A Multi-flow Bi-directional Transmission MAC Protocol For Multi-hop Underwater Acoustic Sensor Network

In recent years,the potential use of the Underwater Acoustic Sensor Network?UWSN?in various applications has gradually attracted researchers'attention.The communication of the underwater network is not connected with the ground network using radio waves,and it mainly depends on the sound waves.A series of difficult problems such as long propagation delay and limited bandwidth make the Medium Access Control?MAC?protocol face huge challenges in the design.For the MAC protocol based on the random access type,the ALOHA protocol originally designed for the radio network is the most basic,and it is also tried to be used underwater under the condition of light load.However,due to the lack of anti-collision mechanism,a large number of collisions will occur,and the cost of retransmission of special data underwater due to the environment is very high.In order to achieve better performance in underwater networks in recent years,many random access-based MAC protocols have been proposed for underwater networks.For example,UWAN-MAC_[22],ALOHA-CA and ALOHA-AN_[21]consider long propagation delays.And shorter control packets to mitigate collisions,but only work in single-hop network scenarios.In order to propose an effective MAC protocol for multi-hop networks,we have studied the MAC protocol based on handshake.Handshake-based MAC protocols,which have been widely used in terrestrial radio channels,are not suitable in underwater environments because they are designed to support high data rates and negligible propagation delays,which are exchanged during the handshake process in underwater acoustic networks Control packets involve large delays.In addition,when relaying in a hop-by-hop handshake in a traditional underwater multi-hop network,the end-to-end delay will increase significantly.Therefore,this paper proposes a MAC protocol suitable for multi-hop underwater acoustic sensor networks,which is called the multi-flow bidirectional transmission MAC protocol.This protocol implements multiple data streams in a multi-hop network to simultaneously transmit data from the sending node to different destination nodes.During the handshake process,the relay node between the source and destination nodes will advance with the next node before the previous node completes the handshake.The hop relay nodes start handshake,while reducing the control packet exchange time in a cascade manner and retaining the multi-hop channel,if the nodes on the data stream have data packets to transmit on the same data stream in the reverse transmission process,then Channels can be reserved during node handshake and data exchange to complete reverse transmission.Once the channel reservation is successful,multiple data packets can be sent to improve channel utilization,reduce end-to-end delay,and achieve better performance in a high-traffic,multi-hop environment.This paper compares the existing MAC protocol with a hop-by-hop handshake in the existing underwater multi-hop network through simulation experiments,and proves that this protocol has higher network performance in multi-hop networks.