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Comparison of constructions of irregular Gallager codes

IEEE TRANSACTIONS ON COMMUNICATIONS 1999年第10期47卷 1449-1454页

作者： Mackay, DJC Wilson, ST Davey, MC Univ Cambridge Dept Phys Cambridge CB3 0HE England

The low-density parity check codes whose performance is closest to the Shannon limit are "Gallager codes" based on irregular graphs. We compare alternative methods for constructing these graphs and present two results. First, we find a "super-Poisson" construction which gives a small improvement in empirical performance over a random construction. Second, whereas Gallager codes normally take N-2 time to encode, we investigate constructions of regular and irregular Gallager codes that allow more rapid encoding and have smaller memory requirements in the encoder. We find that these "fast encoding" Gallager codes have equally good performance.

关键词： hannel coding error correction coding Gaussian channels graph theory iterative probabilistic decoding random codes

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BCH code-based robust audio watermarking in the cepstrum domain

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JOURNAL OF INFORMATION SCIENCE AND ENGINEERING 2006年第3期22卷 535-543页

作者： Liu, Shi-Cheng Lin, Shinfeng D. Natl Dong Hwa Univ Dept Comp Sci & Informat Engn Hualien 974 Taiwan

In this article, a BCH code-based audio watermarking approach performed in the cepstrum domain is proposed. The technique takes advantage of the attack-invariant feature of the cepstrum domain and the error-correction capability of BCH code to increase the robustness of audio watermarking. In addition, the watermarked audio has very high perceptual quality. A blind watermark detection technique is developed to identify the embedded watermark under various types of attacks. Experiment results demonstrate that the proposed technique outperforms the existing audio watermarking techniques against most of the asynchronous attacks.

关键词： audio watermarking cepstrum domain permutation error correction coding BCH code

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One-Pulse FEC coding for Robust CELP-Coded Speech Transmission Over Erasure Channels

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IEEE TRANSACTIONS ON MULTIMEDIA 2011年第5期13卷 894-904页

作者： Gomez, Angel M. Carmona, Jose L. Gonzalez, Jose A. Sanchez, Victoria Univ Granada Fac Ciencias Dept Signal Theory Networking & Commun E-18071 Granada Spain

In this paper, we present an improved quantization scheme for the redundancy data of a forward error correction (FEC) technique proposed for the transmission of code-excited linear prediction (CELP)-coded speech over erasure channels. The use of a FEC-based error protection scheme is motivated by the well-known fact that, after a frame erasure, the previous excitation is not available and a desynchronization between the encoder and the decoder long-term prediction (LTP) filters appears, causing an additional distortion which is propagated to subsequent frames. LTP synchronization can be recovered by means of a single-pulse representation of the previous excitation. No additional delay is introduced by this technique which only requires a small transmission bandwidth increase. In this paper, we focus on the efficient encoding of this pulse. Thus, an optimization procedure, which takes into account the overall synthesis error, is proposed in order to provide better pulse-position and pulse-amplitude quantization codebooks. Moreover, by extending the previous procedure, an efficient joint position-amplitude quantization can be obtained. Objective quality tests applied to our proposal show that, by means of the proposed codebooks, the number of bits required to represent the resynchronization pulse is effectively reduced. In addition, a discontinuous transmission mechanism is derived from the cost functional used during joint position-amplitude quantization, further reducing the bit-rate.

关键词： Adaptive codebook code-excited linear prediction (CELP) error correction coding error propagation frame erasure speech coding

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Improving channel decoder performance on the CDMA forward link

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IEEE TRANSACTIONS ON WIRELESS COMMUNICATIONS 2005年第3期4卷 1064-1072页

作者： Messier, GG Krzymien, WA Univ Calgary Dept Elect & Comp Engn Calgary AB T2N 1N4 Canada Univ Alberta Dept Elect & Comp Engn Edmonton AB T6G 2V4 Canada TRLabs Edmonton AB T6G 2V4 Canada

This work improves channel decoder performance on the code-division multiple-access (CDMA) forward link through more accurate calculation of the channel code trellis path metrics used to decode convolutional and turbo codes. This is achieved by performing the metric calculations with better channel state estimates. Channel state estimation involves determining desired signal amplitude and interference plus noise variance at the channel decoder input. Two options are presented for performing this estimation. Standard estimation is a simple scheme that results from assuming all CDMA forward link interference and noise can be lumped into a single additive white Gaussian noise process. Improved estimation is a new and more accurate technique that separately accounts for the intracell interference and intercell interference plus thermal noise processes. Simulations show that the decoding of convolutional and turbo codes is significantly improved by the more accurate channel state information provided by improved estimation.

