Dissertations / Theses: 'Cooperative diversity'

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Guerrero, Laura Yadira. "Cooperative diversity for distributed multicarrier relaying systems." Thesis, King's College London (University of London), 2017. https://kclpure.kcl.ac.uk/portal/en/theses/cooperative-diversity-for-distributed-multicarrier-relaying-systems(773aaeec-11e4-43b7-a1ff-cd3a86644a52).html.

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We introduce a Cooperative Distributed Multistage Spatial Diversity (CDMSD) scheme. By means of prior derived relaying topologies our algorithm relies on a robust and low complexity transceiver entity. CDMSD is implemented such as to improve throughput enhancement, coverage extension and spectral efficiency improvement. The benefits are provided by achieving full diversity and frequency selectivity. Simulation results are presented and compare to traditional non-distributed networks to support the analytical framework. Additionally fractional frame duration and transmitted power control are implemented to achieve higher data transmission rates. Providing a performance near optimum, our protocol has gained significantly in research momentum, mainly due to its ability to boost capacity and its inherent attribute of scalability to ad hoc and wireless sensor networks. CDMSD makes full use of MC-CDMA frequency domain spreading properties by introducing immerse collaboration and distributed frequency diversity in a multi-hop network architecture which has drawn much attention in industry and academia in terms of reliable performance.

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Moço, Andreia Vieira. "Cooperative diversity schemes for wireless communication systems." Master's thesis, Universidade de Aveiro, 2008. http://hdl.handle.net/10773/2055.

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Mestrado em Engenharia Electrónica e Telecomunicações
A presente dissertação insere-se na área das comunicações sem fios, ou mais especificamente na temática da diversidade cooperativa. Neste trabalho é feito o estudo, implementação e avaliação do desempenho de esquemas de diversidade cooperativa de baixa complexidade para sistemas de comunicação móvel. Estes esquemas são mapeados em modelos de simulação baseados em OFDMA e são completamente simulados em CoCentric System Studio. Os resultados obtidos com os modelos desenvolvidos mostram que os esquemas de diversidade cooperativa atenuam os efeitos do desvanecimento induzido pela propagação multipercurso, aumentando desta forma a capacidade e cobertura dos sistemas wireless. Os ganhos são particularmente altos quando as perdas de percurso são consideráveis, como é o caso das zonas urbanas densas. ABSTRACT: This dissertation is inserted into the wireless communication, or more specifically, into the cooperative diversity field. within this thesis, the performance of low-complexity cooperative diversity schemes projected for mobile communication systems are studied, implemented and evaluated. These schemes are mapped into simulation models based on OFDMA and are fully simulated in the CoCentric System Studio environment. The obtained results show that the proposed cooperative schemes for the uplink communication mitigate fading induced by multipath propagation, thereby increasing the capacity and coverage of wireless systems. Cooperation gains are particularly high when multipath losses are considerable, as is the case for dense urban regions.

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Teodoro, Sara Helena Marques. "Distributed coding for systems with cooperative diversity." Doctoral thesis, Universidade de Aveiro, 2011. http://hdl.handle.net/10773/6045.

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Doutoramento em Engenharia Electrotécnica
O presente trabalho propõe-se a divulgar as mais significativas técnicas de esquemas cooperativos, de forma a ultrapassar alguns dos problemas dos sistemas móveis sem fios da próxima geração, estendendo a área de cobertura destes sistemas, assim como a sua capacidade e fiabilidade. O estudo de diversos esquemas cooperativos é efetuado em termos de capacidade e de taxa de erros, fazendo variar o número de relays e de antenas em cada elemento do sistema. Diversos algoritmos com aplicação em sistemas cooperativos são desenvolvidos e propostos ao longo desta tese, como códigos espaço-frequência aplicados de forma distribuída nos relays, para sistemas baseados na tecnologia OFDM e sob diversos cenários próximos da realidade. Os sistemas cooperativos são particularmente úteis em situações em que o caminho direto entre dois terminais não está acessível ou tem uma fraca qualidade de transmissão. Tendo este aspeto em consideração, e pretendendo ter a máxima eficiência espetral e máxima diversidade, um algoritmo com precodificação é também proposto para múltiplos relays, cada um equipado com uma ou duas antenas. A formulação matemática associada aos algoritmos propostos é apresentada, assim como a derivação da probabilidade de erro teórica. O desempenho dos sistemas assistidos por relays usando os algoritmos propostos é comparado em relação a outros esquemas cooperativos equivalentes e a esquemas não-cooperativos, considerando cenários com diferentes qualidades de canal, daí advindo importantes conclusões em relação a estes sistemas.
Cooperative schemes are promising solutions for cellular wireless networks aiming to improve system fairness, extend coverage and increase capacity. Measurements of these system performances are made in terms of BER and capacity for different configurations, by varying the number of relays and of antennas equipping each node. In this work we propose and evaluate distributed space-frequency codes applied to cooperative systems in a distributed way, with application in OFDM systems and considering realistic scenarios. Moreover, the use of relays is of significant interest to allow radio access in situations where a direct path is not available or has poor quality. Thus, a data precoded relay-assisted scheme is also proposed for a system cooperating with multiple relays, each equipped with either a single antenna or two-antenna array. Mathematical formulation of the proposed algorithms is derived as well as the pairwise error probability. We further present the performances of the proposed algorithms apllied in relay-assisted schemes, and compare them with equivalent cooperative and non-cooperative schemes, for several channel quality scenarios, through which important conclusions are achieved.
FCT/FSE

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Laneman, J. Nicholas. "Cooperative diversity in wireless networks : algorithms and architectures." Thesis, Massachusetts Institute of Technology, 2002. http://hdl.handle.net/1721.1/29272.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, Dept. of Electrical Engineering and Computer Science, 2002.
Includes bibliographical references (p. 179-187).
To effectively combat multipath fading across multiple protocol layers in wireless networks, this dissertation develops energy-efficient algorithms that employ certain kinds of cooperation among terminals, and illustrates how one might incorporate these algorithms into various network architectures. In these techniques, sets of terminals relay signals for each other to create a virtual antenna array, trading off the costs-in power, bandwidth, and complexity-for the greater benefits gained by exploiting spatial diversity in the channel. By contrast, classical network architectures only employ point-to-point transmission and thus forego these benefits. After summarizing a model for the wireless channel, we present various practical cooperative diversity algorithms based upon different types of relay processing and re-encoding, both with and without limited feedback from the ultimate receivers. Using information theoretic tools, we show that all these algorithms can achieve full spatial diversity, as if each terminal had as many transmit antennas as the entire set of cooperating terminals. Such diversity gains translate into greatly improved robustness to fading for the same transmit power, or substantially reduced transmit power for the same level of performance. For example, with two cooperating terminals, power savings as much as 12 dB (a factor of sixteen) are possible for outage probabilities around one in a thousand. Finally, we discuss how the required level of complexity in the terminals makes different algorithms suitable for particular network architectures that arise in, for example, current cellular and ad-hoc networks.
by J. Nicholas Laneman.
Ph.D.

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Bletsas, Aggelos Anastasiou 1975. "Intelligent antenna sharing in cooperative diversity wireless networks." Thesis, Massachusetts Institute of Technology, 2005. http://hdl.handle.net/1721.1/33876.

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Thesis (Ph. D.)--Massachusetts Institute of Technology, School of Architecture and Planning, Program in Media Arts and Sciences, 2005.
Includes bibliographical references (p. 143-152).
Cooperative diversity has been recently proposed as a way to form virtual antenna arrays that provide dramatic gains in slow fading wireless environments. However, most of the proposed solutions require simultaneous relay transmissions at the same frequency bands, using distributed space-time coding algorithms. Careful design of distributed space-time coding for the relay channel is usually based on global knowledge of some network parameters or is usually left for future investigation, if there is more than one cooperative relay. We propose a novel scheme that eliminates the need for space-time coding and provides diversity gains on the order of the number of relays in the network. Our scheme first selects the best relay from a set of M available relays and then uses this "best" relay for cooperation between the source and the destination. Information theoretic analysis of outage probability shows that our scheme achieves the same diversity-multiplexing gain tradeoff as achieved by more complex protocols, where coordination and distributed space-time coding for M relay nodes is required. Additionally, the proposed scheme increases the outage and ergodic capacity, compared to non-cooperative communication with increasing number of participating relays, at the low SNR regime and under a total transmission power constraint.
(cont.) Coordination among the participating relays is based on a novel timing protocol that exploits local measurements of the instantaneous channel conditions. The method is distributed and allows for fast selection of the best relay as compared to the channel coherence time. In addition, a methodology to evaluate relay selection performance for any kind of wireless channel statistics is provided. Other methods of network coordination, inspired by natural phenomena of decentralized time synchronization, are analyzed in theory and implemented in practice. It was possible to implement the proposed, virtual antenna formation technique in a custom network of single antenna, half-duplex radios.
by Aggelos Anastasiou Bletsas.
Ph.D.

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Jardine, Allan. "Cooperative diversity in wireless networks : frameworks and analysis." Thesis, University of Edinburgh, 2007. http://hdl.handle.net/1842/12284.

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In spatial diversity, independently fading signals can be received by antenna elements separated by a small distance. Combining of the received signals can lead to an increase in the capacity and reliability of communications over the wireless channel. Spatial diversity can be achieved in a cellular network by sharing information between Mobile Terminals (MTs) where one MT acts as a relay supporting the data transmitted from the source in the first instance by forwarding information to the destination in the second instance. Due to the cooperation between MTs this is termed cooperative diversity. Initially this thesis considers the effect of cooperative diversity in an environment where MTs are equipped with two antenna elements, effectively combining the fast-fading combating techniques of cooperative diversity and multiple-antennas. Cooperative diversity transmission can be performed by a number of different protocols, which are termed Protocols I-V. Imposing system constraints on the network in order to make a fair comparison between the protocols, in-particular the traditional single-hop channel, allows the benefits of cooperative diversity to fully be established. An information theory approach is developed using multiple antenna techniques to provide a framework for cooperative diversity. It is shown that cooperative diversity can offer significant improvements in terms of probability of outage and capacity. In-particular, an adaptive cooperative diversity protocol is developed to select the optimal protocol dependent on channel conditions which shows a 4.25dB increase in capacity, at the 5% outage level, for a single user.

