Unequal Error Protection Codes Research Articles

A Serial Unequal Error Protection Code System Using Multilevel Trellis Coded Modulation with Ring‐type Signal Constellations for AWGN Channels

AbstractWe propose a serial unequal error protection (UEP) code system for use with information sources that contain a mixture of both important and less important data. To achieve UEP, the proposed scheme uses a form of Trellis coded modulation (TCM) which encodes the data by switching between some codes that use different signal constellations. So we propose ring‐type signal constellations with M levels of importance (MRING). Also, as no extra information about which code is used is added, the receiver estimates which code was used in the transmitter by examining the received signal points. In this paper, theoretical analyses of the 2RING signal constellations (that is, for M = 2) and TCM codes are presented, and the effectiveness and the validity of the system for additive white Gaussian noise (AWGN) channels are confirmed using theoretical analyses and computer simulations. Copyright © 2010 Institute of Electrical Engineers of Japan. Published by John Wiley & Sons, Inc.

Image Watermarking Scheme With Unequal Protection Capability Based on Error Correcting Codes

We propose a novel image watermarking scheme capable of providing unequal protection levels to different regions. In the scheme, we firstly construct the unequal error protection (UEP) code by designing an unequal coding space using algebra means, then we divide the image into high protection region, low protection region and non-protection region, and use the UEP code to encode the bits generated by high and low protection regions simultaneously and form the watermark bits to embed in the non-protection region. On the receiver side, the extracted bits with UEP capability can restore the high protection region more correctly than the low protection region after the efficient decoding algorithm is applied.

Decentralised distributed fountain coding: asymptotic analysis and design

A class of generic decentralised distributed fountain coding schemes is introduced and the tools of analysis of the performance of such schemes are presented. It is demonstrated that the developed approach can be used to formulate a robust code design methodology in a number of instances. We show that two non-standard applications of fountain codes, fountain codes for distributed source coding and fountain codes for unequal error protection lie within this decentralised distributed fountain coding framework.

On Unequal Error Protection of Convolutional Codes From an Algebraic Perspective

In this paper, convolutional codes are studied for unequal error protection (UEP) from an algebraic theoretical viewpoint. We first show that for every convolutional code there exists at least one optimal generator matrix with respect to UEP. The UEP optimality of convolutional encoders is then combined with several algebraic properties, e.g., systematic, basic, canonical, and minimal, to establish the fundamentals of convolutional codes for UEP. In addition, a generic lower bound on the length of a UEP convolutional code is proposed. Good UEP codes with their lengths equal to the derived lower bound are obtained by computer search.

UEP Concepts in Modulation and Coding

First unequal error protection (UEP) proposals date back to the 1960's (Masnick and Wolf; 1967), but now with the introduction of scalable video, UEP develops to a key concept for the transport of multimedia data. The paper presents an overview of some new approaches realizing UEP properties in physical transport, especially multicarrier modulation, or with LDPC and Turbo codes. For multicarrier modulation, UEP bit-loading together with hierarchical modulation is described allowing for an arbitrary number of classes, arbitrary SNR margins between the classes, and arbitrary number of bits per class. In Turbo coding, pruning, as a counterpart of puncturing is presented for flexible bit-rate adaptations, including tables with optimized pruning patterns. Bit- and/or check-irregular LDPC codes may be designed to provide UEP to its code bits. However, irregular degree distributions alone do not ensure UEP, and other necessary properties of the parity-check matrix for providing UEP are also pointed out. Pruning is also the means for constructing variable-rate LDPC codes for UEP, especially controlling the check-node profile.

Creation of Unequal Error Protection Codes for Two Groups of Symbols

Creation of Unequal Error Protection Codes for Two Groups of SymbolsThis article presents problems of unequal information importance. The paper discusses constructive methods of code generation, and a constructive method of generating asymptotic UEP codes is built. An analog model of Hamming's upper bound and Hilbert's lower bound for asymptotic UEP codes is determined.

New Table-Switching and Data-Multiplexing Schemes of Rate-Compatible Punctured Convolutional Codes for Unequal Error Protection

In this letter, rate-compatible punctured convolutional (RCPC) codes are further investigated for the application to unequal error protection (UEP). Besides the rate-compatible restriction, we show that puncturing tables should be switched in a special way called soft-switching to guarantee the designed UEP performance. A new data-multiplexing scheme is also proposed for RCPC codes which can achieve similar UEP performance as the conventional scheme but requires no extra zero-padding for frame termination to improve the system throughput.

