Study On The Fast Prediction Based On The Ray Tracing Algorithm In Macro Cell Environment

The ray-tracing method is simple and most widely used in the area of site-specific propagation prediction. Ray tracing algorithm mainly based on the virtual source tree in this paper which can predict the radio channel accurately. However, this algorithm with the deterministic model is based on precise geographical environment database, which means a large amount of input data in urban environment. For macro cell city environment, directly use of the whole map may lead hours or even days of computational time. However, most of the buildings have little or no effect on the radio propagation, the ray paths through these buildings are abandoned because they have little impact on the final result. Thus, an algorithm which aimed at identifying the effective building set is needed. Based on the outdoor radio wave propagation model and the ray tracing model, a pre-processing method which can select the effective buildings is proposed.According to the technology, the ray tracing method based on virtual source tree and the related parameters are presented. The basis for actual 3-D wave propagation prediction is the use of accurate 3-D digital map for the environment, so the basic theory of the digital map and the storage are introduced here. In this paper, the original data are stored in.mif and.mid files, which the 2-D projection information and height information are preserved. The preprocessing technology is divided into three parts, in order to select the buildings which have large effects on radio wave propagation. Part A is those buildings which located in the ellipse with the transmit and receive antennas as the focus and given appropriate eccentricity. Part B is those buildings which are directly visible to the viewpoint. Traditional visibility algorithm does not suitable to the urban macro-cell environment, so in this paper the visible judge is finished with the assistant of Open GL. Part C is those buildings which do not belong to Part A, but they have proper orientation and size. After three kinds of buildings are determined, they are combined with appropriate rules, then two comparison picture of 2-D and 3-D are drawn by using Matlab.The accuracy of the algorithm need to be tested after we get the result. Firstly, the result of pre-processing algorithm is regarded as input data, in order to analyzing theinfluence of the pre-processing algorithm on ray path, path loss and the RMS delay spread. Secondly, in the preprocessing algorithm, there are two kinds of data has great influence on the final result. The first one may called pre-processing parameter, most of them are the parameters of Part C. In order to clarify the influence of these parameters on the results, the optimization of the geometrical parameters has been performed with the reference to CPU time and calculation precision. The second one is the limit number, which has great influence of the calculation time. With these parameters, a good foundation for the practical application of the pre-processing algorithm in the macro cell environment has been set up. Results show that a computation time saving of the order of 90% or more can be achieve with little degradation in prediction accuracy.