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This book constitutes the thoroughly refereed post-conference proceedings of the 7th International ICST Conference on Mobile Multimedia Communications (MOBIMEDIA 2011) held in Cagliari, Italy, in September 2011 The 26 revised full papers presented were carefully selected from numerous submissions and focus topics such as quality of experience, dynamic spectrum access wireless networks in the TV white spaces, media streaming, mobile visual search, image processing and transmission, and mobile applications.



Quality of Experience

Tackling the Sheer Scale of Subjective QoE

Maximum Likelihood Difference Scaling (MLDS) used as a method for subjective assessment of video quality alleviates the inconveniencies associated with high variation and biases common in rating methods. However, the number of tests in a MLDS study rises fairly quickly with the number of samples that we want to test. This makes the MLDS studies not scalable for the diverse video delivery environments commonly met in pervasive media networks. To tackle this issue we have developed an active learning approach that decreases the number of MLDS tests and improves the scalability of this method.

Vlado Menkovski, Georgios Exarchakos, Antonio Liotta

On the Quality Assessment of H.264/AVC Video under Seamless Handoffs

This paper examines the quality assessment of video streaming applications in a heterogeneous wireless environment, where the user hands off across inter-technology radio access networks. Three different scenarios have been considered: scenario with seamless handover using the media handover framework to initiate handover, seamless handoff combined with rate adaptation that is based on Rate-Distortion and seamless handoff with rate adaptation that is optimized using network bandwidth and packet loss parameters. The results from two video sequences have shown that both objective quality evaluation and the subjective evaluation (double stimulus- SDSCE, DSCQS) are optimized under the combined seamless handover and rate adaptation functionalities.

Ilias Politis, Tasos Dagiuklas, Lampros Dounis

Reduced-Reference Image Quality Assessment Based on Edge Preservation

Assessing the subjective quality of processed images through an objective quality metric is a key issue in multimedia processing and transmission. In some scenarios, it is also important to evaluate the quality of the received images with minimal reference to the transmitted ones. For instance, for closed-loop optimisation of image and video transmission, the quality measure can be evaluated at the receiver and provided as feedback information to the system controller. The original images - prior to compression and transmission - are not usually available at the receiver side, and it is important to rely at the receiver side on an objective quality metric that does not need reference or needs minimal reference to the original images.

The observation that the human eye is very sensitive to edge and contour information of an image underpins the proposal of our reduced reference (RR) quality metric, which compares edge information between the distorted and the original image.

Results highlight that the metric correlates well with subjective observations, also in comparison with commonly used full-reference metrics and with a state-of-the-art reduced reference metric.

Maria G. Martini, Barbara Villarini, Federico Fiorucci

On Measuring the Perceptual Quality of Video Streams over Lossy Wireless Networks

This paper studies the perceptual quality of video streams over lossy wireless networks. The focus is on investigating the impact on the perceived video quality of both physical error impairments and packet losses due to network congestion, by using objective and subjective evaluation methods. Extensive video quality assessments have shown that packet losses due to congestion are more severe than packet losses due to the physical error on the objective video quality. Furthermore, the comparison of MOS among different spatial resolution video sequences of the same bit rate indicates that a better perceived video quality can be achieved for lower resolution when the network is characterized by both high BER and network load.

Ilias Politis, Michail Tsagkaropoulos, Tasos Dagiuklas, Lampros Dounis

The Correlation Dimension: A Video Quality Measure

Correlation dimension is a measure of the multidimensional complexity of an object. Stemming from the area of chaos theory and having several applications involving the study of the convergence and the recurring patterns of random signals, it has been proven to be a possible way to assess video quality. Based on its meaning in the multidimensional space of color fractals, it can be used, in the context of a fractal’s intrinsic similarity to natural shapes and colours, to quantify the aesthetic and harmonic properties of an image. Our approach in the assessment of the perceived quality of a video stream is based on the analysis of the fractal dimension of video signals expressed in the CIE L*a*b* color space. This colour space has a strong resemblance to the human visual perception system, thus making its Δ



norm relevant for the measurement of the perceptual difference between colours, and hence useful for image quality assessment. The fractal dimension is computed through the correlation dimension definition. In this paper we expose the experimental results obtained in a simulation of a real-life scenario: the streaming of a video of a football game over a busy network.

