Quasi-cyclic LDPC code construction for implementation of parallel joint row-column decoding

针对普通低密度校验(LDPC)码制约行列联合(JRC)译码算法并行度提高的问题,基于块渐进边增长(BPEG)算法,提出了一种用于并行JRC译码的LDPC码构造方法.该方法构造的准循环LDPC码(QC-LDPC)基矩阵由含r(r为大于1的整数)行的行组构成,允许一个行组内的r行进行并行JRC运算.仿真结果表明,用上述构造方法构造的LDPC码与BPEG码的误码性能相当.硬件实现表明,用此构造码的并行译码器的速率能达到典型传统准循环译码器的3倍以上,为面向译码器的LDPC码构造提供了范例.     

Optimal code rates for the Lorentzian channel: Shannon codes and LDPC codes

We take an information-theoretic approach to obtaining optimal code rates for error-control codes on a magnetic storage channel approximated by the Lorentzian channel. Code rate optimality is in the sense of maximizing the information-theoretic user density along a track. To arrive at such results, we compute the achievable information rates for the Lorentzian channel as a function of signal-to-noise ratio and channel density, and then use these information rate calculations to obtain optimal code rates and maximal linear user densities. We call such (hypothetical) optimal codes "Shannon codes." We then examine optimal code rates on a Lorentzian channel assuming low-density parity-check (LDPC) codes instead of Shannon codes. We employ as our tool extrinsic information transfer (EXIT) charts, which provide a simple way of determining the capacity limit (or decoding threshold) for an LDPC code. We demonstrate that the optimal rates for LDPC codes coincide with those of Shannon codes and, more important, that LDPC codes are essentially capacity-achieving codes on the Lorentzian channel. Finally, we use the above results to estimate the optimal bit-aspect ratio, where optimality is in the sense of maximizing areal density.     

降低多载波通信峰均比的方法探讨

分析了多载波通信系统中高峰均比问题的来源、峰均比的特性以及大峰均比对系统性能的影响,介绍了选择性映射方法、部分传输序列方法、数字信号裁剪方法等几种比较有效和实用的降低峰均比的方法,描述了这些方法的原理、实现方法和优缺点,比较了这些方法的性能和实现代价,在这些方法的基础上提出了低峰均比多载波通信系统的一般性实现方案.     

Superresolution by use of code division multiplexing

Traditional methods for superresolution have sacrificed field of view for resolution. These methods multiplexed different parts of signals' spectrum on different carriers, and thus managed to transfer a wider range of frequency, in a manner that is similar to frequency division multiplexing in classical communication. We propose code division multiplexing for such an application, which has been shown to have superior capabilities. To enable such mutiplexing we propose a unique setup that creates an incoherent cosine transform of the image. A theoretical analysis of the setup is obtained and later compared with the empirical results.     

Geometric superresolution by code division multiplexing

In many highly resolved optical systems the resolution is limited not by the optics but by the CCD's nonzero pixel size. As a result, overall resolution is decreased. Here we propose a novel approach to enhancing resolution beyond the limit set by the CCD's pixels. This method does not involve additional mechanical elements, such as those used for microscans. In this scheme neither the CCD nor additional elements are moved. The geometric superresolving procedure is based on code-division multiplexing, with all its inherent benefits, such as relative noise immunity to single-tone interference. A setup is proposed for coherent and incoherent illumination, with slight modifications for the latter. A theoretical analysis of the setup is presented and compared with empirical results. This scheme is shown to enhance one-dimensional image resolution with the use of only a simple mask that doubles image resolution. This method can easily be expanded to two-dimensional images and to resolution-enhancement factors greater than 2.     

Analysis of search stratagem utilisation

Scientometrics - In interactive information retrieval, researchers consider the user behaviour towards systems and search tasks in order to adapt search results and to improve the search experience...     

