## 3 Communication in IoT
### Commonly Used Sensors for Smart Farming and Heavy Metal Identification
\begin{table}
\begin{tabular}{c c c c c c} \hline \hline
**Wireless Technology** & **Wireless Standard** & **Network Type** & **Operating Frequency** & **Data Rate** & **Max. Range** & **Power** \\ \hline \multirow{4}{*}{WiFi} & IEEE 802.11a, 11b, & \multirow{4}{*}{WLAN} & 2.4, 3.6, 5 GHz & 6–780 Gbps & 100 m & Low \\  & 11g & 11n, 11 ac, & 60 GHz & & \\  & 12d & & & & \\ Z-wave & Z-wave & Mesh & 908.42 MHz & 100 kbps & 30 m & Ultra-low \\  & Bluetooth & (Formerly IEEE & WPAN & 2400–2483.5 MHz & 1–3 Mbps & 100 m & Ultra-low \\  & 802.15.1) & & 908.42 MHz or & & & \\
6 LowPAN & IEEE 802.15.4 & WPAN & 2400–2483.5 MHz & 250 kbps & 100 m & Ultra-low \\  & Sigfox & Sigfox & WPAN & 908.42 MHz & 10–1000 bps & 30–50 km & High \\  & LoRaWAN & LoRaWAN & WPAN & Various & 0.3–50 kbps & 2–15 km & Moderate \\  & BluetoothSmart & & & & & \\ (BLE) & IoT Inter-connect & WPAN & 2400–2483.5 MHz & 1 Mbps & 100 m & Ultra-low \\ Zigbee & IEEE 802.15.4 & Mesh & 2400–2483.5 MHz & 250 kbps & 10 m & Ultra-low \\  & RFID & Many standards & Point to Point & 13.56 MHz & 423 kbps & 1 m & Ultra-low \\  & NFC & ISO/IEC 13157 & Point to Point & 13.56 MHz & 424 kbps & 0.1 m & Ultra-low \\  & CPRS & 3 GPP & GERAN & GSM 850, 1900 MHz & 171 kbps & 25 km/10 km & Moderate \\ EDGE & 3 GPP & GERAN & GSM 850/1900 MHz & 384 kbps & 26 km/10 km & Moderate \\ HSDPA/HSUPA & 3 GPP & UTRAN & 850/1700/1900 MHz & 0.70–50 Mbps & 27 km/10 km & High \\  & LTE & 3 GPP & GERAN/UTRAN & 700–2600 MHz & 0.1–1 Gbps & 28 km/10 km & High \\  & ANT+ & ANT + Alliance & WSN & 2.4 GHz & 1 Mbps & 100 m & Ultra-low \\ Cognitive Radio & IEEE 802.22 WG & WRAN & 54–862 MHz & 24 Mbps & 100 km & Ultra-low \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Widely used IoT wireless technologies. textured soil type with low electrical conductance conditions. In addition to this, there is ECHO-10 HS soil moisture sensor which is a new addition in the soil moisture sensor family and possesses high-frequency oscillation, which enables the sensors to accurately measure soil moisture in any of the soil or soilless media with minimum salinity and textural effects. In order to measure soil water content and salinity, [PERSON] et al. [100] used 5 TE sensors at different soil depths to assess dielectric permittivity (Ka) and electrical conductivity (ECa). It is to be noted that 5 TE sensors are based on frequency domain reflectometry (FDR); therefore, they use a fixed frequency wave of broadband signal which makes the device cheaper and more compact. [PERSON] et al. [101] deployed hydro probe2 sensors to evaluate near surface soil water and determine in situ water retention function. Hydro probe sensors are advantageous due to their linear signal response. On the contrary, hydro probe sensors are not suitable for sandy soils [102]. [PERSON] et al. [103] used an MP406 soil moisture sensor to verify the saturated condition of the expansive soil layer. They also used this sensor to measure volumetric water content values in the soil column during the wetting and drying process [104]. In order to maintain the indoor ecosystem services, air quality plays an essential role. In this regard, MIKROE gas sensors are used to monitor the air quality [105; 106]. To evaluate and assess the vegetation change and study physiological and metabolic response of corn fields and paddy fields, the Pogo II VWC has been widely used [107; 108]. [PERSON] et al. [109] used Portable X-ray Fluorescence Spectroscopy (PXRF) to assess the heavy metal content in soil for which they covered 301 farmland soils from Fuyang in Zhejiang Province, in the southern Yangtze River Delta, China. Conventional methods for heavy metal detection such as Atomic Absorption Spectrometry (AAS), Atomic Fluorescence Spectrometry (AFS), and Inductively Coupled Plasma Optical Emission Spectroscopy (ICP-OES), are expensive and lengthy procedures which are executed in laboratories. Therefore, these methods are not taken into consideration for rapid testing and high-density evaluation of soil heavy metals contamination.