Combined decoupled clock and integer‑estimable models applied to CDMA + FDMA single-difference network RTK

• Published in: GPS solutions Vol. 28; no. 4; p. 180
• Main Authors: Pu, Yakun, Zha, Jiuping, Su, Yong, Zhang, Xiao, Zhao, Chuanbao, Zhang, Baocheng
• Format: Journal Article
• Language: English
• Published: Berlin/Heidelberg Springer Berlin Heidelberg 01.10.2024; Springer Nature B.V
• Subjects: Ambiguity resolution (mathematics); Atmospheric Sciences; Automotive Engineering; Bias; Code Division Multiple Access; Earth and Environmental Science; Earth Sciences; Electrical Engineering; Frequency division multiple access; Geophysics/Geodesy; Global positioning systems; GLONASS; GPS; Hardware; Integers; Ionosphere; Kinematics; Original Article; Real time; Space Exploration and Astronautics; Space Sciences (including Extraterrestrial Physics; White noise; Network real-time kinematic (NRTK); Common-clock model (CC); Frequency-division multiple access (FDMA); Ambiguity resolution (AR); Decoupled-clock model (DC); Global navigation satellite systems (GNSS); Integer-estimability (IE)
• ISSN: 1080-5370; 1521-1886
• DOI: 10.1007/s10291-024-01726-3

Accurate estimation of atmospheric delays and reliable ambiguity resolution (AR) are major challenges in implementing network real-time kinematic (NRTK) positioning technology. Previous studies on NRTK positioning have focused on using a double-differenced (DD) model, which restricts the flexibility of interpolated atmospheric delays and lacks a rigorous strategy for GLONASS AR due to the frequency-division multiple access (FDMA) regime. In this contribution, the ionosphere-weighted single-differenced RTK (IW-SD-RTK) model is proposed to obtain more accurate and flexible interpolation of SD atmospheric delays. Then, the influence of the short-term variation in the receiver hardware biases on the estimation of SD ionospheric delays is analyzed by comparing the common clock (CC) and decoupled clock (DC) IW-SD-RTK models, where the receiver hardware biases are treated as constant in the CC-IW-SD-RTK model and as white noise in the DC-IW-SD-RTK model. Furthermore, to improve the compatibility and interoperability of code division multiple access (CDMA) and FDMA in NRTK positioning, a novel integer-estimable (IE) FDMA model is employed for GLONASS AR. The results demonstrate that the DC-IW-SD-RTK model obtains more accurate and stable ionospheric delays than the CC-IW-SD-RTK model, and the DC-IW-SD-RTK model also outperforms the CC-IW-SD-RTK model in NRTK user positioning performance. Additionally, compared to standalone GPS, the incorporation of GPS and GLONASS observations improves the ADOP by approximately 42%, 45%, and 49% and the user 3-dimensional positioning precision by approximately 10%, 34%, and 19% for small-, medium-, and large-scale networks, respectively. The mean time to first fix (TTFF) is also improved by 36%.