Leo Satellite Communication System Simulation And Performance Analysis

Low earth orbit (LEO: Low Earth Orbit) satellite communication systems are abstract of the actual system. When designing a simulation system, we hope it with full function, and work flow of the simulation system is as close as possible to the real system. And implementation manner is simplified to reduce the complexity of the system. LEO satellite communication system could play an important role in future mobile communication due to their characteristics, such as global coverage and low propagation delay. Due to the particularity of LEO satellite communication system, such as the long period and the huge funds needed in the construction and the difficulty to change after system being finished, the precise simulation before the implementation of the LEO satellite network is necessary.In this dissertation, ground core network, user terminal and satellite nodes of LEO satellite communication system are modeled. One working mode of the constellation satellites system which is named transparent transponder one is simulated by OPNET Modeler software, and working flow and system specification related to network layer are also verified. Finally, when abnormal situations occur in the system, especially when a gateway of ground core network becomes invalid, analyze the influence on the system.Chapter 1 gives brief introduction of satellite communication system structure and current development, making the detailed introduction about signaling system work flow of the LEO communication satellite system. Then the main work of this dissertation is introduced.In chapter 2, mainly makes a comprehensive analysis for the ground core network models of LEO communication satellite system, including the gateway stations, routers and the central database HLR (Home Location Register) node models. Besides, user terminal node is also modeled. The simulation results can verify the call flow and the security flow of the LEO communication satellite system.In chapter 3, the OPNET modeling of constellation satellite node with multiple-beam antenna is designed. The satellite node is more versatile for combining with the OPNET software's characteristic including the orbital document, the multiple beam antenna modeling and the wireless pipeline stages. Because multiple-beams antenna between transmitter and receiver have different pattern, uplink handover process is independent from downlink one. Combining with the radio resources management of the system, handover performance of the system is verified by simulation.Chapter 4 gives analysis for the abnormal state of LEO communication satellite system, including call being interrupted, the recovery procedure of the invalid gateway and disaster recovery design of the central database HLR. The signaling loss ratio caused by invalided gateway is obtained by simulation.The dissertation is summarized in chapter 5. Finally, the future research work is pointed out.