Yiannis Andreopoulos

University College London, Londinium, England, United Kingdom

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Publications (65)64.49 Total impact

  • Source
    Y. Andreopoulos, N. Mastronarde, M. van der Schaar
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    ABSTRACT: The proliferation of wireless multihop communication infrastructures in office or residential environments depends on their ability to support a variety of emerging applications requiring real-time video transmission between stations located across the network. We propose an integrated cross-layer optimization algorithm aimed at maximizing the decoded video quality of delay-constrained streaming in a multihop wireless mesh network that supports quality-of-service. The key principle of our algorithm lays in the synergistic optimization of different control parameters at each node of the multihop network, across the protocol layers-application, network, medium access control, and physical layers, as well as end-to-end, across the various nodes. To drive this optimization, we assume an overlay network infrastructure, which is able to convey information on the conditions of each link. Various scenarios that perform the integrated optimization using different levels ("horizons") of information about the network status are examined. The differences between several optimization scenarios in terms of decoded video quality and required streaming complexity are quantified. Our results demonstrate the merits and the need for cross-layer optimization in order to provide an efficient solution for real-time video transmission using existing protocols and infrastructures. In addition, they provide important insights for future protocol and system design targeted at enhanced video streaming support across wireless mesh networks
    IEEE Journal on Selected Areas in Communications 12/2006; · 3.12 Impact Factor
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    M. van der Schaar, Y. Andreopoulos, Zhiping Hu
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    ABSTRACT: The quality-of-service (QoS) guarantees enabled by the new IEEE 802.11 a/e Wireless LAN (WLAN) standard are specifically targeting the real-time transmission of multimedia content over the wireless medium. Since video data consume the largest part of the available bitrate compared to other media, optimization of video streaming for this new standard is a significant factor for the successful deployment of practical systems. Delay-constrained streaming of fully-scalable video over IEEE 802.11 a/e WLANs is of great interest for many multimedia applications. The new medium access control (MAC) protocol of IEEE 802.11e is called the Hybrid Coordination Function (HCF) and, in this paper, we will specifically consider the problem of video transmission over HCF Controlled Channel Access (HCCA). A cross-layer optimization across the MAC and application layers of the OSI stack is used in order to exploit the features provided by the combination of the new HCCA standard with new versatile scalable video coding algorithms. Specifically, we propose an optimized and scalable HCCA-based admission control for delay-constrained video streaming applications that leads to a larger number of stations being simultaneously admitted (without quality reduction to any video flow). Subsequently, given the allocated transmission opportunity, each station deploys an optimized Application-MAC-PHY adaptation, scheduling, and protection strategy that is facilitated by the fine-grain layering provided by the scalable bitstream. Given that each video flow needs to always comply with the predetermined (a priori negotiated) traffic specification parameters, this cross-layer strategy enables graceful quality degradation whenever the channel conditions or the video sequence characteristics change. For instance, it is demonstrated that the proposed cross-layer protection and bitstream adaptation strategies facilitate QoS token rate adaptation under link adaptation mechanisms that utilize different physical layer transmission rates. The expected gains offered by the optimized solutions proposed in this paper are established theoretically, as well as through simulations.