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Vien, Quoc-Tuan. "Cooperative diversity techniques for high-throughput wireless relay networks." Thesis, Glasgow Caledonian University, 2013. http://eprints.mdx.ac.uk/11685/.

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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.

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Neves, Darlene Maciel. "Channel estimation and parameters acquisition systems employing cooperative diversity." Doctoral thesis, Universidade de Aveiro, 2013. http://hdl.handle.net/10773/11963.

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Doutoramento em Engenharia Eletrotécnica e Telecomunicações
This work investigates new channel estimation schemes for the forthcoming and future generation of cellular systems for which cooperative techniques are regarded. The studied cooperative systems are designed to re-transmit the received information to the user terminal via the relay nodes, in order to make use of benefits such as high throughput, fairness in access and extra coverage. The cooperative scenarios rely on OFDM-based systems employing classical and pilot-based channel estimators, which were originally designed to pointto-point links. The analytical studies consider two relaying protocols, namely, the Amplifyand-Forward and the Equalise-and-Forward, both for the downlink case. The relaying channels statistics show that such channels entail specific characteristics that comply to a proper filter and equalisation designs. Therefore, adjustments in the estimation process are needed in order to obtain the relay channel estimates, refine these initial estimates via iterative processing and obtain others system parameters that are required in the equalisation. The system performance is evaluated considering standardised specifications and the International Telecommunication Union multipath channel models.
Este trabalho tem por objetivo o estudo de novos esquemas de estimação de canal para sistemas de comunicação móvel das próximas gerações, para os quais técnicas cooperativa são consideradas. Os sistemas cooperativos investigados neste trabalho estão projetados para fazerem uso de terminais adicionais a fim de retransmitir a informação recebida para o utilizador final. Desta forma, pode-se usurfruir de benefícios relacionados às comunicações cooperativas tais como o aumento do rendimento do sistema, fiabilidade e extra cobertura. Os cenários são basedos em sistemas OFDM que empregam estimadores de canal que fazem uso de sinais piloto e que originalmente foram projetados para ligações ponto a ponto. Os estudos analíticos consideram dois protocolos de encaminhamento, nomeadamente, Amplify-and-Forward e Equalise-and-Forward, ambos para o caso downlink. As estatísticas dos canais em estudo mostram que tais canais ocasionam características específicas para as quais o filtro do estimador e a equalisação devem ser apropridamente projetados. Estas características requerem ajustes que são necessários no processo de estimação a fim de estimar os canais, refinar as estimativas iniciais através de processos iterativos e ainda obter outros parâmetros do sistema que são necessários na equalização. O desempenho dos esquemas propostos são avaliados tendo em consideração especificações padronizadas e modelos de canal descritos na International Telecommunication Union.

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Perera, Ovitigalage Prasad Nalaka. "Cooperative diversity for performance enhancement of vehicular ad hoc networks." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/87980/1/Ovitigalage%20Prasad%20Nalaka_Perera_Thesis.pdf.

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This project was a step forward in introducing suitable cooperative diversity transmission techniques for vehicle to vehicle communications. The contributions are intended to aid in the successful implementation of future vehicular safety and autonomous controlling systems. Several protocols were introduced for vehicles to communicate effectively without losing connectivity. This study investigated novel protocols in terms of diversity-multiplexing trade-off and outage for a range of potential vehicular safety and infotainment applications.

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Ni, Min. "Cooperative Distributed Transmission and Reception." Digital WPI, 2013. https://digitalcommons.wpi.edu/etd-dissertations/325.

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" In telecommunications, a cooperative scheme refers to a method where two or more users share or combine their information in order to increase diversity gain or power gain. In contrast to conventional point-to-point communications, cooperative communications allow different users in a wireless network to share resources so that instead of maximizing the performance of its own link, each user collaborates with its neighbours to achieve an overall improvement in performance. In this dissertation, we consider different models for transmission and reception and explore cooperative techniques that increase the reliability and capacity gains in wireless networks, with consideration to practical issues such as channel estimation errors and backhaul constraints. This dissertation considers the design and performance of cooperative communication techniques. Particularly, the first part of this dissertation focuses on the performance comparison between interference alignment and opportunistic transmission for a 3-user single-input single- output (SISO) interference channel in terms of average sum rate in the presence of channel estimation errors. In the case of interference alignment, channel estimation errors cause interference leakage which consequently results in a loss of achievable rate. In the case of opportunistic transmission, channel estimation errors result in a non-zero probability of incorrectly choosing the node with the best channel. The effect of these impairments is quantified in terms of the achievable average sum rate of these transmission techniques. Analysis and numerical examples show that SISO interference alignment can achieve better average sum rate with good channel estimates and at high SNR whereas opportunistic transmission provides better performance at low SNR and/or when the channel estimates are poor. We next considers the problem of jointly decoding binary phase shift keyed (BPSK) messages from a single distant transmitter to a cooperative receive cluster connected by a local area network (LAN). An approximate distributed receive beamforming algorithm is proposed based on the exchange of coarsely- quantized observations among some or all of the nodes in the receive cluster. By taking into account the differences in channel quality across the receive cluster, the quantized information from other nodes in the receive cluster can be appropriately combined with locally unquantized information to form an approximation of the ideal receive beamformer decision statistic. The LAN throughput requirements of this technique are derived as a function of the number of participating nodes in the receive cluster, the forward link code rate, and the quantization parameters. Using information-theoretic analysis and simulations of an LDPC coded system in fading channels, numerical results show that the performance penalty (in terms of outage probability and block error rate) due to coarse quantization is small in the low SNR regimes enabled by cooperative distributed reception. An upper/lower bound approximation is derived based on a circle approximation in the channel magnitude domain which provides a pretty fast way to compute the outage probability performance for a system with arbitrary number of receivers at a given SNR. In the final part of this dissertation, we discuss the distributed reception technique with higher- order modulation schemes in the forward link. The extension from BPSK to QPSK is straightforward and is studied in the second part of this dissertation. The extension to 8PSK, 4PAM and 16QAM forward links, however, is not trivial. For 8PSK, two techniques are proposed: pseudobeamforming and 3-bit belief combining where the first one is intuitive and turns out to be suboptimal,the latter is optimal in terms of outage probability performance. The idea of belief combining can be applied to the 4PAM and 16QAM and it is shown that better/finer quantizer design can further improve the block error rate performance. Information-theoretic analysis and numerical results are provided to show that significant reliability and SNR gains can be achieved by using the proposed schemes. "

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Chen, J., and K. Djouani. "A multi-user cooperative diversity for wireless local area networks." Scientific Research Publishing, 2008. http://encore.tut.ac.za/iii/cpro/DigitalItemViewPage.external?sp=1000783.

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In this paper, an idea of using space-time block coding (STBC) in multi-user cooperative diversity has been exploited to improve the performance of the transmission in wireless local area networks. The theoretical and simulation results show that, using STBC approaches can always achieve the better performance than existing techniques without introducing the space-time coding. By analyzing the throughput and frame error ratio (FER) of the two different STBC cooperative schemes, we find the trade-off between throughput and reliability. The location of the relay is crucial to the performance, which supposes a rule for future crosslayer design.

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Fang, Wei. "Cooperative diversity aided direct-sequence code-division multiple-access systems." Thesis, University of Southampton, 2008. https://eprints.soton.ac.uk/64701/.

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In relay-assisted direct-sequence code-division multiple-access (DS-CDMA) systems, the distance between the relay and the destination receiver may be significantly shorter than that between the source transmitter and the destination receiver. Therefore, the transmission power of the relay may be significantly reduced in comparison to that of the source transmitter. In this thesis, we investigate the dependence of the achievable bit error ratio (BER) performance of DS-CDMA systems on the specific locations of the relays as well as on the power-sharing among the source transmitters and relays, when considering different propagation pathloss exponents. This thesis is focused on the class of repetition-based cooperation aided schemes, including both amplify-and-forward (AF) as well as decode-and-forward (DF) schemes, with an emphasis on lowcomplexity AF schemes. In our study, the signals received at the destination receiver from the source transmitters as well as from the relays are detected based on a range of diversity combining schemes having a relatively low-complexity. Specifically, the maximal ratio combining (MRC), the maximum signal-to-interference-plus-noise ratio (MSINR) and the minimum mean-square error (MMSE) principles are considered. We propose a novel cooperation aided DS-CDMA uplink scheme, where all the source mobile terminals (MTs) share a common set of relays for the sake of achieving relay diversity. As shown in our study, this low-complexity AF-based cooperation strategy is readily applicable to the challenging scenario where each source MT requires the assistance of several separate relays in order to achieve relay diversity. Another novel cooperation scheme is proposed for the downlink of DS-CDMAsystems, where the downlink multiuser interference (MUI) is suppressed with the aid of transmitter preprocessing, while maintaining the relay diversity order facilitated by the specific number of relays employed, despite using simple matched-filter (MF) based receivers. The transmitter preprocessing schemes considered include both the zero-forcing (ZF) and the MMSE-assisted arrangements, which belong to the class of linear transmitter preprocessing schemes. Furthermore, these transmitter preprocessing schemes are operated under the assumption that the base station’s transmitter employs explicit knowledge about the spreading sequences assigned to the destination MTs, but requires no knowledge about the downlink channels. Our study demonstrates that the proposed relay-assisted DS-CDMA systems using transmitter preprocessing are capable of substantially mitigating the downlink MUI, despite using low-complexity MF receivers.

