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    Assessing the performance of BDS-3 for multi-GNSS static and kinematic PPP-AR
    (Elsevier, 2023) Öğütçü, Salih Sermet; Alçay, Salih; Özdemir, Behlül Numan; Li, Pan; Zhang, Yize; Konukseven, Ceren; Atiz, Ömer Faruk
    As of 2021, a total of four different GNSS constellations - namely, GPS, GLONASS, Galileo, and BDS-3 - can be used with Full Operational Capability (FOC). In this work, the contribution of BDS-3 FOC to GPS + GLONASS + Galileo (GRE) PPP-AR is inves-tigated, considering the three different cut-off angles (7 degrees, 30 degrees, and 45 degrees) and different lengths of static observation sessions (24-, 12-, 6-, 3-, 1-, 0.5-, 0.25-hour). The data of 31 IGS-MGEX stations is processed with GRE PPP-AR and GREC3 (GPS + GLONASS (using float mode) + Galileo + BDS-3) PPP-AR modes. The results showed that BDS-3 degraded the horizontal (except for 24-h sessions) and ver-tical accuracy of static GRE PPP-AR solutions regardless of the elevation cutoff angle and observation time. The kinematic results showed that BDS-3 significantly contributed to the accuracy of GRE kinematic PPP-AR for 30 degrees and 45 degrees cutoff angles. The convergence time analysis showed that BDS-3 only contributes to GRE kinematic PPP-AR for the vertical component.(c) 2022 COSPAR. Published by Elsevier B.V. All rights reserved.
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    Performance investigation of LAMBDA and bootstrapping methods for PPP narrow-lane ambiguity resolution
    (Taylor & Francis Ltd, 2021) Atiz, Omer Faruk; Ogutcu, Sermet; Alcay, Salih; Li, Pan; Bugdayci, Ilkay
    Precise point positioning with ambiguity resolution (PPP-AR) is a powerful tool for geodetic and time-constrained applications that require high precision. The performance of PPP-AR highly depends on the reliability of the correct integer carrier-phase ambiguity estimation. In this study, the performance of narrow-lane ambiguity resolution of PPP using the Least-squares AMBiguity Decorrelation (LAMBDA) and bootstrapping methods is extensively investigated using real data from 55 IGS stations over one-month in 2020. Static PPP with 24-, 12-, 8-, 4-, 2-, 1- and 1/2-h sessions using two different cutoff angles (7 degrees and 30 degrees) was conducted with three PPP modes: i.e. ambiguity-float and two kinds of ambiguity-fixed PPP using the LAMBDA and bootstrapping methods for narrow-lane AR, respectively. The results show that the LAMBDA method can produce more reliable results for 2 hour and shorter observation sessions compared with the bootstrapping method using a 7 degrees cutoff angle. For a 30 degrees cutoff angle, the LAMBDA method outperforms the bootstrapping method for observation sessions of 4 h and less. For long observation times, the bootstrapping method produced much more accurate coordinates compared with the LAMBDA method without considering the wrong fixes cases. The results also show that occurrences of fixing the wrong integer ambiguities using the bootstrapping method are higher than that of the LAMBDA method.