Study On GPS IF Signal Simulation And Weak Signal Acquistion, Tracking Algorithm

GPS receiver has been widely used. However, the reliability and accuracy of general GPS receiver suffers from limitations indoors or in urban canyons. In these perturbed signal environments, the signal strength is less than -150dBm and the general receiver only has a sensitivity of -130dBm. So improving the sensitivity of GPS receiver becomes the problem that should be addressed.Signal acquisition and tracking is critical for a GPS receiver to function in perturbed signal environments. The design of weak signals acquisition and tracking algorithm has become the key to achieve high sensitivity. GPS signal simulator which can be used to simulate GPS signal and interference, is the foundation of algorithm verification. Above all, this thesis includes three parts.1. GPS IF signal simulator design. Based on the analyzing of GPS signal and errors, the GPS L1 carrier interfered by multipath effects and white noise are simulated based on mathematical models. A user interface is designed for GPS IF signal simulator.2. Weak signal acquisition. In order to enhance the acquisition sensitivity, firstly, the coherent-noncoherent integration was adopted to eliminate the restrictions on coherent integration gain. Secondly, the differential coherent integration, which allows a 1.5 dB SNR improvement in processing loss as compared to noncoherent methods, is proposed. At last, the FFT based code and carrier acquisition algorithm is implemented to improve the acquisition speed and accuracy instead of the traditional method.3. Weak GPS signal tracking. Traditional non-linear PLL is vulnerable to noise interference. In this thesis, the simplified adaptive kalman, EKF based weak signal carrier phase tracking loop are proposed. The tracking loop model has been simplified and optimized by covariance medication and adaptive algorithm.The simulation shows that:The characteristics of simulation signals are consistent with the real one. The noncoherent integration, differential integration acquisition algorithm can acquire the weak signal at the CNR of 25dB/Hz with the frequency, code accuracy of 2.5Hz and 0.2 code. Kalman, EKF tracking algorithm can effectively track weak signal at the CNR of26,24dB/Hz.