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1.
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   

2.
Though many compression methods are based on the use of variable length codes, there has recently been a trend to search for alternatives in which the lengths of the codewords are more restricted, which can have useful applications, such as easier processing and fast decoding. This paper explores the construction of variable-to-fixed length codes, which have been suggested long ago by Tunstall. Using new heuristics based on suffix trees, the performance of Tunstall codes can in some cases be improved by more than 40%.  相似文献   

3.
This paper considers the problem of detecting the optimal spreading codes (OSC) in a given code set for a direct sequence-code division multiple access system that employs despreading sequences weighted by adjustable chip waveforms. Due to computational complexity required to detect the OSC in a code set, a simple and efficient strategy is introduced. Analysis and numerical results show that the proposed strategy can successfully distinguish the spreading codes being most suitable references for a given code set in which the candidate spreading codes have equal crosscorrelation properties.  相似文献   

4.
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   

5.
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   

6.
A trie represented by a double-array enables us to search a key fast with a small space. However, the double-array uses extra space to be updated dynamically. This paper presents a compact structure for a static double-array. The new structure keeps character codes instead of indices in order to compress elements of the double-array. In addition, the new structure unifies common suffixes and consists of less elements than the old structure. Experimental results for English keys show that the new structure reduces space usage of the double-array up to 40%.  相似文献   

7.
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   

8.
We obtain extremal binary self-dual codes of parameters [64,32,12] as binary images of self-dual codes over R1, R2 and R3 by employing different methods. We then apply the extension theorem to these codes to obtain a number of extremal binary self-dual codes of length 66 with trivial automorphism groups. Fifteen of the codes we obtain have new ββ values in W66,3, of which only three were known to exist before. We also find nine codes with new ββ values in W66,1, thus updating the list of such known codes.  相似文献   

9.
Similarity search with hashing has become one of the fundamental research topics in computer vision and multimedia. The current researches on semantic-preserving hashing mainly focus on exploring the semantic similarities between pointwise or pairwise samples in the visual space to generate discriminative hash codes. However, such learning schemes fail to explore the intrinsic latent features embedded in the high-dimensional feature space and they are difficult to capture the underlying topological structure of data, yielding low-quality hash codes for image retrieval. In this paper, we propose an ordinal-preserving latent graph hashing (OLGH) method, which derives the objective hash codes from the latent space and preserves the high-order locally topological structure of data into the learned hash codes. Specifically, we conceive a triplet constrained topology-preserving loss to uncover the ordinal-inferred local features in binary representation learning. By virtue of this, the learning system can implicitly capture the high-order similarities among samples during the feature learning process. Moreover, the well-designed latent subspace learning is built to acquire the noise-free latent features based on the sparse constrained supervised learning. As such, the latent under-explored characteristics of data are fully employed in subspace construction. Furthermore, the latent ordinal graph hashing is formulated by jointly exploiting latent space construction and ordinal graph learning. An efficient optimization algorithm is developed to solve the resulting problem to achieve the optimal solution. Extensive experiments conducted on diverse datasets show the effectiveness and superiority of the proposed method when compared to some advanced learning to hash algorithms for fast image retrieval. The source codes of this paper are available at https://github.com/DarrenZZhang/OLGH .  相似文献   

10.
Authors and searchers usually express the same things in many different ways, which causes problems in free text searching of text databases. Thus, a switching tool connecting the different names of one concept is needed. This study tests the effectiveness of a thesaurus as a search-aid in free text searching of a full text database. A set of queries was searched against a large full text database of newspaper articles. The search-aid thesaurus constructed for the test contains the usual relationships of a thesaurus, namely equivalence, hierarchical, and associative relationships. Each query was searched in five distinct modes: basic search, synonym search, narrower term search, related term search, and union of all previous searches. The basic searches contained only terms included in the original query statements. In the synonym searches, the terms of the basic search were extended by disjunction of the synonyms given by the search-aid thesaurus without modifying the overall logic of the basic search. Likewise, the basic search was extended in turn with the narrower terms and with the related terms given by the search-aid thesaurus. The last search mode included the basic terms and all the terms used in the previous searches. The searches were analyzed in terms of relative recall and precision; relative recall was estimated by setting the recall of the union search to 100%. On the average the value of relative recall was 47.2% in the basic search, compared with 100% in the union search; the average value of precision decreased only from 62.5% in the basic search to 51.2% in the union search.  相似文献   

11.
基于变长Turbo码的联合信源信道译码通过构造联合译码平面网格图,具有比比特级译码更好的性能.但平面网格图复杂,使变长Turbo码译码复杂度高.基于此,构造了一个空间网格图,提出基于变长Turbo码的低复杂度联合信源信道译码方法.仿真结果表明,该算法比平面网格图计算复杂度减少约3.8%,在SER(symbol error ratio)为10-4时,获得Eb/N0增益约为0.2dB.  相似文献   

12.
对一类有理数域上的代数曲线,构造出了它们的K2群中的一些元素,并证明了这些元素之间一些有趣的线性关系;同时,还讨论了这些元素的整性质.  相似文献   

13.
By using a bilinear transformation and some linear algebraic techniques, new matrix bounds of the solution of the continuous algebraic Lyapunov equation (CALE) are derived in this paper. Comparing to existing works, these obtained matrix bounds are less restrictive and are easy to be calculated. A numerical example is also given to demonstrate the merits of the present results.  相似文献   

