# WLQRP: A Weighting Link-Quality-Based Routing Protocol for Underwater Sensor Networks
## 1 Introduction  
The ocean has an abundance of fuel, minerals, and biological resources, and it is a main channel for global transportation [1]. The oceans hold vast reserves of fuel, minerals, and biological resources, serving as a vital global transportation route. Over the past century, nations have progressively increased their investments in oceanic research. As oceanic development accelerates, the need for underwater communication becomes increasingly urgent. The underwater environment has become a focus of significant attention due to advancements in sensing technology, leading to the emergence of underwater wireless sensor networks (UWSNs) as a promising option for exploration. Underwater wireless sensor networks (UWSNs) constitute a critical component of underwater communication technology, playing a pivotal role in underwater monitoring, development, and defense applications [2, 3]. Unlike terrestrial wireless sensor networks (WSNs), UWSNs employ acoustic signals rather than radio frequencies for wireless communication. However, UWSNs face several inherent limitations, including prolonged and variable delays, narrow bandwidth, slowsignal decay, elevated error rates, and substantial noise [4; 5]. Consequently, link quality assumes paramount importance when forwarding messages to the sink node. The majority of sensor nodes are battery-powered, rendering them challenging to replace or recharge once deployed underwater. Therefore, energy efficiency ranks as a primary concern when designing routing protocols tasked with collecting sensor data and routing it to the sink node. Moreover, UWSN sensor nodes drift with hydrodynamics, necessitating the consideration of network dynamics stemming from topological fluctuations. In response to these challenges, this paper seeks to introduce a location-independent and energy-efficient routing protocol, wherein data packets are forwarded hop-by-hop from source sensor nodes to the sink node. The underwater acoustic communication routing protocol mainly solves the problem of data transmission between multiple nodes. The topology structure of the network, the period of data generation, the direction of data flow, and the flexibility of node deployment all affect the design of the routing protocol. In the past, two routing strategies have been presented: deterministic routing and opportunistic routing. In deterministic routing, if the network conditions do not change over time, the sender always selects the same node as the best next-hop node. In opportunistic routing, even if the network conditions do not change over time, the sender can choose different nodes as the optimal next-hop node [6; 7; 8]. Due to the unpredictability of link quality in underwater environments compared to changes in terrestrial radio links, opportunistic routing protocols can better handle changing network dynamics than deterministic routing schemes and are more suitable for networks in dynamic underwater environments [9]. The opportunistic routing protocol we propose leverages channel awareness and is designated as the weighting link-quality-based routing protocol (WLQRP). In contrast to conventional routing protocols, which predominantly focus on selecting the next-hop node when choosing relay nodes, WLQRP attaches greater significance to link quality's influence. WLQRP scrutinizes historical transmission success records among nodes, encompassing not only the past transmission success rate between nodes and their immediate next-hop nodes but also factoring in link quality to subsequent next-hop nodes. This comprehensive channel quality evaluation during data packet transmission culminates in selecting the optimal hop for each data packet. Consequently, WLQRP enhances relay node selection efficiency, elevates data packet transmission success rates, curtails packet retransmissions, and diminishes energy consumption. Furthermore, WLQRP can harness topological information to circumvent connectivity gaps and shadow regions during routing, effectively minimizing the likelihood of encountering voids.