Design And Mplementation Of Protocal Software For Satellite Mobile Communication Experiment System

Satellite communication technology has the advantages of long communication distance,large coverage,wide frequency band,and large capacity,and is not affected by natural disasters such as typhoon,tsunami and earthquake as well as man-made wars.It is widely used in scenarios such as disaster relief,military af-fairs,exploration,and remote areas communication.It is the key technology to achieve the goal of enabling people to communicate with anyone at anytime in anywhere.This paper studied the design and implemen-tation of satellite mobile communication system protocol stack which is compatible with terrestrial mobile communication system.At first,this paper studied the satellite mobile communication technology and focused on the differences between the satellite communication and the terrestrial communication scenes.The overall architecture of the satellite mobile communication is described and the protocol stack for satellite communication scenarios is introduced bearing the difference between satellite and terrestrial communication in mind,Secondly,this paper proposed a solution to the access problem considering the long-time delay of satellite transmission and rapid TA change brought by satellite rapid movement.The solution is divided into two parts:the physical layer part and the MAC layer part.At the physical layer,a random access preamble sequence structure based on polarity extension is proposed to adapt to the long delay in the satellite transmission.At the same time,a new TA adjustment strategy based on downlink tracking is proposed to adapt to rapid changes in TA.At the MAC layer,a data structure of random access response suitable for LEO satellite environment is designed to cope with long delay,and a reasonable time is allocated for the timeAlignmentTimer timer to adapt to the rapid change of TA.These modifications allow the communication system to adapt to the long delays and rapid TA changes in satellite transmission scenario,while achieving compatibility with terrestrial communication systems.Finally,the entire communication system including the protocol stack was implemented using the open SDR software and hardware.The hardware device uses usrpb210,three computers,e3372 dongle and or-dinary commercial mobile phones;the software uses EURECOM launched OpenAirInterface(OAI).First of all,different computers are configured to meet the requirements of implementation,then the core network software and base station software were installed in different computers,then the configurations and database parameters are appropriately set so that the homemade SIM card inserted into the UE can access the base station and core network.Finally,the performance test is carried out and the result of the test is that the transmission rate of the constructed communication system is high and stable.