# An Energy Efficient Routing Approach for IoT Enabled Underwater WSNs in Smart Cities
## 3 Motivation for U-(ACH)\({}^{2}\): Underwater Implementation of (ACH)\({}^{2}\)
#### Network Model  
We have considered an underwater wireless network, where we dealt with three types of nodes. Normal nodes gather information regarding the surrounding region and transmit it to the CH node. CH will further send the aggregated packets to the sink node. Normal nodes can also forward the  
Figure 1: General Architecture of U-(ACH)\({}^{2}\). sensed data straight to the sink if they lie nearer to the sink node. In our proposed scheme, the sink is either positioned at the top of the water surface or specified otherwise. One of the most famous techniques used for the sharing of location information is localization. In order to start network configuration, every node in WSN requires the area IDs, link status, relative coordinates, and received signal strengths of all other nodes in order to transmit data packets. However, this technique is itself a big technical challenge for researchers ([PERSON] et al., 2018). U-(ACH)\({}^{2}\) is a localization based routing protocol, where all sensor nodes newscast a HELLO packet to the entire structure. In this study, we have used a range-free localization algorithm. In this technique, the mobile beacon node with an antenna is utilized to provide the data regarding distance and location for every other anonymous node. By doing so, all of the nodes get localized by their neighbors. However, the node with less remaining energy than the required energy cannot send a HELLO packet, since these nodes are not able to participate in further transmission. At the point when a node gets a HELLO packet from its neighbor, it examines the remaining energy and signal strength of the neighbor under certain conditions. If the neighbor meets the given conditions of residual energy and signal strength, then the neighbor turns into the next hop for transmitting the data to the next level. Depending upon the information provided in HELLO packets, every node attains complete information of all other sensor nodes and sink node(s). In the proposed study, \"switch to next node\" is a function that is considered and called when a current node is dead or at the time of traversing for re-election, the node generates no response. The reason behind for calling switching function is that the node contains very less residual energy than the required energy and it cannot broadcast the HELLO packet. Furthermore, the effected node cannot participate anymore in the transmission of data packets and, hence, becomes isolated. U-(ACH)\({}^{2}\) is a clustering based routing protocol, where CHs are selected on the basis of remaining energy. The remaining energy needs to be examined in order to select CHs. Therefore, the nodes having superlative remaining power are preferred ([PERSON] et al., 2018). For the sake of reducing the load on CHs, the optimum number of clusters is selected that results in balanced cluster size. For this, a selection criterion is defined that depends upon the 10 m distance of a selected CH from other elected CH, as demonstrated in Figure 2. The reasoning behind the distance measure is to balance the load factor on each cluster. By doing so, many clusters would be equally loaded with the associated cluster members otherwise some clusters would have many associated cluster members while other clusters may be found under load. To avoid this controversy, the distance measure is considered in this study. As per the results detailed in ([PERSON] et al., 2018), the ideal number of CHs for a network containing 100-nodes is proposed to be nearby 3-5. In any case, it ought to be noticed that the rate proposed by ([PERSON] et al., 2018) is determined dependent on the direct correspondence of CHs with the BS and, consequently, for the structures that utilize multi-hop transmission to move the collected data of CHs to the sink node or the schemes with various energy utilization, the forms may differ. In the proposed study, in total 225 nodes were selected.