Dissertations / Theses on the topic 'Mean Opinion Score'

Orientador: Leonardo de Souza Mendes
Dissertação (mestrado) - Universidade Estadual de Campinas, Faculdade de Engenharia Elétrica e de Computação
Made available in DSpace on 2018-08-17T15:12:52Z (GMT). No. of bitstreams: 1 Barison_Dherik_M.pdf: 8956445 bytes, checksum: 9549370d08573863a0f2bab25d076945 (MD5) Previous issue date: 2010
Resumo: A proposta desta dissertação é avaliar a qualidade de chamadas VoIP cifradas com diferentes algoritmos de criptografia através do OpenVPN, com o objetivo de identificar as diferenças de resultados entre os algoritmos de criptografia e também entre as chamadas cifradas e as não cifradas. Esta avaliação ocorrerá utilizando o MOS (Mean Opinion Score), um método que permite indicar a satisfação do usuário quanto a qualidade da comunicação. As chamadas VoIP cifradas irão ocorrer em diferentes cenários de rede que apresentam diversos problemas, tais como perda de pacotes, pacotes fora de seqüência, atraso, largura de banda de rede, etc. Estes cenários foram baseados em algumas situações reais de uso e serão emulados através da ferramenta Traffic Control do Linux, capaz de manipular os pacotes enviados por qualquer uma das interfaces de rede. Os cenários também terão diferentes larguras de banda de rede, para avaliar a influência das mesmas em algumas situações.
Abstract: The purpose of this work is to evaluate the quality of encrypted VoIP calls with different cipher algorithms through OpenVPN software, in order to identify differences in results between encryption algorithms and also differences between non-encrypted and encrypted calls. This evaluation will do by the MOS (Mean Opinion Score), a method to indicate user satisfaction of communication quality. The encrypted VoIP calls will occur in different network scenarios that present different problems, like packet loss, out-of-order packets, delay, network bandwidths, etc. These scenarios were based on some real situations of use and will be emulated with the Traffic Control tool from Linux, able of handling the packages sent by any available network interface. The scenarios will also have different network bandwidths to assess its importance in some situations.
Mestrado
Telecomunicações e Telemática
Mestre em Engenharia Elétrica

In recent years, there has been a significant increase in the demand for streaming of high quality videos on the smart mobile phones. In order to meet the user quality requirements, it is important to maintain the end user quality while taking the resource consumption into consideration. This demand caught the attention of the research communities and network providers to prioritize Quality of Experience (QoE) in addition to the Quality of Service (QoS). In order to meet the users’ expectations, the QoE studies have gained utmost importance, thus creating the challenge of evaluating it in such a way that the quality, cost and energy consumption are taken into account. This gave way to the concept of QoE-aware sustainable throughput, which denotes the maximal throughput at which QoE problems can be still kept at a desired level. The aim of the thesis is to determine the sustainable throughput values from the QoE perspective. The values are observed for different delay and packet loss values in wireless and mobile scenarios. The evaluation is done using the subjective video quality assessment method. In the subjective assessment method, the evaluation is done using the ITU-T recommended Absolute Category Rating (ACR). The video quality ratings are taken from the users, and are then averaged to obtain the Mean Opinion Score (MOS). The obtained scores are used for analysis in determining the sustainable throughput values from the users’ perspective. From the results it is determined that, for all the video test cases, the videos are rated better quality at low packet loss values and low delay values. The quality of the videos with the presence of delay is rated high compared to the video quality in the case of packet loss. It was observed that the high resolution videos are feeble in the presence of higher disturbances i.e. high packet loss and larger delays. From considering all the cases, it can be observed that the QoE disturbances due to the delivery issues is at an acceptable minimum for the 360px video. Hence, the 480x360 video is the threshold to sustain the video quality.

