The Experts below are selected from a list of 273 Experts worldwide ranked by ideXlab platform

Lajos Hanzo - One of the best experts on this subject based on the ideXlab platform.

  • Iterative Source and channel decoding relying on correlation modelling for wireless video transmission
    IET Communications, 2013
    Co-Authors: Yongkai Huo, Tao Wang, Robert G. Maunder, Lajos Hanzo
    Abstract:

    Since joint Source-channel decoding (JSCD) is capable of exploiting the residual redundancy in the Source signals for improving the attainable error resilience, it has attracted substantial attention. Motivated by the principle of exploiting the Source redundancy at the receiver, in this treatise we study the application of iterative Source channel decoding (ISCD) aided video communications, where the video signal is modelled by a first-order Markov process. Firstly, we derive reduced-complexity formulas for the first-order Markov modelling (FOMM) aided Source decoding. Then we propose a bit-based iterative horizontal vertical scanline model (IHVSM) aided Source decoding algorithm, where a horizontal and a vertical Source Decoder are employed for exchanging their extrinsic information using the iterative decoding philosophy. The iterative IHVSM aided Decoder is then employed in a forward error correction (FEC) encoded uncompressed video transmission scenario, where the IHVSM and the FEC Decoder exchange softbit-information for performing turbo-like ISCD for the sake of improving the reconstructed video quality. Finally, we benchmark the attainable system performance against a near-lossless H.264/AVC video communication system and the existing FOMM based softbit Source decoding scheme, where The financial support of the RC-UK under the auspices of the India-UK Advanced Technology Centre (IU-ATC) and that of the EU under the CONCERTO project as well as that of the European Research Council’s Advanced Fellow Grant is gratefully acknowledged. The softbit decoding is performed by a one-dimensional Markov model aided Decoder. Our simulation results show that Eb=N0 improvements in excess of 2.8 dB are attainable by the proposed technique in uncompressed video applications.

  • Iterative two-dimensional error concealment for low-complexity wireless video uplink transmitters
    2012
    Co-Authors: Yongkai Huo, Tao Wang, Robert G. Maunder, Lajos Hanzo
    Abstract:

    Since joint Source-channel decoding is capable of exploiting the residual redundancy in the encoded Source signals for improving the attainable error resilience, it has attracted substantial attention. Motivated by the principle of exploiting the Source redundancy at the receiver, in this treatise we study the application of iterative Error Concealment (EC) for low-complexity uplink video communications, where the video signal is modelled by a first-order Markov process. Firstly, we derive reduced-complexity formulas for the first-order Markov modelling aided Source decoding. Then we propose a bit-based iterative EC algorithm, where a horizontal and a vertical Source Decoder are employed for exchanging their information using the iterative decoding philosophy. This scheme may be combined with low-complexity video codecs, provided that they retain some of the redundancy residing in the video signals and are capable of estimating the softbit information representing each bit of the video pixels. As application examples, we test our proposed two-dimensional iterative EC in both Wyner-Ziv video coded and uncompressed video transmission scenarios. Finally, we benchmark the attainable system performance against the existing first-order Markov process based softbit Source decoding scheme, where the softbit decoding is performed by a one-dimensional Markov model aided Decoder, as well as by the existing pixel-domain Wyner-Ziv video scheme. Our simulation results show that Eb/N0 improvements in excess of 6 dB are attainable by the proposed technique in uncompressed video home-networking applications. Furthermore, up to 21.5% bitrate reduction is achieved by employing our proposed iterative error concealment technique in a Wyner-Ziv video coding scheme.

  • VTC Fall - Joint Optimization of Iterative Source and Channel Decoding Using Over-Complete Source-Mapping
    2007 IEEE 66th Vehicular Technology Conference, 2007
    Co-Authors: A.q. Pham, Lie-liang Yang, Lajos Hanzo
    Abstract:

