Rozprawy doktorskie na temat „Cooperative Relaying Systems”

Cooperative relaying techniques have recently received significant interests from both academia and industry due to their ability to provide spatial diversity to address the ever increasing demand for extended network coverage, higher data rates without sacrificing extra power resources, greater mobility and enhanced reliability. This thesis mainly considers two themes. Firstly, in the context of self-powered multiple-input-multiple-output (MIMO) full-duplex (FD) relaying, our research focuses on design and performance analysis of MIMO FD relaying systems in the presence of practical transmission impairments. Namely, the impact of spatial fading correlation, imperfect channel state information (CSI), loopback self-interference (LI), and co-channel interference (CCI) on the system performance are investigated. Secondly, in the context of wirelessly-powered MIMO HD relaying, our research focuses on energy beamforming which is used to maximize the overall harvested energy so as to enable longer-distance wireless power transfer when compared to the single antenna nodes. Namely, in the presence of MIMO relaying systems, hop-by-hop information and energy beamforming is proposed where the transmitted signal is steered along the strongest eigenmode of each hop. The wirelessly powered relay scavenge energy from the source information radio-frequency (RF) signal through energy beamforming, where both the time-switching receiver (TSR) and power-splitting receiver (PSR) are considered, then uses the harvested energy to forward the source message to the destination. Our research focuses on developing a comprehensive analytical framework for deriving new closed-form expressions for the outage probability and ergodic capacity for amplify-and-forward (AF) relaying systems, including simpler tight bounds and asymptotic high signal-to-noise (SNR) ratio analysis. First, the optimization problem for the design of source, relay, and destination precoding and/or decoding weight vectors which maximizes the overall signal-to-interference-plus-noise ratio (SINR) is formulated. Then, in order to get closed-form precoding and decoding weight vectors, a sub-optimal solution based on null space projection designed to completely suppress the LI and/or CCI is proposed, through which a closed-form overall SINR is presented. Simulation results show the exactness and tightness of the proposed exact and bound analytical expressions, respectively.

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.

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.

XIMENES, L. R. Tensor-based MIMO relaying communication systems. 2015. 134 f. Tese (Doutorado em Engenharia de Teleinformática) – Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2015.
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In cooperative communication systems, two or more transmitting terminals are combined to increase the diversity and/or the power of the signals arriving at a particular receiver. Therefore, even if the devices do not have more than one antenna, or if a significant propaga- tion loss is present between the two communicating nodes, the various transmitting elements can act as a virtual antenna array, thus obtaining the benefits of the multiple antenna (MIMO) systems, especially the increase in the capacity. Recently, tensor decompositions have been introduced as an efficient approach for channel estimation in cooperative com- munication systems. However, among the few works devoted to this task, the utilization of the PARAFAC tensor decomposition for modeling the received signals did not allow the development of techniques for joint symbol and channel estimation. Aiming to avoid the use of pilot sequences, which limits the overall spectral efficiency by dedicating a portion of the bandwidth only for the channel estimation task, the objective of this thesis is to provide new tensor-based strategies, including transmission systems and semi-blind receivers, for one-way two-hop MIMO relaying systems. Based on a Khatri-Rao space-time coding at the source and two different Amplify-and-Forward (AF) relaying strategies, two transmission schemes are proposed. For these systems, named PT2-AF and NP-AF, the received signals at the destination node follow respectively a PARATUCK2 and a nested PARAFAC tensor model. Exploiting uniqueness properties of these tensor models which are established in the thesis, several semi-blind receivers are derived. Some of these receivers are of iterative form us- ing an ALS algorithm, whereas some other ones have closed-form solutions associated with Khatri-Rao factorizations. Some simulation results are finally presented to illustrate the per- formance of the proposed receivers which are compared to some state-of-the-art supervised techniques
Em comunicações cooperativas, dois ou mais terminais de transmissão são combinados para aumentar a diversidade e/ou a potencia dos sinais que chegam a um determinado receptor. Portanto, mesmo que os dispositivos não disponham de mais de uma antena, ou que então haja uma grande perda por propagação entre dois pontos comunicantes, os diversos elementos transmissores podem atuar como um arranjo virtual de antenas, obtendo-se assim vantagens dos sistemas de múltiplas antenas (MIMO), sobretudo o aumento da capacidade de transmissão. Recentemente, a chamada analise tensorial tem se mostrado uma abordagem eficiente então para a estimação de canais em sistemas com diversidade cooperativa. Contudo, nos poucos trabalhos dedicados a essa tarefa, a utilização da decomposição tensorial PARAFAC para a modelagem dos sinais recebidos não possibilitou o desenvolvimento de técnicas de estimação conjunta de canais e símbolos. Com a idéia de se evitar o uso de sequencias de treinamento, que limita a eficiência espectral da transmissão por dedicar uma parte da largura de banda apenas para a tarefa de estimação dos canais, o objetivo desta tese é prover novas estratégias de comunicação, em termos de sistemas de transmissão e receptores semi-cegos, baseados em tensores adaptados a sistemas cooperativos MIMO unidirecionais de dois saltos. Dois sistemas de transmissão são propostos utilizando uma codificação espaço-temporal do tipo Khatri-Rao na fonte e duas estrategias de processamento Amplify-and-Forward (AF) no relay. Para estes sistemas, nomeados PT2-AF e NP-AF, os sinais recebidos no chamado nó de destino satisfazem os modelos tensoriais do tipo PARATUCK2 e Nested PARAFAC. Explorando as propriedades de unicidade destes modelos tensoriais estabelecidas nesta tese, vários receptores semi-cegos são derivados. Alguns destes receptores são do tipo ALS, enquanto outros são de soluções baseadas na factorização de produtos de Khatri-Rao. Resultados de simulação são apresentados para ilustrar os desempenhos dos receptores propostos em comparação a alguns estimadores supervisionados

