Delay-Constrained Data Transmission Methods In Flying Ad Hoc Networks

Due to the flexibility,ease of deployment,low cost and scalability,UAV(Unmanned Aerial Vehicle)has been widely used in different scenarios.However,single-UAV systems are limited in their simple functions and coverage,hence they cannot expand to more applications.In order to overcome the shortcomings of the single-UAV systems,the network that establishes an ad hoc mode with the cooperations among different UAVs,called FANETs(Flying Ad Hoc Networks),is used to expand the application area.In FANETs,each UAV can communicate with GB(Ground Base)in a single-hop or multi-hop manner,and act as a source node or as a relay node to help other UAVs transmit packets.Compared with the single-UAV systems,the flexibility and scalability of FANETs allow UAVs to select different communication modes while also permitting UAVs to fly freely within a certain area to expand the monitoring scope.Although FANETs have many advantages,the high-speed mobility of UAVs causes the dramatic changes in network topology,in which case the multi-hop path selected for a source and GB will be quickly out of service.The instability of the link state among UAVs requires the relay nodes to frequently exchange messages with their neighbors to maintain the connectivity,which not only reduces bandwidth utilization but also increases the single-hop transmission delay.In addition,the signals transmitted among UAVs are susceptible to external interference,which affects the reliability of single-hop transmission in FANETs to some extent.The dynamic topologies increase the cost to collecte global information for each node,but the absent of global information does not effectively reduce interference signals and control the congestion level of the links.Therefore,it is a key and difficult issue to design a data transmission method which not only adapts to the dynamic topologies,but also meets the requirements of delay constraint.This dissertation focus on the delay-constrained data transmission methods in FANETs that includes four problems: delay-constrained routing problem,energy efficiency maximization problem,interference control problem,and congestion control problem.1.This dissertation proposes a delay-constrained stochastic routing algorithm.To solve the problem of real-time routing adapted to the dynamic topologies,a delay-constrained stochastic routing algorithm is proposed.In the absence of end-to-end delay information,the packet can arrive at GB within the delay threshold,while improving the network throughput and reducing the consumption of network resources.The algorithm requires each sender to select a set of available relays according to the location and channel state of its neighbors,and calculates the transition probability for each node in the set by combining the residual delay of the packet with the distance from the relay node to GB.According to the transition probability and local channel state,the senders transmit the packet to the relay nodes.The convergence of the algorithm is proved and its performances are verified by simulation.2.This dissertation proposes an energy efficient and delay aware transmission algorithm.To solve the problem of the energy efficiency maximization with meeting the requirement of real-time transmission,an energy-efficient and delay-aware transmission algorithm is proposed.In the absence of global information case,the algorithm can effectively reduce the energy consumption of the entire network,and enable each packet meet the requirement of delay constraint.The energy consumption of nodes,the single-hop transmission delay and the distance to GB are viewed as optimization objectives,and dual decomposition technique is used to eliminate the coupling constraints among data streams.Then the solution of the problem is obtained based on gradient method.On the premise of pre-determined optimal path,each relay node uses the cooperative transmission and the solution obtained to transmit the packets to GB.The time complexity and optimality of the algorithm are analyzed and its performances are verified by simulation.3.This dissertation proposes a delay-constrained interference control algorithm.To solve the interference control problem with end-to-end delay constraints,a delay-constrained interference control algorithm is proposed to reduce the interference signals on each link without the global channel states,while ensuring the reliability and real-time of data transmission.The algorithm calculats the average cumulative interference level to reduce the amount of messages exchanged among nodes,estimates the single-hop transmission delay according to the residual delays of data packets and the distance between nodes,and takes it as the local delay constraint.Combine the dual decomposition method and single-hop transmission delay to eliminate the coupling relationship among data streams.The relay nodes get the solution of the problem according to the local channel state and tansmit the packet to GB.The performances of the algorithm are analyzed and its convergence is proved.4.This dissertation proposes a delay-constrained congestion control algorithm.To solve the problem of congestion control with meeting the requirement of end-to-end transmission performance,a delay-constrained congestion control algorithm is proposed,which can reduce the congestion level on each link without end-to-end congestion information,and meet the delay constraint as well as improve network throughput.The algorithm introduces a delay scale factor as the weight that the delay threshold is allocated to each link proportionally,and combines it with the dual method to eliminate the coupling constraints among data streams.Because the changes of channel states lead to different delays on each link,the sources and relay nodes update the data generation rate and dual parameters asynchronously according to the received local information,and transmit the packet to GB by using the obtained optimal values.The performances of the algorithm are analyzed and its convergence is proved.