Dynamic Topology And Network Overhead Research For Ocean FANETs Routing Protocol

With the strong support for marine industry,the demand for wireless communication technology in offshore operations is gradually increasing,but research on the ocean Internet is still in preliminary stage.Due to the complex ocean environment and broad area,traditional self-organizing network(Ad Hoc Network)cannot be well used in the ocean scene.In order to solve this problem,a self-organizing network called FANETs(Flying Ad Hoc Networks)composed of multiple small UAVs can gain great advantages in applications such as marine patrol and marine search and rescue with its excellent economic prospects,high flexibility and rapidity in completing tasks.As a key technology in FANETs,routing protocol is mainly used to determine different transmission paths through different node distribution,however,due to the high mobility and short connectivity of UAV(Unmanned Aerial Vehicle)nodes,the network topology changes more frequently,making the traditional ad hoc networks routing protocols cannot be applied well in FANETs.Therefore,this paper optimizes the traditional routing protocol based on the network characteristics of FANETs,so that it can be better applied to ocean environment,the specific work is as follows:Firstly,the OLSR(Optimized Link State Routing Protocol)protocol was selected based on the analysis of network characteristics in ocean FANETs and traditional routing protocols.The feature of FANETs network in ocean scene are measured by using the optimal link quality indicator ETX(Expected Transmission Count),namely OLSR-ETX protocol.Then,an optimal MPR(Multi Point Relay)set selection algorithm based on node link expiration time and residual energy is proposed.On the one hand,because the traditional OLSR protocol selects MPR according to the connection degree of nodes,the characteristics of fast dynamic change of nodes and short link connection time in FANETs may lead to those nodes with a higher degree of connectivity move out of the communication range.Therefore,this paper recalculates the ETX indicator by considering the speed and relative position of UAVs to predict the node link expiration time(Link Expiration Time).On the other hand,due to the limitation of payload in small UAVs,sufficient battery capacity is required,so an energy threshold is introduced to avoid selecting those nodes with low energy as MPR.The simulation results with the NS-3(Network Simulator)tool show that the new algorithm has better performance than the original one.Finally,A HELLO information transmission based on genetic algorithm is proposed.Specific to unnecessary network overhead in the ocean FANETs network,which is caused by a fixed time interval value approach to send HELLO packets in the standard OLSR protocol.Each node could select the better parameters for the HELLO packets interval value depending on the network topology changes,further hoping to improve network routing overhead without damaging end-to-end delay and packets delivery ratio.The NS-3 simulation results show that the OLSR-ETX protocol optimized by the GA algorithm could save about 10%of the overhead.