Hamming Coding of DCT-Compressed Images Over Noisy Channels

Theoretical and simulation results of using Hamming codes with the two-dimensional discrete cosine transform (2D-DCT) at a transmitted data rate of 1 bit/pixel over a binary symmetric channel (BSC) are presented. The design bit error rate (BER) of interest is 10^-2. The (7, 4), (15, 11), and (31, 26) Hamming codes are used to protect the most important bits in each 16 by 16 transformed block, where the most important bits are determined by calculating the mean squared reconstruction error (MSE) contributed by a channel error in each individual bit. A theoretical expression is given which allows the number of protected bits to achieve minimum MSE for each code rate to be computed. By comparing these minima, the best code and bit allocation can be found. Objective and subjective performance results indicate that using the (7, 4) Hamming code to protect the most important 2D-DCT coefficients can substantially improve reconstructed image quality at a BER of 10^-2. Furthermore, the allocation of 33 out of the 256 bits per block to channel coding does not noticeably degrade reconstructed image quality in the absence of channel errors.     

基于Hash函数和汉明码的半脆弱水印算法

提出了一种基于Hash函数和汉明码的分散式相关块半脆弱水印算法,用于图像完整性认证及内容篡改定位。将原始图像划分为互不重叠的块,进行多次Logistic混沌映射,定位每个块的相关块,得到汉明码编码需要的bit序列;进行汉明码编码,认证图像的完整性。实验结果表明,本文方案有较好的图像保护能力,能检测和定位各种恶意篡改,例如插入、模糊、锐化、对比度修改和爆裂位,能成功抵抗VQ攻击。     

比特交织Turbo编码调制的8PSK符号映射

基于对Turbo编码器输出的系统比特和校验比特的不等错误保护(UEP),提出了一种新的比特交织Turbo编码调制(BITCM)的8PSK符号映射方案,即对于码率为1/3的Turbo码,校验比特映射到8PSK星座点中具有较好传输性能的比特位置上,而系统比特映射到较差传输性能的比特位置上。实现新映射方案的关键是比特交织器的设计。仿真结果表明,新的映射方案在AWGN信道下,误码率为10-3时,可获得大于0.2dB的信噪比增益,而这一增益的获得并没有牺牲频谱效率和增加系统的复杂性。     

块级篡改定位的JPEG图像脆弱水印

 JPEG是一种常见的图像格式,在JPEG图像中进行准确的篡改定位具有重要意义. 本文提出一种新的JPEG图像脆弱水印方案,将每个小块主要内容的Hash比特重新分组,并将每组的模2和作为水印信息. 也就是说每一个小块都对应多个水印比特,每个水印比特也对应多个小块. 载体图像的每个小块中仅嵌入于1比特水印,保证了良好的隐蔽性. 认证时依据图像内容与水印比特的整体匹配情况估计篡改率,再根据每个小块对应的水印信息的被破坏程度判别该小块是否曾被篡改. 理论分析和实验结果标明该方法可以在篡改区域小于1%的情况下准确地找到所有篡改小块.     

A 50-ns CMOS 256 K EEPROM

A 32 K×8 EEPROM (electrically erasable programmable read-only memory), which operates with a single 5-V power supply and achieves 100 K cycle endurance, 50-ns typical read access time, and 1-ms page programming time, equivalent to 16 μs/byte, was designed. A double-poly, double-metal, n-well CMOS process with 1.25-μm minimum feature size was developed to manufacture the device. The required and optional extended JEDEC standards for software data protection and chip clear are implemented along with parity check, toggle bit, page-load timer, and data-protection status bit. A modified Hamming code, which uses four parity bits per byte, was implemented to detect and correct single-bit errors     

Construction of some binary linear codes of minimum distance five

A method of constructing binary linear codes that have a minimum Hamming distance of five is presented. The author proposes a general formulation of the parity check matrix for the desired code and then derives necessary conditions for the code to have a minimum distance of five. Some new codes that satisfy the necessary conditions are described. Some efficient new codes are obtained. In particular, a (47,36,5) code is obtained that has six more information bits than the best previously known code with 11 check bits     

Design of Embedded Self-Testing Checkers for t-UED and BUED Codes

In this article we present a new method for designing self-testing checkers for t-UED and BUED codes. The main idea of this method is to map words of the considered code to words of a code of the same type in which the value of t or the number of check bits is reduced and repeating this with the obtained words until a parity code is obtained, or to translate the code words into words of a code for which such a mapping is possible. First we consider Borden codes for t = 2 ^k – 1, Bose, and Bose-Lin codes. The mapping operation is realized by averaging weights and check symbol values of the code words. The resulting checkers have a simple and regular structure. This structure is independent on the set of code words that is provided by the circuit under check. The checkers are very well suited for use as embedded checkers since they are self-testing with respect to single stuck-at faults under very weak assumptions. All three checker types can be tested with 2 or 3 code words. We also propose a novel approach to design checkers for Blaum codes that require much less code word tests than existing solutions.     

