共查询到20条相似文献，搜索用时 31 毫秒
1.
One of the main challenges of coding theory is to construct linear codes with the best possible parameters. Various algebraic and combinatorial methods along with computer searches are used to construct codes with better parameters. Given the computational complexity of determining the minimum distance of a code, exhaustive searches are not feasible for all but small parameter sets. Therefore, codes with certain algebraic structures are preferred for both theoretical and practical reasons. In this work we focus on the class of constacyclic codes to first generate all constacyclic codes exhaustively over small finite fields of order up to 9 to create a database of best constacyclic codes. We will then use this database as a building block for a search algorithm for new quasi-twisted codes. Our search on constacyclic codes has revealed 16 new codes, i.e. codes with better parameters than currently best-known linear codes. Given that constacyclic codes are well known, this is a surprising result. Moreover, using the standard constructions of puncturing, shortening or extending a given code, we also derived 55 additional new codes from these constacyclic codes. Hence, we achieved improvements on 71 entries in the database of best-known codes. We use a search strategy that is comprehensive, i.e. it computes every constacyclic code for a given length and shift constant, and it avoids redundantly examining constacyclic codes that are equivalent to either cyclic codes or other constacyclic codes. 相似文献
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Mehmet Ozen 《Journal of The Franklin Institute》2007,344(5):790-799
We investigate the structure of codes over Galois rings with respect to the Rosenbloom-Tsfasman (shortly RT) metric. We define a standard form generator matrix and show how we can determine the minimum distance of a code by taking advantage of its standard form. We compute the RT-weights of a linear code given with a generator matrix in standard form. We define maximum distance rank (shortly MDR) codes with respect to this metric and give the weights of the codewords of an MDR code. Finally, we give a decoding technique for codes over Galois rings with respect to the RT metric. 相似文献
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The communication systems and disk or tape memory can sometimes cause clusters of errors, namely burst errors. There have been many designs in order to detect and even correct such errors. Recently, a new class of codes called m-spotty byte error correcting codes has found applications in high speed memory systems that employ random access memory chips wide Input/Output data, especially at 8, 16, or 32 bits. The MacWilliams identity provides the relationship between the weight distribution of a code and that of its dual code. Also, an interesting new metric called Rosenbloom–Tsfasman metric has been studied as an alternative metric for linear codes recently. In this paper, we combine these two interesting topics and introduce the m-spotty Rosenbloom–Tsfasman weights and the m-spotty Rosenbloom–Tsfasman weight enumerator of a binary code. Moreover, we prove a MacWilliams identity for the m-spotty Rosenbloom–Tsfasman weight enumerators. 相似文献
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Iván Blanco-Chacón Dionís Remón Camilla Hollanti Montserrat Alsina 《Journal of The Franklin Institute》2014
We develop a new transmission scheme for additive white Gaussian noisy (AWGN) channels based on Fuchsian groups from rational quaternion algebras. The structure of the proposed Fuchsian codes is nonlinear and nonuniform, hence conventional decoding methods based on linearity and symmetry do not apply. Previously, only brute force decoding methods with complexity that is linear in the code size exist for general nonuniform codes. However, the properly discontinuous character of the action of the Fuchsian groups on the complex upper half-plane translates into decoding complexity that is logarithmic in the code size via a recently introduced point reduction algorithm. 相似文献
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Ethical codes in the digital world: comparisons of the proprietary,the open/free and the cracker system 总被引：1，自引：0，他引：1
Jukka Vuorinen 《Ethics and Information Technology》2007,9(1):27-38
The digital world provides various ethical frames for individuals to become ethical subjects. In this paper I examine – in
a Foucauldian and Luhmannian way – the differences between three systems of communication: the proprietary, the open/free
and the cracker system. It is argued that all three systems provide a different set of ethical codes which one can be subjected
to. The language of each system is restricted and they cannot understand each other, they merely consider each other as the
environment. The systems generate a diversity of ethical codes as they give different shapes to digital objects. To proprietary
software companies digital objects are an instrument of financial profit. The free software/open source movement emphasises
transparency; the end user must be able to view and alter the source code. The cracker scene sees digital objects in a different
way. For this particular system, only copy-protected digital objects are appealing. Copy protection binds its target to the
world of matter. Breaking the protection is the ultimate challenge and a way to gain honour and status inside the cracker
scene. A copy-protected digital object is simultaneously an utmost example of the hidden source code (the open/free system),
a perfect artefact that can be owned and sold (the proprietary system) and a challenge to be cracked (the cracker system). 相似文献
6.
