Since the 1950s, hidden Markov models (HMMS) have seen widespread use in electrical engineering. Foremost has been their use in speech processing, pattern recognition, artificial intelligence, queuing theory, and communications theory. However, recent years have witnessed a renaissance in the application of HMMs to the analysis and simulation of digital communication systems. Typical applications have included signal estimation, frequency tracking, equalization, burst error characterization, and transmit power control. Of special significance to this thesis, however, has been the use of HMMs to model fading channels typical of wireless communications. This variegated use of HMMs is fueled by their ability to model time-varying systems with memory, their ability to yield closed form solutions to otherwise intractable analytic problems, and their ability to help facilitate simple hardware and/or software based implementations of simulation test-beds. The aim of this thesis is to employ and exploit hidden Markov fading models within an iterative (turbo) decoding framework. Of particular importance is the problem of channel estimation, which is vital for realizing the large coding gains inherent in turbo coded schemes. This thesis shows that a Markov fading channel (MFC) can be conceptualized as a trellis, and that the transmission of a sequence over a MFC can be viewed as a trellis encoding process much like convolutional encoding. The thesis demonstrates that either maximum likelihood sequence estimation (MLSE) algorithms or maximum <I> a posteriori</I> (MAP) algorithms operating over the trellis defined by the MFC can be used for channel estimation. Furthermore, the thesis illustrates sequential and decision-directed techniques for using the aforementioned trellis based channel estimators <I>en masse</I> with an iterative decoder. / Master of Science

In this thesis, we present low latency general concatenated code structures suitable for parallel processing. We propose parallel decodable serially concatenated codes (PDSCCs) which is a general structure to construct many variants of serially concatenated codes. Using this most general structure we derive parallel decodable serially concatenated convolutional codes (PDSCCCs). Convolutional product codes which are instances of PDSCCCs are studied in detail. PDSCCCs have much less decoding latency and show almost the same performance compared to classical serially concatenated convolutional codes. Using the same idea, we propose parallel decodable turbo codes (PDTCs) which represent a general structure to construct parallel concatenated codes. PDTCs have much less latency compared to classical turbo codes and they both achieve similar performance. We extend the approach proposed for the construction of parallel decodable concatenated codes to trellis coded modulation, turbo channel equalization, and space time trellis codes and show that low latency systems can be constructed using the same idea. Parallel decoding operation introduces new problems in implementation. One such problem is memory collision which occurs when multiple decoder units attempt accessing the same memory device. We propose novel interleaver structures which prevent the memory collision problem while achieving performance close to other interleavers.

Deux défis de la théorie du codage algébrique sont traités dans cette thèse. Le premier est le décodage efficace (dur et souple) de codes de Reed--Solomon généralisés sur les corps finis en métrique de Hamming. La motivation pour résoudre ce problème vieux de plus de 50 ans a été renouvelée par la découverte par Guruswami et Sudan à la fin du 20ème siècle d'un algorithme polynomial de décodage jusqu'au rayon Johnson basé sur l'interpolation. Les premières méthodes de décodage algébrique des codes de Reed--Solomon généralisés faisaient appel à une équation clé, c'est à dire, une description polynomiale du problème de décodage. La reformulation de l'approche à base d'interpolation en termes d'équations clés est un thème central de cette thèse. Cette contribution couvre plusieurs aspects des équations clés pour le décodage dur ainsi que pour la variante décodage souple de l'algorithme de Guruswami--Sudan pour les codes de Reed--Solomon généralisés. Pour toutes ces variantes un algorithme de décodage efficace est proposé. Le deuxième sujet de cette thèse est la formulation et le décodage jusqu'à certaines bornes inférieures sur leur distance minimale de codes en blocs linéaires cycliques. La caractéristique principale est l'intégration d'un code cyclique donné dans un code cyclique produit (généralisé). Nous donnons donc une description détaillée du code produit cyclique et des codes cycliques produits généralisés. Nous prouvons plusieurs bornes inférieures sur la distance minimale de codes cycliques linéaires qui permettent d'améliorer ou de généraliser des bornes connues. De plus, nous donnons des algorithmes de décodage d'erreurs/d'effacements [jusqu'à ces bornes] en temps quadratique.

International Telemetering Conference Proceedings / October 18-21, 2004 / Town & Country Resort, San Diego, California / This paper presents a joint source-channel decoding scheme based on a JPEG2000 source coder and an LDPC channel coder. At the encoder, JPEG2000 is used to perform source coding with certain error resilience (ER) modes, and LDPC codes are used to perform channel coding. At the decoder, after one iteration of LDPC decoding, the output codestream is then decoded by JPEG2000. With the error resilience mode switches on, the source decoder detects the position of the first error within each codeblock of the JPEG2000 codestream. This information is fed back to the channel decoder, and incorporated into the calculation of likelihood values of variable nodes for the next iteration of LDPC decoding. Our results indicate that the proposed method has significant gains over conventional separate channel and source decoding.

