基于FPGA的数字下变频的设计与实现

数字下变频是中频信号处理系统中常用的技术手段,可在保证信号不失真的情况下有效降低采集信号的速率,便于后级处理器执行FFT等信号处理算法。提出一种基于FPGA的数字下变频方法,使用FPGA实现数控振荡器,产生正交的正、余弦样本信号,将采样的数字信号做正交化处理;实现级联积分梳状滤波器,合理抽取采样信号,降低信号频率;最后通过半带滤波器和FIR低通滤波器对整个信道进行整形滤波。充分发挥FPGA硬件并行化处理的优势,实现复杂的信号处理算法的高效执行,测试结果表明该方法可行有效,能够满足实际使用要求。     

一种卫星导航抗干扰天线数字信号正交分解方法

提出了一种基于 FIR 滤波器的卫星导航抗干扰天线数字信号正交分解方法。首先, 根据卫星导航信号在抗干扰天线中的中频中心频率及带宽信息确定带通滤波器的通带、阻带响应以及滤波器阶数等参数。接下来,采用 Parks-McClellan 算法分别设计滤波系数偶对称和奇对称的带通滤波器。最后,将抗干扰天线中 AD 采样后的中频数字实信号分别通过以上偶对称和奇对称的带通滤波器即可得到 I、Q 两路信号。本文所提方法具有计算量小、精度高且易于工程实现的特点。通过对实测数据分析验证了本文所提方法的有效性。     

带宽给定条件下的全数字接收机频率规划

本文分析了带宽给定条件下,全数字接收机中频频率与采样频率的约束关系;导出了采样频率给定条件下,使得数字滤波器过渡带宽最大的中频频率表达式.最后,本文以GPS P(Y) 码接收机频率规划为例给出了设计实例.     

孔径抖动对中频采样系统信噪比影响的研究

孔径抖动对中频(或射频)带通采样系统信噪比的影响非常严重.理论上,尽管相同带宽的中频信号和基带信号可以用相同的频率进行采样,但中频采样受孔径抖动等因素的影响更大,其采样技术要求也更高.如果在中频采样系统中解决不好孔径抖动问题,很可能根本采集不到正确的信号.本文通过分析孔径抖动产生的原因,孔径抖动与ADC (模数转换器)的信噪比以及与被采样信号上限频率之间的关系,找出了由孔径抖动决定的被采样信号的上限频率与ADC模拟带宽之间存在差距的原因,并发现了过采样率与处理增益及孔径抖动之间的关系.最后,介绍了几项减小孔径抖动的具体措施.     

接收机直接中频采样的方法与实现

对传统中频信号处理进行分析,在窄带信号采样定理的基础上得出了利用现有的高速数字器件可以实现直接进行中频信号数字处理的几种结构,最后给出了在实际中可行的通用中频采样方案。     

毫米波雷达数字复数下变频正交采样方法研究

运用数字化的直接下变频技术,在进行滤波器采样的同时,达到了信号下变频目的 ,从工程实践的层面降低了难度.通过推导和计算,将得出的最优化采样频率应用到毫米波雷达中频信号采样过程中,仅用一个模数转换器(ADC)和相关器件完成了系统的整体设计,降低了施工成本,提高了信号处理的速度和准确率.     

新型便携式激光测距仪的原理及方案设计

提出了一种新型双频调制方式的相位式激光测距系统.该系统采用石英晶体滤波器对测距信号进行滤波,使用一套独特的基于欠采样测距信号的信号处理算法,灵活地解决了测尺频率、石英晶体滤波器中心频率、模数转换采样频率三者的匹配问题;同时给出了系统的方案设计以及与基于数字同步检测系统方案的对比.     

数字中频正交采样及其FPGA实现

为满足高性能信号处理的要求,需要直接对中频信号进行采样得到正交的两路信号.分析了直接中频正交采样的基本原理,给出了其中最重要的滤波器设计思想及其在FPGA上的硬件实现方法,并仿真验证该方法的有效性.理论分析和实验结果表明,这一方法可以满足高性能信号处理的要求.     