    IEEE Transactions on Mobile Computing 07/2006; 5(6):755- 768. · 2.40 Impact Factor
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    K. Masselos, Y. Andreopoulos, T. Stouraitis
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    ABSTRACT: Several input-traversal schedules have been proposed for the computation of the 2D discrete wavelet transform (DWT). In this paper, the row-column, the line-based and the block-based schedules for the 2D DWT computation are compared with respect to their execution time on a very long instruction word (VLIW) digital signal processor (DSP). Implementations of the wavelet transform according to the considered schedules have been developed. They are parameterized with respect to filter pair, image size, and number of decomposition levels. All implementations have been mapped on a VLIW DSP. Performance metrics for the implementations for a complete set of parameters have been obtained and compared. The experimental results show that each implementation performs better for different points of the parameter space
    Circuits and Systems, 2006. ISCAS 2006. Proceedings. 2006 IEEE International Symposium on; 06/2006
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    Y. Andreopoulos, M. van der Schaar, Z. Hu, S. Heo, S. Suh
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    ABSTRACT: Delay-constrained streaming of fully-scalable video over IEEE 802.11a/e wireless (WLANs) is of great interest for many emerging multimedia applications. In this paper, we consider the problem of video transmission over HCF controlled channel access (HCCA), which is part of the new medium access control (MAC) protocol of IEEE 802.11e. A cross-layer optimization across the MAC and application layers is used in order to exploit the features provided by the new HCCA standard, as well as by the versatility of new state-of-the-art scalable video coding algorithms. Under pre-determined delay constraints for streaming, the proposed cross-layer strategy leads to a larger number of stations being simultaneously admitted (without any loss in the video quality) than in systems that utilize application-layer only optimizations. At the same time, the fine-grain layering provided by the scalable bitstream facilitates prioritization and unequal retransmissions of packets at the MAC layer thereby enabling graceful quality degradation under channel-capacity limitations and delay constraints. The expected gains offered by the optimized solutions proposed in this paper are established through simulations
    Acoustics, Speech and Signal Processing, 2006. ICASSP 2006 Proceedings. 2006 IEEE International Conference on; 06/2006 · 4.63 Impact Factor
  • Source
    [show abstract] [hide abstract]
    ABSTRACT: We propose an integrated cross-layer optimization algorithm for maximizing the decoded video quality of delay-constrained streaming in a quality-of-service (QoS) enabled multi-hop wireless mesh network. The key to our algorithm is the synergistic optimization of control parameters at each node of the multi-hop network, across the protocol layers - application, network, medium access control (MAC) and physical (PHY) layers, as well as end-to-end, i.e. across the various network nodes. To drive this optimization, we assume an overlay network infrastructure, which conveys information on the conditions of each link. Quantitative results are presented that demonstrate the merits and the need for cross-layer optimization in an efficient solution for real-time video transmission using existing protocols and infrastructures
    Acoustics, Speech and Signal Processing, 2006. ICASSP 2006 Proceedings. 2006 IEEE International Conference on; 06/2006 · 4.63 Impact Factor
  • Source
    K. Masselos, Y. Andreopoulos, T. Stouraitis
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    ABSTRACT: The two-dimensional discrete wavelet transform (2D DWT) is becoming one of the standard tools for image and video compression systems. Various input-traversal schedules have been proposed for its computation. Here, major schedules for 2D DWT computation are compared with respect to their performance on a very long instruction-word (VLIW) digital signal processor (DSP). In particular, three popular transform-production schedules are considered: the row-column, the line based and the block based. Realisations of the wavelet transform according to the considered schedules have been developed. They are parameterised with respect to filter pair, image size and number of decomposition levels. All realisations have been mapped on a VLIW DSP, as these processors currently form an attractive alternative for the realisation of signal, image and video processing systems. Performance metrics for the realisations for a complete set of parameters have been obtained and compared. The experimental results show that each realisation performs better for different points of the parameter space.
    IEE Proceedings - Vision Image and Signal Processing 05/2006;
  • IEEE Journal on Selected Areas in Communications. 01/2006; 24:2104-2115.
  • Mihaela van der Schaar, Yiannis Andreopoulos, Zhiping Hu
    IEEE Trans. Mob. Comput. 01/2006; 5:755-768.
