Thesis (M.S.)--Virginia Polytechnic Institute and State University, 1994. / Vita. Abstract. Includes bibliographical references (leaves 148-154). Also available via the Internet.

Orientador: Jaime Portugheis / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Eletrica e de Computação / Made available in DSpace on 2018-08-11T03:16:26Z (GMT). No. of bitstreams: 1 Nascimento_VagnerValedo_M.pdf: 1654073 bytes, checksum: fe7023b9741222f4780c06c588baf3a4 (MD5) Previous issue date: 2007 / Resumo: Este trabalho apresenta um estudo sobre a decodificação turbo q-ária em sistemas FFH-CDMA. Para alcançar o principal objetivo do estudo, foi desenvolvido um algoritmo para implementar a decodificação suave q-ária. Este algoritmo se baseia em uma adaptação do método de decodificação de Chase para suportar alfabetos q-ários. A proposta de decodificação iterativa (turbo) define um procedimento para viabilizar a realimentação dos símbolos q-ários decodificados e de suas respectivas confiabilidades em cada iteração do decodificador. Simulações foram realizadas considerando canais gaussianos e FFH-CDMA. Os resultados obtidos nas simulações demonstram uma considerável melhoria no desempenho dos sistemas com a decodificação turbo q-ária, sem comprometer a complexidade. Entretanto, a utilização dos códigos produto reduzem a eficiência espectraf do sistema, sendo necessário, assim, compensá-Ia através do aumento do alfabeto do código q-ário. Palavras-chave: Códigos q-ários, Códigos Produto, Decodificação Suave, Decodificação TUrbo, SISO, Sistemas FFH-CDMA / Abstract: This work presents a study of q-ary turbo decoding applied to FFH-CDMA systems. To attain the main objective of this dissertation, an algorithm to implement the q-ary soft decoding was designed. Specifically, an adaptation of the Chase decoding method was proposed to comply with q-ary symbols requirements. The proposal of iterative (turbo) decoding makes possible the feedback of the decoded q-ary symbols and its reliabilities in each decoder iteration. Simulations were done considering Gaussian and FFH-CDMA channels. The results obtained in the simulations indicate a better system's performance when the q-ary turbo decoding is applied, without compromising complexity. However, the use of product codes decreases the system's spectral efficiency. Thus, it is necessary to increase the q-ary code's alphabet in order to mitigate this decréase. Keywords: Non-Binary Codes, Product Codes, Soft Decoding, Turbo Decoding, SISO, FFH-CDMA / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

M.Ing. (Electrical & Electronic Engineering) / Coding is indispensable in modem communications and storage systems. For instance, a Reed-Solomon error-correction code ensures higher data integrity for the Compact Disc (CD) system. Modulation codes, such as the( d, k) codes, can furthermore be employed to enable synchronization between transmitter and receiver (or between the read and write processes in storage systems), and also to achieve compliance with bandwidth restrictions. In some cases, a 'combined' code is designed to function both as an error control code and a (d, k) modulation code. In this study, we consider such an existing class of error control (d, k) block codes. Of particular interest is the performance of these codes, determined mostly in terms of the probability of block error over certain selected channels. It is important to be able to judge or predict the performance of a communication system in terms of the probability of receiving incorrect information, and this probability depends not only on the specific error control code used, but also on the statistical structure of the channel error processes. The main contributions of this thesis are seen to be the following: 1) New codes and improvements on previous codes, originating from the generalization of existing theory. 2) Mathematical bounds and approximations on block error rates, compared with measured results from computer simulations.

Ph.D. (Electrical & Electronic Engineering) / In the ideal communication system no noise is present and error free communication is possible. In practice, however, several factors influence the correctness of· the communication. One of the most important of these factors is the synchronization of the message. Synchronization techniques form an integral part of data communication systems and without synchronization no comprehensible message can be received. An example of a communication system in which synchronization errors occur is the plesiochronous communication network which is used in many telephone networks [49,50]. A common problem with the use of the multiplexers in such a network is that output pulses may occur that do not contain valid data, due to minor discrepancies in the clock frequencies of the incoming signals. These inserted bits are termed ''justification bits" and their presence is signaled over the link by the justification control bits or stuffing control bits, which are included in the frame [49 and 50]. Synchronization of the network is dependent, among other factors, on the correct decoding of the stuffing control bits. Synchronization at the receiver can also be lost when the frame markers are not recognizable due to errors on the channel...

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