改进的分段多项式建模的电离层相位去污染新方法

时变电离层的相位污染使天波超视距雷达(OTHR)的回波多普勒谱展宽.近年来已发展了基于分段的相位多项式参数建模和高阶模糊函数的方法估计和校正电离层的相位污染.由于实际电离层信道为时变的且不可预测,因此,采用预先确定阶数的建模方法有较大的局限性.本文提出了一种改进的方法来选择相位多项式建模的阶数.该方法引入三个判决准则对分段后的信号作建模阶数的自适应选择.实验结果表明,改进后的算法比原有的分段相位多项式参数估计方法以及其他两种电离层校正方法具有更好的性能,特别在校正快速变化的电离层相位污染时具有更为明显的优势.     

返回散射回波去电离层相位污染方法比较与分析

高频信号利用电离层的反射作用进行目标探测,探测距离远,范围广,可应用于气象、军事预警、海面检测等领域.但是对于海上目标,尤其是舰船等慢速目标,由于海杂波的强烈干扰,致使信杂比很低,要求较长时间的相干积累时间.而电离层的时变性和多径效应的存在严重影响相干积累的效果.本文主要论述国内外学者就此问题提出的各种去电离层相位污染方法,并对其做了对比和分析.     

A universal prediction lemma and applications to universal datacompression and prediction

A universal prediction lemma is derived for the class of prediction algorithms that only make inferences about the conditional distribution of an unknown random process based on what has been observed in the training data. The lemma is then used to derive lower bounds on the efficiency of a number of universal prediction and data compression algorithms. These bounds are nonasymptotic in the sense that they express the effect of limited training data on the efficiency of universal prediction and universal data compression     

掩星观测中电离层延迟对LEO卫星轨道误差的响应

从Haselgrove和Budden方程出发，模拟了GPS信号在电离层中的传播过程，利用GPS/MET实验中5组GPS和LEO卫星的实际轨道，分别模拟了无LEO卫星轨道扰动和有轨道扰动情况下的GPS信号在电离层中的传播，并生成了对应的电离层延迟量，以同步生成的模拟精度序列为参照，就掩星观测中电离层延迟对LEO卫星轨道误差的响应程度进行了估计和分析，初步结果显示：在掩星观测中，电离层延迟对LEO卫星轨道误差的响应比中性层延迟要弱得多，这可能同采用了电离层掩星观测的采样频率比中性层采样频率低两个数量级的技术手段有关。     

The combined use of satellite differential Doppler and ground-based measurements for ionospheric studies

The use of satellite differential Doppler measurements to study latitudinal variations ofF-region electron density is described. It is shown that the ambiguity in the total phase path length may be resolved employing either incoherent scatter radar measurements or vertical-incidence ionosonde data, together with some assumptions concerning east-west gradients at the latitude of the observing station. Sample results are given showing the location of the midlatitude trough of electron density observed at Millstone Hill through observations of the U.S. Navy Navigation Series satellites.     

A model relating wearout to breakdown in thin oxides

A model has been developed relating wearout to breakdown in thin oxides. Wearout has been described in terms of trap generation inside of the oxide during high voltage stressing prior to breakdown. Breakdown occurred locally when the local density of traps exceeded a critical value and the product of the electric field and the higher leakage currents through the traps exceeded a critical energy density. The measurement techniques needed for determining the density of high-voltage stress generated traps have been described along with the method for coupling the wearout measurements to breakdown distributions. The average trap density immediately prior to breakdown was measured to be of the order of low-10¹⁹/cm³ in 10 nm thick oxides fabricated on p-type substrates stressed with negative gate voltages. The model has been used to describe several effects observed during measurements of time-dependent-dielectric-breakdown distributions. The area dependence of breakdown distributions, the differences in the breakdown distributions during constant current and constant voltage stressing, and the multi-modal distributions often observed were simulated using the model. The model contained the provision for incorporation of weak spots in the oxide     

Design considerations for a femtosecond pulse laser balancing self phase modulation, group velocity dispersion, saturable absorption, and saturable gain

This paper describes the design and operating characteristics of a femtosecond pulse ring dye laser that employs the combined effects of self phase modulation, group velocity dispersion, saturable absorption, and saturable gain to generate pulses as short as 27 fs.     

