LMSS遮蔽衰减预测模式进一步分析与改进

本文用世界上几个地区较为系统的测量数据进一步检验了有关ＬＭＳＳ树林遮蔽衰减的ＥＲＳ预测模式，发现该模式有较大的预测误差。也对Ｌｏｏ模式进行了评述和分析。然后，基于所述测量数据，通过回归分析，对ＥＲＳ和Ｌｏｏ模式进行了改进，其中考虑了仰角和光学遮蔽度两者的影响。所得改进模式都足够简单易用，而且预测精度较高。     

LMSS遮衰减预测模式进一步分析与改进

本文用世界上几个地区较为系统的测量数据进一步检验了有关ＬＭＳＳ树林遮蔽衰减的ＥＲＳ预测模式，发现该模式较大的预测误差。     

卷积交织去交织快速算法的实现

本文介绍了用ＴＭＳ３２０Ｃ２５芯片实现卷积交织／去交织的快速算法。ＴＭＳ３２０Ｃ２５芯片是高性能数字信号处理器，具备高速控制的灵活性和阵列处理器的数值运算能力。由于移动卫星通信信道的多径衰落和遮蔽效应，接收机容易出现突发差错，所以移动卫星通信信道设备常采用卷积交织／去交织编解码方法，改善通信质量。本文根据卷积交织／去交织的原理，提出了一个快速算法，并用ＴＭＳ３２０Ｃ２５的汇编语言实现了快速算法。利     

基于计算机视觉的雷达遮蔽角测量系统设计与实现

传统雷达遮蔽角测量方法耗时长、精度低,难以满足快速准确进行雷达遮蔽角测量需求.文中基于计算机视觉测角原理,设计了雷达遮蔽角自动测量系统的总体结构和应用模式,提出了相机畸变矫正、安装误差补偿、轮廓识别提取等关键环节的实现方法,并与传统测量方法进行了对比验证.测试结果表明,基于计算机视觉的雷达遮蔽角测量方法能够大幅提高测量...     

混合维空间遮蔽关系的表示与推理

从某个视点观察两个三维空间中的对象时，一个对象遮住另一个对象的现象被称为空间遮蔽关系．在空间推理和机器视觉领域，它是一种重要的面向观察者的空间关系．LOS和ROC等现有的遮蔽关系模型都是基于RCC(区域连接演算)的，因而不能支持混合维空间对象．但在3维GIS等遮蔽关系的应用领域中，空间对象的维数是多样的．为此提出了混合维空间遮蔽关系模型MSO．首先将RCC扩展到混合维得到了MRCC，然后基于MRCC定义了混合维遮蔽关系，最后研究了MRCC的复合推理方法．     

Internet／Intranet计算模式与应用体系结构

本文讲述了Ｉｎｔｅｒｎｅｔ／ｉｎｔｒａｎｅｔ的Ｂ／Ｓ计算模式的特征，并与终端—主机计算模式、传统的Ｃ／Ｓ计算模式进行比较。在分析了Ｂ／Ｓ计算模式发展的三个阶段后，讨论了各阶段对应的Ｗｅｂ技术和应用的特点，其中包括Ｗｅｂ连接数据库的几种方法。特别关注了基于新一代Ｗｅｂ技术的应用体系结构     

非同步轨道卫星移动业务馈送链路的干扰研究

本文讨论了卫星移动通信中由于ＮＧＳＯ／ＭＳＳ馈送链路与ＧＳＯ／ＦＳＳ共享频率而引起的干扰问题，作为解决手段引入了反向频率工作模式。通过对具体数据的分析表明，这一模式可以有效地减轻两个系统之间的干扰，是协调ＮＧＳＯ与ＧＳＯ间干扰的一种最具吸引力的方案。     

烟幕对光电侦察效果的影响及战斗使用原则

本文通过分析烟幕对光的散射和吸收原理，定量分析研究了烟幕对光电侦察效果的影响，给出了烟幕遮蔽条件下对目标的发现和识别概率模型，同时分析了影响烟幕遮蔽效果的因素，确定烟幕战斗使用的一般原则。     

