GPS World, March 2018

FIGURE 4 Average dual and triple frequency static float PPP horizontal solution accuracy for 20 global stations Data collected from tracked GPS GLONASS Galileo and BeiDou satellites in early 2016 FIGURE 3 Typical conventional multi GNSS PPP float horizontal positioning accuracy for station GMSD Nakatane Japan March 24 2017 G GPS R GLONASS E Galileo and C BeiDou FIGURE 3 shows typical multi GNSS float non ambiguityfixed horizontal positioning performance at multi GNSS station GMSD in Nakatane Japan on March 24 2017 As with all modes of GNSS data processing more significant improvement with additional constellations can be seen in sky obstructed situations Related to multi constellation processing is triplefrequency processing afforded by the latest generation of GPS satellites and the Galileo and BeiDou constellations More frequencies mean more measurements although with the same satellite to receiver measurement geometry as dualfrequency measurements Again additional signals require additional equipment delay modeling in this case especially for the processing of GPS L1 L2 and L5 observables For processing of four constellation data available from 20 global stations in early 2016 FIGURE 4 shows the average reduction of float non ambiguity fixed horizontal error from dual to triple frequency processing of approximately 40 after the first five minutes of measurement processing 44 GPS WORLD WWW GPSWORLD COM MARCH 2018 In terms of positioning this result for this time period with a limited number of triple frequency measurements means a reduction in average horizontal positioning error from 43 to 26 centimeters within the first five minutes of data collection PPP with ambiguity resolution or PPP AR was seen as a potential solution to the PPP initial solution convergence problem analogous to AR in RTK Various researchers put forward methods in the form of expanded measurement models to isolate pseudorange and carrier phase equipment delays to estimate carrier phase ambiguities These methods remove receiver equipment delays through implicit or explicit between satellite single differencing and estimate satellite equipment delays in the network product solution either as fractional cycle phase biases or altered clock products FIGURE 5 illustrates the difference between a typical GPS float and fixed solution for station CEDU Ceduna Australia on June 28 2017 Initial solution convergence time is reduced and stable few centimeter level solutions are reached sooner FIGURE 5 Typical float red and fixed pink GPS PPP horizontal solution error at geodetic station CEDU Ceduna Australia on June 28 2017 FIGURE 6 Averaged horizontal error from 70 global sites in mid 2016 using fourconstellation triple frequency processing