation method is demonstrated by enhancing the ABER of AF relay networks at all SNR levels (i.e., low, high, optimal SNR levels). This is shown when disparity between the ABER and the EBER at a low SNR level is reduced, and this helps to calculate the accurate BER of AF relay networks under any SNR levels using either the ABER or EBER. The proposed methods are examined under different channels environments, as in practice the channel of each hop of an AF relay network can be located in a different environment. When both hops are located in the same environment, the fading channels of the hops are equal, while for different environments, the fading channels of the hops are different. Furthermore, relay location is also investigated for the aforementioned ABER and EBER, and a new method for determining the relationship between the EE and EBER with relay location is derived.

Download or read book Wireless Information and Power Transfer written by Derrick Wing Kwan Ng and published by John Wiley & Sons. This book was released on 2019-01-29 with total page 318 pages. Available in PDF, EPUB and Kindle. Book excerpt: em style="mso-bidi-font-style: normal;"Wireless Information and Power Transfer offers an authoritative and comprehensive guide to the theory, models, techniques, implementation and application of wireless information and power transfer (WIPT) in energy-constrained wireless communication networks. With contributions from an international panel of experts, this important resource covers the various aspects of WIPT systems such as, system modeling, physical layer techniques, resource allocation and performance analysis. The contributors also explore targeted research problems typically encountered when designing WIPT systems.

Download or read book Energy Efficient Cooperative Wireless Communication and Networks written by Zhengguo Sheng and published by CRC Press. This book was released on 2014-11-11 with total page 223 pages. Available in PDF, EPUB and Kindle. Book excerpt: Compared with conventional communications, cooperative communication allows multiple users in a wireless network to coordinate their packet transmissions and share each other's resources, thus achieving high-performance gain and better service coverage and reliability. Energy Efficient Cooperative Wireless Communication and Networks provides a comprehensive look at energy efficiency and system design of cooperative wireless communication. Introducing effective cooperative wireless communication schemes, the book supplies the understanding and methods required to improve energy efficiency, reliability, and end-to-end protocol designs for wireless communication systems. It explains the practical benefits and limitations of cooperative transmissions along with the associated designs of upper-layer protocols, including MAC, routing, and transport protocol. The book considers power efficiency as a main objective in cooperative communication to ensure quality-of-service (QoS) requirements. It explains how to bring the performance gain at the physical layer up to the network layer and how to allocate network resources dynamically through MAC/scheduling and routing to trade off the performance benefits of given transmissions against network costs. Because the techniques detailed in each chapter can help readers achieve energy efficiency and reliability in wireless networks, they have the potential to impact a range of industry areas, including wireless communication, wireless sensor networks, and ad hoc networks. The book includes numerous examples, best practices, and models that capture key issues in real-world applications. Along with algorithms and tips for effective design, the book supplies the understanding you will need to achieve high-performing and energy efficient wireless networks with improved service coverage and reliability.

Download or read book Coherent Cooperative Relaying in Low Mobility Wireless Multiuser Networks written by Stefan Berger and published by Logos Verlag Berlin GmbH. This book was released on 2010 with total page 337 pages. Available in PDF, EPUB and Kindle. Book excerpt: In this thesis, several important aspects of cooperative wireless multiuser networks are investigated. The focus lies on coherent two-hop relaying networks where several amplify-and-forward (AF) relays assist the communication between multiple source-destination pairs. First, the impact of local oscillator (LO) imperfections and I/Q imbalance at the relays on two-hop relaying is investigated. A special focus lies on the comparison between frequency division duplexing (FDD) and time division duplexing (TDD) relays. Based on the observation that the direction in which a channel between two wireless nodes is measured has an impact on the estimate, phase synchronization requirements for coherent relaying networks are then found. Several channel estimation protocols that differ in the direction in which the single-hop channels are measured are furthermore identi'ed and their performance is compared. Next, a very simple phase synchronization scheme is presented that provides a set of relays with a common LO phase. Two coherent beamforming schemes, namely multiuser zero-forcing (MUZF) and multiuser minimum mean squared error (MMSE) relaying, are then investigated. Finally, a real-world demonstrator for distributed wireless communication networks (called RACooN Lab) is presented. It was used to implement coherent cooperative communication schemes on a practical two-hop relaying network.

Download or read book Performance Analysis of Cooperative Networking with Multi Channels written by Praveen Kumar Devulapalli and published by CRC Press. This book was released on 2024-07-18 with total page 123 pages. Available in PDF, EPUB and Kindle. Book excerpt: This book covers wireless cooperative communication and advanced communication techniques for research scholars and post-graduate students. Features: • This book will be the reference book for cooperative communication. • It addresses the problems in small-scale cooperative communication. • It presents cooperative routing algorithms for large-scale cooperative networks with the constraint of throughput and transmission time. • It presents energy- efficient transmission approach by making use of multiple radio terminals. • It presents adaptive routing algorithm for large-scale cooperative network under mobility environment.

