Application Study Of Week Signal Acquisition In BD? Civil Signal Reception

With the development of the satellite navigation and positioning technologies, the scenes in which the satellite signal receiver is used become more difficult than before. The ordinary receivers could never meet the positioning needs where the signals are masked seriously, such as in the houses, in the forests, in the subway and so on. In order to promote the development of the satellite navigation and positioning technologies and enhance the performance of the receiver's capture in the places where the satellite signals are weak, the paper has done the research about the technologies used in the receiving of Beidou civil signals. The main research contents are as the following.Firstly, we have selected the modulation of NH(Neumann-Hoffman) BDII-B1 I branch navigation signal code for the target signal, learned about the structure of the signals in branch navigation and the generation principle of ranging code(CB1I code), and determined the local code in capture technology of this paper is CB1 I code by the simulation analysis of the auto correlation and cross-correlation characteristics between the CB1 I code, the NH code and the superposition of CB1I-NH code. Then we put the code into correlation algorithm of 1ms with the received signal, after that we put the results into the 20 ms coherent integration. Secondly, we made sure that the scope of carrier shifts is between-10 KHz,the deviation of CB1I's speed is from-12.66 Hz to +12.66 Hz, the power of receiving the weak signals is-176 dBW, the corresponding noise-signal ratio is-38 dB,etc, by analyzing the results of the calculation. Thirdly, we used MATLAB for the 8 satellite simulation, and then we got the sampling frequency is 16.368 MHz, the intermediate frequency is 4.092 MHz, the carrier frequency is 5KHz, and the signal-to-noise ratio of digital intermediate frequency signal is-38 dB,etc, which offered the data-source foe the research of the capture technology. Fourthly,after getting the data source, for the target signal, we analyzed and compared the serial time search catch, frequency of parallel search and parallel code phase search capture technology that commonly used. At the same time, we made a sort of improvement on the parallel code phase search technology, and chose the improved method of parallel code phase search capture as the basic structure of the capture technology in the article. Then we have analyzed and compared the coherent integral, incoherent integral and differential coherent integral these three classical weak signal capture technologies, made a improvement to overcome their weaknesses, and finally we got the method of capture which called Bits Flip Coherent Integration.Finally, we used incoherent integral and differential coherent integral and Bits Flip Coherent Integration, these three capture technologies used in the places where the signals are weak, to simulate the capture of the simulation data-source given above. The results suggested that it's not steady to capture the signals from the branch of BDII-B1 I by using original algorithm in capturing weak signals when the signal strength is below-178 dBW. However the algorithm we have improved was successful to realize the capture of weak signals of which strength is 180 dBW when it has been 60 times for integrals. After the successful verification, we used development tool System Generator 2014.4 provided by the company named Xilinx to make a hardware simulation and then we transformed the results of simulation into IP core. After that, we put the core into the development tool called Vivado to synthesize, to realize, and to simulate. The final results of simulation suggested that the improved algorithm was able to meet the application-requirements both in the effect of the capture and in the consumption of the hardware.