Real-Time Centimeter-Accuracy GPS: Initializing While in Motion (Warm Start Versus Cold START)

Abstract

The initialization of real-time centimeter-accuracy GPS (i.e., based on carrier phases) can be performed while in motion. Although included results are postprocessed, the algorithms are currently being implemented for real-time navigation, and the results will be essentially the same. The goal of the initialization procedure is to determine the double-difference carrier phase integer ambiguities. This paper reports the benefit to the initialization procedure of additional knowledge or constraints. As an example, it shows the speedup (meaning fewer epochs, not computational speed) of the initialization procedure and increased reliability using a priori knowledge of the average ellipsoidal height of the antenna phase center on a marine platform. As another example, it shows the benefit of prior knowledge of one or two double-difference integer biases, either alone or coupled with a priori knowledge of the ellipsoidal height of the antenna phase center.