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  • 301. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    On the Performance of ROI-Based Image Transmission Using Cooperative Diversity2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we examine the spatial diversity of cooperative communications for image transmission without deploying multiple antennas at the transmitter. We propose a novel region of interest (ROI)-based scheme for image transmission over wireless cooperative/relay fading channels. By having the relay terminal assist the direct communications, we can increase the resilience for ROI against the error-prone fading channels. Our proposed scheme significantly improves the performance of ROI compared to the direct communications (no-cooperation) and conventional relay networks without performing any forward error correction. Although we focus on the adaptive decode-forward (ADF) relay protocol, our proposed scheme can be easily adopted to any other relaying protocol such as fixed decode-forward (FDF), amplify-forward (AF), hybrid decode-amplify-forward (HDAF), and distributed-Alamouti space--time coding. Simulation results show that under the the same total transmit power constraint our proposed scheme significant outperforms the conventional ones in terms of bit error rate (BER) and peak signal-to-noise ratio (PSNR).

  • 302. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Performance Analysis of Cooperative Spatial Multiplexing with Amplify-and-Forward Relays2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Cooperative spatial multiplexing (CSM) systems can achieve high spatial multiplexing gain in wireless relay networks since each single-antenna relay forwards simultaneously a different subset of source messages to the destination. In this paper, the performance of CSM with amplify-and-forward (AF) relays are presented. Specifically, we derive exact closed-form expressions for symbol error probability (SEP) and achievable spectral efficiency of CSM with linear receiver in dissimilar Rayleigh fading channels. Assessing the SEP performance in the high signal-to-noise regime, we further show that CSM with AF relays obtains the first order of diversity gain. Furthermore, it has been observed that CSM outperforms two well-known cooperative diversity systems, e.g., selection combining and maximal ratio combining, in term of spectral efficiency. We also perform Monte-Carlo simulations to validate our analysis.

  • 303. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Robust EZW Image Transmission Scheme Using Distributed-Alamouti Codes in Relay Networks2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    A robust image transmission scheme deploying distributed-Alamouti space-time code (STC) over wireless relay networks is proposed. Specifically, we propose a cross-layer design combining application, networking, and physical layer to enhance the quality of multimedia data over error-prone wireless channels. At the application layer, a coded image sequence based on the wavelet transform is divided into two priorities. The higher priority contains the most significant information of image and the lower priority conveys less important information. At the physical layer, two pre-assigned relays cooperate to form a distributed-Alamouti code which help the source to transmit the low priority sequence of the image over error-prone wireless channels. At the networking layer, among the whole relay nodes in the networks we select two relay nodes which provides the maximum signal-to-noise ratio to convey the higher priority. With this strategy, we implicitly achieve unequal error protection for image transmission without controlling power or varying modulation and coding at the transmitter at the expense of increasing network's overhead (i.e. feedback information). The selection of relays needs limited feedback, hence, enabling our proposed scheme feasible in practical applications. Analytical and simulation results are provided to verify our proposal. It has been shown that the image quality is remarkably enhanced in terms of objective quality using the proposed scheme compared to the conventional transmission schemes.

  • 304. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Fiedler, Markus
    Cross-Layer Design for Integrated Mobile Multimedia Network with Strict Priority Traffic2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In mobile multimedia networks, different traffic classes require various levels of quality of service (QoS). In this paper, we propose a cross-layer design to provide diverse QoS provisions for integrated realtime/non-realtime traffic by jointly taking into account the physical layer, data link layer, and application layer. Specifically, at the physical layer, adaptive modulation and coding (AMC) is employed to cope with the time-varying nature of fading channels whereas impairments due to queuing effects are considered at the data link layer. At the application layer, realtime and non-realtime traffic are classified into high and low priority classes, respectively, with strict priority levels. The cross-layer scheme is characterized as a discrete Markov modulated Poisson process. Solving the steady state probability of this Markov model readily enables us to investigate several important performance metrics such as packet drop rate due to buffer overflow and packet error rate due to transmission errors and network impairments. Our proposed cross-layer design is verified by comparing the analytical results with Monte-Carlo simulations. Furthermore, it has been shown that the proposed cross-layer design can flexibly guarantee QoS requirements for each traffic class.

  • 305. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Tsiftsis, Theodoros A.
    Bao, Vo Nguyen Quoc
    Amplify-and-Forward MIMO Relaying with OSTBC over Nakagami-m Fading Channels2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we analyze the performance of dual-hop channel state information (CSI)-assisted amplify-andforward (AF) cooperative networks using orthogonal space-time block codes (OSTBCs) over independent but not identically distributed Nakagami-m fading channels. Specifically, we present closed-form expressions of the outage probability (OP) and the symbol error probability (SEP). The analytical results are given in tractable forms which readily allow us to assess the performance of AF relay systems using OSTBCs. For sufficiently large signal-to-noise ratio, we obtain the asymptotic results for OP and SEP which reveal insights into the effect of fading factors on the diversity and coding gains. It has been shown that between the two hops the more severe link solely determines the diversity and coding gains. In particular, these two gains strictly depend on the fading severity parameters and the channel mean powers of the more rigorous hop, respectively. Numerical results are provided showing an excellent agreement between our analytical results and those of Monte-Carlo simulations for selected scenarios.

  • 306. Duong, Quang Trung
    et al.
    Zepernick, Hans-Jürgen
    Tsiftsis, Theodoros A.
    Bao, Vo Nguyen Quoc
    Performance Analysis of Amplify-and-Forward MIMO Relay Networks with Transmit Antenna Selection over Nakagami-m Channels2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    We analyze the performance of amplify-and-forward (AF) multiple-input multiple-output (MIMO) cooperative networks over independent but not identically distributed Nakagami-$m$ fading channels. Specifically, we consider an AF MIMO relay network where the source deploys the transmit antenna selection scheme to communicate with the destination through the help of a relay. We derive closed-form approximations for outage probability (OP) and symbol error probability (SEP). Moreover, asymptotically tight approximations for OP and SEP have been obtained to facilitate insights on how fading parameters affect the performance. Our analytical results are verified by Monte-Carlo simulations for respective scenarios.

