# A Comprehensive Evaluation of Possible RNSS Signals in the S-Band for the KPS
## 1 Introduction  
As the importance of satellite navigation systems is gradually increasing, several space powers are building their satellite navigation system or modernizing the existing system to improve its performance. The USA and Russia, pioneers of satellite-based positioning technology, are modernizing their Global Navigation Satellite Systems (GNSSs), called the Global Positioning System (GPS) and the Global Navigation Satellite System (GLONASS), respectively. China has established a three-stage gradual development plan for the BeiDou Navigation Satellite System (BDS) development [1], and in August 2020, officially announced the completion of the deployment of BDS-3 with global coverage [2]. Europe aims to complete the construction of the Galileo system with global coverage by the end of 2023 [3] and plans to launch second-generation Galileo satellites in 2024 [4]. Japan and India are operating regional satellite navigation systems, the Quasi-Zenith Satellite System (QZSS), and the Navigation with Indian Constellation (NavIC). Currently, these regional systems are composed of four and seven satellites, respectively, and they plan to launch additional satellites [5,6]. Recently, the government of South Korea officially announced the development of its satellite-based positioning system, called the Korean Positioning System (KPS), to provide services from 2035 [7, 8, 9]. Satellite-based navigation systems can use only the frequency band allocated to the Radio Determination Satellite Service (RDSS) or Radio Navigation Satellite Service (RNSS) regulated by the International Telecommunication Union (ITU). According to the ITU Radio Regulations, downlink satellite navigation signals can use the L-band (1164-1300 MHz,1559-1610 MHz), S-band (2483.5-2500 MHz), and C-band (5010-5030 MHz). Traditionally, the L-band has been preferred for satellite navigation systems. However, the number of signals located in the L-band is increasing rapidly, many researchers have studied the utilization and availability of the S-band or C-band for new RNSS signals. The study on the use of the C-band for RNSS signals began in earnest by adopting Resolution 604 at the World Radicommunication Conference (WRC) held in 2000. The resolution allows for the transmission of navigation signals from the RNSS space station to Earth over the 5010-5030 MHz band. Europe considered the use of the C-band in the early phase of Galileo development. However, due to the technical limitations at that time, the C-band was excluded from the first generation of Galileo [10]. Since then, the use of the C-band was reconsidered for a future generation of Galileo development [11; 12; 13; 14]. According to the previous studies, the use of the C-band causes high free space loss due to the use of frequencies that are three to four times higher than that of the L-band. The C-band also has drawbacks, such as high phase noise and high signal attenuation due to atmosphere and obstacles compared to the L-band. Due to these drawbacks, no RNSS signal is being transmitted through the C-band. At the World Administrative Radio Conference for the Mobile Services held in 1987 (WARC MOB-87), the S-band was additionally allocated to the RDSS on a primary or secondary basis in some countries [15; 16]. After WRC-12, this band was allocated to RDSS on a worldwide primary basis. The use of the S-band also causes high free space loss compared to the L-band but less than that of the C-band. In addition, the payload implementation is simple than when using the C-band. For this reason, South Korea is researching the use of the S-band together with the L-bands. Europe and China are also investigating the use of the S-band for the next generation Galileo and BDS [17; 18; 19; 20; 21; 22; 23]. However, most previous research on the use of the S-band was conducted on new modulation schemes, such as continuous phase modulation (CPM) or orthogonal frequency division multiplexing (OFDM) [17; 18]. The CPM and OFDM schemes provide high spectral efficiency.