Flexible LDPC Decoder Architectures

Flexible channel decoding is getting significance with the increase in number of wireless standards and modes within a standard. A flexible channel decoder is a solution providing interstandard and intrastandard support without change in hardware. However, the design of efficient implementation of flexible low-density parity-check (LDPC) code decoders satisfying area, speed, and power constraints is a challenging task and still requires considerable research effort. This paper provides an overview of state-of-the-art in the design of flexible LDPC decoders. The published solutions are evaluated at two levels of architectural design: the processing element (PE) and the interconnection structure. A qualitative and quantitative analysis of different design choices is carried out, and comparison is provided in terms of achieved flexibility, throughput, decoding efficiency, and area (power) consumptio

Design tradeoffs and challenges in practical coherent optical transceiver implementations

This tutorial discusses the design and ASIC implementation of coherent optical transceivers. Algorithmic and architectural options and tradeoffs between performance and complexity/power dissipation are presented. Particular emphasis is placed on flexible (or reconfigurable) transceivers because of their importance as building blocks of software-defined optical networks. The paper elaborates on some advanced digital signal processing (DSP) techniques such as iterative decoding, which are likely to be applied in future coherent transceivers based on higher order modulations. Complexity and performance of critical DSP blocks such as the forward error correction decoder and the frequency-domain bulk chromatic dispersion equalizer are analyzed in detail. Other important ASIC implementation aspects including physical design, signal and power integrity, and design for testability, are also discussed.Fil: Morero, Damián Alfonso. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. ClariPhy Argentina S.A.; ArgentinaFil: Castrillon, Alejandro. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; ArgentinaFil: Aguirre, Alejandro. ClariPhy Argentina S.A.; ArgentinaFil: Hueda, Mario Rafael. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Córdoba. Instituto de Estudios Avanzados en Ingeniería y Tecnología. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas Físicas y Naturales. Instituto de Estudios Avanzados en Ingeniería y Tecnología; ArgentinaFil: Agazzi, Oscar Ernesto. Universidad Nacional de Córdoba. Facultad de Ciencias Exactas, Físicas y Naturales; Argentina. ClariPhy Argentina S.A.; Argentin

New Algorithms for High-Throughput Decoding with Low-Density Parity-Check Codes using Fixed-Point SIMD Processors

Most digital signal processors contain one or more functional units with a single-instruction, multiple-data architecture that supports saturating fixed-point arithmetic with two or more options for the arithmetic precision. The processors designed for the highest performance contain many such functional units connected through an on-chip network. The selection of the arithmetic precision provides a trade-off between the task-level throughput and the quality of the output of many signal-processing algorithms, and utilization of the interconnection network during execution of the algorithm introduces a latency that can also limit the algorithm\u27s throughput. In this dissertation, we consider the turbo-decoding message-passing algorithm for iterative decoding of low-density parity-check codes and investigate its performance in parallel execution on a processor of interconnected functional units employing fast, low-precision fixed-point arithmetic. It is shown that the frequent occurrence of saturation when 8-bit signed arithmetic is used severely degrades the performance of the algorithm compared with decoding using higher-precision arithmetic. A technique of limiting the magnitude of certain intermediate variables of the algorithm, the extrinsic values, is proposed and shown to eliminate most occurrences of saturation, resulting in performance with 8-bit decoding nearly equal to that achieved with higher-precision decoding. We show that the interconnection latency can have a significant detrimental effect of the throughput of the turbo-decoding message-passing algorithm, which is illustrated for a type of high-performance digital signal processor known as a stream processor. Two alternatives to the standard schedule of message-passing and parity-check operations are proposed for the algorithm. Both alternatives markedly reduce the interconnection latency, and both result in substantially greater throughput than the standard schedule with no increase in the probability of error

FPGA-Based Channel Coding Architectures for 5G Wireless Using High-Level Synthesis

