# Internet of Drones: Routing Algorithms, Techniques and Challenges
## 2 Related Work
CH node reuse is made possible by use of energy harvesting techniques, e.g., the capability of extracting energy from the surrounding environment such as solar power, wind, temperature variations, and magnetic fields. Another CH selection method was introduced in [33] where a fuzzy logic-based energy adequate clustering (FLEAC) method is used on the basis of five fuzzy descriptors. An acceptable amount of research work is available in the literature that exploits the LEACH protocol to increase the energy efficiency of CHs in WSN [34]. Moreover, new distance-based algorithms comprising scalable energy efficient clustering hierarchy (SEECH) have been used for the optimal selection of CHs and enhance the lifetime of the network [35]. In the research done by [36], a security framework has been proposed to handle important issues of security within the IoD coverage area. A need for WSN security also arises because of the worldwide application of WSN. Some challenges faced by ad-hoc networks are also shared with IoDs because WSN is a special type of ad-hoc network. Crossbow tool [37] is a determining agent of different topologies in the network. Similarly, in order to reduce road congestion and urban pollution, ref. [38] developed WSN to gather traffic and environmental data. This helps environmental monitoring and substantial mobility of traffic in urban area. In the context of WSN, ref. [39] have worked to revisit clustering algorithms and parameters. The developed cluster structure facilitates an organised data assembly plus aggregation of network units for the expansion of the IoD. However, some of the issues need to be addressed. One of the crucial issues of IoDs is a decrease in life of nodes, and much work has been done in this field. WSNs comprising UAVs can offer connectivity in disaster-stricken regions in a cost-effective manner [40]. The energy constraint in disaster-stricken areas is also a significant issue [41]. Energy harvesting is deployed in areas where the batteries cannot be easily charged. It is an attractive type of solution as the procured lifetime is ideally infinite [42]. To the best of the authors' knowledge, none of these articles present a detailed survey regarding routing protocols for IoDs. Table 1 presents a comparison of this article with other IoD based routing articles. \begin{table}
\begin{tabular}{c c c c c c} \hline
**Ref. ** & **Year** & **Applications** & **Architecture** & **Routing** & **Future Research Directions** & **Performance Metrics** \\ \hline
[9] & 2018 & ✓ & x & x & x \\ \hline
[8] & 2019 & ✓ & x & x & x \\ \hline
[43] & 2019 & ✓ & x & x & x \\ \hline
[5] & 2021 & ✓ & x & x & x \\ \hline
[44] & 2021 & x & ✓ & x & x \\ \hline
[45] & 2021 & x & x & x & x \\ \hline
[46] & 2022 & x & x & x & x \\ \hline This Work & 20 Contributions:  
The key contributions of this work are as follows:  
1. This article presents the architecture of the IoD. 2. This article investigates the IoD key requirements. 3. This article discusses the routing algorithms for IoDs. 4. This article highlights the future directions and open research challenges related to IoD.