The VLSI implementation complexity of a low density parity check (LDPC) decoder is largely influenced by the interconnect and the storage requirements. This dissertation presents the decoder architectures for regular and irregular LDPC codes that provide substantial gains over existing academic and commercial implementations. Several structured properties of LDPC codes and decoding algorithms are observed and are used to construct hardware implementation with reduced processing complexity. The proposed architectures utilize an on-the-fly computation paradigm which permits scheduling of the computations in a way that the memory requirements and re-computations are reduced. Using this paradigm, the run-time configurable and multi-rate VLSI architectures for the rate compatible array LDPC codes and irregular block LDPC codes are designed. Rate compatible array codes are considered for DSL applications. Irregular block LDPC codes are proposed for IEEE 802.16e, IEEE 802.11n, and IEEE 802.20. When compared with a recent implementation of an 802.11n LDPC decoder, the proposed decoder reduces the logic complexity by 6.45x and memory complexity by 2x for a given data throughput. When compared to the latest reported multi-rate decoders, this decoder design has an area efficiency of around 5.5x and energy efficiency of 2.6x for a given data throughput. The numbers are normalized for a 180nm CMOS process. Properly designed array codes have low error floors and meet the requirements of magnetic channel and other applications which need several Gbps of data throughput. A high throughput and fixed code architecture for array LDPC codes has been designed. No modification to the code is performed as this can result in high error floors. This parallel decoder architecture has no routing congestion and is scalable for longer block lengths. When compared to the latest fixed code parallel decoders in the literature, this design has an area efficiency of around 36x and an energy efficiency of 3x for a given data throughput. Again, the numbers are normalized for a 180nm CMOS process. In summary, the design and analysis details of the proposed architectures are described in this dissertation. The results from the extensive simulation and VHDL verification on FPGA and ASIC design platforms are also presented.

Traditional solutions to information security in communication systems act in the application layer and are oblivious to the effects in the physical layer. Physical-layer security methods, of which information-theoretic security is a special case, try to extract security from the random effects in the physical layer. In information-theoretic security, there are two asymptotic notions of secrecy---weak and strong secrecy This dissertation investigates the problem of information-theoretic strong secrecy on the binary erasure wiretap channel (BEWC) with a specific focus on designing practical codes. The codes designed in this work are based on analysis and techniques from error-correcting codes. In particular, the dual codes of certain low-density parity-check (LDPC) codes are shown to achieve strong secrecy in a coset coding scheme. First, we analyze the asymptotic block-error rate of short-cycle-free LDPC codes when they are transmitted over a binary erasure channel (BEC) and decoded using the belief propagation (BP) decoder. Under certain conditions, we show that the asymptotic block-error rate falls according to an inverse square law in block length, which is shown to be a sufficient condition for the dual codes to achieve strong secrecy. Next, we construct large-girth LDPC codes using algorithms from graph theory and show that the asymptotic bit-error rate of these codes follow a sub-exponential decay as the block length increases, which is a sufficient condition for strong secrecy. The secrecy rates achieved by the duals of large-girth LDPC codes are shown to be an improvement over that of the duals of short-cycle-free LDPC codes.

Digital technology has made complex signal processing possible in communication systems and greatly improved the performance and quality of most modern telecommunication systems. The telecommunication industry and specifically mobile wireless telephone and computer networks have shown phenomenal growth in both the number of subscribers and emerging services, resulting in rapid consumption of common resources of which the electromagnetic spectrum is the most important. Technological advances and research in digital communication are necessary to satisfy the growing demand, to fuel the demand and to exploit all the possibilities and business opportunities. Efficient management and distribution of resources facilitated by state-of-the-art algorithms are indispensable in modern communication networks. The challenge in communication system design is to construct a system that can accurately reproduce the transmitted source message at the receiver. The channel connecting the transmitter and receiver introduces detrimental effects and limits the reliability and speed of information transfer between the source and destination. Typical channel effects encountered in mobile wireless communication systems include path loss between the transmitter and receiver, noise caused by the environment and electronics in the system, and fading caused by multiple paths and movement in the communication channel. In multiple access systems, different users cause interference in each other’s signals and adversely affect the system performance. To ensure reliable communication, methods to overcome channel effects must be devised and implemented in the system. Techniques used to improve system performance and capacity include temporal, frequency, polarisation and spatial diversity. This dissertation is concerned mainly with temporal or time diversity. Channel coding is a temporal diversity scheme and aims to improve the system error performance by adding structured redundancy to the transmitted message. The receiver exploits the redundancy to infer with greater accuracy which message was transmitted, compared with uncoded systems. Sparse graph codes are channel codes represented as sparse probabilistic graphical models which originated in artificial intelligence theory. These channel codes are described as factor graph structures with bit nodes, representing the transmitted codeword bits, and bit-constrained or check nodes. Each constraint involves only a small number of code bits, resulting in a sparse factor graph with far fewer connections between bit and check nodes than the maximum number of possible connections. Sparse graph codes are iteratively decoded using message passing or belief propagation algorithms. Three classes of iteratively decodable channel codes are considered in this study, including low-density parity-check (LDPC), Turbo and repeat-accumulate (RA) codes. The modulation platform presented in this dissertation is a spectrally efficient wideband system employing orthogonal complex spreading sequences (CSSs) to spread information sequences over a wider frequency band in multiple modulation dimensions. Special features of these spreading sequences include their constant envelopes and power output, providing communication range or device battery life advantages. This study shows that multiple layer modulation (MLM) can be used to transmit parallel data streams with improved spectral efficiency compared with single-layer modulation, providing data throughput rates proportional to the number of modulation layers at performances equivalent to single-layer modulation. Alternatively, multiple modulation layers can be used to transmit coded information to achieve improved error performance at throughput rates equivalent to a single layer system / Dissertation (MEng (Electronic Engineering))--University of Pretoria, 2007. / Electrical, Electronic and Computer Engineering / unrestricted

