Research On The Acquisition And Tracking Technology Of INS-aided GPS Receiver

The ability of GPS receivers to acquire and track signal is affected by two factors: low signal-to-noise ratio and high dynamic. In order to enhance receiver performance in acquiring and tracking signal in low signal-to-noise ratio and high dynamic situations, this thesis deeply analyses acquisition and tracking technology of receiver with INS aiding in theory as well as by experiments. The main works include:1. Three main factors affecting the performance of acquisition are analysed in this thesis: Doppler frequency estimate error and code estimate error, coherent integration time, single decision algorithm and multiple decision algorithm. Increasing coherent integration time and multiple decision algorithms are used to increase detection probability in weak signal environments. In oder to reduce mean acquisition time of receiver in cold start, warm start and hot start, velocity information from INS is used to remove the Doppler frequency.2. Delay Lock Loops(DLL) discriminator and Phase Lock Loops(PLL) discriminator used in weak signal environments are also analysed and choised in this thesis. Based on the optimum closed transfer function, the parameters of two order and three order loop filter are designed. The main sources of errors in a PLL(the thermal noise, the oscillator phase noise, the oscillator vibrations and the impact of dynamics) are analysed, the results show that the thermal noise and Doppler shift are the most predominant and had a conflict on the design of the PLL. So the optimum bandwidth PLL algorithm is designed to solve the problem. In order to remove the dynamic and reduce the thermal noise, the structure of INS-aided GPS receiver tracking loop was designed. The minimum bandwidth of INS-aided tracking loop is also given.3. At last, static and high dynamic test are given to verify upper method. The static test results show that the software GPS receiver designed in this thesis can successfully acquire and tack signal. Increasing coherent integration time and reducing loop bandwidth can increase receiver's acquisition and tracking performance in weak signal environment. The optimum bandwidth of tracking loop was useful. The high dynamic test shows that the designed three order loop and INS-aided two order loop can meet the needs for a receiver with an acceleration of 10g and an jerk of 10g/s. INS-aided three order loop can meet the needs for a receiver with an acceleration of 100g and an jerk of 100g/s.