Algorithm Research On Predicting The Strength Of Wave Based On GIS

Radio propagation prediction plays an important role in modern wireless communications, radio and television systems. Accurate prediction for the strength of wave propagating in the micro-cells is very significant for the establishment and maintenance of a residence district. Traditional prediction methods are statistic and based on measured data, which requires that there be statistic similarity between residence districts. However, with the enlarging of the capability of the system, the divisions of residence districts are getting smaller, even micro-miniature districts appear, which causes the lose of the relation of the statistic comparability between districts so that traditional methods become invalid. Presently, there need some new improved prediction ways in which the covering range of wave is predicted and the characteristic of wave propagation is analyzed. In this paper, GIS-based ray tracing prediction method combined with geometric diffraction theory is studied.At first, this paper introduces the concept of an urban cell, the necessity of setting up prediction model for the strength of wave and some important prediction algorithms, and the main research content of this paper.After that, many prediction models are studied. Due to the complicated conditions in urban areas of a city, there are different prediction models, which are suitable to different environments and different district standards. And, this paper studies and analyzes DPM and SPM models with different construction ways.The prediction model of ray tracing propagation is the focus of this paper. Now, most prediction models are only suitable to predicting the strength of wave under big district standards. However the trend of modern wireless communications is micro-cell. The ray tracing model suitable to micro-cell is intensively studied in this paper. The ray tracing in general meaning needs a large amount of computation, therefore, we need to find an applicable solution. Based on mirror-image method and tube-tree method, a three dimensional ray tracing model is presented. In the model, the reflection surface and diffraction points, able to make contribution to radio propagation in valid areas, are found by determining the effective areas of the reflection source and the diffraction source, based on the fictitious source method so that the tree structure of data source can be set up. The method in this paper uses the concept of radiation source tree as reference and improves it and adds the receiving point into the tree structure consisting of transmitting source, reflection source and diffraction source. The tree structure stands for the whole propagation paths, which makes computation faster and more efficient.At last, researches are made for how to solve the incompatibility between the data format of standard GIS maps and the data storage format of the database of radio propagation model.