天线模式项散射分析与天线RCS减缩

天线的散射场是由结构散射场和模式散射场两项组成。理论分析和实验结果表明，后者对天线的雷达散射截面（ＲＣＳ）的贡献比前者要大得多，有效地克服模式散射场将会明显地降低天线的ＲＣＳ。本文提出了一种以克服面天线模式用射场达到降低天线雷达截面的模式项消去法减缩天线ＲＣＳ技术，并在几种天线模型上进行了实验。实验结果证明，这种技术减缩天线ＲＣＳ的效果，不管在天线工作频带内还是频带外均可达到１０￣１５ｄＢ。模式项     

烟幕对光电侦察效果的影响及战斗使用原则

本文通过分析烟幕对光的散射和吸收原理，定量分析研究了烟幕对光电侦察效果的影响，给出了烟幕遮蔽条件下对目标的发现和识别概率模型，同时分析了影响烟幕遮蔽效果的因素，确定烟幕战斗使用的一般原则。     

S-band LMS propagation channel behaviour for differentenvironments, degrees of shadowing and elevation angles

Experimental land mobile satellite (LMS) propagation data have been processed in order to characterise the behaviour of this channel under narrow-band transmission conditions for different environments, degrees of shadowing and elevation angles. Measurements were carried out at S-band. The transmitter was located on a small plane flying parallel to the road with elevations ranging from 40° to 80°. For the analysis of the received amplitude series, they were classified for each environment and elevation angle, into three different states according to the degree of shadowing experienced. This was done in order to develop a Markov chain based propagation simulator. The global (slow+fast) signal variations within each state are modelled using the Loo distribution (Rice+log-normal). Average distribution parameter values for each state, elevation angle and environment type are reported. The average state probabilities, slow variations' correlation lengths and other parameters are also presented. Finally, a software implementation is described based on a Markov chain+Loo distribution model that is capable of reproducing the complex envelope variations in the received signal due to shadowing and multipath     

Elevation Dependent Shadowing Model for Mobile Communications via High Altitude Platforms in Built-Up Areas

An empirical propagation prediction model is described for mobile communications from high altitude platforms (HAPs) in different types of built-up areas. The model introduced here is defined as a function of the angle of elevation. The target frequencies are selected from the 2 to 6 GHz frequency band prospective for 3G and 4G mobile systems, namely at 2.0,3.5, and 5.5 GHz. This new HAP model recognizes two cases - line of sight (LOS) and non-line of sight (NLOS) between a HAP and a user at street level. The simulation of the urban environment is based on a statistical approach. Additional shadowing path loss is calculated using the uniform theory of diffraction for NLOS conditions. Normal distribution of the additional shadowing path loss was distinguishable from the simulation results. The shadowing path loss is defined as a function of the elevation angle. The results of the empirical model developed for idealized conditions are verified by measurements taken from a remote-controlled airship in different types of urban environment. Close correlation was achieved between the theoretical model and the experimental data. The HAP elevation dependent shadowing model is easy to implement and can be used for realistic planning and simulations of mobile networks provided via HAPs in built-up areas.     

Modeling and simulation of mobile satellite propagation

Mobile satellite systems are subject to severe fading due to blockage of the line-of-sight (LOS) path by roadside vegetation. A thorough understanding of the fading effects is necessary for the design of a reliable land-mobile satellite system. Analytical and empirical models are presented for predicting fade statistics for vegetative shadowing of mobile satellite terminals. A software simulator for generating simulated fade data is also presented. A physical model relating physical path parameters to propagation model parameters is presented, and results using the model are shown     

A Modified Loo Model with Partially Blocked and Three Dimensional Multipath Scattering: Analysis,Simulation and Validation

