81 research outputs found
On optimal and near-optimal turbo decoding using generalized max operator
No full textMotivated by a recently published robust geometric programming approximation, a generalized approach for approximating efficiently the max* operator is presented. Using this approach, the max* operator is approximated by means of a generic and yet very simple max operator, instead of using additional correction term as previous approximation methods require. Following that, several turbo decoding algorithms are obtained with optimal and near-optimal bit error rate (BER) performance depending on a single parameter, namely the number of piecewise linear (PWL) approximation terms. It turns out that the known max-log-MAP algorithm can be viewed as special case of this new generalized approach. Furthermore, the decoding complexity of the most popular previously published methods is estimated, for the first time, in a unified way by hardware synthesis results, showing the practical implementation advantages of the proposed approximations against these method
Non-recursive max* operator with reduced implementation complexity for turbo decoding
No full textIn this study, the authors deal with the problem of how to effectively approximate the max?? operator when having n > 2 input values, with the aim of reducing implementation complexity of conventional Log-MAP turbo decoders. They show that, contrary to previous approaches, it is not necessary to apply the max?? operator recursively over pairs of values. Instead, a simple, yet effective, solution for the max?? operator is revealed having the advantage of being in non-recursive form and thus, requiring less computational effort. Hardware synthesis results for practical turbo decoders have shown implementation savings for the proposed method against the most recent published efficient turbo decoding algorithms by providing near optimal bit error rate (BER) performance
On Practical Implementation and Generalizations of max* Operator for Turbo and LDPC Decoders
No full textdoi:10.1155/2007/25361 Research Article Performance Analysis of SSC Diversity Receivers over Correlated Ricean Fading Satellite Channels
No full textThis paper studies the performance of switch and stay combining (SSC) diversity receivers operating over correlated Ricean fading satellite channels. Using an infinite series representation for the bivariate Ricean probability density function (PDF), the PDF of the SSC output signal-to-noise ratio (SNR) is derived. Capitalizing on this PDF, analytical expressions for the corresponding cu-mulative distribution function (CDF), the moments of the output SNR, the moments generating function (MGF), and the average channel capacity (CC) are derived. Furthermore, by considering several families of modulated signals, analytical expressions for the average symbol error probability (ASEP) for the diversity receivers under consideration are obtained. The theoretical analy-sis is accompanied by representative performance evaluation results, including average output SNR (ASNR), amount of fading (AoF), outage probability (Pout), average bit error probability (ABEP), and average CC, which have been obtained by numerical techniques. The validity of some of these performance evaluation results has been verified by comparing them with previously known results obtained for uncorrelated Ricean fading channels. Copyright © 2007 P. S. Bithas and P. T. Mathiopoulos. This is an open access article distributed under the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original work is properly cited. 1
Performance improvement techniques for the DVB-RCS2 return link air interface
No full textThis paper presents performance improvement techniques for the second-generation digital video broadcast return channel via satellite air interface, which can be used for supporting future demands for Tbit/s traffic requirements. In particular, we have investigated minimum-shift keying (MSK) type of continuous phase modulation (CPM) waveforms by considering both single-carrier and multi-carrier transmission and single-amplitude and multi-amplitude signals, which improve the spectral efficiency. In addition, we consider frame timing and synchronization techniques, which make synchronization more accurate and robust. Our research has shown that the MSK single-carrier frequency-division multiple access (SC-FDMA) outperforms the quadrature phase-shift keying SC-FDMA in terms of resilience to distortion with the performance gap increasing when the amplifier shows a milder distortion. The performance of a multi-amplitude CPM scheme, based upon the superposition of two single-amplitude MSK signals at the radio frequencies level, is also investigated. In comparison with other equivalent linear modulation schemes, performance evaluation results have been shown that the proposed multi-amplitude CPM scheme significantly improves the spectral efficiency in the presence of adjacent channel interference. Finally, we have proposed a viable and efficient methodology, which enables reliable and accurate timing and frequency synchronization for the SC-FDMA satellite return link. This involves a combination of global positioning system (GPS)-based pre-compensation of differential timing between user terminals, preamble detection in an integrated random access channel, and user channel frequency estimation based on repetitive symbols in the time domain
