Ray-Tracing-Based Analyzing And Predicating Of Interferences In GSM Networks

Interference is a key factor affecting the operation of GSM networks, and also makes a significant impact on voice quality, call droping, handoff and network congestion. How to reduce or eliminate interference is a key issue in network planning and optimization. Under the existing increasingly serious interference and varieties of circumstances in 2/3G networks, the traditional radio propagation prediction models are unfit because of their low forecasting accuracy and few types of interferences considered.The thesis develops a ray-tracing-based radio propagation model, which utilizes 3D digital maps to consider the influence of actual geographical information on the propagation of the downlink radio from BTS, including direct rays, reflection rays and diffraction rays, and calculates the singnal strength received at the different sites in networks; based on this model, the location of interference in networks can be precisely identified. The line and plane parameter equations and vector products are employed to find out the intersections of the rays and the surfaces of buildings, thus the computation is speeded up.By making use of the 3D geographical information system ArcGIS, SQL Server 2005 and C# programming languages, the prototype of ray-tracing-based interference analysis is developed. The system is applied to calculate the received signal strength and analyze the cochannel and adjcent channel interferences in the real GSM networks in Guangdong Province. The emprical evidences indicate that the model and the prototype can provide efficient and accurate analysis results.In chapter one, the significance of interference analysis in GSM networks is introduced, the present methods for analyzing and locating interferences are discussed, and the advantages of ray tracing model are also explained. In chapter two, the developing of the ray-tracing-based propagation model is elaborated. In chapter three, analysis of the coverage and interferences based on the ray tracing model is described, and the scheme of correcting of the propagation model is presented. Then, the architecture and its components of the prototype of interference analysis are given in chapter four. Through specific case studies, the applying of ray tracing model to analyzing of the interferences in real GSM networks is explained in chapter five, and the results indicates that the ray tracing model can provide analyzing results with higher efficiency and precision. In the end of the paper, the work mentioned above is summarized and suggestions for future works are also given.