Abstract The thesis concentrates on evaluating and improving performances of various multiple-input multiple-output (MIMO) relaying scenarios that are particularly relevant to future wireless systems. A greater emphasis is placed on important practical situations, considering relay deployments, availability of channel state information (CSI), limitations of spectrum, and information secrecy. Initially, the performance of a non-coherent amplify-and-forward (AF) MIMO relaying is analyzed when the relay is deployed with the relay-to-destination channel having a line-of-sight (LoS) path. The main attention is given to analyzing the performance of orthogonal space-time block coded based non-coherent AF MIMO system. Exact expressions of statistical parameters and performance metrics are derived considering the instantaneous signal-to-noise ratio (SNR) received at the destination. These performance metrics reveal that a strong LoS component in relay-destination channel always limits the performance promised by MIMO scattering environment when both nodes have multiple antennas. The thesis also considers scenarios in MIMO two-way relaying (TWR) with physical layer network coding (PNC) mapping at the relay. PNC mapping becomes complex with multiple streams being combined at the relay node. Joint precoder-decoder schemes are considered to ease this, and various studies are carried out depending on the CSI. The zero-forcing criterion is used at the nodes when perfect CSI is available. For the imperfect CSI scenario, a robust joint precoder-decoder design is considered. The precoder and decoder matrices are obtained by solving optimization problems, which are formulated to maximize sum-rate and minimize weighted mean square error (WMSE) under transmit power constraints on the nodes. Next, a precoder-decoder scheme for MIMO underlay device-to-device (D2D) communication system is investigated by considering two D2D modes; PNC based D2D and direct D2D. The joint design is based on minimizing mean square error (MSE) which is useful to mitigate interference, and to improve the performance of both D2D and cellular communications. Distributed and centralized algorithms are proposed considering bi-directional communication in both D2D and cellular communications. System performance is discussed with two transmit mode selection schemes as dynamic and static selection schemes. The results show that the PNC based D2D mode extends the coverage area of D2D communication. Finally, secure beamforming schemes for the PNC based MIMO TWR systems are investigated when multiple eavesdroppers are attempting to intercept the user information. The CSI of the user-to-eavesdropper channels is imperfect at the users. The channel estimation errors are assumed with both ellipsoidal bound and Gaussian Markov uncertainty models. Robust optimization problems are formulated considering both scenarios to design beamforming vectors at the users and relay. Numerical results suggest that the proposed algorithms converge fast and provide higher security
Tiivistelmä Tässä väitöskirjassa keskitytään arvioimaan ja parantamaan suorituskykyä useissa moniantennitoistinjärjestelmissä, jotka ovat ajankohtaisia tulevaisuuden langattomissa verkoissa. Erityisesti työssä analysoidaan tärkeitä käytännön tilanteita, sisältäen toistimien sijoittamisen, kanavatiedon saatavuuden, rajoitetun taajuuskaistan ja tiedon salauksen. Aluksi epäkoherentin, vahvistavan ja jatkolähettävän moniantennitoistimen suorituskykyä analysoidaan tilanteessa, jossa toistin on sijoitettu siten, että kohteeseen on suora yhteys. Suorituskyvyn arvioinnin pääkohteena on ortogonaalinen tila-aika-tason lohkokoodattu epäkoherentti vahvistava ja jatkolähettävä moniantennitoistin. Työssä johdetaan tarkat lausekkeet tilastollisille parametreille ja suorituskykymittareille ottaen huomioon hetkellinen signaalikohinasuhde vastaanottimessa. Nämä suorituskykymittarit ilmaisevat, että toistimen ja kohteen välillä oleva vahva suoran yhteyden komponentti rajoittaa sitä suorituskykyä, jota moniantennijärjestelmän hajontaympäristö ennustaa. Työssä tutkitaan myös kahdensuuntaisia moniantennitoistimia, jotka käyttävät fyysisen kerroksen verkkokoodausta. Koodauksesta tulee monimutkaista, kun monia datavirtoja yhdistetään toistimessa. Tämän helpottamiseksi käytetään yhdistettyä esikoodaus-dekoodausmenetelmää, jota tutkitaan erilaisten kanavatietojen tapauksissa. Täydellisen kanavatiedon tapauksessa käytetään nollaanpakotuskriteeriä. Epätäydellisen kanavatiedon tapauksessa käytetään robustia yhdistettyä esikoodaus-dekoodausmenetelmää. Esikoodaus- ja dekoodausmatriisit saadaan ratkaisemalla optimointiongelmat. Nämä ongelmat on muodostettu maksimoimaan summadatanopeus, ja minimoimaan painotettu keskineliövirhe, kun optimointirajoitteina ovat solmujen lähetystehot. Seuraavaksi esikoodaus-dekoodausmenetelmää tutkitaan moniantennijärjestelmässä, jossa käytetään kahdentyyppistä laitteesta-laitteeseen (D2D) kommunikaatiomenetelmää: fyysisen kerroksen verkkokoodaukseen pohjautuvaa D2D- ja suoraa D2D-kommunikaatiota. Yhteissuunnittelu perustuu keskineliövirheen minimointiin, joka on hyödyllistä, kun halutaan vähentää häiriötä ja parantaa molempien verkkojen suorituskykyä. Työssä ehdotetaan hajautettuja ja keskitettyjä algoritmeja tilanteessa, jossa käytetään kaksisuuntaista kommunikaatiota molemmissa verkoissa. Järjestelmän suorituskykyä arvioidaan, kun käytetään kahta eri lähetystilan valintaa, dynaamista ja staattista. Tulokset osoittavat, että fyysisen kerroksen verkkokoodaukseen pohjautuva D2D kasvattaa D2D-kommunikaatiojärjestelmän kantamaa. Lopuksi, turvallisia keilanmuodostustekniikoita arvioidaan fyysisen kerroksen verkkokoodaukseen pohjautuvassa kahdensuuntaisessa moniantennitoistinjärjestelmässä, kun useat salakuuntelijat yritävät siepata käyttäjätiedon. Käyttäjillä on epäideaalinen kanavatieto heidän ja salakuuntelijoiden välisten linkkien kanavista. Kanavatiedon estimointivirheitä arvioidaan ellipsoidisella ja Gauss-Markov-epävarmuusmallilla. Robustit optimointiongelmat, joissa suunnitellaan keilanmuodostusvektorit käyttäjän ja toistimen välille, muodostetaan molemmille malleille. Numeeriset tulokset osoittavat, että ehdotetut algoritmit konvergoituvat nopeasti ja tarjoavat korkeamman turvallisuuden

