In this paper we improve the rate-distortion performance of a previously proposed video coder based on frame replenishment and adaptive mean-removed vector quantization. This is realized by determining for each block of a given frame the optimal encoding mode in the rate-distortion sense. The algorithm is a new contribution to very low bit rate video coding with adaptive vector quantization suitable for videophone applications. Experimental results comparing the two coders for several test sequences at different bit rates are provided.

Projektet som beskrivs i denna rapport utgör modifieringen av videokonferensprogrammet Jitsi Meet, där öppen källkod tillåter anpassning av tjänsten för videoinspelning. Den mottagna videoströmmen som utgör samtalet mellan två deltagare skall sparas till disk, för att sedan möjliggöra för utredning och analys av sessionens videokvalitet. För att uppnå behoven för denna kvalitetskontroll krävdes en inspelning av mottagen video med jämförbar klarhet och komposition till originalet. Olika tillvägagångssätt utvärderades för att fullborda videoströmmens utvinning. Av de tre ansatser som presenterade sig valdes framtagandet av en inspelningsfunktion på klientsidan, en lösning som nyttjar användarens webbläsare för att utföra uppgiften. Jitsi Meet stöds av standardiserade teknologier inom webbaserad mediahantering, vilket möjliggjorde för tillämpningen av intilliggande metoder och verktyg i inspelningsfunktionens utveckling. Den resulterande inspelningsfunktionen utgör ena parten i ett tvåsidigt system, där den modifierade webbklienten agerar mottagare för en särskild mobilapplikations videoström. Enskilda bildrutor från enheternas videoinspelningar jämfördes via dess strukturella likheter och brusanalys, där skillnader i videons kvalitet före och efter strömning uppenbarade sig genom konkreta värden. Undersökning av resulterande grafer indikerar att särskilda händelser så som förändrad bithastighet, försvunna bildrutor och andra avvikelser kan identifieras med hjälp av den framtagna mätuppställningen. Projektet har därmed uppnått målet att producera en inspelningslösning för strömmad video som kan användas i kontroll av videokvalitet. Därmed ges goda förutsättningar för fortsatt arbete med utvärdering av kvalitet för videosamtal. / The project described in this report is the modification of the video conferencing software Jitsi Meet, where its open-source code allows for customization for the purpose of video recording. The received video stream that constitutes the conversation between two participants shall be saved to disk, to then allow for the examination and analysis of the session’s video quality. To meet the needs of this quality control, a recording of the received video with comparable clarity and composition to the original was required. Various approaches were evaluated to allow for the extraction of the video stream. Of the three approaches that presented themselves, the development of a recording function on the client side was chosen, a solution that uses the user's web browser to perform the task. Jitsi Meet is based on standardized technologies in web-based media management, which enabled the use of adjacent methods and tools in the development of its recording solution. The resulting recording solution forms one part of a two-sided system, where the modified web client acts as a receiver for a particular mobile application's video stream. Individual frames from the devices' video recordings were compared via their structural similarities and noise analysis, where differences in video quality before and after streaming revealed themselves through measured values. Study of the resulting graphs indicates that special events such as changing bit rates, missing frames and other deviations can be identified with the help of this measurement setup. The project has thus achieved its goal of producing a recording solution for streamed video that can be used in video quality control. This provides good conditions for continued work with evaluation of the quality of video calls.