We propose strategies to achieve a high-throughput FPGA architecture for quasi-cyclic low-density parity-check codes based on circulant-1 identity matrix construction. By splitting the node processing operation in the min-sum approximation algorithm, we achieve pipelining in the layered decoding schedule without utilizing additional hardware resources. High-level synthesis compilation is used to design and develop the architecture on the FPGA hardware platform. To validate this architecture, an IEEE 802.11n compliant 608 Mb/s decoder is implemented on the Xilinx Kintex-7 FPGA using the LabVIEW FPGA Compiler in the LabVIEW Communication System Design Suite. Architecture scalability was leveraged to accomplish a 2.48 Gb/s decoder on a single Xilinx Kintex-7 FPGA. Further, we present rapidly prototyped experimentation of an IEEE 802.16 compliant hybrid automatic repeat request system based on the efficient decoder architecture developed. In spite of the mixed nature of data processing—digital signal processing and finite-state machines—LabVIEW FPGA Compiler significantly reduced time to explore the system parameter space and to optimize in terms of error performance and resource utilization. A 4x improvement in the system throughput, relative to a CPU-based implementation, was achieved to measure the error-rate performance of the system over large, realistic data sets using accelerated, in-hardware simulation

Design and implementation of decoders for error correction in high-speed communication systems