On the SINR Statistics of a VFDM Cognitive Spectrum Sharing System: equation (6) coefficients
No full text<p>Dataset for the scientific paper "On the SINR Statistics of a VFDM Cognitive Spectrum Sharing System"</p>
A Novel Methodology for HYIP Operators' Bitcoin Addresses Identification
No full textBitcoin is one of the most popular decentralized cryptocurrencies to date. However, it has been widely reported that it can be used for investment scams, which are referred to as high yield investment programs (HYIP). Although from the security forensic point of view it is very important to identify the HYIP operators' Bitcoin addresses, so far in the open technical literature no systematic method which reliably collects and identifies such Bitcoin addresses has been proposed. In this paper, a novel methodology is introduced, which efficiently collects a large number of the HYIP operators' Bitcoin addresses and identifies them based upon a novel analysis of their transactions history. In particular, a scraping-based method is first proposed which is able to collect more than 2,000 HYIP operators' Bitcoin addresses from the Internet thus providing a large number of the HYIPs' samples. Second, a supervised machine learning technique, which classifies, whether or not, specific Bitcoin addresses belong to the HYIP operators, is introduced and its performance is evaluated. The proposed classification method is based upon two novel approaches, namely the rate conversion technique that mitigates the effect of Bitcoin price volatility and the sampling technique that reduces the computational amount without sacrificing the classification performance. By employing close to 30,000 real Bitcoin addresses, extensive performance evaluation results obtained by means of computer simulation experiments have shown that the proposed methodology achieves excellent performance, i.e., 95% of the HYIP addresses can be correctly classified, while maintaining a false positive rate less than 4.9%. In order to further validate the proposed classifier's ability to detect the HYIP operators' Bitcoin addresses, our designed classifier has been tested against a recently published list of the HYIP addresses maintaining its excellent detection accuracy by achieving a 93.75% success rate. © 2013 IEEE
Individual and combined assessment of ser680asn fsh receptor and fshβ-211 g>t gene polymorphisms in ovarian response in ivf/icsi program
No full textBackground: Molecular biology tools, such as the detection of Single Nucleotide Polymor-phisms (SNPs), have been considered to assist in the management of ovarian stimulation protocols. Purpose: The aim of this study was to evaluate the impact of two polymorphisms, the Asn680Ser pol-ymorphism of the FSHR gene, and the FSH β subunit (FSHβ) gene polymorphism-211 G>T, in a Greek population of women undergoing IVF/ICSI program in our center. In addition, a control group of fertile women was studied to verify whether there are differences in the genotype distribution between fertile and infertile population for both polymorphisms, as the FSHβ gene polymorphism-211 G>T is studied for the first time in the Greek population. Results: The FSH β-211 G>T polymorphism, studied for the first time in the infertile Greek popula-tion, appears to be quite rare. When studying the two polymorphisms separately, statistically signifi-cant differences were obtained that concerned the LH levels. Discussion: According to the combination analysis of the two polymorphisms by the number of al-leles, women with 2-3 polymorphic alleles needed more days of stimulation, but there were no differences in pregnancy rates. Conclusion: This molecular genetic study helps to elucidate whether the polygenic combination of the Asn680Ser and FSH β subunit-211 G>T gene polymorphisms is of additive value in the prediction of ovarian response to exogenous gonadotropins. © 2021 Bentham Science Publishers
Multibranch scan-and-wait combining receivers over correlated Nakagami-m fading channels
No full textModulation Techniques
No full textDigital Satellite Communications focuses on the study and design of efficient and flexible physical layers for broadband mobile and fixed satellite links. The chapters address long-term developments for advanced physical layer techniques in broadband communications, fixed and mobile terminals, and 4G evolutions with a potential convergence between different technologies. A general description of satellite systems and services is provided which organizes the material into a generalized and readable framework. The approach is both analytical and descriptive. The book provides a unified view of essential topics, including: - fundamental theories - channel coding and modulation - synchronization and parameter estimation - distortions and countermeasures - diversity techniques - multiplexing and multiple access schemes - software radio Digital Satellite Communications is ideal for researchers and students in the fields of communication and signal processing
- …
