基于迹变换和旋转增量调制特征的模糊人脸识别

为提高各种不同特殊场景下的模糊人脸识别精确性和鲁棒性,本文提出一种基于迹变换和旋转增量调制编码的特征提取方法.该方法将通信语音编码技术与图像变换技术相结合,首先通过迹线旋转扫描整幅图像,并对迹线上的采样信息进行增量调制编码,从而获得多角度的全局有序结构特征,然后用支持向量机对样本图像的这些特征进行训练以分类并识别图像....     

数字滤波器设计中采样频率的作用和影响

在“数字信号处理”课程的学习和教学中,数字滤波器设计中采样频率的作用是一个较难理解和容易混淆的概念,本文详细讨论了采和频率在数字滤波器设计中的作用和影响,从数学原理和物理概念两方面说明了采样频率的作用以及产生概念错误的原因。     

对光纤通信中几个问题的研究

本文对光纤通信中几个问题进行了探讨，通过对这些问题的研究，将有助于对光纤通信技术的正确理解，便于解决光纤通信系统中出现的问题。     

关于光数字段（链路）的误码性能测试问题和建议

就光缆数字通信工程的验收提出采用ＣＣＩＴＴＭ．５５０、Ｍ．５５５和Ｍ．５５７建议对投入业务限值的计算和测量误码性能存在的问题及看法，并提出了建议。     

远距离高稳定光纤频率传递技术研究

针对卫星导航系统对高稳定、远距离频率信号传递需求,对光纤频率传递技术原理进行了简要介绍,设计了基于电子相位补偿原理的光纤频率传递系统,并进行了实验验证。实验结果表明,通过单纤双向往返传输的相位补偿方案,实现了100 km光纤频率传递链路相位噪声的实时补偿,频率稳定度为1.13×10~(-14)@1 s,2.19×10~(-17)@10~(4 )s,抵消了光纤链路所处环境温度变化引入的附加相位噪声。     

InGaAsP PBC型激光二极管的弛豫频率和调制特性的研究

本文对BC型激光二极管(LD)从理论上导出弛豫振荡频率公式,并在实验上得到了验证.研制出高速LD组件,其调制频率可以达到5.3GHz.并在一公里光纤链路上测量了检测信号的载噪比、互调失真等特性.结果表明:该LD组件可用于直接传输C波段卫星下行信号(3.7～4.2GHz)的副载波复用光纤通信系统.     

Kramers-Kronig接收机的技术问题和实用性探究(特邀)

Kramers-Kronig(KK)接收机能从光信号的强度信息中重建相位信息,突破了单个光探测器只能检测和处理光信号强度信息的局限,是近年来光通信系统的一个研究热点。该接收机可以补偿光纤色散带来的损伤,降低系统对载波功率比的要求,能显著地提高接收机灵敏度,大大增加了系统容限和传输距离。在接收端仅用单个光探测器,极大地降低了同时检测光信号强度和相位的成本,在成本敏感的数据中心之间的光互联网络中有着光明的应用前景。然而,该接收机也存在着一定的技术问题,这可能会阻碍其在实际系统中的应用。文章介绍了KK接收机的原理和应用,对其技术问题和解决方案进行了系统地分析。同时,文章也从实用化角度出发,介绍了该接收机方案在实际系统中遇到的挑战,总结了现有的解决方案。最后,文章对该接收机未来的研究方向进行了探讨。     

稳定灵活的时钟复位模块提升采样示波器性能

由于对DSO(数字采样示波器)越来越快的需求，大多数电子工程师很容易忘记了串行采样示波器，往往只是仅仅将它们作为普通的采样示波器，而安捷伦的客户，又容易将它们当作DCA(数字通信分析仪)。采样示波器是实时示波器的前一代产品，通常具有更便宜的价钱，但有更宽的带宽。当实时示波器现在才有超过10GHz的带宽时，采样示波器十多年前就已经能传输近它十倍的带宽。     

数字光纤通信系统实用化的一些问题

简述了对数字光纤通信系统实用化的要求,测试和调整。     

Evaluation of the describing function of a delta modulation system in the region of slope overload

In feedback systems containing a delta modulation device, nonlinear slope overload distortions often lead to stability problems. These can be investigated by applying the describing-function concept. Therefore, a numerical method for calculating the complex describing function of a delta modulation system is presented in this paper. The results are presented as computer plots as well as in the form of coefficients of a polynomial regression.     