  • 307. Duursma, Rick
    et al.
    Fiedler, Markus
    Iterative computations of bit rate summary statistics at inlet and outlet of a discrete time fluid queue2006Konferensbidrag (Refereegranskat)
    Abstract [sv]

    Pappret addresserar ett tidsdiskret flödes-kömodell med fokus på bithastighetsstatistik såsom bithastighetshistogramm och autokorrelation. Flödesmodell, kömodell, tidsdiskret modell, prestandaberäkning

  • 308.
    Ekhator, Stephen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Evaluating Kismet and NetStumbler as Network Security Tools & Solutions.2010Självständigt arbete på avancerad nivå (masterexamen)Studentuppsats (Examensarbete)
    Abstract [sv]

    The thesis is about deploying Kismet application software to capture wireless networks, analysis the capture data packets if there is any vulnerability and then compare the results with NETSH captures . NETSH is a Netstumbler alternative which comes as default in Windows vista.

  • 309.
    Ekramian, Elnaz
    Blekinge Tekniska Högskola, Fakulteten för datavetenskaper, Institutionen för datalogi och datorsystemteknik.
    Automation of the test methods for packet loss and packet loss duration in the Ixia platform2018Självständigt arbete på avancerad nivå (masterexamen), 20 poäng / 30 hpStudentuppsats (Examensarbete)
    Abstract [en]

    Today’s technology has a strong tendency towards automation. As a matter of fact, the tremendous improvement of science in the recent years brought new ideas regarding to accelerate the scientific process that is not separated of automation. This paper also deals with automation of manual tests that were used to analyze packet loss and packet loss duration in a network. These two metrics were chosen based on their importance they have in the communication technology, also based on the weak points that were found in the manual processes. This experiment is done in the Ixia platform that was an appropriate test bed to design an automation framework.After a comprehensive research on network and communication we could choose packet loss and packet loss duration as two important parameters that are under test several times per day. Therefore, based on the properties that are used for automation, these two metrics had the priority compare to other metrics. We could create a framework that works correspond to the manual test process. For this purpose, Tcl programming language is used. The script that was written with this high-level language can communicate with the graphical user interface, configuring all the connected devices, measuring mentioned metrics and ultimately save the result in a csv file.Finally, we could reach to the main objective of this project which was to show how positively automatic method can affect on the quality of test in terms of accuracy, time and manpower saving.

  • 310.
    Eleburuike, Ismail
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap.
    Soetan, Simeon Adekunle
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap.
    An Energy Efficient Protocol Based on Hierarchical Routing Technique for WSN2010Självständigt arbete på avancerad nivå (masterexamen)Studentuppsats (Examensarbete)
    Abstract [en]

    The area of wireless sensor networks (WSNs) is one of the emerging and fast growing fields in the scientific world. This has brought about developing low cost, low-power and multi-function sensor nodes. However, the major fact that sensor nodes run out of energy quickly has been an issue and many energy efficient routing protocols have been proposed to solve this problem and preserve the longetivity of the network. This is the reason why routing techniques in wireless sensor network focus mainly on the accomplishment of power conservation. Most of the recent publications have shown so many protocols mainly designed to minimize energy consumption in sensor networks. This thesis work proposes a hierarchical routing technique which shows energy efficiency. Our technique selects cluster head with highest residual energy in each communication round of transmission and also takes into account, the shortest distance to the base station from the cluster heads. Simulation results show that hierarchical routing technique with different level of hierarchy prolongs the lifetime of the network compared to other clustering scheme and the energy residual mean value after some communication rounds of simulation increases significantly.

  • 311.
    Elhag, Omer
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap.
    Fast Back Projection Algorithm for Bi-Static SAR Using Polar Coordinates2012Självständigt arbete på avancerad nivå (masterexamen)Studentuppsats (Examensarbete)
    Abstract [en]

    Synthetic Aperture Radar (SAR) plays a significant role in geophysical studies and remote sensing applications. SAR inherits the benefits of imaging RADAR over the other optical sensors such as working in all weather conditions and working independently of sunlight. In addition to these benefits SAR generates a finer resolution 2-D image compared to conventional (real) aperture radar. Due to the sole merits of Ultrawideband-Ultrawidebeam (UWB) Bistatic SAR, this thesis introduces and analyzes a fast time domain algorithm for its image formation. This algorithm inherits the advantages of time-domain algorithms over frequency domain ones. It divides the full synthetic aperture into subapertures. Each subaperture generates a polar grid image. The key point is that the subaperture polar images have very low resolution in cross range (the angular direction); this means that they can be calculated on a pixel grid that is coarse in the angular direction. The final image is obtained by combining all subaperture polar images after converting them to the final high-resolution Cartesian image, in this conversion interpolation is used. Since the subaperture images contain far fewer pixels in cross range than the final image, far fewer operations are required to be executed as compared to Global Backprojection GBP. Due to using the polar grid, the proposed algorithm is named Bistatic Polar-FBP (Bi-PFBP). It is found that although for N×N scene image with N aperture positions the Bi-PFBP computational load is less by approximately a factor of √N as compared to GBP, the image quality generated by each one of them is almost the same.

  • 312. Eliasson, Charlott
    Quality of Experience and Quality of Service in the Context of an Internet-based Map Service2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [sv]

    Användarexperiment där användaren fick betygssätta en tjänst som stördes på nätverksnivå. Vi kunde bekräfta ett välkänt sammanhang mellan användarreaktion och responstider. Karttjänst, Quality of Experience (QoE), Quality of Service (QoS), responstid, MOS

  • 313. Eliasson, Charlott
    et al.
    Fiedler, Markus
    Dimensioning study for road user charging2008Konferensbidrag (Refereegranskat)
    Abstract [sv]

    Vägavgiftslösningar baserade på konceptet med tunna klienter är beroende av tidskorrekta leveranser av positioner för lastbilar till leverantören av vägavgiftssystemet, som sedan utför kartjämförelsen samt uträkningen av vägavgifter. För att undvika dataförluster och sena leveranser måste en ordentlig dimensionering av systemet genomföras, vilket tas upp i denna rapport. Vi undersöker möjligheterna att använda befintliga mobila och trådlösa system (framför allt GPRS, UMTS och WLAN) till både streaming och bulköverföring av positioneringsdata och vi fastställer förnuftiga kombinationer av samplings- och rapporteringsintervall med tanke på effektiv och ekonomisk rapportering. Det valda tillvägagångssättet med erforderlig kapacitet öppnar upp för tolkningar av resursbehoven för de olika kommunikationsteknologierna. Vi framhåller även ett par fällor angående dimensioneringen, framför allt gällande de mönster enligt vilka data skickas, som kan förorsaka överbelastning på serversidan i systemet. Det blir tydligt att mobila nätverk på ett bra sätt kan hantera den belastningen som tillkommer vid rapportering av lastbilar, medan bulköverföring via trådlösa hot-spots kan användas som en komplimenterande lösning. Vägavgiftssystem, dimensionering, GPRS, UMTS, WLAN