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    M. van der Schaar, Y. Andreopoulos
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    ABSTRACT: Existing research on Universal Multimedia Access has mainly focused on adapting multimedia to the network characteristics while overlooking the receiver capabilities. Alternatively, part 7 of the MPEG-21 standard entitled Digital Item Adaptation (DIA) defines description tools to guide the multimedia adaptation process based on both the network conditions and the available receiver resources. In this paper, we propose a new and generic rate-distortion-complexity model that can generate such DIA descriptions for image and video decoding algorithms running on various hardware architectures. The novelty of our approach is in virtualizing complexity, i.e., we explicitly model the complexity involved in decoding a bitstream by a generic receiver. This generic complexity is translated dynamically into "real" complexity, which is architecture-specific. The receivers can then negotiate with the media server/proxy the transmission of a bitstream having a desired complexity level based on their resource constraints. Hence, unlike in previous streaming systems, multimedia transmission can be optimized in an integrated rate-distortion-complexity setting by minimizing the incurred distortion under joint rate-complexity constraints.
    IEEE Transactions on Multimedia 07/2005; · 1.75 Impact Factor
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    ABSTRACT: A number of emerging resolution-scalable image and video coding algorithms have recently shown very promising performance due to the use of overcomplete wavelet representations. In these applications, the overcomplete discrete wavelet transform (ODWT) is derived starting from the critically-sampled subbands of the DWT (complete representation) of a certain decomposition (resolution) level. This process, which is a complete-to-overcomplete DWT (CODWT), is used for wavelet domain operations that require shift invariance. Specifically, both the encoder and decoder independently construct the overcomplete representation at the best accuracy possible, given the critically-sampled subbands of a certain resolution level. In contrast to the classical approach for performing the CODWT, which is a multi-rate calculation scheme that requires the reconstruction of the input spatial-domain signal, in this paper we propose a new, single-rate calculation scheme, which is formalized for the general case of an arbitrary decomposition (resolution) level. Based on derived symmetry properties, a simple implementation structure of the proposed approach provides interesting tradeoffs for the required multiplication budget in comparison to the conventional approach. This leads to a complexity-scalable solution that fits the versatile requirements of scalable coding environments. The use of the proposed single-rate calculation scheme of the CODWT is demonstrated in several image and video coding systems.
    Signal Processing. 01/2005;
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    Sig. Proc.: Image Comm. 01/2005; 20:1-19.
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    ABSTRACT: Modern video coding applications require data transmission over variable-bandwidth wired and wireless network channels to a variety of terminals, possibly having different screen resolutions and available computing power. Scalable video coding technology is needed to optimally support these applications. Recently proposed wavelet-based video codecs employing spatial-domain motion-compensated temporal filtering (SDMCTF) provide quality, resolution and frame-rate scalability while delivering compression performance comparable to that of H.264, the state-of-the-art in single-layer video coding. These codecs require quality-scalable coding of the motion vectors to support a large range of bit-rates with optimal compression efficiency. In this paper, the practical use of prediction-based scalable motion-vector coding in the context of scalable SDMCTF-based video coding is investigated. Extensive experimental results demonstrate that, irrespective of the employed motion model, our prediction-based scalable motion-vector codec (MVC) systematically outperforms state-of-the-art wavelet-based solutions for both lossy and lossless compression. A new rate-distortion optimized rate-allocation strategy is proposed, capable of optimally distributing the available bit-budget between the different frames and between the texture and motion information, making the integration of the scalable MVC into a scalable video codec possible. This rate-allocation scheme systematically outperforms heuristic approaches previously employed in the literature. Experiments confirm that by using a scalable MVC, lower bit-rates can be attained without sacrificing motion-estimation efficiency and that the overall coding performance at low rates is significantly improved by a better distribution of the available rate between texture and motion information. The only downside of scalable motion-vector coding is a slight performance loss incurred at high bit-rates.
