【2024】Assessing all-frequency GPS/Galileo/BDS PPP-RTK in GNSS challenging environments.
时间：2024-08-06
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PPP-RTK (network-based real-time kinematic precise point positioning) can achieve instantaneous centimeter-level positioning using only a single GNSS receiver under the premise of precise satellite orbits, satellite clocks, satellite code/phase biases, and atmospheric corrections. It is usually reported that PPP-RTK needs two or more frequencies of measurements as the phase biases are conventionally defined in terms of wide-lane and narrow-lane combinations. Although single-frequency PPP-RTK has been proven achievable, the signals demonstrated in most open studies are usually limited to specific frequencies such as GPS L1 or similar. However, in GNSS challenging environments, satellite signal losses can repeatedly take place on any frequency, which is likely to disable conventional PPP-RTK algorithms prescribing particular signal frequencies. Therefore, we apply the observable-specific code and phase bias (OSB) concept to PPP-RTK and investigate whether the integer properties of PPP ambiguities on any frequency or frequency combination can be fully recovered after such OSB corrections, i.e., all-frequency PPP-RTK, to address the satellite signal loss problem in GNSS adverse environments. In particular, all-frequency PPP-RTK is able to process any number, any choice, or any combination of GNSS signal frequencies rather than the prescribed frequencies. We carried out both static and vehicle-born experiments using a regional GPS/Galileo/BDS network over seven days. In the static experiment, six signal clusters across the three constellations (i.e., L1/E1/B1C, L5/E5a/B2a, E5b/B2I/B2b, B1I, B3I, and L2/E6) were tried to perform single-frequency single-epoch PPP-RTK. Each cluster of signals (except L2/E6) shares the same frequency (i.e., overlap frequency among constellations). We found that the average ambiguity fixing rate was 95.8% and the mean positioning precisions were 1.9, 1.6, and 5.4 cm in the east, north, and up components, respectively, in terms of RMS errors. In the vehicle-borne experiment, the ambiguity fixing rate at GNSS challenging epochs was improved by 15 percentage points and the horizontal positioning errors were reduced by over 30% when switching from conventional to all-frequency PPP-RTK.
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