Research On Simulation And Modeling For GEO Satellite Mobile Communication System Based On OPNET

Satellite mobile communication system has became an important component in mobile communication field, because its spotbeam coverage is very large and its relay carrier stays in the space which is not easy to be destroyed. Especially, Geosynchronous Eearth Orbit (GEO)satellite mobile communication system has the characteristic that the system is stable, three stars can cover all areas except the poles and the frequent handover is not necessary. Thus, the research of GEO Satellite mobile communication system has attracted increasing attention in the field of satellite mobile communication. In real application, the construction of GEO satellite mobile communication system is a complicated project, So the research of the simulation and modeling of GEO satellite communication system is quite necessary.The background of this paper is based on the research of certain satellite commucation system project, and research for building the simulation model of GEO satellite mobile communication system on OPNET is done. The main researching contents are given as following:Firstly, the architecture of system, frequency division multiplexing (FDM) technology,time-division-multiple-access (TDMA) technology and working process of system in Gestationary Earth Orbit Mobile Radio Interface (GMR-1) standard is studied deeply in theory. The mapping from logical channel to physical channel, the spotbeam selection algorithm and the timing synchronization algorithm are analysed in detail, as well as the commucation process including transmission schedule of system information, access, paging,communication, network interruption and call clearing. Moreover, some details in GMR-1 system is simplified and modified in this paper.Secondly, the mechanism of model construction based on OPNET is introduced.According to GMR-1 standards, the model of the satellite, the Mobile Earth Stations (MES)and the gateway stations (GS) is build by OPNET as well as the corresponding processing model. The multibeam antenna for users is designed and the communication link model is analyzed. Different functions of the system are realized.Then, three different scenarios of network simulation are set up, The performance of spotbeam seletion process, the determination of the spotbeam selection parameters, the situation of timing synchronization, and performance of access, paging and interruption are simulated and analysed. The simulation results show that system performaces can meet the demand. The rationality and correctness of the system design solutions are verified. This work povides guidance and advice for the construction of the latter actual system.Finally, considering the antenna's oscillation phenomenon, the performance of spotbeam selection for some users under antenn oscillation is analyzed. Thus,an improved spotbeam selection algorithm is proposed. This algorithm could dynamically set hysteresis by the distance between the Mobile Earth Station and Gateway Station of it's spotbeam. By simulating and comparing, it shows that improved algorithm can descrease the wrong times of spotbeam selection under antenn oscillation and develop performance of antenn oscillation.