    The intentionally imposed or inherent unintentional residual redundancy found in Source encoded bitstreams can be exploited for supporting joint SoftBit-Source decoding and channel decoding, which has the potential of improving both error correcting capability as well as the subjective audio or video quality of communication systems. As a potent error concealment technique, the softbit-based Source decoding, proposed by Adrat Vary and Spittka exploits the residual redundancy or correlation inherent in the Source codec parameters for mitigating the effects of transmission errors. However, when using efficient Source encoders, limited Source redundancy is left in the Source- encoded bitstream. In this scenario the SoftBit-Source Decoder (SBSD) may have a limited extrinsic information contribution which results in no system performance improvements beyond two decoding iterations. In our novel approach, we partition the total available bit budget between the Source and channel codecs in order to improve the attainable error correcting capability and hence to maximize the overall system's performance. More explicitly, the inherent redundancy in the encoded bit- stream is intentionally increased with the aid of over-complete mapping, and extrinsic information transfer (EXIT) charts are used for designing a suitable mapping of the Source-coded bits to the modulated symbols, leading to an approximately 2dB signal-to-noise gain.

  • Iterative channel equalization, channel decoding and Source decoding
    2005 IEEE 61st Vehicular Technology Conference, 1
    Co-Authors: Jin Wang, Lie-liang Yang, Lajos Hanzo
    Abstract:

    The performance of soft Source decoding is evaluated over dispersive AWGN channels. By employing Source codes having error-correcting capabilities, such as reversible variable-length codes (RVLC) and variable-length error-correcting (VLEC) codes, the soft-in/soft-out (SISO) Source Decoder benefits from exchanging information with the MAP equalizer, and effectively eliminates the intersymbol interference (ISI) after a few iterations. It was also found that the soft Source Decoder is capable of significantly improving the attainable performance of the turbo receiver provided that channel equalization, channel decoding and Source decoding are carried out jointly and iteratively. At SER0=1/sup -4/ the performance of this three-component turbo receiver is about 2 dB better in comparison to the benchmark scheme carrying out channel equalization and channel decoding jointly, but Source decoding separately. At this SER value, the performance of the proposed scheme is about 1 dB worse than that of the 1/2 -rate convolutional coded non-dispersive AWGN channel.

Marc Adrat - One of the best experts on this subject based on the ideXlab platform.

  • Reduced-Search Source Decoders for Iterative Source-Channel Decoding
    2011
    Co-Authors: Laurent Schmalen, Peter Vary, Marc Adrat
    Abstract:

    Iterative Source-channel decoding (ISCD) exploits the residual redundancy of Source codec parameters by using the Turbo principle. However, ISCD might require more computational complexity than available as the utilized soft decision Source Decoder (SDSD) can be computationally quite expensive. In this paper we propose a reduced-search SDSD, based on the M-algorithm known from channel decoding, which considerably reduces the complexity of the receiver. Furthermore, we show that by slightly modifying the quantization at the transmitter, the complexity can be further reduced without noticeable performance losses. Complexity figures are given for all approaches as well as a simulation example showing the performance of the complexity-reduced SDSD in an ISCD framework.

  • Complexity-reduced iterative Source-channel decoding by conditional quantization
    2008 5th International Symposium on Turbo Codes and Related Topics, 2008
    Co-Authors: Laurent Schmalen, Marc Adrat, Peter Vary, Thorsten Clevorn
    Abstract:

    Iterative Source-channel decoding (ISCD) exploits the residual redundancy of Source codec parameters by using the Turbo principle. However, ISCD might require more computational complexity than available. The main reason is that the utilized soft decision Source Decoder (SDSD) can be computationally quite expensive. In this paper we propose a joint Source-channel coding approach which reduces the computational complexity of the SDSD by slightly modifying the quantizer such that the complexity of the Source Decoder is reduced. The complexity of the SDSD is further reduced by transforming the SDSD equations into the logarithmic domain. We give analytical expressions for the expected quality loss by the modified quantizer, simulation results showing the overall ISCD system performance, as well as complexity figures.

  • Turbo decodulation: iterative combined demodulation and Source-channel decoding
    IEEE Communications Letters, 2005
    Co-Authors: Thorsten Clevorn, Marc Adrat, Johannes Brauers, Peter Vary
    Abstract:

    We propose the combination of iterative demodulation and iterative Source-channel decoding as a multiple turbo process. The receiver structures of bit-interleaved coded modulation with iterative decoding (BICM-ID), iterative Source-channel decoding (ISCD), and iterative Source coded modulation (ISCM) are merged to one novel turbo system, in which in two iterative loops reliability information is exchanged between the three single components, demodulator, channel Decoder and (softbit) Source Decoder. Simulations show quality improvements compared to the different previously known systems, which use iterative processing only for two components of the receiver.

