# BDS-3 Time Group Delay and Its Effect on Standard Point Positioning
## 1 Introduction
The basic status information of the BDS-3 satellites is listed in Table 1. A new satellite attitude mode, signals, and atomic clocks have been applied on the BDS-3 satellite. Five frequencies are used to transmit signals: Backward-compatible old signals B1I (1561.098 MHz) and B3I (1268.52 MHz) and three new open service signals B1C (1575.42 MHz), B2a (1176.45 MHz) and B2b (1207.14 MHz). The B3I signal of the BDS-3 satellites is consistent with that of BDS-2, which uses binary phase-shift keying (BPSK) modulation according to the B3I Interface Control Document (ICD) [20]. The B1C signal has two signal components: A data component (B1C_data) and a pilot component (B1C_pilot), which use the binary offset carrier (BOC) and a quadrature multiplexed binary offset carrier (QMBOC) modulation, respectively, according to the B1C ICD [21]. Similar to the B1C signal, the B2a signal also has two signal components, a data component (B2a_data) and a pilot component (B2a_pilot), but the B2a signal components use the same modulation mode BPSK according to the B2a ICD [22]. The B1C signal shares the same frequency as the GPS L1 and Galileo E1 signals; the B2a signal matches the GPS L5 and Galileo E5a signals; and the B2b signal is compatible with the Galileo E5b signal. Similarly, the BDS-3 B2b signal also matches the BDS-2 B2I signal but uses a different modulation type [23]. The frequencies, signal components, modulations, wavelengths and chip rates of the BDS-3 open service signals are listed in Table 2. [PERSON] et al. [23] analysed the characterization of the BDS-3 satellite GNSS signals with the iGMAS network. The results indicated that the satellite-inducedcode bias was negligible at all signals of the BDS-3 satellite, while BDS-3 triple-carrier combinations of small inter-frequency clock bias (IFCB) variations with peak amplitudes of approximately 1 cm can be recognized. [PERSON] et al. [24] analysed the orbits of two BDS-3 satellites, C27 and C28, and the results showed that the median of the observed residuals computed using code observations and the solved initial orbits were better than four, when the new code signal was utilized. Until now, BDS-3e has been analysed by many experts and scholars. However, limited research has focused on BDS-3 satellites, especially for the TGD correction. GNSS (e.g., GPS, GLONASS, BDS and Galileo) codes are well known to be affected by TGD parameters. The TGD correction model for GPS, BDS-2 and Galileo was investigated in detail by [PERSON] et al. [10]. Nevertheless, the TGD correction model of the old signals and new signals of BDS-3 have not been summarized and investigated in detail. From this background, the aim of this paper is to investigate the impact of TGD correction on BDS-3 positioning. \begin{table}
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This paper is organized as follows. After this introduction, the TGD correction models of BDS-3 are developed to cover all critical BDS-3 positioning scenarios. In the following section, the experimental data and processing strategies are presented. Then, we analysed the impact of TGD correction on SPP for BDS-2, BDS-3 and the BDS-2 + BDS-3 combination. Finally, the conclusions are given.