## 4 Energy Conserving Solutions in Wireless Networking-Based IoT
### Energy Conserving Solutions for WLAN-Based IoT  
When IoT devices are connected to the Internet through a representative WLAN, _i.e._, IEEE 802.11 WiFi network, power consumption for driving the WiFi interface should be controlled in an energy conservative manner. The solutions we will review include: overload control for the access network, IEEE 802.11 PSM optimization, resolving multi-hop communication collisions, and handling multiple heterogeneous radio interfaces.  
\begin{table}
\begin{tabular}{c c c c c c c} \hline \hline
**Category** & **Solution** & **Approach** & **Scheme** & **Metric** & **Control** & **Evaluation** \\ \hline \multirow{9}{*}{Overload control, resource allocation} & \multirow{3}{*}{[38]} & Extended access baring (EAB), extended wait timer and delay tolerant indicator, prioritization mechanism & Back off mechanism probability & Energy efficiency, access delay, access probability & Distributed & Simulation \\  & & & & probability  
\begin{table}
\begin{tabular}{r c c c c c c} \hline
**Category** & **Solution** & **Approach** & **Scheme** & **Metric** & **Control** & **Evaluation** \\ \hline \multirow{8}{*}{Paging cycle, DRX mechanism} & [42, 43] & Extending paging cycle & Duty cycling & Energy efficiency, end-to-end delay & Centralized/Distributed & Analysis, simulation \\  & [48] & Longer DRX cycles for LTE devices & Duty cycling & Energy efficiency, reporting interval & Centralized/Distributed & Simulation \\  & [47] & Extended DRX mechanism & Duty cycling & Energy efficiency & Centralized/Distributed & Qualitative analysis \\  & [44] & Increased DRX cycle of devices operating & Duty cycling & Energy efficiency & Centralized/Distributed & Experiment \\  & [45] & State determine introduced to determine & Duty cycling & Energy efficiency & Centralized/Distributed & Experiment \\  & [46] & Network assisted standby timer for MTC & Duty cycling & Energy efficiency & Centralized/Distributed & Experiment \\  & [49] & Service-Instance Oriented Energy & Duty cycling & Energy efficiency & Centralized & Experiment \\  & [49] & Management & Duty cycling & Energy efficiency & Centralized & Experiment \\  & [50] & UE Power Saving Mode & Duty cycling & Energy efficiency & Distributed & Qualitative analysis \\  & [51] & Allowed time period for sleep after & Duty cycling & Energy efficiency & Centralized/Distributed & Qualitative analysis \\  & [52] & Reduction in maximum bandwidth, transmit power and half duplex operation & Transmit power & Energy efficiency, end-to-end delay & Centralized & Qualitative analysis \\  & [53] & RSSI based connection establishment & Transmit power & Energy efficiency, end-to-end delay & Distributed & Experiment \\  & [54] & Device data transfer during initial & Transmit power & Energy efficiency & Distributed & Experiment \\  & communication & control & Energy efficiency & Distributed & Experiment \\  & [55] & Energy efficient long range data transfer & Transmit power & Transmit power & Energy efficiency & Distributed & Experiment \\ \end{tabular}
\end{table}
Table 1: _Cont._  
\begin{table}
\begin{tabular}{c c c c c c c} \hline
**Category** & **Solution** & **Approach** & **Scheme** & **Metric** & **Control** & **Evaluation** \\ \hline Gateway and device & [56, 59] & Gateway calculated L1 based device & Duty cycling & Energy efficiency, packet transfer time & Centralized & Simulation \\ Encryption & & & SNR, throughput and RSSI level based & Transmit power & Energy efficiency, end-to-end delay & Centralized/Distributed & Simulation \\ management of heterogeneous radio interfaces & [60] & Interface selection & control & end-to-end delay & Centralized/Distributed & Simulation \\  & [61] & Controlled interface switching based on environmental parameters & Transmit power & Energy efficiency & Centralized/Distributed & Experiment \\  & [62] & Controlled interface switching based on environmental parameters & Transmit power & Energy efficiency & Centralized/Distributed & Experiment \\ \hline \end{tabular}
\end{table}
Table 1: _Cont._