Research On The Low Complex Acquisition Techniques Of Pseudo Code Under A Large Dynamic And High Spreading Gain Environment

With the development of communication technology,LEO(Low Earth Orbit)satellite communication is playing a more and more important role in national economic and defense,because of its miniaturization,low cost,short development cycle and other characteristics.Direct Sequence Spread Spectrum System(DSSS)has many advantages such as good security,low probability of being intercepted and captured,strong anti-jamming ability and so on.Owing to the above advantages,Direct Sequence Spread Spectrum has been widely used in LEO satellite communication.However,the LEO satellite has a large angular velocity,and the radial acceleration and acceleration relative to the ground is also very large,all these factors result in much more difficult in communicating with the ground terminals.Firstly,relative to the local PN code,the received signal has a carrier Doppler shift up to tens kHz or even hundreds kHz because of constant motion between LEO and ground terminals.Furthermore,because of the requirements of concealment,high depth of the spread gain is necessary in LEO communications.Moreover,as the hardware resources can be used for on-board signal processing is increasingly limited because of its miniaturization.So research on the low complex acquisition techniques of pseudo code under a large dynamic and high spreading gain environment is of great significant.Firstly,this paper discusses the synchronization of spreading code under large Doppler frequency shift condition.And the impact of Doppler frequency on correlation peak is also analyzed and simulated.Secondly,the paper gets the frequency step sizes applied in FFT parallel acquisition algorithm.Then based on the frequency step sizes just obtained,the paper gives a detailed description on FFT time-frequency two-dimensional parallel algorithm and shows the corresponding simulation results at the same time.Thirdly,the paper introduces the theory and algorithm steps of direct average method discussed in this topic.Then the paper compares the performance difference between the direct average method and FFT directly acquisition algorithm under the same conditions of hardware resources and symbol rate.Besides,this paper derives the probability of detection and false alarm in the direct average method,whose theoretical curve and simulation curve are also given.Furthermore,according to the requirements of this topic on the hardware platform,the paper finally presents the corresponding implementation scheme,including hardware block diagram and FPGA software program design.Eventually,the paper presents two correlation peak chipscope screenshots obtained through the two acquisition algorithms introduced.The final results show that on the occasion of restricted hardware resources and appointed symbol rate,the direct average method can work with a larger spreading gain than FFT directly acquisition method,and the acquisition performance is also better.