Research on the Implementation of GPS Pseudolite Based on FPGA
|School||Hubei University of Technology|
|Course||Power Electronics and Power Drives|
|Keywords||Global Positioning System Direct Sequence Spread Spectrum Pseudo-random noise code Navigation message SigalTap II Logic Analyzer|
Since the end of the sixties, the U.S. military put forward the concept of NAVSTAR GPS, the GPS system now have been met the best positioning system standard at that time. Because GPS system can give an unlimited number of users with accurate PVT(position velocity time), It has a very wide range of applications. However, the accuracy, reliability, information integrity, and many other advantages of GPS system must meet the following conditions those are the geometric distribution space of at least four visual SV (GPS satellite) and the integrity and reliability of their RF encoding signal. Therefore, GPS receivers, in some closed place (such as steel frame structure of plants, tunnels, closed office and so on),may have lost their normal function. So GPS pseudo-satellite is an effective way to solve this problem. Pseudo-satellites can be used to test the GPS signal receiving equipment in a shield plants or locate the staffs in a mine tunnel. In addition, while the U.S. military GPS systems are used in precision positioning service(PPS, General civil system for standard positioning service that is SPS),and it is using Antispoofing (AS) and the selective availability (SA) of the two features to achieve encryption(SA on May 1, 2000 disabled), the research of GPS signal is the necessary way to manufacture the jammer. For example, the GPS constellation can be simulated by using pseudo-satellite so that it can disturb or give error command to the enemy equipment which may be error navigated. Therefore, researching the GPS pseudo-satellites and its code is very essential.The program’s idea is for the complete simulation of dual-band GPS signal. Then it is necessary for the research and analysis to the details of real GPS signal. This article is mainly directed against the study which includes GPS digital signal coding, the analysis of navigation message, as well as the hardware implementation. These are the necessary process and methods to achieve pseudo-GPS satellites. The first chapter introduces GPS navigation system development, the status and the trend of development GPS signal. In the Chapter II, there is a detailed study of pseudo-random noise code (C / A code and P code) and direct sequence spread spectrum technology (DSSS). Chapter III mainly introduces the navigation message in detail. For the implementation of the program, navigation message is the key to pseudolite. Therefore it is necessary to illustrate every one bit. Chapter IV includes the implementation methods and debug results. It also includes a part of the program code and simulation graphics.There is a method of that is using the Cyclone II series FPGA EP2C5Q208C8 which is manufactured by ALTERA company as the core chip of system to achieve hardware design program. The chip has rich resources. It has 4608 Les,142 user IO pin,117Kbits RAM and 2 PLL these can provide a powerful hardware support to system. In addition, it is using VerilogHDL to achieve C/A code and P code and system control and the Navigation message stored in the FPGA-chip ROM. Experimental results will be simulated and will be tested by SigalTap II Logic Analyzer which provided by QuartusII and digital oscilloscope.