基于PE模型的电波传播特性预测技术研究

PE模型已经被广泛地应用于电波传播特性预测技术的研究,并成为解决电波传播问题的主要工具。通过对抛物方程推导过程中由于对伪微分算子Q的处理而产生的误差进行分析,表明PE模型在预测小仰角的电波传播时具有很好的计算精度。对基于PE模型的电波传输损耗理论模型进行计算机仿真,得到电波传播损耗的理论计算值,通过与实测数据进行对比,验证了PE模型用于电波传播特性预测的正确性,并且对理论模型的计算结果稍微偏小的原因做了分析。     

复杂地形中的电波传播损耗预测研究

远距离不规则复杂地形中,电波传播损耗计算精度较低,对此,文中提出了一种基于地理信息系统并根 据实际地形提高电波传播损耗计算精度的算法模型,构建了可视化的软件显示平台。首先,根据国际电信联盟(ITUR) 的P 系列电波传播建议书,结合实际地理信息情况获取了地形和环境因子的数据。然后,通过数字地图模型,针对 传播路径上各种不同地形区域,分别建立传播模型来计算电波传播损耗,并完成仿真计算界面的设计和实现。最后,给 定收发天线高度和频率,依据实际地形,建立完整的电波传播模型进行仿真实验。结果表明,该算法模型不仅能得到传 播路径上每一个点的损耗,而且与传统的Hata 模型对比,该算法在不同区域和地形中敏感度更高,可以有效提升传播 损耗计算精度,更适用于计算实际地形中远距离不规则复杂地形下的电波传播损耗,帮助改善通信质量。     

基于飞行轨迹的无人机通信信道仿真

通过分析无人机之间无线链路的传播损耗、多普勒频率和多径时延等特征参数,提出一种基于三射线的无人机通信信道模型,并给出了无人机飞行轨迹在不同坐标系中的转换公式及已知飞行轨迹求解信道模型参数的方法。最后针对两种不同的典型飞行场景,对无人机通信链路的多径时延、传输损耗及多普勒频率算法进行了仿真验证,并获得了基于飞行轨迹的无人机空空数据链信道模型。该模型对无人机数据链系统参数选取、物理层算法设计和性能分析等具有重要意义。     

预估城镇小区电波传播损耗的一种三维抛物方程算法

为城镇小区电波传播问题建立了一种三维抛物方程模型,并且用二维分部傅立叶变换方法求解。计算了几种不同地形上建筑物障碍分布的小区电波传播衰减因子,和UTD理论及数值积分方法计算出的结果吻合得比较好,从而验证该模型的有效性,同时也说明了三维抛物方程模型能更准确地反映出小区建筑物宽度对场的绕射作用,为城镇小区电波传播问题的估算提供了一种更为准确的算法模型。     

弯折谱估计在抛物型方程模型电波传播中的应用研究

射线追踪法求解入射余角时与电波频率无关,且存在部分区域多值或无值问题,此外平面波谱估计的平面波前假设违背了非均匀大气条件下的电波传播特性.针对上述问题,提出了一种基于弯折谱估计进行抛物方程模型海面电波传播的计算方法.通过对光滑表面条件下的抛物方程模型计算结果进行弯折谱估计得到入射余角,再将其用于粗糙海面的抛物方程模型求解.该方法可以唯一的估计任意距离上的入射余角,避免了计算当前值需要用到基于该值估计参数的悖论.对射线追踪法、平面波谱估计和弯折谱估计的估计特性进行了仿真分析,数值试验验证了该方法应用于粗糙海面抛物方程求解的可行性和性能.     

超短波电台传播特性仿真系统

根据确定性传播模型,在地理信息系统的基础上,实现了一种基于HLA技术的超短波通信仿真系统。仿真系统包括超短波(VHF)收/发电台、电波传播算法模型、仿真控制等模块,各节点通过RTI(运行支撑环境)构成了一个分布式仿真结构,可实现超短波通信系统的点对点通信、点对面通信、多套电台组网通信的性能仿真。并给出了在某典型场景中超短波电台语音传输质量、数据传输质量的仿真结果,同时给出了在不同位置布设电台的传播损耗分布。     

基于matlab的复杂地形下障碍物机械损耗传播研究

建立了陡峭地形和光滑地形下电波的传播模型,并用matlab进行模拟仿真,得到了不同地形下传播因子的伪彩图。然后对比了光滑地形和陡峭地形的传播损耗结果,光滑地形和平静海面的传播损耗结果,发现障碍物对无线电传播的影响很大,反射介质对无线电传播影响较小。     

月表无线信道仿真

基于自由空间传播模型(ITM)对月表电波传播损耗进行分析,主要考虑了电波的自由空间传播损失,反射、散射和绕射发生的条件以及对电波传输的影响.根据对月表电波的传播分析,建立了月表无线信道仿真模型,并应用Matlab进行了模拟仿真.对于月球通信设备的设计具有参考意义.     

