FDTD-computed diffraction coefficients of generic wedges for predicting RF propagation in wireless communication systems.

摘要

In wireless communication systems, a combination of planning tools and actual measurements are used to determine the location and type of radio equipment that is required to obtain the contiguous radio coverage. The lack of accurate diffraction models for arbitrary material wedges, such as building wall comers and rooftops, gives rise to significant errors in the RF coverage predictions in urban environments.; In this research, we establish numerical techniques based on the finite-difference time-domain (FDTD) method to efficiently obtain accurate diffraction coefficients of generic wedges composed of arbitrary materials. We first develop the time-gating approach to accurately obtain two-dimensional (2D) transverse-electric and transverse-magnetic diffraction coefficients. We then extend this FDTD method to obtain general three-dimensional (3D) diffraction coefficients. We present the accurate 2D and 3D numerical diffraction coefficients for several right-angle arbitrary material wedges. Even though the time-gating FDTD method provides very accurate results, it is computationally inefficient since it requires the use of very large FDTD grids. We thus develop the generalized-total/field-scattered-field (G-TF/SF) formulation for FDTD grids to efficiently obtain diffraction coefficients of arbitrary material wedges. We apply this technique to efficiently obtain the 2D transverse-magnetic diffraction coefficients of an infinite right-angle dielectric wedge and an infinite 45°-angle metal wedge by using a compact FDTD grid. Our results indicate that in 3D the G-TF/SF formulation should allow up to 64:1 reduction in computer storage and running time for diffraction coefficient calculations relative to the previous time-gating approach. Finally, we extend the FDTD techniques to study double-wedge diffraction of generic straight wedges. We develop the method and present results of double-wedge diffraction for the infinite right angle metal double wedge by using a sinusoid modulated gaussian source and an unmodulated gaussian source.; The techniques developed in this research can be used to efficiently obtain general 3D diffraction coefficient libraries for single and double wedges composed of arbitrary materials. These diffraction coefficient libraries can be used in conjunction with existing ray-tracing codes to obtain better estimates of RF propagation for wireless communication systems in urban environments.