# Adaptive Power-Controlled Depth-Based Routing Protocol for Underwater Wireless Sensor Networks
## 2 Related Works  
Routing protocols play a crucial role in determining the forwarding behavior of nodes, and well-designed routing protocols can ensure the efficient delivery of data packets to their intended destinations at a minimal cost. The unique characteristics of the underwater acoustic channel pose significant challenges to the design of routing protocols for underwater wireless sensor networks (UWSNs). In order to address these challenges, researchers have proposed numerous routing protocols specifically tailored for UWSNs. The deep-based routing (DBR) protocol, proposed by [PERSON] et al. in 2008 [6], was the first pressure-based routing protocol for underwater sensor networks. DBR effectively avoids the stringent requirement of acquiring full-dimensional location information for sensor nodes. Instead, it utilizes the depth information of each node to select transmission paths and deliver data to the destination node. The advantages of the DBR routing protocol lie in its elimination of node localization, its simple data packet forwarding strategy, and its wide applicability to various scenarios. However, there are limitations to consider. The greedy strategy employed in DBR, which relies on local information flooding through broadcasts, can result in excessive energy consumption and a reduced network lifetime. Additionally, the absence of intermediate nodes that meet the depth information criteria within the transmission range can lead to routing holes, causing a decline in network performance. To optimize DBR, [PERSON] et al. proposed the energy-efficient depth-based routing (EEDBR) protocol [7]. EEDBR adopts a sender-based routing strategy, where the sender selects the forwarding nodes based on the information of its neighboring nodes, such as depth and remaining energy. By doing so, the sender can choose a limited number of suitable relay nodes, reducing redundant data packets and achieving a balance in energy consumption among sensor nodes. To address the issue of sensor nodes in the mid-depth region consuming their energy earlier compared to higher-depth regions in EEDBR, [PERSON] et al. [8] proposed the enhanced energy-efficient depth-based routing protocol (EEEDBR). The study introduced a partitioning approach and deployed backup nodes specifically in the mid-depth region to mitigate this problem. [PERSON] et al. proposed a hybrid depth-based routing mechanism called energy-balanced hybrid depth-based routing (EBH-DBR) [9] to address the issues of energy imbalance and shortened network lifetime in UWSNs. The study assumed that all nodes were within one-hop range of a surface buoy node. Nodes can transmit data packets directly to the receiving nodes in a one-hop manner or through relay nodes by adjusting their communication range. Network fragmentation is employed to control the number of hops, balancing node energy consumption and achieving a longer network lifetime and higher throughput. [PERSON] et al. [10] proposed the IoT-enabled depth-based routing method (IDBR) to efficiently utilize energy resources. This method not only achieves energy efficiency but also provides insights for the future development of space-air-ground-sea integrated networks. Due to the traditional waiting mechanism used in depth-based protocols, there is a trade-off between network latency and the ability to suppress duplicate packets. The aforementioned depth-based protocols are all multi-route routing protocols. While forwarding duplicate packets improves packet delivery rates, it also introduces issues such as packet collisions and energy consumption. Therefore, in order to reduce energy consumption and enhance the overall performance of UWSNs, many researchers have adopted single-route routing schemes when designing routing protocols. [PERSON] et al. proposed a layer-based energy-efficient routing (LEER) protocol in [11], where nodes select the next hop based on residual energy and one-hop delay for data forwarding. In [12], [PERSON] et al.