# Energy Efficiency for Green Internet of Things (IoT) Networks: A Survey +
## 3 Literature Review
### Taxonomy of Energy Consumption Solutions
#### 3.7.1 Routing Protocols
In this approach, clustering is achieved, and CH nodes are elected at each round. The proposed protocol determines the best location of the MS based on the minimum energy cost for data delivery of CHs and thus reduces energy depletion and lengthens the network lifetime. In [68], the authors also examined a tree-based mobile sink (TBMS) technique. The proposed study implements a sorting algorithm and the multihop technique to generate the routing structure. The proposed method introduces a MS that gathers the data from the sensing field but in a way that reduces the hop distances and thus elongates the network lifetime of the network. However, authors assume that the MS moves randomly in the sensing area. Therefore, there is no guarantee that the MS will cover all the sensing area, or it might take too long when the sensing field are extended. Of course, if the speed of at which MS moves is too slow or fast, then it can cause more delay and high packets loss. However, some important factors such as interference effects and dynamic network topology should be considered when designing WSNs routing protocols. This is because of the challenges that may arise as a result of the characteristics of the environment in which these networks are deployed [79, 115]. * Interference Effect High node density in the sensing field, can lead to interference effects which can adversely affect energy consumption in sensor networks. According to an investigation by [79], interference occurs during transmission and can cause packet loss. In such a case, lost packets need to be retransmitted and every retransmission is energy wasted [73]. Thus, these authors suggested avoiding paths with higher interference levels [116]. In [117], the authors proposed a new routing strategy that chooses a path with less interference of transmitted data. The proposed method balances the traffic load and significantly reduces congestion in the network. An energy aware interference sensitive geographic routing (EIGR) was investigated by [118]. The EIGR adaptively uses an anchor list to guide data delivery and chooses the less interference route from the energy optimal relay region for data delivery. The EIGR adjusts the transmission power which is only required to disseminate the information to the forwarding node. The proposed protocol focuses on reducing interference and minimizing the total energy depletion of the network. Other researchers [119] have addressed the problem of interference in WSNs, and here the proposed scheme detects the shortest path from source node to the ultimate receiver which avoids interference areas based on an ad hoc, on-demand distance vector (AODV) protocol. [PERSON], et al. [120] introduced a full-duplex BackCom network,where a novel time-hopping spread-spectrum (TH-SS)-based multiple-access scheme was implemented. The proposed protocol enabled simultaneous forward/backward information transfer from one device to another. The interference in such networks is suppressed by the proposed multiple-access scheme based on the TH-SS technique and allows wireless energy harvesting from interference. However, these strategies did not consider the interference caused by neighboring nodes of the next-hop node. Increasing the surrounding neighbor nodes adjacent to each node (within transmission range) generates an increase in interference [121]. As a result, increasing the packets loss and decreasing the network lifetime. * Dynamic Network Topology With multi-hopping, sensor nodes depend on intermediate nodes in the network to disseminate their packets to the final destination. Some of these intermediate nodes may be failed or blocked due to exposure to physical damage, interference, harsh environment or lack of power during transmitting and receiving packets [122]. The probability of node failure rises with the increases in the sensing field and number of sensor nodes.