Research On Low Access Delay MAC Protocol In Aerospace Ad Hoc Networks

Aerospace ad hoc networks feature fast movement and wide coverage.Compared to the traditional networking modes of satellites or ground control centers,it has the advantages of shorter network delay and stronger survivability,so it must be the key technology for the future coordinated operations between military aircrafts.TTNT,Tactical Targeting Network Technology,has the characteristics of low delay and high reliability.The essence of TTNT is to control the media access load by monitoring channel utility and pursue high packet delivery reliability at the cost throughput.Therefore,for the high-performance of aerospace ad hoc networks,the real-time and accurate channel monitoring mechanism and distributed channel access algorithm based on load control are the key technologies.A frame scheduling method based on load statistical and adaptive threshold is proposed in this thesis.Firstly,the load statistics is researched and the load statistical method based on the serial number of burst is proposed.In this method,the current channel's load is determined by the serial number of burst without physical layer.Secondly,the priority threshold is studied.The expression of the highest priority threshold is analyzed and the influencing factors are derived.The recursive relationship between the remaining priority thresholds is deduced.Thirdly,the setting method of the highest priority threshold is researched.Because the threshold cannot be calculated by the formula and it will change during the period of operation,the method of adaptive threshold is proposed.The method uses the probability of successful transmission of the frame as feedback information,and it can accurately adjust the real threshold of system during the period of operation.Then,the channel access method of low-priority frame is studied.The reason why the reliability of high-priority frame is low and the throughput is unstable due to the back-off window is analyzed.Finally,the scheduling method of frame is proposed.In this method,the scheduling time of low-priority frame is calculated by the low-priority traffic and the channel remaining bandwidth of each node,and the channel access method of low-priority frame is controlled according to the scheduling time.The high reliability of high-priority frame and the stability of throughput are guaranteed.In this thesis,the Aerospace ad hoc network model is built on OPNET simulation software.Under this model,network simulation is performed by setting different network load and network size parameters.The simulation results show that the scheduling method of frame based on load statistical and self-adaptive threshold can effectively adjust the threshold adaptively to the real threshold of system during the period of operation,and it can ensure the low latency and high reliability of high-priority service.