HFC上行通道的QPSK信号窄带干扰抑制

QPSK是HFC上行通道一种有效的调制方法,将HFC上行通道的输入噪声抽象为一个窄带干扰模型,对其采取非线性抑制措施,构造了一个非线性窄带干扰抑制器,把非线性的DLMS2和DRILS2应用到QPSK调制系统,对其各项性能进行了仿真研究。     

宽带HFC网络回传通路输入噪声抑制的研究

在HFC网络回传通路各类噪声中,输入噪声占有相当大的比重.本文将输入噪声抽象为一种窄带干扰,从数字信号处理的角度对其采取非线性抑制措施,并把归一化FTF算法运用到了该干扰抑制器中,提高了信号处理的实时性.在QPSK调制系统下仿真看到其信噪比和误码率改善都很可观.     

宽带HFC网络中的调制方式与窄带干扰抑制的分析

在整个5－42MHz回传通路频带内，对采用16QAM调制方式的HFC系统，构造了一个非线性窄带干扰抑制器，并应用非线性算法对带宽小于100kHz的窄带噪声进行非线性抑制。     

宽带HFC网络中的调制方式与窄带干扰抑制的分析

宽带HFC网上的上行通道存在严重的噪声和干扰，制约着HFC网双向业务的开通。本在整个5－42MHz回传通道频带内，对采用160QAM调制方式的HFC系统，构造了一个非线性窄带干扰抑制器，并应用非线性算法对带宽小于100kHz的窄带噪声进行非线性抑制。     

MIMO—OFDM系统的半盲迭代接收机

针对存在多载波窄带干扰的多输入多输出正交频分复用系统，本文提出了基于马尔可夫链蒙特卡罗方法的迭代接收机．该方法不仅可以精确地估计出信道脉冲响应，还可以估计出噪声方差以及脉冲噪声发生的位置，这样接收机能够对窄带干扰区别对待，从而有效提高系统性能．该方法的另一个优点是，易于和软输入软输出译码结合，从而完成Turbo接收．仿真结果表明，在慢衰落信道下，与理想信道状态信息下的接收算法仅有3dB差别.     

DS扩频系统抗多窄带干扰方法研究

针对AR过程的窄带干扰,本文构建了DS扩频系统多窄带干扰下的信号模型,给出了统一的观测模型,并用线性、非线性滤波方法对其进行干扰抑制。仿真结果表明,所建模型是有效的,而且滤波方法对多个窄带干扰仍有很好的抑制性能,且非线性滤波的性能要优于线性滤波。     

Dither信号理论分析及仿真

模拟数字转化器(ADC)具有典型的非线性特性,其输出噪声对输入信号存在着依赖关系.为了降低ADC的非线性,对减性Dither量化器控制系统进行了数学分析,得出了使量化器输出噪声与输入信号无关所需要满足的充分必要条件.并利用LabVIEW搭建了减性Dither 量化器控制系统数字仿真平台, 对系统分别加入宽带白噪声Dither信号和窄带正弦Dither信号,仿真结果表明适当地选取Dither信号将有效地改善ADC的性能.     

基于功率谱线模型的脉冲UWB系统干扰分析

在脉冲调制TH-PPM UWB(跳时-脉位调制超宽带无线通信系统)频谱分析的基础上研究了UWB系统对于传统窄带接收机带内干扰的分析模型.与传统的分析方法不同,本文将UWB系统对于窄带接收机的带内干扰等效为带内的白噪声干扰和离散多音干扰,生动的反映出UWB频域的连续和离散部分对窄带系统的干扰.同时,基于相关接收理论,进一步分析了M-PAM调制方式下接收机的平均符号错误概率.通过大量的仿真分析,可以得到一个重要的结论:随着带内离散干扰功率的增加,UWB对窄带接收机的影响越来越近似为等效高斯噪声.     

长短扩频码下直扩系统抗干扰性能分析

在扩频码采用理想随机序列和短周期序列两种情况下,对直接序列扩频系统在宽带噪声干扰、窄带噪声干扰和单频干扰下的抗干扰性能进行了分析和比较,并仿真验证,分析结果对军用扩频系统的设计和应用有指导意义。     

存在噪声情况下非线性放大器的信噪比变化

通过对叠加窄带噪声的确定的正弦波信号输入到非线性放大器时的输出信噪比进行广泛研究表明,在输入信噪比大时,通过限幅器,当输入信噪比小时,在非高斯噪声情况下,通过乘幂放大器往往可以改善输出信噪比。本文将具有饱和特性的乘幂形非线性放大器的输入—输出特性,用5次幂多项式表示,首先,导出对窄带高斯噪声和窄带非高斯噪声都能适用的信噪比改善率的一般表达式,接着,通过数值计算研究了输出信噪比随输入信噪比的变化。结果表明,这种非线性放大器,在输入信噪比大时近似于软限幅,在输入信噪比小时近似于乘幂放大器,对于非高斯噪声,输入信噪比在除0dB附近以外的全部范围内,输出信噪比往往得到改善。     

窄带连续波干扰下宽带接入网上行信道MER研究

窄带连续波是宽带接入网上行信道的典型干扰。为了研究此时的宽带接入网系统性能,推导了窄带连续波干扰的特征函数模型,并以此为依据,建立了系统模型,获得了基于窄带噪声的宽带接入网上行信道QPSK系统调制误码率(MER)与载噪比(C/N)的关系曲线,并对系统模型的MER仿真曲线进行了分析。为提高宽带接入网系统性能和排查干扰提供了有效的理论依据。     

A digital technique to estimate second-order distortion usinghigher order coherence spectra