    Signal Processing: Image Communication. 01/2005;
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    ABSTRACT: We introduce an efficient and flexible framework for temporal filtering in wavelet-based scalable video codecs called unconstrained motion compensated temporal filtering (UMCTF). UMCTF allows for the use of different filters and temporal decomposition structures through a set of controlling parameters that may be easily modified during the coding process, at different granularities and levels. The proposed framework enables the adaptation of the coding process to the video content, network and end-device characteristics, allows for enhanced scalability, content-adaptivity and reduced delay, while improving the coding efficiency as compared to state-of-the-art motion-compensated wavelet video coders. Additionally, a mechanism for the control of the distortion variation in video coding based on UMCTF employing only the predict step is proposed. The control mechanism is formulated by expressing the distortion in an arbitrary decoded frame, at any temporal level in the pyramid, as a function of the distortions in the reference frames at the same temporal level. All the different scenarios proposed in the paper are experimentally validated through a coding scheme that incorporates advanced features (such as rate-distortion optimized variable block-size multihypothesis prediction and overlapped block motion compensation). Experiments are carried out to determine the relative efficiency of different UMCTF instantiations, as well as to compare against the current state-of-the-art in video coding.
    Signal Processing: Image Communication. 01/2005;
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    ABSTRACT: A new transform is proposed that derives the over- complete discrete wavelet transform (ODWT) subbands from the critically sampled DWT subbands (complete representation). This complete-to-overcomplete DWT (CODWT) has certain advantages in comparison to the conventional approach that performs the in- verse DWT to reconstruct the input signal, followed by the à-trous or the lowband shift algorithm. Specifically, the computation of the input signal is not required. As a result, the minimum number of downsampling operations is performed and the use of upsampling is avoided. The proposed CODWT computes the ODWT subbands by using a set of prediction-filter matrices and filtering-and-downsampling operators applied to the DWT. This formulation demonstrates a clear separation between the single-rate and multirate compo- nents of the transform. This can be especially significant when the CODWT is used in resource-constrained environments, such as resolution-scalable image and video codecs. To illustrate the applicability of the proposed transform in these emerging appli- cations, a new scheme for the transform-calculation is proposed, and existing coding techniques that benefit from its usage are surveyed. The analysis of the proposed CODWT in terms of arith- metic complexity and delay reveals significant gains as compared with the conventional approach.
    IEEE Transactions on Signal Processing 01/2005; 53:1398-1412. · 2.81 Impact Factor
  • Mihaela van der Schaar, Yiannis Andreopoulos
    IEEE Transactions on Multimedia. 01/2005; 7:471-479.
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    ABSTRACT: Computer networks and the internet have taken an important role in modern society. Together with their development, the need for digital video transmission over these networks has grown. To cope with the user demands and limitations of the network, compression of the video material has become an important issue. Additionally, many video-applications require flexibility in terms of scalability and complexity (e.g. HD/SD-TV, video-surveillance). Current ITU-T and ISO/IEC video compression standards (MPEG-x, H.26-x) lack efficient support for these types of scalability. Wavelet-based compression techniques have been proposed to tackle this problem, of which the Motion Compensated Temporal Filtering (MCTF)-based architectures couple state-of-the-art performance with full (quality, resolution, and frame-rate) scalability. However, a significant drawback of these architectures is their high complexity. The computational and memory complexity of both spatial domain (SD) MCTF and in-band (IB) MCTF video codec instantiations are examined in this study. Comparisons in terms of complexity versus performance are presented for both types of codecs. The paper indicates how complexity scalability can be achieved in such video-codecs, and analyses some of the trade-offs between complexity and coding performance. Finally, guidelines on how to implement a fully scalable video-codec that incorporates quality, temporal, resolution and complexity scalability are proposed.© (2004) COPYRIGHT SPIE--The International Society for Optical Engineering. Downloading of the abstract is permitted for personal use only.