  • Iterative Source-channel Decoder using extrinsic information from softbit-Source decoding
    2001 IEEE International Conference on Acoustics Speech and Signal Processing. Proceedings (Cat. No.01CH37221), 2001
    Co-Authors: Marc Adrat, R. Vary, Julian Spittka
    Abstract:

    In digital mobile communications, efficient compression algorithms are needed to encode speech or audio signals. As the determined Source parameters are highly sensitive to transmission errors, robust Source and channel decoding schemes are required. This contribution deals with an iterative Source-channel decoding approach where a simple channel Decoder and a softbit-Source Decoder are concatenated. We mainly focus on softbit-Source decoding which can be considered as an error concealment technique. This technique utilizes residual redundancy remaining after Source coding. We derive a new formula that shows how the residual redundancy transforms into extrinsic information utilizable for iterative decoding. The derived formula opens several starting points for optimizations, e.g. it helps to find a robust index assignment. Furthermore, it allows the conclusion that softbit-Source decoding is the limiting factor if applied to iterative decoding processes. Therefore, no significant gain will be obtainable by more than two iterations. This will be demonstrated by simulation

  • ICASSP - Iterative Source-channel Decoder using extrinsic information from softbit-Source decoding
    2001 IEEE International Conference on Acoustics Speech and Signal Processing. Proceedings (Cat. No.01CH37221), 1
    Co-Authors: Marc Adrat, Peter Vary, Julian Spittka
    Abstract:

    In digital mobile communications, efficient compression algorithms are needed to encode speech or audio signals. As the determined Source parameters are highly sensitive to transmission errors, robust Source and channel decoding schemes are required. This contribution deals with an iterative Source-channel decoding approach where a simple channel Decoder and a softbit-Source Decoder are concatenated. We mainly focus on softbit-Source decoding which can be considered as an error concealment technique. This technique utilizes residual redundancy remaining after Source coding. We derive a new formula that shows how the residual redundancy transforms into extrinsic information utilizable for iterative decoding. The derived formula opens several starting points for optimizations, e.g. it helps to find a robust index assignment. Furthermore, it allows the conclusion that softbit-Source decoding is the limiting factor if applied to iterative decoding processes. Therefore, no significant gain will be obtainable by more than two iterations. This will be demonstrated by simulation.

Julian Spittka - One of the best experts on this subject based on the ideXlab platform.

  • Iterative Source-channel Decoder using extrinsic information from softbit-Source decoding
    2001 IEEE International Conference on Acoustics Speech and Signal Processing. Proceedings (Cat. No.01CH37221), 2001
    Co-Authors: Marc Adrat, R. Vary, Julian Spittka
    Abstract:

    In digital mobile communications, efficient compression algorithms are needed to encode speech or audio signals. As the determined Source parameters are highly sensitive to transmission errors, robust Source and channel decoding schemes are required. This contribution deals with an iterative Source-channel decoding approach where a simple channel Decoder and a softbit-Source Decoder are concatenated. We mainly focus on softbit-Source decoding which can be considered as an error concealment technique. This technique utilizes residual redundancy remaining after Source coding. We derive a new formula that shows how the residual redundancy transforms into extrinsic information utilizable for iterative decoding. The derived formula opens several starting points for optimizations, e.g. it helps to find a robust index assignment. Furthermore, it allows the conclusion that softbit-Source decoding is the limiting factor if applied to iterative decoding processes. Therefore, no significant gain will be obtainable by more than two iterations. This will be demonstrated by simulation

  • ICASSP - Iterative Source-channel Decoder using extrinsic information from softbit-Source decoding
    2001 IEEE International Conference on Acoustics Speech and Signal Processing. Proceedings (Cat. No.01CH37221), 1
    Co-Authors: Marc Adrat, Peter Vary, Julian Spittka
    Abstract:

    In digital mobile communications, efficient compression algorithms are needed to encode speech or audio signals. As the determined Source parameters are highly sensitive to transmission errors, robust Source and channel decoding schemes are required. This contribution deals with an iterative Source-channel decoding approach where a simple channel Decoder and a softbit-Source Decoder are concatenated. We mainly focus on softbit-Source decoding which can be considered as an error concealment technique. This technique utilizes residual redundancy remaining after Source coding. We derive a new formula that shows how the residual redundancy transforms into extrinsic information utilizable for iterative decoding. The derived formula opens several starting points for optimizations, e.g. it helps to find a robust index assignment. Furthermore, it allows the conclusion that softbit-Source decoding is the limiting factor if applied to iterative decoding processes. Therefore, no significant gain will be obtainable by more than two iterations. This will be demonstrated by simulation.

Peter Vary - One of the best experts on this subject based on the ideXlab platform.

  • Reduced-Search Source Decoders for Iterative Source-Channel Decoding
    2011
    Co-Authors: Laurent Schmalen, Peter Vary, Marc Adrat
    Abstract:

    Iterative Source-channel decoding (ISCD) exploits the residual redundancy of Source codec parameters by using the Turbo principle. However, ISCD might require more computational complexity than available as the utilized soft decision Source Decoder (SDSD) can be computationally quite expensive. In this paper we propose a reduced-search SDSD, based on the M-algorithm known from channel decoding, which considerably reduces the complexity of the receiver. Furthermore, we show that by slightly modifying the quantization at the transmitter, the complexity can be further reduced without noticeable performance losses. Complexity figures are given for all approaches as well as a simulation example showing the performance of the complexity-reduced SDSD in an ISCD framework.

  • Iterative Source-channel decoding with cross-layer support for wireless VoIP
    2010
    Co-Authors: Tobias Breddermann, Peter Vary, Helge Lüders, Ismet Aktas, Florian Schmidt
    Abstract:

    This paper presents a cross-layer approach for iterative Source-channel decoding (ISCD) in wireless VoIP networks. The novelty of the proposed method is the incorporation of both, speech bits as well as protocol header bits, into the ISCD process. The header bits take the role of pilot bits having perfect reliability. These bits are distributed over the frame as strong supporting points for the MAP Decoder which. results in a significant enhancement of the output speech quality compared to the benchmark scheme using ISCD for speech only. For this approach, we exploit cross-layer concepts that support the direct communication between non-adjacent layers. These concepts enable the iterative exchange of extrinsic information between the Source Decoder located on the application layer and the channel Decoder located on the physical layer. This technique can also be applied to audio and video transmission.

  • Complexity-reduced iterative Source-channel decoding by conditional quantization
    2008 5th International Symposium on Turbo Codes and Related Topics, 2008
    Co-Authors: Laurent Schmalen, Marc Adrat, Peter Vary, Thorsten Clevorn
    Abstract:

    Iterative Source-channel decoding (ISCD) exploits the residual redundancy of Source codec parameters by using the Turbo principle. However, ISCD might require more computational complexity than available. The main reason is that the utilized soft decision Source Decoder (SDSD) can be computationally quite expensive. In this paper we propose a joint Source-channel coding approach which reduces the computational complexity of the SDSD by slightly modifying the quantizer such that the complexity of the Source Decoder is reduced. The complexity of the SDSD is further reduced by transforming the SDSD equations into the logarithmic domain. We give analytical expressions for the expected quality loss by the modified quantizer, simulation results showing the overall ISCD system performance, as well as complexity figures.

  • Iterative Source-coded equalization: turbo error concealment for ISI channels
    2007 IEEE 8th Workshop on Signal Processing Advances in Wireless Communications, 2007
    Co-Authors: Laurent Schmalen, Thorsten Clevorn, Peter Vary
    Abstract:

    In this paper, we analyze the behavior of soft decision Source decoding for ISI channels and present an iterative scheme similar to Turbo equalization allowing to combat efficiently intersymbol interference effects. In a first step, we investigate the behavior of different index assignments in the quantizer and show that gains are possible by iterative processing without any channel (de)coding. In a second step, we use short block codes resulting in redundant index assignments at the transmitter. The receiver does not perform any explicit channel decoding but exploits the additional redundancy of the index assignment in the soft decision Source Decoder. Furthermore, we show that a very simple channel precoder permits even larger gains without any additional decoding complexity. Moreover, the extension towards a flexible multi-mode system allowing a trade-off between channel quality and quantization quality over a wide range of channel conditions is presented.