Bogdan Budescu, Alexandru Căliman, Mihai Ivanovici

Dynamic Spectrum Access Wireless Networks in the TV White Spaces

TV White Spaces Exploitation for Signal Distribution

The new spectrum regulation policies for dynamic spectrum access, especially those concerning the use of the white spaces in the Digital Terrestrial Television (DTT) bands, arise the need for fast and reliable signal identification and classification methods. In this paper we present a two-stage identification method for signals in the white spaces, using combined energy detection and feature detection. The band of interest is divided by means of the Discrete Wavelet Packet Transformation (DWPT) in sub-bands where the signal power is calculated. Modulation classifiers taking into account the statistical parameters of the signal in the wavelet domain are used as features for identifying the modulation schemes, in this case specifically for the DVB-T broadcast standard. As a possible application we are considering an indoor short-range distribution system for video signals.

Mauro Fadda, Maurizio Murroni, Vlad Popescu, Vlad Cristian Stoianovici

A Spectrum Sensing Algorithm for White Spaces Detection Validated in Real Environments

Cognitive Radio Systems have been proposed as the solution to spectrum scarcity, and Spectrum Sensing a good way to detect which frequencies are being used by primary users and avoid interferences. When primary signals are unknown, energy detection is the best while easiest technique for the sensing process. In this paper, we consider energy detection based spectrum sensing for narrowband signals in the TV wideband. Simulations are performed to obtain ROC curves. Designed detector has been validated both with signals generated in the laboratory and with real signals captured from the radio space.

Irati Lázaro, Maurizio Murroni, Iratxe Redondo, Mikel Sánchez, Manuel Vélez

Cooperative Spectrum Sensing for Geo-Location Databases

Spectrum sensing techniques are the key components for identifying and exploiting unused radio spectrum resources in the perspective of the cognitive radio paradigm. Based on the centralized cooperative sensing techniques, vast generalized databases named geo-location databases (GL-DB) can be deployed in order to centralize sensing and general radio spectrum data for the benefit of secondary cognitive radio users. The authors propose a hybrid conceptual application that involves spectrum sensing and a Human Network Interaction (HNI) model with the purpose of perceptually representing, in an immersive way, the available GL-DB information from a specific location for a natural user perception and interaction with the area of interest.

Mauro Fadda, Maurizio Murroni, Vlad Popescu, Vlad Cristian Stoianovici

Spectrum Occupancy and Hidden Node Margins for Cognitive Radio Applications in the UHF Band

This paper presents the study of the spectrum occupancy in the UHF frequency band (470-870MHz) in Bilbao area, Spain. The study has been performed at three different sites and at different height to determinate the hidden node margin, the main problem of the cognitive radio. The objective of the paper is to determinate by signal power measuring if the cognitive device will be able to detect and distinguish the empty and occupied channel to carry out the communication. The results from the spectrum measurements taken in all the sites have been analyzed and compared to the official spectrum regulation. The study reveals that the spectrum occupancy is minimum, thus there are a lot of white spaces in this band.

Miren Alonso, Irati Lázaro, Maurizio Murroni, Pablo Angueira, Manuel Vélez, J. Morgade, Mikel Sánchez, Pablo Prieto

Media Streaming

Delay Model for Super-Frame Based Resource Reservation in Distributed Wireless Networks

This paper proposes an analytical framework for evaluating the delay performance of super-frame (SF) based MAC schemes with distributed resource reservation in IEEE 802.11e enhanced distributed channel access (EDCA). SF-based resource reservation (RR) schemes divide the airtime into service intervals (SIs) with contention-free period (CFP) for providing guaranteed QoS for RTSNs and contention access period (CAP) for pledging fairness toward other sessions. The proposed analytical framework models the delay performance of RTSNs that obtain dedicated resources in a distributed manner. In addition, the optimization of system parameters, such as size of transmission opportunity (TXOP) and SI are studied in order to enhance the overall network capacity. The accuracy of the analytical framework is verified through numerical simulation and analytical results, which also suggest that the optimum resource allocation and SI can be found for improving the network capacity.

Xiaobo Yu, Pirabakaran Navaratnam, Klaus Moessner

A Method for Detection/Deletion via Network Coding for Unequal Error Protection of Scalable Video over Error-Prone Networks

The development of universal systems for video streaming needs transmission strategies that exploit the characteristics of the transmission medium such as a wireless network. Scalable video coding allows partial decoding of the video for multiple demands or under severe reception conditions. Network coding increases the transmission rate and provides error control at network level. We propose a detection/deletion system for error reduction in presence of channel noise. We combine the error detection capabilities of the network code with erasure decoding and unequal error protection to improve the visual quality of the video.