中频带通采样技术在数字接收机中的应用研究

针对数字接收机在工程应用中的数据瓶颈问题,对中频带通采样技术进行了研究,讨论并计算了不同中频信号频率与中频带宽条件下的带通采样频率,分别在窄带中频数字接收机、宽带中频数字接收机两种典型情况下进行了计算机仿真验证。仿真结果表明,中频带通采样技术在降低采样频率的同时,不会导致信息量的丢失,能够较好地从带通采样数据中获取有价值的信息。     

最小方差无偏估计方法提高Gm-APD啁啾调制光子雷达的测距精度

啁啾调制光子雷达由于探测器Gm-APD的死时间限制了采样频率和调制带宽的提高,FFT进行信号处理时存在着固有的频域采样间隔,使得测距精度的提高受到很大限制.按照啁啾光子雷达接收机的信号处理过程对回波信号进行了推导,获得了系统回波中频信号的解析表达式,并采用最小方差无偏估计的方法对中频频谱进行处理,最后对该方法进行了仿真...     

Accurate identification of periodic oscillations buried in white or colored noise using fast orthogonal search

We use a previously introduced fast orthogonal search algorithm to detect sinusoidal frequency components buried in either white or colored noise. We show that the method outperforms the correlogram, modified covariance autoregressive (MODCOVAR) and multiple-signal classification (MUSIC) methods. Fast orthogonal search method achieves accurate detection of sinusoids even with signal-to-noise ratios as low as -10 dB, and is superior at detecting sinusoids buried in 1/f noise. Since the utilized method accurately detects sinusoids even under colored noise, it can be used to extract a 1/f noise process observed in physiological signals such as heart rate and renal blood pressure and flow data.     

Improved Single‐Tone Frequency Estimation by Averaging and Weighted Linear Prediction

This paper addresses estimating the frequency of a cisoid in the presence of white Gaussian noise, which has numerous applications in communications, radar, sonar, and instrumentation and measurement. Due to the nonlinear nature of the frequency estimation problem, there is threshold effect, that is, large error estimates or outliers will occur at sufficiently low signal‐to‐noise ratio (SNR) conditions. Utilizing the ideas of averaging to increase SNR and weighted linear prediction, an optimal frequency estimator with smaller threshold SNR is developed. Computer simulations are included to compare its mean square error performance with that of the maximum likelihood (ML) estimator, improved weighted phase averager, generalized weighted linear predictor, and single weighted sample correlator as well as Cramér‐Rao lower bound. In particular, with smaller computational requirement, the proposed estimator can achieve the same threshold and estimation performance of the ML method.     

Over-determined Fx-Newton algorithm for active control of low-frequency sinusoids in the vibration and noise radiated by a cylindrical shell

An over-determined multi-channel Fx-Newton algorithm is proposed for active control of structural vibration. The theoretical principle of this algorithm is first derived in the frequency domain and the implementation of the algorithm is then introduced in the time domain. Analytical results show that the rate of convergence of this algorithm is close to that of the Fx-Newton algorithm, and faster than that of the Fx-LMS algorithm. Experiments are also conducted on a raft mounted in a cylindrical shell to test the effects of active-passive vibration isolation with the Fx-Newton algorithm and the proposed over-determined Fx-Newton algorithm. The effects of attenuation of both algorithms are also evaluated on the sinusoids in the radiated noise. The results reveal that at some frequencies where the sinusoids are not suppressed by the Fx-Newton algorithm, the over-determined Fx-Newton algorithm, however, can effectively suppress their presence both in the vibration of the base plate and in the normal vibration of the cylindrical shell. Hence the over-determined Fx-Newton algorithm has excellent effect of global vibration control, and can well attenuate the sinusoids in the noise radiated by the cylindrical shell.     