Mobile data traffic will continue to show rapid growth in the coming years; however the data revenue is not rising fast enough to ensure the operators’ profitability. Therefore, mobile operators must seek new approaches to find out what service does the customers need and what quality makes the customers satisfied in order to keep their increasingly sophisticated customers satisfied at the same time minimizing their revenue gap. This paper investigate the effect of mobile cellular network performance and contextual factors on smartphone users’ satisfaction, this was done via crowdsourcing through an experiment where an Android Application and a user Survey were included, which is able to evaluate and analyze the perceived quality of experience (QoE) for YouTube service for Android Smartphone users. To achieve this goal, the App NPT performs measurements of objective quality of service (QoS) parameters, whereas the survey carriers out collecting subjective user opinion. The result show that network performance parameters do impact the MOS (Mean Opinion Score) exponentially, either in a positively or negatively way, however, multiple parameters need to be considered together in order to draw a more accurate correlation with QoE. In addition, QoE are heavily affected by many other contextual factors, such as age and gender as well as users location. QoE are also impacted by several subjective factors, such as user expectation. Not always the highest throughput will lead to the best QoE, and not always the best technology (LTE) deserves the best MOS. Even though user received very high downlink throughput, their MOS value may still be low due to they might think the video were not fun to watch and the quality has not meet their expectation.

The demand for efficient video coding techniques has increased in the recent past, resulting in the evolution of various video compression techniques. SVC (Scalable video coding) is the recent amendment of H.264/AVC (Advanced Video Coding), which adds a new dimension by providing the possibility of encoding a video stream into a combination of different sub streams that are scalable in areas corresponding to spatial resolution, temporal resolution and quality. Introduction of the scalability aspect is an effective video coding technique in a network scenario where the client can decode the sub stream depending on the available bandwidth in the network. A graceful degradation in the video quality is expected when any of the spatial, temporal or the quality layer is removed. Still the amount of degradation in video quality has to be measured in terms of Quality of Experience (QoE) from the user’s perspective. To measure the degradation in video quality, video streams consisting of different spatial and temporal layers have been extracted and efforts have been put to remove each layer starting from a higher dependency layer or the Enhancement layer and ending up with the lowest dependency layer or the Base layer. Extraction of a temporally downsampled layer had challenges with frame interpolation and to overcome this, temporal interpolation was employed. Similarly, a spatial downsampled layer has been upsampled in the spatial domain in order to compare with the original stream. Later, an objective video quality assessment has been made by comparing the extracted substream containing fewer layers that are downsampled both spatially and temporally with the original stream containing all layers. The Mean Opinion Scores (MOS) were obtained from objective tool named Perceptual Evaluation of Video Quality (PEVQ). The experiment is carried out for each layers and also for different test videos. Subjective tests were also performed to evaluate the user experience. The results provide recommendations to SVC capable router about the video quality available for each layer and hence the network transcoder can transmit a specific layer depending on the network conditions and capabilities of the decoding device.
Efterfrågan på effektiva video kodningstekniker har ökat under de senaste åren, vilket resulterar i utvecklingen av olika tekniker videokomprimering. SVC (Scalable Video Coding) är den senaste ändringen av H.264/AVC (Advanced Video Coding), vilket ger en ny dimension genom att möjligheten att koda en videoström till en kombination av olika sub strömmar som är skalbara i områden som motsvarar rumslig upplösning, tidsupplösning och kvalitet. Introduktion av skalbarhet aspekten är en effektiv video kodningsteknik i ett nätverk scenario där kunden kan avkoda sub strömmen beroende på den tillgängliga bandbredden i nätverket. En elegant nedbrytning i videokvaliteten förväntas när någon av den rumsliga, tidsmässiga eller kvaliteten skiktet avlägsnas. Fortfarande mängden nedbrytning i videokvalitet måste mätas i termer "Quality of Experience" (QoE) från användarens perspektiv. För att mäta försämring i video-kvalitet, har videoströmmar består av olika rumsliga och tidsmässiga skikt hämtats och ansträngningar har lagts för att ta bort varje lager från ett högre beroende lager eller förbättrande lagret och slutar upp med den lägsta beroendet lagret eller basen skikt. Extraktion av ett tidsmässigt nedsamplas lager hade problem med ram interpolation och för att övervinna detta, var temporal interpolering används. På liknande sätt har en rumslig nedsamplas skikt har uppsamplas i rumsdomänen för att jämföra med den ursprungliga strömmen. Senare har en objektiv videokvalitet bedömning gjorts genom att jämföra den extraherade underströmmen med färre lager som nedsamplade både rumsligt och tidsmässigt med den ursprungliga strömmen innehållande alla lager. De genomsnittliga yttrande poäng (MOS) erhölls från objektivt verktyg som heter Perceptuell utvärdering av Videokvalitet (PEVQ). Experimentet utförs för varje skikt och även för olika test video. Subjektiva tester utfördes också för att utvärdera användarupplevelsen. Resultaten ger rekommendationer till SVC kapabel router om videokvaliteten för varje lager och därmed nätverket kodomvandlaren kan överföra ett visst lager beroende på nätverksförhållanden och kapacitet avkodnings anordningen.
Tilak Varisetty, 518, Gamlainfartsvägen, Annebo, Karlskrona -37141, Mobil: 0723060131