Download or read book Design and Analysis of New Wireless Transmission Strategies for Cooperative Relay Networks written by Gayan Lasintha Amarasuriya Aruma Baduge and published by . This book was released on 2013 with total page 180 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooperative relay technologies are currently being researched to address the ever-increasing demand for higher data rates, extended coverage, greater mobility, and enhanced reliability. This thesis thus focuses on (1) developing new physical-layer wireless technologies for cooperative relay networks and (2) ascertaining their viability through performance analysis. Specifically, (i) new system and channel models, (ii) signaling and relay-processing algorithms, (iii) joint relay-antenna selection strategies, (iv) joint transmit-receive beamforming techniques, and (v) comprehensive performance analysis frameworks are developed for one-way, two-way, and multi-way cooperative relay networks. Our first research focuses on developing a comprehensive analytical framework for deriving closed-form performance bounds of multi-hop amplify-and-forward (AF) relay networks. Specifically, mathematically-tractable, asymptotically-exact end-to-end signal-to-noise ratio bounds are first formulated, and thereby, the outage probability and average bit error rate bounds are derived. In our second work, adaptive multiple-relay selection strategies are designed and analyzed for multi-relay AF networks to optimize the tradeoffs among the system performance, complexity, and wireless resource usage. Our third research investigates joint antenna and relay selection strategies, which are optimal in the sense of the achievable diversity gains, for multiple-input multiple-output (MIMO) one-way relay networks and MIMO two-way relay networks. Finally, joint transmit/receive zero forcing transmission strategies are developed for MIMO multi-way relay networks for optimizing the achievable diversity-multiplexing trade-off. The key design criterion of the aforementioned transmission designs is to leverage spatial diversity and/or spatial multiplexing gains available among distributed single-antenna and/or multiple-antenna wireless terminals through distributed transmission and efficient signal processing. Moreover, the fundamental relationships among the data rate, coverage, and reliability metrics are characterized, and thereby, the detrimental impact of practical wireless transmission impairments on the performance of the aforementioned transmission strategies are quantified. The insights obtained through these analyses are then used to refine our physical-layer designs to achieve desirable trade-offs between the system performance, resource usage and implementation complexity.

Download or read book Cooperative Wireless Communications written by Yan Zhang and published by CRC Press. This book was released on 2009-03-10 with total page 518 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooperative devices and mechanisms are increasingly important to enhance the performance of wireless communications and networks, with their ability to decrease power consumption and packet loss rate and increase system capacity, computation, and network resilience. Considering the wide range of applications, strategies, and benefits associated wit

Download or read book Stochastic Network Optimization with Application to Communication and Queueing Systems written by Michael Neely and published by Springer Nature. This book was released on 2022-05-31 with total page 199 pages. Available in PDF, EPUB and Kindle. Book excerpt: This text presents a modern theory of analysis, control, and optimization for dynamic networks. Mathematical techniques of Lyapunov drift and Lyapunov optimization are developed and shown to enable constrained optimization of time averages in general stochastic systems. The focus is on communication and queueing systems, including wireless networks with time-varying channels, mobility, and randomly arriving traffic. A simple drift-plus-penalty framework is used to optimize time averages such as throughput, throughput-utility, power, and distortion. Explicit performance-delay tradeoffs are provided to illustrate the cost of approaching optimality. This theory is also applicable to problems in operations research and economics, where energy-efficient and profit-maximizing decisions must be made without knowing the future. Topics in the text include the following: - Queue stability theory - Backpressure, max-weight, and virtual queue methods - Primal-dual methods for non-convex stochastic utility maximization - Universal scheduling theory for arbitrary sample paths - Approximate and randomized scheduling theory - Optimization of renewal systems and Markov decision systems Detailed examples and numerous problem set questions are provided to reinforce the main concepts. Table of Contents: Introduction / Introduction to Queues / Dynamic Scheduling Example / Optimizing Time Averages / Optimizing Functions of Time Averages / Approximate Scheduling / Optimization of Renewal Systems / Conclusions

Download or read book Security and Data Reliability in Cooperative Wireless Networks written by Emad Hassan and published by CRC Press. This book was released on 2018-04-27 with total page 503 pages. Available in PDF, EPUB and Kindle. Book excerpt: Following a detailed overview of cooperative communications and the physical layer security, this book proposes relay and jammer selection schemes for security in one-way cooperative networks and to improve physical layer security in two-way cooperative networks. It also proposes a Cooperative Hybrid Self-Healing scheme to enhance the confidentiality of the data collected by UWSN. It ends with a proposal called Self-Healing Cluster Controlled Mobility (SH-CCM) scheme based on hybrid cooperation between both Proactive and Reactive peers and the sick sensors at both network and cluster levels to guarantee the security in UWSN.

