# An In-Depth Assessment of the New BDS-3 B1C and B2a Signals
## 7 Discussion  
BDS-3 was put into operation at the end of July 2020; the new signals B1C and B2a broadcast by BDS-3 satellites are not available in BDS-2. In the past year, a large number of positioning performance evaluations of SPP [24], PPP [25] and RTK [26] of BDS-3 have been published. However, there are few studies evaluating the BIC and B2A signal performance of BDS-3 in-depth. Therefore, a comprehensive and in-depth performance evaluation of the new signals is very helpful for high-precision positioning applications and interoperability with other GNSS.  
The carrier-to-noise ratio is an important parameter that characterizes the strength of the GNSS signals. After a large amount of data analysis, we found that BDS-3 has a significant improvement over BDS-2 at the traditional B1I and B3I frequency points, especially the improvement of B1I, which has reached 4-5 dB/Hz. It can be concluded that the signal strength of BDS-3 BIC and B2a is significantly better than B1I, B2I and B3L. Correspondingly, the signal strength of other GNSS co-frequency points is very close to the BIC and B2a signals of BDS-3. The evaluation results in this contribution reflect that the new signal of BDS-3 has good signal strength. Especially, the abnormal carrier-to-noise ratio of BDS-2 disappeared on the BDS-3 satellite.  
CC and MP are used to evaluate the accuracy of the code observation. In fact, the accuracy of the code observation of the BDS-3 satellites was minorly improved than BDS-2, while the accuracy of the code observations on BIC and B2a is better than that of B1I, B2I and B3I. However, the code observation accuracy of B3I is better than that of BIC, which can be comparable to B2a. If only the single-frequency BDS code observation is used for positioning, B3I and B2a are preferred. The accuracy of the ranging code of other GNSS at the same frequency is equivalent to that of the BIC and B2a of the BDS-3 satellites. The evaluation result of the code observation can provide a basis for the selection of different frequencies.  
DD and zero-baseline were used for an accurate evaluation of the carrier phase. Even so, the hardware thermal noise of the two Trimble receivers used in zero-baseline is still different, so DD observations may absorb unmodeled errors. The results of all carrier evaluations can reflect the relative accuracy of carriers at different frequencies. The DD accuracy of B1I, B2I and B3I frequency points are in the order of 2-2.5 mm, while the DD accuracy of B1C and B2a is in the range of 1-1.5 mm, which is significantly higher than the previous BDS signal. The DD accuracy of other GNSS at the same frequency is also in the range of 1-1.5 mm. As can be seen, the DD accuracy of BIC/L1/E1 is significantly higher than that of B2a/L5/E5a. The calculation result of the zero-baseline also confirms  
Figure 18: Galileo GPS calculation results of zero-baseline.  
the above conclusion. The zero-baseline accuracy of B1C/L1/E1 is significantly higher than that of B2a/L5/E5a. Therefore, through the data analysis in this contribution, it can be inferred that the carrier on B1C/L1/E1 has the best accuracy and stability and is more suitable for high-precision positioning.  
This contribution makes a detailed study of the characteristics of the new B1C/B2a signal and the old B1I/B2I/B3I signal of BDS-3 and separately discusses the GEP/MEO/IGSO satellites. Furthermore, the B1C/B2a signal was compared and analyzed with other GNSS signals at the same frequency. The research results of The contribution can provide an important reference for frequency selection in scenarios such as single-frequency pseudo-range positioning, single-frequency carrier phase differential positioning, and dual-frequency positioning. In addition, the signal accuracy evaluation results can provide prior information for algorithm design and model establishment in high-precision positioning. These analysis results can lay a solid foundation and provide an important reference for the use of BDS-3 new signals.