## 2 Literature Review
### Discussion
#### Challenges  
Despite its advantages, a sensor node network faces the crippling challenge of needing human power or elaborate methods like autonomous helicopters for initial deployment. This challenge can quickly devolve into an insurmountable hurdle when the target terrain is remote, vast and hostile. However, once deployed, sensor nodes can function independently for several years. The obvious physical proximity of the nodes to fires presents another hurdle. Some nodes are likely to be damaged in the intense heat generated by fires. Retrieving and replacing these non-functional nodes are additional maintenance issues that will need to be accounted for during planning and resource allocation. Additionally, many wilderness zones are protected by laws or ordinances against introduction of unnatural/non-native objects, which can complicate the installation of these nodes. \begin{table}
\begin{tabular}{c c c c c c c c c} \hline \hline
**Name of** & **Location** & **Sensor Types** & **Range** & \begin{tabular}{c} **Communication** \\ **Type** \\ \end{tabular} & **Processing** & **Power Source** & **Year** \\ \hline FireVisNet [39] & USA & Temperature, relative humidity, wind speed and direction & 138-393 m & 900-930 MHz radio & ATmega1281 & 24 V and 12 V) and four batteries (12 V) & 2006 \\ \hline [PERSON] et al. [40] & Spain & \begin{tabular}{c} Temperature (NTC), relative humidity (t2 ESSA, \\ SHIT11), pressure (MS5540B), soil moisture (Decagon \\ ECS), light intensity (S8265) \\ \end{tabular} & 100 m (comm) & Xbee/LR-WPAN & ATmega1281 & Two AA batteries & 2010 \\ \hline [PERSON] [41] & Lebanon & \begin{tabular}{c} Relative humidity and temperature (SHIT10), smoke, \\ carbon monoxide (MQ-5) \\ \end{tabular} & Unknown & Zigbee & PICI6877A & \begin{tabular}{c} Solar (17.26 V), \\ 700 mAh \\ lithium-ion battery \\ \end{tabular} & 2014 \\ \hline [PERSON] et al. [32] & China & \begin{tabular}{c} Relative humidity and temperature (SHIT11), smoke \\ (MS5100), carbon monoxide (EC805-CO), carbon dioxide (S-100) \\ \end{tabular} & 20 m & Zigbee & 8051 (included in \\  & & & & & & & \\ \hline [PERSON] et al. [42] & Spain & \begin{tabular}{c} Relative humidity and temperature (SHIT57), gas \\ (carbon monoxide, carbon dioxide) \\ \end{tabular} & 25 m (SN), 1.6 km (CN) & \begin{tabular}{c} 433 MHz EM \\ between SN and GW, \\ 1.6 km (CN) \\ \end{tabular} & \begin{tabular}{c} 1600 mAh Lithium \\ CROM/CFRShew \\ GW and CN \\ \end{tabular} & 2016 \\ \hline Lutakamale and Kaigee [43] & Tanzania & Temperature (LM3 SD2), smoke (MQ-2), relative humidity and temperature (DHIT22) & 100-120 m (SN to GW) & Zigbee between SN and GW, CSM/CFRShew & Two 3.27 V \\ \hline SISVIA Vajalica y & Spain & \begin{tabular}{c} Waspnotte gas board (temperature, humidity, light intensity, carbon monoxide, carbon dioxide) \\ \end{tabular} & 70 m & Zigbee & ATmega1281 & \begin{tabular}{c} Rechargeable AA \\ and solar panel \\ \end{tabular} & 2017 \\ \hline Smart Forests [45] & Brazil & Temperature, relative humidity & 100 m & \begin{tabular}{c} WPAN, Bluetooth \\ Low Energy \\ \end{tabular} & N/A & Batteries & 2018 \\ \hline Kadir [46] & Indonesia & Temperature, humidity, smoke, carbon dioxide & Unknown & Zigbee & Unknown & \
\begin{tabular}{c} Direct power \\ supply \\ \end{tabular} & 2018 \\ \hline \hline LADSensors [47] & Portugal & Temperature, humidity, air pressure, carbon dioxide & 300 m (SN) & LoRa & Unknown &
\begin{tabular}{c} Solar and \\ supercapacitors for \\ energy storage \\ \end{tabular} & 2018 \\ \hline \end{tabular}
\end{table} 
Table 1: Summary of sensor nodes designed for early wildfire detection.