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.     

Discriminator Detection of Wide-Band PCM/FM

The performance of discriminator detection of wide-band PCM/FM is investigated. Formulas are derived that allow one to predict system performance with the effects of both predetection and postdetection filtering accounted for. In particular, for a postdetection equivalent noise bandwidthbit time product b0T=2, it is shown that best results are obtained with a modulation index ?=0.6. Furthermore, it is shown that performance to within 1.5 dB of theoretical can be obtained.     

Probability Density of the Maximum Likelihood Elevation Estimate of Radar Targets

The probability density of the maximum likelihood estimate of elevation angle of a radar target in the presence of multipath is calculated. For detectable signals that have low signal-to-noise ratios, the density is a mixture of a Gaussian density and a delta function at the horizon.     

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.     

概率密度函数分析监测发动机气动不稳定征兆

对某型单轴涡喷发动机节流过程中的喘振故障进行了试验研究。在手工关闭放气带的情况下,该型发动机的共同工作线确定地穿越喘振区域,从最大状态收油门减速将会导致该型发动机进入不稳定工作。数据分析中发现压气机第一级静子机匣壁面静压对节流最为敏感,且静压脉动分量的概率密度函数分布随节流有规律地发生变化。定义了概率密度函数特征值θ来量化这种变化。进一步的数据分析表明,θ可以反映压气机第一级端部的流动分离情况,可以作为试验发动机节流过程中的气动稳定性指标。与直接检测模态扰动和短周期扰动相比,监测θ的变化可以为该型发动机提供较长的失速预警时间。      

Cancellation of Unwanted Spectral Components in an FM Multivibrator System

The performance of FM multivibrator systems for high quality communications applications is limited by the presence of unwanted spectral components. A theory is presented for an improved system in which unwanted spectral components are cancelled, achieved by generating a cancelling component in a square-law device. The cancelling component tracks the unwanted component in both frequency and amplitude over a wide bandwidth of signal frequencies. Reductions in magnitude of the unwanted components by at least 16 dB are predicted; reductions of better than 14 dB have been achieved in practice.     

Data Association and Track Management for the Gaussian Mixture Probability Hypothesis Density Filter

The Gaussian mixture probability hypothesis density (GM-PHD) recursion is a closed-form solution to the probability hypothesis density (PHD) recursion, which was proposed for jointly estimating the time-varying number of targets and their states from a sequence of noisy measurement sets in the presence of data association uncertainty, clutter, and miss-detection. However the GM-PHD filter does not provide identities of individual target state estimates, that are needed to construct tracks of individual targets. In this paper, we propose a new multi-target tracker based on the GM-PHD filter, which gives the association amongst state estimates of targets over time and provides track labels. Various issues regarding initiating, propagating and terminating tracks are discussed. Furthermore, we also propose a technique for resolving identities of targets in close proximity, which the PHD filter is unable to do on its own.     

基于概率假设密度滤波器的多目标跟踪方法

在总结分析现有多目标跟踪方法的基础上,重点阐述了一种新的基于概率假设密度的多目标滤波跟踪方法,利用带有新生目标检测功能的概率假设密度滤波方法,通过仿真算例,与传统的MHT方法和GM-PHD方法进行了跟踪性能对比,说明了概率假设密度滤波器在强杂波和新生目标未知情况下的优越性。     

Error Probability in Binary Digital Communication in the Presence of an Interfering Signal

The presence of an interferring signal i(t) in a binary coherent symmetric channel is investigated. The probability of error is maximum when i(t) is antipodal to the transmitted signal, so(t) or s1 (t). The error probability is derived in the presence of a delayed interfering signal - so (t - r), where r is the time delay. An example of phase shift keying signals is given.     

用子波系数概率密度函数研究湍流多尺度结构的间歇性

用热线风速仪在充分发展平板湍流边界层中测量流向速度信号的时间序列并进行湍流多尺度结构统计特性的实验研究。用热线风速仪以高于对应最小湍流时间尺度的分辨率精细测量风洞中平板湍流边界层不同法向位置的流向速度分量的时间序列信号,用子波分析对湍流脉动速度信号进行多尺度分解,将推广的自相似性(ESS)应用于子波分析。用子波系数的概率密度函数验证了多尺度相干结构对间歇性的影响,并证明与距壁面距离有关。对比研究了提取湍流边界层多尺度相干结构前后湍流多尺度结构函数间歇性的变化规律及概率密度函数的变化规律,验证了多尺度相干结构是湍流边界层产生奇异标度律的原因。当这些相干结构被分离出后,由子波系数计算的ESS标度律就回到K olm ogorov线性标度律,这一现象在整个湍流边界层都是很明显的。      

Transmission Characteristics of an FM Signal Through a Hard Limiting Repeater

The response of an FM detector to an FM signal which is passed through a hard limiting repeater together with additive Gaussian noise is described. A general expression of the output SNR is derived that enables the determination of the threshold behavior. To clarify the feature of a transmission characteristic, a comparison with a linear repeater is also made. The output SNR is found to be larger than that of the linear system for all practical values of input CNR's.     