<p>With the growing demand for high data rate communication services, multi-carrier communication schemes have started to become the method of choice in many applications. In this thesis, multi-carrier communication systems are studied and various methods for improving their achievable bit rate arc proposed.</p> <p>Filtered multitone (FMT) is a multi-carrier communication scheme which is implemented using a modulated filter bank structure. In this thesis, an efficient design method for the prototype filter of the FMT system is proposed. This design method allows improvement of the achievable hit rate by efficient evaluation of the inherent trade-off between the sub channel spectral containment provided by the prototype filter and the intersymbol interference (lSI) that the filter generates. Numerical results further demonstrat.e the effectiveness of the proposed design method. The insight gained from this design is also used to determine the optimal number of subchannels in FMT systems. Moreover, since the presence of lSI in FMT subchannels outputs renders the conventional water-filling power loading algorithm suboptimal, we propose an efficient power loading algorithm for Fl\IT that enables higher achievable bit rates.</p> <p>Discrete multitone (DMT) is a popular multi-carrier communication scheme, mainly due to its rather low complexity. However. DMT suffers from poor subchannel spectral characteristics. In this thesis, a family of bi-windowed DMT transceivers is proposed that provide both improved sub channel 8pectral containment at the transmitter and improved spectral selectivity at the receiver, without requiring the cyclic prefix to be longer than the order of the channel impulse respon8e. The window8 arc designed in a channel independent manner and are con8trained to produce sub channel outputs that arc free from lSI. Furthermore, the design allows the interisubchannel interference (leI) to be controlled in such a way that it can be mitigated using a relatively simple minimum mean square error (MMSE) successive interference cancellation scheme. Numerical results demonstrate the significant gain in the achievable bit rate obtained Ly the proposed scheme.</p> / Doctor of Philosophy (PhD)

Tese de Mestrado Integrado. Engenharia Informática e Computação. Faculdade de Engenharia. Universidade do Porto. 2012

近年來，一個具有壅塞控制機制的傳輸協議DCCP被提出，期能取代UDP成為不可靠傳輸的主流協議。我們以NS-2網路模擬器和實際網路進行實驗，發現DCCP無法與其他傳輸協議公平分享頻寬，因此現行DCCP的設計，尚無法完全取代UDP。此外，目前DCCP以調整封包間隔的方式進行壅塞控制，也不適用於講求時效性的網路服務。 本研究首先以實驗證明，當網路情況不佳時，DCCP無法與其他傳輸協議公平的分享頻寬；當使用DCCP傳輸越洋長距離網路電話，如遇頻寬不足時，會因頻寬競爭力較弱而無法維持通話品質。本研究提出可變速率方法(Flexible Bit-rate)調整時效性網路服務的封包大小來進行壅塞控制，在維持一定服務品質之前提下，促進網路的和諧。我們在一個實際網路的實驗環境中評估以UDP、DCCP及可變速率三種方式傳輸網路電話封包的效能，結果顯示透過可變速率方法，能有效降低網路電話的封包遺失率，維持通話品質。 / With congestion-control ability, Datagram Congestion Control Protocol (DCCP) is expected to replace UDP as a mainstream unreliable transport protocol. But our study found that DCCP is not able to get a fair share of bandwidth under the competition of others transport protocols no matter in NS-2 simulation or real world networking environments. Furthermore, any congestion control protocol that postpones the transmission of packets may not be adequate to support time-sensitive network services. To maintain the quality of time-sensitive network services as well as to be TCP-friendly when facing network bandwidth fluctuation, we propose a Flexible Bit-rate congestion control mechanism for VoIP to adjust their data rate. Our experiments show that Flexible Bit-rate congestion control method could effectively reduce the packet loss rate and to maintain VoIP quality as compared with UDP and DCCP. Furthermore, it can have a much better bandwidth efficiency and adjust better to network fluctuation.

The 2006 International Technology Roadmap for Semiconductors projects that for 2020, interconnects will be as narrow as 14 nm and will operate at frequencies as high as 50GHz. For a wire that operates at ultra-high frequencies, such that skin depth and the mean free path of the electrons are in the same order, skin effect and surface scattering should be considered simultaneously. This is known as the anomalous skin effect (ASE). The objective of this work is to identify the challenges and opportunities for using GSI interconnects in the nanometer and GHz regime. The increase in the resistivity of a thin wire caused by the ASE is studied. The delay of a digital transmission line resulting from this effect is modeled. Compact models are presented for the bit-rate limit of transmission lines using a general form of resistance that for the first time simultaneously considers dc resistance, skin effect, and surface scattering. A conventional low-loss approximation that is only valid for fast rising signals is also relaxed. The impact of size effects on the design of multi-level interconnect networks is studied. For high-performance chips at the 18 nm technology node, it is shown that despite a more than four times increase in the resistivity of copper for minimum-size interconnects, the increase in the number of metal levels is negligible (less than 7%), and interconnects that will be affected most are so short that their impact on chip performance is inconsequential. It is shown that for low-cost applications where very few wiring pitches are normally used, the number of metal levels needed to compensate for the impact of size effects on the average rc delay of a copper interconnect is drastically high. An optimization methodology has been presented for power distribution interconnects at the local level. For a given IR drop budget, compact models are presented for the optimal widths of power and ground lines in the first two metal levels for which the total metal area used for power distribution is minimized.

