In this thesis, we study the effect of channel estimation on the performance of distributed space-time coding (DSTC) in amplify-and-forward (AF) cooperative networks. The relay based transmission takes two phase. In phase I, the source transmits a block of symbols, which include training symbols and data to destination. After receiving signals at relay, the DSTC is adopted to re-encode signals in order to achieve diversity gain at relay nodes. At destination, the signals received in two phase are combined and used to detected data symbols. In the thesis, for AF cooperative networks, the signal received at destination is effected the multiplication of channel coefficients on the source to relay and relay to destination links. Before detection, channel coefficients of all links need to be estimated. We propose a semiblind method to estimate the channel coefficients of direct link and the relay links. The semi-blind channel estimation scheme, exploits a small number of training symbols and second-order statistics of received signals. To improve the detection quality, the channel estimation is modified by treating the detected symbols as extra training symbols. Through simulation, it shows that the proposed channel estimation and the modification leads to obvious performance improvement.

In this thesis, a novel pre-coded direct-sequence code division multiple access (DS-CDMA) associated with the multiple-input multiple-output (MIMO) antennas, along with Alamouti¡¦s space-time block code (ST-BC) is considered. In the transmitter, the idea of hybrid pre-coded is exploited; it can be employed to counteract the inter-symbol interference (ISI) introduced by the channel fading duo to multipath propagation, and can be used to exacting the full information of channel impulse response (CIR) in the receiver for semi-blind channel estimation. Under this transceiver framework, we develop a semi-blind adaptive MIMO-CDMA receiver, based on the linearly constrained constant modulus (LCCM) criterion, for symbol recovery. Furthermore, to reduce the complexity of receiver design, the framework of the generalized sidelobe canceller (GSC) associated with the recursive least-squares (RLS) algorithm is adopted, and the gradient approach is applied to track the desired user¡¦s amplitude, simultaneously, and is named as the GSC-CM-IQRD-RLS algorithm. Via computer simulations, the superior performance and the advantages of proposed scheme is verified; it outperforms the conventional LCMV-based algorithm, and slightly better than the convention CM-GSC-RLS receiver, with the paid of spectral efficient.

