A Modified Method Based on the Discrete Sliding Norm Transform to Reduce the PAPR in OFDM Systems

Orthogonal frequency division multiplexing (OFDM) is a modulation technique that allows the transmission of high data rates over wideband radio channels subject to frequency selective fading by dividing the data into several narrowband and flat fading channels. OFDM has high spectral efficiency and channel robustness. However, a major drawback of OFDM is that the peak‐to‐average power ratio (PAPR) of the transmitted signals is high, which causes nonlinear distortion in the received data and reduces the efficiency of the high power amplifier in the transmitter. The most straightforward method to solve this problem is to use a nonlinear mapping algorithm to transform the signal into a new signal that has a smaller PAPR. One of the latest nonlinear methods proposed to reduce the PAPR is the L₂‐by‐3 algorithm, which is based on the discrete sliding norm transform. In this paper, a new algorithm based on the L₂‐by‐3 method is proposed. The proposed method is very simple and has a low complexity analysis. Simulation results show that the proposed method performs better, has better power spectral density, and is less sensitive to the modulation type and number of subcarriers than L₂‐by‐3.     

发射药颗粒间摩擦系数测定及其对装填密度的影响

为测量发射药颗粒间的摩擦系数并探究其对装填密度的影响,以表面涂有石墨的发射药颗粒为研究对象,采用传统的斜面仪来测量静摩擦系数; 对于滚动摩擦系数的测定,基于离散单元法,模拟发射药颗粒堆积过程,得到模拟堆积角与滚动摩擦系数间的线性拟合方程,再基于实验所测堆积角进行参数标定获取参数值,二次拟合结果说明该参数测定方法可行。模拟结果表明,堆积角随着滚动摩擦系数的增大而增大。通过模块装填模拟,探究摩擦系数对装填密度的影响,结果表明,随着摩擦系数的增大,模块所装发射药的颗粒数越小,装填密度越小,说明摩擦系数对模块装填密度的影响是一个不可忽略的因素。     

火炮发射药床冲击破碎动力学仿真研究

为了研究发射装药引起膛炸的基本原理,确保火炮武器系统发射过程安全,实现末端毁伤效应,从理论分析计算的角度出发,基于离散单元法,建立了火炮发射药床冲击破碎动力学仿真模型,模拟了大口径火炮发射药床在燃气流冲击载荷下的破碎过程,并与有限元计算软件LS-DYNA的结果进行对比,结果表明,离散单元法和有限元法计算结果几乎一致,验证了该方法的准确性。该计算方法对发射装药发射安全性研究具有一定理论实用价值。     

提高弹载雷达测速精度的方法研究

基于弹载雷达系统高精度目标信息测量的性能需求,本文提出对FFT频谱数据检测结果采用扩展比值插值算法进行处理,以减少目标速度信息测量误差。仿真试验验证了该方法对提高测量精度的有效性,该方法在实际应用中实现了高精度目标信息测量,从而为提高弹载雷达系统性能、实现对目标的精确跟踪提供有力技术基础。     

一个完善的秘密分享方案

可验证秘密分享在实用密码学领域内是一个非常重要的工具,它在密钥管理协议、门限或分布式签名协议、电子商务、多方安全计算及团体式密码系统等许多方面都有极为广泛的应用。针对一类突发事务须及时、安全解决的特点, 利用离散对数问题的难解性,在假设初始化阶段和秘密恢复阶段始终有一位值得信赖的分发者参与的情况下,提出了一个可公开验证的门限秘密分享方案。     

一个基于两个数学难题的签名方案的分析

分析了文献[4]中提出的基于大数分解和离散对数难题的签名方案,指出文献[4]中提出的方案在离散对数可解时即是不安全的。     

JPEG2000及其编码系统的实现

随着多媒体技术应用领域的扩大，小波图像压缩研究日趋成熟。因此，国际标准化组织(ISO)指定了新一代的图像压缩标准：JPEG2000。首先介绍了JPEG2000的特点，然后介绍了JPEG2000的编码系统的实现过程，重点讨论了JPEG2000的技术核心：离散小波变换和EBCOT技术。最后，通过使用VC^ 6．0实现JPEG2000的编码算法，并对两种图像压缩格式进行了比较，给出了一个详细的实验结果。     

频谱泄漏对正弦相位调制干涉测量精度的影响

在正弦相位调制(SPM)干涉仪中,若调制频率或者采样频率发生变化将使干涉信号出现频谱泄漏,减小了谐波分量的幅值,在测量结果中引入了误差。对频谱泄漏的产生及其对测量精度的影响进行了理论分析,获得了频谱泄漏引入测量误差的计算方法。实验测得频率漂移量在-0.3~0.3Hz内,得到的频谱泄漏引入的误差为0.3~7.9nm,当超出这个范围时,频谱泄漏误差将迅速增长。实验结果与模拟分析结果一致。     

Statistically matched wavelet-based method for detection of power quality events

This article presents a new technique for the detection of power quality (PQ) events by using statistically matched wavelet. The statistically matched wavelet is designed based on the characteristics of the PQ event using the concept of fractional Brownian motion. The proposed technique is compared with Daubechies wavelet to show its superiority in the detection of PQ events. To classify the detected events, an iterative closest point algorithm is used which classifies the detected event even in the presence of outlier points and Gaussian noise. The method is applied to classify the various PQ events like transient, sag, swell and harmonics and the results are simulated using MATLAB version 7.3.     

离散坐标法和LOWTRAN7辐射传输计算的比较

在不同波段和不同大气条件下，利用离散坐标法和ＬＯＷＴＲＡＮ７计算了大气顶向上和地面向下辐射率，并进行了比较．在一般情况下，两者的差别小于２０％，说明用ＬＯＷＴＲＡＮ７计算有较好的精度．