| For its unique advantage, satellite communication system has developedrapidly and become an essential part of telecommunication in the future. Withpeople's growing needs of wideband multimedia services and the operation ofInternet, broad band satellite communication has been an essential means forimplementing personal communication without gaps and internet high speedchannel in the sky globally. While C(6/4GHz), X(8/7GHz), Ku(14/12GHz) bandsatellite communication system can't meet the needs of large bandwidth, highspeed, small aperture terminal applications now, the Ka band satellitecommunication system has such merits: broad bandwidth available, smalldisturbance, small terminal equipment, etc. Therefore, it can offer brand-newmethod for some new services, such as high-speed satellite communication,kilo-mega bits bandwidth digital transmission, high definition TV (HDTV) andpersonal communication, etc. It is the development trend of the future satellitecommunication to utilize Ka band or higher frequency band to construct thesatellite communication system. Thus, the research and development of Ka bandsatellite communication system has extremely important consequence to thesatellite communication service development in our country.However, in Ka band, with the rising of frequency, the influence to signalsof all kinds of factors increases gradually. Rain attenuation is a main factor thataffects the communication capability and the quality of transmission in Ka bandsatellite communication. Therefore, in order to ensure the transmission quality,reliability and economical efficiency, we must master the rainfall attenuationinfluence of earth station setting areas accurately while designing the earth-spacesatellite communication links.In the first and second chapter, this paper introduced the present study statusof rain attenuation and mechanism and influence of the rain attenuation,discussed widely used application rain attenuation prediction models: ITU-Rmodel. In chapter three, this paper discussed rain attenuation compensationmethods and introduced some typical compensation methods: the technology ofdividing and collecting including position dividing, frequency dividing, velocitydividing, the technology of power control including open loop power control,close loop power control, feed back power control, adaptive technique includingadaptive TDMA, adaptive CDMA, adaptive coding, etc.Based on the rain data of 65 typical sits in China, and the character of Chinaterrain, this paper adopted model ITU-R. Rain attenuation on up link 20GHz anddown link 30GHz in Ka band satellite orbit position: 62°E, 92°E and 122°E wascalculated. Combined with terrain and climate distribute status in China, weanalyzed Ka band rain attenuation in China, and summarized the terraincharacters of Ka band satellite communication system in China: ① With a vastterritory, the rainfall in China distributes extremely unevenly, for the rain rate isthe primary factor which affects the rain attenuation and the distribution of therain attenuation is uneven too. The terrain difference is significant. The biggestrain attenuation site is located in Fu Jian Yangjiang (40.37dB), while the least isonly 0.79dB, which is located in Xin Jiang Dachaidan. ② The distribution of Kaband rain attenuation in China is zonal from contour map of Ka band rainattenuation in China. The trend is descending from the southeast to the northwest.It reaches the top in Yangjiang, and drops to the bottom in the northwest ofXinjiang.The virtue of multi-beam antenna is that frequency can be reused and thecapacity of satellite communication system can be improved by times. Then thevaluable frequency resource can be used efficiently. The radius of multi-beamcoverage is smaller;the difference of beam's fringe and center's power is not big.It has high gain, and the earth station can be made smaller which can greatlyreduce the cost of system.Based on concrete terrain status and the analysis of rain attenuationcharacters in China, this research adopt immobile satellite which orbit position is92°E and down link frequency is 20GHz to do simulation. The aim is to get thebest percent that is the percent of the areas that can be compensated occupyingthe whole number of beams in China. From the research, we can get the numberis 19 thus the distribution of satellite communication beams in Ka band in Chinais made surely. Then the optimized relation between the distribution of beams andthe area which can be compensated is obtained. By the virtue of multi-beamantenna, the power of satellite transmitter was distributed which can reduce therain attenuation of each beam. The effect of optimized power control is obviousby analyzing the result of compensation: the area which can be compensated isbigger after using the method of optimized power control, and with the augmentof rain attenuation, the superiority is more evidence. Then we can reach theconclusion that multi-beam optimized power control is efficient in reducing rainattenuation.This paper adopts open loop up link power control when the rain attenuationis heavy and only using multi-beam optimized power control can not compensaterain attenuation in Ka band. This method is applied in big and medium earthstations. The research is on rain attenuation compensation prediction. Because inopen loop up link power control, the rain attenuation of up link can not beobtained directly, frequency conversion is adopted this paper, using receiveddown link rain attenuation to get up link rain attenuation through frequencyconversion, and then using up link rain attenuation to predict next period up linkrain attenuation which can improve the predicted precision of rain attenuationthrough adding revised parameters. The simulation results show that this methodis feasible. We must give the chosen parameter k because the data we picked is inheavy rain and rain attenuation is heavy, when the weather is good, it can alsomeet the need of system.The Ka band rain attenuation we calculate and the analysis of rainattenuation in this paper can be used as the important reference when designingthe presetting rain attenuation redundancy of Ka band satellite communicationsystem. The method of optimized power control with up link power control canbe considered when designing multi-beam satellite communication system. Thenumber of the distribution of beams, revised parameters and the chosen of controlperiod can offer fundamental theory in the study of rain attenuation compensationprediction in Ka band satellite communication system in China. |
PDF Full Text Request