海上蒸发波导条件下电波传播的分析

抛物方程方法已经被广泛地应用于电磁波传播的研究,并成为解决电磁波传播问题主要的工具。应用抛物方程和电波传播的基本理论,计算了电磁波在蒸发波导和标准大气中的传输损耗,得到了电波的空间传播损耗图,与射线理论的射线描迹技术得到的结论是一致的,但是抛物方程方法求解速度快,具有很好的实时计算特性,并且能弥补目前射线描迹技术尚不能精确描述空间场分布的缺点,因此更具有实用价值。     

森林中电波传播的抛物方程法

抛物方程法能处理非均匀介质环境中的电波传播问题,并可用FFT步进算法快速求解,在电波传播中得到了广泛运用.该文用抛物方程法求解了森林中的电波传播问题,并将计算结果与Tamir侧面波模型的结果进行比较,二者吻合很好.最后用抛物方程法分析了森林中电波传播的特性.     

基于传播图论的多链路信道仿真及其在TDOA定位系统性能评估中的应用

为了解决在真实环境下到达时间差(time difference of arrival, TDOA)定位性能评估所面临的测量成本高、不可控干扰因素较多等问题,提出了一种利用传播图论多链路信道仿真来评估TDOA定位系统性能的方法. 即采用传播图论的方法生成不同的信道冲激响应,并通过软件无线电装置产生经信道畸变的射频信号,作为多个TDOA传感器的输入,形成一种新型的TDOA定位检测方法. 首次将复杂外场采用射频仿真的方式,针对城市环境中的TDOA系统构建4个测试场景,对TDOA系统的定位精度进行检验. 仿真结果表明,被测的多链路定位系统在信号带宽不小于200 kHz条件下表现出良好且稳定的性能. 此外,本文提出的嵌入衍射机制的图论建模方法,相比传统图论更为有效地提升了TDOA定位误差的仿真准确度.     

一种新的无线电波传播路径损耗模型

使用渗流网格建模无线电波的随机传播环境,在此基础上使用随机射线方法,从概率论的角度得到若干路径损耗的解析公式.经过与经典路径损耗模型以及其他由非波动方法得到的路径损耗模型的比较之后,从逻辑上推断出一个新的路径损耗模型.对新模型中参数的取值范围进行了讨论和分析,最后使用城市密集传播地区的测量数据验证新的路径损耗模型的精确性.     

Radio propagation at 900 MHz in underground coal mines

This paper reports on experimental results of radio propagation in two underground coal mines. Measurements were performed at 900 MHz on horizontal and vertical polarization in typical coal mine operational zones. Values of propagation loss in dB/100 m are derived. Additional losses due to coal mine curvatures and common coal mining equipment obstructions are also presented. A hybrid tunnel propagation model consisting of the free space propagation model and the modified waveguide propagation model is used to explain some measurement results. Based on these results, we believe that microcellular radio communications systems are feasible in coal mines     

Investigation of radio channel uncertainty in distance estimation in wireless sensor networks

The distance estimation between nodes is a crucial requirement for localization and object tracking. Received signal strength (RSS) measurement is one of the used methods for the distance estimation in wireless networks. Its main advantage is that there are no additional hardware requirements. This paper describes a lateration approach for localization and distance estimation using RSS. For the purpose of investigation of RSS uncertainty, several scenarios were designed for both indoor and outdoor measurements. The first set of RSS measurement scenarios was proposed with the intention of hardware independent investigation of radio channel. For the second set of measurements, we employed IRIS sensor nodes to evaluate the distance estimation with certain devices. The experiments considered also obstacles in the radio channel. The results obtained in the proposed scenarios present usability of the method under different conditions. There is also a signal propagation model constructed from measured data at a node, which subsequently serves for distance determination.     

Numerical characterization and modeling of subject-specific ultrawideband body-centric radio channels and systems for healthcare applications

The paper presents a subject-specific radio propagation study and system modeling in wireless body area networks using a simulation tool based on the parallel finite-difference time-domain technique. This technique is well suited to model the radio propagation around complex, inhomogeneous objects such as the human body. The impact of different digital phantoms in on-body radio channel and system performance was studied. Simulations were performed at the frequency of 3-10 GHz considering a typical hospital environment, and were validated by on-site measurements with reasonably good agreement. The analysis demonstrated that the characteristics of the on-body radio channel and system performance are subject-specific and are associated with human genders, height, and body mass index. Maximum variations of almost 18.51% are observed in path loss exponent due to change of subject, which gives variations of above 50% in system bit error rate performance. Therefore, careful consideration of subject-specific parameters are necessary for achieving energy efficient and reliable radio links and system performance for body-centric wireless network.     

