Designing And Modeling The Time Synchronization Protocol For UAV Ad Hoc Networks With Narrow Beam Directional Antennas

Unmanned aerial vehicles(UAVs)can carry out bait,reconnaissance,surveillance,target indication and damage assessment in the battlefield area,even unmanned attack.It has become an important combat unit in modern warfare.Researchers have suggested that building UAV Ad hoc networks over the battlefield can not only ensure UAVs cooperate in accomplishing various combat missions,but also can build multi-hop,flexible and efficient communication link for other combat units in the theater of war and provide communications security for the modern warfare under the condition of informatization.In order to improve the stealth performance of UAVs under the condition of over-the-horizon,the next generation of advanced UAV data link system has to use narrow beam directional communication with good RF stealth performance and anti-jamming capability.In this paper,we analyze the advantages of the synchronous networking under narrow beam directional communication.we explores the master-slave synchronization protocol and the fine synchronization efficiency analysis method for the UAV Ad hoc networks.The main contributions of the paper are as follows:1.We propose a narrow-beam-directional master-slave synchronization protocol for UAV Ad hoc networks.In this protocol,the node that initiate time synchronization in the network is recorded as the master node and the node that is synchronized with the master node is recorded as the slave node.The master-slave synchronization process contains two phases:coarse synchronization phase and fine synchronization phase.During the coarse synchronization phase,the master node initiates the synchronization process by broadcasting a coarse synchronization frame.During the fine synchronization phase,the slave nodes that receive coarse synchronization frame successfully will interact directionally with the master node through the fine synchronization request frame and the fine synchronization response frame to eliminate the clock deviation.The slave node that have finished the synchronization will continue to broadcast the coarse synchronization frame to the neighbor node as a master node,thus realizes the time synchronization of the whole network.At the same time,the protocol takes into account the two communication modes,namely,directional transmissionomnidirectional reception and directional transmission-directional reception.The simulation results show the effectiveness of the protocol.2.Aiming at the process of slave node contending to send fine synchronization request frame,we carry on the mathematical modeling and the analysis and find the optimal value of the fine synchronous random competition window under different network conditions.The single-hop transmission distance of UAV nodes is large,and there may be a large signal propagation delay between master and slave nodes.Therefore,the effectiveness of fine synchronization between master-slave nodes plays an important role in improving synchronization accuracy.From the propsed synchronization protocol,it can be seen that during the synchronization,there may be multiple slave nodes have aligned with the master node after coarse synchronization phase.In order to prevent multiple slave nodes from simultaneously sending fine synchronization request frames to the master node,we adopt a transmission competition mechanism based on random backoff and listening.Obviously,the value of random backoff parameters has a significant effect on the fine synchronization efficiency.In this paper,we propose a two-dimensional Markov chain model for fine synchronization request frame transmission process.We find the optimal value of the fine synchronous random competition window by solving the model,which provides the theoretical support for the optimization of synchronization efficiency.