GPS/BDS/Galileo precise orbit determination using triple-frequency uncombined observation model

The navigation satellite of the four global navigation satellite system (GNSS) transmitting multi-frequency signals becomes a prevailing trend. In this contribution, a triple-frequency (TF) uncombined (UC) precise orbit determination (POD) method based on IGS clock datum is developed and its ambiguity resolution strategy is proposed. The hardware delay of carrier phase is divided by time-invariant and variant components. Then the UC observation model is given by re-parameterizing the unknown parameters. The step-by-step ambiguity fixing method, i.e. the extra-wide-lane, wide-lane and narrow-lane ambiguities fixed in sequence, is deduced by using double-differenced ambiguities in a network. With the GPS IIF, BDS-2 and Galileo being able to transmit triple-frequency signals, the four POD tests are conducted: ionospheric-free (IF) POD of frequency 1/2, IF POD of frequency 1/3, UC POD of frequency 1/2, UC POD of TF signals. The three metrics of external orbit product, day boundary discontinuities and satellite laser ranging are used to validate the POD product accuracy. Results show that a subtle improvement are received with the addition of the third frequency observations. However, the improvement of GPS TF POD results with respect to L1/L2 POD is about 10%, which may be the signal power of L5 is stronger than that of L2. © 2021, Surveying and Mapping Press. All right reserved.