Research And Realization Of SINS-Aided GPS Deeply Integrated Navigation System

With the rapid development of science & technology, many kinds of navigation systems have been developed. As it would be difficult for one single system to meet navigation requirements under global, all-weather and various complex environments, so research on integrated navigation system by combining two or more systems has become a hot spot worldwide. Currently loosely or tightly integrated navigation system of GPS-aided SINS is widely applied in China. But the problems of integrated navigation system or GPS receiver, such as susceptible to interference, and poor dynamic performance etc, still can not be solved. However, deeply integrated navigation system through inertial-aided GPS will be able to enhance receivers'capability of anti-interference and dynamic performance. It provides a practical solution for integrated navigation system of low-cost, small size, low power consumption, high precision, high reliability, high stability and high integrity.The research background of this paper is "Domestic-Made Low-Cost CORS Base Station Receiver Technology" of national "863" Special Projects. Firstly a high-performance GPS receiver loop was designed to realize the navigation positioning algorithm based on dual-frequency P-code, and then successfully developed an engineering propotype of high-performance dual-frequency GPS receiver, that break through one of the key technologies of GPS/SINS deeply integration. Secondly, this paper carried out the key technology research on GPS/SINS deeply integrated navigation system. With the help of successful design and development of digital interferometric closed-loop polarization maintaining fiber optic IMU, it further improved the stability, reliability and availability of the navigation system, realized three tasks:SINS-aided GPS signal acquisition, design of tracking baseband loop, and analysis of GPS/SINS deeply integrated navigation algorithm. Finally, a specific design and solution was provided and comparison experiments were carried out.The main tasks include the following aspects:(1) The design of a small-size IMU based on fiber optic gyros and flexible quartz accelerometers was completed and assembled; analysis and performance testing of FOG and quartz accelerometer was respectively carried out; and calibration and compensation of the IMU as a whole part was conducted. The bias stability reached 0.5 deg/h for FOG and 0.5 mg for accelerometer after compensation.(2) A high-performance, general-purpose GPS receiver based on DSP, FPGA was designed. A highly efficient fast acquisition method of GPS L1 carrier and C/A code was designed, and second-time high-precision signal acquisition was applied to realize the purpose of fast acquisition and high precision. For various impacts on the baseband loop caused by different dynamic environment, a third-order Costas-PLL carrier loop aided by second-order AFC was designed to ensure a high and stable precision tracking for L1 carrier and C/A code of GPS signal through automatic loop switching.(3) Based on the realization of general-purpose GPS receiver baseband loop, acquisition, tracking and demodulation processing for GPS L1-P code, L2 carrier, and L2-P code through semi-codeless method was achieved. Therefore dual-band and dual-code signal processing were realized. Four measurements, L2 carrier frequency, carrier phase, L1-P code phase, and L2-P code phase, were increased comparing with the general-purpose receiver, which allows the following navigation algorithm to calculate the ionosphere error with more accuracy, and provides more measurements for carrier integer ambiguity calculation.(4) Through analysis of the impact factors of the receiver's signal acquisition performance, the relationship among acquisition probability, the probability of false acquisition, acquisition time and the sensitivity of acquisition was studied. An acquisition method was designed to decrease the acquisition time through reducing signal search range aided by SINS, and to increase capture probability and sensitivity through increasing integration time. Error of receiver's tracking loop was also analyzed. Design of SINS-aided tracking loop was realized to improve the dynamic performance, anti-interruption and anti-multipath of tracking loop.(5) The technologies of applying dual-band dual-code pseudorange measurements to correct the ionosphere error and using carrier-ADR smoothing to reduce multipath error were realized. At the same time, three different levels of deeply integrated navigation filter algorithms between GPS/SINS were analyzed. The advantages and disadvantages of different level deeply integration algorithms were also discussed.(6) The testing and experimental system of dual-frequency receiver was built up. The testing results verified the performance of the developed engineering prototype dual-frequency receiver. Meanwhile an inertial-aided GPS deeply integrated navigation testing system was also set up, and static and dynamic testing for the deeply integrated system based on pseudorange and pseudorange rate Kalman filter was carried out. Testing results show that the deeply integrated navigation system has a better performance in anti-interruption and under dynamic environment than the loosely and tightly integrated GPS/SINS systems. It laid a good foundation for the future experimental research on SINS/GPS deeply integrated system.Although this paper only uses GPS as study example, as all satellite navigation systems work under the same operating principles, so the research results are also applicable to other satellite navigation systems (GLONASS, GALLIEO, and COMPASS, etc).