ITC/USA 2007 Conference Proceedings / The Forty-Third Annual International Telemetering Conference and Technical Exhibition / October 22-25, 2007 / Riviera Hotel & Convention Center, Las Vegas, Nevada / An acoustic modem employing direct-sequence spread-spectrum (DSSS) signaling is considered with LDPC coding. The underwater acoustic channel is tracked using a Kalman filter which requires accurate data decisions. To improve KF performance and reduce the overall error rate, joint iterative LDPC decoding and channel estimation is proposed based on a factor graph and sum-product algorithm approximation. In this scheme, the decoder posterior log likelihood ratios (LLRs) provide data decisions for the KF. Decoder extrinsic LLRs are similarly incorporated into the detector LLRs to yield improved priors for decoding. Error rate simulations of the overall modem are provided for a shallow-water channel model with Ricean/Rayleigh fading.

International Telemetering Conference Proceedings / October 25-28, 1993 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Soft-decision correlation decoding with retransmission requests for block codes is proposed and the resulting performance is analyzed. The correlation decoding rule is modified to allow retransmission requests when the received word is rendered unreliable by the channel noise. The modification is realized by a reduction in the volume in Euclidean space of the decoding region corresponding to each codeword. The performance analysis reveals the typical throughput - reliability trade-off characteristic of error control systems which employ retransmissions. Performance comparisons with hard-decision decoding reveal performance improvements beyond those attainable with hard-decision decoding algorithms. The proposed soft-decision decoding rule permits the use of a simplified codeword searching algorithm which reduces the complexity of the correlation decoder to the point where practical implementation is feasible.

International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Low-Density Parity-Check (LDPC) codes are powerful codes capable of nearly achieving the Shannon channel capacity. This paper presents a tutorial introduction to LDPC codes, with a detailed description of the decoding algorithm. The algorithm propagates information about bit and check probabilities through a tree obtained from the Tanner graph for the code. This paper may be useful as a supplement in a course on error-control coding or digital communication.

För ett framgångsrikt varumärke är det viktigt att konsumenterna ser på företaget på samma sätt som företaget ser på sig själv. Det vill säga att ett företags identitet stämmer överens med företagets image. Om identitet och image faller långt ifrån varandra kan problem uppstå för företaget och det blir svårare att reparera sin image (Kapferer, 2005). När en ny juicebar intog den svenska marknaden med ett annorlunda koncept som alkoholfri cocktailbar ställdes identitet och image mot varandra. Med hjälp av Stuart Halls teori om encoding/decoding, Kapferers Brand Identity Prism och associationsteorier undersöktes Juiceverkets image och identitet. Det visade sig att det existerar ett gap mellan dem. Vissa delar av identiteten stämde överens med mottagarnas image av företaget, medan andra delar inte gjorde det. Ett gap existerar mellan mottagarnas image av företaget som fokus på hälsa, medan företaget menar att de inte är ett hälsoföretag. Mottagarna tolkar också företaget som trendigt och modernt medan Juiceverket menar att de undviker att följa trender. Kanske den största skillnaden i gapet mellan Juiceverkets identitet och image står i företagets identifiering av sig själva som en alkoholfri cocktailbar, medan mottagarna beskriver företaget som en trendig juicebar med hälsofokus.