OLIVEIRA, P. M. R. PARATUCK-N semi-blind receivers for multi-hop cooperative MIMO relay systems. 2017. 51 f. Dissertação (Mestrado em Engenharia de Teleinformática)–Centro de Tecnologia, Universidade Federal do Ceará, Fortaleza, 2017. / Submitted by Renato Vasconcelos (ppgeti@ufc.br) on 2017-09-09T02:17:00Z No. of bitstreams: 1 2017_dis_pmroliveira.pdf: 1188957 bytes, checksum: 745420c86668fea09707dfcc7364adf8 (MD5) / Rejected by Marlene Sousa (mmarlene@ufc.br), reason: Prezado Pedro: 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. Na capa as informações relativas a hierarquia institucional deve ser em língua portuguesa, Nome da INSTITUIÇÃO; do CENTRO; do DEPARTAMENTO e do PROGRAMA DE PÓS-GRADUAÇÃO. Nesta ordem. Todas as informações devem está em negrito e em caixa alta. Retire a informação Master’s Degree Dissertation e também o nome do estado e o mes. Deixe apenas o nome da cidade e o ano. 2. Na folha de rosto (que segue a capa) Veja o modelo de apresentação das informações de acordo com o template. Apenas o titulo deve ficar em inglês as demais informações são em português. A partir da folha de rosto, todas as outras devem ficar em inglês. Não use negrito nessa folha. Deixe apenas o nome da cidade e o ano. A ficha catalográfica deve vir depois da folha de rosto e as palavras relacionadas aos assuntos devem ser em português. 3. A folha de aprovação naõ deve ter nenhuma informação em negrito. Veja o tamanho da fonte. 4. A dedicatória deve ser depois da folha de aprovação e não é em negrito. 5. A palavra Acknowledgments é em caixa alta, negrito e centralizada na folha. Não use negrito no texto. As folhas prétextuais devem ser contadas mas não são numeradas. Retire numeração. 6. O resumo deve vir antes do Abstract, mesmo quando o trabalho for em língua inglesa. A palavra resumo é em caixa alta, negrito e centralizada na folha. Não use negrito no texto e nem use parágrafos. A palavra abstract é em caixa alta, negrito e centralizada na folha. Não use negrito no texto e nem use parágrafos. 7. As palavras List of Figures, List of Tables, Acronyms, Notation e Sumary são em caixa alta, negrito e centralizada na folha. Não use negrito no texto 8. O sumário está fora dos padrões. Veja uso de maiusculo, minusculo, negrito e itálico nas seções. Não coloque em formato de capítulos e nem coloque as pre-textuais no sumário. Use a palavra referencias e não bibliografia 9. Na lista de referências, Coloque os nomes dos autores entrando pelo sobrenome, seguido do pré nome. Ex. ALMEIDA, A. Se vc optar por abreviar os nomes em toda a lista eles devem ser abreviados. Se vc optar em colocar por extenso em toda e lista deve ficar por extenso para haver uma padronização. Os títulos das publicações devem ser destacadas com o uso do negrito (não use aspas). Com exceção dos artigos de periódicos que devem ser destacados o nome das revistas e não o titulo do artigo. Ao citar os artigos coloque as abreviações v. n. p. e não vol. no e pp. Após essas correções, enviaremos o nada consta por e-mail. Att. Marlene Rocha mmarlene@ufc.br on 2017-09-11T12:55:01Z (GMT) / Submitted by Renato Vasconcelos (ppgeti@ufc.br) on 2017-09-14T13:32:11Z No. of bitstreams: 1 2017_dis_pmroliveira.pdf: 1155061 bytes, checksum: 0da92fa912cabfa49b279fbe8c199877 (MD5) / Rejected by Marlene Sousa (mmarlene@ufc.br), reason: Prezado Pedro e Renato: Será que foi enviada a versão certa? Tenho a impressão que já fiz as recomendações de correção e o Pedro afirma que corrigiu, mas a versão que abri no Repositório ainda esta sem as alterações que solicitei. Marlene on 2017-09-14T16:38:31Z (GMT) / Submitted by Renato Vasconcelos (ppgeti@ufc.br) on 2017-10-03T13:47:30Z No. of bitstreams: 1 2017_dis_pmroliveira.pdf: 1357256 bytes, checksum: 308dc86c85e412f7947531cc8692dd60 (MD5) / Approved for entry into archive by Marlene Sousa (mmarlene@ufc.br) on 2017-11-08T17:23:03Z (GMT) No. of bitstreams: 1 2017_dis_pmroliveira.pdf: 1357256 bytes, checksum: 308dc86c85e412f7947531cc8692dd60 (MD5) / Made available in DSpace on 2017-11-08T17:23:03Z (GMT). No. of bitstreams: 1 2017_dis_pmroliveira.pdf: 1357256 bytes, checksum: 308dc86c85e412f7947531cc8692dd60 (MD5) Previous issue date: 2017-07-28 / Cooperative communication systems is a promising research field nowadays due to its advantages, like the increase of the received power, better quality of signal, and spatial diversity gains. Specifically, multi-hop systems are a very important part of cooperative communications, since they have the advantage of needing less transmission power than the direct systems. Also, multiple-input multiple-output (MIMO) systems are present in several standards of communications, providing some advantages, like the spatial multiplexing gains. Based on this scenario, this work proposes two semi-blind receivers based on the Kronecker product, that jointly estimate the symbol and the channels in a multi-hop Amplify-and-Forward (AF) MIMO relay-assisted system (AF protocol is widely used, due to its great performance and easy implementation). We consider a transmission scheme using a simplified Khatri-Rao space-time (KRST) coding at the source node, combined with an AF scheme at the relay nodes. We show that the third-order tensor of signals received by the destination node satisfies a PARATUCK-(K+1) decomposition, where K is the number of relays. This tensorial modeling enables a semi-blind estimation of symbols and channels with the use of a few pilot symbols. The first receiver called Least-Squares Kronecker-Factorization (LS-KF) is based on a factorization of the Kronecker product matrix between the symbols and the channel matrices. The other receiver called Least-Squares Kronecker-Rearrangement (LS-KR) is based on a rearrangement of this Kronecker product matrix, in order to achieve a rank-1 matrix. The performance of these receivers is evaluated by means of computational simulation results proving their efficiency in estimating the channels and, hence, providing a low Symbol Error Rate (SER). The proposed algorithms in the multi-hop scenario were compared to each other and with the two-hop and three-hop scenarios. The proposed algorithms in the multi-hop scenario were better at all simulations, providing a lower SER and better channels estimations. / Sistemas de comunicações cooperativas são um importante campo de pesquisa atualmente devido às vantagens que oferecem, como o aumento da potência recebida, melhor qualidade de sinal, e ganhos de diversidade espacial. Particularmente, sitemas multi-saltos são uma importante parte das comunicações cooperativas, uma vez que tais sistemas precisam de menos potência de transmissão se comparados a sistemas diretos. Por outro lado, sistemas MIMO (Multiple-Input Multiple-Output) estão presentes em diversos padrões de comunicação, provendo algumas vantagens, como ganhos de multiplexação espacial. Com base nesse cenário, o presente trabalho propõe dois receptores semi-cegos baseados no pro- duto de Kronecker, que estimam conjuntamente os símbolos e os canais de um sistema AF (Amplify- and-Forward) MIMO cooperativo com multiplos saltos (O protocolo AF é bastante usado, devido a sua grande performance e fácil implementação). É considerado um esquema de transmissão usando uma codificação simplificada KRST (Khatri-Rao Space-Time) na fonte, combinada com um esquema AF no relays. É mostrado que o tensor de terceira ordem dos sinais recebidos pelo destino satisfazem uma decomposição tensorial PARATUCK-(K+1), em que K é o número de relays. Esse modelo tensorial permite uma estimação semi-cega dos símbolos e canais, com o uso de alguns símbolos pilotos. O primeiro algoritmo, chamado de Least-Squares Kronecker-Factorization (LS-KF), é baseado em uma fatorização da matrix do produto de Kronecker entre as matrizes de símbolos e canal. Já o outro algoritmo, chamado de Least-Squares Kronecker-Rearrangement (LS-KR), é baseado no re- arranjo dessa matrix do produto de Kronecker, com o objetivo de conseguir uma matrix com rank 1. A performance desses receptores é avaliada através do resultado de simulações computacionais, provando sua eficiência em estimar os canais e prover uma baixa SER (Symbol Error Rate). Os algo- ritmos propostos no cenário multi-hop são comparados um com o outro e com os cenários two-hop e three-hop. Os algoritmos propostos no cenário multi-hop tiveram melhores performance em todas as simulações, resultando numa menor SER e melhores estimações dos canais.