Avec l'hétérogénéité des réseaux et la demande croissante de services multimédias, la Qualité d'Expérience (QoE) devient un facteur déterminant de réussite ou d’échec de ces services. Dans cette thèse, nous avons d’abord analysé l'impact des paramètres de qualité sur l'engagement de l'utilisateur, afin de comprendre l’effet des paramètres vidéo (temps de démarrage, qualité intrinsèque, taux de blocage) et la popularité du service sur l'engagement de l'utilisateur. Nos résultats ont montré que le taux de blocage et la popularité du service sont des paramètres critiques qui impactent fortement la satisfaction et l'engagement de l’utilisateur, tandis que, le temps de démarrage a moins d’impact. Ensuite, les approches subjectives de QoE comme le Mean Opinion Score (MOS) ont été traité dans cette thèse, où les utilisateurs sont appelés à donner une note de satisfaction en fonction des informations de contextes. Une analyse statistique des résultats obtenus à partir de tests utilisateurs a montré que le type de terminal et de contenu sont des paramètres qui impactent fortement le MOS. En plus, des modèles mathématiques d’estimation de QoE en fonction des informations de contextes ont été proposés. Enfin, deux techniques d’optimisations ont été proposées : Le MDASH (MOS Dynamic Adaptive Streaming over HTTP) pour l’optimisation vidéo de flux partageant les mêmes ressources, de manière à garantir une certaine QoE pour tous les utilisateurs. Et une optimisation de livraison, basée sur des fonctions d’utilités dans laquelle, une fonction globale d'utilité est calculée en fonction de différentes contraintes (qui dépendent fortement des stratégies des acteurs de la chaîne de livraison)
With the network heterogeneity and increasing demand of multimedia services, Quality of Experience (QoE) becomes a crucial determinant of the success or failure of these services. In this thesis, we first propose to analyze the impact of quality metrics on user engagement, in order to understand the effects of video metrics (video startup time, average bitrate, buffering ratio) and content popularity on user engagement. Our results show that video buffering and content popularity are critical parameters which strongly impacts the end-user’s satisfaction and user engagement, while the video startup time appears as less significant. On other hand, we consider subjective approaches such as the Mean Opinion Score (MOS) for evaluating QoE, in which users are required to give their assessment according to contextual information. A detailed statistical analysis of our study shows the existence of non-trivial parameters impacting MOS (the type of device and the content type). We propose mathematical models to develop functional relationships between the QoE and the context information which in turn permits us to estimate the QoE. A video content optimization technique called MDASH (for MOS Dynamic Adaptive Streaming over HTTP) is proposed, which improves the perceived QoE for different video sessions sharing the same local network, while taking QoE fairness among users as a leitmotiv. We also propose a utility-based approach for video delivery optimization, in which a global utility function is computed based on different constraints (e.g. target strategies coming from the actors of the delivery chain)

The main objective of this thesis is to provide a smooth video playout on the mobile device over wireless networks. The parameters that specify the wireless channel include: bandwidth variation, frame losses, and outage time. These parameters may affect the quality of the video negatively, and the mobile users may notice sudden stops during the playout video, i.e., the picture is momentarily frozen, followed by a jump from one scene to a different one. This thesis focuses on eliminating frozen pictures and reducing the amount of video data that need to be transmitted. In order to eliminate frozen scenes on the mobile screen, we propose three different techniques. In the first technique, the video frames are split into sub-frames; these sub-frames are streamed over different channels. In the second technique the sub-frames will be “crossed” and sent together with other sub-frames that are from different positions in the streaming video sequence. If some sub-frames are lost during the transmission a reconstruction mechanism will be applied on the mobile device to recreate the missing sub-frames. In the third technique, we propose a Time Interleaving Robust Streaming (TIRS) technique to stream the video frames in different order. The benefit of that is to avoid losing a sequence of neighbouring frames. A missing frame from the streaming video will be reconstructed based on the surrounding frames on the mobile device. In order to reduce the amount of video data that are streamed over limited bandwidth channels, we propose two different techniques. These two techniques are based on identifying and extracting a high motion region of the video frames. We call this the Region Of Interest (ROI); the other parts of the video frames are called the non-Region Of Interest (non-ROI). The ROI is transmitted with high quality, whereas the non-ROI is interpolated from a number of references frames. In the first technique the ROI is a fixed size region; we considered four different types of ROI and three different scenarios. The scenarios are based on the position of the reference frames in the streaming frame sequence. In the second technique the ROI is identified based on the motion in the video frames, therefore the size, position, and shape of the ROI will be different from one video to another according to the video characteristic. The videos are coded using ffmpeg to study the effect of the proposed techniques on the encoding size. Subjective and objective metrics are used to measure the quality level of the reconstructed videos that are obtained from the proposed techniques. Mean Opinion Score (MOS) measurements are used as a subjective metric based on human opinions, while for objective metric the Structural Similarity (SSIM) index is used to compare the similarity between the original frames and the reconstructed frames.

