M.Ing. (Electric and Electrical Engineering) / From the day the first 'apple' was eaten, a species of people existed that wants to misuse other people, This species is normally the first to use new technology to their advantage. It is essential for our own security to restrict the boundaries of their playing-field and to fill the field it self with potholes. This however should be a continuous process, for their dexterity tends to evolveas fast as new techniques are mastered. Firstly this thesis entails the analysis of the boundaries of the playing field of authentication systems without security. The boundaries of authentication systems with security is established with a unique technique. Concluding the first part of the thesis, a new method of code designing for this playing-field is proposed. Reordering the potholes on the playing-field is the subject of the second part of the thesis. Anew public key system is described for this purpose. A novel implementation of insertion/deletion error correcting codes is presented in this new system. To conclude the thesis, a thorough analysis of this public key system is presented.

A common feature of text input tools is spell checking. It exists in search engines, email clients and of course in word processors like Microsoft Word. By having a spell checker when you are typing you can be more efficient than if you had to check the spelling with a separate proofing tool. Spell checking is a common request by the users of the room planning software CET Designer which is developed by Configura. In this thesis Windows Spell Checking API is evaluated and compared to alternative spell checkers. A prototype of an integrated spell checker in CET Designer text tool is then implemented with Windows Spell Checking API.

D.Ing. / This thesis is dedicated to an analysis of fundamental topics and issues related to deterministic insertion/deletion correcting and detecting codes. The most important contributions in this respect are the construction of a multiple insertion/deletion correcting code for run-length limited sequences and the construction and applications of multiple deletion (insertion) detecting codes. It is shown how run-length constraints and higher order moments can be combined to create a code which is simultaneously multiple insertion/deletion error correcting and runlength constrained. A systematic form of this code is presented, whereby any arbitrary run-length constrained sequence can be made into a multiple insertion/deletion correcting codeword by adding a prefix. This prefix is appended to the run-length constrained sequence in such a way that the resulting codeword is itself run-length constrained. Furthermore, it is shown that, despite the run-length constraints, the resulting code is guaranteed to have a better asymptotic rate than the Helberg code, the only other known non-trivial deterministic multiple insertion/deletion correcting code. We consider insertion/deletion detecting codes and present a multiple deletion (insertion) detecting code. It is shown that this code, which is systematic, is optimal in the sense that there exists no other systematic multiple deletion (insertion) detecting code with a better rate. Furthermore, we present a number of applications of such codes. In addition, further related topics of interest are considered. Firstly, jitter as a fundamental cause of insertion/deletion errors is investigated and as a result a counterpart to the signal-to-noise ratio in the amplitude domain is proposed for the time domain. Secondly, motivated by the correspondence of Levenshtein and Varshamov-Tenengol’ts codes, we investigate the insertion/deletion correcting capability of the single asymmetric error correcting Constantin-Rao codes within a wider framework of asymmetric error correcting and insertion/deletion correcting code structure correspondences. Finally, we propose a generalisation of Tenengol’ts’ construction for multiple non-binary insertion/deletion correction.

The use of uniformly distributed auxiliary random noise in the polarity-coincidence correlator has been described in the past. It has the advantage of constructional simplicity. It also gives an unbiased and consistent estimate of the correlation function. In this thesis, the method of using auxiliary random noise is extended to the multi-level digital correlator. It is found that any random noise of which the characteristic function has periodic zeros can be used as an auxiliary noise, that uniformly distributed noise is a special case, and that quantizing the auxiliary random noise has the same effect as directly quantizing the input signals. The mean-square error of this modified digital correlator is analyzed in detail. It differs from the mean-square error of the direct correlator only by a term which is inversely proportional to the total number of samples taken, provided that the power spectrum of the auxiliary noise is wide enough. This additional error is the combined effect of sampling, quantizing and adding auxiliary noise. It can be reduced to any desired value by taking a larger number of samples, by using a higher sampling rate, or by quantizing more finely. For completeness, the mean-square errors of the digital correlator, the Stieltjes correlator and the modified Stieltjes correlator are also derived. The mean-square error of the modified polarity-coincidence correlator, which is a special case of the modified digital correlator, is compared with the error of the multi-level modified digital correlator. Despite its constructional simplicity, the modified polarity-coincidence has a much larger error than the multi-level correlator. A small increase in the number of quantization levels reduces the error considerably. The implementation of a modified digital correlator with coarse quantization is also considered. A fast direct multiplier is designed to obtain high operation speed. Finally, the use of pseudo-random noise as an auxiliary noise is discussed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

