Research On The Channel Access And Relative Positioning Protocol Of UAV Swarm Ad Hoc Networks

In recent years,the new concept of UAV swarm combat has been widely concerned by researchers.The UAV swarm consists of a large number of small,inexpensive,highly mobile UAV nodes.The nodes interconnect through wireless ad hoc network technology and build a functional intelligent warfare system,which is important in military application.Closely combining characteristics of the UAV swarm with operational requirements,we find it hard to design a flexible and highly efficient protocol stack for UAV swarm ad hoc networks,and it has become a research hotspot in this field.In this paper,we focus on two difficult problems in the design of the protocol stack for UAV swarm ad hoc networks: the channel access protocol and the relative positioning protocol.The main contributions are summarized as follows:(1)There are lots of nodes in the UAV swarm network,and the UAV can be easily destroyed by enemies and needs to be replenished quickly during the process of the task.Frequent network exiting and entry of nodes leads to high mutual synchronization overhead for all nodes in the network,so it is difficult to obtain high channel utilization by the channel access and sharing way of time division multiple access(TDMA).In contrast,the channel access based on carrier sense multiple access(CSMA)does not depend on node synchronization,it is highly flexible,and permits nodes to access to the network quickly,so it is more suitable for UAV swarm ad hoc networks.At present,the carrier sense channel access protocol has been widely used in short-distance wireless networks,and these protocols generally adopt a random backoff method to avoid signal collision.However,under the condition of long-distance UAV swarm networking,can the above channel access protocols remain optimal network performance?In this paper,we study the channel access protocol with carrier sense/ random backoff.Through mathematical modeling,we analyze the relationship between the saturation throughput performance and the random backoff slot quantitatively in the rapid dynamic changes of,and describe the correlation between the optimal random backoff slot and network topology structure.Due to the rapid dynamic changes of the UAV swarm ad hoc network topology structure,the optimal value of the random backoff slot is difficult to set accurately in practical applications.We further adopt the method of P persist instead of random backoff to avoid collisions,and analyze the network saturation throughput of the carrier sense/ P persist protocol,and reveal the relationship between the number of nodes and the optimal contending transmission probability P.It is proved that P persist is able toachieve better saturation throughput performance than the random backoff protocol.In practice,under the condition that the size of UAV swarm ad hoc network is relatively stable,due to the total number of nodes in the network,we can determine the value of the optimal contending sending probability P according to the conclusion of this paper.(2)The relative positioning is the foundation for nodes in the UAV swarm ad hoc network to avoid collisions,cover intensively and operation intelligently against enemies.Based on the known information of the distance between nodes,we propose an efficient relative positioning protocol for UAV swarm ad hoc networks.The protocol adopts distributed competition method,and randomly generates four coordinate reference nodes in the current positioning cycle,and ensures that the remaining nodes in the network can receive the four coordinate references correctly,so as to achieve relative positioning.The execution cycle of the relative positioning protocol is determined by the changing speed of the network topology.We further use the method of Markov chain modeling to analyze the relationship between the value of distributed competition parameters and the relative positioning completion time,and determine the value of the optimal distributed competition parameters in a certain network scale.The simulation results demonstrate the validity of the proposed protocol and the correctness of the modeling analysis.