Adaptive delta modulation

An adaptive-delta-modulation system is described taking advantage of the storage of the line digit pattern in the holding register of a delayed-delta-modulation system, to produce a significant improvement in signal/quantisation-noise ratio.     

Statistical delta modulation

This report describes the results of a study of Statistical Delta Modulation (SDM), a new method of digital transmission of analog information [1]. In this method the system design is tailored to the statistical properties of the input data so as to provide analog reconstruction values with a minimum mean squared error. The method of system design is an iterative procedure in which conditional means are evaluated based upon actual input data. The report presents the theory of operation of the system and describes the results of a computer simulation in which such questions as the effects of sampling rate, channel noise, system memory, and mismatched input processes are discussed. At the present time only a brief comparison has been made with conventional techniques. It was found that at low sampling rates and for a particular non-Gaussian process, sampling rate reductions of 38 percent could be achieved relative to a conventional delta modulation system at the same SNR performance.     

Two-loop ternary adaptive delta modulation

A 2-loop ternary adaptive delta-modulation system is described which produces a peak s.n.r. of 20.5 dB, and for an s.n.r. of 15 dB, its dyamic range is 22dB when the input signal is RC shaped noise band limited to 2.5 kHz and the sampling rate is 8 kHz.     

Frequency modulation and variable-slope delta modulation in SCPC satellite transmission

This paper analyzes and presents subjective assessments of the performance that can be expected with FM, companded FM, and vaniable-slope delta modulation in single-channel-per-carrier (SCPC) service to small earth stations. In addition, it points out some of the problems that may be encountered in applying FM and digital techniques to an operational system.     

Linear and adaptive delta modulation

New results are presented, offering insight into the performance and optimization of linear and adaptive delta modulation, together with a comparison with pulse code modulation. The results are applied to three cases of practical interest: television, speech, and broadband signals. The results are presented as follows: first, a characterization of the quantization noise of linear delta modulation (DM) is given; second, an adaptive DM system which seems promising for television and speech is evaluated; and third, a comparison between PCM and adaptive DM is made for speech, television, and broadband signals. It is concluded that 1) the adaptive system provides DM with a companding capability, 2) adaptive DM offers a bit rate or channel bandwidth reduction capability in comparison with PCM for television signals, 3) adaptive DM appears better suited to television and speech signals than linear DM, 4) the maximum S/N performance of adaptive DM is the same as that of linear DM, 5) the companding improvement offered by adaptive DM is not limited by the same practical considerations as those of PCM, and 6) the S/N performance of adaptive DM is the same for both Gaussian and exponential signal densities.     

Interframe slope overload for television-picture noise reduction

Results of experiments on the temporal slope-overload phenomenon obtained with a 625 line/5.5 MHz digital television interframe delta modulator are reported. Whereas pictures containing genuine movement are heavily degraded, still pictures contaminated by noise can be rendered usable: s.n.r. improvements from 17 dB (original) to 34 dB (processed) have been obtained     

An all-MOS integrated delta modulation codec

A linear delta modulation (LDM) codec has been produced with a p-channel aluminum-gate MOS IC process technology. A distortion, which is produced by granular size fluctuation, is discussed. The conclusion is obtained that an MOS integrated LDM codec, which is applicable to voice communication purposes, can be produced.     

Nonlinear frequency modulation by noise

Prior analyses of frequency modulation by noise have assumed a perfectly linear modulator. The effect of nonlinearity on spectral shape and bandwidth is exhibited in one specific case of interest. In the linear case, a discrete spectral line may exist at carrier frequency; it is shown that such a line can never exist under nonlinear modulation.     

Running average error reduces overload noise in delayed delta-modulation systems

A simple but effective method to reduce overload noise and improve the overall performance in delta-modulation (DM) systems is presented in this paper. Two identical DM encoders operate on a different time-basis in such a manner that a running average of the error signal from the first encoder is taken into consideration by the second one. The resulting operation is a time adaptation process yielding diminished overload noise during overload bursts. Results obtained by computer simulation for speech signals show an overall signal-to-quantization noise ratio (SQNR) improvement up to 2.5 dB at optimum step size over classical schemes.