Download or read book Spectrum Sharing in Wireless Networks written by John D. Matyjas and published by CRC Press. This book was released on 2016-11-17 with total page 697 pages. Available in PDF, EPUB and Kindle. Book excerpt: Spectrum Sharing in Wireless Networks: Fairness, Efficiency, and Security provides a broad overview of wireless network spectrum sharing in seven distinct sections: The first section examines the big picture and basic principles, explaining the concepts of spectrum sharing, hardware/software function requirements for efficient sharing, and future trends of sharing strategies. The second section contains more than 10 chapters that discuss differing approaches to efficient spectrum sharing. The authors introduce a new coexistence and sharing scheme for multi-hop networks, describe the space-time sharing concept, introduce LTE-U, and examine sharing in broadcast and unicast environments. They then talk about different cooperation strategies to achieve mutual benefits for primary users (PU) and secondary users (SU), discuss protocols in a spectrum sharing context, and provide different game theory models between PUs and SUs. The third section explains how to model the interactions of PUs and SUs, using an efficient calculation method to determine spectrum availability. Additionally, this section explains how to use scheduling models to achieve efficient SU traffic delivery. The subject of the fourth section is MIMO-oriented design. It focuses on how directional antennas and MIMO antennas greatly enhance wireless network performance. The authors include a few chapters on capacity/rate calculations as well as beamforming issues under MIMO antennas. Power control is covered in the fifth section which also describes the interference-aware power allocation schemes among cognitive radio users and the power control schemes in cognitive radios. The sixth section provides a comprehensive look at security issues, including different types of spectrum sharing attacks and threats as well as corresponding countermeasure schemes. The seventh and final section covers issues pertaining to military applications and examines how the military task protects its data flows when sharing the spectrum with civilian applications.

Download or read book Cooperative Relaying and Resource Allocation in Future generation Cellular Networks written by Xiaoxia Zhang and published by . This book was released on 2015 with total page 126 pages. Available in PDF, EPUB and Kindle. Book excerpt: Driven by the significant consumer demand for reliable and high data rate communications, the future-generation cellular systems are expected to employ cutting-edge techniques to improve the service provisioning at substantially reduced costs. Cooperative relaying is one of the primary techniques due to its ability to improve the spectrum utilization by taking advantage of the broadcast nature of wireless signals. This dissertation studies the physical layer cooperative relaying technique and resource allocation schemes in the cooperative cellular networks to improve the spectrum and energy efficiency from the perspectives of downlink transmission, uplink transmission and device-to-device transmission, respectively. For the downlink transmission, we consider an LTE-Advanced cooperative cellular network with the deployment of Type II in-band decode-and-forward relay stations (RSs) to enhance the cell-edge throughput and to extend the coverage area. This type of relays can better exploit the broadcast nature of wireless signals while improving the utilization of existing allocated spectral resources. For such a network, we propose joint orthogonal frequency division multiplexing (OFDM) subcarrier and power allocation schemes to optimize the downlink multi-user transmission efficiency. Firstly, an optimal power dividing method between eNB and RS is proposed to maximize the achievable rate on each subcarrier. Based on this result, we show that the optimal joint resource allocation scheme for maximizing the overall throughput is to allocate each subcarrier to the user with the best channel quality and to distribute power in a water-filling manner. Since the users' Quality of Service (QoS) provision is one of the major design objectives in cellular networks, we further formulate a lexicographical optimization problem to maximize the minimum rate of all users while improving the overall throughput. A sufficient condition for optimality is derived. Due to the complexity of searching for the optimal solution, we then propose an efficient, low-complexity suboptimal joint resource allocation algorithm, which outperforms the existing suboptimal algorithms that simplify the joint design into separate allocation. Both theoretical and numerical analyses demonstrate that our proposed scheme can drastically improve the fairness as well as the overall throughput. As the physical layer uplink transmission technology for LTE-Advanced cellular network is based on single carrier frequency division multiple access (SC-FDMA) with frequency domain equalization (FDE), this dissertation further studies the uplink achievable rate and power allocation to improve the uplink spectrum efficiency in the cellular network. Different from the downlink OFDM system, signals on all subcarriers in the SC-FDMA system are transmitted sequentially rather than in parallel, thus the user's achievable rate is not simply the summation of the rates on all allocated subcarriers. Moreover, each user equipment (UE) has its own transmission power constraint instead of a total power constraint at the base station in the downlink case. Therefore, the uplink resource allocation problem in the LTE-Advanced system is more challenging. To this end, we first derive the achievable rates of the SC-FDMA system with two commonly-used FDE techniques, zero-forcing (ZF) equalization and minimum mean square error (MMSE) equalization, based on the joint superposition coding for cooperative relaying. We then propose optimal power allocation schemes among subcarriers at both UE and RS to maximize the overall throughput of the system. Theoretical analysis and numerical results are provided to demonstrate a significant gain in the system throughput by our proposed power allocation schemes. Besides the physical layer technology, the trend of improving energy efficiency in future cellular networks also motivates the network operators to continuously bring improvements in the entire network infrastructure. Such techniques include efficient base station (BS) redesign, opportunistic transmission such as device-to-device and cognitive radio communications. In the third part of this dissertation, we explore the potentials of employing cooperative relaying in a green device-to-device communication underlaying cellular network to improve the energy efficiency and spectrum utilization of the system. As the green base station is powered by sustainable energy, the design objective is to enhance both sustainability and efficiency of the device-to-device communication. Specifically, we first propose optimal power adaptation schemes to maximize the network spectrum efficiency under two practical power constraints. We then take the dynamics of the charging and discharging processes of the energy buffer at the BS into consideration to ensure the network sustainability. To this end, the energy buffer is modeled as a G/D/1 queue where the input energy has a general distribution. Power allocation schemes are proposed based on the statistics of the energy buffer to further enhance the network efficiency and sustainability. Theoretical analysis and numerical results are presented to demonstrate that our proposed power allocation schemes can improve the network throughput while maintaining the network sustainability at a certain level. Our analyses developed in this dissertation indicate that the cooperative transmission based on cooperative relaying can significantly improve the spectrum efficiency and energy efficiency of the cellular network for downlink transmission, uplink transmission and device-to-device communication. Our proposed cooperative relaying technique and resource allocation schemes can provide efficient solutions to practical design and optimization of future-generation cellular networks.

