Research Of RS Code Technology In Space Optical Communication

With the development of communication technology, the method of communication brings forth the fresh continuously .Using high frequency laser to communicate on space satellite have become modern communication a new focus today. Because of the effect of decline , noise and influence , the signals will cause serious distortion during transmission. Therefore , it must adopt an effective error control method which has very strong error-correcting ability to ensure the error rates within the range of permission . RS (Reed-Solomen) code have strong error-correcting ability in both random mistake and sudden mistake.Firstly, space optical communication system was summaried in this paper, and then the channel characteristics were analyzed, we establish two-type channel models respectively: corresponding air conditions, we establish Gaussian channel; I make a simple introduction of channel-encode and error control system at first, and then explain RS code algorithms and principle , put forward laser communication design scheme, the key technologies such as encode, interleaving, decode are particularly discussion. The whole structural design and algorithms program have finished on FPGA and the performance verification have applied in Matlab. Experiment results showed that it has a good performance, and can reach to the system demand.while corresponding free space conditions, we establish Possion channel.In allusion to these two models, based on channel coding theory, we design two-type schemes of channel coding: corresponding Gaussian channel,we adopt interleaving convolution code ; while corresponding Possion channel,we make use of RS code,BCH code cascaded. Passing through Matlab simulation and analyzing its performance verification.we have proved two-type schemes feasible and each item satisfied.They are fitly appiled in their channel respectively.At present, the main method of communications transfers are microwave FDDI system and so on. Microwave-communications can save a great quantity of material to compare with Wire-communications, and can span the intricacy landform easily. And can buildup the communications net with the points and lines combined flexibly.In this way it can make the user who live on the island, mountainous area or countryside exchange the information expediently with the help of trunk line. But compare with FDDI-communications system, Microwave-communications also has some shortcomings just like narrow frequency, channel capacitance limited, code frequency lower and so on. The line of FDDI-communications system has a large capacitance, it is not disturbed easily by environment, but it must have the public channels for install the FDDI. The project construction will be hard and cost longtime and a lot of money if the landform situation badly. Space light-communications combine the merits of FDDI-communications and microwave-communications , it does not only have a large capacitance but also no need to pave the FDDI system. It uses laser to be the carrier of information, it can be used to communicate from space to the land. The transmission characteristic is the light can be transmitted straight and can transmit without wave-guide in the free space. So the Space light-communications obtain the fast development during more than ten years. It becomes one of the most cogent communications methods.Microwave-communications started to be used as an advanced communications technology in the fiftieth of last century. It becomes one of the important transmit method to communicate with the fast development because of the fast speed of construction, stable quality, easy to maintenance and lower cost, it can also save a lot of colored metal and span the intricacy landform easily to compare with the Wire-communications. But because the Micro-communications line capacitance limited, the Space light-communications technology was created then.To compare with the Micro-communications, Space light-communications has those merits as below:1.It increase the channel width, make the information capacitance bigger : the frequency of microwave is about between several GHz to more than ten GHz, but the frequency of laser is about hundreds of THz, it is much bigger about 5 times than Microwave. So it can increase the transmit speed greatly.2.Small size and light weight: Because the energy of Space light-communications used well, this make the weight of sending set and its power supply system become lighter. And also because of the short wave of laser, with the same requirement of radiation corner and receiving point of view, the antenna caliber of launching and receiving can be also reduced.3.Direction-sense is much better, density of power increased: the length of laser wave is about between micron and submicron but radio and microwave length is between several ten centimeters and millimeters .4.The highly of keeping secret : because the width of laser is much narrower than the microwave ,to catch and disturb the narrower laser is very difficult. It can suffice the requirement of keeping secret and disturbance proof, in this way it make communications more safety.5. Deep space is a good transmission media for the light-wave. Light-wave will waste less when transmit in the deep space. To transmit the same equipment of data and information ,light-communications is the best choice.Space light-communications has the big capacitance and high speed merit.Because it will not be affected by the atmosphere when transmit in the space, space can be looked upon as a good stage for space light-communications to show its merit.RS code increase the ability of disturb proof greatly for the space light-communications system, exert the very important function in space light-communications system. Now RS code (255,223)has become the standard code in the deep space communications for grade contact system between NASA and ESA. In addition, RS code is used widely for computer memorizer, digital tape, Compact Disc and disk. It is mainly used to correct the untidy of the surface causing the mistake. (ex. Disfigurement or dust make the"reading or writing magnetic head and media"changed). For example RS code (15,9) is the standard correcting code for the light storage system. Recently, RS code is used in the daily life on DVB and HDTV.The assignment of the essay is according to the item requirement,combine the characterizer of the space light-communications system,make the RS code(255,223) which is suitable for the CCSDS standard interlace ,disinterlace ,coding,then dowload to the CMOS chip (FPGA) in order to carry out the wave emulational.Compare the coding data with the original data,then can check the validity and practicability of the design.At last do some contrast and analysis about correcting on the Matlab.With the development of the channel coding theory, the technology of the channel coding is used widely in the communications engineering area. Especially with the rising of space light-communications, it supply the much wider space for the channel coding. Without any overstatement, with using coding technology in the space light-communications system, to control the mistake of data transmission, reduce the wrong code frequency, increase the dependability of the data transmission, make the stable communications come true. Channel coding technology must have nice future and bright foreground.