数字处理多频记发器信号收发系统的算法与硬件实现

本文提出一种用数字方法处理多频信号的新算法,并介绍了这种算法硬件实现的概况。实验表明,高效率的算法与高效率的硬件设计相结合,使得用数字处理方法实现的多频信号收发系统在成本价格、体积、功耗、性能各方面都优于其它方法实现的系统。实验系统是可编程控制的,一套硬件既可以处理前向信号,又可以处理后向信号。测试表明,各项指标均已满足GB3971.3—83国标中的有关要求。实验系统是多路复用的,平均每路使用集成电路11片,大部分为74系列中规模电路和8位微处理器及其外围芯片,超大规模集成电路的用量每路平均不到0.2片。     

一种新型的数字多频信号接收器

本文介绍了一种数字多频信号接收器的新设计方案。该方案采用数字信号抽取的方法,使分离多频频率的滤波器组在较低的抽样率下工作,从而使所需的运算量大为降低。这样的滤波器组由多相网络、数字正弦变换(DST)和数字余弦变换(DCT)的连接来实现。由于DCT和DST的输出互为正交,为多频的检测提供了条件。用这种方法设计的多频信号接收器具有工作速度低和运算效率高的特点。     

多电平QAM数字微波系统中的导频插入载波恢复法性能分析

本文对多电平QAM数字微波系统中载波恢复方法之一的导频插入法进行了一全面研究。从能抑制基带信号低频分量的反馈平衡编码入手,导出经反馈平衡编码后的信号功率谱;导出插入导频分量的大小与信号平均功率衰减程度的关系和采用导频插入法的MQAM系统误码率计算公式;分析了信道多径衰落、剩余的信号低频分量对导频的干扰作用;给出了采用导频插入法的MQAM系统性能计算机模拟结果。理论估算和计算机模拟结果均表明,在MQAM系统中,用导频插入载波恢复法能取得较满意的效果,在许多方面,特别是M值很大的情况,优于环路载波恢复法。     

数字正弦双频信号的发生

一、为什么要搞数字信号发生在传统的模拟交换网内,信号音(如拨号音、忙音、回铃音)和多频信号均用模拟方法产生.用模拟方法产生的模拟信号音通过模拟的交换网是大家熟悉的.在交换网络数字化后,模拟信号不能直接通过,必须加接模数转换设备,将模拟信号转变成数字信息后才能接入数字交换网.这样经济上既不合算,体积又增大,理想的办法是直接用数字方法产生信号音或多频信号,使之直接注入数字交换网,这样可以节省投资,又可缩小交换机的体积.并从根本上解决了原来用模拟方法产生信号音时存在的振频和振幅稳定较难解决的问题.总之,采用数字方法直接产生数字信号有其明显的优点,也是数字交换必须解决的一个问题.本文     

数字单频脉冲信号的检测

在电话自动交换网中,频分或时分复用的局间中继电路上的占用、拆线、应答、挂机等信号,有使用带内单频脉冲线路信号方式的。在数字网中,此单频脉冲以数字信号传送,因此,必须设置检测数字单频脉冲信号的专用单元。对这种数字单频信号的检测,可以有多种方法。本文介绍一种用正交复解调加FIR数字滤波的方法,给     

程控交换机全数字音信号及多频信号设计方法

本文以新型数字交换机系统为背景,提出了全数字音信号和多频互控信号的设计方法。讨论了电路原理、编码方式,电平设计和脉冲信号的时序关系。最后给出了电原理图和试验数据结果。     

基于FPGA的高精度时频测量设计与实现

由于数字器件的运行时钟受限,基于数字处理芯片的时频测量的精度很难提高;利用FPGA内部锁相环的特点,设计了采用同频多相的多个时钟同时对输入信号进行测量,对各个时钟的测量值进行平均的高精度时频测量方法;介绍了采用产生多个同频多相时钟的方法,详细说明了采用多个同频多相的时钟同时进行时频测量的具体步骤;实际测量表明,该方法实现较为简单,能够在不提高时钟运行速率的情况下,成倍地提高信号的时频测量精度。     

