GPS-BASED NAVIGATION SYSTEM A NONLINEAR DISCRETE-TIME TRACKING FILTER

摘要

A navigation system that utilizes a discrete-time nonlinear filter to obtain a navigation solution using GPS signals and optional aiding sensor data is described. A nonlinear filter offers improved accuracy over linearized filters at low signal to noise ratios. A discrete-time nonlinear filter guarantees positive-definite calculated covariance matrices under all conditions without requiring any compensation or added parameters. The navigation system receives a modernized global navigation satellite system (GNSS) signal and correlates a digitized copy of the GNSS signal to generate ranging code measurements. A conditional probability density function for the code measurements is determined and used to calculate arbitrary moments of code delay and other expected values. The code measurements and the conditional probability density function are processed in a nonlinear tracking filter to generate recursive navigation state updates, which can be used by an output device, such as a display, to present navigation and tracking information.