In wireless communication systems, the use of multiple antennas, also known as Multiple-Input Multiple-Output(MIMO) communications, is now a widely accepted and important technology for improving their reliability and throughput performance. However, in order to achieve the performance gains predicted by the theory, the transmitter and receiver need to have accurate and up-to-date Channel State Information(CSI) to overcome the vagaries of the fading environment. Traditionally, the CSI is obtained at the receiver by sending a known training sequence in the forward-link direction. This CSI has to be conveyed to the transmitter via a low-rate, low latency and noisy feedback channel in the reverse-link direction. This thesis addresses three key challenges in sending the CSI to the transmitter of a MIMO communication system over the reverse-link channel, and provides novel solutions to them. The first issue is that the available CSI at the receiver has to be quantized to a finite number of bits, sent over a noisy feedback channel, reconstructed at the transmitter, and used by the transmitter for precoding its data symbols. In particular, the CSI quantization technique has to be resilient to errors introduced by the noisy reverse-link channel, and it is of interest to design computationally simple, linear filters to mitigate these errors. The second issue addressed is the design of low latency and low decoding complexity error correction codes to provide protection against fading conditions and noise in the reverse-link channel. The third issue is to improve the resilience of the reverse-link channel to fading. The solution to the first problem is obtained by proposing two classes of receive filtering techniques, where the output of the source decoder is passed through a filter designed to reduce the overall distortion including the effect of the channel noise. This work combines the high resolution quantization theory and the optimal Minimum Mean Square Error(MMSE) filtering formulation to analyze, and optimize, the total end-to-end distortion. As a result, analytical expressions for the linear receive filters are obtained that minimize the total end-to-end distortion, given the quantization scheme and source(channel state) distribution. The solution to the second problem is obtained by proposing a new family of error correction codes, termed trellis coded block codes, where a trellis code and block code are concatenated in order to provide good coding gain as well as low latency and low complexity decoding. This code construction is made possible due to the existence of a uniform partitioning of linear block codes. The solution to the third problem is obtained by proposing three novel transmit precoding methods that are applicable to time-division-duplex systems, where the channel reciprocity can be exploited in designing the precoding scheme. The proposed precoding methods convert the Rayleigh fading MIMO channel into parallel Additive White Gaussian Noise(AWGN) channels with fixed gain, while satisfying an average transmit power constraint. Moreover, the receiver does not need to have knowledge of the CSI in order to decode the received data. These precoding methods are also extended to Rayleigh fading multi-user MIMO channels. Finally, all the above methods are applied to the problem of designing a low-rate, low-latency code for the noisy and fading reverse-link channel that is used for sending the CSI. Simulation results are provided to demonstrate the improvement in the forward-link data rate due to the proposed methods. Note that, although the three solutions are presented in the context of CSI feedback in MIMO communications, their development is fairly general in nature, and, consequently, the solutions are potentially applicable in other communication systems also.

