Research On The Key Technology Of Embedded GPS/MIMU Integrated Navigation

High-tech modern wars declare that precision guided munitions have made a significant impact in recent armed conflicts, and the low-cost technology of navigation and guidance unit is a key in the consuming guided munitions. Having such advantages as high precision, low-cost, low-size, low-weight, low-power, powerful capability of anti-jamming and high dynamics, et al., embedded GPS/MIMU integrated navigation systems have extensive application value in the projectile and precision guided munitions. This dissertation addresses key technologies of embedded GPS/MIMU integration such as MIMU-aided GPS signal acquisition, MIMU-aided GPS signal tracking, MIMU-aided GPS navigation, GPS/MIMU ultra-tightly coupled navigation, proposing a full solution for the embedded GPS/MIMU integrated navigation system. The main contributions include the following aspects:(1) Benefits and drawbacks of non-coherent and coherent integration are analyzed from the aspects of probability of detection, probability of false alarm and the acquisition search time. Coherent integration requires a shorter integration time to achieve the same acquisition sensitivity versus a comparable non-coherent integration. Non-coherent integration is more tolerant to residual frequency errors and is not affected by the navigation data bits. According to their benefits and drawbacks, aided GPS signal coherent integration acquisition(ephemeris and almanac aiding, time and approximate user position aiding, GPS/MIMU estimated doppler aiding) is presented for the fast acquisition applications. The simulated results show that performance of the aided acquisition method can improve 4.5dB/Hz in the condition of 95% probability of detection than non-aiding GPS signal acquisition, and the time of aided acquisition is reduced from several hundred seconds to several seconds.(2) In order to obtain the best DLL/PLL/FLL performance, we select discriminators and their normalization algorithms with the highest processing gain and the least linearization effect. Considering the total tracking errors such as thermal noise, oscillator phase noise, dynamic stress error, et al., we design the structure of GPS receiver tracking loop for high dynamic applications. Doppler frequency from carrier is proportional to that from code, so Doppler information from the carrier tracking loop is selected to aid the code tracking loop. Dual mode structure is adopted as the high dynamic GPS receiver carrier tracking loop. One is a FLL-assisted-PLL mode for high dynamics, and the other is a PLL mode for low dynamics. The mode is switched according to the lock status.Considering the total tracking errors and different oscillators, the structure of MIMU-aided GPS receiver tracking loop is also designed. The structure of Doppler information from the carrier aided code tracking loop is adopted. The optimal loop bandwidth of MIMU-aided PLL is designed based on different oscillators such as a 1.1 Hz loop bandwidth of the MIMU-aided 3rd order PLL for OCXO, and 2.14Hz for TCXO. Finally according to the designed MIMU-aided GPS receiver tracking loop, the anti-jamming simulation is performed. Simulation results show that anti-jamming performance of the MIMU-aided receiver has 11dB improvement at least, compared to traditional GPS receiver.(3) The GPS navigation filter is investigated. In order to eliminate the clock components, that is, the receiver clock offset and clock offset rate, the pseudorange measurements and Doppler measurements are differenced across satellites. Compared to the least square algorithm, the navigation filter adopted can improve the positioning precision. According to the GPS navigation filter, the MIMU-aided GPS navigation filter is designed, in which the measurements are the pseudorange and Doppler difference across satellites. Also the structure of the adaptive Kalman filter is designed for low-cost, low-precision MEMS IMU. Finally, Test results show that using adaptive Kalman filter, perfect performance can be achieved for the low-cost MIMU aided GPS navigation so that the positioning accuracy is better than 5m, velocity accuracy is better than 0.1 m/s on the static condition, the level attitude errors are better than 0.2°, heading attitude error is better than 0.2°(with heading aiding).(4) In order to improve the performance of dynamics and anti-jamming, the dissertation presents a GPS/MIMU ultra-tightly coupled navigaton algorithm. The vector-based tracking structure of GPS receiver which is the foundation of GPS/MIMU ultra-tightly coupled navigaton algorithm is introduced firstly. Three local pre-processing algorithms for GPS correlated sample signals are presented for GPS vector-tracking architecture:least mean square curve fitting, linear Kalman pre-filter and non-linear Kalman pre-filter. The GPS/MIMU ultra-tightly coupled navigaton algorithm can be achieved by replacing the GPS navigaton filter in GPS vector-tracking structure with an integrated GPS/MIMU navigation filter. The local pre-processing algorithm is used to update an GPS/MIMU navigation filter. The navigation solution together with GPS parameter corrections are used in a tracking predictor to generate high-sampling-rate carrier and code replicas. The structure of reduced-dimension Kalman filter is adopted for the GPS/MIMU navigation filter in order to improve the performacne of GPS/MIMU navigation filter. Finally, regarding the strong nonlinearity of GPS corrlelator output signal, UKF is first presented for GPS local pre-processing algorithm, and the performance of GPS local pre-processing algorithm using UKF is evaluated.(5) Test methods and results are presented and the system performance evaluation are given. The main performances are as follows:1) In the embedded GPS/MIMU integrated navigation system, TTFF(Time To First Fix) of ephemeris aiding GPS is better than 10s. 2) The GPS positioning accuracy is better than 5m and velocity accuracy is better than 0.1 m/s on the static condition. On the dynamic condition, the accuracy of the designed GPS receiver is comparable to that of commercial GPS receiver.3) For the embedded GPS/MIMU integrated navigation system on the static condition, the positioning accuracy is better than 5m, velocity accuracy is better than 0.1 m/s, and the attitude errors are less than 0.2 degrees with yaw aiding.The contribution of this dissertation is not only applicable for GPS, but also for other GNSS such as GLONASS, GALLIEO, BDⅡ.