In this thesis, the impact of packet losses on the quality of received videos sent across a network that exhibit normal network perturbations such as jitters, delays, packet drops etc has been examined. Dynamic behavior of a normal network has been simulated using Linux and the Network Emulator (NetEm). Peoples’ perceptions on the quality of the received video were used in rating the qualities of several videos with differing speeds. In accordance with ITU’s guideline of using Mean Opinion Scores (MOS), the effects of packet drops were analyzed. Excel and Matlab were used as tools in analyzing the peoples’ opinions which indicates the impacts that different loss rates has on the transmitted videos. Statistical methods used for evaluation of data are mean and variance. We conclude that people have convergence of opinions when losses become extremely high on videos with highly variable scene changes

This thesis contains description of the present methods and algoritms for measuring the quality of telephone call on the PBX Asterisk. Further develop the concept of a system for measuring and implementing the call embbeded system VOIPAC PXA270M. Based on theoretical analysis is carried out discussions between C, Java and PHP,which results in the selection of appropriate programming language suitable for implementation in embedded system. The concept is realized by creating an application written in a particular programming language. Part of this work is verification created application using experimental measurments of telecommunications system. The results of experimental measurements are discussed in the final evaluation.

In the current mobile telecommunication market, with slow growth in mobile subscriptions and increasing traffi demand, each mobile operator needs to manage their customer loyalty in order to maintain position in the market. To retain their customer's loyalty, the user quality of satisfaction needs to be preserved. Integrating a Quality of Experience (QoE) approach into a radio resource scheduling scheme can be a means to improve user quality of satisfaction to a service. However, the enhancement of existing resource allocation management to support a QoE-based resource scheduling scheme needs a careful consideration since it will impact the mobile operator's investment cost. A profitability assessment of QoE-based resource allocation is required as a basis for the mobile operator to forecast their potential benefit of QoE-based resource scheduling deployment. This thesis investigated the profitability of deploying QoE-based radio resource management (RRM) in terms of revenue loss compared to proportional fair (PF) scheduling, a widely used resource allocation scheme, in delivering a streaming video service. In QoE-based RRM, a buffering percentage experienced by a user was considered in the resource allocation decision process. The two scheduling schemes were simulated in different network configurations. User satisfaction was quantified in terms of mean opinion score. Given the degree of satisfaction for each user, a number of users who would be likely to churn was obtained. A cost-benefit assessment was then conducted by predicting revenue loss due to customer churn. The results from the simulation and cost analysis show that although QoE-based resource scheduling provides users with a higher degree of satisfaction for more base stations, the utilization of a QoE-based resource scheduler does not offer significant benefit to the network operator with regard to revenue loss and deployment cost when compared to a PF scheduler. This outcome indicates that if the business target is to reduce customer churn, then the operator should utilize a PF scheduler for their RRM scheme.
Den nuvarande mobiltelefonimarknaden kännetecknas av svag tillväxt av nya kunder men ett ökat nyttjande bland existerande kunder av företagens tjänster. Kundlojalitet har blivit en avgörande faktor för att uppnå en stark marknadsposition. Kundernas upplevda kvalitet utav mobiltjänsterna behöver upprätthållas på en hög nivå för att tillfredställa denna lojalitet. Att applicera en upplevad kvalitet (QoE) metod i en radio resurs kan vara ett medel till att förbättra kundernas upplevda kvalitet av mobiltj änsten. För att undersöka ifall en sådan tjänst är lönsam är det dock nödvändigt att en lönsamhetskalkyl genomförs, där investeringskostnad och systemets driftkostnad vägs mot eventuella intäkter. En lönsamhetsbedömning av QoE-baserad resursallokering krävs som grund för mobiloperatören att förutse deras potentiella fördelar med QoE-baserad resursschemaläggning. Denna uppsats undersöker lönsamheten av att implementera QoE i termer av förlorade intäkter, jämfört med proportionell rättvis (PF) schemaläggning, i att leverera en videoströmservice. I QoE-baserad RRM användes buffertprocentandel som användes av användarna i resursallokeringsprocessen.  De två olika systemen simulerades genom att använda olika antal basstationer i mobilnätverkskonfigurationen. Användarnöjdhet kvantifierades genom att låta användarna betygsätta tjänsten, detta värde användes därefter till att uppskatta hur många av kunderna som sannolikt ej skulle återanvända tjänsten. En lönsamhetskalkyl genomfördes genom att prediktera förlorade intäkter med avseende på kunderna som ej skulle återanvända tjänsten. Resultaten från simulerings- och lönsamhetsberäkningen visade att även om QoE erbjuder en högre kundnöjdhet av tjänsten och tillfredsställelse för er basstationer, så leder inte en QoE-implementering till signikanta fördelar för nätverket i termer av förlorade intäkter och investeringskostnader jämfört med ett PF schemaläggare. Detta indikerar att om ett företags mål är att höja kundlojaliteten, då skall företaget applicera en PF schemaläggare istället för QoE.

