Banville, S., Collins, P., Zhang, W., & Langley, R. B. (2014). Global and Regional Ionospheric Corrections for Faster PPP Convergence. *Navigation,* *61*, 115–124. https://doi.org/10.1002/navi.57

Article
Google Scholar

Belehaki, A., Tsagouri, I., Altadill, D., Blanch, E., Borries, C., Buresova, D., Chum, J., Galkin, I., Juan, J. M., Segarra, A., Timoté, C. C., Tziotziou, K., Verhulst, T. G. W., & Watermann, J. (2020). An overview of methodologies for real-time detection, characterisation and tracking of traveling ionospheric disturbances developed in the TechTIDE project. *Journal Space Weather Space Climate,* *10*, 42.

Article
Google Scholar

Boehm, J., Niell, A., Tregoning, P., & Schuh, H. (2006). Global mapping function (GMF): A new empirical mapping function based on numerical weather model data. *Geophysical Research Letters*. https://doi.org/10.1029/2005GL025546

Article
Google Scholar

Ciraolo, L., Azpilicueta, F., Brunini, C., Meza, A., & Radicella, S. M. (2007). Calibration errors on experimental slant total electron content (TEC) determined with GPS. *Journal of Geodesy,* *81*, 111–120. https://doi.org/10.1007/s00190-006-0093-1

Article
Google Scholar

Collins, P., Lahaye, F., Héroux, P., & Bisnath, S. (2008). Precise point positioning with ambiguity resolution using the decoupled clock model. 21st International Technical Meeting of the Satellite Division of the Institute of Navigation, ION GNSS 2008*,* 3, 1549–1556.

De Oliveira, P. S., Morel, L., Fund, F., Legros, R., Monico, J. F. G., Durand, S., & Durand, F. (2017). Modeling tropospheric wet delays with dense and sparse network configurations for PPP–RTK. *GPS Solutions,* *21*, 237–250. https://doi.org/10.1007/s10291-016-0518-0

Article
Google Scholar

Wen,D., Zhang, X.,Tong,Y., Zhang,G.,Zhang, M.,&Leng,R.(2015). GPS-based ionospheric tomography with a constrained adaptive simultaneous algebraic reconstruction technique. Journal of earth system science, 124(2), 283-289.https://doi.org/10.1007/s12040-015-0542-4

Article
Google Scholar

Ge, M., Gendt, G., Rothacher, M., Shi, C., & Liu, J. (2008). Resolution of GPS carrier-phase ambiguities in Precise Point Positioning (PPP) with daily observations. *Journal of Geodesy,* *82*, 389–399. https://doi.org/10.1007/s00190-007-0187-4

Article
Google Scholar

Geng, J., & Shi, C. (2017). Rapid initialization of real-time PPP by resolving undifferenced GPS and GLONASS ambiguities simultaneously. *Journal of Geodesy,* *91*, 361–374. https://doi.org/10.1007/s00190-016-0969-7

Article
Google Scholar

Geng, J., Li, X., Zhao, Q., et al. (2019). Inter-system PPP ambiguity resolution between GPS and BeiDou for rapid initialization. *Journal of Geodesy,* *93*(3), 383–398.

Article
Google Scholar

Geng, J., Meng, X., Dodson, A., et al. (2010). Rapid re-convergences to ambiguity-fixed solutions in precise point positioning. *Journal of Geodesy,* *84*, 705–714. https://doi.org/10.1007/s00190-010-0404-4

Article
Google Scholar

Guo, F., Li, X., Zhang, X., & Wang, J. (2017). The contribution of Multi-GNSS Experiment (MGEX) to precise point positioning. *Advances in Space Research,* *59*, 2714–2725. https://doi.org/10.1016/j.asr.2016.05.018

Article
Google Scholar

Haines, G. V. (1988). Computer programs for spherical cap harmonic analysis of potential and general fields. *Computers & Geosciences,* *14*, 413–447. https://doi.org/10.1016/0098-3004(88)90027-1

Article
Google Scholar

Hernández-Pajares, M., Juan, J. M., & Sanz, J. (1999). New approaches in global ionospheric determination using ground GPS data. *Journal of Atmospheric and Solar-Terrestrial Physics,* *61*, 1237–1247. https://doi.org/10.1016/S1364-6826(99)00054-1

