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Electromagnetic wave propagation model needs to be corrected before it is used to predict wireless signal coverage. Control of the correction error will directly affect the accuracy of coverage prediction. A method to reduce the correction error is introduced in this paper. In this way, we carry out the test along concentric circles, which is unusual in such tests; and take an appropriate means for data process, so that we can reduce correction errors. Introduction Electromagnetic wave propagation in real space is very complicated and much more complex in the mobile communication system, which is mainly displayed in three aspects: (1)The openness of wireless channel. When electromagnetic wave transmits in open space, the wireless channels are easily affected by all kinds of interference signals. (2)The complexity and diversity of propagation environment. The mobile communication system works both in big cities with high buildings and small villages in mountains. (3)The random mobility of users. Users might call anywhere, such as in rooms, in a high-speed train or car. Above three aspects have a great influence on the propagation of electromagnetic wave in a mobile communication system, therefore it is hard to accurately predict the path loss of wireless channel in the system. Generally, wireless propagation models are built to predict the path loss, so as to estimate the field strength of received signals. Propagation models commonly used in mobile communication network planning are mostly empirical models, which are mathematical model summarized from a large number of measured data, for example, Okumura-Hata’s model, COST231-Hata model, COST231-Walfisch-Ikegami model and SPM model, etc. Empirical models have the advantages of convenient use and simple calculation. However, due to different propagation characteristics are in different areas, if empirical models are mechanically copied in all areas, a great error will generate between calculation results and actual values. Especially in China, because of the vast area of the country and various types of geography in different places, if you want to apply a model in different regions, some parameters must be modified, which means that a model correction is needed. Nevertheless, we have to notice that there will be errors in correction of propagation model. There are mainly two sources causing errors: errors from test data for correction and error from correction algorithm. Errors from test data are mainly composed of three aspects: GPS errors, digital map errors, and CW (Continuous Wave) test equipment errors. GPS errors depend on the measuring accuracy of GPS equipment; digital map Errors depend on the resolution of digital maps; CW test equipment errors, on one hand, result from the test device itself, on the other hand, from improper operation. Correction algorithm errors are determined by core algorithm, mainly depending on correlation processing method of individual variables in the model and test data. The method introduced in this paper will effectively reduce errors of propagation model correction by improvement of data collection and processing. We will describe the method through the example of Okumura-Hata’s model correction. International Conference on Information Science and Computer Applications (ISCA 2013) © 2013. The authors Published by Atlantis Press 340 Okumura-Hata’s Model Okumura-Hata’s model is one of the most widely used models for signal prediction in urban areas. This model is applicable for frequencies in the range 150MHz to 1500MHz and distances of 1km to 100km.It can be used for the height of base station antenna ranging from 30m to 200m,and the height of receiver antenna ranging from 1m to 10m.The standard formula for median path loss in urban areas is given by L(urban)(dB)=69.55+26.16logf-13.82loghte-a(hre)+(44.9-6.55loghte)logd. (1) Where f is frequency in MHz, hte is effective transmitter antenna height in meters, hre is effective receiver antenna height in meters, d is the T-R separation distance in km, and a(hre) is the correction factor for effective receiver antenna height. For a small and medium sized city, the receiver antenna correction factor is given by a(hre)=(1.1logf-0.7) hre-(1.56logf-0.8)dB. (2) and for a large city, it is given by a(hre)=8.29(log1.54hre)2-1.1dB for f≤300MHZ. (3) a(hre)=3.2(log11.75hre)2-4.97dB for f>300MHZ. (4) To obtain the path loss in a suburban area, the standard formula in Eq.1 is modified as L(suburban)(dB)=L(urban)-2[log(f/28)]2-5.4. (5) And for path loss in open rural areas, the formula is modified as L(rural)(dB)=L(urban)-4.78(logf)2+18.33logf-40.94. (6) Model Correction Process Overview. In order to correct the model, we will replace the constants in Eq.1 with variables. In the cause of our test, the transmitting frequency, antenna height of transmitters and receivers are all fixed, we focus on measuring path loss changes with distance, so we just need to introduce two correction factors k1 and k2. See the following equation L(urban)=69.55+26.16logf-13.82loghte-a(hre)+(44.9-6.55loghte+k1)logd+k2. (7) We can calculate the correction factors of k1 and k2 by Eq.7 after we get path loss from test. Due to fast fading, less test data will lead to greater error of correction result. According to the well-know lee's theorem, when intrinsic length is 40 wavelength and the sampling points is 30 ~ 50, fast fading will be effectively eliminated and slow fading will be kept. In this way, we can find out slow fading trend of signal in local environment to reach the goal of the model correction. Test Site and Route Choice. We choose the urban area of Tianjin as test area. The transmission site is located in a building near Hebei road in the center of Tianjin. Transmitting antenna is 34 meters high with 2dBi gain .Transmitter output power is 5 w and transmission frequency is 876.03 MHz. Concentric circle is usually avoided in choosing test route, to prevent the complexity of data processing increased by data redundancy at same distance. However, we take the way of the concentric circles for testing. The test vehicle runs in ways similar to concentric circles from near to far around the transmission site, so that we can test throughout various terrain environment around

A Method to Reduce Correction Error for Electromagnetic Wave Propagation Model