蒙特卡罗算法在数字单频网信号合成中的应用

在进行地面数字电视规划时,要对信号的服务区范围进行分析和评估,这些评估是通过对欲收信号及干扰信号的电平测算、合成、分析、统计完成的。由于数字系统中＂峭壁效应＂的存在,要求信号预测的地点概率必须高于模拟信号预测50%的概率标准,数字信号预测的地点概率的取值要在70%95%之间才能达到较为满意的接收。同时在单频网组网情况下,地面数字服务接收面临着多信号环境,即覆盖范围内每个接收点都存在多重欲收信号和多重干扰信号的状况。由于数字单频网具有以上特点,所以在进行单频网规划和覆盖预测时必须使用更为科学准确的方法。本文介绍了适合进行数字单频网场强计算分析的蒙特卡罗算法,并结合其特点介绍了该方法在单频网信号评估过程中的应用。     

线性调频多载波系统抗多普勒性能

针对OFDM系统对多普勒频偏的敏感性,在介绍广义多载波系统的基础上,为了进一步改善多普勒频偏下的系统性能,利用线性调频形式的正交信号基代替原有的指数信号基,构成了基于线性调频基的广义多载波通信系统,并给出了各子载波线性调频基的表达式、发射机输出信号和接收机接收信号的表达式。在六径信道模型下,设定多普勒频移为55Hz,225Hz和450Hz,进行了通信系统数字仿真。结果表明,基于线性调频基的广义多载波通信系统具有较好的误码率性能。     

基于FPGA的高精度时频测量设计与实现

由于数字器件的运行时钟受限,基于数字处理芯片的时频测量的精度很难提高;利用FPGA内部锁相环的特点,设计了采用同频多相的多个时钟同时对输入信号进行测量,对各个时钟的测量值进行平均的高精度时频测量方法;介绍了采用产生多个同频多相时钟的方法,详细说明了采用多个同频多相的时钟同时进行时频测量的具体步骤;实际测量表明,该方法实现较为简单,能够在不提高时钟运行速率的情况下,成倍地提高信号的时频测量精度。     

Digital MF Receiver Using Discrete Fourier Transform

In a digital toll switching office a digital multifrequency (MF) receiver may be more economical than the present analog MF receiver. This paper suggests an algorithm that could be used for digital implementation of such a receiver. The algorithm employs discrete Fourier transform and leads to more efficient design than a system using second-order digital bandpass filters. The presented results of computer simulation of the digital MF receiver employing this method indicate satisfactory performance and good immunity to random noise interference.     

Fourier-Based Feature Extraction for Classification of EEG Signals Using EEG Rhythms

In this paper, we propose a method for the analysis and classification of electroencephalogram (EEG) signals using EEG rhythms. The EEG rhythms capture the nonlinear complex dynamic behavior of the brain system and the nonstationary nature of the EEG signals. This method analyzes common frequency components in multichannel EEG recordings, using the filter bank signal processing. The mean frequency (MF) and RMS bandwidth of the signal are estimated by applying Fourier-transform-based filter bank processing on the EEG rhythms, which we refer intrinsic band functions, inherently present in the EEG signals. The MF and RMS bandwidth estimates, for the different classes (e.g., ictal and seizure-free, open eyes and closed eyes, inter-ictal and ictal, healthy volunteers and epileptic patients, inter-ictal epileptogenic and opposite to epileptogenic zone) of EEG recordings, are statistically different and hence used to distinguish and classify the two classes of signals using a least-squares support vector machine classifier. Experimental results, with 100 % classification accuracy, on a real-world EEG signals database analysis illustrate the effectiveness of the proposed method for EEG signal classification.     

基于双口RAM核监测数字示波器设计研究

在核监测中,常将各种传感器输出的信号通过A／D转换器转换为数字信号,然后利用数字信号处理技术对各种核信号进行数字处理。为了准确测量核信号数字波形的各种参数,对基于FPGA双口RAM的数字示波器进行了设计和测试分析。实验表明,该数字示波器能准确获取核信号的数字波形及各种参数的值,可对核信号的波形进行录制、回放和精确分析,为核监测及其仪器准确设计提供有力的保证。     

数字电视中的条件接收系统

数字电视指将传统的模拟信号转化为数字进行处理、传输和接收的系统.数字电视的条件接收系统运用各种数字技术通过对节目的加扰处理,使只有授权用户才能收看被加扰节目,从而保障运营商的利益,保证数字电视发展.本文主要阐述当前数字电视使用的条件接收系统的基本原理,以及实际中应用两种条件接收方式的设计和实现,并比较两种方式的优势和不足.最后介绍当前国内数字电视发展的现状.     