Article
Google Scholar

Hernández-Pajares, M., Juan, J. M., & Sanz, J. (2006). Medium-scale traveling ionospheric disturbances affecting GPS measurements: Spatial and temporal analysis. *Journal of Geophysical Research: Space Physics*. https://doi.org/10.1029/2005JA011474

Article
Google Scholar

Hernández-Pajares, M., Juan, J. M., Sanz, J., & Aragón-Àngel, A. (2012). Propagation of medium scale traveling ionospheric disturbances at different latitudes and solar cycle conditions. *Radio Science,* *47*, 1–22. https://doi.org/10.1029/2011RS004951

Article
Google Scholar

Hernández-Pajares, M., Juan, J. M., Sanz, J., Aragón-Àngel, À., García-Rigo, A., Salazar, D., & Escudero, M. (2011). The ionosphere: Effects, GPS modeling and the benefits for space geodetic techniques. *Journal of Geodesy,* *85*, 887–907. https://doi.org/10.1007/s00190-011-0508-5

Article
Google Scholar

Hu, J., Zhang, X., Li, P., Ma, F., & Pan, L. (2019). Multi-GNSS fractional cycle bias products generation for GNSS ambiguity-fixed PPP at Wuhan University. *GPS Solutions,* *24*, 15. https://doi.org/10.1007/s10291-019-0929-9

Article
Google Scholar

Jakowski, N., Mayer, C., Wilken, V., & Hoque, M. M. (2008). Ionospheric impact on GNSS signals. *Física De La Tierra,* *20*, 11.

Google Scholar

Laurichesse, D., Mercier, F., Berthias, J. P., Broca, P., & Cerri, L. (2009). Integer ambiguity resolution on undifferenced GPS phase measurements and its application to PPP and satellite precise orbit determination. *Navigation,* *56*, 135–149.

Article
Google Scholar

Li, P., Zhang, X., Ren, X., Zuo, X., & Pan, Y. (2016). Generating GPS satellite fractional cycle bias for ambiguity-fixed precise point positioning. *GPS Solutions,* *20*, 771–782. https://doi.org/10.1007/s10291-015-0483-z

Article
Google Scholar

Li, X., Ge, M., Dai, X., Ren, X., Fritsche, M., Wickert, J., & Schuh, H. (2015a). Accuracy and reliability of multi-GNSS real-time precise positioning: GPS, GLONASS, BeiDou, and Galileo. *Journal of Geodesy,* *89*, 607–635. https://doi.org/10.1007/s00190-015-0802-8

Article
Google Scholar

Li, X., Li, X., Liu, G., Feng, G., Yuan, Y., Zhang, K., & Ren, X. (2019a). Triple-frequency PPP ambiguity resolution with multi-constellation GNSS: BDS and Galileo. *Journal of Geodesy,* *93*, 1105–1122. https://doi.org/10.1007/s00190-019-01229-x

Article
Google Scholar

Li, X., Li, X., Ma, F., Yuan, Y., Zhang, K., Zhou, F., & Zhang, X. (2019b). Improved PPP Ambiguity Resolution with the Assistance of Multiple LEO Constellations and Signals. *Remote Sensing,* *11*, 408.

Article
Google Scholar

Li, X., Ma, F., Li, X., Lv, H., Bian, L., Jiang, Z., & Zhang, X. (2019c). LEO constellation-augmented multi-GNSS for rapid PPP convergence. *Journal of Geodesy,* *93*, 749–764. https://doi.org/10.1007/s00190-018-1195-2

Article
Google Scholar

Li, X., & Zhang, X. (2012). Improving the estimation of uncalibrated fractional phase offsets for PPP ambiguity resolution. *Journal of Navigation,* *65*, 513–529. https://doi.org/10.1017/S0373463312000112

Article
Google Scholar

Li, X., Zhang, X., & Ge, M. (2011). Regional reference network augmented precise point positioning for instantaneous ambiguity resolution. *Journal of Geodesy,* *2011*(85), 151–158. https://doi.org/10.1007/s00190-010-0424-0

Article
Google Scholar

Li, Z., Yuan, Y., Wang, N., Hernandez-Pajares, M., & Huo, X. (2015b). SHPTS: Towards a new method for generating precise global ionospheric TEC map based on spherical harmonic and generalized trigonometric series functions. *Journal of Geodesy,* *89*, 331–345. https://doi.org/10.1007/s00190-014-0778-9