A digital spectral method for evaluating second-order distortion of a nonlinear system, which can be represented by Volterra kernels up to second order and which is subjected to a random noise input, is discussed. The importance of departures from the commonly assumed Gaussian excitation is investigated. The Hinich test is shown to be an appropriate test for orthogonality in the system identification. Tests for Gaussianity of two important sources, which are commonly used for Gaussian inputs in nonlinear system identification, are presented: (1) commercial software routines for simulation experiments, and (2) noise generators for practical experiments. The deleterious effects of assuming a Gaussian input when it is not are demonstrated. The random input method for evaluating the second-order distortion of a nonlinear system is compared with the sine-wave input method using both simulation and experimental data. The approach is applied to a loudspeaker in the low-frequency band     

Hard-limiting of two signals in random noise

Two sinusoidal signals and Gaussian noise lying in a narrow band are passed through an ideal band-pass limiter that confines the output spectrum to the vicinity of the input frequencies. The output spectrum, consisting of both discrete and continuous components, is studied in terms of its corresponding autocorrelation function. The discrete output components are identified with the output signals and intermodulation products due to interference between the two input signals. The continuous part of the spectrum is associated with the output noise. The effects of limiting are expressed by ratios among the average powers of the output spectral components. Performance curves are given that show signal suppression, the ratio of output to input SNR's, and the relative strength of the intermodulation terms.     

Optimum Modulation and Channel Filters for Nonlinear Satellite Channels

This is a comparative study of three modulation schemes: QPSK, Offset QPSK(OQPSK), and MSK, in nonlinear satellite channels with adjacent channel interference. Two kinds of typical satellite channel models are used for performance evaluation: one is an INTELSAT type narrow band model and the other is a domestic type wide band model. The transmitter filter and receiver filter are optimized for each combination of modulation scheme, channel model, and an input back-off condition for nonlinear amplifiers. All the combinations considered here have the optimum division of the Nyquist shaping between transmitter filter and receiver filter in common. The filters are a wide band sharp cut-off transmitter filter with flat inband response and a gently rolled-off Nyquist receiver filter with an aperture equalizer (x/sin xor1-(2x)^{2}/cos xequalizer). With these optimized filters, comparisons are made with respect to the bit error rate (BER) performance and phase jitter of the recovered carrier. OQPSK and MSK show superior BER performance to QPSK in the wide band model. However, in the narrow band model, QPSK shows the best BER performance among the three modulation schemes. The phase jitter in the recovered carrier is small for all modulation schemes in the wide band model. But, in the narrow band model, the phase jitter in OQPSK and MSK is four times larger than in QPSK. Generally QPSK is the most preferable modulation scheme in the narrow band model: OQPSK and MSK are most preferable for the wide band model.     

Random Noise Interference and Possible Solutions to its Effects on Image Resolution and Gray Scale

In this paper we report the effect of random noise interference in various portions of the video band spectrum' and attempt to model the human visual mechanism for resolving image in the presence of noise. Broad, narrow and mixed bands of white noise distribution effects throughout the video band are investigated. Good agreement results between the experimental data and predicted performance from computer simulation models. The analysis indicates that noise equalization, by pre-emphasizing and deemphasizing a certain portion of the video, results in a considerable improvement in resolution and gray scale of the image.     

基于DSP的直接序列扩频信号中窄带干扰的抑制算法及实现

直扩系统的抗干扰能力由其处理增益决定,当其处理增益不足以对抗强干扰时,则需寻找其他干扰抑制来提高系统性能。本文研究了一种直扩信号的干扰抑制算法,对其工作原理进行了分析,给出了干扰复制和门限算法,并讨论了其中的非线性运算的DSP实现问题。     

SAGD双水平井随钻磁导向系统的研制及应用

针对实测信号微弱、频变、窄带的特点,设计出低噪声、窄通频带、高精度的数据采集滤波电路,有效地滤除了干扰和噪声,使系统探测精度达到±0.3m左右;根据磁感应强度数据的采集要求,制定了单组数据校验的通信协议,减少了干扰导致的个别数据传输错误对整体数据的影响。     

Adaptive nonlinear filters for narrow-band interference suppressionin spread-spectrum CDMA systems

This paper presents a novel nonlinear filter and parameter estimator for narrow band interference suppression in code division multiple access spread-spectrum systems. As in the article by Rusch and Poor (1994), the received sampled signal is modeled as the sum of the spread-spectrum signal (modeled as a finite state independently identically distributed (i.i.d.) process-here we generalize to a finite state Markov chain), narrow-band interference (modeled as a Gaussian autoregressive process), and observation noise (modeled as a zero-mean white Gaussian process). The proposed algorithm combines a recursive hidden Markov model (HMM) estimator, Kalman filter (KF), and the recursive expectation maximization algorithm. The nonlinear filtering techniques for narrow-band interference suppression presented in Rusch and Poor and our proposed HMM-KF algorithm have the same computational cost. Detailed simulation studies show that the HMM-KF algorithm outperforms the filtering techniques in Rusch and Poor. In particular, significant improvements in the bit error rate and signal-to-noise ratio (SNR) enhancement are obtained in low to medium SNR. Furthermore, in simulation studies we investigate the effect on the performance of the HMM-KF and the approximate conditional mean (ACM) filter in the paper by Rusch and Poor, when the observation noise variance is increased. As expected, the performance of the HMM-KF and ACM algorithms worsen with increasing observation noise and number of users. However, HMM-KF significantly outperforms ACM in medium to high observation noise     

光纤AM-CATV系统附加相位调制法的研究

对外调制光纤ＡＭ－ＣＡＴＶ系统中的附加相位调制法抑制ＳＢＳ的原理,以及相位调制法和抑制ＳＢＳ时光纤ＡＭ－ＣＡＴＶ中的非线性失真与噪声进行了详细分析与计算。