I Introduction

The previous chapters described the hardware and software needed to make GPS observations in the receiver. This chapter focuses on how these observations are processed to form a navigation solution. Fundamentally, a navigation solution is an estimate of the user position plus any other required parameters. The term "state" is used to describe all the parameters to be determined. The typical states in a GPS navigation estimator are three components of position, clock offset, and clock drift. In a moving application, three components of velocity are added. There are many applications described in the companion volume in which GPS is integrated with one or more other sensors, such as an altimeter or an inertial navigation system (INS). In such configurations, the state may be expanded to include specific sensor error states; however, in this chapter, we restrict ourselves to stand-alone GPS navigation estimation.

A navigation algorithm embedded in the GPS receiver combines raw measurements from the signal processor with GPS satellite orbit data to estimate the observer state. This process requires two sets of models a measurement model and a dynamics or process model. The dynamics model describes the evolution of the system state. The measurement model relates the state to the GPS observations.

Section II describes the GPS measurements and Sec. III shows how they may be...