Article
Google Scholar

Liu, Y., Lou, Y., Ye, S., Zhang, R., Song, W., Zhang, X., & Li, Q. (2017). Assessment of PPP integer ambiguity resolution using GPS, GLONASS and BeiDou (IGSO, MEO) constellations. *GPS Solutions,* *21*, 1647–1659. https://doi.org/10.1007/s10291-017-0641-6

Article
Google Scholar

Lou, Y., Zheng, F., Gu, S., Wang, C., Guo, H., & Feng, Y. (2016). Multi-GNSS precise point positioning with raw single-frequency and dual-frequency measurement models. *GPS Solutions,* *20*, 849–862. https://doi.org/10.1007/s10291-015-0495-8

Article
Google Scholar

Mautz, R., Ping, J., Heki, K., Schaffrin, B., Shum, C., & Potts, L. (2005). Efficient spatial and temporal representations of global ionosphere maps over Japan using B-spline wavelets. *Journal of Geodesy,* *78*, 662–667. https://doi.org/10.1007/s00190-004-0432-z

Article
Google Scholar

Odijk, D. (2002). *Fast precise GPS positioning in the presence of ionospheric delays*. Delft University of Technology.

Google Scholar

Odijk, D., Zhang, B., Khodabandeh, A., Odolinski, R., & Teunissen, P. J. G. (2016). On the estimability of parameters in undifferenced, uncombined GNSS network and PPP–RTK user models by means of S-system theory. *Journal of Geodesy,* *90*, 15–44. https://doi.org/10.1007/s00190-015-0854-9

Article
Google Scholar

Olivares-Pulido, G., Terkildsen, M., Arsov, K., Teunissen, P. J. G., Khodabandeh, A., & Janssen, V. (2019). A 4D tomographic ionospheric model to support PPP–RTK. *Journal of Geodesy,* *93*, 1673–1683. https://doi.org/10.1007/s00190-019-01276-4

Article
Google Scholar

Psychas, D., Verhagen, S., Liu, X., Memarzadeh, Y., & Visser, H. (2018). Assessment of ionospheric corrections for PPP–RTK using regional ionosphere modelling. *Measurement Science and Technology,* *30*, 014001. https://doi.org/10.1088/1361-6501/aaefe5

Article
Google Scholar

Ren, X., Chen, J., Li, X., & Zhang, X. (2020). Ionospheric total electron content estimation using GNSS carrier phase observations based on zero-difference integer ambiguity: methodology and assessment. *IEEE Transactions on Geoscience and Remote Sensing*. https://doi.org/10.1109/TGRS.2020.2989131

Article
Google Scholar

Saastamoinen, J. (1972). Contributions to the theory of atmospheric refraction. *Bulletin Géodésique,* *1946–1975*(105), 279–298. https://doi.org/10.1007/bf02521844

Article
Google Scholar

Saito, A., Fukao, S., & Miyazaki, S. (1998). High resolution mapping of TEC perturbations with the GSI GPS Network over Japan. *Geophysical Research Letters,* *25*, 3079–3082. https://doi.org/10.1029/98GL52361

Article
Google Scholar

Schaer S. (1999). Mapping and predicting the Earth's ionosphere using the Global Positioning System*.* Unpublished Ph.D Thesis, University of Bern, Bern.

Schmidt, M., Bilitza, D., Shum, C. K., & Zeilhofer, C. (2008). Regional 4-D modeling of the ionospheric electron density. *Advances in Space Research,* *42*, 782–790. https://doi.org/10.1016/j.asr.2007.02.050

Article
Google Scholar

Teunissen, P., Odijk, D., & Zhang, B. (2010). PPP–RTK: results of CORS network-based PPP with integer ambiguity resolution. *Journal of Aeronautics, Astronautics and Aviation, Series A,* *42*, 223–229.