This thesis dwells on two important problems in the field of video coding; namely rate control and spatial domain intra prediction. While the former is applicable generally to most video compression standards, the latter applies to recent advanced video compression standards such as H.264, VC1 and AVS. Rate control regulates the instantaneous video bit-rate to maximize a picture quality metric while satisfying channel rate and buffer size constraints. Rate control has an important bearing on the picture quality of encoded video. Typically, a quality metric such as Peak Signal-to-Noise ratio (PSNR) or weighted signal-to-noise ratio (WSNR) is chosen out of convenience. However neither metric is a true measure of perceived video quality. A few researchers have attempted to derive rate control algorithms with the combination of standard PSNR and ad-hoc perceptual metrics of video quality. The concept of using perceptual criterion for video coding was introduced in [7] within the context of perceptual adaptive quantization. In this work, quantization noise levels were adjusted such that more noise was allowed where it was less visible (busy and textured areas) while sensitive areas (typically flat and low detail regions) were finely quantized. Macro–blocks were classified into low detail, texture and edge areas depending on a classifier that studied the variance of sub-blocks within a macro-block (MB). The Rate models were trained from training sets of pre -classified video. One drawback of the above scheme as with standard PSNR was that neither accounts for the perceptual effect of motion. The work in [8] achieved this by assigning higher weights to the regions of the image that were experiencing the highest motion. Also, the center of the image and objects in the foreground are perceived as more important than the sides. However, attempts to use perceptual metrics for video quality have been limited by the accuracy of the video quality metrics chosen. In the recent years, new and improved metrics of subjective quality have been invented and their statistical accuracy has been studied in a formal manner. Particularly interesting is the work undertaken by ITU and the Video quality experts group (VQEG). VQEG conducted two phases of testing; in the first pha se, several algorithms were tested but they were not found to be very accurate, in fact none were found to be any more accurate than PSNR based metric. In the second phase of testing a few years later, a few new algorithms were experimented with, and it wa s concluded that four of these did achieve results good enough to warrant their standardization as a part of ITU –T Recommendation J.144. These experiments are referred to as the FR-TV (Full Reference Television) phase-II evaluations. ITU-T J.144 does not explicitly identify a single algorithm but provides guidelines on the selection of appropriate techniques to objectively measure subjective video quality. It describes four reference algorithms as well as PSNR. Amongst the four, the NTIA General Video Quality Model (VQM), [11] is the best performing and has been adopted by American National Standards Institute (ANSI) as a North American standard T1.801.03. NTIA’s approach has been to focus on defining parameters that model how humans perceive video quality. These parameters have been combined using linear models to produce estimates of video quality that closely approximate subjective test results. NTIA General Video Quality Model (VQM) has been proven to have strong correlation with subjective quality. In the first part of the thesis, we apply metrics motivated by NTIA-VQM model within a rate control algorithm to maximize perceptual video quality. We derive perceptual weights using key NTIA parameters to influence QP value used to decide degree of quantization. Our experiments demonstrate that a perceptual quality motivated standard TMN8 rate control in an H.263 encoder results in perceivable quality improvements over a baseline TMN8 rate control algorithm that uses a PSNR