In this digital age, it is more important than ever to have good methods for processing images. We focus on the removal of blur from a captured image, which is called the image deblurring problem. In particular, we make no assumptions about the blur itself, which is called a blind deconvolution. We approach the problem by miniming an energy functional that utilizes total variation norm and a fidelity constraint. In particular, we extend the work of Chan and Wong to use a reference image in the computation. Using the shock filter as a reference image, we produce a superior result compared to existing methods. We are able to produce good results on non-black background images and images where the blurring function is not centro-symmetric. We consider using a general Lp norm for the fidelity term and compare different values for p. Using an analysis similar to Strong and Chan, we derive an adaptive scale method for the recovery of the blurring function. We also consider two numerical methods in this disseration. The first method is an extension of Picards method for PDEs in the discrete case. We compare the results to the analytical Picard method, showing the only difference is the use of the approximation versus exact derivatives. We relate the method to existing finite difference schemes, including the Lax-Wendroff method. We derive the stability constraints for several linear problems and illustrate the stability region is increasing. We conclude by showing several examples of the method and how the computational savings is substantial. The second method we consider is a black-box implementation of a method for solving the generalized eigenvalue problem. By utilizing the work of Golub and Ye, we implement a routine which is robust against existing methods. We compare this routine against JDQZ and LOBPCG and show this method performs well in numerical testing.

In this thesis, we proposed a precoding scheme for semi-blind channel estimation in amplify-and-forward (AF) multipath two-way relay networks (TWRN), where two terminals exchange their information through multi-relays. The precoding scheme, which diminishes computational complexity of semi-blind channel estimator, is used to distinguish received signal at both terminals from multi-relays. By applying a non-redundant linear precoding scheme at multi-relays, we proposed a semi-blind channel estimation to estimate the channel impulse response (CIR) of direct link and the cascaded source-relay-terminal links. Firstly, semi-blind channel estimation adopts least-square (LS) estimation to find the CIR of direct link between both terminals using a smaller number of training symbols. Secondly, the CIR of the cascaded source-relay-terminal links are obtained through second-order statistics (SOS) of received signals at both terminals. Consequently, the proposed scheme can effectively reduce the computational complexity and enhance the spectral efficiency in overall system. Simulation results corroborate the effectiveness of the proposed scheme.

