The Research Of Acquisition And Tracking Algorithm For Weak GPS Signal

In recent years, the use of GPS receiver is becoming widely. However, the generalGPS receiver suffers from limitations in acquisition and tracking GPS signals in the indooror high buildings environments. In these perturbed environments, the signal is becomingvery weak because of occlusion or reflection, and the carrier to noise ratio of signal isalways less than36dB-Hz. Signal acquisition and tracking is critical for a GPS receiver tofunction in weak signal environments. The design of weak signals acquisition and trackingalgorithm has become the key to achieve high sensitivity.The focus of this paper is the research of acquisition and tracking algorithm for weakGPS signal. This thesis also simulates GPS IF signal to generate the foundation ofalgorithm verification. The main contents include the following:1) Based on the analysis of GPS signal characteristics and its mathematical models,the thesis simulates GPS IF signal with Simulink of MATLAB. The simulated signal’sparameters are adjustable. The purpose of signal simulation is to provide GPS IF datasource with controllable properties for subsequent algorithm research.2) On the weak signal acquisition algorithm side, the paper introduces coherent,incoherent and differential coherent integration methods and points out their strengths andweaknesses. Based on this, the batch algorithm can avoid the impact of data bit transitionsthrough increasing the numbers of summation. However, as the numbers of summationincreasing, computational complexity will also increase. The adjacent results comparisonmethod proposed by this thesis can reduce computation effectively and improve thecapture speed. The simulation shows that the improved algorithm has obvious advantageno matter in speed or effect and it can acquire the weak signal at the C/N0of23dB-Hz.3) On the weak signal tracking algorithm side, it introduces the principle ofphase-lock loop, code tracking loop and carrier tracking loop. The traditional methodalways has the loss of lock phenomenon when in the tracking of weak signals the C/N0isextremely low. To improve GPS receiver tracking performance, this article uses theimproved adaptive Kalman filter instead of the phase-locked loop and establishes atracking system of the state equation and measurement equation. The simulation showsthat the improved algorithm can track the weak signal at the C/N0of25dB-Hz.