  • 314. Eliasson, Charlott
    et al.
    Fiedler, Markus
    Jørstad, Ivar
    A criteria-based evaluation framework for authentication schemes in IMS2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    The IP Multimedia Subsystem (IMS) is regarded as one of the most prominent enablers for successful service provisioning across different access network technologies and devices. While new paradigms, e.g. seamless communication, enter the IMS, existing solutions, e.g. for authentication, need to be redefined, which is one of the major activities within the EUREKA!-funded Mobicome project, involving operators, manufacturers and academia. As there exist several candidate solutions for providing seamless authentication, there is a need for a set of criteria that helps to select the candidate that fulfils those criteria in a bestpossible way. Given this background, this position paper proposes a framework of criteria for the evaluation of authentication schemes in IMS. The primary criteria are security, user-friendliness and simplicity. Inbetween these criteria, the secondary criteria can be found. These are awareness, usability and algorithms. Each criterion, both primary and secondary, is then also divided into one or several substantiating sub-criteria. The discussion of the criteria is followed by a description of the evaluation methodology, which comprises both qualitative and quantitative evaluations such as SWOT analysis, use of NIST and ISO guidelines, user rankings, and measurements of authentication times. The paper is concluded with an outlook on future work, including studies and experiments.

  • 315. Eliasson, Charlott
    et al.
    Fiedler, Markus
    Jørstad, Ivar
    Evaluation of Authentication Schemes Based on Security, User-Friendliness and Complexity2008Konferensbidrag (Övrigt vetenskapligt)
    Abstract [sv]

    Ett första ansats för klassificering av sömlösa säkerhetslösningar med tanke på säkerhetsnivå, användarvänlighet och enkelhet som förstahands kriterier samt medvetenhet, användbarhet och algoritmer som andrahands kriterier. Dessutom beskrivs evalueringsmetoder. IMS, säkerhet, sömlös autentifiering, evalueringskriteria

  • 316. Eliasson, Charlott
    et al.
    Zúquete, André
    An Electronic Voting System Supporting Vote Weights2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    Purpose - This paper aims to provide a solution for allowing an arbitrary number of weights and weight values to be used in an electronic voting system. Design/methodology/approach - Robust Electronic Voting System (REVS) was chosen, a voting system designed to support internet voting processes, as the start point for studying the introduction of vote weights. Findings - The work resulted in an internet voting system supporting vote weights, based on REVS. Research limitations/implications - In the solution presented, there is still a problem regarding anonymity, for the case of a single voter with a particular weighted vote. This is a fundamental problem, since it also exists in paper-based elections. Practical implications - This version of REVS has the same properties as the original REVS, apart from the anonymity issue above. Apart from this the process of registering voters got more complicated, since now it includes an extra action for binding a weight. Originality/value - To the best of the authors' knowledge, this modified version of REVS is the first electronic voting system supporting vote weights. Another novelty of this work is the modulus sharing optimization used for the RSA key pairs of each entity.

  • 317. Eliasson, Charlott
    et al.
    Zúquete, André
    An Electronic Voting System Supporting Vote Weights2006Ingår i: Internet Research, ISSN 1066-2243, Vol. 16, nr 5, s. 507-518Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Purpose – This paper aims to provide a solution for allowing an arbitrary number of weights and weight values to be used in an electronic voting system. Design/methodology/approach – Robust Electronic Voting System (REVS) was chosen, a voting system designed to support internet voting processes, as the start point for studying the introduction of vote weights. Findings – The work resulted in an internet voting system supporting vote weights, based on REVS. Research limitations/implications – In the solution presented, there is still a problem regarding anonymity, for the case of a single voter with a particular weighted vote. This is a fundamental problem, since it also exists in paper-based elections. Practical implications – This version of REVS has the same properties as the original REVS, apart from the anonymity issue above. Apart from this the process of registering voters got more complicated, since now it includes an extra action for binding a weight. Originality/value – To the best of the authors' knowledge, this modified version of REVS is the first electronic voting system supporting vote weights. Another novelty of this work is the modulus sharing optimization used for the RSA key pairs of each entity.

  • 318. Elkashlan, Maged
    et al.
    Yeoh, Phee Lep
    Yang, Nan
    Duong, Quang Trung
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Leung, Cyril
    A Comparison of Two MIMO Relaying Protocols in Nakagami- m Fading2012Ingår i: IEEE Transactions on Vehicular Technology, ISSN 0018-9545, E-ISSN 1939-9359, Vol. 61, nr 3, s. 416-1422Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Transmit antenna selection with receive maximal-ratio combining (TAS/MRC) and transmit antenna selection with receive selection combining (TAS/SC) are two attractive multiple-input–multiple-output (MIMO) protocols. In this paper, we present a framework for the comparative analysis of TAS/MRC and TAS/SC in a two-hop amplify-and-forward relay network. In doing so, we derive exact and asymptotic expressions for the symbol error rate (SER) in Nakagami-mfading. Using the asymptotic expressions, the SNR gap between the two protocols is quantified. Given that the two protocols maintain the same diversity order, we show that the SNR gap is entirely dependent on the array gain. Motivated by this, we derive the SNR gap as a simple ratio of the respective array gains of the two protocols. This ratio explicitly takes into account the impact of the number of antennas and the fading severity parameter m. In addition, we address the fundamental question of “How to allocate the total transmit power between the source and the relay in such a way that the SER is minimized?” Our answer is given in the form of new compact expressions for the power allocation factor, which is a practical design tool that optimally distributes the total transmit power in the network.

