Papers by Nikolaos Thomos
We propose a novel scheme for error resilient image transmission. The proposed scheme employs a p... more We propose a novel scheme for error resilient image transmission. The proposed scheme employs a product coder consisting of LDPC codes and RS codes in order to deal effectively with bit errors. The efficiency of the proposed scheme is based on the exploitation of determinate symbols in Tanner graph decoding of LDPC codes and a novel product code optimization technique based on error estimation. Experimental evaluation demonstrates the superiority of the proposed system in comparison to recent state-of-the art techniques for image transmission.
A novel scheme is proposed for the transmission of JPEG2000 image streams over wireless channels.... more A novel scheme is proposed for the transmission of JPEG2000 image streams over wireless channels. The proposed scheme exploits the block-based coding structure of the JPEG2000 streams and employs optimized product codes consisting of Turbo codes and Reed-Solomon codes in order to deal effectively with burst errors. The optimization is based on information extracted directly from the compressed JPEG2000 streams. Experimental evaluation demonstrates that the proposed scheme outperform other recent algorithms for the wireless transmission of images.
We investigate the problem of collaborative video streaming in overlay networks. We exploit path ... more We investigate the problem of collaborative video streaming in overlay networks. We exploit path and source diversity, as well as basic processing capabilities of network,nodes in order to increase the overall throughput and improve,the video quality at the clients. We consider an architecture where,several streaming servers simultaneously deliver video information to a set of clients. The servers apply Raptor
We present a novel scheme for the transmission of H.264/AVC video streams over packet loss networ... more We present a novel scheme for the transmission of H.264/AVC video streams over packet loss networks. The proposed scheme exploits the error resilient features of H.264/AVC codec and employs Reed-Solomon codes to protect effectively the streams. A novel technique for adaptive classification of macroblocks into three slice groups using Flexible Macroblock Ordering is also proposed. The optimal classification of mac-
In this paper, we investigate the problem of recovering source information from an incomplete set... more In this paper, we investigate the problem of recovering source information from an incomplete set of network coded data with help of prior information about the sources. We study the theoretical performance of such systems under maximum a posteriori (MAP) decoding and examine the influence of the data priors and, in particular, source correlation on the decoding performance. We also propose a low complexity iterative decoding algorithm based on message passing for decoding the network coded data. The algorithm operates on a graph that captures the network coding constraints, while the knowledge about the source correlation is directly incorporated in the messages exchanged over the graph. We test the proposed method on both synthetic data and correlated image sequences and demonstrate that the prior knowledge about the statistical properties of the sources can be effectively exploited at the decoder in order to provide a good reconstruction of the transmitted data.
This paper addresses the problem of the distributed delivery of correlated data sources with help... more This paper addresses the problem of the distributed delivery of correlated data sources with help of network coding. Network coding provides an alternative to routing algorithms and offers improved system performance, robustness and throughput, with no need of deploying sophisticated routing strategies. However, the performance is directly driven by the number of innovative data packets that reach the receiver. If the number of received innovative data packets is significantly small, the decoder cannot perfectly recover the transmitted information. However, we show that the correlation between the data sources can be used at decoder for effective approximate decoding. We analytically investigate the impact of the network coding algorithm, and in particular, of the size of finite fields on the decoding performance. Then, we determine an optimal field size that minimizes the expected decoding error, which represents a trade-off between quantization of the source data and probability o...
Growth codes are a subclass of Rateless codes that have found interesting applications in data di... more Growth codes are a subclass of Rateless codes that have found interesting applications in data dissemination problems. Compared to other Rateless and conventional channel codes, Growth codes show improved intermediate performance which is particularly useful in applications where performance increases with the number of decoded data units. In this paper, we provide a generic analytical framework for studying the asymptotic performance of Growth codes in different settings. Our analysis based on Wormald method applies to any class of Rateless codes that does not include a precoding step. We evaluate the decoding probability model for short codeblocks and validate our findings by experiments. We then exploit the decoding probability model in an illustrative application of Growth codes to error resilient video transmission. The video transmission problem is cast as a joint source and channel rate allocation problem that is shown to be convex with respect to the channel rate. This application permits to highlight the main advantage of Growth codes that is improved performance (hence distortion in video) in the intermediate loss region.
