Integrated Signal Design Of Communication And Navigation Based On LEO Satellite

Satellite navigation system can provide global coverage,low-cost and highprecision space-time services.Once it came out,it has been widely used all over the world,and has become the basis and core of international space-time information services.However,satellite navigation system also has its inherent problems.The navigation signals broadcast by Medium-Earth orbit and Geostationary-Earth orbit satellites have been transmitted for tens of thousands of kilometers,and the landing level is low.They are easy to be blocked by trees and buildings,as well as other communication systems and even malicious interference.Taking satellite navigation system as the core,supplemented by other means,to provide space-time services with wider coverage area,higher accuracy and more robust method has become the consensus in the field of international space-time technology.The integration of communication and navigation is one of the core means.Thanks to the extremely wide coverage of communication and the increasing information transmission capacity,relying on the communication network to supplement,backup and enhance the satellite navigation system,it shows significant synergy advantages.In2020,with the completion and operation of beidou-3 global satellite navigation system,China has initially established a fully autonomous and controllable global space-time service infrastructure.Facing the needs of future application development,the goal of building a more ubiquitous,integrated positioning,navigation,and timing(PNT)system by 2035 is put forward.As an important part of the integrated PNT system,the integrated technology of Beidou navigation satellite and LEO communication satellite has become a hot research direction in this field.According to the degree of fusion,integration technology can be divided into two levels: information enhancement and signal fusion.Therefore,this thesis first studies the design methods of navigation enhancement signal in the integrated system.After analyzing the required specifications of navigation enhanced signal,combined with the characteristics of Beidou signal,a navigation enhanced signal framework based on LEO satellite is established.The simulation results show that the enhanced signal has better performance in compatibility,ranging performance and anti-multipath ability.For the level of signal fusion,then the integrated waveform design project based on LEO satellite is discussed.Considering the characteristics that the high-power amplifier on the satellite will work in the nonlinear saturation region,based on the phase optimized constant envelope transmission(POCET)technology,the complex subcarrier modulation technology is used.A multi-frequency and multi-signal component constant envelope multiplexing technology based on phase optimized constant envelope transmission technology is proposed to realize the integrated signal of communication and navigation.The simulation results show that this method can ensure the constant envelope characteristics of the integrated signal transmitted by the satellite,and is superior to the BPSK signal of the same level in root mean square(RMS)bandwidth performance,meeting the ranging performance requirements required in the current engineering.Finally,this thesis further explores the influence of non-carrier modulation technology on the complex signal.By analyzing the influence of dependent signals on the multiplexing results of POCET,phase optimized constant envelope transmission of correlation signals,called cs-pocet,is proposed.This method can realize the constant envelope multiplexing of dependent signals.Simulation results show that CS-POCET method avoids the distortion of communication signal caused by intermodulation components composed of uncorrelated signal components at the cost of 3.71%multiplexing efficiency loss,and there is almost no loss in RMS bandwidth performance.