微弱裂纹信号的稀疏编码提取

针对重大技术装备中关键基础部件早期裂纹信号提取困难这一问题,提出一种基于独立分量分析（ICA）的稀疏编码收缩（SCS）去噪方法,即采用泛化高斯模型（GGM）在ICA空间中估计信号独立系数的概率密度函数（PDF）,并利用最大后验（MAP）估计方法进行非线性去噪的微弱信号提取方法。通过对不同信噪比的含噪微弱裂纹信号的提取研究,结果表明,此方法能提取出输入信噪比低于-27dB的微弱信号,且波形与频谱均能较好的和原信号保持一致。同时,其去噪效果远远好于小波降噪方法,是一种较好的微弱信号提取方法。     

Reducing the mean squared error of quantile-based estimators by smoothing

Many univariate robust estimators are based on quantiles. As already theoretically pointed out by Fernholz (in J. Stat. Plan. Inference 57(1), 29–38, 1997), smoothing the empirical distribution function with an appropriate kernel and bandwidth can reduce the variance and mean squared error (MSE) of some quantile-based estimators in small data sets. In this paper we apply this idea on several robust estimators of location, scale and skewness. We propose a robust bandwidth selection and bias reduction procedure. We show that the use of this smoothing method indeed leads to smaller MSEs, also at contaminated data sets. In particular, we obtain better performances for the medcouple which is a robust measure of skewness that can be used for outlier detection in skewed distributions.     

Reducing the Sonic Boom Level by Heating the Oncoming Airflow

Technical Physics Letters - We present the results of calculations of the level of sonic boom in the presence of local heating of the airflow in front of a slender body during its supersonic flight...     

Reducing the risk of intradialytic hypotension by altering the composition of the dialysate

Hypotension is the most common complication of outpatient hemodialysis sessions, with a reported prevalence of 4% to 31%, depending on which definition has been used and whether patients are symptomatic and nursing interventions were required. Dialysis centers which mix the dialysate in the dialysis machine have the opportunity to individualize the composition of the dialysate for patients. This permits a choice of dialysate sodium, potassium, calcium, magnesium, bicarbonate, acetate, and citrate concentrations and temperature. Studies have reported a higher intradialytic systolic blood pressure and fewer episodes of intradialytic hypotension when using a higher dialysate sodium, calcium, magnesium concentrations and lower temperature, but no clinical advantage for changing the potassium, bicarbonate, or citrate for acetate concentrations. The introduction of newer technology allowing real time measurements of plasma electrolyte concentrations will potentially allow changing the dialysate composition to reduce the risk of intradialytic hypotension without increasing the risk of positive electrolyte balances.     

Reducing sample size by tightening test conditions

The inspection of measurement devices according to statistical sampling plans allows conclusions to be drawn about the reliability of a whole population of devices. However, confirming high reliability levels requires large sample sizes and is thus expensive or even infeasible. For example, a reliability of 99.5% can only be guaranteed with 90% confidence by inspecting each item in a population of 280 (see ISO 2859‐2). When reliability is judged by not exceeding a certain threshold, this research provides a convenient solution allowing considerably more efficient sampling plans. Under certain distributional assumptions, in particular, we have proved that if 100q% of a population meets a tighter threshold Δ/γ, then at least 100p% of the population meets threshold Δ(with p>q, γ>1). The importance and effect of different distributional assumptions are demonstrated and relevant scenarios for the parameters (p,q,γ) presented. Verifying that a smaller portion of devices comply requires smaller sample sizes. Costs may thus decrease when more stringent specifications are verified. For example, up to 98% of utility meters in Germany are required to measure correctly at inspections, to ensure a reliability of 95% in the future. Instead of applying costly sampling plans to meters in use to demonstrate these high reliability levels, this research enables the sample size to be reduced, eg, by half.     

Reducing ergonomic risks by job rotation scheduling

The proverb “a change is as good as a rest” expresses one of the main advantages of job rotation. In this article, we examine ways to set-up effective job rotation schedules that balance ergonomic risks among workers. The practical relevance of the problem is comprehensively discussed on examples from the automobile industry. We present the ergonomic job rotation scheduling problem and show that it is NP-hard in the strong sense. Therefore, the development of specialized solution methods is important. Exploiting the problem structure, we propose a fast and effective smoothing heuristic which can be integrated into solution methods for computing initial solutions and/or as a local re-optimization procedure. We find that integrating the smoothing heuristic into a suited tabu search approach is particularly recommendable. In computational experiments, this combination of approaches is able to solve almost all instances of a practical data set in very short computation times of some seconds, whereas the standard solver FICO Xpress and the best-known heuristic from literature perform considerably worse concerning computation time and solution quality.     