Esta tesis estudia la distribución de ficheros en redes inalámbricas, analizando diferentes mecanismos que permiten optimizar la transmisión en términos de ancho de banda y calidad de experiencia. Concretamente, la tesis se centra en la transmisión de ficheros en canales multicast. Dicha transmisión resulta adecuada en ciertos entornos y tiene múltiples aplicaciones, algunas de las cuales se presentan en este trabajo. La tesis analiza en profundidad FLUTE (File Delivery over Unidirectional Transport), un protocolo para el envío fiable de ficheros en canales unidireccionales, y presenta algunas propuestas para mejorar la transmisión a través de dicho protocolo. En este sentido, una de las bases de este protocolo es el uso de un mecanismo llamado Tabla de Envío de Ficheros (FDT), que se utiliza para describir los contenidos transmitidos. Este trabajo analiza cómo la transmisión de la FDT afecta al funcionamiento del protocolo FLUTE, y proporciona una metodología para optimizar el envío de contenido mediante FLUTE. Por otro lado, en la transmisión de ficheros por multicast resulta esencial ofrecer un servicio fiable. Entre los distintos mecanismos utilizados por FLUTE para ofrecer fiabilidad, este trabajo analiza principalmente los códigos de corrección AL-FEC (Application Layer ¿ Forward Error Correction), los cuales añaden redundancia a la transmisión para minimizar los efectos de las pérdidas en el canal. Al respecto, esta tesis evalúa los códigos LDPC Staircase y LDPC Triangle, comparando su funcionamiento bajo diferentes condiciones de transmisión. Además, en el caso de tener un canal de retorno, una de las principales contribuciones de esta tesis es la propuesta de códigos LDPC adaptativos para servicios de descarga de ficheros. En esta clase de códigos, el servidor de contenidos cambia dinámicamente la cantidad de protección FEC proporcionada en función de las pérdidas que detectan los usuarios. La evaluación demuestra el buen funcionamiento de estos códigos en distintos entornos. / De Fez Lava, I. (2014). Evaluation of a content download service based on FLUTE and LDPC for improving the Quality of Experience over multicast wireless networks [Tesis doctoral]. Editorial Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/37051 / TESIS / Premios Extraordinarios de tesis doctorales

Channel coding plays a vital role in telecommunication. Low-Density Parity- Check (LDPC) codes are linear error-correcting codes. According to the 3rd Generation Partnership Project (3GPP) TS 38.212, LDPC is recommended for the Fifth-generation (5G) New Radio (NR) shared channels due to its high throughput, low latency, low decoding complexity and rate compatibility. LDPC encoding chain has been defined in 3GPP TS 38.212, but some details of LDPC encoding chain are still required to be explored in the MATLAB environment. For example, how to deal with the filler bits for encoding and decoding. However, as the reverse process of LDPC encoding, there is no information on LDPC decoding process for 5G NR shared channels in 3GPP TS 38.212. In this thesis project, LDPC encoding and decoding chains were thoughtfully developed with MATLAB programming based on 3GPP TS 38.212. Several LDPC decoding algorithms were implemented and optimized. The performance of LDPC algorithms was evaluated using block error rate (BLER) v.s. signal to noise ratio (SNR) and CPU time. Results show that the double diagonal structure-based encoding method is an efficient LDPC encoding algorithm for 5G NR. Layered Sum Product Algorithm (LSPA) and Layered Min-Sum Algorithm (LMSA) are more efficient than Sum Product Algorithm (SPA) and Min-Sum Algorithm (MSA). Layered Normalized Min-Sum Algorithm (LNMSA) with proper normalization factor and Layered Offset Min-Sum Algorithm (LOMSA) with good offset factor can optimize LMSA. The performance of LNMSA and LOMSA decoding depends more on code rate than transport block. / Kanalkodning spelar en viktig roll i telekommunikation. Paritetskontrollkoder med låg densitet (LDPC) är linjära felkorrigeringskoder. Enligt tredje generationens partnerskapsprojekt (3GPP) TS 38.212, LDPC rekommenderas för den femte generationens (5G) nya radio (NR) delade kanal på grund av dess höga genomströmning, låga latens, låga avkodningskomplexitet och hastighetskompatibilitet. LDPC kodningskedjan har definierats i 3GPP TS 38.212, men vissa detaljer i LDPC kodningskedjan krävs fortfarande för att utforskas i Matlabmiljön. Till exempel hur man hanterar fyllnadsbitar för kodning och avkodning. Men som den omvända processen för LDPC kodning finns det ingen information om LDPC avkodningsprocessen för 5G NR delade kanaler på 3GPP TS 38.212. I detta avhandlingsprojekt utvecklades LDPC-kodning och avkodningskedjor enligt 3GPP TS 38.212. Flera LDPC-avkodningsalgoritmer implementerades och optimerades. Prestandan för LDPC-algoritmer utvärderades med användning av blockfelshalt (BLER) v.s. signal / brusförhållande (SNR) och CPU-tid. Resultaten visar att den dubbla diagonala strukturbaserade kodningsmetoden är en effektiv LDPC kodningsalgoritm för 5G NR. Layered Sum Product Algorithm (LSPA) och Layered Min-Sum Algorithm (LMSA) är effektivare än Sum Product Algorithm (SPA) och Min-Sum Algorithm (MSA). Layered Normalized Min-Sum Algorithm (LNMSA) med rätt normaliseringsfaktor och Layered Offset Min-Sum Algorithm (LOMSA) med bra offsetfaktor kan optimera LMSA. Prestandan för LNMSA- och LOMSA-avkodning beror mer på kodhastighet än transportblock.