# Energy Efficiency for Green Internet of Things (IoT) Networks: A Survey +
## 5 Research Gaps  
The literature review demonstrated the existence of many avenues for minimizing energy wasted and lengthening the network lifetime. It presented many possibilities and identified numerous limitations. This paper has scrutinized the literature to obtain an insight into the perspectives addressed by previous researchers and the gaps left by existing solutions. In the sensing field, sensor nodes depend on other intermediate nodes to forward their data. Some sensor nodes send their data over single or multiple hops to arrive the BS through CH nodes. The CH node can become overloaded due to the number of surrounding nodes that are connected and forwarded their data to it. The probability of retransmitting some of these packets at the CH nodes will increase. Therefore, data delivered by the sensor nodes must be prioritized at CH nodes based on the energy consumed by each packet. However, no report has been presented assigning high priority to packets that come from the furthest distances to the CH nodes. Since these packets more quickly exhaust the network resources because they require more links and nodes to reach their ultimate destination, one of our studies suggests the introduction of a novel scheduling algorithm called the long hop (LH) to optimize energy used in sensor networks [127]. The LH algorithm assigns high priority to the scheduling of packets arriving after a greater number of hops, from longer distances. These packets serve first at the CH nodes to prevent them from being retransmitted, and so conserving energy. The literature review also introduced the energy consumed due to delivering data from the source node to the required destination. Based on the multihop concept, the transmitted packets access multiple nodes and experience a greater number of hops to reach the intended destination. Each node involved in the transmission process has many forwarding nodes. However, a higher number of forwarding nodes causes higher energy consumption. Thus, another research work introduces a new routing strategy that sends data to the next-hop node within a shorter transmission distance and fewer forwarding nodes to optimize the energy consumption. The proposed protocol evades delivering packets to nodes that have many forwarding nodes, therefore balancing the load traffic and enhancing the network performance and lifetime of the network. There have been relatively a large and growing studies of literature reports attempts to minimize the energy depletion of sensor networks, this author believes that there are only a few research studies on theoretical energy analysis of sensor nodes based on less transmission distance, interference and the creation of CH nodes. Interference is also one of the main factors that cause data collisions and consequent energy wastage. A node with fewer neighbors has less overhearing and interference. Therefore, one of previous works presents a new routing method that elects the next-hop node to be one with least transmission distance and fewer neighbor nodes and thus less interference [163]. The proposed scheme also introduces a new method that selects CH nodes around a single BS based on lower transmission distances. Both techniques minimize energy depletion and lengthen the lifetime of network. As shown in the literature, previous research focused on efficient transmission data in the WSNs and IoT applications. However, most of these studies considered either eliminating redundant data or monitoring active devices remotely. Thus, the author believes that investigating both the filtering of redundant data and the remote monitoring of the behavior and condition of the smart objects. These works will decrease the volume of data forwarded which, sequentially, will minimize the process of scheduling and routing data on each device on the network, consequently minimizing the energy consumption and success the IoT technology.