Study On The Algorithms Of Predicting The Radio Propagation Characteristics In Complex Environments

Along with the rapid development of high frequency radio technology, predicting characteristics of radio propagation in complex environments has become an important research subject. The accurate electromagnetic data of battlefield environments are absolutely necessary for constructing martial wireless systems such as radar-warning, electronic warfare, automatic command etc. For the rational layout and optimization of modern mobile communication system, the accurate electromagnetic data of the urban microcells environments are very important references.Among the present radio propagation models, many models which based on ray tracing method can't deal with irregular terrain and complex atmosphere structures synchronously. So they can't predict the radio propagation characteristics in complex environments accurately. But the parabolic equation (PE) method which deduced from the wave equation can overcome the shortcoming, and so the PE model is the most precise one for predicting the radio propagation in troposphere. Accordingly, mainly based on the PE method, the dissertation studies the two-dimensional parabolic equation (2DPE) model which used to predict radio propagation on large size troposphere and the three-dimensional parabolic equation (3DPE) model which used to predict radio propagation in urban microcells.When constructing the 2DPE model, a wide angle parabolic equation (WAPE) is chose which can be evaluated by the split-step Fourier transforms (SSFT) algorithm through comparing the present several PE model. The prediction errors brought by the WAPE itself and the SSFT algorithm are analyzed in detail and an approach of minimizing the errors is brought forward. For getting the WAPE initial fields, the Green function of WAPE in two-dimensional boundless plan is calculated and the approach of getting the WAPE initial field by the Green function is also proposed. Comparing this approach with the others which are commonly used to calculate the PE initial fields at present, the former is more accurate and more universal. A discrete mixed Fourier transform (DMFT) which is an efficient form of the SSFT algorithm under the impedance boundary conditions is not only studied in detail but also implemented step by step. The formulas of the DMFT have amended the errors in the published literature. Comparing several irregular terrain models, the most precise one at present is chosen for the WAPE model while being used to predict the radio propagation in large size troposphere.Based on this terrain model, the approach of predicting radio propagation on irregular terrain by using the WAPE model is expatiated. Next,the effects of the tropospheric atmosphere on radio propagation are introduced in detail and the approaches of dealing with the atmosphere structures by the WAPE model is explored adequately. Subsequently, a routine for extracting the terrain elevation profile on the Earth's great circle plane from digital map is developed and accordingly a radio propagation model which named WAPE has been constructed based on digital map.For predicting attenuation characteristics of radio propagation in urban microcells, a vector three-dimensional parabolic equation (3DPE) model with wide-angle is constructed by using the electromagnetic potential function. Comparing it with the earlier others which expressed by an arbitrary field component, the 3DPE model in this paper is not only simple on the form but also economical on solution. Aim at evaluating the 3DPE quickly, a highly efficient SSFT algorithm is proposed which is so called approach of decomposed the field into odd and even parts. For the case of a single building distributing on flat ground, different methods of the 3DPE model dealing with the buildings'vertical boundary surfaces under different wave incidence are brought forward: for the condition of vertical wave incidence, an approach of forward difference combining the Fourier transform is proposed ; for the condition of oblique wave incidence, a two-dimensional Fourier series-expanding method is introduced, and the calculated formulas of the series based on the approach of field-decomposed are also presented. These formulas have amended some errors of the formulas appearing in the published literature. Based on them, radio propagation in urban microcells which comprise several buildings is predicted by the 3DPE model at last and the excellent results are obtained.