Waterjet penetration simulation by hybrid code of SPH and FEA

The creativity of this work is combining finite element analysis (FEA) and smoothed particle hydrodynamics (SPH) methods to simulate the waterjet (WJ) penetration process. In WJ penetration, the waterjet undergoing extremely large deformation will introduce the distortion of mesh in FEA. To overcome this difficulty, the coupled method of SPH and FEA was developed, in which the waterjet was modeled by SPH particles and the target material was modeled by finite elements. The two parts interacted by contact algorithm of “nodes-to-surface”. Utilizing this hybrid model, waterjet with high velocity penetrating the target materials was calculated and the mechanism of erosion was depicted. The computation result gives the relationship between the jet velocity and the erosion capacity, including the depth of penetration and mass removal, which was compared with the experimental data.     

条码检测仪在条码质量检测中的应用

条码符号印制质量是影响条码自动识别系统运行效率的重要因素之一,条码质量检验工作和条码质量控制过程对保证条码符号的质量起着重要作用。条码检测仪是用于检验条码符号质量的仪器,扫描反射率曲线是分析、评价条码符号印制质量的基础,通过扫描反射率曲线分析-质量分级检测方法可分析条码的各个质量参数,并综合评价条码的质量和评定符号等级。实践证明:在生产过程中采用条码检测仪对条码的尺寸参数和光学特性参数进行监控,能有效提高条码的印制质量。     

Hydrodynamics code calculations of debris clouds produced by ball-plate impacts

When a metal projectile hits a thin metal plate at a high enough velocity to penetrate it, a cloud of debris is produced, whose structure for normal impacts provides a unique test for hydrodynamic computer simulation. Since the equations of state (EOS) of the materials involved are a vital ingredient for hydrocode calculations, we would like to determine how important it is to use an accurate EOS. This paper reports results of benchmark calculations of hypervelocity impacts of a lead sphere on a lead plate where significant vaporization occurs. The results are somewhat sensitive to the EOS used, particularly in the regime where the material is expanded. The results are greatly affected when an attempt is made to include nonequilibrium effects by allowing negative pressures in the EOS.     

直冷电冰箱的降噪改进

对噪声较高的某类型直冷电冰箱进行噪声频谱分析,在此基础上对不同的降噪措施进行了分析和实验研究,最终获得了很好的降噪效果.     

适合行列合并译码算法的LDPC码的构造

针对低密度奇偶校验(LDPC)码译码器使用行列合并(RCJ)译码算法时存在的流水线冲突问题,提出了一种构造适合行列合并译码算法的LDPC码的方法。该构造方法在渐进添边(PEG)构造算法的基础上,加入行运算顺序的约束条件,使得利用该算法构造的LDPC码在行运算顺序上相邻两行内的非零块不同时共用一列,从而避免了硬件布局布线冲突,减少了流水线延时,提高了译码速率。仿真结果表明,用这种方法构造的LDPC码与全球微波互联接入(WiMAX)标准给出的LDPC码的译码性能相当,而且有效地减少了译码迭代次数,降低了硬件实现复杂度,提高了LDPC译码器吞吐率。     

Analysis of LDPC Code in Hybrid Communication Systems

Free-space optical (FSO) communication is of supreme importance for designing next-generation networks. Over the past decades, the radio frequency (RF) spectrum has been the main topic of interest for wireless technology. The RF spectrum is becoming denser and more employed, making its availability tough for additional channels. Optical communication, exploited for messages or indications in historical times, is now becoming famous and useful in combination with error-correcting codes (ECC) to mitigate the effects of fading caused by atmospheric turbulence. A free-space communication system (FSCS) in which the hybrid technology is based on FSO and RF. FSCS is a capable solution to overcome the downsides of current schemes and enhance the overall link reliability and availability. The proposed FSCS with regular low-density parity-check (LDPC) for coding techniques is deliberated and evaluated in terms of signal-to-noise ratio (SNR) in this paper. The extrinsic information transfer (EXIT) methodology is an incredible technique employed to investigate the sum-product decoding algorithm of LDPC codes and optimize the EXIT chart by applying curve fitting. In this research work, we also analyze the behavior of the EXIT chart of regular/irregular LDPC for the FSCS. We also investigate the error performance of LDPC code for the proposed FSCS.