| Satellite-to-ground and inter-satellite communications is key technology of formation flying satellites.And compared to other communication techonologies, Spread Spectrum has the advantages of low probability of intercepting,a high immunity to interference,hiding the useful information and multiple-access communication ability.In modern information times,it has been one of the three high-techonology communication means and is developing from military use to commercial environment.Thus,how to use spread spectrum techonology on micro-satellite has very important significance.The paper use DSSS (Direct Sequence Spread Spectrum) on the satellite communication and study indepth exploration, especially channel model, modulation techonology and simultaneous techniques.With comparing and analysis, establish satellite-to-ground channel model which is on the verge of reality system, radicateπ/4-QPSK modulation and slove the problem of PN acquisition in the condition of great frequency of fset and low SNR. At last, establishing DSSS system use systemview.Channel model has been simulated and analysed on the probability distribution model, then discusse the effect of multipath fading and Doppler shift in the micro-satellite communication.In order to improve the reality of the model using systemview simulate the experience model COST207.Supply transmitter and receiver of DSSS system, analyse the performance of m sequence and GOLD code, use a kind of newly modulationπ/4-QPSK , and identify the improvement of convoluotional encoding and technology of interleave in DSSS system.Compare and analyse the methods of PN acquisition,supply a method of PN acquisition suitable micro-satellite communication.Implement PN acquisition in the condition of great frequency of fset and low SNR..Use early-late gate implement PN tracing, and use costas implement carrier timing.Using Systemview emulate DSSS system, certificate the precision of algorithm and the feasibility of project. |