低密度奇偶校验（LDPC）码是一种具有稀疏奇偶校验矩阵的线性分组码,其性能可逼近香农限。由于其具有优异的性能,非常适合在未来的无线通信系统中应用,已成为信道编码领域的研究热点。DVB—s2是欧洲数字视频广播项目组在2003年开发出来的第二代卫星广播标准,采用了LDPC码作为前向纠错码。文章在分析LDPC码的基础上,研究... 相似文献
7.
The problem considered here is the optimal scheduling of a Boolean expression on a single-processor system. We consider a Boolean expression in which each Boolean variable represents the binary outcome (or return code) of a program module. The result of the expression may be known without executing all modules (e.g. an OR-operation is terminated as soon as one of the operands returns the value 1), so that the order in which the modules are executed influences the cost involved in finding the result. The optimisation discussed here consists in finding the operand arrangement that minimizes the average execution cost. The cost of each module represents the consumption of resources such as CPU time, elapsed time, number of input-outputs, etc. The assumptions regarding the modules are: (i) No module execution is the pre-requisite for the execution of another module. (ii) At each execution, the return code and the cost of a module do not depend on the sequence of execution. (iii) Over a number of executions, the return code and the cost of a module may be statistically dependent or a deterministic function of return codes and costs of other modules.A prototype scheduler is presented, that implements a sub-optimal strategy. It stores the Boolean expression in tabular form, passes control to a module at a time, as needed for the Boolean computation, measures the cost of execution and decides empirically what operand arrangement is more advantageous. 相似文献
8.
Catherine Watson Jeff McCarthy Jennifer Rowley 《International Journal of Information Management》2013
This exploratory online questionnaire-based study confirms the findings from earlier studies in the pre-smart phone era regarding consumers’ negative attitudes towards mobile marketing communications. This study shows that these attitudes persist despite increasing frequency of use and increased functionality of mobile phones in the smart phone era. Consumers perceive their mobile device to be for personal communication, and prefer to be able to exercise control over their interaction with organisations. Findings suggest that acceptance can be enhanced by permission marketing, trust-building, creating a sense of being in control, and useful and entertaining website content. Accordingly, pull technologies seem to hold particular promise for mobile marketing communications. This study, therefore, proceeds to explore use of and attitudes towards an important pull technology, QR codes. QR codes, two-dimensional bar codes, can be scanned to provide access to websites, information and applications. Despite their potential, uptake is low. Users in this study who had scanned a QR code had used them to access a variety of different content on different types of items and in different locations. The most frequently accessed type of content was information on a web site, the two most common locations for a scanned QR code were a newspaper or magazine advert, or outdoor advert or poster, and the two most common locations at which scanning was performed were in the street and at home. Ease of use, utility and incentives are drivers to continued use whilst lack of knowledge about how-to scan or of the benefits of QR codes may hinder adoption. Recommendations are offered for practice and for further research. 相似文献
9.