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Ning, Haishi. "Cooperative strategies design based on the diversity and multiplexing tradeoff." Thesis, Imperial College London, 2012. http://hdl.handle.net/10044/1/9497.

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This thesis focuses on designing wireless cooperative communication strategies that are either optimal or near-optimal in terms of the tradeoff between diversity and multiplexing gains. Starting from classical cooperative broadcast, multiple-access and relay channels with unit degree of freedom, to more general cooperative interference channels with higher degrees of freedom, properties of different network topologies are studied and their unique characteristics together with several advanced interference management techniques are exploited to design cooperative transmission strategies in order to enhance data rate, reliability or both at the same time. Moreover, various algorithms are proposed to solve practical implementation issues and performance is analyzed through both theoretical verifications and simulations.

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Tope, Michael A. "Performance evaluation of a cooperative diversity enhanced ad hoc network." Thesis, Monterey, Calif. : Springfield, Va. : Naval Postgraduate School ; Available from National Technical Information Service, 2002. http://library.nps.navy.mil/uhtbin/hyperion-image/02Dec%5FTope.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, December 2002.
Thesis advisor(s): John C. McEachen, R. Clark Robertson, Daniel M. Rosser. Includes bibliographical references (p. 73-75). Also available online.

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Alnawayseh, Saif Enad Ahmad. "Coded cooperative diversity with low complexity encoding and decoding algorithms." Thesis, Swansea University, 2011. https://cronfa.swan.ac.uk/Record/cronfa42648.

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One of the main concerns in designing the wireless communication systems is to provide sufficiently large data rates while considering the different aspects of the implementation complexity that is often constrained by limited battery power and signal processing capability of the devices. Thus, in this thesis, a low complexity encoding and decoding algorithms are investigated for systems with the transmission diversity, particularly the receiver diversity and the cooperative diversity. Design guidelines for such systems are provided to provide a good trade-off between the implementation complexity and the performance. The order statistics based list decoding techniques for linear binary block codes of small to medium block length are investigated to reduce the complexity of coded systems. The original order statistics decoding (OSD) is generalized by assuming segmentation of the most reliable independent positions of the received bits. The segmentation is shown to overcome several drawbacks of the original order statistics decoding. The complexity of the OSD is further reduced by assuming a partial ordering of the received bits in order to avoid the highly complex Gauss elimination. The bit error rate performance and the decoding complexity trade-off of the proposed decoding algorithms are studied by computer simulations. Numerical examples show that, in some cases, the proposed decoding schemes are superior to the original order statistics decoding in terms of both the bit error rate performance as well as the decoding complexity. The complexity of the order statistics based list decoding algorithms for linear block codes and binary block turbo codes (BTC) is further reduced by employing highly reliable cyclic redundancy check (CRC) bits. The results show that sending CRC bits for many segments is the most effective tecnhique in reducing the complexity. The coded cooperative diversity is compared with the conventional receiver coded diversity in terms of the pairwise error probability and the overall bit error rate (BER). The expressions for the pairwise error probabilities are obtained analytically and verified by computer simulations. The performance of the cooperative diversity is found to be strongly relay location dependent. Using the analytical as well as extensive numerical results, the geographical areas of the relay locations are obtained for small to medium signal-to-noise ratio values, such that the cooperative coded diversity outperforms the receiver coded diversity. However, for sufficiently large signal-to-noise ratio (SNR) values, or if the path-loss attenuations are not considered, then the receiver coded diversity always outperforms the cooperative coded diversity. The obtained results have important implications on the deployment of the next generation cellular systems supporting the cooperative as well as the receiver diversity.

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Pang, Kun. "Collaborative HARQ Schemes for Cooperative Diversity Communications in Wireless Networks." Thesis, The University of Sydney, 2008. http://hdl.handle.net/2123/2559.

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Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

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Pang, Kun. "Collaborative HARQ Schemes for Cooperative Diversity Communications in Wireless Networks." School of Electrical & Information Engineering, The University of Sydney, 2008. http://hdl.handle.net/2123/2559.

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Master of Philosophy
Wireless technology is experiencing spectacular developments, due to the emergence of interactive and digital multimedia applications as well as rapid advances in the highly integrated systems. For the next-generation mobile communication systems, one can expect wireless connectivity between any devices at any time and anywhere with a range of multimedia contents. A key requirement in such systems is the availability of high-speed and robust communication links. Unfortunately, communications over wireless channels inherently suffer from a number of fundamental physical limitations, such as multipath fading, scarce radio spectrum, and limited battery power supply for mobile devices. Cooperative diversity (CD) technology is a promising solution for future wireless communication systems to achieve broader coverage and to mitigate wireless channels’ impairments without the need to use high power at the transmitter. In general, cooperative relaying systems have a source node multicasting a message to a number of cooperative relays, which in turn resend a processed version message to an intended destination node. The destination node combines the signal received from the relays, and takes into account the source’s original signal to decode the message. The CD communication systems exploit two fundamental features of the wireless medium: its broadcast nature and its ability to achieve diversity through independent channels. A variety of relaying protocols have been considered and utilized in cooperative wireless networks. Amplify and forward (AAF) and decode and forward (DAF) are two popular protocols, frequently used in the cooperative systems. In the AAF mode, the relay amplifies the received signal prior to retransmission. In the DAF mode, the relay fully decodes the received signal, re-encodes and forwards it to the destination. Due to the retransmission without decoding, AAF has the shortcoming that noise accumulated in the received signal is amplified at the transmission. DAF suffers from decoding errors that can lead to severe error propagation. To further enhance the quality of service (QoS) of CD communication systems, hybrid Automatic Repeat-reQuest (HARQ) protocols have been proposed. Thus, if the destination requires an ARQ retransmission, it could come from one of relays rather than the source node. This thesis proposes an improved HARQ scheme with an adaptive relaying protocol (ARP). Focusing on the HARQ as a central theme, we start by introducing the concept of ARP. Then we use it as the basis for designing three types of HARQ schemes, denoted by HARQ I-ARP, HARQ II-ARP and HARQ III-ARP. We describe the relaying protocols, (both AAF and DAF), and their operations, including channel access between the source and relay, the feedback scheme, and the combining methods at the receivers. To investigate the benefits of the proposed HARQ scheme, we analyze its frame error rate (FER) and throughput performance over a quasi-static fading channel. We can compare these with the reference methods, HARQ with AAF (HARQ-AAF) and HARQ with perfect distributed turbo codes (DTC), for which correct decoding is always assumed at the relay (HARQ-perfect DTC). It is shown that the proposed HARQ-ARP scheme can always performs better than the HARQ-AAF scheme. As the signal-to-noise ratio (SNR) of the channel between the source and relay increases, the performance of the proposed HARQ-ARP scheme approaches that of the HARQ-perfect DTC scheme.

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Alabed, Samer. "Computationally Efficient Spatial and Cooperative Diversity Techniques for Wireless Communication Networks." Phd thesis, TU Darmstadt, 2012. https://tuprints.ulb.tu-darmstadt.de/2984/1/Samer_Alabed_Computationally_Efficient_Spatial_and_Cooperative_Diversity_Techniques_for_Wireless_Communication_Networks.pdf.

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Several techniques are recently proposed to improve the robustness of wireless communication systems, increase the throughput, and overcome channel impairments such as multi-user interference and multi-path fading. Among them, using multiple-antennas is one of the most remarkable techniques as it allows to improve the error performance and the data rate without an increase in the frequency bandwidth or transmitted power. However, multiple-antenna techniques are not applicable in all ad-hoc networks due to hardware constraints. As an alternative, cooperative diversity techniques have been proposed to achieve gains similar to that of multiple-antenna techniques. In this thesis, we develop computationally efficient multiple-antenna and cooperative diversity techniques for wireless communication networks which offer an improved tradeoff between computational complexity, error performance, and data rate. We first consider space-time block coding for conventional multiple antenna systems. We propose a low complexity decoder for quasi-orthogonal space-time block codes. Both the coherent and non-coherent implementations of this decoder are developed. The proposed decoder can provide a substantially improved tradeoff between the complexity and performance as compared to state-of-the-art decoding techniques. The proposed decoder enjoys a nearly linear decoding complexity and it approximately achieves the optimal performance of the maximum-likelihood decoder. Recently, cooperative diversity strategies for two-way wireless relay networks have been proposed using the amplify-and-forward and the decode-and-forward protocols. Although the simultaneous bidirectional decode and-forward transmission has been shown to outperform other decode-and-forward strategies, it has mainly two disadvantages: high relay decoding complexity and the impossibility to use the direct link between the communicating terminals. In this thesis, we propose novel coherent and non-coherent simultaneous bidirectional decode-and-forward distributed space-time coding strategies that provide a higher coding gain and enjoy a substantially lower relay decoding complexity than the state-of-the-art strategies at the same symbol rate. In the proposed strategies, the communicating terminals can benefit from the direct link which is not exploited by other existing simultaneous bidirectional transmission strategies. Various differential distributed space-time coding strategies for two-way relay networks using the amplify-and-forward protocol which do not require channel state information either at the relays or at the terminals have been proposed. The simultaneous two-way differential distributed space-time coding strategy using the amplify-and-forward protocol has been shown to outperform the conventional differential four-phase strategy in the low to medium signal-to-noise ratio region. However, there are mainly three disadvantages associated with it: I) the relay power wasted for transmitting redundant information at either side, ii) the direct link between the communicating terminals can not be used and iii) the considerable bias at high signal-to-noise ratio. In this work, amplify-and-forward differential distributed space-time coding strategies for two-way wireless relay networks are developed, that provide a higher coding gain than the state-of-the art strategies. In the proposed strategies, the relays do not waste power to transmit redundant information at either side and the communicating terminals can fully use the direct link between them. Although differential distributed space-time coding strategies do not require channel state information at the relays, they are associated with a low error performance, a high latency, and decoding complexity. Another strategy used in relay networks relies on coherent processing of the relay signals using distributed beamforming techniques. This strategy enjoys a good error performance and low decoding complexity while offering an optimal decoding delay. However, a common requirement in distributed beamforming is the availability of perfect channel state information at all nodes. To avoid this requirement, we introduce a distributed differential beamforming strategy that combines the differential diversity and the distributed beamforming strategy while retaining the benefits of both approaches. The proposed strategy does not require channel state information at any node and enjoys a good error performance, optimal delay, and low decoding complexity.