关键词： code-division multiple-access (CDMA) electromagnetic radiative interference error correction coding estimation Gaussian processes land mobile radio cellular systems multipath channels sequences turbo coding Viterbi decoding Walsh sequences

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Comparing Analytical, Micromagnetic and Statistical Channel Models at 4 Tcbpsi Patterned Media Recording

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IEEE TRANSACTIONS ON MAGNETICS 2012年第5期48卷 1826-1832页

作者： Chua, M. Elidrissi, M. R. Eason, K. Zhang, S. H. Qin, Z. L. Chai, K. S. Tan, K. P. Cai, K. Chan, K. S. Goh, W. L. Dong, Y. Victora, R. H. ASTAR Data Storage Inst Singapore 117608 Singapore Nanyang Technol Univ Sch Elect & Elect Engn Singapore 637457 Singapore Univ Minnesota Ctr Micromagnet & Informat Technol Dept Elect & Comp Engn Minneapolis MN USA

Bit patterned media recording (BPMR) is a candidate technology proposed to extend the areal density growth capability of magnetic recording systems. In conventional granular magnetic recording (CGMR), bits of information are recorded onto a number of randomly distributed magnetic grains. The difficulty for the granular media approach is that due to the randomness of the grains, a certain minimum number of grains are required in order to maintain the media signal to noise ratio (SNR). This requires smaller grains as the bits are shrunk and we end up with either unstable, or unwriteable grains as per the well-known media-trilemma. In BPMR, instead of random positions, the "grains" are ordered into a well-defined lattice of magnetic islands. Because of this ordering, the media SNR is no longer determined by the number of grains per bit as in CGMR, but is defined by the geometrical and magnetic distributions of the fabrication process of the media. Analytical models exist for BPMR, that flip grains in the media based on the switching field distribution (SFD) and the knowledge of the applied head field. On the other side, a statistical model for CGMR has been proposed that measures probabilities of grains flipping based on micromagnetic simulations, named the grain flipping probability (GFP) model. In this work, we adapt the GFP model for BPMR and perform a comparison between densities predicted via the analytical and GFP models, by processing the signals from these models with the appropriate detectors and LDPC (low density parity check) decoders.

关键词： Codes error correction error correction coding error detection coding signal processing

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A secure and robust object-based video authentication system

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EURASIP JOURNAL ON APPLIED SIGNAL PROCESSING 2004年第14期2004卷 2185-2200页

作者： He, DJ Sun, QB Tian, Q Inst Infocomm Res Singapore 119613 Singapore

An object-based video authentication system, which combines watermarking, error correction coding (ECC), and digital signature techniques, is presented for protecting the authenticity between video objects and their associated backgrounds. In this system, a set of angular radial transformation (ART) coefficients is selected as the feature to represent the video object and the background, respectively. ECC and cryptographic hashing are applied to those selected coefficients to generate the robust authentication watermark. This content-based, semifragile watermark is then embedded into the objects frame by frame before MPEG4 coding. In watermark embedding and extraction, groups of discrete Fourier transform (DFT) coefficients are randomly selected, and their energy relationships are employed to hide and extract the watermark. The experimental results demonstrate that our system is robust to MPEG4 compression, object segmentation errors, and some common object-based video processing such as object translation, rotation, and scaling while securely preventing malicious object modifications. The proposed solution can be further incorporated into public key infrastructure (PKI).

关键词： watermark authentication error correction coding cryptographic hashing digital signature

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Index coding With Side Information

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IEEE TRANSACTIONS ON INFORMATION THEORY 2011年第3期57卷 1479-1494页

作者： Bar-Yossef, Ziv Birk, Yitzhak Jayram, T. S. Kol, Tomer Technion Israel Inst Technol Dept Elect Engn IL-32000 Haifa Israel Google Haifa Engn Ctr IL-20692 Haifa Israel IBM Corp Almaden Res Ctr San Jose CA 95120 USA

Motivated by a problem of transmitting supplemental data over broadcast channels (Birk and Kol, INFOCOM 1998), we study the following coding problem: a sender communicates with n receivers R-1, ... ,R-n. He holds an input x is an element of {0, 1}(n) and wishes to broadcast a single message so that each receiver R-i can recover the bit x(i). Each R-i has prior side information about x, induced by a directed graph G on n nodes;R-i knows the bits of x in the positions {j vertical bar (i, j) is an edge of G }. G is known to the sender and to the receivers. We call encoding schemes that achieve this goal INDEXcodes for {0, 1}(n) with side information graph G. In this paper we identify a measure on graphs, the minrank, which exactly characterizes the minimum length of linear and certain types of nonlinear INDEX codes. We show that for natural classes of side information graphs, including directed acyclic graphs, perfect graphs, odd holes, and odd anti-holes, minrank is the optimal length of arbitrary INDEX codes. For arbitrary INDEX codes and arbitrary graphs, we obtain a lower bound in terms of the size of the maximum acyclic induced subgraph. This bound holds even for randomized codes, but has been shown not to be tight.