metric. Our experimental results on a set of 11 sequences show on an average reduction of 6% in bitrate using the proposed algorithm for the same perceptual quality as standard TMN-8. The second part of our thesis work deals with spatial domain intra prediction used in advance video coding standard such as H.264. The H.264 Advanced Video coding standard [36] has been shown to achieve video quality similar to older standards such as MPEG2 and H.263 at nearly half the bit-rate. Generally, this compression improvement is attributed to several new tools that were introduced in H.264 – including spatial intra prediction, adaptive block size for motion compensation, in-loop de-blocking filter, context adaptive binary arithmetic coding (CABAC), and multiple reference frames. While the new tools allow better coding efficiency, they also introduce additi onal computational complexity at both encoder and decoder ends. We are especially concerned here on the impact of Intra prediction on the computational complexity of the encoder. H.264 reference implementations such as JM [29] search through all allowed intra-rediction “modes” in order to find the optimal mode. While this approach yields the optimal prediction mode, it comes at an extremely heavy computational cost. Hence there is a lot of interest into well -motivated algorithms that reduce the computational complexity of the search for the best prediction mode, while retaining the quality advantages of full-search Intra4x4. We propose a novel algorithm to reduce the complexity of full search by exploiting our knowledge of the source statistics. Specifically, we analyze the transform domain energy distribution of the original 4x4 block in different directions and use the results of our analysis to eliminate unlikely modes and reduce the search space for the optimal I ntra mode. Experimental results show that the proposed algorithm achieves quality metrics (PSNR) similar to full search at nearly a third of the complexity. This thesis has four chapters and is organized as follows, in the first chapter we introduce basics of video encoding and subsequently present exiting work in the area of perceptual rate control and introduce TMN-8 rate control algorithm in brief. At the end we introduce spatial domain intra prediction. In the second chapter we explain the challenges present in combining NTIA perceptual parameters with TMN8 rate control algorithm. We examine perceptual features used by NTIA from a video compression perspective and explain how the perceptual metrics capture typical compression artifacts. We next present a two pass perceptual rate control (PRCII) algorithm. Finally, we list experimental results on set of video sequences showing on an average of 6% bit-rate reduction by using PRC-II rate control over standard TMN-8 rate control. Chapter 3 contains part-II of our thesis work on, spatial domain intra prediction . We start by reviewing existing work in intra prediction and then present the details of our proposed intra prediction algorithm and experimental results. We finally conclude this thesis in chapter 4 and discuss direction for the future work on both our proposed algorithms.

Conselho Nacional de Desenvolvimento Científico e Tecnológico / The objective of this study was to evaluate the productive and morphogenesis in pastures sudan grass or millet, on the behavioral aspects and performance of cull cows. Were used 22 cull cows from the cross between Charolais and Nellore, age and average initial live weight of 8 years and 448 kg, kept under continuous grazing pearl millet (Pennisetum americanum (L.) Leeke) or sudan grass (Sorghum bicolor cv. sudanense). The experimental period was 63 days, divided into 3 periods (21 days each). The experimental design was completely randomized with two treatments and five repetitions (area) for the variables related to the productive pastures; ten replicates (animals) to behavioral parameters, and three replications (area) for the morphogenesis of grasses. There were no differences (P<0.05) for