阐述了巴克码组的定义和7位巴克码识别器的组成框图。在MAX PLUS2软件平台上,给出了利用现场可编程门阵列器件设计7位巴克码识别器电路,为了便于对设计的7位巴克码识别器进行检测,该电路还设计了一个周期为31位长的模拟7位巴克码产生器,并进行了编译和波形仿真。综合后下载到可编程器件EPF10K10LC84-4中,测试结果表明,达到了预期的设计要求。 相似文献
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In wireless communications, the channel is typically modeled as a random, linear, time-varying system that spreads the transmitted signal in both time and frequency due to multi-path propagation and Doppler effects. Estimated channel parameters allow system designers to develop coherent receivers that increase the system performance. In this paper, we show how time-frequency analysis can be used to model and estimate the time-varying channel of a multi-carrier spread spectrum (MCSS) system using a complex quadratic sequence as the spreading code. We will show that for this spreading code, the effects of time delays and Doppler frequency shifts, caused by the mobility of environment objects, can be combined and represented effectively as time shifts. The discrete evolutionary transform (DET), as a time-frequency analysis method, enables us to estimate the effective time shifts via a spreading function and to use them to equalize the channel. Using the effective time shifts, the time-varying channel can be represented simply as linear-time invariant system by embedding the Doppler shifts that characterize the time-varying channel into effective time shifts. The channel parameters are used to estimate the data bit sent. To illustrate the performance of the proposed method we perform several simulations with different levels of channel noise, jammer interference, and Doppler frequency shifts. 相似文献
12.
一种基于自修改代码技术的软件保护方法 总被引：1，自引：0，他引：1
提出一种基于自修改代码(SMC)技术的软件保护方法,该方法通过将关键代码转换为数据存储在原程序中,以隐藏关键代码;受保护的可执行文件执行过程中,通过修改进程中存储有隐藏代码的虚拟内存页面属性为可执行,实现数据到可执行代码的转换. 实验证明,此软件保护方法简单,易实现,可以有效提高SMC的抗逆向分析能力. 相似文献
13.
Tornado码二部图构造是一个非常重要的问题。基于PEG算法构造LDPC码二部图时显现的各种优点,本文提出了一种改进的PEG构图算法。仿真结果表明,改进的算法比原PEG算法有更快的执行速度,并且基于此算法构造的Tornado码也比原始的Tornado码有更好的性能。 相似文献
14.
本文用开球去刻画分形几何中开集条件（OSC）的开集,并得出一些结论。这些结论对一类函数迭代系统（ISF）是否满足开集条件,只需通过验证是否满足一维等价不等式组,而给出了肯定的回答。 相似文献
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Cheng-Chun Chang 《Journal of The Franklin Institute》2010,347(7):1368-1373
Low-density generator matrix (LDGM) codes have recently drawn researchers’ attention thanks to their satisfying performance while requiring only moderate encoding/decoding complexities as well as to their applicability to network codes. In this paper, we aim to propose a fast simulation method useful to investigate the performance of LDGM code. Supported by the confidence interval analysis, the presented method is, for example, 108 times quicker than the Monte-Carlo computer simulation for bit-error-rate (BER) in 10−10 region. 相似文献
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m序列扩频系统抗干扰能力分析 总被引：1，自引：0，他引：1
扩频技术由于其本身具备的优良性能而得到广泛应用,其最主要的应用是军事抗干扰通信,直扩系统则是这一领域应用最多的奇扩频方式之一。本文以基于m序列的直扩系统为例,详细分析了其抗各类干扰的能力,指出m序列的相关性和随机性是扩频系统抗干扰的直接原因,提出寻找理想的扩频码来提高扩频系统的抗干扰能力。 相似文献
20.
《Information processing & management》2020,57(6):102288
Deep hashing has been an important research topic for using deep learning to boost performance of hash learning. Most existing deep supervised hashing methods mainly focus on how to effectively preserve the similarity in hash coding solely depending on pairwise supervision. However, such pairwise similarity-preserving strategy cannot fully explore the semantic information in most cases, which results in information loss. To address this problem, this paper proposes a discriminative dual-stream deep hashing (DDDH) method, which integrates the pairwise similarity loss and the classification loss into a unified framework to take full advantage of label information. Specifically, the pairwise similarity loss aims to preserve the similarity and structural information of high-dimensional original data. Meanwhile, the designed classification loss can enlarge the margin between different classes which improves the discrimination of learned binary codes. Moreover, an effective optimization algorithm is employed to train the hash code learning framework in an end-to-end manner. The results of extensive experiments on three image datasets demonstrate that our method is superior to several state-of-the-art deep and non-deep hashing methods. Ablation studies and analysis further show the effectiveness of introducing the classification loss in the overall hash learning framework. 相似文献