Noise factor and antenna gains in the signal/noise equation for over-the-horizon radar

A recommended form of the signal-to-noise equation that includes both internal and external system noise and signal/noise processing losses is discussed. The recommended form conforms to the internationally accepted definition of system operating noise factor but is extended to include signal/noise processing. The predetection signal-to-noise ratio (SNR) of a radar or communication system is proportional to the power gain of the transmit antenna and the directive gain of the receive antenna, and is inversely proportional to the operating noise factor of the receiving system. The operating noise factor is approximately equal to the product of the external noise factor and the signal/noise processing factor when the system is external noise limited, as is usually the case for over-the-horizon (OTH) radar.<>     

Energy Detection of a Random Process in Colored Gaussian Noise

A likelihood receiver for a Gaussian random signal process in colored Gaussian noise is realized with a quadratic form of a finite-duration sample of the input process. Such a receiver may be called a "filtered energy detector." The output statistic is compared with a threshold and if the threshold is exceeded, a signal is said to be present. False alarm and detection probabilities may be estimated if tabulated distributions can be fitted to the actual distributions of the test statistic which are unknown. Gamma distributions were fitted to the conditional probability densities of the output statistic by equating means and variances, formulas for which are derived assuming a large observation interval. A numerical example is given for the case in which the noise and signal processes have spectral densities of the same shape or are flat. The optimum filter turns out to be a band-limited noise whitener. The factors governing false alarm and detection probabilities are the filter bandwidth, the sample duration, and the signal level compared to the noise. Two sets of receiver operating characteristic curves are presented to complete the example.     

Comments on "Optimum Bandwidth of a Low-Pass Filter for Detection of a Pulse in Nonstationary Noise"

In a recent correspondence1 a calculation of the optimum bandwidth of a low-pass RC filter for the detection of a pulse signal in nonstationary noise was presented. The purpose of this correspondence is: 1) to point out additional references to the work which has been conducted in the stationary noise case, and 2) to present an interesting alternate derivation of the expected output noise power for the nonstationary noise case.     

噪声调制连续波雷达信号波形射频隐身特性

雷达信号波形的射频(RF)隐身性能是雷达系统能否适应现代战场环境的重要因素,雷达射频隐身信号波形设计是现代雷达系统设计中的重要课题.首先,在介绍随机噪声信号雷达原理的基础上,基于Schleher截获因子阐述了噪声调制连续波雷达信号波形的射频隐身特性.然后,分析了高斯噪声相位和频率调制连续波雷达输出自相关函数和高斯噪声相...     

The Effect of Hard Limiting an Angle-Modulated Signal Plus Noise

The effect of hard limiting an angle-modulated signal plus narrow-band Gaussian noise is analyzed. Several examples are considered?sinusoidal angle modulation, Gaussian angle modulation, and biphase angle modulation. The general conclusion is that when a zonal band-pass filter is used, which rejects dc and second harmonics, an angle-modulated signal plus Gaussian noise provides the same output signal-to-noise ratio as shown by Davenport for a CW signal plus Gaussian noise. However, when a narrow bandpass filter is used, which has a bandwidth approximately equal to the input angle-modulated signal, an angle-modulated signal plus Gaussian noise has a better output signal-to-noise ratio than a CW signal plus Gaussian noise.     

An Adaptive Threshold System for Nonstationary Noise Backgrounds

The problem of detecting target signals in an ocean environment using active sonar is complicated by the nonstationary background which usually consists of both ambient ocean noise and reverberation. on. In this paper a signal processing system capable of detecting a signal in nonstationary noise is introduced. This system makes use of the mean and variance time functions of the nonstationary noise background in order to design estimation filters which will cope with the nonstationarity. Appropriate statistics of the noise and signal (tone burst) plus noise have been obtained and are used to determine the probabilities of false alarm and detection and the receiver operating characteristics.     

Detection of Known Signals in Nonstationary Noise

The basic design of a nonlinear, time-invariant filter is postulated for detecting signal pulses of known shape imbedded in nonstationary noise. The noise is a sample function of a Gaussian random process whose statistics are approximately constant during the length of a signal pulse. The parameters of the filter are optimized to maximize the output signal-to-noise ratio (SNR). The resulting nonlinear filter has the interesting property of approximating the performance of an adaptive filter in that it weights each frequency band of each input pulse by a factor that depends on the instantaneous noise power spectrum present at that time. The SNR at the output of the nonlinear filter is compared to that at the output of a matched filter. The relative performance of the nonlinear system is good when the signal pulses have large time-bandwidth products and the instantaneous noise power spectrum is colored in the signal pass band.     

Weak Signal Detection in Non-Gaussian Noise of Unknown Level

An adaptive threshold detector to test for the presence of a weak signal in additive non-Gaussian noise of unknown level is discussed. The detector consists of a locally optimum detector, a noise level estimator, and a decision device. The detection threshold is made adaptive according to the information provided by the noise level estimator in order to keep a fixed false-alarm probability. Asymptotic performance characteristics are obtained indicating relationships among the basic system parameters such as the reference noise sample size and the underlying noise statistics. It is shown that, as the reference noise sample size is made sufficiently large, the adaptive threshold detector attains the performance of a corresponding locally optimum detector for detecting the weak signal were the noise level known.     