Michele Sanna, Ebroul Izquierdo

Multiple Description Coded Video Streaming with Multipath Transport in Wireless Ad Hoc Networks

Multiple description coding (MD coding or MDC) generates multiple decodable bitstreams for a single source to combat packet loss, which is suitable for video streaming in error-prone wireless ad hoc networks. In this paper, two problems are investigated for MD coded video streaming in wireless ad hoc networks. The first problem addresses multipath selection for balanced two-description coded video streaming. We formulate an interference-aware MDC multipath routing for single-radio networks by employing a time-division link scheduling method to eliminate wireless interference, and ultimately obtain an optimal path selection corresponding to the minimum achievable distortion. A heuristic solution is developed for the interference-aware multipath routing, by defining a path metric taking into account interference, link bandwidth and link “up” probability. The second problem addresses MDC redundancy control according to varying channel conditions of multiple paths. We design an unbalanced redundant slice based two-description video coding, which optimally selects the amount of inserted redundancy for each description. Simulation results demonstrate the effectiveness of the proposed MDC multipath routing scheme and the unbalanced MD video coding approach over heterogeneous paths.

Yuanyuan Xu, Ce Zhu

Mobile Multipath Cooperative Network for Real-Time Streaming

Access links are often times the bottlenecks of wireless wide area networks (WWAN). The prevalent use of multimedia applications on mobile devices introduces an ever increasing traffic load on WWAN access links, leading to traffic congestion and unsatisfactory user experiences. In this paper, we introduce a mobile multipath cooperative network. In the system, multiple paths are dynamically established among cooperative devices over WWAN and WLAN so that multiple descriptions of a multimedia stream can be transported over distinct end-to-end paths between two mobiles. As a result, the capacities of multiple wireless access links can be utilized to enhance quality of experience of a multimedia application. We also introduce a MDC rate adaptation algorithm that jointly adapts the source coding rates among multiple paths. Our lab experiments show that real-time streaming with multiple description coding benefits significantly from the proposed cooperative network and subsequently enhance the quality of user experience for multimedia applications.

Viji Raveendran, Phanikumar Bhamidipati, Xun Luo, Xiaolong Huang

Multi-stream Rate Adaptation Using Scalable Video Coding with Medium Grain Scalability

Multiple video streaming in a shared channel with constant bandwidth requires rate adaptation in order to optimize the overall quality. In this paper we propose a multi-stream rate adaptation framework with reference to the scalable video coding (SVC) extension of the H.264/AVC standard with medium grain scalability (MGS) and quality layer (QL). We first provide a general discrete multi-objective problem formulation with the aim to maximize the sum of assigned rates while minimizing the differences among distortions under a total bit-rate constraint. A single-objective problem formulation is then derived by applying a continuous relaxation to the problem. We also propose a simplified continuous semi-analytical model that accurately estimates the rate-distortion relationship and allows us to derive an optimal and low-complexity procedure to solve the relaxed problem. The numerical results show the goodness of our framework in terms of error gap between the relaxed and its related discrete solutions, the significant performance improvement with respect to an equal-rate adaptation scheme, and the lower complexity with respect to a sub-optimal algorithm proposed in the literature.

Sergio Cicalò, Abdul Haseeb, Velio Tralli

The Role of Log Entries in the Quality Control of Video Distribution

Diversification of university teaching with the help of video lectures has become much more common during the past few years. Once videos have become an essential part of teaching arrangements, whoever organizes the teaching must also pay attention to factors related to videos in quality system work for teaching. In the video production process it is the factors related to video transmission that exert influence on the usability of videos and set limitations for their production. A lot of information about those factors can be obtained from the media server log files. The particular focus of this paper is on the functionality of the connection between a server and a client and its effect on users. The paper deals with information obtained from a media server’s log file, describes the activities around collection and handling of log data, and introduces a preliminary classification for monitoring video transmissions. The results obtained from the media server’s log files are presented in accordance with that classification system at the end of the paper.

