# Energy Efficiency in Short and Wide-Area IoT Technologies--A Survey
## 2 IoT Technologies  
The focus of this section is to provide an overview of the LPSAN and LPWAN technologies that are considered in this work, starting from their main functionalities, features and characteristics. Energy efficiency and power consumption, being the focus of this work, are analyzed in detail in Sections 3 and 4. On the one hand, RFID (and NFC), Zigbee, Bluetooth (and BLE) are reported as LPSAN representative technologies. On the other, Sigfox, LoRa (and LoRaWAN), are mentioned as proprietary LPWAN solutions, while NB-IoT, LTE-M, and EC-GSM-IoT are taken into account as 3 GPP-standardized LPWAN technologies. A classification of the main IoT technologies studied in this paper is represented in Figure 1, while a comparison of the technologies described in the following, based on their main characteristics, is provided in Table 2.  
\begin{table}
\begin{tabular}{p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt} p{56.9 pt}} \hline \hline
**Reference** & **Focus** & \
\begin{tabular}{c} **Technology** \\ **Description** \\ \end{tabular} & **EE Metrics** &
\begin{tabular}{c} **EE** \\ **Taxonomy** \\ \end{tabular} & **Open Issues** & **Description** \\ \hline
[23] & WSNs & yes & no & yes & yes &
\begin{tabular}{c} Classification of techniques for reducing energy consumption in WSNs. \\ \end{tabular} \\ \hline
[24] & WSNs & no & yes & yes & yes &
\begin{tabular}{c} Focus on EE in heterogeneous networks, relay communications, MIMO and OFDM schemes. \\ \end{tabular} \\ \hline
[25] & WSNs & yes (limited) & no & yes & yes &
\begin{tabular}{c} Analysis of EE techniques based on applications. \\ \end{tabular} \\ \hline
[26] & Smart Grid & yes & no & yes & yes &
\begin{tabular}{c} Study of EE in smart grids, including wireless, wired line and optical communications. EE through renewable energies. Power reduction techniques for green data centers. \\ \end{tabular} \\ \hline
[27] & \
\begin{tabular}{c} Smart Grid, IoT generics \\ \end{tabular} & yes & yes & yes (limited) & yes &
\begin{tabular}{c} Review of IoT-based EPES applications. \\ EE constraints and challenges associated with IoT EPES. \\ \end{tabular} \\ \hline
[28] & \
\begin{tabular}{c} Cellular \\ Networks \\ \end{tabular} & yes & no & yes (limited) & yes &
\begin{tabular}{c} Analysis EE vs. coverage trade-offs in \\ 5G. EE through LTE/5G cooperative management schemes. Introduction of Switch On/Off mechanisms. \\ \end{tabular} \\ \hline
**This paper** & \begin{tabular}{c} **IoT (LPSANs and LPWANs)** \\ \end{tabular} & \begin{tabular}{c} **yes** \\ **(Section 2)** \\ \end{tabular} & \begin{tabular}{c} **yes** \\ **(Section 3)** \\ \end{tabular} & \
\begin{tabular}{c} **yes** \\ **(Section 4)** \\ \end{tabular} &
\begin{tabular}{c} **Metrics for evaluating the EE in IoT systems. A classification of EE methods and techniques for LPSANs and LPWANs. A review of power and energy consumption models for LPSANs and LPWANs.** \\ \end{tabular} \\ \hline \hline \end{tabular}
\end{table}
Table 1: A comparison of surveys on Energy Efficiency (EE) and consumption in communication systems.  
Figure 1: Low-Power Internet of Things (IoT) Technologies.