Research On Key Technology Of Underwater Acoustic Communication Networks Using Directional Transmission

In recent years,with the people's further exploration of marine development,underwater acoustic communication network technology has attracted extensive attention and has received unprecedented attention and application in military and civilian fields.Especially in the military field,it is critical to naval operations that the underwater battlefield of modern warfare has gradually evolved into a network-centered,underwater submersible nodes,underwater robots,submarines,and other combat units forming a network of teams to coordinate operations and frequent information exchanges are required,and they are highly efficient and reliable,also covert network communications.Therefore,improving the coverage of the underwater acoustic communication network,increasing the communication distance of the network node,enhancing the efficiency and reliability of the network communication,and realizing the concealed communication can greatly improve the naval combat capability.In previous studies of underwater acoustic communication networks,network's nodes are mostly equipped with non-directional transducers,adopting an omnidirectional data transmission mode,and sending data packets to the surrounding in a "broadcast" manner.This kind of data transmission mode is not conducive to energy convergence,it will reduce the network node single-hop transmission distance and network coverage significantly,lead to packet collisions easily,affect neighboring node communications and reduce network efficiency,at the same time it also disadvantageous to the hidden communication of network nodes.Directional communication technology can guide underwater acoustic signals to a specific direction and generate directional beams in that direction,so that the beam main lobe aligns with the target direction and achieves the effect of directional communication.Compared with traditional omni-directional underwater acoustic communication networks,underwater acoustic communication networks using directional communication technology can get many advantages: increase the single-hop transmission distance and network coverage of network nodes,reduce packet collisions and interference to adjacent nodes,and improve the network,and also increase communication concealment.It can well meet the needs of both the military and the people.Although there have been some relatively mature research results on wireless sensor networks for directional transmission and reception in the radio field,however,due to the great differences between underwater channels and radio channels,mature technologies in wireless sensor networks cannot be directly applied to underwater acoustic communication networks.In view of this,this paper studies several key technologies of underwater acoustic communication network based on directional transceiver,such as neighbor discovery mechanism,Medium Access Control(MAC)layer protocol,routing protocol and cross-layer design,and designs several practical neighbor discovery mechanisms and network protocols.Aiming at the difficulty of finding the neighbor nodes in the underwater acoustic communication network based on directional transceiving,and the hidden terminal problem and “deaf” node problem caused by gain asymmetry in the underwater acoustic communication network based on directional transceiving,this paper proposes a neighbor node discovery method based on HELLO/REPLY two-way handshaking mechanism in the underwater acoustic communication network based on directional transceiving.In the neighbor node discovery mechanism,only directional transmission is adopted to transmit and receive signals,so that hidden terminal problems caused by gain asymmetry can be avoided,and network coverage can be increased;The time is divide into a neighbor discovery time slot and a listen reply time slot,a node in that time slot is found to send a hello signal,then the reply signal of the neighbor node is received,the node in the listen reply time slot listen to the hello signal sent by the source node,and then the reply signal is replied,and the node realizes neighbor node discovery through a competitive hello / reply two-way handshake mechanism through direct discovery and indirect discovery,so that the problem of “deaf" node can be overcome,and the neighbor node discovery efficiency is improved.Simulation results show that under different network node density and the number of transmit antenna beam sectors,the neighbor discovery mechanism has shorter average discovery delay and higher neighbor discovery rate than the random two-way neighbor discovery mechanism.In order to solve the problem of unstable topology and frequent redundancy of data packets in underwater acoustic communication network,this paper proposes a neighbor discovery mechanism for directional transceiving underwater acoustic communication network.In the proposed neighbor discovery mechanism,the network nodes have two data transmission modes: directional and omni-directional.The neighbor nodes of the new nodes in the network are divided into two types: the neighbor nodes in the omni-directional transmission range and the neighbor nodes in the directional transmission range.The neighbor node discovery mechanism can complete the neighbor node discovery process by selecting some nodes from the neighbor nodes in the omni-directional transmission range as the neighbor node representatives.The proposed neighbor discovery mechanism does not require all neighbor nodes