This thesis is focused on the design and implementation of binary low-density parity-check (LDPC) code decoders for high-speed modern communication systems. The basic of LDPC codes and the performance and bottlenecks, in terms of complexity and hardware efficiency, of the main soft-decision and hard-decision decoding algorithms (such as Min-Sum, Optimized 2-bit Min-Sum and Reliability-based iterative Majority-Logic) are analyzed. The complexity and performance of those algorithms are improved to allow efficient hardware architectures. A new decoding algorithm called One-Minimum Min-Sum is proposed. It reduces considerably the complexity of the check node update equations of the Min-Sum algorithm. The second minimum is estimated from the first minimum value by a means of a linear approximation that allows a dynamic adjustment. The Optimized 2-bit Min-Sum algorithm is modified to initialize it with the complete LLR values and to introduce the extrinsic information in the messages sent from the variable nodes. Its variable node equation is reformulated to reduce its complexity. Both algorithms were tested for the (2048,1723) RS-based LDPC code and (16129,15372) LDPC code using an FPGA-based hardware emulator. They exhibit BER performance very close to Min-Sum algorithm and do not introduce early error-floor. In order to show the hardware advantages of the proposed algorithms, hardware decoders were implemented in a 90 nm CMOS process and FPGA devices based on two types of architectures: full-parallel and partial-parallel one with horizontal layered schedule. The results show that the decoders are more area-time efficient than other published decoders and that the low-complexity of the Modified Optimized 2-bit Min-Sum allows the implementation of 10 Gbps decoders in current FPGA devices. Finally, a new hard-decision decoding algorithm, the Historical-Extrinsic Reliability-Based Iterative Decoder, is presented. This algorithm introduces the new idea of considering hard-decision votes as soft-decision to compute the extrinsic information of previous iterations. It is suitable for high-rate codes and improves the BER performance of the previous RBI-MLGD algorithms, with similar complexity.Esta tesis se ha centrado en el diseño e implementación de decodificadores binarios basados en códigos de comprobación de paridad de baja densidad (LDPC) válidos para los sistemas de comunicación modernos de alta velocidad. Los conceptos básicos de códigos LDPC, sus prestaciones y cuellos de botella, en términos de complejidad y eficiencia hardware, fueron analizados para los principales algoritmos de decisión soft y decisión hard (como Min-Sum, Optimized 2-bit Min-Sum y Reliability-based iterative Majority-Logic). La complejidad y prestaciones de estos algoritmos se han mejorado para conseguir arquitecturas hardware eficientes. Se ha propuesto un nuevo algoritmo de decodificación llamado One-Minimum Min-Sum. Éste reduce considerablemente la complejidad de las ecuaciones de actualización del nodo de comprobación del algoritmo Min-Sum. El segundo mínimo se ha estimado a partir del valor del primer mínimo por medio de una aproximación lineal, la cuál permite un ajuste dinámico. El algoritmo Optimized 2-bit Min-Sum se ha modificado para ser inicializado con los valores LLR e introducir la información extrínseca en los mensajes enviados desde los nodos variables. La ecuación del nodo variable de este algoritmo ha sido reformulada para reducir su complejidad. Ambos algoritmos fueron probados para el código (2048,1723) RS-based LDPC y para el código (16129,15372) LDPC utilizando un emulador hardware implementado en un dispositivo FPGA. Éstos han alcanzado unas prestaciones de BER muy cercanas a las del algoritmo Min-Sum evitando, además, la aparición temprana del fenómeno denominado suelo del error. Con el objetivo de mostrar las ventajas hardware de los algoritmos propuestos, los decodificadores se implementaron en hardware utilizando tecnología CMOS de 90 nm y en dispositivos FPGA basados en dos tipos de arquitecturas: completamente paralela y parcialmente paralela utilizando el método de actualización por capas horizontales. Los resultados muestran que los decodificadores propuestos e implementados son más eficientes en área-tiempo que otros decodificadores publicados y que la baja complejidad del algoritmo Modified Optimized 2-bit Min-Sum permite la implementación de decodificadores en los dispositivos FPGA actuales consiguiendo una tasa de 10 Gbps. Finalmente, se ha presentado un nuevo algoritmo de decodificación de decisión hard, el Historical-Extrinsic Reliability-Based Iterative Decoder. Este algoritmo introduce la nueva idea de considerar los votos de decisión hard como decisión soft para calcular la información extrínseca de iteracions anteriores. Este algoritmo es adecuado para códigos de alta velocidad y mejora el rendimiento BER de los algoritmos RBI-MLGD anteriores, con una complejidad similar.Aquesta tesi s'ha centrat en el disseny i implementació de descodificadors binaris basats en codis de comprovació de paritat de baixa densitat (LDPC) vàlids per als sistemes de comunicació moderns d'alta velocitat. Els conceptes bàsics de codis LDPC, les seues prestacions i colls de botella, en termes de complexitat i eficiència hardware, van ser analitzats pels principals algoritmes de decisió soft i decisió hard (com el Min-Sum, Optimized 2-bit Min-Sum y Reliability-based iterative Majority-Logic). La complexitat i prestacions d'aquests algoritmes s'han millorat per aconseguir arquitectures hardware eficients. S'ha proposat un nou algoritme de descodificació anomenat One-Minimum Min-Sum. Aquest redueix considerablement la complexitat de les equacions d'actualització del node de comprovació del algoritme Min-Sum. El segon mínim s'ha estimat a partir del valor del primer mínim per mitjà d'una aproximació lineal, la qual permet un ajust dinàmic. L'algoritme Optimized 2-bit Min-Sum s'ha modificat per ser inicialitzat amb els valors LLR i introduir la informació extrínseca en els missatges enviats des dels nodes variables. L'equació del node variable d'aquest algoritme ha sigut reformulada per reduir la seva complexitat. Tots dos algoritmes van ser provats per al codi (2048,1723) RS-based LDPC i per al codi (16129,15372) LDPC utilitzant un emulador hardware implementat en un dispositiu FPGA. Aquests han aconseguit unes prestacions BER molt properes a les del algoritme Min-Sum evitant, a més, l'aparició primerenca del fenomen denominat sòl de l'error. Per tal de mostrar els avantatges hardware dels algoritmes proposats, els descodificadors es varen implementar en hardware utilitzan una tecnologia CMOS d'uns 90 nm i en dispositius FPGA basats en dos tipus d'arquitectures: completament paral·lela i parcialment paral·lela utilitzant el mètode d'actualització per capes horitzontals. Els resultats mostren que els descodificadors proposats i implementats són més eficients en àrea-temps que altres descodificadors publicats i que la baixa complexitat del algoritme Modified Optimized 2-bit Min-Sum permet la implementació de decodificadors en els dispositius FPGA actuals obtenint una taxa de 10 Gbps. Finalment, s'ha presentat un nou algoritme de descodificació de decisió hard, el Historical-Extrinsic Reliability-Based Iterative Decoder. Aquest algoritme presenta la nova idea de considerar els vots de decisió hard com decisió soft per calcular la informació extrínseca d'iteracions anteriors. Aquest algoritme és adequat per als codis d'alta taxa i millora el rendiment BER dels algoritmes RBI-MLGD anteriors, amb una complexitat similar.Català Pérez, JM. (2017). Design and implementation of decoders for error correction in high-speed communication systems [Tesis doctoral no publicada]. Universitat Politècnica de València. https://doi.org/10.4995/Thesis/10251/86152TESI

