# An In-Depth Assessment of the New BDS-3 B1C and B2a Signals
## 1 Introduction  
Since the influence of the signal modulation method, the disturbance of the GNSS signal-in-space transmission, the decoding accuracy of the receiver and thermal noise, the raw observations of the GNSS receiver (including code and carrier phase observations) have noise or errors [1]. The BDS system construction can be divided into three steps, and its third-generation system named BDS-3 was completed in July 2020 [2]. The evaluation of the BDS satellite signal performance can be traced back to the previous generation BDS-2 system. [PERSON] et al. [3] evaluated the signal quality, carrier-to-noise ratio, the accuracy of code and carrier observations of the first MEO-1 satellite of the BDS-2 system, and compared it with the performance of GPS and Galileo satellites. [PERSON] et al. [4] used the zero-baseline single difference (SD) to evaluate the performance of the BDS-2 satellites, where the accuracy of code observation is about 33 cm, and the accuracy of carrier observation is about 2 mm. However, the code observations of the BDS-2 satellites have systematic errors related to elevation [5]. Compared with the Beidou-2 MEO satellites, the rubidium atomic clock and hydrogen atomic clock with better performance are carried on the new MEO navigation satellites of Beidou-3 [6], and the center frequency, bandwidth and modulation method of the signal was further improved [7].  
The BDS-3 satellites have been broadcasting new signals different from BDS-2, and the exploration of their performance by the GNSS scientists and engineers is still in the preliminary stage. It is worth noting that before the BDS-3 satellites were launched, China had launched five Beidou-3 test satellites (BDS-3e), including two IGSO and three MEO satellites [8]. Then the launch speed of the BDS-3 satellites was accelerated, and there are currently more than 20 BDS-3 satellites, as shown in Appendix A. [PERSON] et al. [5] evaluated the signal performance of five BDS-3 experimental satellites, and the results show that it is at the same level as GPS L1/L2/L5 and Galileo E1/E5a/E5b signals. [PERSON] [9] predicted the performance of the BDS-3 global constellation through the performance of the BDS-3e satellites. Similar to BDS-2, BDS-3 also transmits signals at B1, B2 and B3, but some new signals were added in [2,10]), which are detailed in a later section. Most of the existing literature analyzes the existing GPS, GLONASS and Galileo signals, while the analysis of BDS satellite signals only includes BDS-2 and a few BDS-3E satellites. Moreover, there are few studies on B1C and B2a signals of BDS-3 and their contrast with GPS and Galileo signals at the same frequency, lacking a thorough, comprehensive analysis and review. In this contribution, the characteristics of the new signal of the BDS-3 global constellation are comprehensively and in-depth evaluated by the authors.  
The structure of this article is as follows: First, the new signal of BDS-3 is introduced in detail. Then, the evaluation of the signal strength and the accuracy of observations are carried out, including the comparison of the BDS-3 new signal and the BDS-2 signal, with the comparison of BDS-3 new signal and GPS/Galileo. The accuracy of different signals is evaluated using two linear combination observations of CC and MultiPath (MP); the accuracy of the carrier phase is evaluated using the zero-baseline method. The PPP accuracy is used to evaluate new signals. The last of this contribution contains discussion and conclusions.