  • 319.
    Elnourani, Mohamed
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för signalbehandling.
    COGNITIVE RADIO AND GAME THEORY: OVERVIEW AND SIMULATION2008Självständigt arbete på avancerad nivå (masterexamen)Studentuppsats (Examensarbete)
    Abstract [en]

    This thesis aims to clearly describe the cognitive radio and its components and operations. Moreover, it aims on describing the expected outcome from the most common techniques that are proposed for use in cognitive radios. In addition, it describes the basic principles of game theory and some simple game models that can be used to analyze the efficiency of the optimization algorithms. Furthermore, it investigates the use of load balancing algorithm and genetic algorithm in optimizing the decision making operation in cognitive radios. Matlab software simulations were carried out and the results show the promising benefit of using those two algorithms along with game theory in optimizing the dynamic spectrum allocation process.

  • 320.
    Emmelin, Lars
    et al.
    Blekinge Tekniska Högskola, Institutionen för fysisk planering.
    Söderblom, Ingmarie
    Spelet om 3G: en förstudie av mastfrågan2002Rapport (Refereegranskat)
    Abstract [en]

    Utbyggnaden av 3G-systemets fysiska infrastruktur kan ses som ett spel med tre huvudaktörer: operatörerna, staten och kommunerna. Staten har delat ut licenser med mycket ambitiösa krav på täckning och utbyggnadstakt. Operatörerna, å sin sida, har ett intresse av den utbyggnad som ger bäst ekonomi och marknadsposition, vilket inte nödvändigtvis innebär att de har ett intresse av vare sig den hastighet eller täckningsgrad de själva drivit fram i skönhetstävlingen. Kommunerna ska slutligen handlägga ansökningarna om bygglov från operatörerna; kraven på utbyggnadshastighet är här ett uppenbart problem. Utbyggnaden av infrastrukturen för 3G-systemet är principiellt intressant långt utöver de konkreta planerings- och miljöproblemen. Den illustrerar hur ?hållbar utveckling? hanteras i praktiken. Teknik och utvecklingsoptimismen har inte på något påvisbart sätt balanserats mot miljöintressen. I 3G är dessa avvägningar flyttade ned till kommuner och länsstyrelser. Besluten om 3G illustrerar det strategiska beslutsfattandets centrala dilemma: avvägningen mellan ?att våga och att väga?. Nyckelord: 3G, UMTS, bygglov, miljöprövning, infrastruktur

  • 321. Engelke, Ulrich
    Modelling Perceptual Quality and Visual Saliency for Image and Video Communications2010Doktorsavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The evolution of advanced radio transmission technologies for third and future generation mobile radio systems has paved the way for the delivery of mobile multimedia services. This is further enabled through contemporary video coding standards, such as H.264/AVC, allowing wireless image and video applications to become a reality on modern mobile devices. The extensive amount of data needed to represent the visual content and the scarce channel bandwidth constitute great challenges for network operators to deliver an intended quality of service. Appropriate metrics are thus instrumental for service providers to monitor the quality as experienced by the end user. This thesis focuses on subjective and objective assessment methods of perceived visual quality in image and video communication. The content of the thesis can be broadly divided into four parts. Firstly, the focus is on the development of image quality metrics that predict perceived quality degradations due to transmission errors. The metrics follow the reduced-reference approach, thus, allowing to measure quality loss during image communication with only little overhead as side information. The metrics are designed and validated using subjective quality ratings from two experiments. The distortion assessment performance is further demonstrated through an application for filter design. The second part of the thesis then investigates various methodologies to further improve the quality prediction performance of the metrics. In this respect, several properties of the human visual system are investigated and incorporated into the metric design. It is shown that the quality prediction performance can be considerably improved using these methodologies. The third part is devoted to analysing the impact of the complex distortion patterns on the overall perceived quality, following two goals. Firstly, the confidence of human observers is analysed to identify the difficulties during assessment of the distorted images, showing, that indeed the level of confidence is highly dependent on the level of visual quality. Secondly, the impact of content saliency on the perceived quality is identified using region-of-interest selections and eye tracking data from two independent subjective experiments. It is revealed, that the saliency of the distortion region indeed has an impact on the overall quality perception and also on the viewing behaviour of human observers when rating image quality. Finally, the quality perception of H.264/AVC coded video containing packet loss is analysed based on the results of a combined subjective video quality and eye tracking experiment. It is shown that the distortion location in relation to the content saliency has a tremendous impact on the overall perceived quality. Based on these findings, a framework for saliency aware video quality assessment is proposed that strongly improves the quality prediction performance of existing video quality metrics.

  • 322. Engelke, Ulrich
    Perceptual Quality Metric Design for Wireless Image and Video Communication2008Licentiatavhandling, sammanläggning (Övrigt vetenskapligt)
    Abstract [en]

    The evolution of advanced radio transmission technologies for third generation mobile radio systems has paved the way for the delivery of mobile multimedia services. In particular, wireless image and video applications are among the most popular services offered on modern mobile devices to support communication beyond the traditional voice services. The large amount of data necessary to represent the visual content and the scarce bandwidth of the wireless channel impose new challenges for the network operator to deliver high quality image and video services. Link layer metrics have conventionally been used to monitor the received signal quality but were found to not accurately reflect the visual quality as it is perceived by the end-user. These metrics thus need to be replaced by suitable metrics that measure the overall impairments induced during image or video communication and accurately relate them to subjectively perceived quality. In this thesis, we focus on objective metrics that are able to quantify the end-to-end visual quality in wireless image and video communication. Such metrics may then be utilised to support the efficient use of link adaptation and resource management techniques and thus guarantee a certain quality of service to the user. The thesis is divided into four parts. The first part contributes an extensive survey and classification of contemporary image and video quality metrics that may be applicable in a communication context. The second part then discusses the development of the Normalised Hybrid Image Quality Metric (NHIQM) that we propose for prediction of visual quality degradations induced during wireless communication. The metric is based on a set of structural features, which are deployed to quantify artifacts that may occur in a wireless communication system and also are well aligned to characteristics of the human visual system (HVS). In the third part, three metric designs are discussed that utilise the same structural feature set as a basis for quality prediction. Incorporation of further HVS characteristics into the metric design will then improve even more the visual quality prediction performance. The design and validation of all proposed metrics is supported by subjective quality experiments that we conducted in two independent laboratories. Comparison to other state of the art visual quality metrics reveals the ability of the proposed metrics to accurately predict visual quality in a wireless communication system. The last part contributes an application of NHIQM for filter design. In particular, the filtering performance of a de-blocking de-ringing post filter for H.263 video sequences is analysed with regards to visual quality of the filtered sequence when applying appropriate filter parameter combinations.