基于全局透射边界条件的宽角抛物方程电波预测模型

提出了一种新型的基于全局透射边界条件（non-local boundary condition,NLBC）的Greene近似宽角抛物方程（wide-angle parabolic equation,WAPE）电波预测模型,用于求解对流层远距离复杂环境中的电磁波传播特性.采用有限差分法（finite difference method,FDM）求解WAPE得到了三对角线性方程组,可以快速地求解整个空间的电场分布,也可以对不规则的地表环境进行精确建模.本文提出的WAPE模型解决了传统的PE离轴传播角度偏小的问题,将电波的最大传播仰角提升至约50°,同时大大减小了计算区域中上边界吸收层的设置尺寸,从而提高了PE的计算效率.实验证明,当伪微分算子的相位误差不超过0.002时,Tappert、Claerbout和Greene近似形式得到的最大传播角分别为20°、35°和45°.最后,通过与经典的光学双射线模型进行对比,证明本文提出的基于NLBC的Greene近似WAPE模型的可计算传播仰角更大,对上边界处反射电磁波有良好的吸收效果.因此,本文的模型适用于对流层远距离复杂环境中电磁波传播特性的精确预测.     

起伏地形双向抛物线方法的计算与验证研究

双向抛物线方法是复杂环境下电波传播计算中的一种重要方法,提出一种新的不规则地形下双向抛物线方程用于电波传播的计算方法,该算法在求解过程中记录了所有波源的历史路径,结合具体路径对双向抛物线方法进行相位修正,并在步进过程中,对不同极化下障碍物表面的边界条件进行了重新处理,对目前采用的阶梯模型进行了改进。在此基础上,提出使用矩量法来精确验证近距离不同极化下双向抛物线方法的计算精度。通过实例分析,证明了起伏地形下新算法计算的精确性。     

Wideband characterisation of fading outdoor radio channels at 1800 MHz to support mobile radio system design

The characteristics of mobile radio channels place fundamental limits on the performance of mobile radio communication systems. Reliable information about these characteristics are obtained in this paper by analysing wideband propagation measurements, which were performed by using an high performance wideband channel sounder in mountainous areas in the German Alps and in typical urban areas in Munich. In addition to well known results obtained from propagation measurements in similar scenarios [1, 2], novel aspects of practical relevance enable for a realistic analysis of the performance of mobile radio systems in terms of the discussed channel parameters and support a compromise between system costs and the quality of signal processing with respect to the system availability and reliability.     

A simplified analytical model for predicting path loss in urban andsuburban environments

An analytical propagation model has recently been developed to predict radio signal attenuation in urban and suburban environments. This analytical model explicates the path loss as a result of signal reduction due to free space wavefront spreading, multiple diffraction past rows of buildings, and building shadowing. It is applicable for cellular mobile services as well as personal communications services (PCS) in both macro- and microcellular environments. Good accuracy was found for this analytical model by comparing the predictions with numerous measurements made in various propagation environments. However, since the analytical model involves multiple-dimension integration to calculate the signal attenuation due to multiple diffraction past rows of buildings, the model in its original format does not lend itself to easy implementation into a radio system planning tool. A simplified version of the analytical model is developed in this paper, which can be used for three different propagation scenarios with base-station antenna above, below, and near the average rooftop level     

基于机器学习和卫星图像的路径损耗预测

基于反向传播神经网络（back propagation neural network,BPNN）构建了一种路径损耗预测模型. 通过卫星图像的红、绿、蓝（red, green and blue,RGB）通道的颜色信息来表征无线通信电波传播路径的环境特征,结合路测点与基站的距离特征构建数据集,迭代训练网络参数,以预测传播路径损耗. 结果表明,对跨基站路测点的预测结果与实测数据之间的相关系数达到0.83,绝对平均误差控制在0.66 dB,标准差控制在6.65 dB,说明在缺乏某一场景的详细模型和材质参数时,本文模型也能可靠预测无线通信电波的传播路径损耗. 此外,本文信道模型与传统信道建模方法多方面的对比与分析表明,本文模型在相同计算资源下可以提供和传统信道建模方法相差很小的预测结果,同时大大缩短预测所需的时间,说明本文模型对传播路径损耗做出快速预测的能力可以用于无线通信网络系统的优化.