Reliable Networking And Transmissions For Underwater Acoustic Networks

The features of low available bandwidth,high bit error rate,and long propagation delay in underwater acoustic channels bring many challenges to the reliable data delivery in underwater acoustic networks.The dissertation studies the medium access control(MAC)in the link layer,reliable routing and multi-hop forwarding in the network layer,and end-to-end reliability control from the perspective of the network protocol architecture,with the aim at achieving both link-level and path-level reliable networking and transmissions.The main research works and contributions are summarized as follows:1)Medium access control under space-time coupling:This work studies the principle oftransmission collisions in the underwater acoustic medium.We point out that the longpropagation delay makes the coupling of space and time,which determines the transmis-sion collisions in MAC.To address this challenge,we derive the space-time collision-free conditions and the probability for collision-free transmissions.Specially,we proofthat the underwater acoustic MAC has an annulus area for simultaneous transmissions.We further study a capacity maximization based collision-free MAC scheduling,whichis formulated as a mixed integer non-linear programming(MINP)problem.Based onanalysis of optimal scheduling strategies,we further design heuristic algorithms to solvethe problem.Simulation results show that our proposed algorithm reaches the optimalMAC scheduling in Star networks,and also outperforms the existing algorithm in Meshnetworks.2)Distance-vector based opportunistic routing:This work proposes a distance-vectorbased opportunistic routing(DVOR)protocol to address the communication void regionand long detour problems in depth-based routing protocols.DVOR stablishes the distancevectors by exploring the query mechanisms in sensor networks.It is a light-weight routingprotocol,since it does not need complex signaling exchanges to select relay candidates andcoordinate the packet forwarding among potential relays.DVOR can effectively avoid thecommunication void region and the long detour,thus achieves opportunistic and reliablepacket forwarding.Simulation results show that DVOR outperforms the existing DBRand DUOR protocols in packet delivery ratio,average hop counts and end-to-end delay.3)Cross-layer end-to-end reliable opportunistic transmissions:To achieve reliable transmissions,this work proposes a cross-layer forward error control(CL-FEC)mechanism,which adopts fountain codes for packet-level FEC and channel codes for bit-level FEC.CL-FEC does not rely on the per-packet acknowledgment by implementing opportunistic transmissions,which can address the error-prone feature of underwater acoustic channels.Furthermore,we propose a discrete stochastic approximation based online algorithm to optimize the end-to-end throughput to further improve CL-FEC,which can address the long propagation delay in underwater acoustic channels.Simulation results show that CL-FEC can improve the transmission throughput.