The probability of undetected error P[formula omitted](є) for the primitive triple-error-correcting BCH codes of blocklength 2[formula omitted]  1, used solely for error detection on a binary symmetric channel with crossover probability є ≤ 1/2, is examined. It is shown that for odd values of m, P[formula omitted(є) increases monotonically with є. For even values of m, this is not necessarily true. However, for a fixed є, as m increases, P[formula omitted](є) approaches 2‾[formula omitted] where p is the number of parity bits. The extended double and triple-error-correcting primitive BCH codes are also examined. The undetected error probability of these codes is shown to have similar characteristics as the non-extended cases. An improved upper bound on the probability of undetected error which is valid for any linear code is derived. Comparison of this improved upper bound with the Kasami upper bound for some classes of codes is shown. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

An automatic repeat request (ARQ) scheme with memory and soft error detectors has been recently proposed by Benelli. Its performance was studied mainly through computer simulation. In this thesis, a generalized version of this ARQ scheme is examined. The selection of certain thresholds and weights to minimize the bit error rate in systems using a fixed number of packet repeats is considered. The evaluation of the average number of transmissions per packet in systems in which negatively acknowledged packets are retransmitted until successfully received is described. Finally, the performance of the memory ARQ scheme with forward error correction is analyzed. / Applied Science, Faculty of / Electrical and Computer Engineering, Department of / Graduate

M.Ing.

Orientadores: Jaime Portugheis, Celso de Almeida / Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação / Made available in DSpace on 2018-08-26T15:56:15Z (GMT). No. of bitstreams: 1 Santos_LailsonFerreirados_M.pdf: 1842807 bytes, checksum: dc8a5492d7e9a3e4224974176413f42c (MD5) Previous issue date: 2014 / Resumo: Esta dissertação analisa decodificadores LDPC (do inglês, Low-Density Parity-Check) sobre GF(q) de baixa complexidade num canal AWGN de entrada binária. É realizada uma revisão bibliográfica dos algoritmos binários baseados na técnica bit-flipping e seus desempenhos são comparados. As principais contribuições deste trabalho estão relacionadas com a investigação do algoritmo de decodificação WSF (do inglês, Weighted Symbol-Flipping} para códigos LDPC não binários. O algoritmo WSF é composto por duas partes: função de troca e regra de seleção do novo símbolo candidato. Primeiramente, é demonstrado que a regra de seleção do novo símbolo candidato baseada nos valores absolutos das saídas do canal observado, é equivalente a uma baseada em distâncias euclidianas. Também é verificado que a variação do valor do fator peso do algoritmo WSF sem o mecanismo de detecção de laços infinitos, não influencia no desempenho do decodificador, podendo ser ignorado. E por final, é proposto um algoritmo SF (do inglês, Symbol-Flipping) para códigos LDPC não binários, sendo que a função de troca é baseada apenas nos valores inteiros das síndromes e troca múltiplos bits em paralelo. O algoritmo SF obteve um melhor desempenho do que WSF para ordem do campo de Galois grandes / Abstract: This dissertation analyzes low complexity decoding algorithms for low-density parity-check (LDPC) codes over GF(q) in a binary input AWGN (BI-AWGN) channel. A literature review of binary algorithms based on bit-flipping techniques is presented and their performances are compared. The main contributions of this dissertation is associated with the investigation about weighted symbol-flipping (SF) algorithm for nonbinary LDPC codes. The weighted SF algorithm has two main parts: the symbol-flipping function and the new candidate symbol rule. First, it is demonstrated that a rule for choosing the new candidate symbol based on absolute values of observed channel outputs is equivalent to a rule based on Euclidean distances. Then, it is verified that the weighting factor of flipping function has negligible impact on algorithm performance. Motivated by this fact, a SF decoding algorithm is proposed whose flipping function requires only syndrome values and flips symbols in parallel. It is observed that SF decoding outperforms WSF for q-ary codes with large q / Mestrado / Telecomunicações e Telemática / Mestre em Engenharia Elétrica

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