Error Spreading Control in Image Steganographic Embedding Schemes Using Unequal Error Protection

A steganographic scheme proposed by van Dijk and Willems can alter a relatively small amount of bits to hide the secret compared to other schemes while reducing the distortion and improving the resistance against the steganalysis. However, one bit error in the embedding scheme by van Dijk and Willems may result in multibit error when extracting the hidden data. This problem is called as error spreading. It is observed that only some single-bit errors suffer from error spreading. In this paper, we propose a new steganographic solution which takes advantage of unequal error protection codes and allows for the different protection of different secret bits. Thus the proposed solution can effectively protect bits which could suffer from error spreading. In addition, it saves parity bits, thus greatly reducing the amount of bit alterations compared to the relevant previous schemes. Experimentation using various test images indicates that the proposed solution achieves the tradeoff between the performance and the protection of the embedded secret.

Turbo Equalization With Single-Parity Check Codes and Unequal Error Protection Codes

The performance of turbo equalization with interleaved single-parity check codes on partial-response channels is evaluated. Single-parity check codes are weak codes, but are shown to have modest performance gain. The proposed system achieves gains of 3.5, 3.4, 2.7, and 2.4 dB with code rates of 19/20,24/25,49/50, and 63/64, respectively, at a BER of 10-5. The complexity of the proposed decoder is significantly lower than that of turbo equalization using standard low-density parity-check codes. These single-parity check codes are modified to be unequal error protection codes, designed to decrease the probability that Viterbi error events span Reed-Solomon symbol boundaries, resulting in a decrease of the sector error rate. Once such code gains an additional 0.1 dB over a single-parity check code of the same code rate of 24/25

Source-optimized irregular repeat accumulate codes with inherent unequal error protection capabilities and their application to scalable image transmission

The common practice for achieving unequal error protection (UEP) in scalable multimedia communication systems is to design rate-compatible punctured channel codes before computing the UEP rate assignments. This paper proposes a new approach to designing powerful irregular repeat accumulate (IRA) codes that are optimized for the multimedia source and to exploiting the inherent irregularity in IRA codes for UEP. Using the end-to-end distortion due to the first error bit in channel decoding as the cost function, which is readily given by the operational distortion-rate function of embedded source codes, we incorporate this cost function into the channel code design process via density evolution and obtain IRA codes that minimize the average cost function instead of the usual probability of error. Because the resulting IRA codes have inherent UEP capabilities due to irregularity, the new IRA code design effectively integrates channel code optimization and UEP rate assignments, resulting in source-optimized channel coding or joint source-channel coding. We simulate our source-optimized IRA codes for transporting SPIHT-coded images over a binary symmetric channel with crossover probability p. When p = 0.03 and the channel code length is long (e.g., with one codeword for the whole 512 x 512 image), we are able to operate at only 9.38% away from the channel capacity with code length 132380 bits, achieving the best published results in terms of average peak signal-to-noise ratio (PSNR). Compared to conventional IRA code design (that minimizes the probability of error) with the same code rate, the performance gain in average PSNR from using our proposed source-optimized IRA code design is 0.8759 dB when p = 0.1 and the code length is 12800 bits. As predicted by Shannon's separation principle, we observe that this performance gain diminishes as the code length increases.

On Unequal Error Protection LDPC Codes Based on Plotkin-Type Constructions

We introduce a new family of unequal error protection (UEP) codes, based on low-density parity-check (LDPC) component codes and Plotkin-type constructions. The codes are decoded iteratively in multiple stages, and the order of decoding determines the level of error protection. The level of UEP among the code bits is also influenced by the choice of the LDPC component codes and by some new reliability features incorporated into the decoding process. The proposed scheme offers a very good tradeoff between code performance on one side and encoding/decoding and storage complexity on the other side. The novel approach to UEP also allows for finding simple approximations for the achievable degrees of UEP, which can be used to govern practical code design implementations

A low-complexity FEC assignment scheme for motion JPEG2000 over wireless network

An FEC (forward error correction) assignment scheme for motion JPEG2000 is proposed, which is dedicated to video transmission over wireless network. While most existing unequal error protection code assignment schemes are based on trial-and-error iterations, which are computationally intensive and thus unsuitable for real-time applications, the proposed scheme uses the slope of the rate-distortion curve to choose a code for each quality layer. The FEC code for the first layer is chosen so that the probability of error in the layer is limited to a given permissible range. Comparison with conventional schemes demonstrates that the proposed scheme can provide the PSNR performance similar to that of conventional schemes, while its execution time is much lower.