the productive and behavioral function in animal treatments. Pastures millet showed higher (P<0.10) canopy height (32.69cm vs 20.29 cm), number of leaves per tiller (4.74 vs 3.06), number of green leaves (4.26 vs 2.55), number of adult leaves (2.34 vs 1.08), number of young leaves (1.92 vs 1.47) and leaf appearance rate (0.147 vs 0.080), compared to pastures sudan grass. The rates of dry matter, crude protein and supply of leaf blade, were higher in the first 21 days of use of pastures (130.77 kg/ha of dry matter (DM), 170.4 g / kg DM and 3.63%; respectively). The stocking was similar in the first two periods (2329.2 and 1843.5 kg / ha PV), and over the last experimental period (1261.5 kg / ha of PV). Average daily gain and gain body condition score were similar across periods (mean of 1.00 kg/day and 0.23 points, respectively). The time devoted to grazing (613 minutes), number of steps per minute (8.8) and number of feeding stations per minute (10.9) were higher in the first experimental period, while the rate of bites per minute (47.41) was higher in the third trial. Sudan grass pastures are similar regarding the parameters of productive grazing millet with similar reflections on the performance and behavior of animals. However, the present potential of millet pastures above the vegetative sudan grass. With the advance of the growing season pastures for significant changes in the structures of pastures, which reflect the performance and behavior of animals. / O objetivo desse trabalho foi de avaliar os parâmetros produtivos e morfogênicos de pastagens de milheto ou capim sudão, sobre os aspectos comportamentais e de desempenho de vacas de descarte. Foram utilizadas 22 vacas de descarte oriundas do cruzamento entre as raças Charolês e Nelore, de idade e peso vivo médios iniciais de 8 anos e 448 kg, mantidas sob pastejo contínuo em pastagem de milheto (Pennisetum americanum (L.) Leeke) ou capim sudão (Sorghum bicolor cv. sudanense). O período experimental foi de 63 dias, divididos em 3 períodos (21 dias cada). O delineamento experimental foi o inteiramente casualizado com dois tratamentos e cinco repetições (área) para as variáveis relacionadas aos parâmetros produtivos das pastagens; dez repetições (animais) aos parâmetros comportamentais e três repetições (área) para as características morfogênicas das gramíneas. Não houve diferenças (P<0,05) para os parâmetros produtivos e comportamentais dos animais em função dos tratamentos. Os perfilhos de milheto demonstraram maiores (P<0,10) altura de dossel (32,69 cm vs 20,29 cm), número de folhas por perfilho (4,74 vs 3,06), número de folhas vivas (4,26 vs 2,55), número de folhas adultas (2,34 vs 1,08), número de folhas jovens (1,92 vs 1,47) e taxa de aparecimento foliar (0,147 vs 0,080), em relação as pastagens de capim sudão. As taxas de acúmulo de matéria seca (130,77 kg de matéria seca (MS)/ha), proteína bruta (170,4 g/kg de MS) e oferta de lâminas foliares (3,63%), foram maiores nos primeiros 21 dias de utilização das pastagens. A carga animal foi semelhante nos dois primeiros períodos experimentais (2329,2 e 1843,5 kg/ha de PV), sendo essas superiores a do último período de utilização das pastagens (1261,5 kg/ha de PV). O ganho médio diário de peso vivo não alterou com o avançar do ciclo vegetativo das pastagens (média de 1,00 kg/dia). O tempo destinado ao pastejo (613 minutos), número de passos por minuto (8,8) e número de estações alimentares por minuto (10,9), foram maiores no primeiro período experimental; enquanto a taxa de bocados por minuto (47,41) foi maior no terceiro período experimental. Pastagens de capim sudão são semelhantes quanto aos parâmetros produtivos em relação a pastagens de milheto condicionando igualdade no desempenho e comportamento dos animais. Entretanto, as pastagens de milheto apresentam potenciais forrageiro superiores ao capim sudão. Com o avançar o ciclo vegetativo das gramíneas há mudanças expressivas nas estruturas das pastagens, as quais refletem no desempenho e comportamento dos animais.