CAPES / Códigos corretores de erros estão presentes em quase todos os sistemas modernos de comunicação e armazenamento de dados. Erros durante essas operações são praticamente inevitáveis devido a ruído e interferências nos meios de comunicação e degradação dos meios de armazenamento. Quando um sistema exige alto desempenho, os correspondentes algoritmos (codificador e decodificador) são implementados em hardware. O projeto de pesquisa apresentado nesta tese, um chip dedicado para uma nova família de decodificadores baseados em conjuntos de informação, é parte de um amplo projeto que visa obter um decodificador com desempenho semelhante à decodificação de máxima verossimilhança (MLD), porém com hardware muito mais simples, demonstrando assim que o uso dessa técnica (decodificação por conjuntos de informação), até então proibitiva devido à complexidade do hardware, poderia tornar-se viável. Visando simplificar o hardware, o primeiro passo foi modificar o algoritmo original de Dorsch para reduzir o número de ciclos de clock necessários para decodificar uma mensagem. As principais modificações realizadas foram na redução de Gauss-Jordan e no número de palavras-código candidatas, consideravelmente reduzidas em relação ao algoritmo original de Dorsch. Este algoritmo modificado foi primeiramente implementado utilizando linguagem de descrição de hardware e avaliado em diferentes famílias de FPGAs, onde demonstrou-se o mesmo ser viável, mesmo para grandes códigos. O algoritmo foi implementado posteriormente em um chip dedicado (ASIC), utilizando tecnologia CMOS, a fim de completar a demonstração da viabilidade de sua implementação e uso efetivo. / Error-correcting codes are present in almost all modern data communications and data storage systems. Errors during these operations are practically inevitable because of noise and interference in communication channels and degradation of storage media. When topperformance is required, the corresponding algorithms (encoder and decoder) are implemented in hardware. The research project presented in this dissertation, a dedicated chip for a new family of decoders based on information sets, is part of a broad project targeting the development of a new decoder capable of achieving near maximum likelihood decoding (MLD) performance, however with a much simpler hardware, thus demonstrating that the use of this technique (decoding based on information sets), previously prohibitive due to the complexity of the hardware, could now be feasible. Aiming to simplify the hardware, the first step was to modify the original Dorsch algorithm to reduce the number of clock cycles needed to decode a message. The main modifications performed were in the Gauss Jordan elimination procedure and in the number of candidate codewords, which was highly reduced with respect to original Dorsch algorithm. This modified algorithm was first implemented using a hardware description language and evaluated in different FPGA families, where the viability was demonstrated. The algorithm was later implemented in a dedicated chip (ASIC) using CMOS technology in order to complete the demonstration of the feasibility of their implementation, and effective use.

CAPES / Códigos corretores de erros estão presentes em quase todos os sistemas modernos de comunicação e armazenamento de dados. Erros durante essas operações são praticamente inevitáveis devido a ruído e interferências nos meios de comunicação e degradação dos meios de armazenamento. Quando um sistema exige alto desempenho, os correspondentes algoritmos (codificador e decodificador) são implementados em hardware. O projeto de pesquisa apresentado nesta tese, um chip dedicado para uma nova família de decodificadores baseados em conjuntos de informação, é parte de um amplo projeto que visa obter um decodificador com desempenho semelhante à decodificação de máxima verossimilhança (MLD), porém com hardware muito mais simples, demonstrando assim que o uso dessa técnica (decodificação por conjuntos de informação), até então proibitiva devido à complexidade do hardware, poderia tornar-se viável. Visando simplificar o hardware, o primeiro passo foi modificar o algoritmo original de Dorsch para reduzir o número de ciclos de clock necessários para decodificar uma mensagem. As principais modificações realizadas foram na redução de Gauss-Jordan e no número de palavras-código candidatas, consideravelmente reduzidas em relação ao algoritmo original de Dorsch. Este algoritmo modificado foi primeiramente implementado utilizando linguagem de descrição de hardware e avaliado em diferentes famílias de FPGAs, onde demonstrou-se o mesmo ser viável, mesmo para grandes códigos. O algoritmo foi implementado posteriormente em um chip dedicado (ASIC), utilizando tecnologia CMOS, a fim de completar a demonstração da viabilidade de sua implementação e uso efetivo. / Error-correcting codes are present in almost all modern data communications and data storage systems. Errors during these operations are practically inevitable because of noise and interference in communication channels and degradation of storage media. When topperformance is required, the corresponding algorithms (encoder and decoder) are implemented in hardware. The research project presented in this dissertation, a dedicated chip for a new family of decoders based on information sets, is part of a broad project targeting the development of a new decoder capable of achieving near maximum likelihood decoding (MLD) performance, however with a much simpler hardware, thus demonstrating that the use of this technique (decoding based on information sets), previously prohibitive due to the complexity of the hardware, could now be feasible. Aiming to simplify the hardware, the first step was to modify the original Dorsch algorithm to reduce the number of clock cycles needed to decode a message. The main modifications performed were in the Gauss Jordan elimination procedure and in the number of candidate codewords, which was highly reduced with respect to original Dorsch algorithm. This modified algorithm was first implemented using a hardware description language and evaluated in different FPGA families, where the viability was demonstrated. The algorithm was later implemented in a dedicated chip (ASIC) using CMOS technology in order to complete the demonstration of the feasibility of their implementation, and effective use.