to participate in the neighbor discovery process,and the neighbor discovery process does not send redundant information,which can greatly reduce the network load and improve the network efficiency.This paper verifies the performance of the proposed neighbor discovery mechanism through theoretical calculation and software simulation analysis.The theoretical results are in good agreement with the simulation results.The simulation results also show that the number of neighbor nodes involved in the neighbor discovery process in the proposed neighbor discovery mechanism is less than the number of neighbor nodes in the omni-directional transmission range.Aiming at the problem of "deaf" node and hidden terminal caused by low throughput and directional data transmission technology in underwater acoustic communication network.A dual-channel underwater acoustic communication network MAC protocol(DADC-MAC protocol)based on directional transceiver is proposed.In the protocol,the underwater acoustic channel is divided into a data transmission channel and a busy prompt message channel,a node transmits a control frame and a data packet by using the data transmission channel,a transmitting node and a receiving node transmit a channel busy prompt message by using the busy prompt message channel in the communication process to inform the adjacent node of the ongoing communication so as to avoid the collision of the data packet,and a neighbor node discovery mechanism and a directional network allocation vector are also adopted in the protocol.DADC-MAC protocol can overcome the hidden terminal problem and deaf node problem in the network.Simulation results show that dadc-MAC protocol can complete more effective communication in the same time compared with MACA protocol and D-MAC protocol,which can significantly improve the throughput performance of underwater acoustic communication network based on directional transceiver.In order to solve the problems of low throughput,poor communication concealment and hidden terminal in underwater acoustic communication network,a directed transceiving underwater acoustic communication network MAC protocol based on sequential continuous handshaking mechanism is proposed.In the protocol,each node transmits and receives data in a directional mode,and does not need any prior information about the position of the neighboring node.The high-efficiency collision-free operation of the network is realized by sending RTS signals sequentially and continuously by sending nodes,maintaining the relative position information table of adjacent nodes and directional virtual carrier monitoring,etc.The protocol also effectively solves the hidden terminal problem caused by asymmetric gain in the network,obviously increases the network coverage and improves the communication concealment.Simulation results show that the proposed MAC protocol can significantly improve the throughput performance of underwater acoustic communication network.Aiming at the problems such as low delivery rate of data packets,high end-to-end delay,and delays in underwater acoustic communication network,a multi-path underwater acoustic communication network routing protocol(UMDR protocol)based on directional transmission and reception was proposed.In the UMDR protocol,each node maintains a routing table,which is different from the routing table maintained by the nodes in most routing protocols.In the UMDR protocol,the routing table maintained by the node records all possible arrival paths of the current node to other nodes in the network.The routing table is updated in real time by listening to packets sent within the network.Because multiple routes to any destination node are recorded in the routing table,when one of the routes is busy,the UMDR protocol can immediately select one of the standby routes to continue the packet sending process.When a packet delivery failure occurs on the network,the UMDR protocol initiates the route discovery process.Simulation results show that the proposed multi-path routing protocol can significantly increase the packet delivery rate and reduce the end-to-end delay of the network.Aiming at the limitation of hierarchical design on the performance of underwater acoustic communication network,a MAC/router cross-layer solution was proposed.In this scheme,the node is equipped with a smart underwater acoustic transducer.The transducer consists of multiple equal-sized transmit beam sectors.Each transducer beam sector has multiple transmit ranges and can be used as required during signal transmission.Flexible adjustment of transducer emission range.In the cross-layer design,the MAC protocol is based on the carrier sense multiple access method with a collision avoidance mechanism,combined with directional virtual carrier monitoring and other technologies,and the traditional directional network configuration vector update and four-way data transmission mode are adjusted to better Play the advantages of intelligent underwater acoustic transducers,reduce interference to neighboring nodes,reduce packet collisions,and improve network efficiency.At the same time,an underwater acoustic communication network routing protocol is proposed based on the minimum number of hops.When sending data packets,a node preferentially selects the path to reach the destination node with the least number of hops to transmit data packets.Simulation results show that the proposed MAC/routing cross-layer solution can significantly increase the network packet delivery ratio and reduce the network end-to-end delay.