This thesis investigates the semi-blind channel estimation in uplink (UL) of Orthogonal Frequency Division Multiple Access (OFDMA) systems based on subspace decomposition. We exploit the orthogonality between signal subspace and noise subspace induced by virtual carriers (VCs) and cyclic prefix (CP) and the property of that the exclusive sub-carriers set is assigned to each user to estimate and identify the channels for each user individually. In OFDMA systems, when some users don¡¦t communicate with base station, the sub-carriers of non-active user provide extra redundancy for channel estimate to enhance the accuracy of channel estimation. Furthermore, the sufficient channel identifiability condition is developed. Furthermore, a novel scheme, called as virtual carriers recovery (VCR) scheme, is proposed to improve the performance of the subspace-based channel estimation method. It suppresses the noise interference by recovering the VCs to zeros at receiver. The simulation results illustrate that the enhancement of VCR scheme is particularly apparent for the partially loaded OFDMA system at low signal to noise ratio (SNR). In addition, the VCR scheme increases the convergence rate of the subspace-base semi-blind channel estimation.

Conselho Nacional de Desenvolvimento CientÃfico e TecnolÃgico / Em comunicaÃÃes 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 propagaÃÃo entre dois pontos comunicantes, os diversos elementos transmissores podem atuar como um arranjo virtual de antenas, obtendo-se assim vantagens dos sistemas de mÃltiplas antenas (MIMO), sobretudo o aumento da capacidade de transmissÃo. Recentemente, a chamada analise tensorial tem se mostrado uma abordagem eficiente entÃo para a estimaÃÃo de canais em sistemas com diversidade cooperativa. Contudo, nos poucos trabalhos dedicados a essa tarefa, a utilizaÃÃo da decomposiÃÃo tensorial PARAFAC para a modelagem dos sinais recebidos nÃo possibilitou o desenvolvimento de tÃcnicas de estimaÃÃo conjunta de canais e sÃmbolos. Com a idÃia de se evitar o uso de sequencias de treinamento, que limita a eficiÃncia espectral da transmissÃo por dedicar uma parte da largura de banda apenas para a tarefa de estimaÃÃo dos canais, o objetivo desta tese à prover novas estratÃgias de comunicaÃÃo, 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 codificaÃÃo espaÃo-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 nà de destino satisfazem os modelos tensoriais do tipo PARATUCK2 e Nested PARAFAC. Explorando as propriedades de unicidade destes modelos tensoriais estabelecidas nesta tese, vÃrios receptores semi-cegos sÃo derivados. Alguns destes receptores sÃo do tipo ALS, enquanto outros sÃo de soluÃÃes baseadas na factorizaÃÃo de produtos de Khatri-Rao. Resultados de simulaÃÃo sÃo apresentados para ilustrar os desempenhos dos receptores propostos em comparaÃÃo a alguns estimadores supervisionados. / 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.

L’estimation de canal joue un rôle important dans les communications mobiles sans fil et en particulier dans les systèmes multi-antennes MIMO. Contrairement aux techniques classiques d’estimation de canal basées sur des séquences d’apprentissage ou des symboles pilotes, les techniques aveugles ne nécessitent aucune insertion de symboles d'apprentissage et permettent d'augmenter le débit utile. Les principales difficultés des techniques aveugles résident dans l’ambiguïté présente sur les estimées. Les techniques d’estimation semi-aveugles, basées sur les mêmes méthodes que l’estimation aveugle, sont plus robustes. Elles exploitent l’information aveugle ainsi que l’information provenant d’un nombre réduit de symboles d’apprentissage. Cette estimation du canal de communication est très utile dans les systèmes MIMO et permet de précoder le signal MIMO-OFDM en lui appliquant un pré-mélange permettant d'améliorer les performances. De nombreux types de précodeurs existent et leurs performances varient en fonction des critères d'optimisation retenus (Water-Filling, MMSE, Equal Error, max-SNR, max-d min …), mais aussi avec la qualité de l'estimation du canal de communication. Nous étudions dans cette thèse l’impact de l’utilisation de l’information du canal (CSI) provenant des méthodes d’estimation aveugle et semi-aveugle, dans l’application des précodeurs linéaires MIMO. Nous présentons également une étude statistique de l’erreur d’estimation provenant de ces méthodes. L’optimisation de ces précodeurs nous mène par la suite à exploiter un autre procédé permettant l’amélioration des performances : les codes correcteurs d’erreur. Nous nous intéressons particulièrement aux codes LDPC non-binaires et leur association avec les précodeurs linéaires MIMO. Nous montrons qu’une adaptation est possible et s’avère bénéfique dans certains cas. L’optimisation de cette association nous a permis de proposer un nouveau précodeur basé sur la maximisation de l’information mutuelle, robuste et plus performant. / Channel estimation plays an important role in wireless mobile communications, especially in MIMO systems. Unlike conventional channel estimation techniques based on training sequences or pilot symbols, blind techniques does not require the insertion of training symbols and allow higher throughput. The main problems of the blind lies in the ambiguity over the estimated channel. Based on the same methods as the blind estimation, the semi-blind estimation techniques are more robust. They exploit the blind information along with information provided by a small number of training symbols. The channel estimation is useful in MIMO systems and allows the precoding of the MIMO-OFDM signal by applying a pre-mixture in order to improve performance. Many types of precoders exist and their performance varies depending not only on the optimization criteria (Water-Filling, MMSE, Equal Error, max-SNR, max-d min ...), but also on the estimated channel. In this thesis we study the impact of using the channel information (CSI) from the blind and semi-blind estimation techniques to apply MIMO linear precoders. We also present a statistical study of the estimation error of these methods. The optimization of these precoders leads eventually to use another process allowing more performance improvement: the error correcting codes. We are particularly interested in non-binary LDPC codes and their association with linear MIMO precoders. We show that a matching is possible, and is beneficial in some cases. The optimization of this combination has allowed us to propose a new robust and more efficient precoder based on the maximization of mutual information.