New results on unequal error protection using LDPC codes

In this letter, we propose a new scheme to construct low-density parity-check (LDPC) codes that are suitable for unequal error protection (UEP). We derive UEP density evolution (UDE) formulas for the proposed ensemble over the binary erasure channel (BEC). Using the UDE formulas, high performance UEP codes can be found. Simulation results depict an improvement in the bit error rate of more important bits in comparison with previous results on UEP-LDPC codes.

Constructing linear unequal error protection codes from algebraic curves

We show that the concept of generalized algebraic geometry codes which was introduced by Xing, Niederreiter, and Lam (see ibid., vol.45, p.2498-2501, Nov. 1999) gives a natural framework for constructing linear unequal error protection codes.

Notes on a construction of error correcting codes

AbstractThis paper proposes a new construction method for error correcting codes and its decoding method. The code proposed in this paper (code KI) maps the symbol of error correcting codes over a certain finite field onto another class of error correcting codes. In this sense, the code can be interpreted as a generalization of the conventional error correcting codes. The proposed codes have the following features. (1) The codes are fundamentally suitable for unequal error protection (UEP) codes. (2) Maximum likelihood decoding can be used efficiently in part. (3) There exists a coding parameter enabling improvement of performance in comparison to the conventional codes in the region of small SN ratios. In this paper, the principle of the proposed codes, encoding method, decoding method, and performance are discussed. Further, it is shown that the proposed codes provide a chance to discuss the problems of efficiency enhancement, synchronization characteristics, and unequal error correcting characteristics from a new point of view. © 2003 Wiley Periodicals, Inc. Electron Comm Jpn Pt 3, 86(11): 65–74, 2003; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjc.1155

Modified Plotkin bound for unequal error protection codes

The modified Plotkin bound for unequal error protection (UEP) codes is derived. Based on the separation vector of UEP codes, the authors adopt the average separation of all information digits of a given UEP code, and replacing it with minimum distance in the normal Plotkin bound leads to the new bound, which is valid for both linear and nonlinear UEP codes.

Soft-combining technique for LUEP codes

Decoding of linear unequal error protection (LUEP) codes using soft-combining is presented. Codewords are repeated and combined until the desired reliability is obtained. The decoding is performed in the spectral domain, offering reduced implementation complexity. Simulations show a significant performance improvement with soft-combining compared to soft decision decoding.

Path-compatible pruned convolutional (PCPC) codes

Path pruning, a new coding concept to achieve free distance enlargement for convolutional codes, is proposed. Through path pruning, every convolutional code can be used for unequal error protection (UEP), no matter whether it is originally a UEP code. To avoid undesired path discontinuity and reduce possible path distance loss, a cascaded implementation together with a path-compatible criterion is proposed, under which path-compatible pruned convolutional (PCPC) codes are constructed. Necessary and sufficient conditions are also derived for a subclass of PCPC codes whose decoding can be done by a single decoder for the parent code. Finally, some PCPC codes with good UEP capabilities found by computer search are given.

Unequal error protection TCM codes

A family of unequal error protection (UEP) codes using multilevel codes and a four-way partition of one-dimensional lattice is considered. The non-regular set partitioning combined with nonuniform signal constellation yields codes with large minimum distance and small path multiplicity. However, this is not in itself sufficient for reliable coding gain estimation. New code search methods are introduced for better estimation of actual coding gain results. Codes are presented which permit resolution of phase ambiguities while providing gain comparable to the best previously published results.

A Multimode and Variable‐Rate Voice Communications System with Source‐Matched Error Protection for Mobile Communications

AbstractThis paper presents a performance evaluation of the multimode Fast Variable Rate CELP coder developed by CSELT S.p.A. in the UMTS Code Division Testbed (CODIT) Project [1] for applications involving channels with time‐varying error characteristics. The radio channel is statistically modelled by one Rician or Rayleigh‐distributed desired signal and several uncorrelated Rayleigh plus log‐normally shadowed interfering signals, propagating according to two different laws: a dual path loss law with a turning point (microcellular environment) and a single path loss law (macrocellular environment). For channels with these error characteristics, each mode of the Fast Variable Rate CELP coder has a particular allocation of bits between source and channel coding stages, leading to an unequal error protection code tailored to suit the different error sensitivities of the source bits. It is shown that, on the basis of the sensitivity evaluation of source bits to errors, according to two different error sensitivity measures. Forward Error Correction whose power is matched to the error sensitivity of the source bits can be used. Increased robustness of source bits to errors can thus be obtained while satisfying bandwidth requirements.