  • 323. Engelke, Ulrich
    et al.
    Barkowsky, Marcus
    Callet, Patrick Le
    Zepernick, Hans-Jürgen
    Modelling Saliency Awareness for Objective Video Quality Assessment2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Existing video quality metrics do usually not take into consideration that spatial regions in video frames are of varying saliency and thus, differently attract the viewer's attention. This paper proposes a model of saliency awareness to complement existing video quality metrics, with the aim to improve the agreement of objectively predicted quality with subjectively rated quality. For this purpose, we conducted a subjective experiment in which human observers rated the annoyance of videos with transmission distortions appearing either in a salient region or in a non-salient region. The mean opinion scores confirm that distortions in salient regions are perceived much more annoying. It is shown that application of the saliency awareness model to two video quality metrics considerably improves their quality prediction performance.

  • 324. Engelke, Ulrich
    et al.
    Kaprykowsky, Hagen
    Zepernick, Hans-Jürgen
    Ndjiki-Nya, Patrik
    Visual Attention in Quality Assessment2011Ingår i: IEEE signal processing magazine (Print), ISSN 1053-5888, E-ISSN 1558-0792, Vol. 28, nr 6, s. 50-59Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Perceptual quality metrics are widely deployed in image and video processing systems. These metrics aim to emulate the integral mechanisms of the human visual system (HVS) to correlate well with visual perception of quality. One integral property of the HVS is, however, often neglected: visual attention (VA) [1]. The essential mechanisms associated with VA consist mainly of higher cognitive processing, deployed to reduce the complexity of scene analysis. For this purpose, a subset of the visual information is selected by shifting the focus of attention across the visual scene to the most relevant objects. By neglecting VA, perceptual quality models inherently assume that all objects draw the attention of the viewer to the same degree.

  • 325. Engelke, Ulrich
    et al.
    Kusuma, Tubagus Maulana
    Zepernick, Hans-Jürgen
    Perceptual Quality Assessment of Wireless Video Applications2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    The rapid evolution of wireless networks is driven by the growth of wireless packet data applications such as interactive mobile multimedia applications, wireless streaming services, and video-on-demand. The largely heterogeneous network structures, severe channel impairments, and complex traffic patterns make the wireless networks much more unpredictable compared to their wired counterparts. One of the major challenges with the roll-out of these services is therefore the design of wireless networks that fulfill the stringent quality of service requirements of wireless video applications. In this paper, the applicability of perceptual image quality metrics for real-time quality assessment of Motion JPEG2000 (MJ2) video streams over wireless channels is investigated. In particular, a reduced-reference hybrid image quality metric (HIQM) is identified as suitable for an extension to video applications. It outperforms other known metrics in terms of required overhead and prediction performance.

  • 326. Engelke, Ulrich
    et al.
    Kusuma, Tubagus Maulana
    Zepernick, Hans-Jürgen
    Caldera, Manora
    Reduced-reference metric design for objective perceptual quality assessment in wireless imaging2009Ingår i: Signal Processing-Image Communication, ISSN 0923-5965 , Vol. 24, nr 7, s. 525-547Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    The rapid growth of third and development of future generation mobile systems has led to an increase in the demand for image and video services. However, the hostile nature of the wireless channel makes the deployment of such services much more challenging, as in the case of a wireline system. In this context, the importance of taking care of user satisfaction with service provisioning as a whole has been recognized. The related user-oriented quality concepts cover end-to-end quality of service and subjective factors such as experiences with the service. To monitor quality and adapt system resources, performance indicators that represent service integrity have to be selected and related to objective measures that correlate well with the quality as perceived by humans. Such objective perceptual quality metrics can then be utilized to optimize quality perception associated with applications in technical systems. In this paper, we focus on the design of reduced-reference objective perceptual image quality metrics for use in wireless imaging. Specifically, the Normalized Hybrid Image Quality Metric (NHIQM) and a perceptual relevance weighted L_p-norm are designed. The main idea behind both feature-based metrics relates to the fact that the human visual system (HVS) is trained to extract structural information from the viewing area. Accordingly, NHIQM and L_p-norm are designed to account for different structural artifacts that have been observed in our distortion model of a wireless link. The extent by which individual artifacts are present in a given image is obtained by measuring related image features. The overall quality measure is then computed as a weighting sum of the features with the respective perceptual relevance weight obtained from subjective experiments. The proposed metrics differ mainly in the pooling of the features and amount of reduced-reference produced. While NHIQM performs the pooling at the transmitter of the system to produce a single value as reduced-reference, the L_p-norm requires all involved feature values from the transmitted and received image to perform the pooling on the feature differences at the receiver. In addition, non-linear mapping functions are developed that relate the metric values to predicted mean opinion scores (MOS) and account for saturations in the HVS. The evaluation of prediction performance of NHIQM and the L_p-norm reveals their excellent correlation with human perception in terms of accuracy, monotonicity, and consistency. This holds not only for the prediction performance on images taken for the training of the metrics but also for the generalization to unknown images. In addition, it is shown that the NHIQM approach and the perceptual relevance weighted L_p-norm outperform other prominent objective quality metrics in prediction performance.

  • 327. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för datavetenskap och kommunikation.
    Human Observer Confidence in Image Quality Assessment2012Ingår i: Signal processing. Image communication, ISSN 0923-5965, E-ISSN 1879-2677, Vol. 27, nr 9, s. 935-947Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Mean opinion scores obtained from subjective quality assessment are widely used as a ground truth for the development of predictive quality models. The underlying variance between observer ratings is typically quantified using confidence intervals, which do not provide any direct insight into the underlying causes of the disagreement. For better understanding of human visual quality perception and to develop more accurate models, it is important to identify the factors that impact on the variations in quality ratings. This work considers one such factor: observer confidence. This consideration is motivated by the view that quality assessment is a difficult task and hence quality ratings are provided with varying levels of confidence. The first goal of this paper is to analyse the results of an experiment to determine association between observer confidence and image quality judgement. Secondly, models are developed that aim to predict mean observer confidence as a complementary measure to the widely used mean opinion scores. It is shown that there is indeed a strong interrelation between quality perception and confidence, resulting in predictive models of high accuracy.