This thesis describes the use of a multi-amplitude minimum shift keying (MAMSK) signal in various types of wireless communication system. A MAMSK signal is a bandwidth efficient modulation scheme obtained by superimposing ℳ minimum shift keying (MSK) signals with unequal amplitudes. The overall phase of a MAMSK signal is controlled by the phase of the largest component MSK signal which allows the use of a low-complexity differential detector. A closed form expression for the average bit error rate (BER) for coherent detection of an MAMSK in AWGN is derived and is shown to achieve the same BER as that of square constellation quadrature amplitude modulation (QAM) with the same average transmit power. We describe the design and implementation of a STBC-based MIMO radio system in conjunction with MAMSK modulation. The proposed system provides high capacity data transmission by carrying information not only in the phases but also in the amplitude. Despite using a simple MAMSK differential receiver the system achieves performance within 1 dB of coherent detection. The existing MSK modems in conjunction with STBC could easily be modified to construct the proposed system. The MAMSK modulation scheme is extended to a multiuser relaying network where two nodes cooperate in a half-duplex environment to achieve diversity gain. The cooperative scheme is based on superposition modulation using a decode-and-forward (DF) strategy. In the proposed scheme, each node simultaneously transmits its own and the relayed signals by superimposing one on the other. A MAMSK signal is an excellent choice for this type of cooperative communication due its being obtained by a superposition technique. The proposed system exploits the overall phase of a MAMSK signal which allows differential detection and as a result it provides the lowest decoding complexity and memory requirements among the existing superposition based cooperation schemes. The performance of the system is evaluated by simulation, where it is shown that the MAMSK cooperative system outperforms a conventional DF scheme in terms of both power and bandwidth efficiency.

The demand for ever larger, more efficient, reliable and cost effective communication networks necessitates new network architectures, such as wireless ad hoc networks, cognitive radio, relaying networks, and wireless sensor networks. The study of such networks requires a fundamental shift from thinking of a network as a collection of independent communication pipes, to a multi-user channel where users cooperate via conferencing, relaying, and joint source-channel coding. The traditional centralized networks, such as cellular networks, include a central controller and a fixed infrastructure, in which every node communicates with each other via a centralized based station (BS). However, for a decentralized network, such as wireless ad hoc networks and wireless sensor networks, there is no infrastructure support and no central controllers. In such multi-user wireless networks, the scheduling algorithm plays an essential role in efficiently assigning channel resources to different users for better system performance, in terms of system throughput, packet-delay, stability and fairness. In this dissertation, our main goal is to develop practical scheduling algorithms in wireless ad hoc networks to enhance system performance, in terms of throughput, delay and stability. Our dissertation mainly consists of three main parts. First, we identify major challenges intrinsic to ad hoc networks that affect the system performance, in terms of throughput limits, delay and stability condition. Second, we develop scheduling algorithms for wireless ad hoc networks, with various considerations of non-cooperative relays and cooperative relays, fixed-rate transmission and adaptive-rate transmission, full-buffer traffic model and finite-buffer traffic model. Specifically, we propose an opportunistic scheduling scheme and study the throughput and delay performance, with fixed-rate transmissions in a two-hop wireless ad hoc networks. In the proposed scheduling scheme, we prove two key inequalities that capture the various tradeoffs inherent in the broad class of opportunistic relaying protocols, illustrating that no scheduling and routing algorithm can simultaneously yield lower delay and higher throughput. We then develop an adaptive rate transmission scheme with opportunistic scheduling, with the constraints of practical assumptions on channel state information (CSI) and limited feedback, which achieves an optimal system throughput scaling order. Along this work with the consideration of finite-buffer model, we propose a Buffer-Aware Adaptive (BAA) scheduler which considers both channel state and buffer conditions to make scheduling decisions, to reduce average packet delay, while maintaining the queue stability condition of the networks. The proposed algorithm is an improvement over existing algorithms with adaptability and bounded potential throughput reduction. In the third part, we extend the methods and analyses developed for wireless ad hoc networks to a practical Aeronautical Communication Networks (ACN) and present the system performance of such networks. We use our previously proposed scheduling schemes and analytical methods from the second part to investigate the issues about connectivity, throughput and delay in ACN, for both single-hop and two-hop communication models. We conclude that the two-hop model achieves greater throughput than the single-hop model for ACN. Both throughput and delay performances are characterized.

Dans les communications coopératives, deux ou plusieurs terminaux de transmissionsont combinés pour accroître la diversité et/ou la puissance des signaux arrivant à un récepteur. Récemment, l'analyse tensorielle s'est avérée une approche efficace pour l'estimation de canaux dans les systèmes coopératifs. Cependant, parmi les quelques travaux consacrés à cette tâche, l'utilisation de la décomposition tensorielle PARAFAC pour modéliser les signaux reçus ne permet pas l'estimation conjointe des symboles et des canaux de communication. Afin d'éviter l'utilisation de séquences de symboles pilotes, l'objectif de cette thèse est de fournir de nouvelles approches tensorielles, en termes de systèmes de transmission et de récepteurs semi-aveugles, pour des systèmes de communication MIMO avec relai mono-directionnels, à deux sauts. Deux systèmes de transmission sont proposés en utilisant un codage spatio-temporel du type Khatri-Rao et deux stratégies de traitement Amplify-and-Forward (AF) au relai. Pour ces systèmes, appelés PT2-AF et NP-AF, les signaux reçus au niveau de la destination satisfont respectivement des modèles tensoriels du type PARATUCK2 et nested PARAFAC. En exploitant les propriétés d'unicité de ces modèles tensoriels établies dans la thèse, plusieurs récepteurs semi-aveugles sont dérivés. Certains de ces récepteurs sont du type ALS, tandis que d'autres sont des solutions non itératives basées sur des factorisations de produits de Khatri-Rao. Des résultats de simulation sont présentés pour illustrer les performances des récepteurs proposés qui sont comparés à des estimateurs supervisés
In cooperative communication systems, two or more transmitting terminals arecombined to increase the diversity and/or the power of the signals arriving at aparticular receiver. Recently, the so-called tensor analysis has been an efficient approach for channel estimation in systems with cooperative diversity. However, among the few works devoted to this task, the utilization of the PARAFAC tensor decomposition for modeling the received signals did not allow the development of techniques for joint symbol and channel estimation. Aiming to avoid the use of pilot-based sequences, the objective of this thesis is to provide new tensor-based strategies, including transmission systems and semi-blind receivers, for one-way two-hop relaying systems. Based on a Khatri-Rao space-time coding at the source and two different Amplify-and-Forward (AF) relaying strategies, two transmission systems are proposed. For these systems, named PT2-AF and NP-AF, the received signals at the destination node follow respectively a PARATUCK2 and a nested PARAFAC tensor model. Exploiting uniqueness properties of these tensor models which are established in the thesis, several semi-blind receivers are derived. Some of these receivers are of iterative form using an ALS algorithm, whereas some other ones are close-form solutions associated with Khatri-Rao factorizations. Some simulation results are finally presented to illustrate the performance of the proposed receivers which are compared to some state-of-the-art supervised techniques

