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  • About
  • The Global ETD Search service is a free service for researchers to find electronic theses and dissertations. This service is provided by the Networked Digital Library of Theses and Dissertations.
    Our metadata is collected from universities around the world. If you manage a university/consortium/country archive and want to be added, details can be found on the NDLTD website.
21

Forward Error Correction for Packet Switched Networks

Valverde Martínez, David, Parada Otte, Francisco Javier January 2008 (has links)
<p>The main goal in this thesis is to select and test Forward Error Correction (FEC) schemes suitable for network video transmission over RTP/UDP. There is a general concern in communication networks which is to achieve a tradeoff between reliable transmission and the delay that it takes. Our purpose is to look for techniques that improve the reliability while the realtime delay constraints are fulfilled. In order to achieve it, the FEC techniques focus on recovering the packet losses that come up along any transmission. The FEC schemes that we have selected are Parity Check algorithm, ReedSolomon (RS) codes and a Convolutional code. Simulations are performed to test the different schemes.</p><p>The results obtained show that the RS codes are the more powerful schemes in terms of recovery capabilities. However they can not be deployed for every configuration since they go beyond the delay threshold. On the other hand, despite of the Parity Check codes being the less efficient in terms of error recovery, they show a reasonable low delay. Therefore, depending on the packet loss probability that we are working with, we may chose one or other of the different schemes. To summarize, this thesis includes a theoretical background, a thorough analysis of the FEC schemes chosen, simulation results, conclusions and proposed future work.</p>
22

Power Characterization of a Gbit/s FPGA Convolutional LDPC Decoder

Li, Si-Yun January 2012 (has links)
In this thesis, we present an FPGA implementation of parallel-node low-density-parity-check convolutional-code (PN-LDPC-CC) encoder and decoder. A 2.4 Gbit/s rate-1/2 (3, 6) PN-LDPC-CC encoder and decoder were implemented on an Altera development and education board (DE4). Detailed power measurements of the FPGA board for various configurations of the design have been conducted to characterize the power consumption of the decoder module. For an Eb/N0 of 5 dB, the decoder with 9 processor cores (pipelined decoder iteration stages) has a bit-error-rate performance of 10E-10 and achieves an energy-per-coded-bit of 1.683 nJ based on raw power measurement results. The increase in Eb/N0 can effectively reduce the decoder power and energy-per-coded-bit for configurations with 5 or more processor cores for Eb/N0 < 5 dB. The incremental decoder power cost and incremental energy-per-coded-bit also hold a linearly decreasing trend for each additional processor core. Additional experiments are performed to account for the effect of the efficiency of the DC/DC converter circuitry on the raw power measurement data. Further experiments have also been conducted to quantify the effect of clipping thresholds, bit width for each processor core on bit-error-rate (BER) performance, power consumption, and logic utilization of the decoder. A “6Core" decoder with growing bit-width log-likelihood ratios (LLRs) has been found to have a BER performance near that of a “6Core" 6-bit decoder while consuming similar power, and logic utilization to that of a 5-bit “6Core" decoder.
23

Tradeoffs between retransmission and forward error correction in the RTP stack

Döser, Erman January 2014 (has links)
Video conferencing applications has reached worldwide usage in recent years by the help of the improvements in network infrastructures for public services. Media data covers a significant ratio of data traffic over IP networks. However, it is challenging to ensure a decent quality of service (QoS) on public networks in terms of video and audio quality. The main factor that may cause degradation in media playback quality is packet losses. There are various techniques available to conceal packet losses in lossy channels. According to the application needs and channel characteristics such as loss patterns and round trip times, retransmission or forward error correction techniques may be applied at application level. These two techniques have different challenges which lead to tradeoffs between them, thus one might be chosen over the others. In this thesis work, retransmission’s worst case performances under considered packet loss patterns and various round trip times are compared to performances of forward error correction schemes. In addition, implementation details with respect to the relevant RFCs are provided as an example to give a better judgement on the obtained results. Results obtained under the packet loss patterns that are generated with a simple Gilbert-Elliot 2-state model shows that forward error correction techniques are a reasonable choice of error concealing in the real-time transport protocol (RTP) stack where round trip time in the channel is greater than 200 ms. In addition, bandwidth overhead revealed by forward error correction stays higher than retransmission’s bandwidth overhead in all sample runs. In cases where round trip times are high, then the choice of forward error correction scheme is bound to the packet loss pattern. In the results section, it is obtained that ReedSolomon performs well in terms of residual packet losses, which are the packets not being recovered, and bandwidth overhead when losses occur in long bursts.
24