  • 328. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    On Confidence and Response Times of Human Observers in Subjective Image Quality Assessment2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Mean opinion scores obtained in subjective image quality experiments are widely accepted as measures of perceived visual quality. They have, however, a strong limitation regarding the reliability of the rated quality, since there is no explicit information as to whether the human observer experienced difficulties when judging image quality. We thus suggest that additional information about the observers confidence should be provided along with the actual quality measure. In this paper, we analyse two ways of obtaining this confidence measure; firstly as a confidence score given by the human observer and secondly as an indirect measure of the observers response time to provide the quality score. We reveal strong relationships of confidence scores and response times to the quality scores. We further propose a model to predict observer confidence based on the quality scores and response times.

  • 329. Engelke, Ulrich
    et al.
    Maeder, Anthony
    Zepernick, Hans-Jürgen
    The Effect of Spatial Distortion Distributions on Human Viewing Behaviour when Judging Image Quality2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    In wireless communication, distortions are induced into an image through both lossy source coding and an error prone channel. The combination thereof causes complex distortion patterns in the visual content which vary strongly in their spatial distribution, some being uniformly spread and others being locally clustered. In the context of image quality, it is of interest to identify as to how the distribution of the distortions impact on the visual attention of human observers and thus on the perceived quality. For this reason, we conducted an experiment in which fifteen participants were asked to rate the quality of eighty distorted images and their corresponding reference images, while we recorded their gaze patterns using an eye tracker. The test images contained a wide range of artifact magnitudes, both locally and globally distributed, and were created using a wireless channel simulation model. We then correlate the visual gaze patterns of the human observers with local energy measures of the distortions in order to identify the effect of distortion distributions on the viewing behaviour of human observers when judging image quality. The outcomes serve to improve the prediction performance of objective image quality metrics that we previously proposed.

  • 330. Engelke, Ulrich
    et al.
    Pepion, Romuald
    Callet, Patrick Le
    Zepernick, Hans-Jürgen
    Linking Distortion Perception and Visual Saliency in H.264/AVC Coded Video Containing Packet Loss2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, distortions caused by packet loss during video transmission are evaluated with respect to their perceived annoyance. In this respect, the impact of visual saliency on the level of annoyance is of particular interest, as regions and objects in a video frame are typically not of equal importance to the viewer. For this purpose, gaze patterns from a task free eye tracking experiment were utilised to identify salient regions in a number of videos. Packet loss was then introduced into the bit stream such as that the corresponding distortions appear either in a salient region or in a non-salient region. A subjective experiment was then conducted in which human observers rated the annoyance of the distortions in the videos. The outcomes show a strong tendency that distortions in a salient region are indeed perceived as much more annoying as compared to distortions in the non-salient region. The saliency of the distorted image content was further found to have a larger impact on the perceived annoyance as compared to the distortion duration. The findings of this work are considered to be of great use to improve prediction performance of video quality metrics in the context of transmission errors.

  • 331. Engelke, Ulrich
    et al.
    Rossholm, Andreas
    Zepernick, Hans-Jürgen
    Lövström, Benny
    Quality Assessment of an Adaptive Filter for Artifact Reduction in Mobile Video Sequences2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we examine an adaptive deblocking deringing filter for mobile video sequences in H.263 format. The considered filter has been designed with reference to the constraints of computational complexity and working memory of mobile terminals. The post filter suggested by the International Telecommunications Union (ITU) in Recommendation H.263 App. III is also included as a reference. Given that fidelity metrics such as the peak signal-to-noise ratio (PSNR) do not necessarily correlate well with video quality as experienced by the user, we consider in this paper objective quality metrics that can incorporate knowledge about the user's perception into the quality assessment. Guidelines for choosing filter parameters in relation to user-perceived video quality are obtained from the numerical results.

  • 332. Engelke, Ulrich
    et al.
    Vuong, Xuan Nguyen
    Zepernick, Hans-Jürgen
    Regional Attention to Structural Degradations for Perceptual Image Quality Metric Design2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, regional attention to structural degradations in images is analyzed to improve perceptual quality prediction performance of objective image quality metrics. Subjective experiments were conducted to identify regions-of-interest for a set of natural images. A region-selective metric design is then applied to four objective image quality metrics which were trained and validated with respect to quality prediction accuracy and generalization to unknown images. For this purpose, data is used from subjective quality experiments conducted at two independent laboratories. It is shown that the region-selective design is highly beneficial for the considered objective image quality metrics, in particular, prediction accuracy can be significantly increased.

  • 333. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    A Framework for Optimal Region of Interest-based Quality Assessment in Wireless Imaging2010Ingår i: Journal of Electronic Imaging (JEI), ISSN 1017-9909, E-ISSN 1560-229X, Vol. 19, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Images usually exhibit regions that particularly attract the viewer's attention. These regions are typically referred to as regions-of-interest (ROI) and the underlying phenomenon in the human visual system is known as visual attention (VA). In the context of image quality one may expect that distortions occuring in the ROI are perceived as being more annoying, as compared to distortions in the background. However, VA is only seldom taken into account in existing image quality metrics. In this paper, we thus provide a VA framework to extend existing image quality metrics with a simple VA model. The performance of the framework is evaluated on three contemporary image quality metrics. We further consider the context of wireless imaging where a broad range of artifacts can be observed. To facilitate the VA based metric design, we conducted subjective experiments to both obtain a ground truth for the subjective quality of a set of test images and to identify ROI in the corresponding reference images. A methodology is further discussed to optimize the VA metrics with respect to quality prediction accuracy and generalization ability. It is shown that the quality prediction performance of the three considered metrics can be significantly improved by deploying the proposed framework.