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Seddik, Karim G. "Diversity in cooperative networks how to achieve and where to exploit /." College Park, Md.: University of Maryland, 2008. http://hdl.handle.net/1903/8177.

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Thesis (Ph. D.) -- University of Maryland, College Park, 2008.
Thesis research directed by: Dept. of Electrical and Computer Engineering . Title from t.p. of PDF. Includes bibliographical references. Published by UMI Dissertation Services, Ann Arbor, Mich. Also available in paper.

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20

Poulimeneas, Dimitrios. "Back-pressure-like mechanisms on relay selection policies for cooperative diversity systems." Thesis, KTH, Reglerteknik, 2015. http://urn.kb.se/resolve?urn=urn:nbn:se:kth:diva-167794.

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The topic of the current thesis is the reduction of the average packet delay in two-hop wireless cooperative networks with buffer-aided relays. This type of networks is of particular interest since it constitutes the building block for extended networks with multiple hops and numerous relays. Back-pressure-like algorithms are developed for the HRS and max − link relay selection schemes. First, an algorithm is developed and applied for both the HRS and the max − link protocols. It reduces the average delay considerably, but, in the case of the max − link the diversity of the system is reduced resulting in higher outage probabilities. For this reason, a new algorithm is developed that aims at maintaining a high diversity throughout the operation of the network. Distributed implementations of the algorithms are also discussed. The performance of the proposed algorithms is illustrated via simulations.

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Sohaib, Sarmad. "Energy efficient cooperative wireless communications." Thesis, University of Manchester, 2010. https://www.research.manchester.ac.uk/portal/en/theses/energy-efficient-cooperative-wireless-communications(a852e1e2-04ad-4311-8004-53babe529e1b).html.

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Cooperative diversity exploits the broadcast nature of wireless channels and uses relays to improve link reliability. Most cooperative communication protocols are assumed to be synchronous in nature, which is not always possible in wireless communication. Also the relay nodes are assumed to be half duplex which in turn reduces the spectral efficiency. In this thesis, we first present a novel asynchronous cooperative communication protocol exploiting polarization diversity, which does not require synchronization at the relay node. Dual polarized antennas are employed at the relay node to achieve full duplex amplify-and-forward (ANF) communication. Hence the transmission duration is reduced which results into an increased throughput rate. Capacity analysis of the proposed scheme ascertains the high data rate as compared to conventional ANF. Bit error rate (BER) simulation also shows that the proposed scheme significantly outperforms both the non-cooperative single-input single-output and the conventional ANF schemes. Considering channel path loss, the proposed scheme consume less total transmission energy as compared to ANF and non-cooperative scheme in more practical distance range. Thus the proposed scheme is suitable for high rate and energy efficient relay-enabled communication. In addition to that, we also present a novel power allocation scheme for multiple relay nodes that results in efficient cooperative multiple-input multiple-output (MIMO) communication. Considering channel path loss, the total transmission energy is distributed between the source and the relay nodes. The energy distribution ratio between the relay and direct link is optimized such that the quality of received signal is maintained with minimum total transmission energy consumption. We calculate the energy distribution ratio analytically and verified it through computer simulation. With the new power allocation scheme, the system also obtains an increased channel capacity as compared to cooperative scheme with conventional equal power allocation and non-cooperative scheme. Optimal relay positioning with proposed energy allocation scheme is also explored to maximize the capacity.

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Chembil, Palat Ramesh. "Performance analysis of cooperative communication for wireless networks." Diss., Virginia Tech, 2006. http://hdl.handle.net/10919/30080.

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The demand for access to information when and where you need has motivated the transition of wireless communications from a fixed infrastructure based cellular communications technology to a more pervasive adhoc wireless networking technology. Challenges still remain in wireless adhoc networks in terms of meeting higher capacity demands, improved reliability and longer connectivity before it becomes a viable widespread commercial technology. Present day wireless mesh networking uses node-to-node serial multi-hop communication to convey information from source to destination in the network. The performance of such a network depends on finding the best possible route between the source and destination nodes. However the end-to-end performance can only be as good as the weakest link within a chosen route. Unlike wired networks, the quality of point-to-point links in a wireless mesh network is subject to random fluctuations. This adversely affects the performance resulting in poor throughput and poor energy efficiency. In recent years, a new paradigm for communication called cooperative communications has been proposed for which initial information theoretic studies have shown the potential for improvements in capacity over traditional multi-hop wireless networks. Cooperative communication involves exploiting the broadcast nature of the wireless medium to form virtual antenna arrays out of independent single-antenna network nodes for transmission. In this research we explore the fundamental performance limits of cooperative communication under more practical operating scenarios. Specifically we provide a framework for computing the outage and ergodic capacities of non identical distributed MIMO links, study the effect of time synchronization error on system performance, analyze the end-to-end average bit error rate (ABER) performance under imperfect relaying, and study range extension and energy efficiency offered by the system when compared to a traditional system.
Ph. D.

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23

Deng, Qingxiong. "Exploiting Diversity in Broadband Wireless Relay Networks." Digital WPI, 2012. https://digitalcommons.wpi.edu/etd-dissertations/360.

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"Fading is one of the most fundamental impairments to wireless communications. The standard approach to combating fading is by adding redundancy - or diversity - to help increase coverage and transmission speed. Motivated by the results in multiple-input multiple-output technologies, which are usually used at base stations or access points, cooperation commutation has been proposed to improve the performance of wireless networks which consist of low-cost single antenna devices. While the majority of the research in cooperative communication focuses on flat fading for its simplicity and easy analysis, in practice the underlying channels in broadband wireless communication systems such as cellular systems (UMTS/LTE) are more likely to exhibit frequency selective fading. In this dissertation, we consider a frequency selective fading channel model and explore distributed diversity techniques in broadband wireless relay networks, with consideration to practical issues such as channel estimation and complexity-performance tradeoffs. We first study a system model with one source, one destination and multiple decode-and-forward (DF) relays which share a single channel orthogonal to the source. We derive the diversity-multiplexing tradeoff (DMT) for several relaying strategies: best relay selection, random relay selection, and the case when all decoding relays participate. The best relay selection method selects the relay in the decoding set with the largest sum-squared relay-to-destination channel coefficients. This scheme can achieve the optimal DMT of the system at the expense of higher complexity, compared to the other two relaying strategies which do not always exploit the spatial diversity offered by the relays. Different from flat fading, we find special cases when the three relaying strategies have the same DMT. We further present a transceiver design and prove it can achieve the optimal DMT asymptotically. Monte Carlo simulations are presented to corroborate the theoretical analysis. We provide a detailed performance comparison of the three relaying strategies in channels encountered in practice. The work has been extended to systems with multiple amplify-and-forward relays. We propose two relay selection schemes with maximum likelihood sequential estimator and linear zero- forcing equalization at the destination respectively and both schemes can asymptotically achieve the optimal DMT. We next extend the results in the two-hop network, as previously studied, to multi-hop networks. In particular, we consider the routing problem in clustered multi-hop DF relay networks since clustered multi-hop wireless networks have attracted significant attention for their robustness to fading, hierarchical structure, and ability to exploit the broadcast nature of the wireless channel. We propose an opportunistic routing (or relay selection) algorithm for such networks. In contrast to the majority of existing approaches to routing in clustered networks, our algorithm only requires channel state information in the final hop, which is shown to be essential for reaping the diversity offered by the channel. In addition to exploiting the available diversity, our simple cross-layer algorithm has the flexibility to satisfy an additional routing objective such as maximization of network lifetime. We demonstrate through analysis and simulation that our proposed routing algorithm attains full diversity under certain conditions on the cluster sizes, and its diversity is equal to the diversity of more complicated approaches that require full channel state information. The final part of this dissertation considers channel estimation in relay networks. Channel state information is vital for exploiting diversity in cooperative networks. The existing literature on cooperative channel estimation assumes that block lengths are long and that channel estimation takes place within a fading block. However, if the forwarding delay needs to be reduced, short block lengths are preferred, and adaptive estimation through multiple blocks is required. In particular, we consider estimating the relay-to-destination channel in DF relay systems for which the presence of forwarded information is probabilistic since it is unknown whether the relay participates in the forwarding phase. A detector is used so that the update of the least mean square channel estimate is made only when the detector decides the presence of training data. We use the generalized likelihood ratio test and focus on the detector threshold for deciding whether the training sequence is present. We also propose a heuristic objective function which leads to a proper threshold to improve the convergence speed and reduce the estimation error. Extensive numerical results show the superior performance of using this threshold as opposed to fixed thresholds."

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Alexopoulos, Konstantinos. "Performance analysis of decode-and-forward with cooperative diversity and Alamouti cooperative space-time coding in clustered multihop wireless networks." Thesis, Monterey, Calif. : Naval Postgraduate School, 2008. http://edocs.nps.edu/npspubs/scholarly/theses/2008/Sept/08Sep%5FAlexopoulos.pdf.