Ce mémoire de thèse s'inscrit dans le contexte du projet FUTUR financé par l'ANR et concernant le développement de Fonctions optiques pour les Transmissions à très haut débit dans le Réseau coeur et porte sur la génération de sources optiques fibrées très hautes cadences et la caractérisation de fibres optiques microstructurées en verre de Chalcogénure. A cet effet, nous étudions les caractéristiques linéaires et non-linéaires au sein de fibres microstructurées en verre de chalcogénures conçue et réaliser via différentes collaborations dans le cadre du projet de l'ANR FUTUR. Pour cela un grand nombre de méthodes de caractérisations ont été mises au point donnant une comparaison entre une fibre SMF standard et ces fibres microstructurées chalcogénures. Par exemple, un montage interférométrique pour la mesure de la dispersion chromatique pour échantillon court, ou encore de nombreux banc expérimentaux permettant la caractérisation des propriétés non-linéaires de ces fibres (diffusion Raman, diffusion Brillouin, Coefficient non linéaire Kerr...). La seconde partie de ce mémoire présente la mise au point de méthode de conversion d'un battement sinusoïdal en un train d'impulsions hautement cadencé. Il est montré dans ce manuscrit que cette technique a été exploitée au plus prêt de ses limites, par l'obtention d'impulsions extrêmement courtes et par des débits très élevés. Les trains d'impulsions à très hautes cadences ont été caractérisés par un dispositif expérimental SHG-FROG. Une démonstration de la multiplication du débit par deux a été démontrée par l'effet Talbot. / This memory of thesis s' registered voter in the context of the FUTUR project financed by l'ANR and concerning the development of optical finctions fot the high bit-rate transmissions in the Network heart and carries on very high rates optical fibers sources generation and the optical chalcogenide microstructured fiber charaterization. For this purpose, we study the linear and non-linear characteristics of microstructured chalcogenide fibers conceived and realized in various collaborations within the framework of the ANR FUTUR project. For that a great number of characterizations methods were developed giving a comparison between a standard single mode fiber and there microstructured chalcogenide fibers. For exemple, an interferometric setup for the chromatic dispersion measurement for short sample, or many experimental setup allowing the nonlinear properties characterizations as of these fibers (Raman scattering, nonlinear Kerr Coefficient). The second part of this memory presents the settling of sinusoidal beat conversion into a high bit rate generation method. It is shown in this manuscript that this technique was exploited with readiest of its limits, by obtaining extremely short pulses and by very high bit-rate. The pulses train at very high rates were characterized by an experimental device SHG-FROG. A demonstration of the multiplication of the bit-rate by two at summer shown by Talbot effect.

Ce mémoire de thèse présente les travaux effectués pour la réalisation de sources optiques fibrées d’impulsions picosecondes cadencées à 40 GHz dans la bande C des télécommunications. Dans une première partie, nous présentons des études numériques et expérimentales mises en place pour la génération d’un train d’impulsions cadencé à 40 GHz par la compression non-linéaire d’un battement sinusoïdal via un processus de mélanges à quatre ondes multiples. Afin d’obtenir des impulsions stables, le battement sinusoïdal initial est obtenu par la modulation en intensité d’un signal continu grâce à un modulateur Mach-Zehnder piloté au point nul de transmission. Nous démontrons également l’amélioration de la qualité des impulsions générées par la suppression de la diffusion Brillouin stimulée grâce à la mise en place d’isolateurs optiques dans la ligne fibrée de la source. Nous présentons ensuite la génération d’impulsions ultra-courtes grâce à un compresseur non-linéaire composé de quatre étages fibrés. Le train d’impulsions obtenu est alors codé puis multiplexé jusqu’à un débit optique de 160 Gbit/s. Dans la dernière partie, nous présentons les démarches mises en place en vue d’un transfert technologique, telles que la réalisation d’un prototype de la source, la recherche d’antériorité et l’étude de marché. / This thesis presents the work carried out on the realization of fibered 40-GHz picosecond optical pulse sources in the telecommunications C-band. In the first part, we present a numerical and experimental study of the generation of 40-GHz pulse trains thanks to the nonlinear compression of an initial beat-signal by multiple Four-Wave Mixing process. Enhanced temporal stability is achieved by generating the sinusoidal beating thanks to a Mach-Zehnder modulator driven at its zero-transmission working point. In order to improve the quality of the generated pulses, we also demonstrate the suppression of stimulated Brillouin back-scattering by inserting several optical isolators into the compression line. In the next part, we present the generation of low duty-cycle pulse trains by using a nonlinear compressor line based on 4 segments of fiber. The generated pulse trains have been encoded and then multiplexed to achieve a high bit rate signal (160 Gb/s). In the last part, we present the technology transfer steps of this optical source, such as creating a prototype of the source, prior art search and market research.