A model for interference studies relating to multisatellite non-geostationary systems in the mobile satellite service

An option being considered by current and prospective mobile satellite service (MSS) operators is the use of constellations of non-geostationary orbit (NGSO) satellites to provide global personal communications. The scarcity of free spectrum, together with the bandwidth typically required, means that any new MSS system must consider sharing spectrum with other systems and services. Spectrum sharing must be based on defined interference criteria being satisfied. When multiple NGSO satellites are considered there is no accepted method for assessing interference. This paper describes a model used as the basis for a computer simulation of interference scenarios involving MSS, fixed service (FS) and fixed satellite service (FSS) systems. The simulation includes NGSO dynamics, constellations of MSS satellites with multi-spot antennas, multiple geostationary FSS satellites and multiple hop FS links. Interference events are based on C/I calculations, and statistics, such as the percentage of time that the C/I falls below a required protection ratio, are calculated. More generally C/I cumulative distribution functions are produced.     

A planar chart equivalent to Poincaré sphere for expressing state-of-polarization of light

A planar chart for expressing a state of polarization of an arbitrarily polarized light is proposed. The proposed chart is equivalent to the Poincaré sphere, but has an advantage over the Poincaré sphere in that it can be printed on a flat paper. The characteristics of the proposed chart are investigated. The computer-drawn exact chart is shown with important parameter values. Finally, an example of the application of the proposed chart is described.     

A rejection system for interference in TV reception caused bysporadic-E ionospheric propagation

A method to cancel interference waves by extracting them from TV signals through quadrature synchronous detection and then transforming the signals with a Hilbert transform method is introduced. The system eliminates interference waves at any frequency within the TV signal band. It is easily applied to rebroadcast stations, since it is possible to cancel interference waves at the intermediate-frequency stage. The system automatically eliminates a maximum of five interference waves. It suppresses interference waves by more than 40 dB at a desired-to-undesired signal ratio of 10 dB. The system will greatly contribute to eliminating abnormal interference waves caused by the sporadic-E layer as well as other undesired interference with TV signals     

A universal test and maintenance controller for modules and boards

The design of a versatile module test and maintenance controller (MMC) is presented. Driven by structures test programs, an MMC is able to test every chip in a module or PCB via a test bus. More than one test bus can be controlled by an MMC, and can support several bus architectures and many modes of testing. The differences between MMCs on different modules are the test programs that they execute, the number of test buses they control, and the expansion units they use. A simple yet novel circuit, called a test channel, is used in an MMC. The MMC processor can control a test channel by reading/writing its internal registers. Once initialized by the MMC processor, a test channel can carry out most of the testing of a chip. Thus the processor need not deal with detailed test-bus control sequences since they are generated by the test channel. This strategy greatly simplifies the development of test programs. The proposed MMC can be implemented as a single-chip ASIC (application-specific integrated circuit) or by off-the-shelf components. Some of its self-test features are presented     

群智优化路径技术在风景园林规划设计中的运用

风景园林规划设计过程中计算机辅助技术起到了越来越大的作用,特别是在园林道路路径设计方面,有效的最短路径规划可以提升游客的体验。因此,提出一种基于群智优化的dijkstra最短路径规划算法。首先基于风景园林应用创建环境地图;然后对典型的dijkstra最短路径算法进行分析;最后采用群智优化对dijkstra最短路径算法进行改进,并给出信息素浓度更新的方法。仿真测试结果表明,相比传统dijkstra算法,提出的群智优化算法的路径长度更小,可以有效满足园林道路规划的需求。     

