查询词典 frequency bandwidth

to reduce the impact of carrier frequency offset in ofdm system,this thesis designs a new carrier frequency offset estimation scheme for ofdm system.the carrier frequency offset estimation includes acquisition and tracking.we adopt variable step size adaptive algorithm.the acquisition range of the proposed algorithm is as large as one half of the overall signal bandwidth.through this method we can not only avoid the feedback by using forward error correction,but also reduce the times of complex multiplication in order to reduce the power consumption of the system.this algorithm not only has low complexity and fast convergence nut also can improve the demodulation performance of ofdm system.computer simulation illustrates the superior performance of the proposed algorithm with regard to estimation accuracy in both awgn channel and multi—path channel.

摘 要：为了减小正交频分复用系统受频率偏差的影响，在ofdm系统中设计了一种新的载波频偏估计算法。频偏估计包括跟踪和捕获两个阶段，文中采用变步长自适应算法来进行跟踪，这个跟踪算法的捕捉范围是整个信号带宽的一半。通过此方法，不但可以利用前向纠错的方式来避免反馈，而且可以缩减复数乘法的次数以降低计算复杂度和系统功耗。该方法运算复杂度低，并具有较好的收敛性，能改善odfm的解调性能。从计算机的仿真效果可以看出无论是在awgn信道上还是在多径信道上都表现出了卓越的性能。

The main content of this dissertation includes: 1. Research on the theory of ultrasonic power supply, introduce its development process. On the basis of these, fix on the scheme of medical ultrasonic low-power supply. 2. According to the principle of modularized design, divide medical ultrasonic low-power supply into four parts. They are power amplify circuit, power control circuit, frequency automatic tracking circuit and matching circuit. Separately research on their theories and design their circuits and necessary programs, especially, effectively resolve the problem tracking the supersonic vibration system with a narrow syntony frequency bandwidth and a high swing. 3. The matching experiments gain good result, and prove that medical ultrasonic low-power supply is entirely up to the mustard on intellectualization, wide band of working frequency, steady output and high efficiency.

本文工作的主要内容包括： 1、研究了超声功率电源的原理，并回顾了它的发展过程，在此基础之上确定本文医用小功率超声电源的设计方案； 2、按照模块化的设计原则，将医用小功率超声电源的设计分解为功率放大电路、功率控制电路、频率自动跟踪电路和匹配电路等四个部分，分别研究了各部分的原理，在此基础之上进行了具体的电路设计和程序设计，尤其是有效地解决了对谐振频率带宽窄振幅高的超声振动系统的频率跟踪问题； 3、通过与超声振动系统的各项配合实验，取得了很好的实验结果，验证了医用小功率超声电源完全满足智能化、工作频带宽、输出功率稳定、输出效率高的设计要求。

Ricker wavelet whose predominant frequency is 200Hz was chosen as the exciting wave, and the character parameters (predominant amplitude, predominant frequency and frequency bandwidth) of its reflected wave were calculated.

选择主频为200Hz的雷克子波，理论计算原始地震反射波的特征参数（主振幅、主频率、频带宽度）。

Simulation results show that, for the fixed sampling frequency, the error rises with the frequency increasing of periodic signal, and decreases with the attenuation time constant increasing of non-periodic signal. The sampling frequency determines the upper limit of appropriate frequency band directly. The research provides the basis for the selection of cutoff frequency in filter design.

仿真结果表明，在采样频率确定时，对于周期信号，计算误差随频率的增加而增大，而对于非周期信号，计算误差随衰减时间常数的增大而减小，采样频率大小决定了插值法用于分布参数模型的适用频带上限，该研究为滤波器设计中截止频率的选择提供了依据。

This experiment is in frequency adjustment X-mitter about that miniwatt frequency adjustment X-mitter operating principle, analyses the debugging making method and their installation, the microphone changes implication into an audible signal, wave an audible signal being modulated as a result of enlarging the day afer tomorrow being in progress to the carrier wave , producing frequency adjustment, by the fact that air wire launching the frequency adjustment electromagnetic wave to the outside , the radio set just can with frequency adjustment meet hear clear implication.

