Volume Properties for the Wideband Ambiguity Function

It is shown that the volume under the wideband ambiguity function is close to the square of the signal energy. The ambiguity volume is asymptotically conserved as the signal approaches the narrowband case. The narrowband ambiguity volume is a lower bound for the volume of the wideband ambiguity function.     

Standardization of the Definition of the Radar Ambiguity Function

A survey of the literature indicates an inconsistency in the definition of the radar ambiguity function. This correspondence suggests a definition consistent with Woodward's intent.     

Fourier Transform and Ambiguity Function of Piecewise Polynomial Functions

A general systematic procedure is described for computing the Fourier transform and the ambiguity function of waveforms that are piecewise polynomial. The procedure can be implemented by hand or programmed for execution by a digital computer. The main advantage of the technique is that integration is replaced by a finite summation. Examples include the computation of characteristic function, moments, and the ambiguity function of an amplitude modulated linear FM signal.     

Average Ambiguity Function for a Randomly Staggered Pulse Sequence

An average ambiguity function for the envel?pe of a randomly stagger-pulsed radar is defined. This function is related to the characteristic function of the pulse occurrence time statistics, and is numerically evaluated for some special cases.     

Slope Coding of Coherent Pulse-Burst Waveforms

Useful new properties are obtained with a coherent pulse-burst waveform if the FM slopes are allowed to change from pulse to pulse. A design feature using such a "slope-coded" waveform is the ability to transfer, in a controllable manner, ambiguity volume from the range ambiguity peaks to regions located between the peaks (in the frequency direction). Slope coding thus provides a useful mechanism for matching the waveform to the environment; i. e., it permits the signal designer to make some compromise between range ambiguity-peak heights and low-velocity clutter rejection.     

On Computing the Cramer-Rao Bound for a Random Signal

The Cramer-Rao bound for estimating parameters of a random signal is obtained using a sampled data approach. A numerical example is presented to illustrate the result. In two limiting cases, it is shown that this bound converges to the well-known bounds for the point and Rayleigh targets.     

High Power Radar Implementation of Coherent Waveforms

The radar use of coherent burst waveforms to obtain clutter suppression is summarized and problems arising from the high power implementation of such waveforms are discussed. These problems arise from the nonlinear nature of the typical high power radar transmitter and result in loss of subpulse-to-subpulse amplitude and phase accuracies, causing clutter suppression degradation. adaptive control loop used to measure transmission errors and provide continuous updating to minimize such errors is proposed. Residual transmission errors resulting via use of the control loop are calculated and shown to have an insignificant effect upon the clutter suppression properties of the coherent waveform. Experimental verification of control loop performance is presented.     

Doppler Properties of Polyphase Coded Pulse Compression Waveforms

Doppler properties of the Frank polyphase code and the recently derived P1, P2, P3, and P4 polyphase codes are investigated and compared. An approximate 4 dB cyclic variation of the peak compressed signal is shown to occur as the Doppler frequency increases. The troughs in the peak-signal response occur whenever the total phase shift across the uncompressed pulse, due to Doppler, is an odd multiple of ? radians. It is shown that while the P3 and P4 codes have larger zero-Doppler peak sidelobes than the other codes, the P3 and P4 codes degrade less as the Doppler frequency increases. Also, the effects of amplitude weighting and receiver bandlimiting for both zero and nonzero Doppler are investigated.     

On the Limitations of Random Sensor Placement for Distributed Signal Detection

We consider the design of a sensor network for detecting an emitter which if present is known to be located in an interval but whose exact position is unknown. We seek to minimize the total system power consumption subject to detection performance constrains by carefully choosing the thresholds and positions of the sensors. Toward this goal, we propose an iterative algorithm for the optimization problem. Numerical results are given to provide insights into the design of such networks. We show that random sensor placement can perform poorly, in contrast to what many currently believe.     

On Clutter Modeling and the Spectra of Two-Dimensional Gauss-Markov Random Signals

The spectral properties of two-dimensional isotropic clutter signals are examined for the cases in which 1) the clutter has an exponential spatial autocorrelation function, and 2) the clutter is a two-dimensional Gauss-Markov random signal. The one- and twodimensional power spectral densities before and after antenna filtering are obtained, and some of the differences and similarities between these two models are discussed in the context of spectral analysis.     