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Thesis (M.S. in Electrical Engineering)--Naval Postgraduate School, September 2008.
Thesis Advisor(s): Tummala, Murali ; McEachen, John C. "September 2008." Description based on title screen as viewed on October 31, 2008. Includes bibliographical references (p. 95-98). Also available in print.

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Khan, Rana Azeem M. [Verfasser]. "MAC protocols for cooperative diversity in wireless sensor networks / Rana Azeem Muhammad Khan." Paderborn : Universitätsbibliothek, 2014. http://d-nb.info/1061069044/34.

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Avudainayagam, Arun. "Collaborative decoding achieving cooperative diversity in wireless networks using soft-input soft-output decoders /." [Gainesville, Fla.] : University of Florida, 2006. http://purl.fcla.edu/fcla/etd/UFE0013830.

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Butt, M. Majid. "On the Near-Far Gain in Opportunistic and Cooperative Multiuser Communications." Doctoral thesis, Norges teknisk-naturvitenskapelige universitet, Institutt for elektronikk og telekommunikasjon, 2011. http://urn.kb.se/resolve?urn=urn:nbn:no:ntnu:diva-12009.

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In this dissertation, we explore the issues related to opportunistic and cooperative communications in a multiuser environment. In the first part of the dissertation, we consider opportunistic scheduling for delay limited systems. Multiuser communication over fading channels is a challenging problem due to fast varying channel conditions. On the other hand, it provides opportunities to exploit the varying nature of the channel and maximize the throughput by scheduling the user (or users) with good channel. This gain is termed as multiuser diversity. The larger the number of users, the greater is the multiuser diversity gain. However, there is an inherent scheduling delay in exploiting multiuser diversity. The objective of this work is to design the scheduling schemes which use multiuser diversity to minimize the system transmit energy. We analyze the schemes in large system limit and characterize the energy--delay tradeoff. We show that delay tolerance in data transmission helps us to exploit multiuser diversity and results in an energy efficient use of the system resources. We assume a general multiuser environment but the proposed scheduling schemes are specifically suitable for the wireless sensor network applications where saving of transmit energyat the cost of delay in transmission is extremely useful to increase the life of battery for the sensor node. In the first part of the thesis, we propose scheduling schemes withthe objective of minimizing transmit energy for a given fixed tolerable transmission delay. The fixed delay is termed as hard deadline. A group of users with channels better than a transmission threshold are scheduled for transmission simultaneously using superposition coding. The transmission thresholds depend onthe fading statistics of the underlying channel and hard deadline of the data to be scheduled. As deadline is approached, the thresholds decrease monotonically to reflect the scheduling priority for theuser. We analyze the proposed schedulers in the large system limit. We compute the optimized transmission thresholds for the proposed scheduling schemes. We analyze the proposed schemes for practically relevant scenarios when the randomly arriving packets have individual, non--identical deadlines. We analyze the case when loss tolerance of the application is exploited to further decrease the system energy. The transmitted energy is not a convex function oftransmission thresholds. Therefore, we propose heuristic optimization procedures to compute the transmission thresholds and evaluate the performance of the schemes. Finally, we study the effect of outer cell interference on the proposed scheduling schemes. The second part of the thesis investigates the problem of cooperative communication between the nodes which relay the data of other sources multiplex with their own data towards a common destination, i.e. a relay node performs as a relay and data source at the same time. This problem setting is very useful in case of some wireless sensor network (WSN) applications where all the nodes relay sensed data towards a common destination sink node. The capacity region of a relay region is still an open problem. We use deterministic network model to study the problem. We characterizethe capacity region for a cooperative deterministic network with single source, multiple relays and single destination. We also characterize the capacity region when communicating nodes have correlated information to be sent to the destination.
Cross Layer Optimization of Wireless Sensor Networks

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Annavajjala, Ramesh. "Cross-layer design of wideband CDMA systems and cooperative diversity for wireless ad hoc networks /." Connect to a 24 p. preview or request complete full text in PDF format. Access restricted to UC campuses, 2006. http://wwwlib.umi.com/cr/ucsd/fullcit?p3222054.

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Thesis (Ph. D.)--University of California, San Diego, 2006.
Title from first page of PDF file (viewed September 20, 2006). Available via ProQuest Digital Dissertations. Vita. Includes bibliographical references (p. 139-145).

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Azarian, Yazdi Kambiz. "Outage limited cooperative channels protocols and analysis /." Columbus, Ohio : Ohio State University, 2006. http://rave.ohiolink.edu/etdc/view?acc%5Fnum=osu1154740723.

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30

Choi, Gi Wan. "Low-complexity and power-efficient wireless cooperative relay networks with enhanced reliability." Diss., Georgia Institute of Technology, 2013. http://hdl.handle.net/1853/47721.

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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.

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Hussain, Nasir. "Cooperative communication in relay assisted wireless access networks." Thesis, Queensland University of Technology, 2017. https://eprints.qut.edu.au/103528/1/Nasir_Hussain_Thesis.pdf.

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This research investigates the benefits of user cooperation in wireless communications systems. The dynamics of wireless cooperative communication systems are studied by a comprehensive study of two essential characteristics of cooperation, optimal relay selection criteria and practical channel estimation. A novel relay selection model based on realistic channel estimation is proposed and analysed. Furthermore, the gains are experimentally evaluated using a wireless communication testbed. The outcomes of this research reveal that incorporating cooperative techniques with an adaptive relay selection strategy into existing wireless communication can significantly reduce the required power and the impact of wireless channel impairments.

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Ahmed, Sabbir. "Performance of Multi-Channel Medium Access Control Protocol incorporating Opportunistic Cooperative Diversity over Rayleigh Fading Channel." Thesis, Blekinge Tekniska Högskola, Avdelningen för signalbehandling, 2006. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-6171.

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This thesis paper proposes a Medium Access Control (MAC) protocol for wireless networks, termed as CD-MMAC that utilizes multiple channels and incorporates opportunistic cooperative diversity dynamically to improve its performance. The IEEE 802.11b standard protocol allows the use of multiple channels available at the physical layer but its MAC protocol is designed only for a single channel. The proposed protocol utilizes multiple channels by using single interface and incorporates opportunistic cooperative diversity by using cross-layer MAC. The new protocol leverages the multi-rate capability of IEEE 802.11b and allows wireless nodes far away from destination node to transmit at a higher rate by using intermediate nodes as a relays. The protocol improves network throughput and packet delivery ratio significantly and reduces packet delay. The performance improvement is further evaluated by simulation and analysis.
sabbir@linuxmail.org

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Gaspar, Karina da Silveira. "Lideranças femininas em uma instituição financeira de natureza cooperativa: análise das condições que viabilizam as mulheres chegarem a cargos de liderança executiva." Universidade do Vale do Rio dos Sinos, 2016. http://www.repositorio.jesuita.org.br/handle/UNISINOS/5453.

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Este trabalho tem como principal objetivo analisar as condições que viabilizam às mulheres, que compõem a instituição financeira estudada, ocuparem cargos de alta liderança. A investigação foi realizada por meio de pesquisa qualitativa exploratória, através de 21 entrevistas feitas com homens e mulheres em cargos de liderança executiva e intermediária de um sistema de crédito cooperativo brasileiro, composto por 109 empresas. Após feitas as entrevistas, as mesmas foram analisadas com o uso do software NVivo11, além disso, foram feitas reuniões com a profissional responsável pelo tema diversidade na organização, bem como a análise documental, através de averiguação de relatórios. Os resultados da investigação demonstraram que atributos como credibilidade, empoderamento, gestão de pessoas, iniciativa e proatividade, performance, relacionamento e tomada de decisão, são indispensáveis às mulheres que desejam chegar a cargos de alta liderança, mas que essas ainda precisam vencer muitas barreiras impostas tanto na sociedade, como também na organização estudada, pois ainda encontramos situações de preconceito contra a mulher, além do um ambiente estrutura de trabalho não favorecerem a atração e permanência das mulheres em altos cargos de gestão. Os resultados também demonstraram que, devido a ser uma organização cooperativa, sua cultura favorece a inclusão das mulheres, já que traz em sua essência a questão da igualdade, mas alerta que o poder muito disseminado, também característico desse tipo de instituição, pode muitas vezes distorcer a base da cultura organizacional, através da aplicação de viés pessoal do líder. Observou-se que são praticadas ações de desenvolvimento pela organização e que essas são oferecidas de forma igualitária entre homens e mulheres, contudo, devido à necessidade de integração do gênero feminino aos postos de alta liderança, faz-se necessário a criação de medidas mais direcionadas, o que se acredita que o presente trabalho irá colaborar. Por fim, concluiu-se que as perspectivas de futuro para as mulheres que anseiam ocuparem cargos de liderança executiva são muito positivas, já que a organização demonstra o claro desejo de incluir as mulheres nos cargos estratégicos, contudo, é necessário que as mulheres tenham mais atitude, autoconfiança, perseverança e adequada qualificação profissional.
This research has the main objective analyze the conditions that enable women, who make up the studied financial institution, to achieve the top leadership positions. The research was conducted by an exploratory qualitative research through interviews with 21 men and women in executive and middle leadership positions of a Brazilian credit union system, composed of 109 companies. After making the interviews, these are analyzed with the use of NVivo11 software, in addition, meetings were held with the professional responsible for the theme of diversity in the organization, and document analysis through reports of investigation were made. Research results have shown that attributes such as reliability, empowerment, people management, initiative and proactivity, performance, relationships, decision-making, are essential to women who want to get to high leadership positions, but they still need to overcome many barriers imposed both in society and also in the studied organization, because we still find situations of prejudice against women, in addition to a working structure environment does not favor the attraction and retention of women in senior management positions. The results also showed that due to a cooperative organization, its culture promotes the inclusion of women, since it brings in its essence the question of equality, but warns that the very scattered power also characteristic of this type of institution, which can often sometimes distort the basis of organizational culture, through the application of personal leader bias. It was observed that are development actions undertaken by the organization, but that these are offered equitably between men and women, however, due to the need to integrate female to top leadership positions, it is necessary to create actions more directed, which it is believed that this work will contribute. Finally, it was concluded that the future prospects for women who crave occupy executive leadership positions are very positive, as the organization demonstrates a clear desire to include women in strategic positions, however, it is necessary that women have more attitude, confidence, perseverance and appropriate professional qualifications.