FundaÃÃo Cearense de Apoio ao Desenvolvimento Cientifico e TecnolÃgico
Ericsson Brasil
Uma nova geraÃÃo de sistemas de comunicaÃÃes sem fio, 5a GeraÃÃo (5G), à prevista para 2020. Para a 5G, à esperado o surgimento de diversos serviÃos baseados em comunicaÃÃes mÃquina à mÃquina em diferentes Ãreas, como assistÃncia mÃdica, seguranÃa e redes de mediÃÃo inteligente. Cada um com diferentes requerimentos de taxa de transmissÃo, latÃncia, capacidade de processamento, eficiÃncia energÃtica, etc. Independente do serviÃo, os clientes precisam ficar satisfeitos. Isto està impondo uma mudanÃa de paradigmas em direÃÃo à priorizaÃÃo do usuÃrio como fator mais importante no gerenciamento de redes sem fio. Com esta mudanÃa, criou-se o conceito de qualidade de experiÃncia (do inglÃs, Quality of Experience (QoE)), que descreve de forma subjetiva como o serviÃo à percebido pelo usuÃrio. A QoE normalmente à avaliada por uma nota entre 1 e 5, chamada nota mÃdia de opiniÃo (do inglÃs, Mean Opinion Score (MOS)). Neste contexto, conceitos de QoE podem ser considerados com diferentes objetivos, como: aumentar a vida Ãtil de baterias, melhorar a seleÃÃo para acesso à rede e aprimorar a alocaÃÃo dos recursos de rÃdio (do inglÃs, Radio Resource Allocation (RRA)). Com relaÃÃo à RRA, nesta dissertaÃÃo consideram-se requerimentos de QoE na gestÃo dos recursos disponÃveis em um sistema de comunicaÃÃes sem fio, como espectro de frequÃncia e potÃncia de transmissÃo. Mais especificamente, estuda-se um problema de assinalamento de recursos de rÃdio e de alocaÃÃo de potÃncia que objetiva maximizar a mÃnima MOS do sistema sujeito a satisfazer um nÃmero mÃnimo de usuÃrios prÃ-estabelecido. Inicialmente, formula-se um novo problema de otimizaÃÃo considerando restriÃÃes quanto à potÃncia de transmissÃo e quanto à fraÃÃo de usuÃrios que deve ser satisfeita, o que à um importante tÃpico do ponto de vista das operadoras. Este à um problema nÃo linear e de difÃcil soluÃÃo. Ele à entÃo reformulado como um problema linear inteiro e misto, que pode ser resolvido de forma Ãtima usando algoritmos conhecidos de otimizaÃÃo. Devido à complexidade da soluÃÃo Ãtima obtida, propÃe-se uma heurÃstica chamada em inglÃs de Power and Resource Allocation Based on Quality of Experience (PRABE). O mÃtodo proposto à avaliado por meio de simulaÃÃes e os resultados obtidos mostram que sua performance à superior à de outros existentes, sendo prÃxima à da Ãtima.
A new generation of wireless networks, the 5th Generation (5G), is predicted for beyond 2020. For the 5G, it is foreseen an emerging huge number of services based on Machine-Type Communications (MTCs) in different fields, such as, health care, smart metering and security. Each one of them requiring different throughput rates, latency, processing capacity, energy efficiency, etc. Independently of the service type, the customers still need to get satisfied, which is imposing a shift of paradigm towards incorporating the user as the most important factor in wireless network management. This shift of paradigm drove the creation of the Quality of Experience (QoE) concept, which describes the service quality subjectively perceived by the users. QoE is generally evaluated by a Mean Opinion Score (MOS) ranging from 1 to 5. In this context, QoE concepts can be considered with different objectives, such as, increasing battery life, optimizing handover decision, enhancing access network selection and improving Radio Resource Allocation (RRA). Regarding the RRA, in this masterâs thesis we consider QoE requirements when managing the limited available resources of a communication system, such as frequency spectrum and transmit power. More specifically, we study a radio resource assignment and power allocation problem that aims at maximizing the minimum MOS of the users in a system subject to attaining a minimum number of satisfied users. Initially, we formulate a new optimization problem taking into account constraints on the total transmit power and on the fraction of users that must be satisfied, which is an important topic from an operatorâs point of view. The referred problem is non-linear and hard to solve. However, we get to transform it into a simpler form, a Mixed Integer Linear Problem (MILP), that can be optimally solved using standard numerical optimization methods. Due to the complexity of obtaining the optimal solution, we propose a heuristic solution to this problem, called Power and Resource Allocation Based on Quality of Experience (PRABE). We evaluate the proposed method by means of simulations and the obtained results show that it outperforms some existing algorithms, as well as it performs close to the optimal solution.