    11/2004;
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    ABSTRACT: Computer networks and the internet have taken an important role in modern society. Together with their development, the need for digital video transmission over these networks has grown. To cope with the user demands and limitations of the network, compression of the video material has become an important issue. Additionally, many video-applications require flexibility in terms of scalability and complexity (e.g. HD/SD-TV, video-surveillance). Current ITU-T and ISO/IEC video compression standards (MPEG-x, H.26-x) lack efficient support for these types of scalability. Wavelet-based compression techniques have been proposed to tackle this problem, of which the Motion Compensated Temporal Filtering (MCTF)-based architectures couple state-of-the-art performance with full (quality, resolution, and frame-rate) scalability. However, a significant drawback of these architectures is their high complexity. The computational and memory complexity of both spatial domain (SD) MCTF and in-band (IB) MCTF video codec instantiations are examined in this study. Comparisons in terms of complexity versus performance are presented for both types of codecs. The paper indicates how complexity scalability can be achieved in such video-codecs, and analyses some of the trade-offs between complexity and coding performance. Finally, guidelines on how to implement a fully scalable video-codec that incorporates quality, temporal, resolution and complexity scalability are proposed.
    Proc SPIE 11/2004;
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    ABSTRACT: Scalable wavelet-based video codecs using spatial-domain motion compensated temporal filtering require a quality-scalable motion vector codec to support a large range of bit rates with optimal compression efficiency. Introduced is a new prediction-based architecture for quality-scalable motion vector coding that outperforms the state-of-the-art wavelet-based techniques previously proposed in the literature.
    Electronics Letters 08/2004; · 1.04 Impact Factor
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    ABSTRACT: It has been demonstrated recently that 3-D wavelet coding with motion-compensated temporal filtering (MCTF) provides a wide range of spatio-temporal-SNR scalability with state-of-the-art coding performance. However, the coding system is very different from the already standardized motion-compensated DCT (MC-DCT) video coders such as MPEG-2, MPEG-4, or H.26L. Nonetheless, the market acceptance of the new scalable technology will come much easier if backward compatibility to such previous standards would exist. In this paper, we present a new coder architecture where the base layer can be a standard MC-DCT coder, while the enhancement layer is an in-band MCTF codec operating in the overcomplete wavelet domain. First, we propose a simple extension of the scalable 3-D wavelet codec with a standard MC-DCT base layer. As a second step, to improve the performance of the proposed scalable coder over a wide range of bit-rates, we describe several small extensions to the standardized MC-DCT codec structure that can be applied for the base layer coding.
    04/2004;
  • M. van der Schaar, Y. Andreopoulos, Qiong Li
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    ABSTRACT: We discuss the benefits of using realistic rate-distortion-complexity (R-D-C) models to guide ubiquitous multimedia streaming systems. At the server or proxy, on-the-fly bitstream adaptation to varying network conditions and diverse end-devices' processing capabilities can be performed by relying on accurate (pre-computed) R-D-C models. To accommodate various types of receivers with different resources, we introduce the concept of generic complexity metrics (GCMs) which quantify in a generic manner the decoding complexity of a compressed video sequence. A state-of-the-art motion-compensated wavelet-based coding scheme is used to illustrate how R-D-C models can be computed for a particular compression scheme. Finally, we propose a receiver-driven streaming framework and show how R-D-C models can be used to assist real-time wired/wireless multimedia transmission applications.
    Global Telecommunications Conference, 2004. GLOBECOM '04. IEEE; 01/2004

Publication Stats

693 Citations
68 Downloads
3k Views
64.49 Total Impact Points

Institutions

  • 2010–2011
    • University College London
      • Department of Electronic and Electrical Engineering
      Londinium, England, United Kingdom
  • 2006–2009
    • University of California, Los Angeles
      • Department of Electrical Engineering
      Los Angeles, CA, United States
  • 2008
    • University of London
      Londinium, England, United Kingdom
    • Queen Mary, University of London
      • Department of Electronic Engineering
      London, ENG, United Kingdom
  • 2007
    • Imperial College London
      • Department of Electrical and Electronic Engineering
      London, ENG, United Kingdom
    • Bayer HealthCare
      Leverkusen, North Rhine-Westphalia, Germany
  • 2005
    • University of California, Davis
      • Department of Electrical and Computer Engineering
      Davis, CA, United States
  • 2001–2005
    • Free University of Brussels
      • Electronics and Informatics (ETRO)
      Bruxelles, Brussels Capital Region, Belgium