Design And Implementation Of Multi-beam Satellite Communication Simulation System Based On NS3

As a component of aerospace networks,satellites are playing an increasingly important role in the field of global mobile communications,and the simulation and research of satellite communications systems are of great practical significance.At the 3GPP RAN meeting,nonterrestrial network solutions have been incorporated into the fifth-generation mobile communication(5G)standard,aiming to make up for the lack of terrestrial networks in signal coverage and service quality.5G NTN pointed out that non-terrestrial networks and terrestrial networks integration should focus on the elements,including mobility,cell mode,service continuity,frequency planning,link budget,wireless resource management,etc.With4 G and 5G as the entry point,combining the above elements,this thesis design and implement a multi-beam satellite communication simulation platform.The platform has completed the following tasks:First of all,complete the satellite-to-earth link design based on the link budget.The design indicators include satellite transmit power,user receive gain,link loss,and beam antenna gain.The first two indicators can be set according to the actual values of the satellite constellation system and the ground receiver,the link loss is related to the distance between the satellite and the ground.Obtain the ephemeris file related to the satellite motion parameters published by the North American Air Defense Joint Command recently on Celes Trak,and use the SDP4/SGP4 model to obtain the satellite coordinates at the wanted time.According to the distribution of the ground terminal,the distance between the satellite and the ground can be further obtained;the size of the antenna gain is related to the angle at which the user offsets the maximum gain of the antenna,which is determined by the connection between the beam center point,user coordinates and the satellite.The beam antenna model is designed to obtain the gain intensity corresponding to a given angle.In addition,through the movement modeling of the beam center point,the change of the maximum gain direction of the beam can be simulated.The link budget allows users and satellites to access and communicate.Secondly,in a multi-beam satellite communication system,the satellite is used as a base station and its beam is used as a cell.The handover between beams requires the establishment of an X2 interface.The establishment of a large number of unnecessary connections will occupy interface resources,resulting in low efficiency of the simulation system.This thesis proposes the solution of “only adjacency relationship between the cells represented by the beams and inter-satellite X2 links between satellites”.As a beam management entity,the satellite processes and forwards the signaling messages of all subordinate beams,realizes on-board processing.Inter-satellite interaction is completed through the X2 link,and the switching process and signaling content in ground mobile communication are adaptively improved,and beam handover under the same satellite and beam handover between different satellites are realized,so that the multi-beam communication simulation system can meet service continuity.Finally,verify and optimize the system performance through the design of the frequency reuse scheme.In view of the different distributions of the reference signal strength contours in the satellite beam coverage area,the thresholds for determining the edge users of the satellite inner and outer beams are different,and different edge user powers are designed.In addition,the proportion of edge users varies greatly,and the number of resource requests varies greatly.Based on the feedback from the MAC layer spectrum resource scheduling module,this thesis designs a new resource scheduling process to expand or contract the edge frequency band in the soft frequency reuse scheme.Based on the measurement results of edge users,the interference level of the resource block in the interference area is obtained,and the beam with the least interference is selected to allocate the corresponding spectrum resources,and the resource utilization rate is improved while the interference is considered,which verifies the availability and efficiency of the simulation platform.The multi-beam satellite communication simulation system designed and implemented in this thesis can complete the motion simulation of a variety of satellite constellations,multibeam simulation,and user distribution simulation.It has the function of beam switching under the same satellite and beam switching between different satellites to meet service continuity.Aiming at the characteristics of the multi-beam satellite communication system,through the design of the multi-beam dynamic soft frequency reuse scheme,the performance of the simulation platform is verified and improved.