用DFT对连续信号谱分析的误差问题

谱分析是数字信号处理中的一个重要问题,初学者普遍对连续信号谱分析理解不深,尤其是在误差分析时缺乏统一示例,更容易产生困惑。介绍了用离散傅里叶变换(DFT)对连续信号进行谱分析的过程,并详细说明了误差产生的原因和减小误差的方法。而且通过对模拟信号谱分析的实例全面说明了各项误差的影响及解决方案,并应用Matlab直观地进行了分析和对比验证。     

大时带积线性调频信号源幅相误差分析与校正

针对产生LFM信号的数字方法，分析了系统的幅相误差来源，并根据误差频率对其进行了分类。提出了一种将正交调制LFM信号产生系统的幅相误差映射到基带后，在数字域利用复系数FIR滤波器进行校正的方案。针对直接数字波形合成LFM信号产生系统，将误差校正方法简化为直接对存储的数字波形进行预失真处理。最后将校正方法应用于实际系统，结果表明提出的幅相误差校正方案易行、有效，能明显提高输出LFM信号的性能。     

某炮塔数字伺服控制系统误差分析

介绍了数字伺服控制系统的误差源,对由其产生的误差进行了误差分析,并将该分析方法应用于某炮塔数字伺服控制系统,提出降低或削除误差的有效途径,为数字伺服控制系统的设计分析提供参考。     

数字基带信号功率谱分析教学法探索

本文对通信原理教材和本科教学中数字基带信号功率谱分析方法作了简要介绍，指出其存在的不足。提出了基于计算机仿真的数字基带信号功率谱分析教学法，并以CMI码和AMI码为例给出了基于Systemview的功率谱求解方法。实践证明，此方法可以简便有效地完善教学内容。     

平稳随机过程非均匀采样信号的数字谱研究

目前的随机信号分析多是基于作等时间间隔采样以描述信号特征,而实际应用中往往不能避免采样的非均匀性;传统的谱分析方法必然产生原理误差。本文引入平稳随机点过程的知识,建立了广义平稳随机信号的非均匀采样序列模型,推导了其数字频谱的一般公式,分析了具有典型分布函数的随机采样情况。     

数字重采样误差对解调性能的影响分析

采用带通采样的接收端往往要引入数字重采样。研究数字化中频系统中数字重采样误差对解调信噪比的影响。介绍了数字重采样的基本原理以及数字重采样误差产生的原因,分析数字重采样误差对解调性能的影响,并仿真验证了理论分析的正确性。结合典型的调制编码方式对数字重采样误差范围提出了要求,为数字重采样的设计及实现提供了依据。     

一种数字T/R组件幅相误差校正设计

数字T/R组件是数字化雷达的重要组成部分,由于信号产生与接收均使用了数字信号,仪器无法测量信号误差,因此需要对发射、接收通道分别进行幅相误差校正.本文结合一种数字T/R组件的具体设计,介绍了其幅相误差校正方法.     

基于改进M序列的数字噪声源设计及其FPGA实现

常规模拟方法产生的噪声功率谱不平坦且很难控制。为产生高随机、高速度数字噪声,利用多位M序列的长周期伪随机性,截取高位M序列的部分位求和来产生新的M序列,证明其具有高位M序列的性质,并将其用于数字噪声源的设计应用。运用qurtusⅡ软件进行硬件编程仿真,并用matlab对仿真结果进行功率谱分析,证明新方法产生的随机噪声具有高随机、高速度的良好性能,且方法简单实用,具有一定应用价值。     

基于数字滤波的低频随机信号实时功率谱分析仪的实现

对于非平稳随机信号的功率谱分析,采用自相关函数傅里叶变换和直接傅里叶变换分析时,由于存在数据截断,二者从概念上都不能很好地反映随机信号的功率谱.采用参数谱估计方法,则不能实现等百分比带宽分析.对于噪声和结构振动等信号,需要进行等百分比带宽分析.采用滤波法进行功率谱分析,不存在数据截断带来的误差,还可方便地用于等百分比带宽的谱分析.利用数字滤波器可以实现时分和频分复用的特点,结合重抽样技术来实现整个频率轴上的实时功率谱分析.上述算法可以通过高速数字信号处理器(DSP)芯片实时地完成.文中介绍了基于数字滤波的低频随机信号实时功率谱分析仪的实现方法,并给出了实时算法的设计要点.     

全数字接收机的结构及关键技术

全数字接收机是近几年提出的新的接收机结构，它采用高稳定度晶体振荡器产生本地时钟用于解调及采样，载波相差和时钟寒时误差的消除，信号的判定等全部由数字信号处理器来完成，本文介绍了全数字接收机的体系结构，并对其实现的关键技术进行详细的讨论。     

Error rate performance of noncoherent detection of duobinary coded MSK and TFM in mobile radio communication systems

Two continuous phase constant envelope modulation schemes are considered for use in digital mobile radio communication systems. These two schemes, duobinary coded minimum shift keying (MSK) and tamed frequency modulation (TFM), use partial response signaling to achieve efficient power spectrum. Therefore, they are suitable candidates for the application of digital data transmission via mobile radio where spectrum efficiency is an important consideration. The mobile communication channel is characterized by fast Rayleigh fading and cochannel interference resulting from the reuse of the channels. The error rate performance of duobinary coded MSK and TFM has been studied under these environments with noncoherent detection. A closed form expression for the probability of error of duobinary coded MSK with discriminator detection has been derived and evaluated for different cases of fast and slow fading and cochannel interference. The probability of error of duobinary coded MSK and TFM with differential detection has been calculated by numerical integrations for different cases of slow and fast fading and cochannel interference.     

