Research On Evaluationcriterion Forgnss Ranging Code And Secondary Code Optimization

Global Navigation Satellite Systems (GNSS) contains the American GPS, theEuropean Galileo, the Russian CLONASS and the Chinese Compass underconstruction. GNSS is one of national space and information technologyinfrastructures, but also is an important sign of country status and comprehensivestrength. Navigation Satellite signal decides the congenital performance of anavigation system, and it has a decisive influence on compatibility andinteroperability between systems. Design of ranging codes affect the properties ofsignals, includes the performance of acquisition, tracking, anti-jamming, antimultipath and so on. This paper has a deep study on the primary code andsecondary code in the GNSS ranging code and establishes the evaluation criteria toplay a reference role in the design of rangding codes for the future of Compasssystem, and optimizes the current secondary code.First of all, the paper analyses the traditional codes and modernized codes, topoint out that GNSS ranging code improved about code structure, primary codepattern, signal composition, code length and code rate. And the trend of rangingcode is summarized. Then, the primary codes are discussed in representatives ofGPS L1C signal and Galileo L1OS signal. The results illustrate that the newprimary code can provide a better correlation property. After that, secondary codesare analyzed with its generator principle and correlation properties, which showthe secondary code can improve the correlation properties amongst ranging codes,provide additional spectral spreading of narrowband interference a nd improve bitand symbol synchronization. This is built as evaluation criteria of primary codeand secondary code.Secondly, the paper divides five evaluation criteria of GNSS primary codewhich are dependent on the correlation functions for the acquisiti on, tracking androbustness against narrow-band interference. Other parameters like the datamodulation or the Doppler offsets have to be regarded with a particular attention.The final evaluation function built with the weighting of the different relativecriteria values is enabled to select the best code set among different candidates,and proved feasible by simulation.Finally, the acquisition process of secondary code is analyzed and theacquisition threshold function is simulated to point out the importance ofsecondary code optimization. Then the evaluation criteria of secondary code areproposed. The current secondary codes are evaluated to have some disadvantage by the simulation. Two methods of shorter secondary code search are proposed togenerate the optimal codes of length10,20and25. According to the test result, theoptimal codes can provide better performance compared with the currentsecondary codes for various residual Doppler and frequency offsets. What is more,the paper proposed a method of secondary code of length100constructions togenerate codes which are tested by evaluation criteria of secondary code, and theysatisfies the optimal periodic correlation.