基于高斯混合概率假设密度滤波的扫描型光学传感器像平面多目标跟踪算法

高斯混合概率假设密度(GM-PHD)滤波是一种基于随机有限集理论的次优贝叶斯多目标跟踪方法,本文研究了该算法在扫描型光学传感器像平面的多目标跟踪问题.针对典型的锥扫模式和推扫模式,根据其扫描特性建立目标的运动模型和测量模型.介绍高斯混合概率假设密度滤波的基本原理.针对原算法在强杂波环境中的低效率问题,借鉴传统多目标跟踪...     

Matched-Filter Responses of the Linear FM Waveform

Although the properties of the linear FM signal have been studied previously in considerable detail, such studies have involved rather narrow aspects of the theory. This paper extends the work in several respects. By presenting three-dimensional projections of the conventional ambiguity function of the linear FM signal in more detail than was available before, we can study the sidelobe behavior off as well as on the axes, without weighting, with unilateral weighting in the receiver, and with bilateral weighting. These plots reveal interesting properties related to the signal symmetry in time and frequency. The matched-filter response is then extended to include Doppler distortions of the modulation function. The results show that Woodward's ambiguity function is valid only for signals with relatively modest sophistication, even though in most practical situations one is interested only in those undistorted parts of the matched-filter response in the vicinity of the delay axis. Plots of the response are presented for various degrees of distortion, for signals with and without weighting. Lastly, we consider the effects of a mismatch in range acceleration, again for the various cases of interest. The results convey a thorough insight into the properties of chirp radar under a broad range of operational conditions.     

机载卫星通信天线引导概率分析

针对某机载Ka频段卫星通信天线的使用环境,论述其天线角跟踪系统在捷联航姿设备引导下,天线主波束指向卫星目标位置的概率,分析影响天线角跟踪系统引导概率的主要因素,通过消减系统中大误差源保证了天线引导概率,通过扩展主波束指向空域提高了目标落入概率。计算数据和试验验证表明,给出的分析方法可行,设计策略有效。     

Performance of an Ideal Quantum Receiver of a Coherent Signal of Random Phase

An ideal quantum receiver is to detect a coherent narrow-band optical signal in the presence of thermal background radiation. Curves are given both of the average probability of error in a binary communication system transmitting O's (blanks) and 1's (pulses) with equal probabilities, and of the probability of detection for various fixed values of the false-alarm probability.     

FM Threshold Performance of the Frequency Demodulator with Feedback

The FM threshold performance of the frequency demodulator with feedback (FMFB) is experimentally optimized. Rules of thumb for the practical design of the FMFB with limiter in the loop are proposed. Such design rules provide for optimum FMFB threshold performance given specifications of the received signal. Equivalences among the FMFB, phase-locked loop, and limiter- discriminator offer some additional physical insight into the threshold-extending mechanism of the FMFB not presented by previous investigators.     

不可逆Braysson热机的功率密度优化

用有限时间热力学方法优化了恒温热源条件下不可逆Braysson热机的功率密度.指出了其兼顾较高功率和较高效率时压比及高温侧热导率的取值范围,并发现功率密度较大、同时也使热机相应的功率和效率较高时.高温侧换热器的热导率要大于低温侧换热器的热导率.本研究结果可为实际Braysson热机的优化设计提供理论依据.     

Subspace array processing for the suppression of FM jamming in GPS receivers

The mitigation of FM interference in GPS receivers is considered. In difference to commonly assumed wideband and narrowband interferers, the FM interferers are wideband, but instantaneously narrowband, and as such, have clear time-frequency (TF) signatures that are distinct from the GPS coarse acquisition (C/A) spread spectrum code. In the proposed technique, the estimate of the FM interference instantaneous frequency (IF) and the interference spatial signature are used to construct the spatiotemporal interference subspace. The IF estimates can be provided using existing effective linear or bilinear TF methods. The undesired signal arrival is suppressed by projecting the input data on the interference orthogonal subspace. With a multisensor receiver, the distinctions in both the spatial and TF signatures of signal arrivals allow effective interference suppressions. The deterministic nature of the signal model is considered and the known underlying structure of the GPS C/A code is utilized. We derive the receiver signal-to-interference-plus-noise ratio (SINR) under exact and perturbed IF values. The effect of IF estimation errors on both pseudorange measurements and navigation data recovery is analyzed. Simulation results comparing the receiver performances under IF errors in single and multiantenna GPS receivers are provided.