On Uniform Sampling of Amplitude Modulated Signals

For a bandpass waveform produced by the amplitude modulation of a low-pass signal, it is shown that the corresponding bandpass signal may be recovered from its samples taken at a uniform rate which is equal to or less than half the sampling rate called for in applying the classical bandpass sampling theorem.     

Signal-to-Noise Ratio in the Bandpass Output of a Discriminator

A formula is derived for the output signal-to-noise power ratio from a limiter-discriminator that is followed by an ideal (rectangular) bandpass filter. This signal-to-noise ratio is shown to be inversely proportional to the difference between the cube of the upper cutoff frequency and the cube of the lower cutoff frequency. The formula commonly utilized by designers for the discriminator output signal-to-noise ratio was derived for the case of a lowpass filter on the discriminator output. The bandpass and low-pass formulas are compared to indicate 1) the advantage of bandpass filtering for the discriminator output, and 2) the error incurred if the designer employs the low-pass formula to evaluate the performance of a bandpass filter design. Finally, the accuracy of a narrow-band approximation for the bandpass formula is evaluated.     

On the Mapping Associated with the Complex Representation of Functions and Processes

The mapping between function spaces that is implied by the representation of a real ?bandpass? function by a complex ?low-pass? function is explicitly emphasized. The discussion is extended to the representation of random processes where the mapping is between spaces of random processes.     

Modeling and Performance Evaluation of Nonlinear Satellite Links-A Volterra Series Approach

An analytical solution to the problem of modeling bandpass nonlinear channels and evaluating the performance of digital communication systems operating on them is presented. A method based on a Volterra series representation of the overall channel is first proposed, which allows one to extend to nonlinearities with memory the well-known concepts of complex envelope of bandpass signals and low-pass equivalent of bandpass linear systems. The general results previously mentioned are then applied to digital satellite communication systems operating over nonlinear channels. The effect of a nonlinear amplifier located in the satellite is considered, in combination with that of transmitting and receiving filters located in the Earth stations. In addition, both uplink and downlink noise are taken into account. Basic advantages of this approach are the generality it offers to the analysis and the fact that it allows accurate evaluation of the error probability in a short computer time.     

Binary Communication with Large Bandwidth to IF Frequency Ratios

The effect of I F filter bandwidth to I F frequency ratio on the probability of error in a binary bandpass communication system with nonreturn-to-zero (NRZ) and split-phase (SP) signals is investigated. ed. Explicit results are given for the case when the bandpas I F filter is transformed from a single-pole low-pass filter.     

基于低通等效的带通PSWF脉冲产生方法

椭圆球面波函数不存在闭式解,带通 PSWF脉冲信号的实时求解产生限制了 PSWF的应用。针对这一问题,从带通信号低通等效的基本原理出发,分析了带通 PSWF脉冲信号的低通等效形式；在此基础上,反向运用低通等效原理,给出了一种带通 PSWF脉冲重构产生方法,并用 FPGA对该方法进行了设计实现。这一方法将带通 PSWF脉冲信号的产生转化为其低通等效形式的产生,可有效降低信号产生的复杂度,该方法引入了正余弦变换,建立了非正弦 PSWF脉冲产生与正余弦变换技术之间的联系,为 PSWF脉冲的工程应用奠定了基础。     

The Response of Hard-Limiting Bandpass Limiters to PM Signals

The signal-to-noise ratio of the output of a hard-limiting bandpass limiter to a PM signal is calculated by using the probability density function of the random phase variable. The signal-to-noise ratio transfer characteristics are plotted for comparison.     

An Analysis of the Performance of the Oscillating Limiter Driven by FM Signals Corrupted by Noise

The behavior of the oscillating limiter (OL) driven by FM signals is surveyed, and its performance with signal corrupted by noise is investigated. For high values of the carrier-to-noise ratio (CNR), if the frequency deviation of the signal is small in comparison with the locking range of the OL, it is calculated, and experimentally verified, that a system OL discriminator is equivalent to a system bandpass limiter discriminator followed by a linear network whose frequency response has been specified. When the frequency deviation is not so small, the baseband noise power increases with it; a formula is given that allows the calculation of this power when the signal is such that the circuit operates in quasistationary fashion. For low values of the CNR, a mathematical analysis presents unsurmountable difficulties. However, heuristic argumentation leads to an interpretation of the operation of the OL in the threshold region, which is substantiated by an experimental investigation. The results of this paper enable a comparative evaluation of a system OL discriminator and a system bandpass limiter discriminator, to which the former reduces when the feedback path in the OL is open.     

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.     

The Calculation of Frequency-Modulation Distortion in Linear Networks

A numerical method is developed for the calculation of steady-state FM distortion in a linear passive network from the character of the FM signal input and the steady-state transfer characteristics of the network. The method of calculating FM distortion requires the solution of a finite set of linear equations which is accomplished readily by a digital computer. To illustrate the use of the method, the FM distortion introduced by a Chebyshev-response bandpass filter is calculated for a range of network and input signal parameters.     