SOKAL, B. Semi-blind receivers for multi-relaying mimo systems using rank-one tensor factorizations. 2017. 85 f. Dissertação (Mestrado em Engenharia de Teleinformática)-Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017.
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Rejected by Marlene Sousa (mmarlene@ufc.br), reason: Prezado Bruno: Existe uma orientação para que normalizemos as dissertações e teses da UFC, em suas paginas pré-textuais e lista de referencias, pelas regras da ABNT. Por esse motivo, sugerimos consultar o modelo de template, para ajudá-lo nesta tarefa, disponível em: http://www.biblioteca.ufc.br/educacao-de-usuarios/templates/ Vamos agora as correções sempre de acordo com o template: 1. As informações da capa, folha de rosto (que segue a capa) e ficha catalográfica devem ser em língua portuguesa, mesmo que sua dissertação esteja em língua inglesa. A partir da folha de aprovação, devem ser em língua inglesa. 2. Exemplificando a capa, as informações que devem aparecer são pela ordem (Toadas em Maiúsculo e negrito): Nome da universidade, do centro, do departamento e nome do programa; Nome do aluno; Título; Cidade e data. 2. A folha de rosto também tem informações que não são necessárias. Consulte o template para ver uso de maiúsculas, negrito e ordem de apresentação das informações. 3. A ficha catalográfica deve vir antes da folha de aprovação e não depois desta. 4. A folha de aprovação não deve ter as informações do quadro no alto da folha, nem deve ser em negrito. Veja modelo no template. 5. De acordo com a ABNT mesmo escrita em outro idioma, primeiro coloca-se o resumo na língua portuguesa e depois o Abstract. As palavras RESUMO e ABSTRCT vem ser em caixa alta, negrito e no centro da folha. Não devem iniciar com paragrafo. Essa folhas são contadas mas não numeradas. Só a partir da introdução é que são numeradas. 6. Veja no template a ordem das folhas a partir dos agradecimentos e como devem ser apresentadas. 7. Na lista de figuras mantenha o mesmo espaço entre as linhas. 8. O sumário não deve conter as informações anteriores a INTRODUÇÃO, deve ser em negrito e sem recuo de paragrafo. Observe o uso de Caixa alta, itálico nas seções. Após a conclusão devem vir os APÊNDICES e as REFERENCIAS. 9. Na lista de referencias, pela ABNT, deve-se iniciar pelo sobrenome do autor, seguido do prenome. Elaboramos ferramentas para ajuda-lo a gerar as referencias e gerenciadores bibliográficos disponivel em: http://www.biblioteca.ufc.br/ferramentas-de-pesquisa/ Em artigos de revistas usa-se a seguinte nomenclatura para volume, numero e páginas: v. , n. , p. Não se destacam subtítulos e nos artigos de revistas se destaca-se apenas o ´nome da revista. Att. Marlene Rocha 3366-9620 mmarlene@ufc.br on 2017-09-18T11:38:11Z (GMT)
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Cooperative communications have shown to be an alternative to combat the impairments of signal propagation in wireless communications, such as path loss and shadowing, creating a virtual array of antennas for the source. In this work, we start with a two-hop MIMO system using a a single relay. By adding a space-time filtering step at the receiver, we propose a rank-one tensor factorization model for the resulting signal. Exploiting this model, two semi-blind receivers for joint symbol and channel estimation are derived: i) an iterative receiver based on the trilinear alternating least squares (Tri-ALS) algorithm and ii) a closed-form receiver based on the truncated higher order SVD (T-HOSVD). For this system, we also propose a space-time coding tensor having a PARAFAC decomposition structure, which gives more flexibility to system design, while allowing an orthogonal coding. In the second part of this work, we present an extension of the rank-one factorization approach to a multi-relaying scenario and a closed-form semi-blind receiver based on coupled SVDs (C-SVD) is derived. The C-SVD receiver efficiently combines all the available cooperative links to enhance channel and symbol estimation performance, while enjoying a parallel implementation.
Comunicações cooperativas têm mostrado ser uma alternativa para combater os efeitos de propagação do sinal em comunicações sem-fio, como, por exemplo, a perda por percurso e sombreamento, criando um array virtual de antenas para a fonte transmissora. Neste trabalho, toma-se como ponto de partida um modelo de sistema MIMO de dois saltos com um único relay. Adicionando um estágio de filtragem no receptor, é proposta uma fatoração de rank-um para o sinal resultante. A partir deste modelo, dois receptores semi-cegos para estimação conjunta de símbolo e canal são propostos: i) um receptor iterativo baseado no algoritmo trilinear de mínimos quadrados alternados (Tri-ALS) e ii) um receptor de solução fechada baseado na SVD de ordem superior truncada (T-HOSVD). Para este sistema, é também proposto um tensor de codificação espacial-temporal com uma estrutura PARAFAC, o que permite maior flexibilidade de design do sistema, além de uma codificação ortogonal. Na segunda parte deste trabalho, é apresentada uma extensão da fatoração de rank-um para o cenário multi-relay e um receptor semi-cego de solução fechada baseado em SVD's acopladas (C-SVD) é desenvolvido. O receptor C-SVD combina de modo eficiente todos os links cooperativos disponíveis, melhorando o desempenho da estimação de símbolos e de canal, além de oferecer uma implementação paralelizável.

Thesis (Ph. D.)--University of Notre Dame, 2008.
Thesis directed by Thomas E. Fuja and Daniel J. Costello, Jr. for the Department of Electrical Engineering. "December 2008." Includes bibliographical references (leaves 121-126).

