Research On Parallel Acquisition Algorithm Of Baseband Signal Based On BDS And FPGA Implementation

The global navigation satellite system is the embodiment of a country's comprehensive national strength and scientific and technological strength,and it is an indispensable spatial information infrastructure for promoting the rapid development of economy and society and ensuring national security.Many economic and military powers,such as Europe,the United States,Russia and Japan have carried out large research and development investment in satellite navigation system.China has officially launched the independently developed Beidou satellite navigation system.It is the navigation receiver which can most directly reflect the application value of satellite navigation system.The key to the baseband signal processing module in the receiver is the synchronization and tracking of the spread spectrum code,therefore,it is urgent and realistic to study the acquisition of Bei Dou satellite signal for improving the receiver performance and the future development of satellite navigation in our country.Faced with increasingly fierce competition in various countries and increasingly complex radio environment in the world,how to achieve the rapid and accurate acquisition of Beidou satellite signal is the primary issue to be solved.At present,the more mature and commonly used algorithms are time domain serial acquisition algorithm,matching filter acquisition algorithm and pseudo-code parallel acquisition algorithm based on FFT.By comparing and analyzing the advantages and disadvantages of these three algorithms,this thesis chooses the pseudo-code parallel acquisition algorithm based on FFT as the research object,and puts forward some suggestions so as to further improve the capture speed under the premise of ensuring the acquisition accuracy,finally,implements the improved algorithm on FPGA.The main work is as follows:First of all,the structure and characteristics of satellite signal of Beidou ? are studied,and the structure and generation of carrier,ranging code and navigation message are emphasized.Secondly,the principles and characteristics of three commonly used acquisition algorithms are studied,aiming at the pseudo-code parallel algorithm based on FFT,the improvement suggestion combining the mixing front-end extraction and integral accumulation is proposed: First extracting the sampling data which makes the FFT calculation points reduced to 1/5,in order to reduce the amount of FFT computation,and then before the square detection,accumulating the results of IFFT according to a certain period of time to reduce system complexity.Then,the traditional FFT pseudo-code parallel algorithm and the improved algorithm are simulated and verified on the MATLAB software platform.Finally,adopting the EP4CE30F23C8 chip of Altera company to build a Nios ?-based SOPC system using Qsys in Quartus ?,implementing parallel acquisition of Beidou satellite signal in hardware and displaying the capture results on the LCD1602 to verify the correctness and feasibility of the improved algorithm.