Algoritmy pro dekódování Reed-Solomonova protichybového kódu / Algorithms for decoding the Reed-Solomon error control code

Tieftrunk, Tomáš January 2008 (has links)
Thesis discuss about effort to ensure from error, which may occur during transmission over noisy channel. There's used Reed Solomon code. It's block, cyclic and systematic code, which is symbol orientated. Computational process of decoding is mathematically time-consuming. In thesis is closely described Berlekamp-Masey algorithm, used in decoding to evaluate error polynomial. Process is illustrated in application in Matlab. Practical realization uses Reed Solomon code in communication over RS232. Communication is established between computer and microcomputer.
25

Hybrid Channel Coding for Error-Sensitive Class on DS-CDMA Air Interface

Yu, Byungwan 08 September 2003 (has links)
A DS-CDMA system with QPSK modulation and a RAKE receiver is modeled and simulated. A mathematical description of the DS-CDMA system is provided on uplink and downlink. For a multipath channel environment, modeling techniques for AWGN and Rayleigh fading are illustrated. Comparisons are made concerning the performance of CDMA systems with hybrid data rates. The thesis proposes a technique for hybrid channel coding for ARQ (Automatic-Repeat-reQuest) protocol and FEC (Forward Error Correction) scheme that can reduce the error rate significantly. Each of ARQ protocol and FEC scheme gives rise to long latency and significant complexity, respectively, for obtaining the required QoS (Quality of Service). This thesis shows using theoretical analysis and computer simulations that synergistic effects are possible by using both an ARQ protocol and a FEC scheme. / Master of Science
26

Análise de redes ópticas de alta velocidade baseadas na tecnologia CDMA e códigos bidimensionais (comprimento de onda/tempo) / Analysis of high-speed optical wavelength/time CDMA networks

Sanches, Anderson Leonardo 02 March 2010 (has links)
Esta dissertação apresenta uma análise realista de redes OCDMA (acesso múltiplo por divisão de código) baseadas em dois formatos de modulação distintos, qual sejam, OOK (chaveamento on-off) e PPM (modulação por posição de pulso). O desempenho desses formatos de modulação sob dois esquemas de codificação bidimensionais (2-D), isto é, pulsos únicos por linha (SPR) e múltiplos pulsos por linha (MPR) também são avaliados. Em ambos os casos, os efeitos simultâneos de muitos mecanismos dispersivos e ruídos (incluindo a interferência de acesso múltiplo, MAI) que prejudicam o desempenho geral do sistema foram também considerados. Outros mecanismos de degradação foram também incluídos, tais como o ruído de intensidade relativa (RIN) na etapa de transmissão, efeitos dispersivos da fibra óptica, como as dispersões de velocidade de grupo (GVD) e dos modos de polarização de primeira ordem (PMD), assim como os ruídos de batimento, APD, e térmicos na recepção. O efeito da GVD e PMD, bem como a influência dos ruídos, sobre o desempenho dos códigos SPR e MPR também são investigados. Outro efeito estudado nesta dissertação é a influência do fotodetetor APD sobre o ruído de batimento da rede OCDMA não-coerente. Para mitigar os ruídos do sistema e a BER, o algoritmo FEC RS (255,239) foi adotado em ambas as redes analisadas. Novas expressões para a taxa de erro de bit (BER) incluindo todos os ruídos e mecanismos de dispersão são apresentadas para os códigos SPR e MPR. Os resultados indicam que os esquemas de modulação OOK e PPM sem mecanismos adicionais de mitigação da MAI e de outros efeitos de ruídos não são suficientes para acomodar 32 usuários simultâneos em meio livre de erros (BER < \'10 POT.-12\'). Isto ocorre devido à alta BER na entrada do decodificador FEC, que afeta severamente a correção de erros na deteção. / This dissertation presents a comprehensive analysis of an OCDMA (optical code division multiple access) network based on two distinct modulation formats, namely, OOK (on-off keying) and PPM (pulse position modulation). We also investigate how each of these modulation formats performs under two distinct two dimensional (2-D) coding schemes, i.e., single-pulse per row (SPR) and multiple-pulse per row (MPR). For both cases, we have accounted for the simultaneous effect of many different dispersion and noise mechanisms (including multiple access interference, MAI) that impair the overall system performance. We have included the laser relative intensity noise (RIN) at the transmitter side, the fiber dispersive effects, such as group velocity dispersion (GVD) and first order polarization mode dispersion (PMD), as well as beat, APD, and thermal noises at the receiver side. The effect of GVD and PMD, as well as the influence of noises, on the performance of SPR and MPR codes is also investigated. Another effect studied in this dissertation is the influence of the avalanche photodetector (APD) photodetector on the beat noise of an incoherent OCDMA network. To mitigate systems noises and bit error rate (BER), we have adopted a FEC RS (255,239) algorithm in both networks investigated here. New expressions for the BER with all noises and dispersion mechanisms were also derived for the SPR and MPR code schemes. Results indicated that OOK and PPM modulation schemes without additional mechanisms to mitigate MAI and other noise effects are not sufficient to accommodate 32 simultaneous users in an error-free environment (BER < \'10 POT.-12\'). This occurs due to the already high BER at the FEC decoder input, which severely affects forward error corrections at the receiver side.
27