Spatial modulation (SM) is a relatively new and attractive modulation technique for multi-antenna wireless systems. In SM, only one among ns = 2m available transmit antennas, chosen on the basis of m information bits, is activated at a time. A symbol from a conventional modulation alphabet (e.g., PSK) is transmitted through this chosen antenna. Space shift keying (SSK) is a special case of SM. In SSK, instead of sending a symbol from an alphabet, a signal known to the receiver, say a ‘+1’, is transmitted through the chosen antenna. SSK has the advantage of simple detection at the receiver. In this thesis, we are concerned with the performance analysis of SSK in cooperative relaying systems. We consider decode-and-forward (DF) relaying protocol, where the relays decode the received signal and forward the decoded signal towards the destina-tion. We consider three different models of cooperative relaying, namely, i) dual-hop relaying, ii) multi-hop relaying, and iii) cooperative multicasting. We also consider a cyclic-prefix single carrier (CPSC) communication system in a point-to-point chan-nel, and analyze the performance of both SM and SSK in that system under frequency selective fading. Dual-hop relaying: First, we consider a cooperative relaying system consisting of a source node, a destination node, and a relay node. We consider two commonly used re-laying techniques at the relay, namely, i) incremental relaying, and ii) threshold based relaying. We adopt selection combining at the destination. One way to perform se-lection combining operation is to use the knowledge of instantaneous signal-to-noise-ratio (SNR) as a metric for selection. However, in SSK, instantaneous SNR is difficult to be ascertained at the receiver side despite the availability of channel knowledge, be-cause the transmit antenna index itself is not known. To overcome this difficulty, we propose a new metric specific to SSK to carry out selection among the competing links. For the considered relaying schemes, we derive exact analytical expressions for the end-to-end average bit error probability (ABEP) for binary SSK (i.e., SSK with ns = 2) in closed-form. Simulations validate the end-to-end ABEP predicted by the analytical expressions. We then consider a dual-hop cooperative relaying system which consists of multiple relays. We propose a relay selection scheme for this system. In this system too, the des-tination adopts selection combining. Here, we use the proposed metric for both relay selection as well as selection combining. For this system, we derive an exact analytical expression for the end-to-end ABEP in closed-form for binary SSK. Analytical results agree with simulation results. For non-binary SSK (i.e., SSK with ns > 2), we derive an approximate closed-form expression for the end-to-end ABEP. The analytical ABEP results follow the simulated ABEP results closely. Multi-hop relaying: Next, we consider SSK in multi-hop multiple-input multiple-output (MIMO) networks. We consider two different systems of multi-hop coopera-tion, where each node has multiple antennas and employs SSK. In system I, a multi-hop diversity relaying scheme is considered. In system II, a multi-hop multi-branch relaying scheme is considered. In both the systems, we adopt DF relaying, where each relay forwards the signal only when it decodes correctly. We analyze the end-to-end ABEP and diversity order of SSK in both the systems. For binary SSK, our analytical ABEP expression is exact, and our numerical results show that the ABEPs evaluated through the analytical expression overlap with those obtained through simulations. For non-binary SSK, we derive an approximate ABEP expression, where the analyt-ically evaluated ABEP results closely follow the simulated ABEP results. We present comparisons between the ABEPs of SSK and conventional PSK, and show the instances where SSK outperforms PSK. We also present the diversity analyses for SSK in systems I and II, which predict the achievable diversity orders as a function of system parame-ters. Cooperative multicast: Next, we consider SSK in dual-hop DF cooperative multicast networks, where a source node communicates with multiple destination nodes with the help of relay nodes. We consider two different systems of cooperative multicast, namely, system III and system IV, where each node has multiple antennas and employs SSK, and communication happens in two phases. In system III, multiple relay nodes exist between the source and destination nodes. The relays that decode correctly can forward the signal to the destination nodes. We propose and analyze a relay selection scheme for this system. In system IV, the destination nodes can act as relays. Specifically, the destination nodes that decode correctly from the signal received on the direct path from source in the first phase forward to other destination nodes that did not decode correctly. For system III, we derive an exact closed-form expression of end-to-end ABEP for binary SSK, and an approximate closed-form expression of ABEP for non-binary SSK. We also present the diversity analysis for system III which predicts the achievable diversity order as a function of the system parameters. For system IV, we derive approximate closed-form ABEP expressions. The ABEP results obtained through the approximate analysis closely follow those obtained from simulations for both binary and non-binary SSK. Single carrier system: Finally, we study SM and SSK in CPSC systems on MIMO inter-symbol interference (ISI) channels. We present a diversity analysis of MIMO-CPSC systems under SSK and SM signaling. Our analysis shows that the diversity order achieved by (nt, nr ) SSK scheme and (nt, nr , ΘM ) SM scheme in MIMO-CPSC systems under maximum-likelihood detection is nr , where nt and nr denote the number of transmit and receive antennas, respectively, and ΘM denotes the modulation alpha-bet of size M . Bit error rate simulation results validate this predicted diversity order. Simulation results also show that MIMO-CPSC with SM and SSK achieves better per-formance compared to MIMO-OFDM with SM and SSK.

碩士
國立交通大學
電子研究所
100
In this thesis, we study a relay selection (RS) problem in multi-user two-way cooperative relaying systems which multiuser interference is involved. Different from the most research activities, we investigate a more practical scenario which consists of multiple users, multiple relays and a single destination. Regarding the sources and the destination as the mobile handsets and base station, respectively, this scenario is more similar to communication systems in reality compared with those consisting of only one source and one destination. On the other hand, we take multiuser interference into account, however, it is not the case for the most works. Channel orthogonality is assumed frequently in many studies to avoid interference. Nevertheless, such assumption is not so realistic and degrades the bandwidth efficiency. To be closer to reality or more bandwidth efficient, taking the multiuser interference into consideration is necessary. In our work, we consider a code division multiple access (CDMA) system with non-orthogonal spreading sequences. Since signal to interference-plus-noise ratio (SINR) is a benchmark of communication quality, RS based on maximizing the SINR of worse link is performed in our study. Besides, aiming at mitigating the interference, we consider the design of linear filter at each relay as well. The result shows that the linear filter is similar to minimum mean-square error (MMSE) detectors. Furthermore, we simulate the proposed scheme with several different parameters such as the number of users and relays, and the length of spreading sequences. Also, we compare the proposed relay selection method with random relay selection approach, and the result shows that our proposed method has better performance in terms of the bit error rate.

