Computer-implemented methods and apparatus are presented for processing data collected by at least two receivers from multiple satellites of multiple Global Navigation Satellite Systems (GNSS), where at least one GNSS is Frequency Division Multiple Access (FDMA). Data sets are obtained which comprise a first data set from a first receiver and a second data set from a second receiver. The first data set comprises a first FDMA data set and the second data set comprises a second FDMA data set. At least one of a code bias and a phase bias may exist between the first FDMA data set and the second FDMA data set. At least one receiver-type bias is determined, to be applied when the data sets are obtained from receivers of different types. The data sets are processed, based on the at least one receiver-type bias, to estimate carrier floating-point ambiguities. Carrier integer ambiguities are determined from the floating-point ambiguities. The scheme enables Globalnaya Navigatsionnaya Sputnikovaya Sistema (GLONASS) carrier phase ambiguities to be resolved and used in a combined FDMA/Code Division Multiple Access (CDMA)(e.g., GLONASS/Global Positioning System (GPS) centimeter-level solution. It is applicable to real-time kinematic (RTK) positioning, high-precision post-processing of positions and network RTK positioning.