Análise de redes ópticas de alta velocidade baseadas na tecnologia CDMA e códigos bidimensionais (comprimento de onda/tempo) / Analysis of high-speed optical wavelength/time CDMA networks

Anderson Leonardo Sanches 02 March 2010 (has links)
Esta dissertação apresenta uma análise realista de redes OCDMA (acesso múltiplo por divisão de código) baseadas em dois formatos de modulação distintos, qual sejam, OOK (chaveamento on-off) e PPM (modulação por posição de pulso). O desempenho desses formatos de modulação sob dois esquemas de codificação bidimensionais (2-D), isto é, pulsos únicos por linha (SPR) e múltiplos pulsos por linha (MPR) também são avaliados. Em ambos os casos, os efeitos simultâneos de muitos mecanismos dispersivos e ruídos (incluindo a interferência de acesso múltiplo, MAI) que prejudicam o desempenho geral do sistema foram também considerados. Outros mecanismos de degradação foram também incluídos, tais como o ruído de intensidade relativa (RIN) na etapa de transmissão, efeitos dispersivos da fibra óptica, como as dispersões de velocidade de grupo (GVD) e dos modos de polarização de primeira ordem (PMD), assim como os ruídos de batimento, APD, e térmicos na recepção. O efeito da GVD e PMD, bem como a influência dos ruídos, sobre o desempenho dos códigos SPR e MPR também são investigados. Outro efeito estudado nesta dissertação é a influência do fotodetetor APD sobre o ruído de batimento da rede OCDMA não-coerente. Para mitigar os ruídos do sistema e a BER, o algoritmo FEC RS (255,239) foi adotado em ambas as redes analisadas. Novas expressões para a taxa de erro de bit (BER) incluindo todos os ruídos e mecanismos de dispersão são apresentadas para os códigos SPR e MPR. Os resultados indicam que os esquemas de modulação OOK e PPM sem mecanismos adicionais de mitigação da MAI e de outros efeitos de ruídos não são suficientes para acomodar 32 usuários simultâneos em meio livre de erros (BER < \'10 POT.-12\'). Isto ocorre devido à alta BER na entrada do decodificador FEC, que afeta severamente a correção de erros na deteção. / This dissertation presents a comprehensive analysis of an OCDMA (optical code division multiple access) network based on two distinct modulation formats, namely, OOK (on-off keying) and PPM (pulse position modulation). We also investigate how each of these modulation formats performs under two distinct two dimensional (2-D) coding schemes, i.e., single-pulse per row (SPR) and multiple-pulse per row (MPR). For both cases, we have accounted for the simultaneous effect of many different dispersion and noise mechanisms (including multiple access interference, MAI) that impair the overall system performance. We have included the laser relative intensity noise (RIN) at the transmitter side, the fiber dispersive effects, such as group velocity dispersion (GVD) and first order polarization mode dispersion (PMD), as well as beat, APD, and thermal noises at the receiver side. The effect of GVD and PMD, as well as the influence of noises, on the performance of SPR and MPR codes is also investigated. Another effect studied in this dissertation is the influence of the avalanche photodetector (APD) photodetector on the beat noise of an incoherent OCDMA network. To mitigate systems noises and bit error rate (BER), we have adopted a FEC RS (255,239) algorithm in both networks investigated here. New expressions for the BER with all noises and dispersion mechanisms were also derived for the SPR and MPR code schemes. Results indicated that OOK and PPM modulation schemes without additional mechanisms to mitigate MAI and other noise effects are not sufficient to accommodate 32 simultaneous users in an error-free environment (BER < \'10 POT.-12\'). This occurs due to the already high BER at the FEC decoder input, which severely affects forward error corrections at the receiver side.
28

