## 5 Coverage Analysis  
In this section, depending on the designed VTU hardware platforms, the coverage analysis was carried out to reveal the approximate transmission limits of LoRa and NB-IoT technologies. For a typical wireless network, the coverage refers to the maximum distance that enables the received signals to exist above a certain threshold level. For a receiver to detect the desired signal, the RSSI must be greater than the receiver sensitivity [45]. The receiver sensitivity is the minimum signal power level to correctly receive the packets with an acceptable packet error rate (PER). In general, it is expected that the PER should be less than 1% [46]. The higher receiver sensitivity means better coverage to receive signals from further away [47]. The link budget summarizes a communication link that allows for calculating the coverage range of a wireless system. It includes all the gains and losses throughout the propagation path from the transmitter to the receiver [48]. By using the link budget, the received signal power can be calculated as follows:  
Figure 4: VTU prototype hardware designs for LoRa and NB-IoT technologies. \[P_{r}=P_{t}-L_{t}+G_{t}-PL+G_{r}-L_{r} \tag{1}\]  
where \(P_{t}\) is the transmitter output power (dBm), \(PL\) is the path loss (dB), \(G_{t}\) and \(G_{r}\) are the antenna gains (dBi), and \(L_{t}\) and \(L_{r}\) are the losses (dB) from cables/connectors at transmitter and receiver, respectively. Accurately calculating the link budget is critical to provide reliable data transmission. To estimate the coverage range, the maximum allowable path loss can be calculated from the link budget equation as follows:  
\[PL_{max}=P_{t}-L_{t}+G_{t}-S+G_{r}-L_{r}-m \tag{2}\]  
where \(S\) is the receiver sensitivity (dBm) and \(m\) is the fade margin (dB) due to the obstructions and atmospheric attenuation. Clearly, the fade margin is the difference between the RSSI and receiver sensitivity. It should be high enough to guarantee the RSSI is over the receiver sensitivity. Depending on the propagation environment, a certain margin should be reserved to make the link budget more reliable. When considering the unpredictable signal fading on the wireless channel, the fade margin is usually taken in the range of 10-30 dB [46]. In the considered agricultural vehicle tracking application, the uplink channels for LoRa and NB-IoT connectivity technologies have been visualized in Figures 5 and 6, respectively. According to that, the link budgets can be calculated using LoRa and NB-IoT transceiver modules' specifications on their datasheets [41; 43]. Table 1 summarizes the utilized operating parameters of the VTU designs at the transmitting side. Besides, Table 2 summarizes the uplink budget for LoRa and NB-IoT connectivity by using a GW (with SX1301) and LTE BS operating parameters (i.e., receiver sensitivity, connector losses, and antenna gains) on the receiving side. It is especially noteworthy that, for LoRa connectivity, the highest spreading factor (SF12) was used to maximize the transmission range due to its high link budget capability [49]. \begin{table}
\begin{tabular}{l c c} \hline \hline  & **LoRa** & **NB-IoT** \\ \hline RF Transceiver & Microchip RN2483 & Quectel BC95-G \\ \hline Frequency & \(433,868\) MHz & \(800,900,1800\) MHz \\ \hline Bandwidth & \(125\) kHz & \(180\) kHz \\ \hline Transmit power & \(+14\) dBm & \(+23\) dBm \\ \hline Receiver sensitivity & \(-146\) dBm & \(-129\) dBm \\ \hline \hline \end{tabular}
\end{table} 
Table 1: RF transceiver specifications of designed VTUs.