Orthogonal frequency division multiplexing (OFDM) modulator with redundancy has been adopted in many wireless communication systems for higher data rate transmissions. The introduced redundancy at the transmitter allows us to overcome serious inter-block interference (IBI) problems due to highly dispersive channel. However, the selection of redundancy length will affect the system performance and spectral efficiency, and is highly dependent on the length of channel impulse response. In this thesis, based on the pseudorandom postfix (PRP) OFDM scheme we propose a novel block-based OFDM transceiver framework. Since in the PRP-OFDM system the PRP can be employed for semi-blind channel estimation with order-one statistics of the received signal. Hence, for sufficient redundancy case the PRP-OFDM system with the Bayesian decision feedback equalizer (DFE) is adopted for suppressing the IBI and ISI simultaneously. However, for the insufficient redundancy case (the length of redundancy is less than the order of channel), we first propose a modified scheme for channel estimation. To further reduce the complexity of receiver, the maximum shortening signal-to-noise-ratio time domain equalizer (MSSNR TEQ) with the Bayesian DFE is developed for suppressing the IBI and ISI, separately. That is, after knowing the channel state information (CSI) and removing the effect of IBI with MSSNR TEQ, the Bayesian DFE is applied for eliminating the ISI. Via computer simulation, we verify that performance improvement, in terms of bit error rate (BER), compared with the conventional block-based minimum mean square error (MMSE)-DFE can be achieved.

We live in a dynamic world full of noises and interferences. The conventional acoustic echo cancellation (AEC) framework based on the least mean square (LMS) algorithm by itself lacks the ability to handle many secondary signals that interfere with the adaptive filtering process, e.g., local speech and background noise. In this dissertation, we build a foundation for what we refer to as the system approach to signal enhancement as we focus on the AEC problem. We first propose the residual echo enhancement (REE) technique that utilizes the error recovery nonlinearity (ERN) to "enhances" the filter estimation error prior to the filter adaptation. The single-channel AEC problem can be viewed as a special case of semi-blind source separation (SBSS) where one of the source signals is partially known, i.e., the far-end microphone signal that generates the near-end acoustic echo. SBSS optimized via independent component analysis (ICA) leads to the system combination of the LMS algorithm with the ERN that allows for continuous and stable adaptation even during double talk. Second, we extend the system perspective to the decorrelation problem for AEC, where we show that the REE procedure can be applied effectively in a multi-channel AEC (MCAEC) setting to indirectly assist the recovery of lost AEC performance due to inter-channel correlation, known generally as the "non-uniqueness" problem. We develop a novel, computationally efficient technique of frequency-domain resampling (FDR) that effectively alleviates the non-uniqueness problem directly while introducing minimal distortion to signal quality and statistics. We also apply the system approach to the multi-delay filter (MDF) that suffers from the inter-block correlation problem. Finally, we generalize the MCAEC problem in the SBSS framework and discuss many issues related to the implementation of an SBSS system. We propose a constrained batch-online implementation of SBSS that stabilizes the convergence behavior even in the worst case scenario of a single far-end talker along with the non-uniqueness condition on the far-end mixing system. The proposed techniques are developed from a pragmatic standpoint, motivated by real-world problems in acoustic and audio signal processing. Generalization of the orthogonality principle to the system level of an AEC problem allows us to relate AEC to source separation that seeks to maximize the independence, hence implicitly the orthogonality, not only between the error signal and the far-end signal, but rather, among all signals involved. The system approach, for which the REE paradigm is just one realization, enables the encompassing of many traditional signal enhancement techniques in analytically consistent yet practically effective manner for solving the enhancement problem in a very noisy and disruptive acoustic mixing environment.