高误码率下LDPC稀疏校验矩阵重建

针对LDPC重建问题,提出了一种可直接重建LDPC稀疏校验矩阵的算法。首先,根据传统重建算法原理,详细分析了传统重建算法存在的缺陷以及缺陷存在的原因;其次,基于LDPC稀疏矩阵的特性,通过多次随机抽取码字中部分比特序列进行高斯消元,同时为了可靠实现抽取的比特序列能包含校验节点,基于一次抽取包含校验节点的概率,确定多次随机抽取的次数;最后,在误码条件下,基于疑似校验向量关系成立的统计特性和最小错误判决准则,实现稀疏校验向量的判定。仿真结果表明,所提算法在误码率为0.001的条件下,针对目前IEEE 802.11协议中大部分LDPC的重建率能达到95%以上,且噪声稳健性优于传统的重建算法,同时所提重建算法不仅不再需要对校验矩阵稀疏化处理,而且对于双对角线与非双对角线形式的校验矩阵都具有较好的通用性。     

The Design of a High-Performance Error-Correcting Coding Scheme for the Canadian Broadcast Telidon System Based on Reed-Solomon Codes

Error correction can greatly improve the performance and extend the range of broadcast teletext systems. In this paper, the requirements for an error-correcting scheme for broadcast teletext in North America (NABTS) are set down. An error-correction scheme which meets all these requirements is then described. The simplest case employs the one parity bit in each 8 bit byte and no suffix of parity check bits at the end of each data block. The next level also uses a single byte of parity check bits at the end of each data block. Adding a second byte of parity checks at the end of each data block results in a Reed-Solomon code, called theCcode, for each data block. Adding one data block of parity checks afterh - 1data blocks results in a set ofhdata packets being encoded into a bundle, in which verticalCcodes provide powerful interleaving. In a final alternative, two data blocks hold the check bytes for the vertical codewords, and the most powerful coding scheme, the double bundle code, results. The detailed mathematical definitions of the various codes are referred to or described, formulas for performance calculations are referred to, and performance curves are presented for the AWGN channel as well as for measured field data. These performance curves are discussed and compared to the performance of a difference set cyclic code, originally designed for the Japanese teletext system, which corrects any 8 bits in error in a packet.     

A new approach to authentication of binary images for multimedia communication with distortion reduction and security enhancement

A new approach to binary image authentication in multimedia communication with distortion reduction and security enhancement is proposed. Special codes are embedded into the blocks of given images and verified to accomplish the authentication purpose. Enhancement of security in detecting tampered images is achieved by randomly generating the codes and embedding them into randomly selected locations in the image blocks. The reduction of image distortion coming from pixel value replacement in code embedding is carried out by allowing multiple locations for embedding the codes. Security analysis and experimental results are also included to show the effectiveness of the proposed approach.     

基于准循环LDPC码和SLM法降低PAPR的新方法

由于具有频谱利用率高、抗多径衰落能力强等优点,正交频分复用(OFDM)技术已成为通信领域的研究热点之一。但是OFDM技术中存在的高峰均功率比(PAPR),为其实用化设置了障碍。本文提出利用不规则准循环低密度奇偶校验(QC-LDPC)码作为信道编码技术,联合选择映射(SLM)算法抑制高峰均功率比。其中,不规则QC-LDPC码的生成矩阵由校验矩阵中的子矩阵直接构造得到。相对于传统的选择映射算法,该方法能发挥LDPC码和SLM法的联合优势,同时由于采用基于置信传播(BP)的迭代译码算法,计算复杂度低、译码速度快。仿真结果表明,该联合方法既能有效地改善OFDM信号的PAPR特性,又能保证系统获得可靠的误码率性能,且实现简单。      

基于JPEG压缩不变量和数字水印的图像认证方法

提出一种抗JPEG压缩的图像认证算法。根据图像不同块中位置相同的DCT系数之间的大小关系在JPEG压缩之后几乎没有发生变化这一性质,对图像进行分析生成特征编码,并将特征编码加密后以水印方式嵌入图像。认证时只需将待测图像的特征编码与从中抽取出的解密水印进行比较,利用篡改矩阵鉴别是否有内容被篡改,并给出具体的篡改位置。实验结果表明,该算法有很好的抗JPEG压缩性能,并可有效地检测出恶意篡改及其发生的位置。     

一种ECC校验算法的设计与实现

电可擦除可编程存储器(EEPROM)由于工艺结构的局限性而导致数据在存储过程中存在小概率的位反转问题。为解决该现象,设计了基于汉明码的纠错码(ECC)校验系统。结合EEPROM的结构特点和数据存储模式,该系统包含ECC校验码计算模块和数据检错纠错模块,每32 bit数据生成6 bit ECC校验码,具有1 bit/32 bit的纠错力。采用硬件描述语言Verilog HDL设计并实现了该ECC验证系统,并将其应用于基于串行外设接口(SPI)的EEPROM。仿真结果表明ECC验证系统可以保证数据的正确率,提高存储系统的可靠性。     

A quantization-based semi-fragile watermarking scheme for image content authentication

This paper presents a novel semi-fragile watermarking scheme for image content authentication with tampering localization. The proposed scheme uses a non-traditional quantization method to modify one chosen approximation coefficient of each non-overlapping block to ensure its robustness against incidental attacks and fragileness against malicious attacks. The image content authentication starts with extracting watermark using the parity of quantization results from the probe image, where the round operation is used to ensure the semi-fragile property. It then constructs a binary error map and computes two authentication measures with M₁ measuring the overall similarity between extracted and embedded watermarks and M₂ measuring the overall clustering level of tampered error pixels. These two measures are further integrated to confirm the image content and localize the possible tampered areas. Our experimental results show that our scheme outperforms four peer schemes and is capable of identifying intentional tampering and incidental modification, and localizing tampered regions.     