碩士
國立中山大學
通訊工程研究所
100
In wireless communication, multipath fading distorts the phase and the amplitude of received signals and increases error rate, which degrades causes communication quality. Multiple-input-multiple-output (MIMO) techniques can be adopted to achieve diversity gain and reduce error rate. However, MIMO is hard to be implemented in mobile devices due to size limitation. With this regard, cooperative communications are proposed to allow users to cooperate each other’s and then achieve diversity without equipping multiple antennas. On the other hand, if source and relays adopt fixed-rate transmission under time-varying wireless channels, it requires timely feedback about channel-information for transmitters to adjust the rate of channel encoder. To reduce overhead required for aforementioned scheme, we adopt rateless fountain codes in cooperative networks. In recent year, most related studies focus on information-theoretical aspect, but it lacks discussion of practical coding. In our work, we use fountain codes in dual-hop cooperative communication and analyse transmission rate in terms of transmitting time. Fountain code was first proposed as Luby transform codes(LTC) for erasure channels. We combine low-density parity-check code( LDPC code) and LTC in cooperative communication networks, and analyze required transmission time under different cooperative protocols.

碩士
元智大學
通訊工程學系
97
In this thesis, we first develop and analyze a new hybrid cooperative strategy which combines the AF and DF schemes by the channel quality from source to relays. In terms of SNR measurement at relay terminals, the relay will resort to the DF scheme if the channel link is reliable. Otherwise, the relay uses the simple AF scheme for non-reliable channel. The proposed hybrid cooperative technology can fully exploit all relay terminals, and obtain full cooperative diversity order in comparison with the traditional DF scheme. Besides, the simulation result indicates the diversity gain is also better than the traditional AF cooperative strategy. Secondly, for the problem of distributed space-time-coded (STC) cooperative system, we propose a new strategy, which be realized by applying the convolutional channel coding. Based on such STC cooperation, we propose an new asynchronous distributed STC cooperative strategy with the optimal beamforming technology, multiply-constrained minimum variance distortionless response (MC-MVDR). The relays will start cooperation by inserting latency to different time slots. For large frame size, the overall throughput is almost the same as the conventional STC cooperation. Besides, we also derive and analyze the corresponding outage probability at the output of beamformer. The results indicate the more diversity gain can be obtained due to the orthogonal thermal noise at destination. Furthermore, the proposed cooperative strategy can also achieve full diversity.

碩士
中原大學
通訊工程碩士學位學程
105
In this paper, We investigate the performance of a cognitive spectrum sharing system with two-way communication where secondary user assist two-way communication between two primary users by employing two phase cooperative spectrum sharing scheme over Nakagami-m fading channel. Herein, one-end primary user communicates with another primary user with the cooperation of the secondary user in two transmission phase, the relay help to carry out the transmission of the primary users. Between primary users transmission, the secondary user assists their transmission and transmits its own signal by accessing the spectrum based on satisfying the primary system outage constraint. Considering the Nakagami-m fading channel, We derive the expression of the outage probability for both primary and secondary systems. For these expression, We compare it with the other scheme and illustrate that this proposed scheme can offer better spectrum efficiently. Numerical and simulation results validate our theroretical analyses.

Over the past decade, cooperative communication has emerged as an attractive technique for overcoming the shortcomings of point-to-point wireless communication systems. Cooperative relaying improves the performance of wireless networks by creating an array of multiple independent virtual sources transmitting the same information as the source node. In addition, when relays are deployed near the edge of the network, they can provide additional coverage in network blind spots. Interference in the network can also be reduced in cooperative communication systems as the nodes can transmit at lower power levels as compared to equivalent point-to-point communication systems. In practice, the actual benefit of multi-node cooperation is affected by a variety of factors, including the quality of Channel State Information (CSI), the constraints on the feedback and backhaul links, hardware impairments, resource allocation and data processing schemes. This thesis investigates the combined impact of imperfect CSI and Radio Frequency Impairments (RFIs) on distributed relay networks and cellular relaying systems. First, we study the impact of CSI imperfections on single-antenna based dual-hop relaying systems in the presence of RFI over Nakagami-m fading environment. Herein, we consider two most common relaying protocols viz., Amplify-and-Forward (AF) and Decode-and-Forward (DF) to investigate the performance of One-way Relaying (OWR) system. To fully reap the benefits of relaying protocols, CSI of the network is essential. In practice, CSI must be estimated using the pilot symbols prior to the transmission of data symbols. A unified analysis is conducted for both the relaying protocols by deriving the generalized closed-form outage probability expressions with channel estimation error and RFI. Moreover, we also analyze the outage performance with respect to the severity of channel conditions. The analytical results are used to obtain several crucial design insights such as the transmission rate and the combined level of imperfections that the system can handle without affecting its performance. Next, we extend our analysis to the cellular scenario where the wireless network comprises of multi-antenna Base Station (BS), single-antenna multiple users and multiple relays. Herein, we analyze the outage and Expected Spectral Efficiency (ESE) performance of downlink cellular relaying system in a Rayleigh fading environment. In particular, by employing joint antenna and relay selection with multi-user scheduling, we have proposed and analyzed two opportunistic transmission strategies for both AF and DF relaying protocols vii with different implementation complexities in practical scenario when the direct links are in the deep fade. We also deduce the asymptotic outage expressions in the high signal-to-noise ratio regime, from which the impacts of CEE and RFI on the achievable diversity order are highlighted. Moreover, to provide spectrally efficient transmission over traditional unidirectional flow of information, we consider another approach to improve the efficient transmission i.e., Two-Way Relaying (TWR) network. Specifically, we analyze the performance of TWR-AF system with RFI at sources and the relay node. CEE is also considered for TWR network which creates imperfect self-interference cancellation at both sources that exchange the information through a single relay. The expressions for effective end-to-end signal-to-noise plus-distortion-and-error ratio (SNDER) and closed-form expression for the exact analysis of OP are derived by taking a Rayleigh block fading channel. In addition, the combined impacts of RFI and CEE on outage performance of TWR and OWR systems for low and high transmission rates are also evaluated. For further insights, we perform asymptotic analysis of OP and observe irreducible outage floors which act as fundamental performance limits. The last part of the thesis focuses on the comparative study of multi-user multi-relay TWR and OWR cooperative networks. Due to less implementation complexity involved in AF relaying protocol, we focus on AF relay assisted TWR and OWR systems with two groups of users exchanging information opportunistically over the best relay (out of available relay candidates) in the presence of CEE and RFI over Rayleigh fading channels. Considering such practical set-up, we first deduce the pertinent instantaneous end-to-end SNDERs. Specifically, we derive approximate as well as exact closed-form expressions for the outage probability and expected spectral efficiency for both the systems. In addition, simple asymptotic expressions at the high SNR regime are obtained, which facilitate the characterization of the achievable diversity order of the systems. To validate the derived analytical expressions, we have presented simulation results which are sufficiently tight across the entire range of SNRs. We have also optimized power to reduce system outages and emphasize that optimum power allocation can provide noticeable outage performance improvement. Findings of the chapters suggest that full diversity order can be achieved only when the RF front-end hardware is assumed to be perfect, while in practice the imperfections in hardware are inevitable and reduce the diversity order of the system. Moreover, the influence of key parameters such as the number of users and relays on the system performance has been presented with the dependency on the level of RFI. Different design guidelines and possible power allocation between relay and end-user terminals are proposed to improve the system reliability under a total transmit power constraint.