Space-Time Block Coding is an efficient communication technique used in multiple-input multiple-output wireless systems. The complexity with which a Space-Time Block Code (STBC) can be decoded is important from an implementation point of view since it directly affects the receiver complexity and speed. In this thesis, we address the problem of designing low complexity decoding techniques for STBCs, and constructing STBCs that achieve high rate and full-diversity with these decoders. This thesis is divided into two parts; the first is concerned with the optimal decoder, viz. the maximum-likelihood (ML) decoder, and the second with non-ML decoders. An STBC is said to be multigroup ML decodable if the information symbols encoded by it can be partitioned into several groups such that each symbol group can be ML decoded independently of the others, and thereby admitting low complexity ML decoding. In this thesis, we first give a new framework for constructing low ML decoding complexity STBCs using codes over the Klein group, and show that almost all known low ML decoding complexity STBCs can be obtained by this method. Using this framework we then construct new full-diversity STBCs that have the least known ML decoding complexity for a large set of choices of number of transmit antennas and rate. We then introduce the notion of Asymptotically-Good (AG) multigroup ML decodable codes, which are families of multigroup ML decodable codes whose rate increases linearly with the number of transmit antennas. We give constructions for full-diversity AG multigroup ML decodable codes for each number of groups g > 1. For g > 2, these are the first instances of g-group ML decodable codes that are AG or have rate more than 1. For g = 2 and identical delay, the new codes match the known families of AG codes in terms of rate. In the final section of the first part we show that the upper triangular matrix R encountered during the sphere-decoding of STBCs can be rank-deficient, thus leading to higher sphere-decoding complexity, even when the rate is less than the minimum of the number of transmit antennas and the number receive antennas. We show that all known AG multigroup ML decodable codes suffer from such rank-deficiency, and we explicitly derive the sphere-decoding complexities of most known AG multigroup ML decodable codes. In the second part of this thesis we first study a low complexity non-ML decoder introduced by Guo and Xia called Partial Interference Cancellation (PIC) decoder. We give a new full-diversity criterion for PIC decoding of STBCs which is equivalent to the criterion of Guo and Xia, and is easier to check. We then show that Distributed STBCs (DSTBCs) used in wireless relay networks can be full-diversity PIC decoded, and we give a full-diversity criterion for the same. We then construct full-diversity PIC decodable STBCs and DSTBCs which give higher rate and better error performance than known multigroup ML decodable codes for similar decoding complexity, and which include other known full-diversity PIC decodable codes as special cases. Finally, inspired by a low complexity essentially-ML decoder given by Sirianunpiboon et al. for the two and three antenna Perfect codes, we introduce a new non-ML decoder called Adaptive Conditional Zero-Forcing (ACZF) decoder which includes the technique of Sirianunpiboon et al. as a special case. We give a full-diversity criterion for ACZF decoding, and show that the Perfect codes for two, three and four antennas, the Threaded Algebraic Space-Time code, and the 4 antenna rate 2 code of Srinath and Rajan satisfy this criterion. Simulation results show that the proposed decoder performs identical to ML decoding for these five codes. These STBCs along with ACZF decoding have the best error performance with least complexity among all known STBCs for four or less transmit antennas.