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UL, HAQ ANWAAR, and HAROON MALIK. "Cooperative Diversity and Power Consumption in Multi-hop WSN : Effects of node energy on Single Frequency Networks." Thesis, Mittuniversitetet, Avdelningen för informations- och kommunikationssystem, 2014. http://urn.kb.se/resolve?urn=urn:nbn:se:miun:diva-21564.

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At the present time, wireless sensor networks are becoming more and more common and energy consumption is a key factor in the deployment and maintenance of these networks. This thesis compares non-SFN multi-hop and a single frequency network (SFN) or cooperative diversity algorithms with respect to the energy consumed by the nodes. Since the nodes have limited power capacity it is extremely important to have an efficient algorithm. In addition, the behaviour of the network when SFN is employed must be studied and advice offered with regards to improvements in order to achieve preferential results. The effect on the network regarding macro diversity is positive but, the battery energy consumption is still higher and has a drainage effect on the network for simple multi-hop. The report will include background information regarding mobile ad-hoc networks and the relationship with cooperative diversity. It will also deal with how different algorithms affect the energy consumption in multi-hop networks. Simulations will also be presented in Matlab plots for two single frequency network scenarios against a simple multi-hop regarding node energy during the network discovery and decline. Results will include comparative figures which are followed by a discussion concerning the simulation results and its effects. The applications for wireless sensor networks include area monitoring, environmental monitoring, data logging, industrial monitoring, agriculture and the idea can additionally be used for wireless radio and TV distribution. The simulations have been conducted for cooperative diversity algorithms (SFN-A and SFN-D) against an algorithm which does not use cooperative diversity in Matlab. The node energy consumption is compared for both scenarios with regards to both network reachability and decline. The node power is analysed during the reachability of the network from the start to attaining 100% of the discovered network. During network decline, the behaviour of the node energy is studied for algorithms with SFN-A, SFN-D and non SFN. Also, the number of times node transmission occurs with regards to node discovery is also analysed.

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Chin, Yiyong. "Slotted cooperative communication in half duplex relay networks." Thesis, Queensland University of Technology, 2013. https://eprints.qut.edu.au/60551/1/Yiyong_Chin_Thesis.pdf.

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In cooperative communication systems, several wireless communication terminals collaborate to form a virtual-multiple antenna array system and exploit the spatial diversity to achieve a better performance. This thesis proposes a practical slotted protocol for cooperative communication systems with half-duplex single antennas. The performance of the proposed slotted cooperative communication protocol is evaluated in terms of the pairwise error probability and the bit error rate. The proposed protocol achieves the multiple-input single-output performance bound with a novel relay ordering and scheduling strategy.

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Hatefi, Atoosa. "Distributed Coding for Wireless Cooperative Networks." Thesis, Supélec, 2012. http://www.theses.fr/2012SUPL0015/document.

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Cette thèse est consacrée à l'étude théorique et à la conception pratique de schémas de codage conjoint réseau/canal adaptés à différents scénarii de communications dans les réseaux sans fil. Contrairement aux hypothèses conventionnelles retenues dans la littérature (accès multiple orthogonal, absence d'erreurs sur certains liens), les caractéristiques de diffusion et de superposition des signaux propres au canal radio et la présence d'évanouissements lents et de bruit sur tous les liens sont prises en compte dans la formulation du problème et exploitées. Différentes stratégies de coopération au niveau du ou des relais sont examinées et comparées. Le point commun entre toutes ces stratégies est que le système doit fonctionner même en absence de coopération. Seuls le ou les relais et la destination sont informés d'une coopération. Ni les sources, ni le ou les relais ne connaissent l'état du canal à l'émission. Le premier volet de la thèse porte sur le canal à accès multiple avec relais unique (slow fading MARC). Le problème du codage et décodage conjoint canal/réseau (JNCC/JNCD) est étudié sur un plan théorique et pratique. Différentes hypothèses au niveau de l'accès multiple (semi-orthogonal et non-orthogonal) et différents modes de fonctionnement du relais (half-duplex et full-duplex) sont envisagés. Une nouvelle stratégie de coopération adaptative (SDF pour selective decode and forward) est définie dans laquelle le relais calcule et retransmet une fonction déterministe des messages de sources qu'il a pu décoder sans erreur. Le ré-encodage, défini sur un corps fini (corps binaire), est également conçu de manière à assurer que la performance finale au niveau de la destination atteint bien un ordre de diversité 2. Le modèle de canal MARC est par la suite étendu à plusieurs relais (slow fading MAMRC). Une analyse théorique est conduite et des nouveaux schémas JNCC/JNCD permettant de s'approcher des limites théoriques sont décrits. Afin d'assurer la diversité pleine, nous proposons de combiner un codage canal binaire et un codage réseau non-binaire. Pour les deux types de canaux, nous montrons que l'interférence naturellement induite par la diffusion des signaux dans un environnement sans fil, n'est pas un inconvénient mais bien un avantage dès lors qu'on est en mesure de la traiter via des techniques de codage et de décodage sophistiquées (turbo codes et leur décodage, turbo détection). Les gains en termes de capacité (rapportée à une certaine probabilité de coupure) obtenus avec un accès multiple semi-orthogonal ou non-orthogonal sont substantiels comparés à un accès multiple orthogonal (référence). Dans la dernière partie de la thèse, la stratégie de coopération SDF est comparée à deux autres stratégies de coopération s'appuyant sur un procédé de décodage-et-retransmission "souple" (sans prise de décisions intermédiaires) : l'une basée sur les rapports logarithmiques de probabilité a posteriori sur les bits codés et l'autre basée sur l'estimation de l'erreur quadratique moyenne (MSE). Nous vérifions que la stratégie de coopération SDF fonctionne bien dans la plupart des configurations, les stratégies de coopération souples n'améliorant légèrement les performances que dans certains cas extrêmes
With the rapid growth of wireless technologies, devices and mobile applications, the quest of high throughput and ubiquitous connectivity in wireless communications increases rapidly as well. Relaying is undoubtedly a key concept to provide coverage extension and capacity increase in wireless networks. Network coding, which allows the intermediate nodes to share their computation capabilities in addition to their resource and their power, has grabbed a significant research attention since its inception in information theory. It has become an attractive candidate to bring promising performance improvement, especially in terms of throughput, in relay-based cellular networks. Substantial research efforts are currently focused on theoretical analysis, implementation and evaluation of network coding from a physical layer perspective. The question is, what is the most efficient and practical way to use network coding in wireless relay-based networks, and whether it is beneficial to exploit the broadcast and multiple-access properties of the wireless medium to perform network coding. It is in such a context, that this thesis proceeds. In the first part of the thesis, the problem of Joint Network-Channel Coding (JNCC) for a Multiple Access Relay Channel (MARC) is investigated in the presence of multiple access interferences and for both of the relay operating modes, namely, half-duplex and full-duplex. To this end, three new classes of MARC, referred to as Half-Duplex Semi-Orthogonal MARC (HD-SOMARC), Half-Duplex Non-Orthogonal MARC (HD-NOMARC), and Full-Duplex Non-Orthogonal MARC (FD-NOMARC) have been introduced and studied. The relaying function in all of the classes is based on a Selective Decode-and-Forward (SDF) strategy, which is individually implemented for each source, i.e, the relay forwards only a deterministic function of the error-free decoded messages. For each class, an information-theoretic analysis is conducted, and practical coding and decoding techniques are proposed. The proposed coding schemes, perform very close to the outage limit for both cases of HD-SOMARC and HD-NOMARC. Besides, in the case of HD-NOMARC, the optimal allocation of the transmission time to the relay is considered. It is also verified that exploiting multiple access interferences, either partially or totally, results in considerable gains for MARC compared to the existing interference-avoiding structures, even in the case of single receive antenna. In the second part of the thesis, the network model is extended by considering multiple relays which help multiple sources to communicate with a destination. A new class of Multiple Access Multiple Relay Channel (MAMRC), referred to as Half-Duplex Semi-Orthogonal MAMRC (HD-SOMAMRC) is then proposed and analyzed from both information theoretic and code design perspective. New practical JNCC schemes are proposed, in which binary channel coding and non binary network coding are combined, and they are shown to perform very close to the outage limit. Moreover, the optimal allocation of the transmission time to the sources and relays is considered. Finally, in the third part of the thesis, different ways of implementing cooperation, including practical relaying protocols are investigated for the half-duplex MARC with semi-orthogonal transmission protocol and in the case of JNCC. The hard SDF approach is compared with two Soft Decode and Forward (SoDF) relaying functions: one based on log a posterior probability ratios (LAPPRs) and the other based on Mean Square Error (MSE) estimate. It is then shown that SDF works well in most of the configurations and just in some extreme cases, soft relaying functions (based on LAPPR or MSE estimate) can slightly outperform the hard selective one

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Alabed, Samer [Verfasser], Marius [Akademischer Betreuer] Pesavento, and Babak [Akademischer Betreuer] Khalaj. "Computationally Efficient Spatial and Cooperative Diversity Techniques for Wireless Communication Networks / Samer Alabed. Betreuer: Marius Pesavento ; Babak Khalaj." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2012. http://d-nb.info/1106115503/34.