abstract: Practical communication systems are subject to errors due to imperfect time alignment among the communicating nodes. Timing errors can occur in different forms depending on the underlying communication scenario. This doctoral study considers two different classes of asynchronous systems; point-to-point (P2P) communication systems with synchronization errors, and asynchronous cooperative systems. In particular, the focus is on an information theoretic analysis for P2P systems with synchronization errors and developing new signaling solutions for several asynchronous cooperative communication systems. The first part of the dissertation presents several bounds on the capacity of the P2P systems with synchronization errors. First, binary insertion and deletion channels are considered where lower bounds on the mutual information between the input and output sequences are computed for independent uniformly distributed (i.u.d.) inputs. Then, a channel suffering from both synchronization errors and additive noise is considered as a serial concatenation of a synchronization error-only channel and an additive noise channel. It is proved that the capacity of the original channel is lower bounded in terms of the synchronization error-only channel capacity and the parameters of both channels. On a different front, to better characterize the deletion channel capacity, the capacity of three independent deletion channels with different deletion probabilities are related through an inequality resulting in the tightest upper bound on the deletion channel capacity for deletion probabilities larger than 0.65. Furthermore, the first non-trivial upper bound on the 2K-ary input deletion channel capacity is provided by relating the 2K-ary input deletion channel capacity with the binary deletion channel capacity through an inequality. The second part of the dissertation develops two new relaying schemes to alleviate asynchronism issues in cooperative communications. The first one is a single carrier (SC)-based scheme providing a spectrally efficient Alamouti code structure at the receiver under flat fading channel conditions by reducing the overhead needed to overcome the asynchronism and obtain spatial diversity. The second one is an orthogonal frequency division multiplexing (OFDM)-based approach useful for asynchronous cooperative systems experiencing excessive relative delays among the relays under frequency-selective channel conditions to achieve a delay diversity structure at the receiver and extract spatial diversity.
Dissertation/Thesis
Ph.D. Electrical Engineering 2013

Relay-assisted cooperative communication exploits spatial diversity to combat wireless fading, and is an appealing technology for next generation wireless systems. Several relay cooperation protocols have been proposed in the literature. In amplify-and-forward (AF)relaying, which is the focus of this thesis, the relay amplifies the signal it receives from the source and forwards it to the destination. AF has been extensively studied in the literature on account of its simplicity since the relay does not need to decode the received signal. We propose a novel optimal relaying policy for two-hop AF cooperative relay systems. In this, an average power-constrained relay adapts its gain and transmit power to minimize the fading-averaged symbol error probability (SEP) at the destination. Next, we consider a generalization of the above policy in which the relay operates as an underlay cognitive radio (CR). This mode of communication is relevant because it promises to address the spectrum shortage constraint. Here, the relay adapts its gain as a function of its local channel gain to the source and destination and also the primary such that the average interference it causes to the primary receiver is also constrained. For both the above policies, we also present near-optimal, simpler relay gain adaptation policies that are easy to implement and that provide insights about the optimal policies. The SEPs and diversity order of the policies are analyzed to quantify their performance. These policies generalize the conventional fixed-power and fixed-gain AF relaying policies considered in cooperative and CR literature, and outperform them by 2.0-7.7 dB. This translates into significant energy savings at the source and relay, and motivates their use in next generation wireless systems.

Relay-assisted cooperative communication exploits spatial diversity to combat wireless fading, and is an appealing technology for next generation wireless systems. Several relay cooperation protocols have been proposed in the literature. In amplify-and-forward (AF)relaying, which is the focus of this thesis, the relay amplifies the signal it receives from the source and forwards it to the destination. AF has been extensively studied in the literature on account of its simplicity since the relay does not need to decode the received signal. We propose a novel optimal relaying policy for two-hop AF cooperative relay systems. In this, an average power-constrained relay adapts its gain and transmit power to minimize the fading-averaged symbol error probability (SEP) at the destination. Next, we consider a generalization of the above policy in which the relay operates as an underlay cognitive radio (CR). This mode of communication is relevant because it promises to address the spectrum shortage constraint. Here, the relay adapts its gain as a function of its local channel gain to the source and destination and also the primary such that the average interference it causes to the primary receiver is also constrained. For both the above policies, we also present near-optimal, simpler relay gain adaptation policies that are easy to implement and that provide insights about the optimal policies. The SEPs and diversity order of the policies are analyzed to quantify their performance. These policies generalize the conventional fixed-power and fixed-gain AF relaying policies considered in cooperative and CR literature, and outperform them by 2.0-7.7 dB. This translates into significant energy savings at the source and relay, and motivates their use in next generation wireless systems.