Modern methods of speech synthesis are not suitable for restoration of song signals due to lack of vitality and intonation in the resulted sounds. The aim of presented work is to synthesize melismas met in Lithuanian folk songs, by applying Artificial Neural Networks. An analytical survey of rather a widespread literature is presented. First classification and comprehensive discussion of melismas are given. The theory of dynamic systems which will make the basis for studying melismas is presented and finally the relationship for modeling a melisma with nonlinear and dynamic systems is outlined. Investigation of the most widely used Linear Prediction Coding method and possibilities of its improvement. The modification of original Linear Prediction method based on dynamic LPC frame positioning is proposed. On its basis, the new melisma synthesis technique is presented. Developed flexible generalized melisma model, based on two Artificial Neural Networks – a Multilayer Perceptron and Adaline – as well as on two network training algorithms – Levenberg- Marquardt and the Least Squares error minimization – is presented. Moreover, original mathematical models of Fortis, Gruppett, Mordent and Trill are created, fit for synthesizing melismas, and their minimal sizes are proposed. The last chapter concerns experimental investigation, using over 500 melisma records, and corroborates application of the new mathematical models to melisma synthesis of one performer.

Real time video streaming through mobile Internet is increasing day by day and the video  quality can be affected  very badly by network performance issues. Video freezing and video  jumping are one of the serious issues that affect the user experience badly. Hence service providers are interested to evaluate the performance of quality of experience. We  follow the methods from the International Telecommunications Union–Telecommunication Sector(ITU-T)recommendations. In this thesis, we are studying the effect of freezing on user experience by subjective tests and obtaining the mean opinion scores using perceptual video quality assessment tool and analyze  which part of the video is affected mostly by introducing freezein selected parts.

