# A Novel Satellite PRN Code Assignment Method Based on Improved RLF Algorithm  
[PERSON]  
Citation: [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] A Novel Satellite PRN Code Assignment Method Based on Improved RLF Algorithm. Sensors2022222538[[https://doi.org/10.3390/s2155538](https://doi.org/10.3390/s2155538)]([https://doi.org/10.3390/s2155538](https://doi.org/10.3390/s2155538))  
[PERSON]  
Citation: [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON]; [PERSON] [PERSON] A Novel Satellite PRN Code Assignment Method Based on Improved RLF Algorithm. Sensors202222222222222222222222  
there are two types of LEO-based navigation augmentation system: information augmentation and signal augmentation. The use of the LEO constellation in signal augmentation systems has so many advantages by which it can improve the service performance of the GNSS. First of all, the LEO satellites undergo rapid geometry changes [5], which is beneficial for the rapid convergence of PPP (precise point positioning). The results of [PERSON] et al. [6] showed that LEO-augmented GNSS (GPS + BDS + Galileo) can achieve centimeter-level accuracy within 5 min of PPP convergence. [PERSON] et al. [7] discovered that having more LEO satellites leads to a shorter convergence time, and the convergence time can be shortened from 8.2 to 0.8 min by introducing observations from 288 polar-orbiting LEO satellites. The results of [PERSON] et al. [8,9] showed that the LEO augmentation could be significantly reduced the convergence time of the ambiguity-float formal horizontal precision. Secondly, LEO signal augmentation can provide new observations. For occluded environments, such as under overpasses, forests, urban canyons, and even indoors, positioning can be compensated by stronger signals broadcast by the LEO. Taking Iridium as an example, Satellite Time and Location (STL) is a PNT service that was made available through Iridium by Satelles in 2016 [10]. Satelles company tested the STL's service performance indoors in a high-rise building and found an indoor positioning accuracy of 20 m and a timing accuracy at the sub-microsecond level [11,12]. In addition, due to the lower orbit, navigation signals from the LEO satellite are stronger, which adds robustness to the navigation service [13]. For example, Iridium signals are 300 to 2400 times stronger than GNSS on the ground [14], and users have already employed LEO-based signals in environments with high GNSS interference [15]. It is worth recalling that OneWeb [16], SpaceX [17], Boeing [18], China Aerospace Science, Technology (CAST) Corporation [19], and other internationally renowned companies have worked out their plans for LEO constellations with hundreds or thousands of satellites, and [PERSON] et al. successfully demonstrated the potential of these LEO constellations to be leveraged as a platform to provide navigation services [20]. In the future, in order to achieve navigation enhancement, LEO constellations such as Weili, Hongyan and Luojia will broadcast traditional CDMA signals, which means that each LEO satellite has a unique PRN code. However, for hundreds or thousands of satellites from the LEO signal augmentation system, the traditional method places a huge burden on the navigation receiver and PRN code design, while the traditional method is suitable for GNSS constellations consisting of dozens of satellites. Specifically, signal augmentation means that LEO satellites transmit navigation signals independently. Similar to GNSS signals, the LEO navigation signal structure consists of three layers: the carrier wave, PRN code (C/A code for civil and P-code for military), and navigation data. Because LEO satellites are located 500-1500 km away [20], the LEO constellation requires dozens to thousands of satellites to cover the globe (shown in Table 1) and the same number of PRN codes to realize CDMA when using the traditional method where each LEO satellite in a constellation has a unique PRN code.