The Design Of Down-link Frame Construction For Micro-satellite Communication And The Development For Testing Platform

Being the only way to achieve the satellite-earth communication, micro-sattellite communication system is one of the most fundamental and important part of the satellite. This thesis, first of all, has proposed a complete design of communication system, according to the demand of miro-sattellite: small-volume, lightness, and low-power, and satisfied the need the function of communication system for satellite-flying tasks.For satisfying the down-loading of image data shot by CCD camera and achieving the function of distance and velocity measurement cooperating with ground supervision system, this thesis designed two kinds of frame construction affiliated by two types of communication system: the one is Virtual Channel Data Unit (VCDU) data frame construction affiliated by communicating system designed in terms of The Consultative Committee for Space Data Systems (CCSDS); the other is Pulse Code Modulation (PCM) telemeter frame construction affiliated by Unite S Band (USB) transponder system, according to the nation's military standard.Emulated test platform, consisted of testing singal source and receiver, for testing the communication system of micro-sattellite. Testing singal source is used for emulating the down-link data coder; testing channel and data sensor .Testing decoder is used for emulating the down-link data decoder. Testing data source based on PC104 embedded computer platform, aimed at collecting and receiving the sensor data and image data by using customizable A/D expanded board and serial interface expanded board. In order to assure the real-time sensor data intactly, there are two tasks to framing code for sensor data and image data. During working period, so long as sensor data didn't executed the framing work, the framing process of image data is advancing and finally unity VCDU data stream is exported. Down-link data decoder, by using the abundant outer interface of DM642, has achieved the receipt of down data steam. Under the circumstances of Code Composer Studio (CCS), we have finished the synchronous frame and decoding process for various types of data. Besides, we have installed TCP/IP on DSP, combining NDK published by TI, for the purpose of network communication.