## 2 Methodology
### IoT Terminal Design  
The IoT terminal is designed based on the design requirements to operate at the 865.07 MHz frequency band using LoRa payload. It would utilize either LoRa CSS or FHSS for the transmission of data. The terminal would have a LoRa transceiver and antenna capable of transmitting and receiving signals at the specified frequency. It would also have a microprocessor and memory to store and process data, as well as a power source and potential external sensors for data collection. The IoT terminal hosts two main subsystems. The primary subsystem is a microcomputer configured to execute various tasks and measurements. The second subsystem is the radio transceiver with uplink antennas to perform transmission (Tx) operations. The main board is a Raspberry Pi Zero W [33], with a single core 1 GHz CPU and 512 MB of RAM. The specifications operate well in a low-power IoT application with minimal multi-tasking and threading. The deployment of these IoT terminals is planned for the near-equatorial regions specifically remote areas of the desert with high daytime temperatures and cool night-time temperatures. To combat the temperature effects, the IoT device is constructed in a weatherproof box capable of operating in the \(-10\)\({}^{\circ}\)C to \(+50\)\({}^{\circ}\)C range. The host board additionally offers a number of remote interfaces, making it the ideal development environment for satellite communications. These interfaces include an RS485 input, a communication protocol that meets industrial specifications and specifies the physical hardware and electrical interface for point-to-point electrical device communication [34]. This makes it possible for remote sensing applications to use DCTS and for the IoT Terminal to successfully interface with various devices using the Modbus protocol. The main board also allows remote management and a powerful scripting engine to perform controlled tests in an updatable manner. The second subsystem is an ARM Node processor with a Semtech SX1262 Radio for uplink procedures [35]. The radio transceiver operates at a +22 dBm power output between the frequencies of 150 MHz and 960 MHz [35]. All LoRa CSS and LoRa Long-Range Frequency Hopping Spread Spectrum (LR-FHSS) modulations can be used with the uplink radio. In order to test the maximum power permitted for LoRa CSS, the node is also equipped with a +27 dBm power amplifier. Figure 5 shows the system architecture and Figure 6 shows the practical, in-house developed IoT terminal. Antenna selection is a crucial point in establishing a successful link between the LoRa IoT terminal and the satellite. Monopole omnidirectional antennas receive signals equally from all directions, while directional antennas can detect comparatively weaker signals in a specific direction [36]. The gain of the antenna is another parameter that can be utilized to add to the transmitted power of the signal to account for any spatial or atmospheric losses. Omnidirectional antennas work on 2-dimensional planes, radiating a flat signal [37] shown in Figure 7.  
With omnidirectional antennas, the orientation of the antenna either horizontally or vertically, plays a role in how the signal is transmitted to the satellite. LEO satellites orbit from west to east [16], and therefore placing the antenna facing east and horizontally provides the best output signal from the antenna. The typical radiation pattern of an omnidirectional antenna is shown in Figure 7[32]. For LoRa CSS, the terminal would operate using a constant spreading factor to transmit data, allowing for a longer range but a lower data rate. In spread-spectrum communication systems, the bandwidth and data rate of a transmitted signal are determined by spreading parameters. There are several spreading factors that can be utilized in the case of LoRa, each with different trade-offs in terms of range and data rate. For a fixed bandwidth (125 kHz), a smaller spreading factor, such as SF7, leads to a greater data rate, enabling the transmission of more data in less time.