I. Introduction
One of the critical aspects of precise GNSS positioning is the determination of integer carrier phase cycle ambiguities. The carrier phase is the most precise measurement available, but only a fractional part of the phase can be measured. Without determination of the correct integer ambiguity parameters, precise positioning at the centimeter level is difficult to achieve. Since carrier phase ambiguities are integer values of whole cycles, only a specific set of integer values can satisfy certain geometrical constraints. Since a phase measurement is affected by many types of errors, it is not possible to separate these errors and determine the correct ambiguity for a single measurement. However, some GNSS errors are common to groups of GNSS observations [1].