关键词： Broadcast channels code length error correction coding information cost

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An area efficient LDPC decoder using a reduced complexity min-sum algorithm

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INTEGRATION-THE VLSI JOURNAL 2012年第2期45卷 141-148页

作者： Chandrasetty, Vikram Arkalgud Aziz, Syed Mahfuzul Univ S Australia Sch Elect & Informat Engn Mawson Lakes SA 5095 Australia

Hardware implementation of Low-Density Parity-Check (LDPC) decoders using conventional algorithms such as Sum-Product or Min-Sum requires large amount of hardware resources. A rather simplistic way to reduce hardware resources is to reduce the intrinsic message quantization. However this adversely affects the bit error rate (BER) performance significantly. In this paper, a resource efficient LDPC decoder based on a reduced complexity Min-Sum algorithm is presented. It reduces the inter-connect complexity by restricting the extrinsic message length to 2 bits and also simplifies the check node operation. Simulation at the algorithmic level shows that the proposed decoder achieves BER performance better than that of a 3-bit Min-Sum decoder, and therefore addresses the problem of massive BER performance degradation of a 2-bit Min-Sum decoder. The reduction in algorithmic complexity and further hardware optimization of the variable node leads to significant savings in hardware resources compared to 3-bit Min-Sum. An LDPC decoder with a code length of 1152 bits has been implemented on a Xilinx FPGA using the proposed algorithmic and hardware enhancements. With a 0.1 dB BER performance gain to that of 3-bit Min-Sum decoder, the proposed decoder saves about 18% of FPGA slices and provides a higher throughput. (C) 2011 Elsevier B.V. All rights reserved.

关键词： Digital communication error correction coding Iterative decoding Field programmable gate array Logic design

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Coded-Aided Phase Tracking for Coherent Fiber Channels

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JOURNAL OF LIGHTWAVE TECHNOLOGY 2014年第6期32卷 1041-1047页

作者： Pan, Chunpo Kschischang, Frank R. Univ Toronto Edward S Rogers Sr Dept Elect & Comp Engn Toronto ON M5S 2J7 Canada

In coherent optical systems laser phase noise can interact with digital equalization to cause equalization-enhanced impairments, which are a major obstacle for applying higher order modulation formats in coherent optical systems with digital chromatic dispersion compensation. In this paper a code-aided expectation maximization method to track phase noise in such systems is presented. A common measure of laser phase noise is the linewidth. It is shown that with similar to 11% redundancy, the laser linewidth tolerance for 975 km transmission distance can be increased by 50%, or the system reach for a laser linewidth of 5 MHz can be doubled. A phase-noise-robust 16-point 4-4-4-4 ring constellation was found to have better performance compared to 16QAM and a 2-6-8 ring constellations. Performance can be further improved with a lower code rate and fewer pilot symbols. It is also shown that algorithmic complexity can be reduced without significant reduction in the performance by reducing iterations and using low complexity codes.

关键词： Communication systems digital filters equalizers error correction coding optical fiber communication phase noise

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A Multipulse-Based Forward error correction Technique for Robust CELP-Coded Speech Transmission Over Erasure Channels

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IEEE TRANSACTIONS ON AUDIO SPEECH AND LANGUAGE PROCESSING 2010年第6期18卷 1258-1268页

作者： Gomez, Angel M. Carmona, Jose L. Peinado, Antonio M. Sanchez, Victoria Univ Granada Dept Signal Theory Networking & Commun E-18071 Granada Spain

The widely used code-excited linear prediction (CELP) paradigm relies on a strong interframe dependency which renders CELP-based codecs vulnerable to packet loss. The use of long-term prediction (LTP) or adaptive codebooks (ACB) is the main source of interframe dependency in these codecs, since they employ the excitation from previous frames. After a frame erasure, previous excitation is unavailable and a desynchronization between the encoder and the decoder appears, causing an additional distortion which is propagated to the subsequent frames. In this paper, we propose a novel media-specific Forward error correction (FEC) technique which retrieves LTP-resynchronization with no additional delay at the cost of a very small bit of overhead. In particular, the proposed FEC code contains a multipulse signal which replaces the excitation of the previous frame (i.e., ACB memory) when this has been lost. This multipulse description of the previous excitation is optimized to minimize the perceptual error between the synthesized speech signal and the original one. To this end, we develop a multipulse formulation which includes the additional CELP processing and, in addition, can cope with the presence of advanced LTP filters and the usual subframe segmentation applied in modern codecs. Finally, a quantization scheme is proposed to encode pulse parameters. Objective and subjective quality tests applied to our proposal show that the propagation error due to LTP filter can practically be removed with a very little bandwidth increase.

关键词： Adaptive codebook code-excited linear prediction (CELP) error correction coding error propagation frame erasure speech coding

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