Abstract
The poor signal visibility and continuity associated with urban environments together with the slow convergence/reconvergence time of Precise Point Positioning (PPP), usually makes PPP unsuitable for land navigation in cities. However, results based on simulated open areas demonstrated that, once Galileo reaches final operational capability, PPP convergence time will be cut in a half using dual-constellation GPS/Galileo observations. Therefore, it might be possible to extend the applicability of PPP to land navigation in certain urban areas. Preliminary results, based on simulations, showed that GPS/Galileo PPP is possible where buildings are relatively short and satellites minimum visibility requirement is met for most of the time. In urban environments, signal discontinuity and reconvergence still represent the major problem for traditional PPP, which is based on the ionosphere-free combination of two-frequency pseudo-range and carrier phase. An alternative method to mitigate the ionosphere delay is proposed in order to ensure the best positioning performance from multi-frequency PPP. Instead of using the ionosphere-free combination, here low noise dual-or triple-frequency pseudo-range combinations are corrected with ionosphere delay information coming from federated carrier smoothing (Hatch) iono-estimation filters for each satellite. This method provides faster re-convergence time and ensures the best possible positioning performance from the Galileo Alternative BOC modulation in multi-frequency PPP. Indeed, even though Galileo E5 has small tracking noise and excellent multipath rejection, its PPP positioning performance is limited by the influence of E1 signal errors in the ionosphere-free combination, degrading the quality of the measurements.
Highlights
Precise Point Positioning (PPP) [1] is a carrier phase based positioning technique that enables centimeter-level to decimeter-level accuracy, with no need for local reference stations as requiredThis project was sponsored through a studentship agreement between the University of Nottingham and Rockwell Collins UK Limited.with Real Time Kinematic (RTK) techniques
The results presented in [9] proved that the convergence time in PPP would be shorter if the noise on pseudo-ranges could be reduced
Results based on simulated open sky condition demonstrated that Galileo performs better than GPS thanks to an assumed lower E1-E5a ionosphere free (IF) noise with respect to L1-L5
Summary
Precise Point Positioning (PPP) [1] is a carrier phase based positioning technique that enables centimeter-level (static processing) to decimeter-level (kinematic processing) accuracy, with no need for local reference stations as required. For very dense urban canyons multiconstellation GNSS fails to meet the minimum requirements for positioning, most of the time, even considering three systems together [3] Analysis using both simulated [5, 6] and real data [7, 8] showed that, once Galileo reaches final operational status, the PPP convergence time will be cut by more than a half when using both GPS and Galileo observations.
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