| Satellite communication system has experienced rapid development for its unique advantage and has become an essential part of telecommunication in the future. With people's growing needs of wide bandwidth multimedia services,the C(6/4GHz), X(8/7GHz), Ku(14/12GHz) band can't meet the needs of large bandwidth, high speed, small aperture terminal applications,etc.While the Ka band satellite communication system has such merits:Huge bandwidth available,Small disturbance,Small terminal equipment,etc.so it can offer brand-new method for some new services, such as high speed satellite communication, kilo mega bits bandwidth digital transmission , high definition TV (HDTV) and personal communication,etc.It is the development of the future satellite communication to use Ka band or higher frequency band to construct the satellite communication system. Thus, the research and development of Ka band satellite communication system has attached its great importance for the satellite communication service development of our country.However, the Ka band satellite communication system is now confronted with a great challenge-it is easily affected by meteorological factors. Rainfalls,twinkles,as well as atmospheric absorption can all lead to the deterioration of Ka band field-to-air link channel quality,where rain attenuation is the most important restricted factor. The survey data shows that the rain attenuation of uplink of 30GHz will be over 20 dB at some region in more than 0.1% time period.So technique of equalizing rain attenuation in Ka band is one of the most important researches.This paper introduced the characters and the present study status of Ka band satellite communication. Discussed mechanism and influence of the rain attenuation and widely used application rain attenuation prediction models:ITU-R model. Studied on the calculations of Ka-band rain attenuate in China. Cumulative distributions of rain attenuation were given for the orbit position 92°E for the satellite communication system in the Ka-band(30/20GHz) under the condition of linear polarization. These distributions are calculated from rainfall data and geography parameter at the 65 typical stations of China based on the ITU-R model,providing the basic theoretic data for the research of Ka band satellite communication system in China .combined withIn chapter three, this paper discussed rain attenuation compensation methods and introduced some typical compensation methods: the technology of dividing and collecting including position dividing, frequency dividing, velocity dividing, the technology of power control including open loop power control,close loop power control, feed back power control,adaptive technique including adaptive forward error correction, adaptive coding ,adaptive TDMA,adaptive CDMA,etc.Based on rainfall measured data of Ku-band of 2006,2007 and 2008 three years,with the frequency conversion algorithm of rain attenuation got distribution of Ka-band rain attenuation and interval of 2 seconds, 4 seconds, 6 second and 8 second Ka-band rate change of rain attenuation by statistical analysis .fitting the time frame 0.001%～1% of distribution of Ka-band rain attenuation used ITU-R rain attenuation prediction models, validate the validity of ITU-R prediction models in Chang Chun . logarithmic quadric and exponential function as fitting function fitted the time under 0.001% of distribution of Ka-band rain attenuation by least square method, the result indicates logarithmic quadric suitable for low-time distribution of Ka-band rain attenuation .lognormal and power exponent as fitting function fitted distribution of Ka-band rate change of rain attenuation of three-years average of 2006,2007and2008, the result indicates Ka-band rate change of rain attenuation then to power exponent form .Based on the Ka band rain attenuation of 65 typical stations in China ,combined with terrain and climate distribute status in China,summarized the terrain characters of rain attenuation of Ka band satellite communication system in China: (1)The distribution of the rain attenuation is uneven ,the terrain difference is significant. (2)The distribution of Ka band rain attenuation in China is zonal,The law is obvious, and the trend is descending from the southeast to the northwest.(3) he area with great rain attenuation is the southeast of our country.(4) The area with little rain attenuation is the northwest of our country.Combined with the terrain characters of rain attenuation of Ka-band satellite communication system in China,a optimize distribution project which base on multi-beam satellite transmitter has been presented .Based on the rainfall correlation of two places and the principle of shortest from the beam center , beam radius is 400Km and the whole country is covered with 32 beams. Then according to the contour map of Ka-band rain attenuation,beams are classified into three types of area .In order to best suing the power of satellite, by redistributing the finite power of satellite transmitter between beams in each area.The effect of optimized power control is obvious by analyzing the result of compensation: the beams which can be compensated is bigger after using the method of optimized power control, and with the augment of rain attenuation, the superiority is more evidence.Then we can reach the conclusion that multi-beam optimized power control is efficient in reducing rain attenuation.Combining with the complexion of Ka-band rate change of rain attenuation,an ameliorative-arithmetic of power control compensation has been presented .The ameliorative-arithmetic reduces the compensation errors by add an ameliorative parameter based on the basic-arithmetic .Through supposing there is lognormal or power exponent relationship between ameliorative parameter and adjacent rain attenuation change ,the ameliorative parameter is calculated by the corresponding fitting results of cumulative distributions of rate change of rain attenuation .The simulation experiments results shows that:the compensation error has reduced to around 1dBfrom 2-3dB under 10 second forecast time and 2 seconds, 4 seconds, 6 second and 8 second interval .It mean ameliorative-arithmetic is an effectively power compensation method .Gain some rule during compensation process by analyzing experiments results.Due to rainfall process is random,forecast time and interval of compensation could be ascertained depend on the intensity,rate change of rainfall,the ability of power output device and the specific characteristics of the local rainfall.Parameters value are not static ,they based on specific complexion.Then will gain the best compensation effect last.The characteristic of distribution of Ka-band rain attenuation and rate change of rain attenuation by statistical analysis in this paper, as an important theoretical foundation for design the Ka-band satellite communication system link . The power optimize compensation project of rain attenuation of Ka-band multi-beam satellite communication system offer a basic theoretical consult to the study on Ka-band multi-beam satellite communication system in china. The ameliorative power control compensation arithmetic has been presented in paper could offer important consult to the study of power control compensation method in the future. |
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