Wireless Signals Transmission Among Buildings-Reverberation, Diffraction And Path-searching

With the development of society, wireless communication is increasingly important in the field of information transmission. The electromagnetic wave is the main carrier of wireless communication signals. Around us, there are a lot of electromagnetic waves, which are mainly from the mobile communication base stations, broadcasting & television transmission systems, radars, personal communication systems and so on. However, the increase of users requires adding system capacity. So we need to build many mobile communication base stations or improve broadcasting & television transmission systems. According to regulations, when the communication base station is building, we must carry through electromagnetic environment forecasting in order to prevent electromagnetic pollution on the environment and injury to men. In fact, the influence of wave propagation from building is significant. In order to predict the electromagnetic environment more accurately, the radio propagation attenuation from buildings must be taken into account. Ray-tracing is the important method to study the propagation characteristics in buildings. In this paper, taking example for a communication base station, we discussed the concrete method of wave propagation prediction with reverse ray-tracing method and calculate the radio propagation attenuation from buildings.This paper firstly introduced common wave propagation models and the basic principles of ray-tracing, compared the direct with reverse method and gave the reason of using the reverse method. Then it discussed wave propagation prediction method with reverse ray-tracing, including cell-modeling, path-searching and field strength calculation. Finally, it used MATLAB to give the concrete math method and calculate the cell, compared the calculated value with the measured value, analyzed the causes of error and proposed improved method.Now in China, the study of radio wave propagation characteristics with ray-tracing mainly aims at the micro-cellular systems and the base station antenna which is lower than buildings around. This paper aims to establish a common prediction model, in which the base station antenna is higher than buildings around, the horizontal wedge diffraction is introduced and the twice and more reflection and diffraction is ignored in order to improve computational efficiency because the attenuation is higher. This paper's presentation and programming in detail provide the principles, methods and calculation steps for the development of the electromagnetic environment accurate prediction system, lay a foundation for the further research and development.