# Advances in Improving Energy Efficiency of Fiber-Wireless Access Networks: A Comprehensive Overview
## 3 Energy Efficiency Analyses of Radio-and-Fiber Networks
### Power-Saving Techniques in the Optical Domain of FiWi Networks
\begin{table}
\begin{tabular}{c c c} \hline \hline \multirow{2}{*}{**Reference**} & \multirow{2}{*}{**PS Method**} & \multicolumn{2}{c}{**Summary of Contributions Related to the Improvement of FiWi Network Energy Efficiency**} \\ \hline
[25] & ONU sleep mode with ALR & Hybrid PS technique that includes adaptive link rate control and sleep functions. \\ \hline
[26] & WSM & A PS mode that combines the doze and cyclic sleep modes into a single mode. \\ \hline
[27] & ONU sleep mode and WSM & Comparative performance analysis of fast/cyclic and watchful sleep modes \\ \hline
[28] & WSM operation mode with DBA & Performance of watchful sleep mode that utilizes the dynamic bandwidth allocation. \\ \hline
[29] & AWSM for UNUs & An introduction of adaptive watchful sleep mode \\ \hline ONU sleeping mechanisms & [30] & Load-adaptive ONU PS mechanism that adjusts the number of sleeping ONUs based on the overall load on the network. \\ \hline
[16] & PS mechanism based on OSC, GDBA and TSC components & A PS method based on the SIEPON standard. \\ \hline
[31] & Decentralized PS mechanism based on ONU queue manager, TRx controller, sleep manager, OLT queue manager and GDBA components & Decentralized PS solution based on the SIEPON standard. \\ \hline
[32] & Optimization of sleep interval using ANN & Determination of optimal fast/cyclic sleep interval for energy-efficient XG-PON. The ANN model is used to estimate the optimal sleep interval values. \\ \hline
[33,34] & Integer linear programming (ILP) optimization model and heuristic algorithm & An approach for finding the most efficient way to save energy in wireless access networks using heuristics. \\ \hline
[35] & Transmit power scaling and on/off switching & Extensive studies on the impact of changing the transmit power and turning the BSs on and off on the instantaneous power consumption of macro BSs. Real-world measurements are used from a range of different macro BSs to develop linear power consumption models. \\ \hline
[36] & Adaptive PSM & An adaptive PS method in wireless networks that are based on the IEEE 802.11 standard. \\ \hline
[37] & Scheduled PSM based on a time-slicing mechanism & A PS method based on a time-slicing mechanism in a multi-traffic environment with high background traffic. \\ \hline
[38] & PSM based on the execution of the heuristic algorithm & A generic power management model according to which the wake-up scheduling mechanism is controlled by the AP. Proposes two heuristic algorithms to address the downlink scheduling optimization problem, identifying the importance of tuning the length of the beacon interval in order to conserve energy and reduce delay. \\ \hline
[39] & C-PSM & A centralized PS mechanism that improves the EE of wireless clients in an 802.11 infrastructure network. \\ \hline
[40] & SAPSM & A PS method that uses a ML classifier to assign priorities to applications, where applications classified as high-priority can switch to active mode, while traffic classified as low-priority is optimized for EE. \\ \hline \hline \end{tabular}
\end{table} 
Table 1: Summary of related works on PS methods in R&F networks.