碩士
國立交通大學
電機學院通訊與網路科技產業專班
96
The cooperative communication is to realize the MIMO system. The optimum receiver is a highly-complex ML receiver. Hence, the major issue is to design a receiver with low complexity at the destination node with comparable performance as that of the ML receiver. Therefore, we design a receiver to combine the received signals at the Destination node under Decode-and-Forward protocol. The proposed scheme uses the threshold-selection Relay and also uses the maximum SNR detection at the Destination node to minimize the effect that Relay made wrong decision. With this proposed scheme, we also try to find out the optimum threshold value of the Relay. Besides, we derive theoretical bit-error-rate (BER) with BPSK signals for the proposed scheme. We also show that the theoretical BER is tight to the simulated results. The high SNR approximation is made to simplify the theoretical BER, from which we could know that the diversity order of the proposed system lies in 1.5~2 which agrees with previous work.

碩士
國立臺灣海洋大學
通訊與導航工程學系
101
In this paper, an analytical framework for cooperative relaying (dual-hop multi-relaying and direct links) over an in-door composite fading environment is developed. The analytical expressions combined outage and average bit-error-rate (BER) probability are derived and analyzed, in comparison with simulation results, in terms of a variety of log-normal standard deviations and the multi-relay diversity order against the cooperative relaying signal-to-noise (SNR) mean power. Finally, a derived generic closed-form expression for the outage probability based on cooperative dual-hop multi-relaying link, where the asymptotic results and simulations are analyzed with constrained end-to-end power conditions. By utilizing these results, we refine a specific analysis framework combined outage and average error probability using the generality of closed-form expressions. Analytical results demonstrated that our proposed framework will provide a simple and efficient approach for evaluating the impact on shadowing effects, cooperative diversity gain and determining the cooperation power constraint.

碩士
國立臺灣海洋大學
通訊與導航工程學系
102
In this thesis, we explicitly derive the closed-form expressions for the probability density function (PDF) and the cumulative distribution function (CDF) of a composite fading(Rayleigh plus Log-normal) channel based on the Max-Mini relay selection scenario under conditioned signal-to-noise (SNR) power constraint on relay link. The performance analysis in terms of outage probability and Bit-Error-Rate (BER) are compared with our proposed probabilistic approach and the Wilkinson approximation, and corroborated with the exact solution (integral form). The analytical result shows that the proposed scheme approaches the exact solution with promised accuracy, leading to an effective framework of performance analysis for cooperative multi-relaying over a generalized fading environment. These results are extensions of the earlier work using distribution function of the log-normal power-sums with Wilkinson method which only considers in generically correlated log-normal fading environment for indoor application. As a consequence, our probabilistic approach provides a generalized performance analysis of cooperative multi-relaying system in both outdoor and indoor radio links.

Relay-based cooperation promises significant gains in a wireless network as it provides an inde-pendent path between a source and a destination. Using simple single antenna nodes, it exploits the spatial diversity provided by the geographically separated nodes in a network to improve the robustness of the communication system against fading. Among the cooperative commu¬nication schemes, the amplify-and-forward (AF) relaying scheme is considered to be easy to implement since the relay does not need to decode its received signal. Instead, it just forwards to the destination the signal it receives from the source. We analyze the performance of fixed-gain AF relaying with imperfect channel knowledge that is acquired through an AF relay-specific training protocol. The analysis is challenging because the received signal at the destination contains the product (or cascade) of source-relay (SR) and relay-destination (RD) complex baseband channel gains, and additional products terms that arise due to imperfect estimation related errors. We focus on the time-efficient cascaded channel estimation (CCE) protocol to acquire the channel estimates at the destination. Using it, the destination can only estimate the product of SR and RD complex baseband channel gains, but not the two separately. Our analysis encompasses a single AF relay system and an opportunistic system with mul¬tiple AF relays, among which one is selected to forward its received signal to the destination, based on its SR and RD complex baseband channel gains. For a single relay system, we first de¬velop a novel SEP expression and a tight SEP upper bound. We then analyze the opportunistic multi-relay system, in which both selection and coherent demodulation use imperfect channel estimates. A distinctive aspect of our approach is the use of as few simplifying approximations as possible. It results in a new analysis that is accurate at signal-to-noise-ratios as low as 1 dB for single and multi-relay systems. Further, the training protocol is an integral part of the model and analysis. Using an insightful asymptotic analysis, we then present a simple, closed-form, nearly-optimal solution for allocation of energy between pilot and data symbols at the source and relay(s). Further, the optimal energy allocation between a source and a relay is characterized when both together operate under a sum energy constraint, as has often been assumed in the literature. In summary, the sum total of the results in this work provides a rigorous and accurate performance characterization and optimization of cascaded channel estimation for AF relaying.

Relay-based cooperation promises significant gains in a wireless network as it provides an inde-pendent path between a source and a destination. Using simple single antenna nodes, it exploits the spatial diversity provided by the geographically separated nodes in a network to improve the robustness of the communication system against fading. Among the cooperative commu¬nication schemes, the amplify-and-forward (AF) relaying scheme is considered to be easy to implement since the relay does not need to decode its received signal. Instead, it just forwards to the destination the signal it receives from the source. We analyze the performance of fixed-gain AF relaying with imperfect channel knowledge that is acquired through an AF relay-specific training protocol. The analysis is challenging because the received signal at the destination contains the product (or cascade) of source-relay (SR) and relay-destination (RD) complex baseband channel gains, and additional products terms that arise due to imperfect estimation related errors. We focus on the time-efficient cascaded channel estimation (CCE) protocol to acquire the channel estimates at the destination. Using it, the destination can only estimate the product of SR and RD complex baseband channel gains, but not the two separately. Our analysis encompasses a single AF relay system and an opportunistic system with mul¬tiple AF relays, among which one is selected to forward its received signal to the destination, based on its SR and RD complex baseband channel gains. For a single relay system, we first de¬velop a novel SEP expression and a tight SEP upper bound. We then analyze the opportunistic multi-relay system, in which both selection and coherent demodulation use imperfect channel estimates. A distinctive aspect of our approach is the use of as few simplifying approximations as possible. It results in a new analysis that is accurate at signal-to-noise-ratios as low as 1 dB for single and multi-relay systems. Further, the training protocol is an integral part of the model and analysis. Using an insightful asymptotic analysis, we then present a simple, closed-form, nearly-optimal solution for allocation of energy between pilot and data symbols at the source and relay(s). Further, the optimal energy allocation between a source and a relay is characterized when both together operate under a sum energy constraint, as has often been assumed in the literature. In summary, the sum total of the results in this work provides a rigorous and accurate performance characterization and optimization of cascaded channel estimation for AF relaying.