本毕业设计是关于小功率调频发射机工作原理、分析制作方法及其安装调试，在调频发射机中，话筒将话音转化为音频信号，音频信号经放大后对载波进行调制，产生调频波，通过天线向外发射调频电磁波，用调频收音机便可以接听到清楚的话音。

Two common methods of GPS signal coarse acquisition are analyzed and compared in this paper, and an optimized method is adopted. Two common algorithms of calculating fine frequency are analyzed and compared and the conics fitting is designed to calculate the fine frequency. Based on the distributing character of Doppler frequency shift, swing frequency style of Doppler frequency shift search is employed.

对比分析了两种常用的GPS信号粗捕获实现方法，设计了一种优化的实现方法；同时对常用的两种精细载波频率算法进行了比较分析，设计了一种二次曲线拟合的方法计算精细载波频率；基于多普勒频移的分布特点，改变以往顺序搜索的方式，采用跳频搜索的方法。

The traditional analog frequency-sweeping instrument, which mostly uses the LC circuit as the frequency oscillator, is more expensive, too much bigger and heavy to carry. It can only display the curve of amplitude-frequency, but can't used to measure the phase-frequency, and can't used to print the curve of frequency response characteristic either. It brings many discommodity to the user.

传统的模拟式扫频仪大多是用LC电路构成扫频振荡器，它不仅价格昂贵，体积庞大，而且只能显示幅频特性曲线，不能得到相频特性曲线，更不能打印被测网络的频响曲线，给使用者带来诸多不便。

The time-domain response of the induced currents on a scattering object irradiated by a plane wave with a Gaussian pulse in time is expanded as an associate Hermite series in this paper. Using the isomorphism of the associate Hermite function and its Fourier transform, the frequency-domain information can be obtained similarly to the time-domain expansion. According to the corresponding relation between time-domain analysis and frequency-domain analysis, and using the early-time response and the low-frequency information of the induced currents, the non-known coefficients in the expansion series can be decided. The entire responses of the induced currents on the scattering object in both time and frequency domains can be obtained at one time by simultaneous extrapolation computation using both the early-time response and the low-frequency information of the induced currents.

摘要首先根据散射体在高斯脉冲平面波激励下感应电流的能量几乎全部集中在时间轴和频率轴上的有限范围内，该文将时域响应展开为系数待定的连带Hermite级数的叠加，并根据连带Hermite函数的傅里叶变换的自反性，得到与时域响应形式类似的频域响应；然后利用时域方法和频域方法分别计算散射体上感应电流的早时响应和低频信息；最后经过时域和频域联合外推计算，由早时响应和低频信息确定时域和频域响应的待定系数，从而获得了整个时域和频域的完全响应。

A CPU over-frequency method and system is composed of CPU, set module with BIOS ROM and CMOS RAM, control module of peripheral unit, storage module and time clock generation module. CPU over-frquency processing is completed automatically by executing CPU over-frequency program stored in BIOS ROM, meanwhile the highest FSB frequency value of CPU is obtained, and the system and peripheral unit can run at it. A testing for system stability is added to process of CPU over-frequency processing in order to ensure that the FSB frequency is applicable to the operation of CPU and peripheral unit.

一种CPU超频方法以及系统，包括CPU、具BIOS ROM及CMOSRAM的设定模块、外围装置控制模块、存贮器模块以及时钟产生模块组成，经过执行储存于BIOS ROM中的CPU超频程序后，自动完成CPU超频处理，并取得可供系统与外围装置稳定运作的最高的CPU的FSB频率值，于CPU超频处理的过程中，自动加入系统稳定性的测试，确保该FSB频率值适用于CPU与外围装置运作，使系统运作在超频状态下，亦能稳定地工作。

This paper analyzes the principle of chief anti jamming technologies of frequency agile radar FAR frequency diversity radar FDR and self adapt frequency agile radar SAFAR in frequency domain studies the effectiveness measurement methods of these technologies brings forward the self adapt improvement factor which measuring the anti jamming effectiveness of self adapted frequency agile radar .

分析了频率捷变，频率分集，自适应频率捷变等雷达在频域的主要抗干扰技术原理，研究了这些技术的效果度量方法，提出了度量自适应频率捷变雷达抗干扰效果的自适应改善因子。

Among which is the mindset, perceptions and moralities of those who accept mini- military tasks for economic gains.

其中最重要的是心态，观念和道德的人谁接受小型军事任务的经济收益。

In time course imaging, activity peaked 2 days after coronary ligation.

在时程成像检测，活性峰值在冠脉结扎后2天。