###### Abstract  
Nowadays, the Internet of Things enabled Underwater Wireless Sensor Network (IoT-UWSN) is suffering from serious performance restrictions, i.e., high End to End (E2E) delay, low energy efficiency, low data reliability, etc. The necessity of efficient, reliable, collision and interference-free communication has become a challenging task for the researchers. However, the minimum Energy Consumption (EC) and low E2E delay increase the performance of the IoT-UWSN. Therefore, in the current work, two proactive routing protocols are presented, namely: Bellman-Ford Shortest Path-based Routing (BF-SPR-Three) and Energy-efficient Path-based Void hole and Interference-free Routing (EP-VIR-Three). Then we formalized the aforementioned problems to accomplish the reliable data transmission in Underwater Wireless Sensor Network (UWSN). The main objectives of this paper include minimum EC, interference-free transmission, void hole avoidance and high Packet Delivery Ratio (PDR). Furthermore, the algorithms for the proposed routing protocols are presented. Feasible regions using linear programming are also computed for optimal EC and to enhance the network lifespan. Comparative analysis is also performed with state-of-the-art proactive routing protocols. In the end, extensive simulations have been performed to authenticate the performance of the proposed routing protocols. Results and discussion disclose that the proposed routing protocols outperformed the counterparts significantly. energy efficient; void hole; shortest path based routing; EC; depth 1  
M. [PERSON], M.  
1. Localization in IoT-UWSN is quite difficult from terrestrial networks. 2. The dynamically changing environment is difficult to handle in IoT-UWSN as compared to terrestrial sensor networks. 3. IoT-UWSN uses acoustic signals for data transmission. On the contrary, radio signals are used in the terrestrial environment for packets transmission. 4. In IoT-UWSNs, sensor nodes are deployed sparse relative to the terrestrial environment. 5. In IoT-UWSNs, the sensor nodes have limited energy. Therefore, after the sensors deployment in an underwater environment, it is difficult to replace the node's battery as compared to terrestrial ones [3]. The characteristics of limited energy, high End to End (E2E) delay, high bit error rate and limited available bandwidth are the fundamental challenges in the underwater environment. In addition, the use of acoustic signals in the water depth make these issues more complicated, especially energy efficiency [4]. Radio and optical waves are not feasible in UWSNs because they get absorbed and scatter in the water rapidly. On the contrary, acoustic signals are preferred in the underwater environment because of their low absorption and scattering rate. However, they face a high E2E delay due to low propagation speed. Acoustic signals are strong near the source and become weak as moving away from the source [4]. These signals are impaired with noises in the sea due to which signals get attenuated during propagation. This attenuation causes a high bit error rate and if this error is more than a certain threshold, ultimately the packet gets dropped. Furthermore, the major noises in the sea come from the shipping, wind and turbulence. However, intuitively at the bottom of the sea, the environment is much quieter as compared to the sea surface. Due to these reasons, different protocols have been proposed by the researchers in IoT-UWSNs, i.e., Depth Base Routing (DBR) protocol is proposed to avoid the void hole issue in UWSN [5]. In the same way, Weighting Depth Forwarding Area Division DBR (WDFAD-DBR) protocol is suggested to handle the void hole problem [6]. However, it considers only 2-hop neighbor information for forwarder node selection to minimize the chance of void hole presence. Moreover, some backward transmission based protocols are also proposed to tackle the issues of the void hole occurrence, interference and collision-free transmission [7]. However, these strategies have not outperformed.