This paper presents a novel mobile fading channel model, belonging to the class of Loo models, in which the multipath power arrives both in three dimensions (3-D) and in two angular sectors at the azimuth receiver’s plane. Moreover shadowing affects the amplitude of the line of sight (LOS) component, making it time varying and following a lognormal distribution, as required for a Loo model. The Doppler power spectral density (PSD) is analytically calculated, after Fourier transforming the closed form autocorrelation function. Afterwards exact solutions for the probability density function (PDF) of the envelope and phase are presented. What follows are approximate solutions for the second order statistics, i.e. the level crossing rate (LCR) and the average duration of fades (ADF’s). A new, appropriate for 3-D scattering cases, deterministic simulation scheme is developed, which implements the analytical model on a digital computer and is used to test the validity of the approximate solutions. Moreover the deterministic model is thoroughly investigated for all the possible cases, in terms of its convergence to the analytical one. Finally a curve fitting of the LCR to real world data, drawn from channel measurements, will demonstrate the flexibility and usefulness of the modified Loo model.     

一种改进的C.Loo信道模型衰落因子算法

为更好地反映实际无线信道的特性,介绍一种改进的C.Loo信道模型衰落因子算法。原始C.Loo信道模型衰落因子算法中不考虑多普勒频移的影响,本文加载了多普勒频移对衰落因子的影响,并说明其合理性、可行性及优点。     

Shadowing fade margin and coverage probability analysis for HAP mobile communication systems

An existing elevation dependent shadowing model for high‐altitude platform (HAP) mobile communication in built‐up areas is employed to perform the area coverage probability analysis and fading margin computation for HAP mobile communication systems. A generalized expression for the PDF of the received signal power in the HAP coverage is derived. The shadowing fade margin model that can characterize different types of built‐up area is developed. Theoretical relations between shadowing fade margin and outage probability and cell coverage probability are given. Numerical simulation for isoflux coverage HAP‐based system shows that there is great difference in the value of shadowing fade margin under line‐of‐sight and non‐line‐of‐sight conditions for the same outage probability. It is also found that the cell coverage probability is insensitive to the variance of the shadowing fade margin in suburban environment whatever the size of the cell and for small cells in urban high‐rise environments.Copyright © 2012 John Wiley & Sons, Ltd.     

Performance analysis of mobile radio systems over composite fading/shadowing channels with co-located interference

This paper presents an analytical framework for performance evaluation of mobile radio systems operating in composite fading/shadowing channels in the presence of colocated co-channel interference. The desired user and the interferers are subject to Nakagami fading superimposed on gamma shadowing. The paper starts by presenting generic closed-form expressions for the signal-to-interference ratio (SIR) probability density function (pdf). From this pdf, closed-form expressions for the outage probability, the average bit error rate and the channel capacity are obtained in both cases of statistically identical interferers and multiple interferers with different parameters. The newly derived closed-form expressions of the aforementioned metrics allow us to easily assess the effects of the different channel and interference parameters. It turns out that the system performance metrics are predominantly affected by the fading parameters of the desired user, rather than by the fading parameters of the interferers.     

Outage probabilities of cellular mobile radio systems with multipleNakagami interferers

Closed-form expressions for outage probabilities of mobile radio channels experiencing multiple, cochannel, independent Nakagami interferers are derived. This is done for the case of Nakagami fading alone with an arbitrary number of interferers. Analytical results for the case of Nakagami fading combined with log-normal shadowing are obtained for a single interferer. The case of multiple shadowed interferers is examined by simulation. The fading severity parameter in the Nakagami distribution may be varied to model different fading conditions. Interferers with similar and different Nakagami statistics are analyzed. The probability of cochannel interference is related to the reuse distance, which is one of the key parameters in the design of cellular mobile radio systems. In addition, the effects of specifying a minimum signal power requirement for satisfactory reception are investigated. A number of system examples that illustrate applications of the results are included     

Method-of-moments parameter estimation for compound fading processes

A novel and general parameterized fading model for the instantaneous received path power is presented, which accounts for both wide-sense stationary shadowing and small-scale fading. A method-of-moments parameter estimator is derived and implemented using a non-linear least-squares algorithm. Performance is explored by analysis and simulation under different noisy channel scenarios, and compared to exact Cramer-Rao bounds in the case of uncorrelated shadowing, and to idealized CR bounds, where shadowing and small-scale fading processes are assumed to be observed separately, in the case when shadowing correlation was not negligible.