# An Energy Efficient Routing Approach for IoT Enabled Underwater WSNs in Smart Cities
## 1 Introduction  
Water covers the two-third part of the earth in the form of lakes, rivers, streams, oceans, etc. These parts are explored and analyzed for underwater environmental monitoring, geosciences, hiddenresource finding, military surveillance [1, 2], pollution monitoring [3], etc. The aforementioned applications require attention to underwater sensing. However, the investigation by humans is not practically possible everywhere due to the harsh underwater environment. In numerous nations around the globe, smart cities are turning into a reality. These cities add to improving residents' satisfaction by offering types of assistance that are regularly founded on information removed from wireless sensor networks (WSN) and different components of the Internet of Things (IoT). Furthermore, policy management utilizes these smart city information to build its effectiveness by decreasing costs and offering extra services. Nonetheless, the data received at smart city servers are not prone to perturbations. Consequently, physical and PC attacks may take place. Underwater Wireless Sensor Networks gadgets are typically battery controlled and, subsequently, their lifetime is restricted. This issue prompts to lose information loss of the fundamental UWSN application. Similarly, the support cost on the Internet of Underwater Things expands with an immense number of UWSN gadgets. Furthermore, the novel attributes of UWSNs represent a few requirements, such as the high energy utilization, long engendering deferral, and node portability. To help the idea of the IoT enabled Underwater Wireless Sensor Networks (IoT-UWSNs), UWSN has developed as a promising framework. In this paper, our research focus is IoT-UWSNs applications and the challenges faced by the aforementioned. We approved the models by simulations. Therefore, researchers are focusing on moving towards the IoT-UWSNs [4, 5]. IoT-UWSNs design is a novel class of IoT and is characterized as a \"system of smart interconnected submerged objects\". IoT-UWSNs are required to power different practical applications, i.e., underwater investigation, condition observing and debacle avoidance. Due to the aforementioned applications, IoT-UWSN is considered to be one of the prospective advances towards smart cities. A tree-dimensional (3-D) space, sensor network when deployed underwater monitors environmental events and takes appropriate actions according to user requirements. The objective of Underwater Wireless Sensor Networks (UWSNs) is to efficiently transmit the data packets from one place to another place using sensoring nodes [6]. There mainly exists two different forms of nodes in UWSNs: sensor nodes and sink nodes [7]. Sensor nodes are placed underwater in the specified region. Each node senses the desired input data about the neighborhood region and transmits the feedback towards the sink. However, the sink is positioned either at the water surface or inside the water and forwards these assembled data packets to the Base Station (BS). Three different types of signals, such as radio, acoustic, and optical signals, are deployed in Wireless Sensor Networks (WSNs) [8]. Radio and optical waves cannot be used in UWSNs due to high absorption in water, and they are only suitable for small distance communication [9], while later one may suffer from high scattering [4]. However, low frequency acoustic signals can cover more distance when compared to radio waves [10]. Thus, acoustic waves are more suitable for UWSNs [11]. The nodes in UWSNs are accoutered with bounded battery capacity, according to [8, 12] battery substitution is not feasible because of the harsh underwater environment. Thus, to extend network's lifetime in a smart environment, the routing protocol should be energy efficient [13, 14, 15, 16, 17, 18, 19, 20, 21, 22], as in smart cities. Generally, three ways of routing are mostly employed in transmission for smart city communication. Firstly direct transmission; where every sensing node straightly sends a data packet to sink [23].