  • 334. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    An Artificial Neural Network for Quality Assessment in Wireless Imaging Based on Extraction of Structural Information2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    In digital transmission, images may undergo quality degradation due to lossy compression and error-prone channels. Efficient measurement tools are needed to quantify induced distortions and to predict their impact on perceived quality. In this paper, an artificial neural network (ANN) is proposed for perceptual image quality assessment. The quality prediction is based on structural image features such as blocking, blur, image activity, and intensity masking. Training and testing of the ANN is performed with reference to subjective experiments and the obtained mean opinion scores (MOS). It is shown that the proposed ANN is capable of predicting MOS over a wide range of image distortions. This applies to both cases, when reference information about the structure of the original image is available to the ANN but also in absence of this knowledge. The considered ANN would therefore be well suited for combination with link adaption techniques.

  • 335. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Framework for Optimal Region of Interest-based Quality Assessment in Wireless Imaging2010Ingår i: Journal of Electronic Imaging (JEI), ISSN 1017-9909, E-ISSN 1560-229X, Vol. 19, nr 1Artikel i tidskrift (Refereegranskat)
    Abstract [en]

    Images usually exhibit regions that particularly attract the viewer's attention. These regions are typically referred to as regions-of-interest (ROI) and the underlying phenomenon in the human visual system is known as visual attention (VA). In the context of image quality one may expect that distortions occuring in the ROI are perceived as being more annoying, as compared to distortions in the background. However, VA is only seldom taken into account in existing image quality metrics. In this paper, we thus provide a VA framework to extend existing image quality metrics with a simple VA model. The performance of the framework is evaluated on three contemporary image quality metrics. We further consider the context of wireless imaging where a broad range of artifacts can be observed. To facilitate the VA based metric design, we conducted subjective experiments to both obtain a ground truth for the subjective quality of a set of test images and to identify ROI in the corresponding reference images. A methodology is further discussed to optimize the VA metrics with respect to quality prediction accuracy and generalization ability. It is shown that the quality prediction performance of the three considered metrics can be significantly improved by deploying the proposed framework.

  • 336. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Multiobjective Optimization of Multiple Scale Visual Quality Processing2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, multiobjective optimization is applied to determine the optimal feature weights for a multi-resolution image quality metric. The optimization is conducted with respect to two aims; maximization of quality prediction accuracy and generalisation ability to unknown images. A thresholding of the optimal weights is applied to further reduce computational complexity of the quality metric. A detailed discussion of the tradeoff between prediction performance and complexity with respect to the threshold is provided. The metric design and evaluation is supported using mean opinion scores from subjective quality experiments that we conducted in two independent laboratories. Comparison to other state of the art quality metrics reveals the ability of the proposed metric to accurately predict subjective image quality perception.

  • 337. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Multi-resolution Structural Degradation Metrics for Perceptual Image Quality Assessment2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, a multi-resolution analysis is proposed for image quality assessment. Structural features are extracted from each level of a pyramid decomposition that accurately represents the multiple scales of processing in the human visual system. To obtain an overall quality measure the individual level metrics are accumulated over the considered pyramid levels. Two different metric design approaches are introduced and evaluated. It turns out that one of them outperforms our previous work on single-resolution image quality assessment.

  • 338.
    Engelke, Ulrich
    et al.
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för signalbehandling.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för signalbehandling.
    On Perceptual Quality Evaluation of Video Applications for Wireless Ad-hoc Networks2007Konferensbidrag (Refereegranskat)
  • 339. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Optimal Region-of-Interest Based Visual Quality Assessment2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Visual content typically exhibits regions that particularly attract the viewer's attention, usually referred to as regions-of-interest (ROI). In the context of visual quality one may expect that distortions occurring in the ROI are perceived more annoyingly than distortions in the background (BG). This is especially true given that the human visual system is highly space variant in sampling visual signals. However, this phenomenon of visual attention is only seldom taken into account in visual quality metric design. In this paper, we thus provide a framework for incorporation of visual attention into the design of an objective quality metric by means of region-based segmentation of the image. To support the metric design we conducted subjective experiments to both quantify the subjective quality of a set of distorted images and also to identify ROI in a set of reference images. Multiobjective optimization is then applied to find the optimal weighting of the ROI and BG quality metrics. It is shown that the ROI based metric design allows to increase quality prediction performance of the considered metric and also of two other contemporary quality metrics.

  • 340. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Pareto Optimal Weighting of Structural Impairments for Wireless Imaging Quality Assessment2008Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we consider multiobjective optimization for obtaining the feature weights associated with structural image impairments and its application to wireless imaging quality assessment. The proposed framework supports optimization with respect to finding a trade-off between metric prediction accuracy and generalization to unknown images. Evaluation of optimal trade-off solutions for two representative scenarios reveal the benefits of the proposed approach. In particular, quality prediction accuracy of an objective image metric can be strongly increased and negligible features are identified that can be discarded to save computational complexity.

  • 341. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Perceptual Quality Measures for Image and Video Services2006Övrigt (Övrigt vetenskapligt)
  • 342. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Perceptual-based Quality Metrics for Image and Video Services: A Survey2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    The accurate prediction of quality from an end-user perspective has received increased attention with the growing demand for compression and communication of digital image and video services over wired and wireless networks. The existing quality assessment methods and metrics have a vast reach from computational and memory efficient numerical methods to highly complex models incorporating aspects of the human visual system. It is hence crucial to classify these methods in order to find the favorable approach for an intended application. In this paper a survey and classification of contemporary image and video quality metrics is therefore presented along with the favorable quality assessment methodologies. Emphasis is given to those metrics that can be related to the quality as perceived by the end-user. As such, these perceptual-based image and video quality metrics may build a bridge between the assessment of quality as experienced by the end-user and the quality of service parameters that are usually deployed to quantify service integrity.

  • 343.
    Engelke, Ulrich
    et al.
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap, Avdelningen för elektroteknik.
    Psychophysical Assessment of Perceived Interest in Natural Images: The ROI-D Database2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    We introduce a novel region-of-interest (ROI) database for natural image content, the ROI-D database. The database consists of ROI maps created from manual selections obtained in a psychophysical experiment with 20 participants. The presented stimuli were 42 photographic images taken from 3 publicly available image quality databases. In addition to the ROI selections, dominance ratings were recorded that provide further insight into the interest of the selected ROI in relation to the background. In this paper, the experiment is described, the resulting ROI database is analysed, and possible applications of the database are discussed. The ROI-D database is made freely available to the image processing research community.