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Yu, Hyungseok. "Performance of cooperative relaying systems with co-channel interference." Diss., Georgia Institute of Technology, 2012. http://hdl.handle.net/1853/45744.

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The cooperative relaying scheme is a promising technique for increasing the capacity and reliability of wireless communication. Even though extensive research has performed in information theoretical aspect, there are still many unresolved practical problems of cooperative relaying system. This dissertation analyzes the performance of cooperative decode-and-forward (DF) relaying systems in the presence of multiple interferers and improve network throughput for these systems. We propose and summarize various systems in the view of network topology, transmission structure, and slot allocation. We present closed-form expressions for the end-to-end outage probability, average symbol-error-probability, average packet-error-probability, and network throughput of the proposed systems. This dissertation shows that the robustness of the destination against interference is more important than robustness of the relay against interference from an interference management perspective, and increasing the number of branches yields better outage and error performance improvements against shadowing than increasing the number of hops. In cellular networks, the cooperative diversity systems can outperform the dual-Rx antenna system, but only when the relay is located in a relatively small portion of the total cell area with respect the the destination mobile terminal. The results also show that since the effective regions of the uplink and the downlink do not overlap, different relays should be utilized for cell sectorization in the uplink and the downlink. Finally, the proposed variable-slot selection DF scheme can reduce the system complexity and make the maximum throughput point in the low and moderate signal-to-interference-plus-noise ratio region.

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King, Thelma C. "Post-secondary students' and work-site supervisors' perceptions of diversity experiences and needs of students in a school-to-work transition program." Diss., This resource online, 1995. http://scholar.lib.vt.edu/theses/available/etd-06062008-162247/.

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Liu, Qijia. "Power efficiency and diversity issues for peak power constrained wireless communications." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34829.

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Along with the rapidly increasing demand for high data rate communications, orthogonal frequency division multiplexing (OFDM) has become a popular modulation in current and future communication standards. By distributing a high-speed data stream to many parallel low-rate data streams, OFDM is able to mitigate the detrimental effects of multipath fading using simple one-tap equalizers and achieve high spectral efficiency. However, the OFDM signal waveform suffers from large envelop variations, which are usually measured by the peak-to-average power ratio (PAR). In wireless transmitters, many RF components, especially the power amplifiers, are inherently nonlinear and peak power constrained. Therefore, low power efficiency and/or severe nonlinear distortions are the main shortcomings of OFDM systems. In this dissertation, we develop algorithms and analyze performance bounds for peak power constrained wireless communications. To address the balance between power efficiency and nonlinear distortions, we model the peak power constrained OFDM systems in both statistical and deterministic manners. We first propose an error vector magnitude (EVM) optimization algorithm to strictly satisfy the distortion requirements in accordance with communication standards and provide the maximum power efficiency for OFDM transmitters without receiver-side cooperations. Moreover, we develop a multi-channel partial transmit sequence (MCPTS) PAR reduction method for OFDM-based frequency-division multiple access (OFDM-FDMA) multiuser systems, which can achieve significant power efficiency improvement without using side information. Joint MCPTS and power allocation schemes are also proposed to improve the error performance of OFDM-FDMA systems. Furthermore, diversity-enabled communication systems have practical merits in combating channel fadings. Therefore, in the second part of this dissertation, peak power constrained diversity techniques are proposed. The error performance of peak power constrained single-input multiple-output (SIMO) OFDM is studied. Several low-complexity SIMO-OFDM transceiver designs are presented to collect full antenna diversity with respective performance and complexity tradeoffs. The next major piece of work in this dissertation addresses the design of peak power constrained amplify-and-forward (AF) cooperative networks, which enable the cooperative diversity with single-antenna terminals. The effects of the availability of channel state information and the peak power constraint on the diversity performance are theoretically studied. Design criteria for general diversity-enabled AF relaying strategies are established and further applied to the designs in peak power constrained networks. In the end, a general theorem that relates the diversity gain function with the probability density function of instantaneous signal-to-noise ratio is derived and used to analyze the diversity performance of relay selection schemes.

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Baleshan, Tharunie. "Analysis of distributed beamforming in cooperative communications network with phase shifter based smart antenna nodes." Thesis, Queensland University of Technology, 2015. https://eprints.qut.edu.au/84539/1/Tharunie_Baleshan_Thesis.pdf.

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This research study investigates the application of phase shifter-based smart antenna system in distributed beamforming. It examines the way to optimise the transmit power by jointly maximising the directivity of the array antennas and the weight vector for distributed beamforming. This research study concludes that maximising directivity can lead to better transmit power minimisation compared to maximising field intensity. This study also concludes that signal to noise power ratio maximisation subject to a power constraint and power minimisation subject to a signal to noise power ratio constraint yield the same results.

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Crow, Jacob, and Kim Jaeglin. "Cross cultural group projects in higher education and its effects on business school students : A mixed method study of students and young professionals in the business field." Thesis, Linköpings universitet, Företagsekonomi, 2020. http://urn.kb.se/resolve?urn=urn:nbn:se:liu:diva-166753.

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The purpose of this research is to improve the understanding of challenges encountered by students when conducting groupwork and more specifically cross-cultural groupwork; which in turn helps with identifying structural flaws in the way cooperative learning is organized in student groups. More specifically, this study aims at identifying the challenges and opportunities inherent to student group work in order to develop a framework allowing schools and universities to improve the way their structure this exercise. The objective is to find a way for students to experience group work almost as they would in a company in order to teach them key employability skills which are highly valued in the workplace. This study focuses on students and young professionals who had international experiences since both groups can provide insightful information on the challenges and opportunities related to cross-cultural group work. Overall, this paper contributes to better understand the challenges inherent to student group works which stem from motivational issues caused by disruptive behaviours. After explaining why these behaviours are specific to a student environment, we identified the structuration of cooperative learning among the studied organisation as being the main cause for these challenges faced by students. Our contribution then was to provide a new framework for student group work based on Smith’s 5 essential elements to properly structure cooperative learning. We also created a comparative table illustrating the main differences between conducting group work in a company and in a school which professional can use to better understand why students do not always know how to be good in group work. Two frameworks were produced, one is to be used by schools to better structure group work and limit the chances of disruptive behaviour while nurturing skills valuable in the workplace. The second framework provides insights as to why young professionals do not always know how to effectively work in groups even if they experienced it as students.

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Melo, Marco Antonio Beserra de. "Diversidade multiusuÃrio em sistemas cooperativos com mÃltiplos relays: um esquema de seleÃÃo eficiente e de baixa complexidade." Universidade Federal do CearÃ, 2012. http://www.teses.ufc.br/tde_busca/arquivo.php?codArquivo=9400.

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FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
Nesse trabalho, propÃe-se um esquema de seleÃÃo eficiente e de baixa complexidade para redes cooperativas multiusuÃrio multi-relay compostas de um nÃ fonte, L nÃs destinos e N nÃs relays. O esquema proposto primeiro seleciona o melhor destino baseado na qualidade de canal dos links diretos e entÃo seleciona o melhor relay que provÃ o melhor caminho da fonte para o destino selecionado. Considerando-se os protocolos de cooperaÃÃo decodifica-e-encaminha e amplifica-e-encaminha, o desempenho do sistema Ã investigado. ExpressÃes em forma fechada para a probabilidade de bloqueio sÃo obtidas e validadas por simulaÃÃes de Monte Carlo. ComparaÃÃes com o esquema de seleÃÃo Ãtimo sÃo realizadas e demonstram que o desempenho do esquema de seleÃÃo proposto Ã bem prÃximo ao do esquema Ãtimo, com a vantagem de o primeiro possuir uma complexidade menor que o Ãltimo. AlÃm disso, em nossa anÃlise, a fonte pode ser equipada com uma Ãnica antena ou com M mÃltiplas antenas. Uma anÃlise assintÃtica Ã realizada e revela que, independentemente da estratÃgia de cooperaÃÃo empregada, a ordem de diversidade Ã de L+N para o caso da fonte com uma Ãnica antena, enquanto que para o caso multiantena a diversidade Ã igual a ML+N. Os efeitos do nÃmero de nÃs relays e destinos no desempenho do sistema e sua influÃncia na posiÃÃo Ãtima do relay sÃo examinados. AlÃm disso, um compromisso entre desempenho e eficiÃncia espectral Ã observado para o caso em que mÃltiplas antenas sÃo empregadas.
On this work, it is proposed an efficient low-complexity selection scheme for multiuser multi-relay downlink cooperative networks comprised of one source node, L destination nodes, and N relay nodes. The proposed scheme first selects the best destination node based on the channel quality of the direct links and then selects the best relay that yields the best path from the source to the selected destination. Assuming both decode-and-forward and amplify-and-forward relaying strategies, the performance of the considered system is investigated. Closed-form expressions for the outage probability are obtained and validated by means of Monte Carlo simulations. Comparisons with the optimal selection scheme are performed and shows that the performance of the proposed scheme is very close to that of the optimal selection scheme, with the proposed scheme having the advantage of lower complexity than the optimal scheme. Furthermore, in our analysis, the source node may be equipped with either a single antenna or M multiple antennas. An asymptotic analysis is carried out, and it reveals that, regardless of the relaying strategy employed, the diversity order reduces to L+N for the single-antenna source case, whereas it is equal to ML+N for the multiple-antenna source case. The effects of the number of relay and destination nodes on the system performance and its influence on the best relay position are examined. In addition, a trade-off concerning the system performance and spectral efficiency is observed when multiple antennas are employed at the source node.

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Erasmus, Wilma. "Exploring quality and diversity : the role of the teacher in a class of diverse learners." Diss., University of Pretoria, 2011. http://hdl.handle.net/2263/27821.