Download or read book Adaptive Relay Techniques for OFDM based Cooperative Communication Systems written by Xin Gao and published by . This book was released on 2014 with total page 332 pages. Available in PDF, EPUB and Kindle. Book excerpt: Cooperative communication has recently been considered as a key technology for modern wireless standards and next generation wireless networks to improve the quality-of-service (QoS) and extend transmission coverage in a cost-e ective manner. In this thesis, we aim to address the challenges of wireless cooperative communications, and design the e cient OFDM-based relay systems. Starting with the channel accumulation problem in the amplify-and-forward (AF) relay system, we proposed two adaptive guard interval (GI) schemes for single/multiple-relay networks respectively to cover the accumulated delay spread and enhance the transmission e - ciency. Distinct from the traditional adaptive GI, the dynamical GI length can be detected by the destination individually. Numerical results show that the proposed scheme can further save the control signaling overhead without any symbol error rate (SER) performance loss. For multiple-relay systems, a novel relay selection criterion is proposed to achieve the trade-off between the transmission reliability and overhead by considering both the channel gain and the accumulated delay spread. From computer simulations, the proposed relay selection scheme significantly improves the e cient throughput over the multipath channel with variable channel length, Moreover, cooperative systems require an accuracy resource allocation to achieve the high capacity in the two-way decode-and-forward (DF) relay system with time-varying channels and the bidirectional asymmetric tra c. We propose two allocation algorithms, where the total capacity is maximized under a capacity ratio constraint which depends on the tra c-load di erence between the uplink and downlink. The balanced capacity performance shows that the proposed schemes can assure the fairs data rate of the two terminals and improve the overall QoS of the relay network. A low-complexity suboptimal allocation algorithm is proposed for the frequency-division model which separates subcarrier and time/power allocation. Verifying by simulations, the suboptimal scheme can achieve the similar performance with the optimal one with reduced complexity. In order to further enhance the transmission reliability and maintain low processing delay, we propose a novel equalize-and-forward (EF) relay scheme, which can equalizes the channel between source and relay and eliminate the channel accumulation e ect. The relay processing time is reduced by performing the channel estimation and equalization in parallel. In the EF relay, free-delay equalization is realized by presetting the equalizer with the current channel response that is predicted in parallel. Numerical results show that the EF relay can achieve comparable SER performance as the DF relay with much less latency and exhibit low outage probability at the same data rate as compared to traditional AF and DF schemes.