Study On Some Problems For Radio Wave Propagating And Scattering Through Troposphere

The most important impacts on wireless communication systems is from troposphere, clear atmosphere and some meteorologic environments, for example rain, snow, dust-storm and so on. The study on some problems for radio wave propagating and scattering in troposphere is a project, about which some theoretical and experimental results have been given, but there are some new challenges. Some new problems are presented by pursuers on radio wave propagating with the developing of radio-technology, For example: If the precision of calculating and predicting models can satisfy the new request for new frequency, new communication technology, and new precision in future more higher frequency and more higher desire of signal quality; It is important application for military affairs and civilian affairs to control and remodel space environment artificially. if some man-made disturbing can improve the communication quality of radio system, extend the applying fields for military affairs and civilian affairs, exploit new radio communication technology; How to investigate and evaluate the mechanism of the impacts induced by radio wave propagating and scattering in troposphere, how to investigate and evaluate the influencing degree and how to mitigate the effects, using the theory of radio wave propagating through random media.It has the theory and practicality significance for improving performance of communication systems and developing communication technologies to study the propagating and scattering characters of radio wave passing through troposphere. Some problems about propagating and scattering for radio wave through troposphere are studied in this thesis. The main investigated contents and results are following:The mechanism about disturbing the index of clear atmosphere by acoustic wave is investigated. The formulae calculating the scattering cross section of unit volume under acoustic wave disturbing are deduced. The relation between the fluctuant characteristics of refraction index of clear atmosphere and the parameters of acoustic wave is found. Some simulation and discussion are given. The status about the permittivity of meteorologic environments, for example rain, snow, dust-storm and so on. are investigated. The specialties of existing models are analyzed. A improved model for studying the equivalent permittivity of meteorologic environments is given. Some calculating, simulating and discussing are given, rain as an example.Using the model of calculating equivalent permittivity, the method for modifying the parameters of ITU-R model for calculating the specific attenuation induced by rain is discussed by detailedly analyzing the exiting model. The method can improve the precision of evaluating rain attenuation by take the effects of raindrop shape, size distribution, average temperature etc. into account. Some calculating and analyzing are given, and the parameters of ITU-R model for calculating rain-induced specific attenuation are modified under Weibull size distribution. Rain-induced specific attenuation is calculated using the modified results, and that is compared with measured data in Xi'an.The models for predicting rain-induced attenuation are investigated in detail. The method of modeling predicting rain-induced attenuation using no one minute rainfall rate is investigated. A new viewpoint of predicting rain-induced attenuation using 10-minute rain rate is discussed. Based on the rain-induced attenuation of the satellites of Xinnuo-No.1 etc. measured in some areas in China, and the ten minutes rainfall rate measured in Haikou etc., the steps and processes of modeling are researched. The predicting results using the model given in this thesis are evaluated using measured data.Based on the in-depth investigating the statistical peculiarities of rain-induced attenuation time series, the time series of rain-induced attenuation are simulated. An ARIMA model for forecasting the dynamic specialties of rain-induced attenuation is modeled. The spectrum of predicting results using the model given in this thesis accords with that of measured rain-induced attenuation time series. The model given in this thesis is analyzed and evaluated.The SCR(Signal-to-Clutter-Ratio) of a cylinder target in rain is discussed. The results show that the effect of shape of raindrop on SCR changing with polarization state is obvious. So, it is necessary for adjusting polarization state of antenna that SCR need be calculated taking the characters of rainfall in certain area, for example the shape of raindrop, into account. The method used in this thesis is available for snow, dust etc.The characters of received signal in multi-path channel are discussed. The necessary to study the PDFs (probability density functions) in multipath channels is analyzed. The mechanism of weather phenomena impacting on the PDFs in multipath channels, rain, snow etc. for instance, is investigated and analyzed by the theory of radio wave propagating in random media. Some computing and simulating about the effect are made under the assuming of rain environment and isotropy antenna. The simulating results are analyzed. The way used in this thesis is valid for antenna with high gain and narrow beam. The mechanism of producing noise to communication systems by troposphere is investigated. The importance of the effects is analyzed. Based on the introducing for atmospheric noise temperature and antenna noise temperature, the contribution of rain and other sedimentation particles to antenna noise temperature is discussed. The annual CDFs (Cumulative Distribution Functions) of specific attenuation for every zone ITU recommended are simulated based some results in this thesis. The annual CDFs of noise temperature and the reduction of G/T induced by rain in some areas in China are discussed by the prediction model for rain attenuation under the link parameters of the satellites of Xinnuo-No.1 etc. The results show that the contribution of rain to noise temperature can not be neglected. It is necessary to invested in detail the effects of weather phenomena on antenna noise temperature, for instance rain, snow, dust-storm and so on.The possible impacts induced by troposphere weather phenomena, rain, snow, dust-storm etc. for instance, on MIMO communication systems are theoretically introduction. And, it is theoretically analyzed that how troposphere weather phenomena, rain, snow, dust-storm etc. for instance, impact on MIMO communication systems. The effect of attenuation induced by rain or snow etc. on MIMO channel capacity are theoretically discussed, which is computed and simulated under rain environment and given antenna. The results show that it is necessary to take the impacts induced by troposphere weather phenomena, rain, snow, dust-storm etc. for instance, on MIMO communication systems into account.The theory for calculating scattering loss in troposphere scattering communication is analyzed. Scattering loss under acoustic wave disturbing is simulated, which is discussed and compared with that under no acoustic wave disturbing. The results show that the performance and stability of troposphere scattering communication system can be improved by acoustic wave disturbing, which has the theory and practicality significance for extending the applying fields of troposphere scattering communication.