Probability of error analysis of digital partial responsecontinuous phase modulation with two-bit differential detection andoffset receiver diversity in fast Rayleigh fading channels

The performance of constant envelope digital partial response continuous phase modulation (PRCPM) with two-bit differential detection and offset receiver diversity is theoretically analyzed in fast Rayleigh fading channels. A simple closed-form expression for the probability of error is derived and evaluated for cases of practical interest to researchers and designers of land mobile radio systems. It is shown that the dynamic bit error rate (BER) performance is considerably improved using the offset diversity scheme. Thus, many PRCPM signals having a compact power spectrum can be used in future digital mobile radio systems     

离散傅里叶变换误差分析与参数设置

离散傅里叶变换( Discrete Fourier Transform,DFT) 是数字信号处理教学的重点和难点,其参数设置的正确与否直接影响信号频谱分析的准确性。本文对连续与离散周期信号、非周期信号分别进行DFT运算,从時域和频域角度分析实际频谱与理想频谱之间的误差。通过MATLAB仿真,加深学生对DFT的理解,引导学生正确设置DFT参数。     

Spectral sensitivity of power amplifiers to quadrature modulatormisalignment

Misalignments in the quadrature modulator feeding a nonlinear high power amplifier can produce distortion products that lead to spectrum leakage into adjacent channels. Expressions are derived relating the out-of-band spectra to these misalignments and to the complex coefficients of the power series describing the amplifier. For most applications the adjacent channel leakage is proportional to the square of the misalignment error (carrier leak, differential gain, differential phase and level error) except in the case of some higher order products of continuous phase modulations (CPM). A technique for estimating the spectrum for the above situations is described. It involves summing the weighted spectrum of each distortion product. The weighting coefficients can be varied to account for amplifier characteristics, backoff, and misalignment error. The analysis is applicable to linear or continuous phase modulations with or without predistortion. The spectrum estimate is particularly good for continuous phase modulated signals where the error is normally much less than 1 dB     

200 MHz并行多通道实时采样系统的误差校正

本文介绍了作者对２００ＭＨｚ并行多通道实时采样系统中固有的误差：多通道非均匀时间采样误差和增益误差校正的方法。在频域对采样数据进行频谱重建,消除了由于非均匀时间采样引入的高次谐波,使得采样时间误差均值减小到原来的３．８４。同时还对增益误差进行了完全校正,取得了较好的效果。     

Comments on `The impact of NRZ data asymmetry on the performance ofa space telemetry system' by T.M. Nguyen

The commenters point out an error in the continuous power density spectrum given by the terms indicated in the above-titled paper (see ibid., vol.33, no.4, p.343-50, 1991). The continuous component of the spectrum computed directly from an equation given in the paper is shown and differs substantially from that shown in the original figure. Some repercussions as regards other results in the paper are indicated     

A digital power spectrum estimation method for the adaptation of high-speed equalizers

This work presents a method to estimate the power spectrum of digital signals, which is then used to generate an error signal to tune Gbps data rate equalizers for digital communications. The proposed power spectrum estimation method can be realized with standard digital circuits and has been fabricated and tested in 0.35-/spl mu/m CMOS technology for 1-Gbps data rate. Compared with the traditional bandpass filter followed by a rectifier implementation, this method has wider input signal range and is scalable to higher speed technologies beyond the gigahertz range, in addition to largely reduced power dissipation and die area. Also presented are system simulations on the bit-error rate performance and the error space analysis of the proposed method in comparison with the method of using a bandpass filter followed by a rectifier.     

A 1.9-GHz-band GaAs direct-quadrature modulator IC with a phaseshifter

A 1.9-GHz-band direct-quadrature modulator IC has been successfully developed for digital portable telephone use. In the 1.9-GHz high-frequency band, both image and carrier rejections as low as -40 dBc have been obtained with a low-power dissipation of 110 mW at a single power supply of 3.1 V, corresponding to a phase error below 1.1. In order to reduce undesired sideband spectral components required for digital modulation, a newly developed circuit configuration that combines a quadrature phase shifter with drivers for amplitude imbalance compensation and makes spectrum efficiency and low-power dissipation possible is used. The modulator IC may be used in enhanced digital mobile radiocommunication systems such as digital portable telephones     

数字多用表的误差分析及其不确定度的计算与探讨

本文介绍了数字多用表的误差分析．并通过对其表示方法的计算，验证了这种数字仪表能够帮助模拟电参量自动地变成连续用数字编码方式，并且以十进制数字自动显示测量结果．充分证明了这种数字仪表的科学性和使用性．