MF AM grounded dipole for stereo and digital transmissions

Modern MF AM transmitter output impedance has been chosen to be 50 ohms unbalanced. For this reason high power 50 ohms coaxial lines have been designed and manufactured, rigid or almost flexible in order to connect the transmitter in the station building and the far away radiating system at one or more wavelengths. At MF frequencies the radiating system is generally a standard classical monopole where a matching system close to the monopole is needed to obtain maximum radiation efficiency. The proposal here is to use a radiating system made up of a grounded tower close to half a wavelength tall with a cylindrical skirt around the tower's lower part. The skirt is fed directly from the 50 ohm coaxial line at a point whose impedance is very close to 50 ohms, avoiding the matching system and improving the radiation efficiency within a good bandwidth suitable for stereo or digital transmissions. Design permits a low standing wave ratio within the information passband necessary to obtain the lowest information distortion. Scale models have been designed, constructed and measured obtaining similar results as predicted by calculations in the MF frequencies. The advantages of a grounded tower are discussed     

A comparative study of simultaneous vibromyography andelectromyography with active human quadriceps

Vibromyographic (VMG) signals, which are low-frequency vibration signals generated during muscle contraction, were studied in comparison with electromyographic (EMG) signals recorded simultaneously during isometric contraction of the human quadriceps muscles. The comparison was accomplished by evaluating the averaged root mean squared (rms) value, mean frequency (MF), and peak frequency (PF) of the VMG and EMG signals for four muscle contraction levels at joint angles of 30 degrees, 60 degrees, and 90 degrees. The four contraction levels, namely 20, 40, 60, and 80% of maximum voluntary contraction (MVC), were estimated and controlled by the torque readings of a Cybex II dynamometer. It was found that the VMG and EMG under the same conditions on the same muscle group are in general equally sensitive to the levels of muscle contraction. Results show that the rms value of the VMG signal increases linearly, in a manner similar to the EMG rms/%MVC relationship, with increasing muscle contraction levels. Furthermore, the study indicates that the averaged MF (6-24 Hz) and PF (9-19 Hz) of the VMG signals are much lower than the MF (75-109 Hz) and PF (40-80 Hz) of the EMG signals. The slopes of MF/%MVC curves for the VMG and EMG are approximately the same for 60 degrees and 90 degrees joint angles (approximately 3.1 Hz per 20% MVC for VMG and approximately 2.6 Hz per 20% MVC for EMG).(ABSTRACT TRUNCATED AT 250 WORDS)     

The antenna system of a distress buoy for use in a maritime satellite communication system (MARSAT)

Two different types of antenna systems for a distress buoy for use in the maritime satellite communication system (MARSAT) are described. The buoy radiates signals alternately on the frequencies 2182 kHz (medium frequency (MF) beacon) and 1.65 GHz (Lband beacon). TheLband antennas had to be combined with the MF antenna of a commercial buoy. The antenna systems have been tested with success during the application technology satellite (ATS-6) experiments and during a previous European Space Research Organization (ESRO) balloon communication experiment [1].     

Navigational GBOC signals and their energy spectra

The modulation functions (MFs) of generalized binary offset carrier (GBOC) signals of promising satellite radio-navigation systems, such as Galileo (European Union), global positioning system (GPS) (USA), and BeiDou/Compass (China), is estimated. Analytical expressions for the spectral density and energy spectrum of the single component of the GBOC-signal MF are obtained at different pulse multiplicity coefficients N _RSO of rectangular subcarrier oscillations and different duty cycles ρ. The spectra characterizing the important particular cases, namely, binary offset carrier and binary phase-shift keying signals are analyzed by means of the derived general formulas for GBOC signals. The Mathcad software package is used to construct graphs and discuss the properties of the energy spectra of single components entering into the GBOC-signal MF for the following types of modulation: GBOC(1, 1, ρ), GBOC(2, 2, ρ), and GBOC(10, 5, ρ).     

Two Multiplierless Designs for MF Receivers

Admitting coefficients that are sums of powers of 2, two multiplierless designs of digital MF receivers are proposed. Design 1. requires 22 additions per set of six output values. Design 2 requires 11 additions per set of three output values, but there is a strict requirement that the input be a valid MF sequence.     

An EIA/CEA-909 compatible smart antenna system for digital terrestrial broadcasting applications

This paper discusses the theory and design of a smart antenna system for receiving digital terrestrial television signals. The pertinent antenna theory and the associated hardware is presented as is the relationship between the two. Finally, field results using digital terrestrial television signals are presented to evaluate the performance of the smart antenna system.