# Energy Harvesting Techniques for Wireless Sensor Networks/Radio-Frequency Identification: A Review
## 1 Introduction
Therefore, EE solutions have become crucial. The summary of the proposed major existing energy-saving mechanisms is as follows: (i) radio optimization techniques (transmission power control [21; 22], cooperative communication [23; 24], and modulation optimization [25; 26]); (ii) sleep/wakeup schemes (topology control [27; 28], and duty cycling schemes [29; 30; 31]); (iii) energy harvesting and wireless charging (utilizing energy harvesting [32; 33; 34], and wireless charging [35; 36; 37]); (iv) energy-efficient routing and WSN's architecture (cluster architectures [38; 39], multipath routing [40; 41], and relay node placement [42; 43; 44]); and (v) data reduction mechanisms (aggregation [45], adaptive sampling [29], compression [46], and network coding [47]). The summarised taxonomy of green WSNs is given in Figure 2. In the following sections, a detailed discussion on the existing energy-saving mechanisms is presented. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Parameters** & **LoRa** & **Bluetooth** & **LR-WPAN** & \begin{tabular}{c} **Mobile** \\ **Communication** \\ \end{tabular} & **WiMAX** & **WiFi** \\ \hline \multirow{3}{*}{Standard} & LoRaWAN & \multirow{3}{*}{IEEE 802.15.1} & \multirow{3}{*}{802.15.4} & \multirow{3}{*}{3G-UMTS, ( ZigBee)} & \multirow{3}{*}{CDMA2000 4G-LTE-A} & IEEE 802.16 & IEEE 802.11 \\  & & R1.0 & & & & \\ \multirow{3}{*}{\begin{tabular}{c} Energy consumption \\ \end{tabular} } & \multirow{3}{*}{Very Low} & \multirow{3}{*}{\begin{tabular}{c} Bluetooth: \\ Medium; BLE: \\ Very Low \\ \end{tabular} } & Low & Medium & Medium & High \\  & & & & 868/915 & & \\ \multirow{3}{*}{\begin{tabular}{c} Frequency band \\ \end{tabular} } & \multirow{3}{*}{868/900 MHz} & \multirow{3}{*}{2.4 GHz} & \multirow{3}{*}{865 MHz, 2.4 GHz} & \multirow{3}{*}{865 MHz–2 GHz} & \multirow{3}{*}{2–66 GHz} & \multirow{3}{*}{5–60 GHz} \\  & & & & \(\mathrm{GHz}\) & & \\ \multirow{3}{*}{\begin{tabular}{c} Data rate \\ \end{tabular} } & \multirow{3}{*}{0.3–50 Kb/s} & \multirow{3}{*}{1–24 Mb/s} & \multirow{3}{*}{40–250 Kb/s} & \multirow{3}{*}{200 kb/s–1 Gb/s} & \multirow{3}{*}{\
\begin{tabular}{c} 1 Mb/s-1 Gb/s \\ (Fixed) 50–100 Mb/s \\ (mobile) \\ \end{tabular} } \\ \multirow{3}{*}{
\begin{tabular}{c} Transmission range \\ Cost \\ \end{tabular} } & \multirow{3}{*}{\(<\)30 Km} & \multirow{3}{*}{8–10 m} & \multirow{3}{*}{10–20 m} & \multirow{3}{*}{Entire cellular area} & \(<\)50 Km} & \multirow{3}{*}{20–100 m} \\  & & & & & \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary comparison of the using wireless technologies for IoT. \begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Wireless Technology** & **Healthcare** & **Smart Cities** & \
\begin{tabular}{c} **Smart Building** \\ \end{tabular} & **Automotive** & **Industry** &
\begin{tabular}{c} **Local Network** \\ **(M2M)** \\ \end{tabular} \\ \hline Bluetooth (BLE) & very high & low & low & very low & very high & medium \\ LR-WPAN & medium & high & low & very low & low & high \\ LoRa & low & high & high & high & high & high \\ WiFi & low & high & medium & medium & low & high \\ WiMAX & low & very high & high & high & very high & high \\ Mobile & low & high & high & high & medium & very low \\ communication & low & high & high & high & medium & very low \\ \hline \hline \end{tabular}
\end{table} 
Table 2: Suitability of wireless technologies for IoT applications.