Adaptive link quality routing protocol for UASNs with double forwarding modes

Underwater Acoustic Sensor Networks (UASNs) has been used in various fields. However, UASNs is characterized by long delay, poor and time-varying link quality and unequal node distribution. Opportunistic routing (OR) uses broadcast forwarding to overcome poor link quality, but it increases delay compared to unicast forwarding, and most OR protocols cannot overcome routing voids. This paper proposes an Adaptive Link Quality Routing Protocol (ALQR) with double forwarding modes to solve these problems. This protocol innovatively selects the forwarding mode adaptively by link quality and uses distance vectors to construct candidate set to avoid routing voids and long detour. First, a new query algorithm is proposed to obtain the residual energy of neighbors and establish all distance vectors between sensor nodes and sink nodes, reducing the overhead of control packets. Distance vectors guide senders to determine the candidate set and avoid routing voids and long detours based on the shortest path principle. Second, an improved triangle metric is introduced to measure the accurate link quality. Based on this, a novel forwarding strategy combining unicast and broadcast is proposed. The unicast forwarding mode directedly select next hop based on route cost, which shortens the delay. Moreover, a new priority-based waiting-competition mechanism is proposed to determine the forwarding nodes in the broadcast forwarding mode, reducing redundant packets. The simulation results indicate that ALQR outperforms other routing protocols in terms of end-to-end delay and energy consumption when sacrificing little PDR. Specifically, delay is reduced by an average of 37.51% and 19.54% and energy consumption is reduced by an average of 35.01% and 16.41%, compared to DBR and DVOR.