# An Autonomous Wireless Device for Real-Time Monitoring of Water Needs
## 2 Wireless Sensor Networks in the Context of Smart Agriculture
Furthermore, the additional energy consumption because of synchronous communication reduces NB-IoT's end-device lifetime as compared to them. In addition, NB-IoT is not suitable for rural areas that do not benefit from LTE coverage. Thus, for applications that do not have large amount of data to send, Sigfox and Lora are the best options [8; 16]. In the field of agriculture, a long battery lifetime of sensor devices is required. Using temperature, humidity, and electrical conductivity (EC), sensors could significantly reduce water consumption and improve yield, as discussed in [23]. Devices update sensed data a few times per hour, as the environment conditions do not radically change in this time period. Thus, Sigfox and LoRaWAN are ideal for this application. Moreover, various farms do not have LTE cellular coverage, thus NB-IoT is not a solution for agriculture in the near future. Although the LoRa and SigFox technologies have a great technical similarity, LoRa technology was used in this work for two reasons: Firstly, because we wanted to build a WSN that avoided dependence on third parties. One of the main features of this technology is that any user can build \begin{table}
\begin{tabular}{c c c c c c} \hline \hline \multirow{2}{*}{**Parameters**} & \multirow{2}{*}{**ZigBee**} & \multicolumn{2}{c}{**Global System for Mobile**} & \multirow{2}{*}{**Long-Range**} & \multirow{2}{*}{**SigFox**} & \multirow{2}{*}{**NarrowBand IoT**} \\  & & **(GSM)/General Packet Radio** & & & **(LoRa)** & \\  & & **Service (GPSRS)** & & & **(NB-IoT)** \\ \hline \multirow{2}{*}{Standard} & ZigBee Alliance IEEE & N/A & Lora Alliance & IEEE 802.15.4 & \multirow{2}{*}{3 GPP} \\  & 802.15.4 & & IEEE 802.15.4 & & & \\ \hline \multirow{3}{*}{Frequency band} & Unlicensed EM bands & \multirow{3}{*}{Increened bands 900-1800 MHz} & Unlicensed EM bands & \multirow{3}{*}{Increened 18M bands} & \multirow{3}{*}{Increened 12E bands} \\  & 86891543 MHz and & & & & 868915433 MHz & 700, 800, 900 MHz \\  & 24 GHz & & MHz & & \\ \hline Power consumption & Low & Medium & Very Low & Very Low & Medium \\ \hline Data rate & 20, 40, and 250 kbps & Up to 170 kbps & 50 kbps & 100 bps & 200 kbps \\ \hline Latency & 20-30 ms & \textless{}1 s & N/A & N/A & Very Low \\ \hline Communication range & 100 m (open spaces) & 1-10 km & 20 km (nural) & 40 km (nural) & 10 km (nural) \\ \hline End-device cost & Low & Medium & Low & Low & Medium \\ \hline Network Topologies & P2P, tree, star, mesh & Cellular system & Star of stans & Star & Cellular system \\ \hline \multirow{3}{*}{Limitations} & Line-of-sight between & \multirow{3}{*}{Power consumption} & Network size & \multirow{3}{*}{Low range and coverage capabilities (e.e. range \textless{}10\, km)} \\  & the sensor node and the & & & & \\ \cline{1-1}  & coordinator node must & & & \\ \cline{1-1}  & be available & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Comparison between the different communication technologies for end-devices. their own network, thus avoiding having to subscribe in order to use an external network. Secondly, because with LoRa, we can support coverage in remote rural areas. Finally, commercial wireless detection modules such as eKo Pro [24], MicaZ [25], TelosB [26], Zolertia [27], Adcon Telemetry GmbH [28], AquacomSensor Hub Aquaflex [29], Enviroscan [30], or Waspmote [31] for agriculture and its irrigation are still very expensive--usually exceeding 1000.000--making it impossible for smaller farms to implement this type of system, as well as for smart farms, which require a large number of wireless end-devices for data collection that support reliable decision making.