论政府经济职能与非经济职能的关系

政府职能是由政府经济职能与政府非经济职能(包括政治职能和社会职能)构成的职能体系.政府经济职能与非经济职能是政府应该履行的不同职能,两者之间存在着相同之处,也存在着不同之处;两者相互依存,相互制约.政府经济职能目标与非经济职能目标既存在协调的一面,也存在相冲突的一面.在政府要实现的职能目标中,政府优先选择的顺序是不同的,政府经济职能与非经济职能之间相互依存、相互制约的关系决定了政府职能机构体系的复杂性,也决定了政府要有效地履行其职能,就必须使政府各职能部门相互配合和协调.     

焊接电弧波形和图像的同步采集与再现

进行了焊接电弧高速摄像图像和信号波形的同步采集和再现研究,给出了电弧图像和波形再现具体实现技术,并利用该技术成功地进行了电弧光谱信息检测熔滴过渡过程、二氧化碳短路过渡过程和变极性MIG焊电弧行为的研究。     

论制度结构对经济增长的作用

在制度经济学的分析框架里，制度对于经济增长来讲是至关重要的，同时，制度又是有一定结构的，制度结构对于经济增长具有十分重要的作用。从系统论的视角来看，不同的制度结构，其对经济增长的作用是不一样的；从制度融合与冲突的视角看，最有效率的制度安排是能够实现外在制度与内在制度的融合，反之，将会削弱外在制度规则的有效实施，降低制度效率，成为经济增长的绊脚石；从制度效率的视角进行考察，好的制度结构能通过制度效率的提高来促进经济增长，差的制度结构则降低制度效率；如果内在制度与外在制度融合得好，人为设计的制度质量就高，其能够有效实施并发挥出相应的制度效率，从而促进经济的有效增长．相反．就可能对经济增长产哇负作用．     

试论政府转换经济职能的着眼点

政府转换经济职能的含义,主要是处理好政府与企业、管理与服务、直接管理方式与间接管理方式,以及政府机构调整四个方面的关系,中心是解决政府为企业服务的问题,因此,转换政府经济职能应当紧紧抓住服务,认真做好(1)更新观念、确立起企业在经济活动中的主体地位;(2)制订经济计划、行业规划以及完善各项法规条例;(3)以“小政府、大服务”的原则调整政府机构;(4)政府经济职能法制化等方面的工作。     

Ambiguity properties of quadratic congruential coding

The ambiguity characteristics of multiple access frequency hop codes based on standard quadratic congruences are investigated in the light of results obtained for codes based on Costas arrays and extended quadratic congruences. While the autoambiguity properties are found to be very similar to those of Costa codes, i.e. nearly ideal, the cross-ambiguity properties of quadratic congruential codes are much better. These results are valid across the whole class of code sets considered, but they are obtained at some expense in the pulse compression characteristics of the codes. A uniform upper bound is placed on the entire cross-ambiguity function surface, and bounds are placed on the amplitude of spurious peaks in the autoambiguity function. These bounds depend on the time-bandwidth product and code length exclusively and lead naturally to a discussion of the design tradeoffs for these two parameters. Examples of typical autoambiguity and cross-ambiguity functions are given to illustrate the performance of quadratic congruential coding with respect to Costas coding     

Ambiguity resolution of multiple targets using pulse-Dopplerwaveforms

To cancel clutter, both medium-PRF waveforms which are ambiguous in both range and Doppler and high-PRF waveforms which are ambiguous in range but unambiguous in ambiguities, a previous paper has shown that superior results for a single target can be achieved by using a clustering algorithm. Here, the problem of multiple targets is considered. A maximum likelihood (ML) technique which incorporates the clustering algorithm is developed for the multiple target problem. Simulation results show that four targets which have the same speed but are at different ranges can be resolved by using a medium-PRF waveform and employing the ML resolution technique     

Ambiguity function of quadriphase coded radar pulse

Taylor's quadriphase coding (J.W. Taylor, Jr. and H.J. Blinchikoff, ibid., vol.23, no.2, p.156-70, Mar. 1988) is investigated for nonzero Doppler shifts. While the zero-Doppler cut of the ambiguity function (i.e. the autocorrelation) strongly resembles that of the corresponding biphase code, the remaining ambiguity function differs considerably. The ambiguity function of quadriphase code 13 is typified by a diagonal ridge as found in linear FM signals. The ambiguity function of quadriphase code 28A resembles the three parallel ridges of Frank code 16     

A Note on the Ambiguity of Troposcatter Aircraft Interference Patterns

Earlier investigators of troposcatter propagation phenomena have suggested that aircraft-created interference patterns observed at the receiving site can be used to measure aircraft motion within and near the common volume region. A simplified signal and scattering model is used to show that these interference signatures are ambiguous unless prior knowledge of the aircraft trajectory is available.