Description

 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.