TMBOC Signal P-code Direct Acquisition Algorithm And Implementation

Satellite navigation now reflects a country’s comprehensive strength, the United States has a GPS navigation system, the EU’s GALILEO navigation system, the Russia’s GLONASS navigation system, and there are building our country’s Beidou navigation system. In the existing navigation systems, which are mostly using direct sequence spread spectrum(DSSS), and the key is DSSS pseudo-random sequence of code. The main topic on this article is long pseudo-random code sequence, P code has its excellent characteristics, long cycle, code rate, making it more difficult to capture and decrypt by the enemy, therefore it has a higher confidentiality and immunity,being widely used the military field.Conventionally, P code acquisition is based on short-cycle code(C code). This approach appears to capture relatively simple and easy to implement, but the P code is captured depends on the excessive short period code(C code) capture, greatly weakened the benefits of P-code, thereby reducing its immunity and confidentiality. This article is based on the project of navigation receiver for CNSS(Compass Navigation Satellite System), which is the satellite navigation system of China. It needs to design a long period precise ranging code(P code) acquisition module under the new signal modulation system(TMBOC), which can direct acquire the P code without the aid of coarse ranging code(C code) and provide the rough code phase and carrier frequency to the receiver signal tracking unit, to improve combat capability of satellite navigation systems in the navigation warfare environment.In this article, firstly, the theoretical basis of navigation and positioning receiver is introduced, which is spread spectrum communication theory. Then it introduces the DSSS which is the most common form of spread spectrum communications technology. Combined with the characteristics of this paper, the TMBOC modulated signal and a long period ranging code(P code) is strongly introduced. Secondly, after a brief summary of the general DSSS(Direct Sequence Spread Spectrum) signal acquisition and detection methods, five typical direct acquisition algorithms are introduced to accommodate to the long period P code, and then two methods, that are frequency domain parallel code phase search algorithm and match filter/FFT algorithm, are selected to implement the direct acquisition modules. Fourthly, the design and implementation of the two different methods in FPGA, including the architecture, module division, simulation results, hardware consumption, are described in detail. Finally, the suggestion on the further improvement of the direct acquisition module is presented.