One of the most popular ways to exploit the advantages of a multiple-input multiple-output (MIMO) system is using space time block coding. A space time block code (STBC) is a finite set of complex matrices whose entries consist of the information symbols to be transmitted. A linear STBC is one in which the information symbols are linearly combined to form a two-dimensional code matrix. A well known method of maximum-likelihood (ML) decoding of such STBCs is using the sphere decoder (SD). In this thesis, new constructions of STBCs with low sphere decoding complexity are presented and various ways of characterizing and reducing the sphere decoding complexity of an STBC are addressed. The construction of low sphere decoding complexity STBCs is tackled using irreducible matrix representations of Clifford algebras, cyclic division algebras and crossed-product algebras. The complexity reduction algorithms for the STBCs constructed are explored using tree based search algorithms. Considering an STBC as a vector space over the set of weight matrices, the problem of characterizing the sphere decoding complexity is addressed using quadratic form representations. The main results are as follows. A sub-class of fast decodable STBCs known as Block Orthogonal STBCs (BOSTBCs) are explored. A set of sufficient conditions to obtain BOSTBCs are explained. How the block orthogonal structure of these codes can be exploited to reduce the SD complexity of the STBC is then explained using a depth first tree search algorithm. Bounds on the SD complexity reduction and its relationship with the block orthogonal structure are then addressed. A set of constructions to obtain BOSTBCs are presented next using Clifford unitary weight designs (CUWDs), Coordinate-interleaved orthogonal designs (CIODs), cyclic division algebras and crossed product algebras which show that a lot of codes existing in literature exhibit the block orthogonal property. Next, the dependency of the ordering of information symbols on the SD complexity is discussed following which a quadratic form representation known as the Hurwitz-Radon quadratic form (HRQF) of an STBC is presented which is solely dependent on the weight matrices of the STBC and their ordering. It is then shown that the SD complexity is only a function of the weight matrices defining the code and their ordering, and not of the channel realization (even though the equivalent channel when SD is used depends on the channel realization). It is also shown that the SD complexity is completely captured into a single matrix obtained from the HRQF. Also, for a given set of weight matrices, an algorithm to obtain a best ordering of them leading to the least SD complexity is presented using the HRQF matrix.

Indiana University-Purdue University Indianapolis (IUPUI) / HEVC has achieved significant coding efficiency improvement beyond existing video coding standard by employing many new coding tools. Deblocking Filter, Sample Adaptive Offset and Adaptive Loop Filter for in-loop filtering are currently introduced for the HEVC standardization. However these filters are implemented in spatial domain despite the fact of temporal correlation within video sequences. To reduce the artifacts and better align object boundaries in video , a new algorithm in in-loop filtering is proposed. The proposed algorithm is implemented in HM-11.0 software. This proposed algorithm allows an average bitrate reduction of about 0.7% and improves the PSNR of the decoded frame by 0.05%, 0.30% and 0.35% in luminance and chroma.

Austin's Speech Act Theory is a valuable tool for the analysis of a literary text. In interaction, the intentionand purpose-success of linguistic communication can be gauged by establishing whether participants have met felicity conditions and have respected maxims. When the Co-operative Principle is ignored, special effects are achieved and receivers can only make sense of utterances through implicature and inferences based on background knowledge and mutual contextual beliefs. In the drama, Buzani kubawo, characters interact on four levels of time in space and place. They reveal themselves and convey theme through their speech and actions. Conflict is entrenched by lines of force drawn between opposing characters and between sub-worlds contrasted. Cohesion, determined by plot structure, and form, expressed on the endophoric and exophoric levels, give meaning to the drama. The micro-analysis of the wedding scene illustrates how communication can misfire should the playwright allow it! / African Languages / M.A. (African languages)

Austin's Speech Act Theory is a valuable tool for the analysis of a literary text. In interaction, the intentionand purpose-success of linguistic communication can be gauged by establishing whether participants have met felicity conditions and have respected maxims. When the Co-operative Principle is ignored, special effects are achieved and receivers can only make sense of utterances through implicature and inferences based on background knowledge and mutual contextual beliefs. In the drama, Buzani kubawo, characters interact on four levels of time in space and place. They reveal themselves and convey theme through their speech and actions. Conflict is entrenched by lines of force drawn between opposing characters and between sub-worlds contrasted. Cohesion, determined by plot structure, and form, expressed on the endophoric and exophoric levels, give meaning to the drama. The micro-analysis of the wedding scene illustrates how communication can misfire should the playwright allow it! / African Languages / M.A. (African languages)