Study the Effect of FEC on Video Streaming over the Networks

Meresa, Raya, Sabore, Yeshiwondem January 2013 (has links)
Context: Video streaming over best-effort networks is complicated by a number of factors including unknown and time-varying bandwidth, transmission delay, and high packet losses. Excessive packet loss can causes significant degradation in quality of video perceived by users of real-time video applications. Recent studies suggest that error control schemes using Forward Error Correction (FEC) is a good candidate for decreasing the negative impact of packet loss on video quality. With FEC scheme, redundant information is transmitted along with the original information so that the lost original video data can be recovered at least in part from the redundant information. Although sending additional redundancy increases the probability of recovering lost packets, it also increases the bandwidth requirements which in turn increase loss rate of the video stream due to congestion. For this reason FEC is characterized as effective when the redundancy is sufficient to recover the lost data, ineffective when the redundancy is little to recover the lost data and inefficient when the redundancy is high for the lost data. To provide best performance for the streaming application and the network, it is important to determine, in real time, the proper amount of redundant information according to the loss behavior of the network. However it not clears how to choose optimal redundancy given the constraints mentioned above at any given point in time. Objective: This thesis investigated the limitations of existing static FEC schemes and suggested alternative approaches that can achieve effectiveness through sending the appropriate amount of FEC redundancy in real-time. Three dynamic redundancy adaptation control systems On-Off, Proportional, Proportional-Integral have been design and implemented based on existing conventional FEC mechanisms. Moreover the performance evaluation of each mechanism is performed on simulated environment. Method: A performance evaluation methodology using network simulation and key evaluation criteria to test the mechanisms under different network conditions and the scenarios for each different network are considered. The proposed mechanisms were implemented in a simulation environment by using NS2. After the implementation and validation of the techniques, several simulation experiments have been conducted to study the performance of each redundancy adjustment schemes. Results: The result of the simulation experiments and performance analysis showed that both Proportional and Proportional-Integral (PI) redundancy controller based on Adaptive Forward Error Correction (AFEC) mechanisms significantly reduce the number of discarded video blocks as compared with the On-Off based scheme. On the other hand On-Off based AFEC mechanisms added small number of excess redundancy. The amount of excess redundancy added by the Proportional and PI controllers significantly increases as the packet drop rate of the transmission channel increases. Conclusion: Based on the findings of this study, using the PI adaptation based AFEC mechanisms is potentially viable option for enhancing the performance of video streaming applications over the network. / +46762356096 +251929003705/+46739691250
29

EXPERIMENTAL RESULTS FOR PCM/FM, TIER 1 SOQPSK, AND TIER II MULTI-H CPM WITH TURBO PRODUCT CODES

Geoghegan, Mark 10 1900 (has links)
International Telemetering Conference Proceedings / October 20-23, 2003 / Riviera Hotel and Convention Center, Las Vegas, Nevada / Improving the spectral-efficiency of aeronautical telemetry has been a principal area of research over the last several years due to the increasing demand for more data and the limitation of available spectrum. These efforts have lead to the development of the ARTM Tier 1 SOQPSK and Tier II Multi-h CPM waveforms which improve the spectral efficiency by two and three times, as compared to legacy PCM/FM, while maintaining similar detection efficiency. Now that more spectrally efficient waveform options are becoming available, another challenge is to further increase the detection performance. Better detection efficiency translates into additional link margin that can be used to extend the operating range, support higher data throughput, or significantly improve the quality of the received data. It is well known that Forward Error Correction (FEC) is one means of achieving this objective at the cost of additional overhead and increased receiver complexity. However, as mentioned above, spectral efficiency is also vitally important meaning that the FEC must also have a low amount of overhead. Unfortunately, low overhead and high coding gain are generally conflicting trades, although recent work has shown that Turbo Product Codes (TPC) are a particularly attractive candidate. Computer simulations predict that very impressive gains in detection performance are possible for a relatively small increase in bandwidth. The main drawbacks are the additional complexity of the decoding circuitry and an increase in receive side latency. This paper presents the latest simulation and hardware performance results of PCM/FM, SOQPSK, and Multi-h CPM with TPC.
30

