| With the growth of broadband business especially driven by the internetbroadband multimedia business needs,satellite communication has become animportant part of global seamless communication.The well-developed C-band andKu-band relatively crowded,while Ka-band spectrum resources are rich,large capacityof communication,and effective to decrease the size of the ground terminal ofantenna,thus attracting the attention of more and more widely.However,inKa-band,with the rising of frequency,rain attenuation is relatively serious.In order toensure the quality of the satellite link transmission,it must be compensate theattenuation.This paper first summarizes the ka-band satellite communication systemdevelopment present situation at home and abroad, and discusses its developmentadvantages and wide application field in the future.Then mainly analyzes the factorsthat caused attenuation of the Ka-band satellite communication transmittedsignal,emphatically discusses the signal attenuation caused by rainfall.Rainattenuation is associated with rainfall rate,therefore,the paper also discussed thecontent about rainfall rate and summarized the factors affecting the rate of rainfallfirstly,such as the size of the raindrops and their distribution features,the end speed ofrain,etc.Then this section introduces the formula of calculating rainfallrate,finally,lists some rainfall rate cumulative distribution models which are widelyused in the world.This article also discusses rain attenuation prediction models indetail,including ITU-R model,DAH model and its corresponding improvingform,then the detailed comparison has been carried on.It is concluded that theimproved model2and4of DAH model more accord with rain failure characteristicsof ChangChun’s regional in the conditon of the comparison of the data points weresame.The improved model2and4’s mean,standard deviation and mean square rootare smaller than other patterns.Then the paper analyzes the observed rainfall eventsand respectively explores Ka-band signal rain failure characteristics of the haeavyrain,moderate rain,light rain one by one.The conclusion is given that rain attenuationcaused by light rain is around8to10dB in general and it’s sustained time islonger,the failure rate of change is bigger;While maintaining moderate rainattenuation is between16and20dB,short duration time compared with light rain,therain failure changes slowly;When heavy rain occurs,cause very serious rainattenuation more than40dB.So much rain failure for communication link is difficultto accept,but the heavy rain lasts short time and the rain failure changes very slowly.The improvement of communication frequency make the attenuation of the radio waves propagation in the atmosphere increasing,such as Ka-band（20GHz~30GHz），the rain failure can reach dozens of decibels,which greatly limits the system to bepractical,therefore,it’s need to take efficient rain attenuation compensationcountermeasures to alleviate the impact of the rain.In this paper,length later in thispaper mainly discusses the classic rain attenuation compensation method,mainlydiscussed diversity techniques,control techniques,adaptive techniques,etc.ForKa-band communication systems,a single use of the existing resistance to rainattenuation technology can’t meet the goals of higher compensation rainfailure,sometimes may produces large error.Consequently,the paper puts forward amixed rain attenuation compensation technology.This algorithm combines theadaptive power control method based on principle linear forward prediction principlewith rate control,which can predict the rain attenuation value at the moment of naccording to the rain attenuation values before the moment of n,then control theground terminal adjusting the transmission power according to rain down size.Whenthe power control reaches to the limit,it can dynamically lower information rate tofurther compensation according to SNR(Signal to Noise Ratio).The simulation resultsshow that the error of mixed rain attenuation compensation technology reduced to1dB when rain attenuation is not very large.For the big failure,reducing theinformation rate appropriately can effectively reduce BER(Bit Error Rate) to107,ensure that system transport information reliably. |
