## 3 Materials and Methods
### Satellite Network Architecture  
A satellite network consists of three segments: the ground segment, the user segment, and the space segment. Each segment employs distinct protocols for data transmission, message exchange, and communication between nodes. As shown in Figure 2, the network adopts a structured architecture, where node connections are categorized based on the protocols used. In this network, communication follows a structured process, where each segment interacts through predefined protocol pathways. The ground segment consists of a ground control station (GCS), which generates control signals and receives telemetry data from satellites. Communication between the GCS and satellites, including LEO and MEO satellites, primarily relies on the Consultative Committee for Space Data Systems (CCSDS) for secure and reliable data transmission. The GCS also interacts with ground-based components, such as routers (RTs) and gateways (GWs), through the Transmission Control Protocol/Internet Protocol (TCP/IP), facilitating routing and security enforcement via a firewall. The space segment functions as an intermediary, relaying commands and data between the GCS and user devices. MEO satellites process GPS data, while LEO satellites forward IoT and UAV telemetry using the CCSDS and MIOTY. The user segment consists of IoT devices, UAVs, and global navigation satellite system (GNSS) receivers, which communicate with satellites and ground stations through MIOTY and National Marine Electronics Association (NMEA) protocols. IoT data are transmitted via GW\({}_{1}\), while UAV and GNSS data are processed through GW\({}_{2}\). This structured data flow enables the efficient transmission of commands, telemetry, and sensor data across network components, ensuring reliable satellite network operations. Figure 2 illustrates the structured data flow and communication pathways among the network segments.  
The CCSDS [41] is an international standard protocol offering error recovery capabilities and high data reliability for satellite-to-ground communications. This protocol facilitates the reception of status information and the transfer of data from the GCS to MEO and LEO satellites. MIOTY [42], a low-power wide-area network (LPWAN) technology, is used for data communication between IoT devices, UAVs, and gateways. Although it operates at a low transmission rate, it provides long-range communications and robust error recovery, making it effective for large-scale IoT networks. Optimized for low-power  
Figure 2: Satellite network architecture.  
environments, MIOTY minimizes energy consumption in IoT devices. The NMEA [43] standard defines protocols for exchanging navigation data between GNSS receivers and external devices. It facilitates the transmission of GPS data collected by GNSS receivers to external systems using a compact data format. However, actual communication between GNSS receivers and satellites does not rely on NMEA but instead utilizes GPS L1 and L2 signals [44]. These L1 and L2 signals serve fundamentally different functions in GNSS communication, focusing on satellite-based communication, while NMEA is primarily concerned with data formatting and exchange. This study prioritizes the security analysis of the NMEA, excluding the wireless communication vulnerabilities of L1 and L2 signals, as these fall outside the scope of this research. The TCP/IP is another standard protocol used for managing data transmission within terrestrial networks, ensuring stable communication and efficient data exchange between the key components, such as the GCS, RTs, and GWs.