A MAC Protocol For Communication In Constellation Self-organizing Network

Since the end of the last century,study of small satellites has been concerned by scientists in various country's aerospace industry.As a new development in the field of space science and technology,the distributed satellite constellation ad hoc network can use portable and nimble small satellites to replace the complex and huge satellites,because small satellites have the advantages of small fee,strong anti-destroying ability,good performance,high reliability,adaptability,short development cycle and so on.Several small satellites based on the master-slave model complete a large satellite group network to complete the function of GEO and micro satellites formation flying composed by several micro satellites forms the micro satellites network.They collaborate communication,co-chaired the information collection and processing,communication,and they are widely used in deep-space exploration,scientific experiments,detecting three-dimensional mapping observation and military communications applications and other fields.The main work and innovations of this thesis are as follows:1.For small satellites based on the master-slave model to complete a large satellite group network to complete the function of GEO,once being a weapon against satellite nodes,tasks need to leave the network failure or malfunction,if not rebuild the network,the system function will be greatly affected.Since the satellite network has the features of greater number of small satellites,flexible structure,to extend communication,this thesis proposes a mac protocol for random access communications based on automatic conversion constellation from the main mode.This protocol starts with the selection of a parent satellite,which is the data communication and operation controlling center of the whole system,according to the survival time of the satellite link.When a satellite quits or a new satellite joins the satellite communication network,a new parent satellite would be selected to make up a new ad-hoc network.This protocol also makes an analysis on the main technologies that applied in the thesis,such as the MAC mechanism when a subordinate satellite is accessed to the parent satellite,the stability management of the whole system and the techniques of designing the frame format.2.For satellites formation flying,a number of small satellites would fly around the earth in a certain system and communicate with one another in a geometrically close distance to fulfill the task.In case the direct transmission fails,relay satellites will be applied to assist the transmission.By improving the traditional CSMA competitive activation mechanism,this thesis obtains the optimal relay selection mechanism.The transmission rate of each small satellite in the formation flying various and this leads to the delay of the original contention access's transmission period for neglecting the transmission speed of the relay satellite.To solve this problem,this thesis prioritizes the relay satellites according to their transmission speed by using the improved algorithm and selects the relay satellite according to its priority.The simulation result shows that comparing to CSMA competitive mechanism,the improved algorithm reduced the transmission period and improved the throughput performance of the whole communicating system.