SGER: Physics-Based Propagation Models for Wireless Communications

SGER：基于物理的无线通信传播模型

• 批准号: 9910804
• 负责人: Martin Parker
• 金额: $ 7.84万
• 依托单位: University of South Alabama
• 依托单位国家: 美国
• 项目类别: Standard Grant
• 财政年份: 2000
• 资助国家: 美国
• 起止时间: 2000-01-01 至 2002-12-31
• 项目状态: 已结题
• 来源: https://www.nsf.gov/awardsearch/showAward?AWD_ID=9910804&HistoricalAwards=false
• 关键词: SGER; Physics; Based; Propagation; Models

99010804ParkerAn analytic solution of the problem of electromagnetic scattering by a dielectric spherical scatterer resting on, or partially buried in, an infinite perfectly conducting ground plane is formulated using the method of images. This is one of a series of canonical problems introduced to develop new propagation models for wireless communications. The basic assumption is that the earth can be modeled by a sphere whose surface is initially considered to be locally smooth and flat, while all objects above it can be simulated by spheres/spheroids, some of which may be partially buried in the ground. All the spheres/spheroids used in the model range from perfectly conducting on the one extreme to imperfectly conducting- with complex permittivity on the other extreme. The solution of this canonical problem is particularly relevant to analyzing the scattering by complex three-dimensional bodies, such as plastic mines, icebergs, rough surfaces, etc., in which the assumed locally-flat background can be modeled by the ground plane and the complex body can be simulated by a sphere/spheroid or a system of spheres/spheroids in free space or partially buried in the ground plane. The incident wave is assumed to be a uniform plane electromagnetic wave of arbitrary angle of incidence. The method of images is applied to replace the partially buried sphere in a ground plane by two overlapping spheres of equal size, or by two touching spheres of equal size if the sphere is resting on the ground plane, and a supplementary incident plane electromagnetic wave such that the total electric field is satisfied at all points where the ground plane is located in the original problem. The incident, supplementary and scattered fields are expressed in terms of appropriate spherical wave functions. To impose the boundary conditions on the surfaces of the spheres, the translation addition theorem for the spherical wave functions are used to express the coordinate system of the scattered field from one sphere in terms of the coordinate system of the other sphere leading to a matrix equation which can be inverted numerically to recover the scattered field coefficients. The problem is formulated such that the boundary condition on the surface of each sphere can also be satisfied by an iterative approach. This iterative procedure continues until the solution converges, and has the obvious advantage that it does not require matrix inversion since the scattered field coefficients in each iteration are obtained and used in the next iteration. The scattered field coefficients generated by the exact and iterative methods are obtained, from which the scattered field can be evaluated everywhere. In particular, the scattering cross section can be calculated as a function of the sphere radius and permittivity as well as the burial distance for any specified angle of incidence.In order to solve the inverse scattering problem, we employ a radial basis function network which consists of an input layer with four inputs, a hidden layer using Gaussian nonlinearity functions, and an output layer with three outputs. The four inputs in the input layer are the real and imaginary values of the computed scattered field complex coefficients for the TE and TM polarization cases, while the outputs are the electrical radius and burial distance of the training sphere as well as its relative permittivity. This network is then trained using the orthogonal least-squares algorithm with a specified range of the electrical radius and a specified number of learning data samples (50 for each output) to train the network in order to retrieve the radius, burial distance and relative permittivity of the test sphere for new data (usually experimental) which is different from the learning data.***

本文用镜像法给出了无限大理想导电地平面上或部分埋在其中的介质球散射体的电磁散射问题的解析解。这是一系列的规范问题之一，介绍了开发新的无线通信传播模型。基本假设是，地球可以用一个球体来模拟，其表面最初被认为是局部光滑和平坦的，而它上面的所有物体都可以用球体/椭球体来模拟，其中一些可能部分埋在地下。模型中使用的所有球体/椭球体的范围从一个极端的完美导电到另一个极端的不完美导电-复介电常数。这个典型问题的解决方案特别适用于分析复杂三维物体的散射，例如塑料地雷，冰山，粗糙表面等，其中假定的局部平坦背景可以通过地平面来建模，并且复杂体可以通过自由空间中或部分地埋在地平面中的球体/椭球体或球体/椭球体系统来模拟。假设入射波为任意入射角的均匀平面电磁波。图像的方法被施加到替换部分地埋在一个接地平面的两个重叠的球体的大小相等，或由两个接触的球体的大小相等，如果球是休息在接地平面上，和一个补充的入射平面电磁波，使总电场是满足在所有点的接地平面位于在原来的问题。入射场、辅助场和散射场用适当的球面波函数表示。为了将边界条件施加在球体的表面上，使用球面波函数的平移加法定理来表示来自一个球体的散射场的坐标系，该坐标系在另一个球体的坐标系中导致矩阵方程，该矩阵方程可以在数值上求逆以恢复散射场系数。该问题的制定，使每个球的表面上的边界条件也可以满足一个迭代方法。这种迭代过程一直持续到解收敛，并且具有明显的优点，即它不需要矩阵求逆，因为每次迭代中的散射场系数被获得并用于下一次迭代。由精确法和迭代法得到的散射场系数，可以计算出散射场的任意位置。特别是，散射截面可以计算为一个函数的球半径和介电常数，以及埋距离为任何指定的角度incidence.In为了解决逆散射问题，我们采用径向基函数网络，其中包括一个输入层与四个输入，一个隐藏层使用高斯非线性函数，和一个输出层与三个输出。在输入层中的四个输入是TE和TM极化情况下计算的散射场复系数的真实的值和虚值，而输出是训练球的电半径和埋藏距离以及其相对介电常数。然后使用正交最小二乘算法训练该网络，其中具有指定范围的电半径和指定数量的学习数据样本（每个输出50个）以训练该网络，以便针对不同于学习数据的新数据（通常是实验性的）来检索测试球的半径、埋藏距离和相对介电常数。