  • Turbo decodulation: iterative combined demodulation and Source-channel decoding
    IEEE Communications Letters, 2005
    Co-Authors: Thorsten Clevorn, Marc Adrat, Johannes Brauers, Peter Vary
    Abstract:

    We propose the combination of iterative demodulation and iterative Source-channel decoding as a multiple turbo process. The receiver structures of bit-interleaved coded modulation with iterative decoding (BICM-ID), iterative Source-channel decoding (ISCD), and iterative Source coded modulation (ISCM) are merged to one novel turbo system, in which in two iterative loops reliability information is exchanged between the three single components, demodulator, channel Decoder and (softbit) Source Decoder. Simulations show quality improvements compared to the different previously known systems, which use iterative processing only for two components of the receiver.

Amir K. Khandani - One of the best experts on this subject based on the ideXlab platform.

  • Robust Transmission of Multistage Vector Quantized Sources Over Noisy Communication Channels—Applications to MELP Speech Codec
    IEEE Transactions on Vehicular Technology, 2006
    Co-Authors: Farshad Lahouti, Amir K. Khandani, A. Saleh
    Abstract:

    Joint Source-channel coding is an effective approach for the design of bandwidth efficient and error resilient communication systems with manageable complexity. An interesting research direction within this framework is the design of Source Decoders that exploit the residual redundancy for effective signal reconstruction at the receiver. Such Source Decoders are expected to replace the traditionally heuristic error concealment units that are elements of most multimedia communication systems. In this paper, we consider the reconstruction of signals encoded with a multistage vector quantizer (MSVQ) and transmitted over a noisy communications channel. The MSVQ maintains a moderate complexity and, due to its successive refinement feature, is a suitable choice for the design of layered (progressive) Source codes. An approximate minimum mean squared error Source Decoder for MSVQ is presented, and its application to the reconstruction of the linear predictive coefficient (LPC) parameters in mixed excitation linear prediction (MELP) speech codec is analyzed. MELP is a low-rate standard speech codec suitable for bandwidth-limited communications and wireless applications. Numerical results demonstrate the effectiveness of the proposed schemes

  • Vector Trellis Quantization for Noisy Channels
    Advances in Speech Coding, 1991
    Co-Authors: Mohammad Reza Soleymani, Amir K. Khandani
    Abstract:

    The channel coding theorem of information theory indicates that if the rate of a binary sequence is less than the capacity of the channel over which the binary sequence is to be transmitted, then the Source can be reproduced at the channel output with arbitrarily small error probability [1], [2]. Based on this, one can isolate the problem of channel coding from that of Source coding. In other words, channel encoder, channel, and channel Decoder may be considered as a noiseless link between the output of the Source encoder and the input of Source Decoder, as long as Source encoder’s output has a rate less than the capacity of the channel [3]. However, this separation is optimal only asymptotically, i.e., in the limit of arbitrarily complex overall encoders and Decoders involving arbitrarily long blocklengths. In practice, where we encounter the curse of complexity and are forced to deal with finite blocklengths, such a separation results in a certain degree of sub-optimality.

  • ICASSP (4) - Reconstruction of multi-stage vector quantized Sources over noisy channels - applications to MELP codec
    2004 IEEE International Conference on Acoustics Speech and Signal Processing, 1
    Co-Authors: Farshad Lahouti, Amir K. Khandani
    Abstract:

    The design of Source Decoders that employ the residual redundancy at the Source coder output is an interesting research direction in the joint Source channel coding framework. Such Decoders are expected to replace the traditionally heuristic error concealment units that are elements of most multimedia communication systems. In this work, we consider the reconstruction of signals encoded with a multi-stage vector quantizer (MSVQ) and transmitted over a noisy channel. The MSVQ maintains a moderate complexity and, due to its successive refinement feature, is a suitable choice for the design of layered (progressive) Source codes. An approximate MMSE Source Decoder for MSVQ is presented and its application to reconstruction of LPC parameters in MELP is analyzed. Numerical results demonstrates the effectiveness of the proposed schemes.