# WLQRP: A Weighting Link-Quality-Based Routing Protocol for Underwater Sensor Networks
## 2 Related Works  
Starting with this section, we provide an overview of the research performed on routing protocols in USANs. This includes a comprehensive analysis of their strengths, weaknesses, and challenges. It then introduces the WLQRP proposed in this article. In UASN, routing protocols can be divided into three-dimensional location-based routing, depth-based routing, and location-free routing. Three-dimensional position-based protocols include VBF, HH-VBF, AHH-VBF, DFR, FBR, etc. Depth-based routing protocols include DBR, FDBR, VAPR, EEDBR, and Hydro Cast. Location-free routing is divided into cluster routing and beacon routing. The VBF (vector-based forwarding) protocol [10] utilizes the geographic location information of each node to create a virtual pipeline between the source node and the sink node, and the nodes within or closer to the pipeline are more likely to be selected as the next node. However, when the number of nodes in the pipeline is small, the success rate of packet transmission of this routing protocol will be greatly reduced. The energy of nodes within the pipeline will be more easily consumed, which leads to an uneven energy distribution of nodes throughout the submarine network. The HH-VBF (hop-by-hop vector-based forwarding) protocol [11] and AHH-VBF (adaptive hop-by-hop vector-based forwarding) protocol [12], on the other hand, create virtual pipes at each hop to solve the problem of low transmission success rate at low node density. However, when the node density is higher, energy will be wasted excessively, and the data will have more conflicts. With the local topology information, The ACGSOR protocol [13] segmentation scheme divides the end-to-end path into several short opportunistic routing segments. Furthermore, a cooperation mechanism is applied to switch the transmission mode adaptively. However, the protocol consumes more energy. [PERSON] et al. [14] propose an adaptive multi-zone geographic routing protocol (AMGR) that dynamically adjusts the neighbor information acquisition interval according to the topology change speed. In ref. [15], The underwater network is first divided into small cube spaces; thus, the data packets are supposed to be collaboratively transmitted by unit of small cubes logically. [PERSON] et al. studied a different flood-based geographic solution using their directional flooding-based routing (DFR) protocol [16]. In this protocol, each node broadcasts packets to all its neighboring nodes. The decision of whether to forward the packet is based on the BASE_ANGLE, which represents the direction from the sender S to the forwarding party F and the destination party D (the receiver). This decision is made by comparing the BASE_ANGLE to the reference angle included in the package. The change in the underwater channel is addressed by gradually adjusting the reference angle based on the link quality. A smaller flooding area is achieved with a better reference angle. Since obtaining accurate underwater geographic information can be challenging or costly, some protocols make use of partial geographic information. Focused beam routing (FBR) [17] is based on the concept of multiple sensors and multiple channels, using multiple acoustic sources, receivers, and focused beamformers for data transmission. FBR can improve transmission distance and signal quality by focusing acoustic energy in a specific direction, overcoming water absorption and scattering problems. Multiple data streams can be transmitted simultaneously, increasing the data transmission rate and throughput. However, it also has problems in terms of high hardware requirements, diffusion overlap due to the multipath effect, and energy consumption. In [18], [PERSON] et al. propose a distance-vector-based opportunistic routing (DVOR) scheme to address void and detouring. [PERSON], [PERSON] et al. [19] proposed a depth-based routing protocol with a greedy algorithm, DBR (depth-based routing), which differs from other protocols in that it does not need to use specific geographic location information.