# A Novel Signal Design and Performance Analysis in NavCom Based on LEO Constellation
## 2 Related Surveys
### Ground-Based Systems  
Ground-based augmentation systems (GBASs) are defined as the use of a ground reference station network that receives GNSS signals in real-time to calculate the error and broadcast the error correction value to the user terminal through various ground communication networks to realize the error correction of the local position of the user terminal, thereby improving the user's service experience, with a real-time accuracy up to the centimeter level.  
Although GBAS can provide a great performance jump for the user's equipment, most systems that rely on broadcast currently rely on wireless communication methods. The openness of wireless communication and the characteristics of terrestrial radio frequency points in the target frequency range and accessories make the design of target signals easier to separate, as well as making their ability to resist system interference stronger.  
ITU plans to further expand the S-band range for navigation applications, and the compatibility between the target band-related (in-band and adjacent bands) system and RNSS is obviously becoming more and more important to NavCom. At present, systems related to the target band (in-band and adjacent frequency bands) in the terrestrial include Wi-Fi, LTE 4G/5G, Wi-Max, DECT, ZigBee, and BLE.  
From the perspective of signal waveform characteristics, Wi-Fi is a near-field radio transmission technology. The peak power of its transmission is regulated by the IEEE protocols. Specifically, the peak power corresponds to IEEE 802.11 a/n, IEEE 802.11 g, and IEEE 802.11 b, being 30, 20, and 10 dBm, respectively. It also has 14 channels at 20 MHz per channel, and the signal modulation is OFDM [45; 46; 47]. LTE 4G/5G is the current mainstream in mobile communications. It uses beam and power control to achieve high-speed data transmission. The diversity of its modulation methods, the high efficiency of its spectrum utilization, and the use of high frequencies make it more suitable for exclusive working frequencies [48; 49; 50]. Wi-Max is a technology that provides wireless communication access for long-distance backbone networks. It has the characteristics of a large available frequency band and high transmitting power, but the probability of occurrence is extremely small for interference in S-band navigation signals [51; 52; 53]. DECT is a wireless access technology with an isolation frequency. It has a high QoS and is suitable for wireless voice communication, and it is considered to have the potential to enable 5G massive machine-type communications (mMTC) by the European Telecommunications Standards Institute (ETSI) [54; 55; 56]. ZigBee is a low-power, low-data-rate, small-scale wireless access technical specification based on IEEE 802.15.4. It has 16 channels allocated in the 2.4 GHz frequency band, and each channel has a 2 MHz bandwidth. The transmitted power is generally 0-20 dBm. BLE is a small wireless access technology based on IEEE 802.15.1 that is often used for data exchange. For different application scenarios, the maximum allowable transmit power ranges from \(-3\) to 20 dBm [57; 58; 59].