Codificación para corrección de errores con aplicación en sistemas de transmisión y almacenamiento de información

Tesis (DCI)--FCEFN-UNC, 2013Trata de una técnica de diseño de códigos de chequeo de paridad de baja densidad ( más conocidas por sigla en ingles como LDPC) y un nuevo algoritmo de post- procesamiento para la reducción del piso de erro

Flexible encoder and decoder of low density parity check codes

У дисертацији су предложена брза, флексибилна и хардверски ефикасна решења за кодовање и декодовање изузетно нерегуларних кодова са проверама парности мале густине (енгл. low-density parity-check, LDPC, codes) захтевана у савременим комуникационим стандардима. Један део доприноса дисертације је у новој делимично паралелној архитектури LDPC кодера за пету генерацију мобилних комуникација. Архитектура је заснована на флексибилној мрежи за кружни померај која омогућава паралелно процесирање више делова контролне матрице кратких кодова чиме се остварује сличан ниво паралелизма као и при кодовању дугачких кодова. Поред архитектуралног решења, предложена је оптимизација редоследа процесирања контролне матрице заснована на генетичком алгоритму, која омогућава постизање великих протока, малог кашњења и тренутно најбоље ефикасности искоришћења хардверских ресурса. У другом делу дисертације предложено је ново алгоритамско и архитектурално решење за декодовање структурираних LDPC кодова. Често коришћени приступ у LDPC декодерима је слојевито декодовање, код кога се услед проточне обраде јављају хазарди података који смањују проток. Декодер предложен у дисертацији у конфликтним ситуацијама на погодан начин комбинује слојевито и симултано декодовање чиме се избегавају циклуси паузе изазвани хазардима података. Овај приступ даје могућност за увођење великог броја степени проточне обраде чиме се постиже висока учестаност сигнала такта. Додатно, редослед процесирања контролне матрице је оптимизован коришћењем генетичког алгоритма за побољшане перформансе контроле грешака. Остварени резултати показују да, у поређењу са референтним решењима, предложени декодер остварује значајна побољшања у протоку и најбољу ефикасност за исте перформансе контроле грешака.The dissertation proposes high speed, flexible and hardware efficient solutions for coding and decoding of highly irregular low-density parity-check (LDPC) codes, required by many modern communication standards. The first part of the dissertation’s contributions is in the novel partially parallel LDPC encoder architecture for 5G. The architecture was built around the flexible shifting network that enables parallel processing of multiple parity check matrix elements for short to medium code lengths, thus providing almost the same level of parallelism as for long code encoding. In addition, the processing schedule was optimized for minimal encoding time using the genetic algorithm. The optimization procedure contributes to achieving high throughputs, low latency, and up to date the best hardware usage efficiency (HUE). The second part proposes a new algorithmic and architectural solution for structured LDPC code decoding. A widely used approach in LDPC decoders is a layered decoding schedule, which frequently suffers from pipeline data hazards that reduce the throughput. The decoder proposed in the dissertation conveniently incorporates both the layered and the flooding schedules in cases when hazards occur and thus facilitates LDPC decoding without stall cycles caused by pipeline hazards. Therefore, the proposed architecture enables insertion of many pipeline stages, which consequently provides a high operating clock frequency. Additionally, the decoding schedule was optimized for better signal-to-noise ratio (SNR) performance using genetic algorithm. The obtained results show that the proposed decoder achieves great throughput increase and the best HUE when compared with the state of the art for the same SNR performance