  • 344.
    Engelke, Ulrich
    et al.
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för telekommunikationssystem.
    Zepernick, Hans-Jürgen
    Blekinge Tekniska Högskola, Sektionen för teknik, Avdelningen för telekommunikationssystem.
    Quality Evaluation in Wireless Imaging Using Feature-Based Objective Metrics2007Konferensbidrag (Refereegranskat)
    Abstract [en]

    This paper addresses the evaluation of image quality in the context of wireless systems using feature-based objective metrics. The considered metrics comprise of a weighted combination of feature values that are used to quantify the extend by which the related artifacts are present in a processed image. In view of imaging applications in mobile radio and wireless communication systems, reduced-reference objective quality metrics are investigated for quantifying user-perceived quality. The examined feature-based objective metrics provide options for controlling the processing complexity and implementation resources required for performing the quality evaluation. Furthermore, the metrics support the scaling of overhead needed for communicating the image features over the wireless link and the accuracy for predicting the image quality.

  • 345. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Quality of Experience of Multimedia Services: Past, Present, and Future2011Konferensbidrag (Refereegranskat)
    Abstract [en]

    In recent years, the notion of Quality of Experience (QoE) has gained increased attention to represent the quality of a service as it is perceived by the users. Accordingly, QoE amalgamates service integrity quantified by conventional\linebreak Quality of Service (QoS) parameters with non-technical but subjective factors. In this paper, we provide a survey on the evolution of QoE concepts in multimedia systems touching on the past, present, and future aspects. Specifically, the ideas behind QoE are discussed and an overview of related standardization work is provided. On this basis, QoE metrics for speech, image, and video are described. An outlook of future work and challenges is also provided.

  • 346. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Kusuma, Tubagus Maulana
    Perceptual Evaluation of Motion JPEG2000 Quality over Wireless Channels2006Konferensbidrag (Refereegranskat)
    Abstract [en]

    In this paper, we investigate the applicability of perceptual image quality metrics for quality assessment of Motion JPEG2000 (MJ2) video streams over wireless channels. A performance evaluation of MJ2 quality for different levels of source compression and channel coding settings is provided. This reveals insights into the characteristics and suitability of the considered perceptual quality metrics for wireless video quality assessment. In particular, a reduced-reference hybrid image quality metric (HIQM) is identified as the most favorable metric with respect to supporting real-time applications. The findings obtained from the considered scenarios may also guide the design of efficient physical layer functions for wireless video systems.

  • 347. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Kusuma, Tubagus Maulana
    Subjective Quality Assessment for Wireless Image Communication: The Wireless Imaging Quality Database2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    Mean opinion scores (MOS) obtained in image quality experiments are a key component in the transition from subjective to objective measures of perceived quality. In this respect, MOS are widely used to validate objective quality prediction models. To facilitate comparison between models from different laboratories it is desirable to have publicly available image quality databases. Several databases were made available in recent years. In this paper, we introduce the Wireless Imaging Quality (WIQ) database which, unlike any of the previous databases, takes into account the complex nature of a wireless communications link. The database is thus considered as a valuable complement to the existing databases. The distortion model, the test images, and two quality experiments that we conducted are explained in this paper. A number of contemporary objective quality metrics are tested for their quality prediction performance on the database. The WIQ database including test images and MOS is made freely available to the research community.

  • 348. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Maeder, Anthony
    Visual Attention Modeling: Region-of-Interest Versus Fixation Patterns2009Konferensbidrag (Refereegranskat)
    Abstract [en]

    Visual attention (VA) is an integral property of the human visual system. The deployment of a VA model can be beneficial for many image and video applications, such as, compression, transmission, and quality assessment. However, the design of a VA model is highly dependent on the subjective VA data used as ground truth and the application that the model is intended for. In this paper, we discuss two ways of obtaining subjective VA data that can subsequently be used to develop VA models; selective regions-of-interest and visual fixation patterns. The feasibility of both methods will be discussed, in particular, with respect to visual quality assessment.

  • 349. Engelke, Ulrich
    et al.
    Zepernick, Hans-Jürgen
    Maeder, Anthony
    Visual Fixation Patterns in Subjective Quality Assessment: The Relative Impact of Image Content and Structural Distortions2010Konferensbidrag (Refereegranskat)
    Abstract [en]

    The viewing behaviour of human observers during image quality assessment is analysed. In this respect, the relative impact of image content and structural distortions is of particular interest. Two subjective experiments were conducted as a basis for analysis; a region-of-interest (ROI) experiment and an eye tracking experiment under quality assessment task. A correlation analysis and a receiver operating characteristics analysis reveal, that quality assessment takes place mainly within the ROI, indicating a higher impact of the content as compared to the distortions. This seems to be only contradicted by very strong and localised distortions outside the ROI.

  • 350.
    Enohnyaket, John Ako
    Blekinge Tekniska Högskola, Sektionen för ingenjörsvetenskap.
    An Investigation of RF Pollution Caused by IEEE 802.15.4 Body Area Networks2013Självständigt arbete på grundnivå (kandidatexamen)Studentuppsats (Examensarbete)
    Abstract [en]

    Advancement in wireless communication technologies such as wearable sensors together with recent developments in embedded computing area is enabling the design, development and implementation of body area networks. These network developments mainly use the IEEE 802.15.4 which is aimed at low power, short range communications. The body area network is a deployment of an innovative healthcare monitoring application. However, little is known about the impact of 802.15.4 on the performance of other communication devices. Due to the constant increase in devices sharing the unlicensed 2.4GHz ISM band, interference is becoming a problem of interest to researchers. In this thesis, we experimentally investigate the Radio Frequency (RF) pollution Caused by IEEE 802.15.4 body area networks. Measurement was conducted with a shimmer2r node(transmitter) attached to the human body and the Tmote Sky sensor nodes(receivers) which are deployed on three floors of the Telecommunication Network Group (TKN) Technical University(TU) building in Berlin. The average Received Signal Strength Indicator (RSSI), Link Quality Indicator (LQI) and Packet Reception Rate (PRR) was examined as a function of transmitter to receiver distance. The best LQI was observed at 0 dBm and was consistent whereas the worst LQI was at -25 dBm. Lastly, the RF pollution metric was defined based on power levels and the percentage of nodes polluted. With a transmission power level of -15 dBm, the observed RF pollution for a co-located network was minimal while of 0 dBm, the pollution effects were relatively higher.

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