Ismo Hakala, Sanna Laine, Mikko Myllymäki, Jari Penttilä

Mobile Visual Search

Standards for Query Formalization in Mobile Visual Search

The research around visual search is gaining relevance due to the evolution in the generation and usage of digital images. A significant push comes from the mobile visual search topic, due to the widespread proliferation of camera enabled mobile devices. The new scenarios are increasing the urgency of novel solutions for challenging problems such as the efficient coding of compact visual descriptors and the interoperability of distributed visual search query interfaces. Currently, almost every visual search service offers a different retrieval interface and image metadata description format, preventing unified and efficient access. In this context, standardization groups such as ISO/IEC SC29/WG11 (MPEG) and ISO/IEC SC29/WG1 (JPEG) have been working to create unified interfaces for image repositories. In one hand, MPEG provides the ISO/IEC 15938-12 (MPEG Query Format, MPQF), which standardizes a query language for multimedia repositories and has also started an activity for standardizing compact descriptors for visual search (CDVS). On the other hand, JPEG is now finishing the ISO/IEC 24800 (JPSearch), which provides solutions to the image metadata interoperability problem. This paper analyzes how these standardization activities can be combined to satisfy the requirements posed by the mobile visual search scenario, which are their limitations and which are the necessary actions to be taken by the standardization committees in order to overcome them.

Ruben Tous, Jaime Delgado

3D Wide Baseline Correspondences Using Depth-Maps

Points matching between two or more images of a scene shot from different viewpoints is the crucial step to defining epipolar geometry between views, recover the camera’s egomotion or build a 3D model of the framed scene. Unfortunately in most of the common cases robust correspondences between points in different images can be defined only when small variations in viewpoint position, focal length or lighting are present between images. While in all the other conditions ad-hoc assumptions on the 3D scene or just weak correspondences can be used. In this paper, we present a novel matching method where depth-maps, nowadays available from cheap and off the shelf devices, are integrated with 2D images to provide robust descriptors even when wide baseline or strong lighting variations are present.

Marco Marcon, Eliana Frigerio, Augusto Sarti, Stefano Tubaro

Automatic Object Classification and Image Retrieval by Sobel Edge Detection and Latent Semantic Methods

We perform in this paper a comparative study of ability of the proposed novel image retrieval algorithms to provide automated object classification invariant of rotation, translation and scaling. We analyze simple cosine similarity coefficient methods and the SVD-free Latent Semantic method with an alternative sparse representation of color images. Considering applied cosine similarity coefficient methods, the two following approaches were tested and compared: i) the processing of the whole image and ii) the processing of the image that contains edges extracted by the application of the Sobel edge detector. Numerical experiments on a real database sets indicate feasibility of the presented approach as automated object classification tool without special image pre-processing.

Vesna Zeljkovic, Pavel Praks

Image Processing and Transmission

Optimal Interleaving for Robust Wireless JPEG 2000 Images and Video Transmission

In this paper we study the impact of interleaving on JPEG2000 images and video transmission through wireless channels. Based on interleaving impact evaluation, we derive a lower bound limit for the successful images decoding rate in wireless environments. Since the successful decoding rate is of central importance to guarantee Quality of Service to wireless clients, we rely on the derived limit to evaluate the performance of near-optimal interleaved frames using a wireless JPEG 2000 based client/server application. This work is a step toward optimal interleaving for robust Wireless JPEG 2000 based images and video transmission.

Daniel Pascual Biosca, Max Agueh

Interactive Image Viewing in Mobile Devices Based on JPEG XR

Services for high definition image browsing on mobile devices require a careful design since the user experience is heavily depending on the network bandwidth, processing delay, display resolution, image quality. Modern applications require coding technologies providing tools for resolution and quality scalability, for accessing spatial regions of interest (ROI), for reducing the domain of the coding algorithm decomposing large images into tiles. Some state-of-the-art technologies satisfying these requirements are the JPEG2000 and the JPEG XR. This paper presents the design of an interactive high resolution image viewing architecture for mobile devices based on JPEG XR. Display resolution, resolution scalability, image tiling are investigated in order to optimize the coding parameters with the objective to improve the user experience. Experimental tests are performed on a set of large images and comparisons against accessing the images without parameter optimization are reported.

Bernardetta Saba, Cristian Perra, Daniele D. Giusto

The Use of Selected Transforms to Improve the Accuracy of Face Recognition for Images with Uneven Illumination

This paper presents new methods of the illumination normalization in images preprocessed for face recognition system. The main problem in statistical methods of face recognition is illumination. Different lighting conditions between photos taken indoor and outdoor may drastically decrease the level of correct classification. Variations of the illumination lie mostly in low-frequency band, so it is possible to use several transforms operating on frequency domain of an image. This approach is to truncate appropriate number of coefficients in frequency domain to minimize variations under different lighting conditions. This paper presents methods using transforms such as: Two Dimensional Discrete Cosine Transform type II (2D-DCT-II) and two Periodic Piecewise-Linear Transforms, such as: Periodic Haar piecewise Linear Transform (PHL) and Periodic Walsh piecewise-Linear Transform PWL. The main advantage of this approach is that, it does not require any modeling steps and it can be implemented in real-time face recognition systems.