Output Signal-to-Noise Ratios for Amplitude-Modulated Noise-Like Lasers

A general expression of the output SNR of a photodetector is derived for a noise-like laser amplitude-modulated by a stationary Gaussian random modulating signal in the presence of a background light. The electric field Vx(t) of the noise-like laser is assumed to be a stationary narrowband Gaussian random process with zero mean. Two types of modulating signal are considered, the baseband and bandpass modulating signals. More specifically, the effects of the center frequency of the modulating signal, the modulating degree, the bandwidth ration of the noise-like laser to the modulating signal, the effective average quantum rate, and input CNR on output SNR are studied. The detection characteristics of the noise-like laser are also made clear by comparison with the case of a coherent laser.     

Probability Density Function at the Output of the Delay-Lock Discriminator

The first-order probability density at the output of the correlation network of the delay-lock discriminator is determined using the methods developed by Arthur, Kac, and Siegert. The analysis assumes that the input signal is stationary and Gaussian and that the discriminator is locked on. No restrictions are made on the bandpass filter characteristics in the channels.     

On detection using filter banks and higher order statistics

We suggest a method, based on the use of filter bank and higher order statistics (cumulants), for detection of transient signals. The method first uses a bandpass filter bank, which separates the spectrum of the observed signal into narrow frequency bands. Each subfilter of the filter bank is then followed by a cumulant estimator, and thereby suppressing colored noise. By selecting those subfilters that have large output energies, the filter bank can approximate the behavior of a matched filter. Moreover, no a priori information about the waveform of the signal is needed. The performance of the detector is evaluated by using a simulated signal as well as a measured signal. The presented detector is compared with the optimal matched filter detector.     

Analysis of Squaring Circuit Mechanizations in Costas and Squaring Loops

Two different implementations of the carrier recovery loop for suppressed carrier binary phase-shift keyed (BPSK) signals are considered. In particular, the tracking performance of the squaring loop in which the squaring circuit is mechanized by a limiter/multiplier lier combination to produce the absolute value of the incoming signal, followed by appropriate bandpass filtering, is compared with that of the usual squaring loop whose squaring circuit is the timestwo wo multiplier which exhibits a square law characteristic.     

Nonlinearity Model with Variable Knee Sharpness

Soft limiter models used in the past do not provide a convenient way of changing the knee sharpness while maintaining small signal linearity. A new model is described which does this. Both instantaneous characteristics and bandpass limiter characteristics are discussed. The model is also suitable for analyzing and simulating compressors, expanders, and detectors.     

Interference Due to Limiting and Demodulation of Two Angle Modulated Signals

Two angle modulated signals (FM or PM) passing through a limiter and then a demodulator are analyzed. The analysis considers the problem of adjacent carrier interference, direct adjacent channel interference (DACI) or cross talk, and adjacent channel interference (ACI). The analysis of adjacent carrier interference shows that if the 3rd order IM is not to overlap the signal spectra, the carrier frequencies must be separated by 2B where B is the bandwidth of each carrier. The ACI analysis shows that the carrier frequencies must be separated by B+2?m for no ACI, since the demodulator reduces the bandwidth of the 3rd order IM from 3B to 2B+2?m where ?m is the maximum frequency of each baseband. The DACI analysis shows that DACI does not exist in a PM system and is -52 dB for an ideal hard limiter with no bandpass filter. But the DACI is -58 dB for an ideal hard limiter with a more realistic bandpass filter.     

巴特沃斯数字滤波器在自动测试中的应用

本文主要研究巴特沃斯低通数字滤波器在自动测试系统中的应用。讨论了高速采样低速输出的自动测试系统中采用低通数字滤波器的必要性;比较了巴特沃斯低通数字滤波器与多点平均滤波的性能,巴特沃斯滤波器具有较理想的特性;介绍了建立巴特沃斯低通数字滤波器的设计方法,以及在实现实时滤波算法时,克服初始瞬变过程和防止滤波器数值不稳的措施。最后,给出了在长时间陀螺漂移测试中的应用结果。     

Phase Analysis in Multiple-Sensor Receivers with High Signal-to-Noise Ratio

The ideal phase detector characteristic is analyzed for estimating the phase difference between two stochastic input signals. This can essentially be described as a correlation process formed by multiplying the two input signals and extracting the phase. High signal-to-noise ratio conditions are assumed to linearize the system with respect to the noise. The effects of the nonlinearity on the signal are handled in terms of a series expansion and by using low-pass filtering on the receiver output. The mean square error of the system is calculated for some typical parameters.     

Adjacent Channel Interference in a Binary Bandpass Communication System

The effect of adjacent channel interference on the probability of error in a binary bandpass communication system with an integrating and dumping detector is investigated. Narrowband filters are assumed in the receiver of the main signal and transmitters of both main and interfering signals. Plots of the probability of error as a function of signal to noise ratio in the main channel or as a function of carrier frequency difference between the main and interfering signals are presented, assuming that the filters are of the Butterworth type. These figures are helpful in the selection of minimal frequency spacing of adjacent channels.     

Error Probability for NCFSK with Linear FM Jamming

An expression is derived for the probability of error for a conventional binary, noncoherent, frequency-shift-key (NCFSK) communications system under the influence of bandpass Gaussian noise and a linear frequency-modulation jamming waveform. The resulting integral is expressed in terms of the well-known Q function, which depends upon average signal, noise, and jamming powers. The analytical procedures used can be applied to the analysis of the effects of other types of jamming.