# Energy Efficiency for Green Internet of Things (IoT) Networks: A Survey +
## 5 Research Gaps
There are many published studies (e.g., [164; 165; 166]) that introduce a survey of relatively recent techniques and methods proposed for performing data aggregation in WSNs. The survey shows that improve energy consumption by reducing the transmission of redundant data and thus lengthen the network lifetime. In [167], authors have demonstrated a new protocol called Energy-efficient and balanced cluster-based data aggregation algorithm (EEBCDA). The method aims to overcome the energy dissipation issue in the cluster-based aggregation data. In this protocol, the network is classified into rectangular grids of unequal size and the CH node keeps on rotating in each cluster. The CH node in each grid is picked based on the high residual energy. The EEBCDA method balances energy usage in each grid and thus prolong the network lifetime. Researchers reviewed the available literature on the clustering-based aggregation protocol approach in WSN for minimum communications and extend the network lifetime [165]. Researchers have studied and compared some of the state-of-the-art data-gathering techniques considering their trade-off between reliability (i.e., packet loss and reconstruction error) and energy consumptions (i.e., network lifetime) by taking into account both compression and networking aspects [166]. The paper summarizes the results as follows: (i) Distributed source coding (DSC) and transforms and encoding compression (TEC) techniques should be preferred for prolonging the lifetime of the network. (ii) Compressive sensing (CS) should be preferred when high reliability is needed. (iii) Chinese remainder theorem (CRT) should be preferred for its inherent low complexity. However, to the best of the author's knowledge, there is no best solution for all possible applications and that only the trade-off between reliability, energy consumptions and complexity can drive the choice of the data-gathering technique to be used for a specific application. Finally, these methods can broadly be classified into several characteristics and summarized in Table 3, thus, the table presents a summary of previous methods surveyed in this paper. \begin{table}
\begin{tabular}{c c c c c c c c} \hline
**Protocols** & **Mobility** & **Hop Limit** & **Use of Location Info.** & **Type of Protocol** & **Network Improvement** & **Selected CH Node** & **Ref.** \\ \hline LEACH & Fixed & Single hop & No & Routing & Energy-efficiency & Randomly & [77] \\ \hline LEACH-C & Fixed & Single hop & Yes & Routing & Energy-efficiency & A node with more energy in a cluster & [84] \\ \hline E-LEACH & Fixed & Multi-hops & Yes & Routing & Energy-efficiency & A node with the highest remaining energy & [85] \\ \hline EAMMH & Fixed & Multi-hops & Yes & Routing & Energy-efficiency &
\begin{tabular}{c} The main CH should \\ be an optimum \\ distance from these \\ child-CH nodes. \\ \end{tabular} & [86] \\ \hline EAMR & Fixed & Multi-hops & Yes & Routing & Energy-efficiency & A node is selected & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\ \hline HEED & Fixed & Single hop & Yes & Routing & Energy-efficiency & The selected CH node based on the high & [82] \\  & & & & & & \\  & & & & & & \\  & & & & & & \\  & & & & & & \\ \hline H-HEED & Fixed & Single hop & Yes & Routing & Energy-efficiency & The H-HEED finds the center of each cluster and then indicates the node nearest the cluster as a CH. & [90,91] \\ \hline ER-HEED & Fixed & Single hop & Yes & Routing & Energy-efficiency & A node with the highest level of energy is a CH. & [92] \\ \hline E-HEED & Fixed & Multi-hops & Yes & Routing & Energy-efficiency & The CH nodes according to the least transmission distance from the BS. & [93] \\ \hline PEGASIS & Fixed & Multi-hops & No & Routing & Energy-efficiency & Randomly & [83] \\ \hline DORA & Fixed & Multi-hops & No & Routing & Energy-efficiency & Randomly & [98] \\ \hline \end{tabular}
\end{table} 
Table 3: A summary of previous methods surveyed in this paper.