The development of reading competency is one of the most significant pedagogical achievements during the first few years of schooling. Although most children learn to read successfully when exposed to reading instruction, up to 18% of children experience significant reading difficulty (Shaywitz, 1998). As a group, young children with speech impairment are at risk of reading impairment, with approximately 50% of these children demonstrating poor acquisition of early reading skills (Nathan, Stackhouse, Goulandris, & Snowling, 2004; Larivee & Catts, 1999). A number of variables contribute to reading outcomes for children with speech impairment including co-occurring language impairment, the nature and severity of their speech impairment as well as social and cultural influences. An area of research that has received increasing attention is understanding how access to the underlying sound structure or phonological representations of spoken words stored in long-term memory account for reading difficulties observed in children (Elbro, 1996; Fowler, 1991). Researchers have hypothesised that children with speech impairment may be at increased risk of reading disability due to deficits at the level of phonological representations (Bird, Bishop, & Freeman, 1995). Phonological representation deficits can manifest in poor performance on tasks that require children to think about the sound structure of words. Knowledge about the phonological components of words is commonly referred to as phonological awareness. Identifying and manipulating phonemes within words are examples of phonological awareness skills. Some children with speech impairment perform poorly on phonological awareness measures compared to children without speech difficulties (Bird et al., 1995; Carroll & Snowling, 2004; Rvachew, Ohberg, Grawburg, & Heyding, 2003). As performance on phonological awareness tasks is a strong predictor of early reading ability (Hogan, Catts, & Little, 2005), there is an important need to determine if children with speech impairment who demonstrate poor phonological awareness, have deficits at the level of phonological representations. This thesis reports a series of studies that investigated the relationship between phonological representations, phonological awareness, and word decoding ability in children with moderate to severe speech impairment. A child with complex communication needs (CCN) who used Augmentative and Alternative Communication (AAC) was also examined to determine how the absence of effective articulation skills influences the development of phonological representations. The study employed a longitudinal design to compare the performance of nine children (aged 3:09-5:03 at initial assessment) with moderate to severe speech impairment and 17 children with typical speech development on novel assessment measures designed to determine characteristics of children's phonological representations. The tasks required children to judge the accuracy of spoken multisyllable words and newly learned nonwords. The relationships between performance on these tasks and measures of speech, phonological awareness and early print decoding were also examined. Four assessment trials were implemented at six-monthly intervals over an 18-month period. The first assessment trial was administered approximately 6 to12 months before children commenced school. The fourth trial was administered after children had completed 6 to 12 months of formal education. The child with CCN completed three assessment trials over a period of 16 months. Data analyses revealed that the children with speech impairment had significantly greater difficulty (p<0.01) judging mispronounced multisyllable words compared to their peers with typical speech development. As a group, children with speech impairment also demonstrated inferior performance on the judgment of mispronounced forms of newly learned nonwords (p<0.05). No group differences were observed on the judgment of correctly pronounced real and nonword stimuli. Significant group differences on speech production and phoneme segmentation tasks were identified at each assessment trial. Moderate to high correlations (i.e., r = 0.40 to 0.70) were also observed between performance on the phonological representation tasks and performance on phonological awareness and speech production measures at each trial across the study. Although no significant group differences were observed on the nonword decoding task, 4 of the 9 children with speech impairment could not decode any letters in nonwords (compared to only 1 child without speech impairment) at the final assessment trial when children were 6-years-old. Two children with speech impairment showed superior nonword decoding ability at trial 3 and 4. The within-group variability observed on the nonword decoding task highlighted the heterogeneity of children with speech impairment. The performances of four children with speech impairment with differing types of speech error patterns were analysed to investigate the role of phonological representations in their speech and phonological awareness development. The child with delayed speech development and excellent phonological awareness at trial 1, demonstrated superior phonological awareness and word decoding skills at age 6 years, although his performance on phonological representation tasks was inconsistent across trials. In contrast, a child with delayed development and poor early phonological awareness demonstrated weak performance on phonological representation, phonological awareness, and decoding at each successive assessment trial. The child with a high percentage of inconsistent speech error patterns generally demonstrated poor performance on phonological representation, phonological awareness and decoding measures at each of the 4 assessment trials. The child with consistent and unusual speech error patterns showed increasingly stronger performance on the phonological representation tasks and average performance on phonological awareness but limited word decoding ability at age 6. The 11-year-old girl with CCN, whose speech attempts were limited and unintelligible, demonstrated below average performance on phonological representation tasks, suggesting that an absence of articulatory feedback may negatively influence the development of well-specified phonological representations. This thesis provides evidence for the use of receptive tasks to identify differences in the phonological representations of children with and without speech impairment. The findings also provide support for the link between the representation of phonological information in long-term memory and children's speech production accuracy, phonological awareness and print decoding ability. The variable performance of some children with speech impairment and the child with cerebral palsy demonstrate the need to consider individual characteristics to develop an understanding of how children store and access speech sound information to assist their acquisition of early reading skills.

International Telemetering Conference Proceedings / October 30-November 02, 1995 / Riviera Hotel, Las Vegas, Nevada / This paper describes the development of a Reed-Solomon (RS) Encoder-Decoder which implements the RS segment of the telemetry channel coding scheme recommended by the Consultative Committee on Space Data Systems (CCSDS)[1]. The Euclidean algorithm has been chosen for the decoder implementation, the hardware realization taking a systolic array approach. The fully pipelined decoder runs on a single clock and the operating speed is limited only by the Galois Field (GF) multiplier's delay. The circuit has been synthesised from VHDL descriptions and the hardware is being realised using programmable logic chips. This circuit was simulated for functional operation and found to perform correction of error patterns exactly as predicted by theory.