| The navigation satellite inter-satellite link connects all navigation satellites in space.Through two-way measurement and communication,on the one hand,highprecision inter-satellite pseudo range and clock difference observation can be obtained,shortening the ephemeris update cycle,and improving the ability of navigation satellite constellation to maintain the space-time reference independently;on the other hand,For information transmission through inter-satellite,the shortcomings such as limited coverage caused by traditional reliance on ground monitoring networks can be overcome,and the indirect measurement and control of navigation satellite constellation of "one satellite to all,star to all" can be realized.According to the different physical media of signals,navigation satellite inter-satellite links can be divided into two categories: microwave inter-satellite links and optical inter-satellite links.Compared to microwave inter-satellite links with mature technology and engineering business operations,the optical inter-satellite link technology that has emerged in recent years and has significant advantages in high-precision measurement and high-speed communication.In terms of ranging accuracy and full duplex communication rate capabilities,it has increased by 2 and 4 orders of magnitude compared to the current Ka band inter-satellite links.It also has advantages such as resistance to radio interference,equipment miniaturization,and low power consumption,which has high application potential.However,in high dynamic and long-distance space environments,the acquisition and tracking mechanism of optical inter-satellite link signals with directional narrow beams by satellites is very complex.The establishment of their links requires more complex constraints than microwave inter-satellite links,such as the range of viewing field of optical telescopes,laser terminal attitude,and the number of links that can be carried by the terminals.These constraints directly affect the design of integrated signal systems for measurement and communication,as well as the topology of satellite optical inter-satellite link networks.However,there is currently a lack of systematic and in-depth research on these constraints both domestically and internationally.Therefore,under the background that the current navigation satellite laser intersatellite link technology is accelerating and the deployment and application of the whole constellation has not been realized,it is necessary to sort out the complex and diverse constraints of the laser intersatellite link construction,carry out research on the integrated system of navigation satellite laser intersatellite link measurement and communication and the network topology optimization algorithm under the state of the whole constellation,and provide technical support for the overall scheme demonstration of the navigation satellite optical inter-satellite link in the subsequent full constellation state.The main research work and innovation points of this dissertation are as follows:1.Aiming at the BPSK/homodyne coherent detection system and the M-ary direct sequence spread spectrum technology commonly used in the current space optical communication,breaking through the bottleneck of the information code length limited by the pseudo code period in the traditional direct sequence spread spectrum measurement communication system,and proposing a new design method of measurement communication integrated signal(m-DSSS signal)system that can modulate multiple information bits in a single period pseudo random sequence.In order to meet the demand for fast signal acquisition,this dissertation takes the msequence with good autocorrelation,cross correlation,and short period characteristics as an example.Firstly,a multi-channel based m-DSSS signal modulation and demodulation method is designed,and the correlation of the m-DSSS signal is numerically simulated to verify the feasibility of capturing the m-DSSS signal;Then,a mathematical model is established for the anti-interference ability of m-DSSS signal through the additive Gaussian white noise channel,and the communication bit error rate performance of m-DSSS signal is analyzed quantitatively;Finally,under the same spectrum utilization conditions,simulation experiments were conducted to compare the signal acquisition,tracking,and bit error rate capabilities of m-DSSS with the widely used code shift keying(CSK)modulation method,verifying that m-DSSS has better performance compared to CSK.2.Faced with the shortcomings of the traditional inter-satellite link network topology optimization algorithm,which simplified the satellite platform into a particle model,and fully considered the complex constraints involved in the navigation satellite Optical inter-satellite link construction,such as earth occlusion,satellite attitude,laser terminal field of view,the number of links that can be carried by the laser terminal,and permanent links,the optimization goal was to minimize the position accuracy factor(PDOP),point-to-point link delay,and terminal idle rate cost,An improved multi-objective discrete binary particle swarm optimization algorithm is proposed to optimize the topology of navigation satellite optical inter-satellite link network.The main research work includes: First,taking the space configuration of satellite constellation,the laws of satellite orbit movement and attitude change,the laser terminal installation scheme and other conditions as inputs,by constructing the corresponding mathematical model,the various constraints on the establishment of inter-satellite laser links are quantitatively described;Then,according to the characteristics of topology optimization of navigation Satellite Network,a network topology optimization algorithm based on discrete binary multi-objective particle swarm optimization(MODBPSO)is proposed,which breaks through the insufficient expenditure of the existing simulated annealing optimization algorithm based on link crossover mechanism that cannot optimize the utilization of laser terminals;Finally,under the same satellite constellation simulation scenario,a simulation comparison experiment is carried out on the multi-objective optimization effect of MODBPSO and MOSA algorithm,which verifies the advantages of MODBPSO algorithm in multi-objective optimization compared with MOSA algorithm.3.A space-based relay network access node selection scheme based on the Bei Dou navigation satellite is proposed for the characteristics of the mixed constellation configuration of medium to inclined geostationary orbit navigation satellites.Taking the space-based information backbone network based on the hybrid constellation of Beidou navigation satellite as an example,according to the constraints of the relationship between network delay,coverage and the number of relay nodes,this dissertation gives two relay node selection schemes,and simulates and analyzes the performance of the proposed scheme,such as the whole network queuing delay,access signal range,etc.Then,a reference for the future space-based relay network design scheme based on navigation satellite is provided.The simulation test results show that for each MEO orbital plane in the navigation satellite constellation,only two satellites with symmetrical orbital positions need to be selected as relay communication access nodes,which can basically meet the data relay requirements of LEO spacecraft such as space stations whose distance from the earth center is less than 10000 km.The research work of this dissertation can help to promote the construction and improvement of the navigation satellite optical inter-satellite link project,provide technical support for the design of the future space-based information backbone network based on navigation satellites,and lay the foundation for the large-scale application of the subsequent navigation satellite optical inter-satellite link. |
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