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The advent of democracy has witnessed radical changes in the demographic constitution of the learner population in schools. Many teachers now encounter classes that comprise learners from diverse racial, ethnic, religious and language backgrounds. How do these teachers ensure quality education in such a class of diverse learners? Accordingly, this research study set out to explore quality and diversity in a class of diverse learners with particular emphasis on the role of the teacher. The meta-theoretical paradigm that directed it was a combination of constructivism and interpretivism. The methodological paradigm employed a qualitative mode of inquiry and various sampling techniques to select the participants. Convenience sampling was used to select three schools, two classes per school and five learners per teacher, while purposive sampling were used to select two teachers per school. A mix of instruments was used to collect the data, such as semistructured interviews, observations, field notes and a researcher journal. Findings from this study were fivefold. First, the training that teachers received with regard to diversity is insufficient and does not prepare them to teach a class of diverse learners. Second, the role of the teacher is complex and requires them to fulfil more than one role at a time; even though some roles are neglected, the majority of teachers focus on the role of facilitator. More emphasis should be placed on the importance of the roles and how they can contribute to quality in education. Third, teachers must follow an asset-based approach in a class of diverse learners. By using difference as a resource and an asset, teachers will be able to encourage open class discussions, involve learners in the lesson, keep their attention and use this to promote their understanding about complex topics and terms. Fourth, teachers have to make certain adjustments to their teaching style to accommodate diverse learners. It is important for all teachers to examine their own attitudes towards teaching diverse learners in order to provide the best education possible. Finally, certain quality assurance methods are in place at schools, but just how appropriate they are is debatable. New approaches must be developed and utilized to meet the needs of the current social context in South Africa to ensure that quality teaching takes place at schools.
Dissertation (MEd)--University of Pretoria, 2011.
Science, Mathematics and Technology Education
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Phan, Hoc. "Performance Assessment of Cooperative Relay Networks with Advanced Radio Transmission Techniques." Doctoral thesis, Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation, 2013. http://urn.kb.se/resolve?urn=urn:nbn:se:bth-00549.

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In the past decade, cooperative communications has been emerging as a pertinent technology for the current and upcoming generations of mobile communication infrastructure. The indispensable benefits of this technology have motivated numerous studies from both academia and industry on this area. In particular, cooperative communications has been developed as a means of alleviating the effect of fading and hence improve the reliability of wireless communications. The key idea behind this technique is that communication between the source and destination can be assisted by several intermediate nodes, so-called relay nodes. As a result, cooperative communication networks can enhance the reliability of wireless communications where the transmitted signals are severely impaired because of fading. In addition, through relaying transmission, communication range can be extended and transmit power of each radio terminal can be reduced as well. The objective of this thesis is to analyze the system performance of cooperative relay networks integrating advanced radio transmission techniques and using the two major relaying protocols, i.e., decode-and-forward (DF) and amplify-and-forward (AF). In particular, the radio transmission techniques that are considered in this thesis include multiple-input multiple-output (MIMO) systems and orthogonal space-time block coding (OSTBC) transmission, adaptive transmission, beamforming transmission, coded cooperation, and cognitive radio transmission. The thesis is divided into an introduction section and six parts based on peer-reviewed journal articles and conference papers. The introduction provides the readers with some fundamental background on cooperative communications along with several key concepts of cognitive radio systems. In the first part, performance analysis of cooperative single and multiple relay networks using MIMO and OSTBC transmission is presented wherein the diversity gain, coding gain, outage probability, symbol error rate, and channel capacity are assessed. It is shown that integrating MIMO and OSTBC transmission into cooperative relay networks provides full diversity gain. In the second part, the performance benefits of MIMO relay networks with OSTBC and adaptive transmission strategies are investigated. In the third part, the performance improvement with respect to outage probability of coded cooperation applied to opportunistic DF relay networks over conventional cooperative networks is shown. In the fourth part, the effects of delay of channel state information feedback from the destination to the source and co-channel interference on system performance is analyzed for beamforming AF relay networks. In the fifth part, cooperative diversity is investigated in the context of an underlay cognitive AF relay network with beamforming. In the sixth part, finally, the impact of the interference power constraint on the system performance of multi-hop cognitive AF relay networks is investigated.

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Alotaibi, Faisal T. "Distributed space-time block coding in cooperative relay networks with application in cognitive radio." Thesis, Loughborough University, 2012. https://dspace.lboro.ac.uk/2134/10965.

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Spatial diversity is an effective technique to combat the effects of severe fading in wireless environments. Recently, cooperative communications has emerged as an attractive communications paradigm that can introduce a new form of spatial diversity which is known as cooperative diversity, that can enhance system reliability without sacrificing the scarce bandwidth resource or consuming more transmit power. It enables single-antenna terminals in a wireless relay network to share their antennas to form a virtual antenna array on the basis of their distributed locations. As such, the same diversity gains as in multi-input multi-output systems can be achieved without requiring multiple-antenna terminals. In this thesis, a new approach to cooperative communications via distributed extended orthogonal space-time block coding (D-EO-STBC) based on limited partial feedback is proposed for cooperative relay networks with three and four relay nodes and then generalized for an arbitrary number of relay nodes. This scheme can achieve full cooperative diversity and full transmission rate in addition to array gain, and it has certain properties that make it alluring for practical systems such as orthogonality, flexibility, low computational complexity and decoding delay, and high robustness to node failure. Versions of the closed-loop D-EO-STBC scheme based on cooperative orthogonal frequency division multiplexing type transmission are also proposed for both flat and frequency-selective fading channels which can overcome imperfect synchronization in the network. As such, this proposed technique can effectively cope with the effects of fading and timing errors. Moreover, to increase the end-to-end data rate, this scheme is extended for two-way relay networks through a three-time slot framework. On the other hand, to substantially reduce the feedback channel overhead, limited feedback approaches based on parameter quantization are proposed. In particular, an optimal one-bit partial feedback approach is proposed for the generalized D-O-STBC scheme to maximize the array gain. To further enhance the end-to-end bit error rate performance of the cooperative relay system, a relay selection scheme based on D-EO-STBC is then proposed. Finally, to highlight the utility of the proposed D-EO-STBC scheme, an application to cognitive radio is studied.

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Wu, Victor Kai Yuen. "OFDM-based cooperative communications in a single path relay network and a multiple path relay network." Thesis, Available online, Georgia Institute of Technology, 2006, 2006. http://etd.gatech.edu/theses/available/etd-11092006-152421/.

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Loch, Navarro Adrian Carlos [Verfasser], Matthias [Akademischer Betreuer] Hollick, Jon [Akademischer Betreuer] Crowcroft, and Joerg [Akademischer Betreuer] Widmer. "Enabling Efficient, Robust, and Scalable Wireless Multi-Hop Networks: A Cross-Layer Approach Exploiting Cooperative Diversity / Adrian Carlos Loch Navarro. Betreuer: Matthias Hollick ; Jon Crowcroft ; Joerg Widmer." Darmstadt : Universitäts- und Landesbibliothek Darmstadt, 2015. http://d-nb.info/1111112797/34.

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Kailas, Aravind. "Toward perpetual wireless networks: opportunistic large arrays with transmission thresholds and energy harvesting." Diss., Georgia Institute of Technology, 2010. http://hdl.handle.net/1853/34720.

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Solving the key issue of sustainability of battery-powered sensors continues to attract significant research attention. The prevailing theme of this research is to address this concern using energy-efficient protocols based on a form of simple cooperative transmission (CT) called the opportunistic large arrays (OLAs), and intelligent exploitation of energy harvesting and hybrid energy storage systems (HESSs). The two key contributions of this research, namely, OLA with transmission threshold (OLA-T) and alternating OLA-T (A-OLA-T), offer an signal-to-noise ratio (SNR) advantage (i.e., benefits of diversity and array (power) gains) in a multi-path fading environment, thereby reducing transmit powers or extending range. Because these protocols do not address nodes individually, the network overhead remains constant for high density networks or nodes with mobility. During broadcasting across energy-constrained networks, while OLA-T saves energy by limiting node participation within a single broadcast, A-OLA-T optimizes over multiple broadcasts and drains the the nodes in an equitable fashion. Another important contribution of this research is the design and analysis of a novel routing metric called communications using HESS (CHESS), which extends the rechargeable battery (RB)-life by relaying exclusively with supercapacitor (SC) energy, and is asymptotically optimal with respect to the number of nodes in the network.

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Liu, Lingfeng. "Cooperative wireless channel characterization and modeling: application to body area and cellular networks." Doctoral thesis, Universite Libre de Bruxelles, 2012. http://hdl.handle.net/2013/ULB-DIPOT:oai:dipot.ulb.ac.be:2013/209722.

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Cooperative wireless communication is an attractive technique to explore the spatial channel resources by coordination across multiple links, which can greatly improve the communication performance over single links. In this dissertation, we study the cooperative multi-link channel properties by geometric approaches in body area networks (BANs) and cellular networks respectively.

In the part of BANs, the dynamic narrowband on-body channels under body motions are modeled statistically on their temporal and spatial fading based on anechoic and indoor measurements. Common body scattering is observed to form inter-link correlation between links closely distributed and between links having synchronized movements of communication nodes. An analytical model is developed to explain the physical mechanisms of the dynamic body scattering. The on-body channel impacts to simple cooperation protocols are evaluated based on realistic measurements.

In the part of cellular networks, the cluster-level multi-link COST 2100 MIMO channel model is developed with concrete modeling concepts, complete parameterization and implementation methods, and a compatible structure for both single-link and multi-link scenarios. The cluster link-commonness is introduced to the model to describe the multi-link properties. The multi-link impacts by the model are also evaluated in a distributed MIMO system by comparing its sum-rate capacity at different ratios of cluster link-commonness.
Doctorat en Sciences de l'ingénieur
info:eu-repo/semantics/nonPublished

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Dissertations / Theses on the topic 'Cooperative diversity'

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