Geometry extra-redundant almost fixed solutions: A high integrity approach for carrier phase ambiguity resolution for high accuracy relative navigation

Carrier phase (CP) real time kinematic (RTK) GPS techniques have become widely used in high accuracy relative positioning applications. CP RTK can achieve centimeter-level accuracy by resolving the integer carrier phase cycle ambiguities, creating extremely precise ranging measurements. However, in applications that require high integrity in addition to high accuracy, proving the probability of correct fix (PCF) of the CP ambiguities can be an impediment to the relative positioning system achieving high service availability. In this paper a new algorithmic approach, called geometry extra-redundant almost fixed solution (GERAFS), for high accuracy and high integrity commercial or military GPS relative navigation applications is described. The GERAFS technique relies on the fact that occasional incorrect CP ambiguity fixes can still be acceptable from accuracy and integrity perspectives. A method for quantifying the integrity protection levels associated with these so-called ldquoalmost fixed solutionsrdquo is developed. The centimeter level positioning accuracy with high integrity achieved with GERAFS is demonstrated with simulated and recorded test range GPS sensor data.