Research On Key Technologies Of Beidou B1I Weak Signal Acquisition

With the completion of the constellation deployment of Beidou generation III system,the satellite navigation technology based on Beidou system will enter a comprehensive and indepth research stage,and the satellite navigation receiver based on BDS is gradually infiltrating into more application fields.Whether the receiver can successfully capture satellite signals directly affects a series of subsequent operations such as tracking,synchronization and positioning solution.Especially in the working environment of weak satellite signals such as cities,dense forests and underground buildings,it puts forward higher requirements for the acquisition sensitivity of the receiver,while the traditional satellite signal acquisition technology can no longer meet the needs of special environments.Therefore,The research on satellite signal acquisition algorithm for weak signal is a research hotspot at this stage.Taking Beidou BlIsignal as the research object,this paper focuses on Beidou B1I weak signal acquisition technology.Firstly,the signal structure and acquisition principle of Beidou B1I are described,and the basic acquisition algorithm is analyzed in detail.The reason of bit symbol jump of B1I signal and its influence on signal acquisition are analyzed.The simulation results show that the basic acquisition algorithm has poor effect on the signal with bit jump.Aiming at the problem of bit hopping,the acquisition algorithm of short-time correlation matched filter combined with FFT(PMF-FFT)is studied.The simulation results show that the algorithm can eliminate the attenuation of bit hopping to the acquisition peak,but there are some problems,such as low signal energy utilization and high requirements for hardware resources.Secondly,the characteristics of weak signal and its influence on signal acquisition are discussed,the weak signal processing strategy and its limiting factors are analyzed in detail,and the weak signal processing method of incoherent integration based on prolonging the coherent integration time is designed.Based on this,aiming at the problem of attenuation of acquisition correlation value caused by bit jump of D2 navigation message data code of Beidou B1I signal,a D2 weak signal acquisition algorithm based on half bit alternation is designed.According to the characteristics of D2 navigation message,the odd and even signals are divided by using the idea of half bit alternation,and the bit jump signals are eliminated by processing the odd and even signals respectively.Simulation results show that the algorithm is effective in capturing B1I weak signal transmitted by GEO satellite.Then,aiming at the attenuation of acquisition correlation value caused by the bit jump of NH code of D1 navigation message of Beidou B1I signal,a D1 weak signal acquisition algorithm based on pseudo circle correlation is designed.By redefining the local signal,the correlation operation results before and after bit jump are changed from the same sign subtraction to the different sign subtraction to eliminate the attenuation of acquisition peak value.After the analysis of accumulation strategy,This method can also be applied to capture B1I signals transmitted by geo satellites.Simulation experiments verify the effectiveness of the algorithm in capturing B1I weak signals.Finally,the D1 weak signal acquisition algorithm based on pseudo circle correlation is implemented on FPGA.Aiming at the problems of large amount of operation and high consumption of hardware resources,the average sampling method is designed based on Beidou B1I signal structure.The simulation analysis shows that this method can effectively reduce the amount of operation of the algorithm on the basis of ensuring the acquisition effect,The verification results of Modelsim software show that the FPGA design of this method is correct and can meet the requirements of signal acquisition.