一种射频噪声干扰信号品质因素改进方法

针对射频噪声干扰信号直接限幅引起的干扰信号品质降低问题,分析了射频噪声干扰直接限幅造成的影响,在射频噪声干扰信号品质因素理论模型基础上,提出 1种基于双地址序列读取的射频噪声干扰信号品质优化方法。通过设置双地址寻址方式,改进基带噪声数据读取方式,提高限幅条件下的射频噪声干扰信号品质因素。仿真实验表明,该优化方法能够在直接限幅条件下提高干扰信号的品质因素,并基于 FPGA进行了硬件测试,验证了该方法的可行性。     

含噪振动信号中早期碰摩的故障检测研究

 研究了在有噪环境下发动机转子系统早期碰摩故障的检测问题。利用最优参数搜索法改进了独立分量分析( ICA) 算法, 用于求解转子系统振动信号与噪声的盲分离问题。在此基础上, 对分离后的振动信号利用小波包分解进行早期碰摩信号的检测。结果显示最优搜索的ICA 算法运行效率高, 信号分离纯度好, 对振动信号有高效的降噪作用, 并利用小波包分解准确地检测出振动信号中的碰摩信息, 其效果优于小波分解法。信噪分离与小波包分解相结合有望用于工程实践中的早期碰摩故障检测和诊断。     

A Method for Setting a Test Signal Level Relative to Noise

A method is described for adjusting the leval of an RF test signal generator relative to the noise level at the receiver output. The method compares a detected output to a threshold and counts the number of times noise and signal plus noise cross the threshold in a given number of tries. By setting the threshold at a given false alarm probability for noise alone and then adding the test signal and adjusting its level to give a specified detection probability, the signal-to-noise ratio can be calibrated to an accuracy that depends on the number of samples used to measure the probabilities. The false alarm and detection probabilities are given for best accuracy as well as the rms error in signal-to-noise ratio as a function of the number of samples used.     

灵巧噪声干扰本质含义探讨

文章对灵巧噪声干扰概念的表述提出了质疑,在多项质疑中选取了SLB技术进行简要分析,并指出,SLC等抗干扰技术的作用与是否实施灵巧噪声干扰没有直接关系。进一步,基于匹配滤波器理论对灵工j噪声干扰的本质含义进行了分析,指出：灵巧噪声干扰的本质含义是使干扰由多个分量组成,并且使干扰中的每一个分量的频谱都与雷达发射信号的频谱相...     

Noise Generation of a Switching Regulator

Analytical and experimental considerations on the surge and noise generated in a typical switching regulator are discussed. There are two kinds of surges which occur in the switching instants of the transistor. These surges appear as high voltages across the semiconductor elements and decrease their reliabilities. Corresponding to the surge generation, noise voltages appear in the output terminals and may induce malfunctions of a signal processing device connected to the regulator. We analyze these surge and noise voltages by means of high-frequency equivalent circuits.     

FM Laser Noise Effects on Optical Doppler Radar Systems

A detailed analytical study is made of the effect of FM noise on a laser carrier frequency which is used in a Doppler radar. Both long-term drift and short-term FM noise are considered. The case of high modulation index of the noise is permitted by the theory. Forward as well as slanted beams are examined. Curves have been calculated for each case to allow rapid estimates of the bandwidth requirements to accomodate the laser noise. This, in turn, will give the resolution limit of the radar caused by that noise. A summary of the results is given.     

Detection in Laplace Noise

The discrete time detection of a known constant signal in white stationary Laplace noise is considered. Exact expressions describing the performance of both the Neyman-Pearson optimal detector and the suboptimal linear detector are presented. Also, graphs of the receiver operating characteristics are given. The actual performance of the Neyman-Pearson optimal detector is compared to that predicted by a Gaussian approximation to the distribution of the test statistic.     

The Uncertainty of Pulse Position Due to Noise

The time at which a received signal crosses a certain level fluctuates in the presence of noise. In this paper, a theoretical formula for the standard deviation of this thresholding time is obtained. The formula is applied to the detection of a pulse perturbed by Gaussian noise. Two practical detection schemes, the peak amplitude estimator and the double differentiator, are theoretically analyzed and compared. Also, a formula is derived which may be used to determine the efficacy of a false-alarm detection system.     

激光脉冲法背温信号中噪声信号的滤除方法

针对激光脉冲法背温信号中存在的噪声干扰,通过频谱分析确定了噪声信号的频率范围,设计了相应的FIR数字滤波器,并对滤波后存在的残留噪声进行了递推平滑滤波.滤波前后的数据对比表明,该方法能有效滤波背温信号中的噪声.     

On Signal and Noise Level Estimation in a Coherent PCM Channel

Joint maximum likelihood estimators are presented for the signal amplitude and noise power density in a coherent PCM channel with white Gaussian noise and a correlation receiver. The estimates are based upon the correlation coefficient outputs of the receiver. From these estimators, an estimator for the quantity (received signal energy)/bit/,(noise power)/(unit bandwidth) upon which the error probabilities depend, is derived. This estimator is shown to be useful as 1) a point estimator for the signal-to-noise ratio for the higher values of this ratio (about 4 dB or greater), and 2) an easily calculated statistic upon which to base data acceptance or rejection criteria. The acceptance or rejection levels are obtained by the use of confidence interval curves in conjunction with word error probability data.     

Angle Estimation with Adaptive Arrays in External Noise Fields

A method of estimating the angle of arrival of a signal at an array of sensors in an external noise environment is outlined. The development is based on a maximum likelihood estimator and leads naturally to adaptive sum and difference beams which null the external noise sources. An algorithm for estimating angle of arrival, based on the outputs of adaptively distorted sum and differnce beams, is shown to perform well in the presence of sidelobe and/or main beam interference.     

The Counting Phase Detector with VLF Atmospheric Noise

The counting detector offers a simple means of making and averaging digital measurements of signal phase. However, use of the averages can lead to erroneous estimates if the signal has a low carrier-to-noise ratio. How to overcome this problem by using multiple counters is shown here. Characteristics for both Gaussian and impulsive noise are derived, and algorithms for estimating both phase and carrier-to-noise ratio are presented.