DBR-MAC: A Depth-Based Routing Aware MAC Protocol for Data Collection in Underwater Acoustic Sensor Networks

Abstract

Due to long propagation delays, routing discovery is very expensive in underwater acoustic sensor networks. Therefore, depth-based routing (DBR) protocols are usually preferred whose routing discovery cost is almost zero. However, DBR protocols working with broadcast medium access control (MAC) bring severe collisions especially in the data collection network. Moreover, in DBR, all the packets are forwarded from deep to shallow nodes along the direction toward the sink node. The directional packet transmissions may lead to load imbalance, where some nodes undertake most loads and we call these nodes key nodes. However, the majority of existing MAC protocols cannot provide the key nodes priority of accessing channel in the collision domain. It is necessary to design a MAC protocol coupling with DBR. In this paper, we adopt a cross-layer approach to propose a DBR aware MAC protocol called DBR-MAC, which smoothly integrates a handshaking-based MAC and a DBR protocol. It improves the throughput, energy, and time efficiency at the cost of fairness. A depth-based transmission scheduling scheme is introduced based on the depth information, angle information, and overheard one-hop neighboring nodes' transmissions to make key nodes have higher priority to access the channel than other nodes. DBR-MAC is a cross-layer scheme and its directional forwarding tries best to forward packets from source to the floating sink node by the least hops. Moreover, an adaptive depth-based backoff algorithm cuts down the backoff time for the nodes and prevents the congestions at key nodes. Extensive simulations show that the throughput, energy, and time efficiency of DBR-MAC outperform existing MAC protocols when applied in the data collection network.