Study On Propagation Model Tuning Based On WCDMA System

1,IntroductionCompared with the traditional GSM system, the complexity of operation,air-interface and network provided by the WCDMA system, which is one of the 3rd generation mobile communication technology, are all greatly increased. This means the radio network planning of WCDMA is more complex and challenging than GSM. The method and the accumulated experience of GSM network planning are not fit for WCDMA system. Propagation model is the base of WCDMA radio network planning. The accuracy of propagation model decides the rationality of network planning, and even decides whether or not the operators could satisfy users'requirement using relatively economical investment. The radio propagation environment of mobile communication is very complex, and the terrain of each area is different. The radio propagation model is nearly correlated with propagation environment, mainly depending on natural terrain (plain,hill,mountainous area,water area .etc),the number,height,distribution and material character of manual building,vegetation,electromagnetic environment and so on. Further more, radio propagation is also influenced by the radio wave's frequency and mobile station's speed. In order to obtain the propagation model which can reflect the local propagation environment exactly, it is needed a great deal of test to adjust radio propagation model. This paper mostly studies how to choose appropriate propagation model in WCDMA system, and tune the choosing model according to three representative areas.2,The choice of radio propagation model in WCDMA systemBecause of the difference of propagation environment, universal propagation model is not in existence. The classical theoretic model is used for initial analysis. The primary models are Okumura-Hata,CCIR,COST231-Hata and WIM. By means of experimental simulation and engineering practice, we consider Hata andCCIR are unfit for radio network planning for WCDMA system. Because the antenna height and terminal height of this model are fit for small cities and town areas, so this model adapts to radio network planning less than 1.5GHz in small cities and town areas; The COST231-Hata model is obtained from Hata model by measuring radio propagation characters in 2GHz frequency particularly and tuning parameters. Because the applicable range of this model's antenna height is abroad, and anticipative effect can be reached when it is used to various cities, so this model adapts to radio network planning in cities and suburbs. The COST231-WIM model classifies the propagation loss particularly, models the free space loss,diffraction and dispersion loss,the loss between building roof and mobile station separately, so this model adapts to radio network planning in city environment.3,CW testCW test is continuous wave test. The purpose is to collect propagation data in downlink frequency of WCDMA, and tune the Propagation model used in the WCDMA system according to the collected data. So CW test is the basic part of model tuning in this paper. All the CW test divides into three steps: prophase preparation,data collecting and data processing. In order to assure the veracity of collected data, all parts of CW test must be strict, therefore, this paper expatiates the requirements and principles of testing environment,distance,path,antenna height,signal source and so on, combining with engineering practice and the author's personal experience.4,Propagation model tuningIn this paper, every part of Propagation model tuning is expatiated. According to the testing data, we accomplish the curve fitting using least-square, and on the basis of COST231-Hata model, we establish equation group using lean-differential coefficient on the principle of least-error square. Then, we finish model tuning by extracting model coefficient in general city zone,along the river zone and suburb three different areas. Finally, we checkout the tuned modelcombined with the requirement of the mobile communication network planning to propagation model, then compare the result with the untuned model and business planning soft ware, validating the validity and practicality of tuned model.5,ConclusionAt present, there are a lot of business planning soft wares used to model tuning, such as ASSET of Aircom company,PLANET of Marconi Communication Company in England and Atoll of FOSK company in France and so on. But all the soft wares are based on accurate digital map, and the simulation results prove that the method in this paper could reach the effect as well as the special soft ware in some medium and small city, where terrain character is relatively simple.