Will PPP ever replace RTK? Over the past decade, we have seen the convergence of PPP and RTK towards “PPP-RTK,” where satellite orbit/clock/bias corrections are augmented by local atmospheric corrections to enable instantaneous convergence to cm-level accuracies. But how close are we to instantaneous cm-level PPP-AR, without local augmentation?
When I first got involved in GNSS, more than a decade ago, my objective was to reduce the convergence time of PPP solutions. In the past few years, I witnessed this methodology evolve and fast convergence became possible using ambiguity resolution and external atmospheric data. The upcoming years will be a game changer in this area: with GNSS modernization, instantaneous PPP convergence will be possible even without any reference stations nearby.
Back in April, I discussed how applying L5 phase-bias corrections allowed for triple-frequency ambiguity resolution in PPP solutions. I demonstrated how the third frequency could potentially improve convergence times, but did not put too much focus on the estimated L5 biases. In this post, we examine the intra-day time variation of the L5 biases for the 12 block IIF satellites in orbit.
The L5 signals transmitted by the block IIF GPS satellites caught the IGS by surprise. The time-varying inter-frequency phase bias that exists between L1/L2 and L5, also called “line bias”, is significant enough that it requires dissemination to users. Besides the lack of an adequate format, I believe that this initiative has been delayed because the benefits of a third frequency on float PPP are not substantial. To realize the benefits of L5, the IGS needs to embrace PPP-AR!