Forensic audio recordings are usually made with a single covert microphone in non-ideal conditions. In non-ideal conditions the recordings are highly susceptible to various types of noise. The noise is usually broadband noise, co-talker interference, impulsive noise, narrow band noise or convolutional noise. There are existing speech enhancement techniques available to suppress most of the noise types mentioned, but when the noise is of a considerable level the performance of most enhancement techniques tend to decrease significantly. This thesis presents a study of speech enhancement techniques that are applicable to the enhancement of forensic audio recordings or that can be used in a forensic recording environment. It considers both pre-processing and post-processing speech enhancement techniques. This thesis investigates the improvement of some of the existing speech enhancement techniques as well as proposing some new ones. The performance of the improved and proposed speech enhancement techniques were evaluated objectively using the segmental signal-to-noise ratio (SNRseg) and subjectively using the mean opinion score (MOS). A review of the current speech enhancement techniques is presented in the thesis and is also used as a reference in some comparisons. The current speech enhancement techniques considered are those that are applicable to forensic audio recordings. The performance of the existing techniques are assessed in the comparisons with the speech enhancement techniques proposed by this thesis. Two pre-processing speech enhancement techniques are presented in this thesis. The first pre-processing speech enhancement technique is designed to improve existing broadband noise suppression techniques by the use of frequency shift keying (FSK) signals. It is based on a simple concept, which is to insert a known tone of sufficient amplitude into the silent segments of a speech signal prior to transmission. At the receiver the detection of silent or non-speech segments used in estimating the noise, becomes a simpler and more accurate task due to the inserted tone. The second pre-processing speech enhancement technique is designed to suppress a wide range of noises and it is based on zero padding. Zero padding involves inserting a zero value sample in between each speech signal sample prior to transmission. The inserted zero value samples allow accurate characterisation of the noise in the adjacent speech samples. At the receiver the noise is estimated from the sample positions allocated for the zero value samples. Several post-processing speech enhancement techniques are presented in this thesis. The first post-processing speech enhancement technique is designed for the suppression of co-talker interference and it uses a combination of dynamic time warping (DTW) and dual channel adaptive filtering. This technique is proposed for the suppression of co-talker interference, when the co-talker interference or noise reference signal is obtainable at a later instance as in the case of many covert forensic recordings. The corrupted speech signal and the noise reference signal are aligned using DTW and then the co-talker interference is suppressed using a dual channel adaptive filter. The second post-processing speech enhancement technique is designed for broadband noise suppression and is based on spectral subtraction but it incorporates the masking properties of the human auditory system for improved performance. Auditory masking is used to find the masking threshold, below which the noise is no longer perceivable. Only those noise components above the masking threshold are suppressed. This approach is taken to reduce any byproducts such as musical noise. The third post-processing speech enhancement technique is designed for broadband noise suppression and is based on spectral subtraction but it exploits the human auditory systems perception of frequency. Critical band analysis is used to group frequencies that are similarly perceived, which are then treated as a single entity by the enhancement technique.

To be successful in today's competitive market, service providers should look at user's satisfaction as a critical key. In order to gain a better understanding of customers' expectations, a proper evaluations which considers intrinsic characteristics of perceived quality of service is needed. Due to the subjective nature of quality, the vagueness of human judgment and the uncertainty about the degree of users' linguistic satisfaction, fuzziness is associated with quality of experience. Considering the capability of Fuzzy logic in dealing with imprecision and qualitative knowledge, it would be wise to apply it as a powerful mathematical tool for analyzing the quality of experience (QoE). This thesis proposes a fuzzy procedure to evaluate the quality of experience. In our proposed methodology, we provide a fuzzy relationship between QoE and Quality of Service (QoS) parameters. To identify this fuzzy relationship a new term called Fuzzi ed Opinion Score (FOS) representing a fuzzy quality scale is introduced. A fuzzy data mining method is applied to construct the required number of fuzzy sets. Then, the appropriate membership functions describing fuzzy sets are modeled and compared with each other. The proposed methodology will assist service providers for better decision-making and resource management.

Mapping between many different applications and many different underlying technologies is very complicated. Moreover, since users need service continuity and want to get the service in a satisfactory level, firstly, their perception of the service should be measured and secondly, the changes in the underlying technologies should be transparent to users. As a result, there should be ”virtualization layer” between application layer and underlying access technologies whose job is to abstract user perception of the application in terms of network parameters and transfer these requirements to underlying layers. In this thesis, we propose a generic mathematical expression to abstract user perception of application in a unified way for different applications. Since today applications are composite applications, having a generalized expression that has the same form for various applications can ease resource management calculations. We use application service map which is based on quality of experience for resource management.

This diploma thesis focuses on the issue of evaluation VoIP services (from the perspective of QoE) and their quality in university network. It includes theoretical basics of VoIP testing, principals of QoS, and also overview of QoE/MOS measurement methods. Next part describes the test bed and methodology used for measurements and evaluating of results. Site survey results and VoIP quality measurement are evaluated at the end, followed by recommendations that can lead to better VoIP quality in MENDELU wireless network.