# A Novel Signal Design and Performance Analysis in NavCom Based on LEO Constellation
## 1 Introduction
Regarding the existing GNSS navigation frequency bands, the upper L-band (1559-1610 MHz), the lower L-band (1164-1300 MHz), and the S-band (2483.5-2500 MHz) are allocated to the GNSS system by the International Telecommunication Union (ITU). At present, most GNSS systems use an L-band frequency. Although the bandwidths of the upper L-band and lower L-band are much larger than those of the S-band, the rapidly stacking signal of the GNSS system causes L-band frequency resources to be quickly squeezed. On the other hand, the signal propagation loss at the S-band frequency is greater than that at L-band, but in terms of rain attenuation, ionospheric delay, antenna size, antenna gain, and other factors, the S-band has more advantages than the L-band [23; 24]. In addition, a key change has occurred--that is, software-defined radio (SDR) devices have gradually come to replace firmware and the hardware cost will become negligible, especially for transceivers. In short, for the future GNSS, especially the next generation of BDS, the development of the S-band (2483.5 MHz-2500 MHz) has huge potential resource reserves and great experimental worth. Research on the S-band signal system design: The Galileo system has been used to conduct research on and evaluate a signal system based on in-orbit validation (IOV) in an S-band trial operation, where a series of candidate signals, including BOCs (5, 2) and BPSK (1), were evaluated with the modulation of a binary offset carrier with sine and binary phase-shift keying, respectively [25; 26; 27]. [PERSON] and Prof. [PERSON] et al. proposed the use of continuous phase modulation (CPM) to modulate S-band signals and verified that these have a better tracking accuracy, anti-interference properties, and multipath cancellation performance than other candidate modulated signals [28; 29; 30]. [PERSON] et al. proposed the use of a minimum-shift keying (MSK) modulation method for radio determination satellite service (RDSS) spread-spectrum signals named SSMSK and found that SSMSK had a better performance in acquisition, tracking, and user capacity through a performance evaluation [31]. This article is organized as follows. Section 1 reviews the main nodes of the current augmentation system, satellite navigation system, and NavCom signal scheme, respectively, and introduces the target frequency band of the signal scheme proposed in this article and previous research results. Section 2 lists the in-band and adjacent-band satellite-based system and ground-based system services at 2483.5 to 2500 MHz and describes and analyzes the main systems in-band. Section 3 proposes the signal model and generation model and discusses the basic properties of the proposed signal. Section 4 compares the proposed scheme with the in-band spread spectrum signals of existing systems and a candidate signal scheme from the perspective of the performance method, with indicators such as normalized power spectral density (NPSD), Gabor bandwidth, code tracking error, spectral sensitivity coefficient (SSC), code tracking spectral sensitivity coefficient (CT-SSC), multipath error envelope, link budget tradeoff, and bit error rate (BER), as well as discussing the result of the assessment. Finally, Section 5 concludes the paper and discusses the outlook.