临床护理路径在脑卒中患者中的运用及康复效果评价

目的:探讨临床护理路径在脑卒中患者康复中的运用价值。方法 :按照随机数字法分为试验组和对照组各30例,两组患者入院后均给予常规药物治疗和常规护理模式,试验组在常规护理基础上采取临床护理路径模式。比较两组患者入院首日、出院时和出院2个月后的FMA评分和ADL评分,以及均住院时间、平均住院费用和护理满意率。结果:路径组患者的住院时间、住院费用明显低于对照组(P0.05);路径组患者运动功能及日常生活能力和对护理的满意度均明显高于对照组(P0.05)。结论:临床护理路径可提高临床护理质量,增加患者的康复率和满意率。     

Compatibility?A challenge to universal communications Global cables and satellite communication

The prognosis for worldwide communications is discussed from six viewpoints. A look at the future roles of satellites and submarine cables, an evaluation of the advances in international telephone routing, and a CCITT progress report are presented. The technical and economic tasks necessary to achieve compatibility are outlined, and Comsat's organizational structure, and its relationship to international communications, is appraised. Finally, the military communications networks in support of U.S. international and United Nations commitments are described, with reference to possible interconnections with commercial systems.     

A new iterative procedure to solve for scattering and absorption by dielectric objects

We have devised a new iterative technique to improve the Extended Boundary Condition Method (EBCM) frequently used to solve for the scattering and absorption by lossy dielectric objects. This technique has two main features: 1) it requires an initial assumption of the external surface fields, and 2) it partitions the interior of the object into a number of overlapping subregions, thus assuring a more efficient numerical convergence. Preliminary results indicating the enhanced stability of the new iterative EBCM technique are presented.     

连续相位FSK在电缆电视网络中的数据通信

介绍一种ＣＰＦＳＫ调制解调在电缆电视网络中数据通信的实现方法。该电路实用性强，通信可靠性高，并给出了调测方法。     

A model based approach to fault detection for the reverse path ofcable television networks

We present a model based method for reliably detecting faults in the reverse path of cable amplifier networks. This method has the advantage over traditional fixed-bound fault detection techniques in that it is able to accurately detect changes in signal behaviour while tracking signal changes due to environmental effects. The resulting method provides an increase in the fault detection sensitivity while simultaneously providing a decrease in the false alarm rate. We have implemented a general approach based an using a modeling engine to capture the reverse pilot signal behaviour of cable television amplifiers. Two modeling specific engines were developed for this purpose. The first one is based on the use of feedforward neural networks; the second one is based on the use of statistical analysis techniques. The resulting fault detection system, when employing either modeling engine, was able to provide good temporal localization of the onset of fault conditions along with a clear indication of the presence of the fault through its duration     

A model to estimate the path loss in areas with foliage of trees

This paper presents an empirical model to predict attenuation in forest environments considering parameters related to vegetation. Typically, environmental parameters are only included in theoretical models, but they are more difficult to apply. The developed model uses tree density, average tree canopy diameter and foliage density as input parameters. The foliage density is very difficult to determine since it depends on the characteristics of trees. A simple metric of this parameter was obtained by measuring the background light silhouetted by the canopy. The model was developed with measurements obtained in different forest environments for two frequencies within the UHF band (Ultra High Frequency). A procedure was also applied to extend the operating frequency range of the model.     

A sample path property of matched-filter outputs with applications to detection and estimation

The stochastic process at the output of a matched filter, when the latter is excited by its proper signal in additive white noise, has a mean function proportional to its covariance function. Sample path properties of a Gaussian process with the mean proportional to the covariance, conditioned such that it assumes a given value at the instant of the peak in the mean, are independent of signal amplitude. Formal and rigorous proofs and a detection-theoretical interpretation of this result are presented. It is then applied to the calculation of the detection probability of a rectangular signal of unknown time of arrival and to bounding the threshold effect in the estimation of the time of arrival. A novel passage time result is derived in the Appendix.