SVD-based self-embedding image authentication scheme using quick response code features

Image authentication is a type of technique for the content protection of digital images. This technique is able to detect and locate tampered regions on a digital image. In this paper, two self-embedding image authentication approaches are proposed to involve distinctive singular values. Both of them extract self-characteristics of an image as the crucial authentication information for that image. Subsequently, this information is converted into the two dimensional code format and that codes are then embedded into digital image pixels. With the capability of error correction in two dimensional codes, the extracted authentication data, even being detected with a tamper, still can be completely restored and errorless. As well, it can be utilized to detect whether an image has been tampered with or not. According to experimental results, the proposed approaches are superior to other schemes for images that have been modified to a certain attack extent because the authentication data could be completely extracted in more effective way, and the tampered regions could be identified more accurately. In addition, the proposed approaches utilize these complete self-characteristics to restore tampered regions into their original states.     

用于图像篡改定位和恢复的分层半脆弱数字水印算法

设计并实现了一种基于分层的半脆弱数字水印算法,用于图像内容完整性认证,篡改定位和恢复。在嵌入方,将水印信息嵌入到原始图像所有像素的2bit最低有效比特,其中认证水印由奇偶校验码和块与子块之间灰度平均值的比较组成;恢复水印为环面自同构映射块的平均灰度值。在检测方,采用分层思想,分3层对水印进行篡改定位和恢复。实验结果表明,该算法对局部发生的篡改可以有效地检测,精确定位并进行内容恢复,同时能够有效的抵抗矢量量化攻击。     

Improved image tamper localisation using chaotic maps and self-recovery

In this paper an image tamper localisation scheme is proposed in which authentication bits of a 2 × 2 image block are generated using the chaotic maps. Further the scheme is improved by including a self-recovery method to recover the tampered regions. To improve the quality of the recovered image, two different sets of restoration bits of a block are generated and each one is embedded into randomly selected distinct blocks. The proposed tamper detection scheme performs better than some of the recent schemes proposed by the researchers. The experimental results demonstrate the accuracy and fragility of the tamper detection scheme, and the efficacy of the recovery method.     

Modified Iterative Decoding Algorithm for Polar Code Using Maximum Likelihood Estimation

The key challenges in real time voice communication in long term evolution mobile are reduction in complexity and latency. Efficient encoding and decoding algorithms can cater to these. The implementation of such polar code based efficient algorithms is proposed in this paper. The overall latency of 3.8 ms is needed to process 8 bit block length. The novel sub-matrix near to identity matrix is presented. This resulted into minimization of loops among least reliable bits due to iterated parity check matrix. Look-up table based memory mapping is used in encoder to reduce latency while Euclidian decoding technique is used in decoder. The number of iterations is reduced by 50%. The experimentation is performed with additive white Gaussian noise and QPSK modulation. The proposed modified iterative decoding algorithm requires SNR of 5.5 dB and 192 computations for targeted bit error rate of 10^?4. The second proposed method needs 9 dB, 2 iterations for 384 computations. The penalty paid is quantization error of 0.63% due to restricting computations to fourth order series of hyperbolic function with same 8 bit block length.     

Combining fractal image compression and vector quantization

In fractal image compression, the code is an efficient binary representation of a contractive mapping whose unique fixed point approximates the original image. The mapping is typically composed of affine transformations, each approximating a block of the image by another block (called domain block) selected from the same image. The search for a suitable domain block is time-consuming. Moreover, the rate distortion performance of most fractal image coders is not satisfactory. We show how a few fixed vectors designed from a set of training images by a clustering algorithm accelerates the search for the domain blocks and improves both the rate-distortion performance and the decoding speed of a pure fractal coder, when they are used as a supplementary vector quantization codebook. We implemented two quadtree-based schemes: a fast top-down heuristic technique and one optimized with a Lagrange multiplier method. For the 8 bits per pixel (bpp) luminance part of the 512kappa512 Lena image, our best scheme achieved a peak-signal-to-noise ratio of 32.50 dB at 0.25 bpp.     

基于DVB-S2标准的LDPC码编译码器设计研究

研究了DVB-S2标准LDPC码编译码器的硬件结构,以16 200码长和0.6码率为例设计了基于共享内存和后验概率累加储存的译码器结构,不仅吞吐量大,而且寄存器和内存资源的消耗小。仿真分析了同码长不同码率和同码率不同码长的性能,当码长相等时,码率越低,则误码率、误帧率和平均迭代次数一般均越低。同码率不同码长的码组,虽然校验位和信息位的比例相等,但是码长越大,校验位和信息位的约束更强,性能越好。