Tomasz Marcin Orzechowski, Andrzej Dziech, Tomasz Lukanko, Tomasz Rusc

Objective Evaluation of WebP Image Compression Efficiency

Performances of multimedia coding techniques are still improving in terms of compression ratio, coding features, and robustness against errors even if at a slower pace with respect to what we were used to up a decade ago. One of the latest codec which is expected to improve on the state of the art is the WebP algorithm released by Google. With the intent to evaluate the extent of this improvement, in this paper we provide an objective evaluation of the compression efficiency of WebP, by comparing it with alternative algorithms. From the results it appears that the performance of the proposed codec is in line with that of the alternative methods, without achieving any major improvement and lacking several features.

Maurizio Pintus, Giaime Ginesu, Luigi Atzori, Daniele D. Giusto

Mobile Applications

Implementing Mobile Applications with the MIPAMS Content Management Platform

New mobile devices (pda’s, tablets) permit the implementation of new business models as they are always connected and provide multimedia capabilities for capturing images, videos, music or even conversations. Together with an architecture for the secure management and distribution of multimedia content called MIPAMS, we propose a mobile business model with the implementation of a mobile application based on iOS (Apple operating system for mobile devices) for publishing added value content captured with a mobile device.

Xavier Maroñas, Silvia Llorente, Eva Rodríguez, Jaime Delgado

Virtual Device: Media Service Fitness, Selection and Composition Considering Composition Interactivity and Synchronization

The virtual device enables seamless use of application services residing on different devices in the vicinity of the user. In a pervasive environment, numerous service combinations can be selected to undertake a task. Current works aim to determine the best possible media services for composition by considering user preferences, environment capabilities and similarity between requested and available services. Previously, the authors considered all of above as well as potential local and remote content sources and destination devices. Here this is extended by considering end-to-end service latency to determine service fitness. The end-to-end delay of a service instance is important to consider as it directly affects the interactivity of the system. Services are selected for composition based on our fitness model. We model and simulate this issue and explain the results of our experimentation.

Niall Murray, Brian Lee, A. K. Karunakar, Yuansong Qiao, Enda Fallon

Location Based Abstraction of User Generated Mobile Videos

Demand for efficient ways to represent vast amount of video data has grown rapidly in recent years. The advances in positioning services have led to new possibilities of combining location information to video content. In this paper we present an automatic video editing system for geotagged mobile videos. In our solution the system creates automatically a video summary from a set of unedited video clips. Geotags are used to group video clips with the same context properties. The groups are used to create a video summary where the videos from the same group are represented as scenes. The novelty in our solution lies in the combining of geotags with low level content analysis tools in video abstraction. Evaluations of the system prove the concept useful as it improves coherence and enjoyability of the automatic video summaries.

Onni Ojutkangas, Johannes Peltola, Sari Järvinen

Modeling of Network Connectivity in Multi-Homed Hybrid Ad Hoc Networks

A Hybrid Ad Hoc Network consists of self-organized and self-configured mobile nodes, which make use of a fixed gateway to connect to the Internet. When there are two or more gateways to the fixed network, this is referred to with MultiHomed Hybrid Ad Hoc Network. In this scenario, different networks are formed, each one associated with a different gateway. A node can maintain its connectivity to the Internet when moving from a network to another by performing handover procedures and changing its gateway to the Internet. This scenario is quite interesting for its capacity of increasing the geographical extension of a single mobile network. The major contribution of this work is to provide a preliminary modeling of the node connectivity in this framework. We consider a typical architecture with gateways organized in a honey cell structure, where nodes move according to the RDMM (Random Direction Mobility Model), and present a three-state Markov model that describes the moving node behaviour: mobility without route changes, route change, and handover. Notwithstanding the simplicity of the underlying assumptions, the proposed model represents a valid basis for the analysis of the connectivity performance in this scenario, whose accuracy has been proved by means of extensive simulations.

Michele Nitti, Luigi Atzori


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