基于子空间和投影分离的三维正弦信号频率估计算法

本文提出了一种基于子空间和投影分离的三维正弦信号的频率参数估计算法.算法核心思想在于将三维采样数据阵理解为散布在某一维上的二维切片矩阵列,以此来实现对三维采样数据阵列的降维处理,并通过构造投影矩阵来实现信号中各分量的分离,算法可实现信号各分量三维参数自动配对.在整个估计过程中,算法所用矩阵都维持原采样数据阵规模,因而算法整体运算量较小.计算机仿真结果表明所提算法在性能及运算复杂度上均要优于三维情况下的IMDF算法及HOSVD算法.     

ARMA噪声中的正弦波检测

本文提出一种ＡＲＭＡ噪声中正弦波检测的方法，本方法先用改进的Ｐｒｏｎｙ法估计可能存在的正弦波，然后利用一种综合考虑衰减因子以及ＭＵＳＩＣ值的准则从估计结果中区分正统率波的真伪。数值例子表明，本文方法比Ｐｒｏｎｇ方法及ＭＵＳＩＣ方法具有更高的分辨力。     

Frequency estimation performance of several weighted Burgalgorithms

The frequency estimation performance of a set of weighted Burg algorithms is investigated for single complex and real sinusoids in noise. It is demonstrated that in the complex case, an extension of Ibrahim's (1987, 1989) modification of Kaveh and Lipert's (1983) optimum tapered Burg algorithm meets the Cramer-Rao lower bound for a sufficiently high signal-to-noise ratio and a sufficiently large model order. This is in contrast with the original Burg method. In the case of a real sinusoid, the same algorithm most closely approaches this bound, making it the technique of choice for both applications. Spectral resolution is addressed briefly     

Parametric Analysis to Reduce Phase Noise of Frequency Synthesizers for Wireless Communication System

The aim of this paper is analysis and presenting a technique to reduce phase noise of frequency synthesizer for pure signal synthesis. To reduce phase noise of synthesizer, first, we present a mathematical and accurate model of phase noise in phase locked loop based frequency synthesizer with take into account noise of its component. Then we predict output phase noise in term of its parameters. Finally, we describe as effective technique for phase noise in frequency synthesizer. The simulation results show the performance of the frequency synthesizer for the High Speed communication system.     

一种低噪声快速转换频率合成器的设计与实现

介绍了一种低相位噪声、快速转换频率合成器的设计与实现,采用DDS、变带宽、频率预置等多种措施,频率转换时间〈80μs,并对实验结果进行了分析讨论。实验结果表明,该合成器相位噪声具有良好、锁定时间短,适合在超短波电台中应用。     

频率合成相噪相消技术研究

提出了一种新型的基于相位噪声抵消技术的频率合成器设计方法,该方法采用一个相参的锁相环信号在两次频率变换过程中得到输出信号相位噪声的抵消。对相位噪声抵消技术进行了理论分析,并搭建了一个100~2900 MHz 宽带小步进频率源。实验结果表明,在偏离主频10 kHz、100 kHz 处,相位噪声抵消了约20 dB,实验证明该技术对中近区相位噪声抵消效果明显,为超低相噪频率合成器设计提供了一种新的思路。     

Time-Domain Signal Analysis Using Adaptive Notch Filter

Noise reduction and signal decomposition are among important and practical issues in time-domain signal analysis. This paper presents an adaptive notch filter (ANF) to achieve both these objectives. For noise reduction purpose, the proposed adaptive filter successfully extracts a single sinusoid of a possibly time-varying nature from a noise-corrupted signal. The paper proceeds with introducing a chain of filters which is capable of estimating the fundamental frequency of a signal composed of harmonically related sinusoids, and of decomposing it into its constituent components. The order of differential equations governing this algorithm is 2n+1, where n is the number of constituent sinusoids that should be extracted. Stability analysis of the proposed algorithm is carried out based on the application of the local averaging theory under the assumption of slow adaptation. When compared with the conventional Fourier analysis, the proposed method provides instantaneous values of the constituting components. Moreover, it is adaptive with respect to the fundamental frequency of the signal. Simulation results verify the validity of the presented algorithm and confirm its desirable transient and steady-state performances as well as its desirable noise characteristics