An Automatic Repeat Request Strategy for Contention-Free MAC protocol in Underwater Acoustic Communication Networks

The Contention-Free MAC protocol in underwater acoustic communication channels efficiently utilizes the narrow bandwidth of acoustic waves for data transmission. However, since it does not use any handshake protocol before transmitting data, the packet collision rate at the receiving node is often high due to the low propagation speed of acoustic waves in the underwater environment. When collisions occur, transmitting nodes must enter a sleep state and wait for a certain period before waking up and retransmitting the packet. If sensor nodes transition into sleep mode and then return to transmission mode at inappropriate times, it may lead to further collisions in subsequent transmission steps, causing continuous transmission disruptions. In this study, we propose an Automatic Repeat Request for Contention-Free MAC protocol (ARQ_CF). In the ARQ_CF protocol, a sending node with a packet to transmit or one that has just experienced a packet collision will listen to the channel state. Based on the observed channel state and the type of packets it receives, the node calculates an appropriate sleep and wake-up time to avoid further packet collisions. We will simulate and evaluate the effectiveness of the protocol to demonstrate that the ARQ_CF strategy can reduce the number of retransmissions due to packet collisions at the receiving node. As a result, it significantly improves the packet delivery success rate and enhances the efficiency of channel resource utilization for data transmission.