We consider an interactive multiview video streaming (IMVS) system where clients select their pre... more We consider an interactive multiview video streaming (IMVS) system where clients select their preferred viewpoint in a given navigation window. To provide high quality IMVS, many high quality views should be transmitted to the clients. However, this is not always possible due to the limited and heterogeneous capabilities of the clients. In this paper, we propose a novel adaptive IMVS solution based on a layered multiview representation where camera views are organized into layered subsets to match the different clients constraints. We formulate an optimization problem for the joint selection of the views subsets and their encoding rates. Then, we propose an optimal and a reduced computational complexity greedy algorithms, both based on dynamic-programming. Simulation results show the good performance of our novel algorithms compared to a baseline algorithm, proving that an effective IMVS adaptive solution should consider the scene content and the client capabilities and their prefer...
Journal of Communications, 2000
Network coding has recently emerged as an alternative to traditional routing algorithms in commun... more Network coding has recently emerged as an alternative to traditional routing algorithms in communication systems. In network coding, the network nodes can combine the packets they receive before forwarding them to the neighbouring nodes. Intensive research efforts have demonstrated that such a processing in the network nodes can provide advantages in terms of throughput or robustness. These potentials, combined with
This paper addresses the problem of frame interpolation for Wyner-Ziv video coding. A novel frame... more This paper addresses the problem of frame interpolation for Wyner-Ziv video coding. A novel frame interpolation method based on block-adaptive matching algorithm for motion estimation is presented. This scheme enables block size adaptation to local activity within frames using block merging and splitting techniques. The efficiency of the proposed method is evaluated in a Wyner-Ziv video coding scheme. The experimental results demonstrate the superiority of the proposed method over existing frame interpolation techniques.
In this paper, we investigate the problem of recovering source information from an incomplete set... more In this paper, we investigate the problem of recovering source information from an incomplete set of network coded data with help of prior information about the sources. We study the theoretical performance of such systems under maximum a posteriori (MAP) decoding and examine the influence of the data priors and, in particular, source correlation on the decoding performance. We also propose a low complexity iterative decoding algorithm based on message passing for decoding the network coded data. The algorithm operates on a graph that captures the network coding constraints, while the knowledge about the source correlation is directly incorporated in the messages exchanged over the graph. We test the proposed method on both synthetic data and correlated image sequences and demonstrate that the prior knowledge about the statistical properties of the sources can be effectively exploited at the decoder in order to provide a good reconstruction of the transmitted data.
2014 IEEE Visual Communications and Image Processing Conference, 2014
This paper addresses the problem of the distributed delivery of correlated data sources with help... more This paper addresses the problem of the distributed delivery of correlated data sources with help of network coding. Network coding provides an alternative to routing algorithms and offers improved system performance, robustness and throughput, with no need of deploying sophisticated routing strategies. However, the performance is directly driven by the number of innovative data packets that reach the receiver. If the number of received innovative data packets is significantly small, the decoder cannot perfectly recover the transmitted information. However, we show that the correlation between the data sources can be used at decoder for effective approximate decoding. We analytically investigate the impact of the network coding algorithm, and in particular, of the size of finite fields on the decoding performance. Then, we determine an optimal field size that minimizes the expected decoding error, which represents a trade-off between quantization of the source data and probability of decoding error. The network coding with approximate decoding algorithm is implemented in illustrative multimedia streaming and sensor network applications. In both cases, the experimental results confirm the field size analysis and illustrate the effectiveness of approximate decoding of correlated data.
2011 IEEE International Conference on Multimedia and Expo, 2011
In this paper, we present a pull-based dissemination protocol for efficient distribution of scala... more In this paper, we present a pull-based dissemination protocol for efficient distribution of scalable video content in overlay peer-to-peer networks with mesh structures. The proposed protocol employs prioritized network coding, where the network coded packets belong to classes that represent packets of different priorities. For a receiver, the pull procedure begins with the reception of buffer vector messages from the senders, which bring information about the numbers and classes of available packets. The receiver node decides on the rate allocation of the different classes to be requested from each of the senders. The rate allocation is cast as a video quality maximization problem and solved using a hill-climbing algorithm. The simulation results show that the proposed mechanism, which is able to fully adapt to network dynamics, accounts for the unequal packet importances and utilizes the network resources efficiently.
Proceedings. International Conference on Image Processing, 2002
The decoding of convolutional codes using the List Viterbi algorithm is proposed for data hiding ... more The decoding of convolutional codes using the List Viterbi algorithm is proposed for data hiding applications. The per- formance of this technique is evaluated for wavelet-domain information hiding and is shown in many cases to be ad- vantageous in comparison to the widely used Turbo codes for efficient extraction of information embedded in digital images.
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Papers by Nikolaos Thomos