Estudo da diversidade genética e análise de associações de polimorfismo de nucleotídeo (SNP) com resistência às parasitoses gastrintestinais e prolificidade em ovinos da raça Santa Inês / Study of genetic diversity and association analysis of single nucleotide polymorphism (SNP) with resistance to gastrointestinal parasites and prolificacy in Santa Ines sheep

Priscila Silva Oliveira 21 February 2014 (has links)
O principal objetivo deste trabalho foi avaliar a presença de polimorfismos e de possíveis associações com características relacionadas com a resistência às parasitoses gastrintestinais e a prolificidade em ovinos da raça Santa Inês. Para avaliação da resistência às parasitoses gastrintestinais, amostras de fezes e de sangue de aproximadamente 700 animais, infectados naturalmente e oriundos de quatro propriedades diferentes, foram coletadas entre os meses de outubro e novembro de 2011, para avaliação das características condição corporal, grau de anemia avaliado pelo cartão FAMACHA, as características dos pelos dos animais, consistência das fezes, contagem de ovos por grama de fezes, hematócrito, contagem de células brancas, contagem de células vermelhas, hemoglobina e plaquetas. Para a avaliação da prolificidade, 340 ovelhas foram avaliadas quanto ao número total de cordeiros nascidos, divididos pelo número de partos de cada ovelha, assim como a correlação dessa característica com o peso médio ao nascimento de seus cordeiros e a eficiência produtiva da mãe ao parto. Foram selecionados 28 polimorfismos de base única (SNP) para o desenvolvimento deste estudo os quais foram genotipados por meio da plataforma Sequenom MassARRAY iPLEX. Foram analisadas as freqüências alélicas e genotípicas, o equilíbrio de Hardy-Weinberg, os efeitos de substituição alélica, de aditividade e de desvio de dominância. Os resultados obtidos demonstraram variabilidade considerável das características avaliadas na população e da maioria dos polimorfismos estudados. Foi verificado também efeito significativo (p&le;0,05) ou sugestivo (0,05&gt;p&le;0,10) de substituição alélica de pelo menos um SNP para cada uma das características avaliadas, indicando que esses polimorfismos podem auxiliar nos processos de seleção das características relacionadas com a resistência às parasitoses gastrintestinais e com a prolificidade. / The aim of this work was to evaluate the presence of polymorphisms and possible associations with characteristics associated with resistance to gastrointestinal parasites and prolificacy in Santa Ines sheep. To evaluate the resistance to gastrointestinal parasites, feces and blood samples of approximately 700 animals infected naturally and from four different properties, were collected between the months of October and November, 2011 to assess characteristics body condition, degree of anemia measured by FAMACHA card, the characteristics of the hair of sheep, feces consistency, egg counts per gram of feces, hematocrit, white blood cell count, red blood cell count, hemoglobin and platelets count. For the evaluation of prolificacy, 340 sheep were evaluated for the total number of lambs born, divided by the number of births from each dam, as well as the correlation of this feature with the average birth weight of their lambs and productive efficiency of dam. 28 single nucleotide polymorphisms (SNPs) were selected for the development of this study and were genotyped by Sequenom MassARRAY iPLEX platform. Allele and genotype frequencies, the Hardy-Weinberg equilibrium, the effects of allelic substitution, additivity and dominance deviation were analyzed. The results showed considerable variability of the characteristics evaluated in the population in study and in most of the polymorphisms. Significant effect was observed (p &le; 0.05) or suggestive (0.05&gt; p &le; 0.10) for allelic substitution of at least one SNP for each of the evaluated traits, indicating that these polymorphisms may help in the selection processes of characteristics related to resistance to gastrointestinal parasites and prolificacy.

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