Research On Synchronization Technology Of Burst Spread Spectrum Signal Under Low Signal-to-Noise Ratio

Spread spectrum signal has good anti-interference performance,strong confidentiality and can implement code division multiple access.Therefore it is not only applied in civil fields such as mobile communication and navigation and positioning system,but also plays a vital role in deep space communication fields such as satellite measurement and control,space communication and radar.Burst spread spectrum communication system not only has the advantages of traditional spread spectrum communication,but also has the relevant advantages of burst communication system.Compared with continuous signal,it takes a long time to transmit.Burst signals have the characteristics of unknown starting point,unknown ending time and difficulty of judging the duration,which can meet the needs of effective communication in complex and variable communication environment,such as voice transmission in time-varying channel,TDMA time slot communication,frequency hopping signal transmission in military communication,etc.Whether for spread spectrum communication system or burst spread spectrum communication system,communication resources are limited.Using efficient modulation methods such as continuous phase modulation technology can make full use of limited communication resources,make the system work in a very low signal-to-noise ratio environment,and obtain high power utilization and frequency band utilization at the same time.In the actual communication environment,due to the noise interference and time delay,the signal is transmitted under low signal-to-noise ratio,and accurate synchronization is an important guarantee that the signal can be accurately received by the spread spectrum receiver under low signal-to-noise ratio.Therefore,the research of synchronization technology is very important for burst spread spectrum communication.Based on this,how to implement the initial synchronization acquisition of burst spread spectrum signals under low signal-to-noise ratio is discussed in this thesis.Firstly,the traditional acquisition algorithms,such as time-domain serial search algorithm,FFT based frequency parallel search algorithm and cyclic correlation based code phase parallel search algorithm are introduced,and their performances are compared;Secondly,the acquisition algorithms for spread spectrum signals under low signal-to-noise ratio are analyzed and studied,including matched filter acquisition algorithm and partial matched filter combined with FFT(PMF-FFT).In view of the contradiction between the number of FFT points and the length of partial matched filter of PMF-FFT algorithm,an improved PMF-FFT based on the idea of overlap is proposed,which increases the length of some matched filters while keeping the number of FFT points unchanged,so as to increase the correlation peak,and effectively improve the acquisition performance of PMF-FFT algorithm.Through the simulation and comparative analysis of PMF-FFT algorithm and improved PMF-FFT algorithm,the simulation results show that when the Doppler frequency shift is small,the improved algorithm has a greater performance than PMF-FFT algorithm.Next,the circular double block zeroing algorithm(DBZP)is studied,through analysis of the effects of block length,Doppler frequency offset and data reversal on the acquisition performance of DBZP algorithm,the simulation results show that DBZP algorithm can not achieve better acquisition performance under large frequency offset search range and small frequency offset at the same time.In order to solve the contradiction between the acquisition performance under small frequency offset and the frequency offset search range of DBZP algorithm,this thesis proposes an unequal length circular double block correlation zero filling algorithm(ULDBZP)based on DBZP.To keep the total length of double blocks of DBZP unchanged,and ensure that the number of blocks,the length of data sub blocks and zero filling sub blocks are integers,the proportion of data sub blocks and zero filling sub blocks is changed,so as to improve the acquisition performance of the algorithm when the Doppler frequency offset is small.The simulation results and analysis show that ULDBZP algorithm has better acquisition performance than DBZP algorithm when the Doppler frequency offset is small...