14.
刘立冬 《现代情报》2014,34(2):151-153
CNKI系列数据库提供多途径的索引导航方式来全面提升服务功能和效果。针对同一个作者进行“作者发文情况”的检索可以有多种途径去实现,同时,选择的检索途径不同,登录方式和检索结果会有相应差异。以作者姓名为检索字段,以作者的发文情况为检索目的,通过具体的检索实例,为用户提供检索方法和技巧的示范,并在示范过程中,为用户使用作者发文检索功能提供有效地检索建议。另外,对于在作者发文检索使用过程中出现的一些问题,提出针对数据库的改进建议。  相似文献   

15.
The need to economically identify rare subjects within large, poorly mapped search spaces is a frequently encountered problem for social scientists and managers. It is notoriously difficult, for example, to identify “the best new CEO for our company,” or the “best three lead users to participate in our product development project.” Mass screening of entire populations or samples becomes steadily more expensive as the number of acceptable solutions within the search space becomes rarer.The search strategy of “pyramiding” is a potential solution to this problem under many conditions. Pyramiding is a search process based upon the idea that people with a strong interest in a topic or field tend to know people more expert than themselves. In this paper we report upon four experiments empirically exploring the efficiency of pyramiding searches relative to mass screening. We find that pyramiding on average identified the most expert individual in a group on a specific topic with only 28.4% of the group interviewed - a great efficiency gain relative to mass screening. Further, pyramiding identified one of the top 3 experts in a population after interviewing only 15.9% of the group on average. We discuss conditions under which the pyramiding search method is likely to be efficient relative to screening.  相似文献   

16.
Dictionary-based query translation for cross-language information retrieval often yields various translation candidates having different meanings for a source term in the query. This paper examines methods for solving the ambiguity of translations based on only the target document collections. First, we discuss two kinds of disambiguation technique: (1) one is a method using term co-occurrence statistics in the collection, and (2) a technique based on pseudo-relevance feedback. Next, these techniques are empirically compared using the CLEF 2003 test collection for German to Italian bilingual searches, which are executed by using English language as a pivot. The experiments showed that a variation of term co-occurrence based techniques, in which the best sequence algorithm for selecting translations is used with the Cosine coefficient, is dominant, and that the PRF method shows comparable high search performance, although statistical tests did not sufficiently support these conclusions. Furthermore, we repeat the same experiments for the case of French to Italian (pivot) and English to Italian (non-pivot) searches on the same CLEF 2003 test collection in order to verity our findings. Again, similar results were observed except that the Dice coefficient outperforms slightly the Cosine coefficient in the case of disambiguation based on term co-occurrence for English to Italian searches.  相似文献   

17.
A new method of index term dictionary compression in an inverted-file-orientated database is discussed. A technique of word coding that generates short fixed-length codes obtained from the index terms themselves by analysis of monogram and bigram statistical distributions is described. Transformation of the index term dictionary into a code dictionary preserves a word-to-word discrimination with a rate of three synonyms per 1300 terms, at compression ratio up to 90% and at low cost in terms of the CPU time expenditure. When applied in computer network environment, it offers substantial savings in communication channel utilization at negligible response time degradation. Experimental data for 26,113 index term dictionary of the New York Times Info Bank available via a computer network are presented.  相似文献   

18.
An experimental computer intermediary system, CONIT, that assists users in accessing and searching heterogeneous retrieval systems has been enhanced with various search aids. Controlled experiments have been conducted to compare the effectiveness of the enhanced CONIT intermediary with that of human expert intermediary search specialists. Some 16 end users, none of whom had previously operated either CONIT or any of the four connected retrieval systems, performed searches on 20 different topics using CONIT with no assistance other than that provided by CONIT itself (except to recover from computer/software bugs). These same users also performed searches on the same topics with the help of human expert intermediaries who searched using the retrieval systems directly. Sometimes CONIT and sometimes the human expert were clearly superior in terms of such parameters as recall and search time. In general, however, users searching alone with CONIT achieved somewhat higher online recall at the expense of longer session times. We conclude that advanced experimental intermediary techniques are now capable of providing search assistance whose effectiveness at least approximates that of human intermediaries in some contexts. Also analyzed is the cost effectiveness of current intermediary systems. Finally, consideration is given to the prospects for much more advanced systems which would perform such functions as automatic data-base selection and the simulation of human experts, and thereby make information retrieval more effective for all classes of users.  相似文献   

19.
在采用空时码的无线通信系统中,收发2端较差的路径会降低系统的性能.提出了多速率线性离散码(LDC),并对其进行了分析,给出了一种基于矩阵扩展方法的设计算法.多速率LDC是传统LDC和LDC-TAS的BER性能的折中.进而提出了一种性能优于传统LDC-A-TAS算法的多速率LDC自适应发送天线选择(A.TAS)算法.  相似文献   

20.
The performance of a Wideband Code Division Multiple Access (W-CDMA) system using Pseudo Noise (PN) codes and chaotic codes in the presence of a Weibull fading channel is studied in this paper. The W-CDMA system modeled using Gaussian Approximation is analyzed on a Weibull fading channel which fades the amplitude of the transmitted signal randomly according to the Weibull distribution. Closed-form expressions for Bit Error Rate (BER) are derived and expressed in terms of Meijer?s-G function. Performance measures in terms of BER are plotted versus Signal-to-Noise Ratio (SNR) for various values of fading severity, average fading power, and channel memory using PN and chaotic codes. Performance comparison between PN codes and chaotic codes are also analyzed.  相似文献   

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