Google Scholar

Teunissen, P. J. G. (1995). The least-squares ambiguity decorrelation adjustment: A method for fast GPS integer ambiguity estimation. *Journal of Geodesy,* *70*, 65–82. https://doi.org/10.1007/BF00863419

Article
Google Scholar

Tsugawa, T., Kotake, N., Otsuka, Y., & Saito, A. (2007). Medium-scale traveling ionospheric disturbances observed by GPS receiver network in Japan: A short review. *GPS Solutions,* *11*, 139–144. https://doi.org/10.1007/s10291-006-0045-5

Article
Google Scholar

Tsugawa, T., Saito, A., & Otsuka, Y. (2004). A statistical study of large-scale traveling ionospheric disturbances using the GPS network in Japan. *Journal of Geophysical Research: Space Physics*. https://doi.org/10.1029/2003ja010302

Article
Google Scholar

Wang, K., Khodabandeh, A., & Teunissen, P. (2017). A study on predicting network corrections in PPP–RTK processing. *Advances in Space Research,* *60*, 1463–1477. https://doi.org/10.1016/j.asr.2017.06.043

Article
Google Scholar

Wen, D., Yuan, Y., Ou, J., Huo, X., & Zhang, K. (2007). Three-dimensional ionospheric tomography by an improved algebraic reconstruction technique. *GPS Solutions,* *11*, 251–258. https://doi.org/10.1007/s10291-007-0055-y

Article
Google Scholar

Wen, D., Yuan, Y., Ou, J., Zhang, K., & Liu, K. (2008). A hybrid reconstruction algorithm for 3-D ionospheric tomography. *IEEE Transactions on Geoscience and Remote Sensing,* *46*, 1733–1739. https://doi.org/10.1109/TGRS.2008.916466

Article
Google Scholar

Wübbena, G., Schmitz, M., Bagge, A. (2005). PPP–RTK: precise point positioning using state-space representation in RTK networks. In *Proceedings of ION GNSS*, pp. 13–16.

Xiang, Y., Gao, Y., & Li, Y. (2020). Reducing convergence time of precise point positioning with ionospheric constraints and receiver differential code bias modeling. *Journal of Geodesy*. https://doi.org/10.1007/s00190-019-01334-x

Article
Google Scholar

Zha, J., Zhang, B., Liu, T., & Hou, P. (2021). Ionosphere-weighted undifferenced and uncombined PPP–RTK: Theoretical models and experimental results. *GPS Solution*. https://doi.org/10.1007/s10291-021-01169-0

Article
Google Scholar

Zhang, B., Ou, J., Yuan, Y., & Li, Z. (2012). Extraction of line-of-sight ionospheric observables from GPS data using precise point positioning. *Science China Earth Sciences,* *55*, 1919–1928. https://doi.org/10.1007/s11430-012-4454-8

Article
Google Scholar

Zhang, B., Teunissen, P. J. G., & Odijk, D. (2011). A Novel Un-differenced PPP–RTK Concept. *Journal of Navigation,* *64*, S180–S191. https://doi.org/10.1017/s0373463311000361

Article
Google Scholar

Zhang, B., Chen, Y., & Yuan, Y. (2018). PPP–RTK based on undifferenced and uncombined observations: Theoretical and practical aspects. *Journal of Geodesy,* *93*(7), 1–14.

Google Scholar

Zhang, B., Hou, P., Zha, J., & Liu, T. (2021). Integer-estimable FDMA model as an enabler of GLONASS PPP–RTK. *Journal of Geodesy,* *95*, 91. https://doi.org/10.1007/s00190-021-01546-0

Article
Google Scholar

Zheng, D., Yao, Y., Nie, W., Chu, N., Lin, D., & Ao, M. (2020). A new three-dimensional computerized ionospheric tomography model based on a neural network. *GPS Solutions,* *25*, 10. https://doi.org/10.1007/s10291-020-01047-1

Article
Google Scholar

Zheng, D., Yao, Y., Nie, W., Liao, M., Liang, J., & Ao, M. (2021). Ordered Subsets-Constrained ART Algorithm for Ionospheric Tomography by Combining VTEC Data. *IEEE Transactions on Geoscience and Remote Sensing,* *59*, 7051–7061. https://doi.org/10.1109/TGRS.2020.3029819

Article
Google Scholar

Zheng, D., Zheng, H., Wang, Y., Nie, W., Li, C., Ao, M., Hu, W., & Zhou, W. (2017). Variable pixel size ionospheric tomography. *Advances in Space Research,* *59*, 2969–2986. https://doi.org/10.1016/j.asr.2017.03.031

Article
Google Scholar

Zheng, D. Y., Yao, Y. B., Nie, W. F., Yang, W. T., Hu, W. S., Ao, M. S., & Zheng, H. W. (2018). an improved iterative algorithm for ionospheric tomography reconstruction by using the automatic search technology of relaxation factor. *Radio Science,* *53*, 1051–1066. https://doi.org/10.1029/2018rs006588

Article
Google Scholar