Research Of Plasma Sheath's Effect On GPS Signals And Suppression Technology

The plasma sheath will be produced around hypersonic vehicles when it reentry into the earth's atmosphere.The plasma sheath can affect the radio communication between reentry body and ground control stations or space satellites,which can attenuate control signals such as navigation and guidance rapidly.What's worse,the communication between reentry body and ground stations or satellites may be interrupted,forming‘blackout'phenomenon.However,beam-forming technology can improve the reception gain,in order to weaken the blackout effect.Hence,the study of plasma sheath's effect on navigation signals and trying to weaken or eliminate the blackout effect are key technologies needed to be solved in hypersonic vehicle's reentry process.In this paper,with the support of National 863 Program,the issues above are researched.The radio wave propagation characteristics of plasma sheath are analyzed using electromagnetic numerical method.Combining with satellite navigation signal analog technology and mathematical modeling plasma sheath channel,the performance of plasma sheath to satellite navigation is analyzed.Studying the performance and feasibility of beam-forming techniques used in suppressing plasma sheath blackout effect.The main contents and innovations are as follows:After analyzing the wave propagation theory of plasma sheath,the scattering matrix SMM method based on analytical approximation is detailed described.For the traditional FOTD algorithm has a problem that calculation step size is small constrained by Courant constraints,the Unconditionally Stable for the Finite-Difference Time–Domain?US-FDTD?algorithm based on Laguerreexpand is used in calculation of plasma wave propagation.The new algorithm can ensure the accuracy as well as reduce the computing time substantially,which improves the simulation efficiency of wave propagation in complex electron density distribution plasma sheath.In this way,an effective simulation tool is provided for the subsequent research.Then,this paper describes the studying the effect of plasma sheath to satellite navigation propagation characteristics and receiver performance.For different plasma sheath distribution model,different electromagnetic field numerical simulation method?US-FDTD,SMM,FDTD,etc.?are used.Then,the plasma sheath's effect of navigation control signal's amplitude,phase and group delay characteristics is analyzed.Proposed method using electromagnetic field simulation results of radio wave propagation to model plasma sheath transmission channel,and verified it.Using plasma sheath channel model combining analog and reception technology of satellite signal analyze plasma sheath's effect satellite navigation receiver carrier to noise ratio?CNR?and the positioning precision.The results show that for the signal attenuation of plasma sheath,the CNR of satellite received signal scales down and position error increases.The group delay changes caused by plasma sheath directly affect pseudo-range measurement accuracy,increasing positioning result error.Finally,using this method simulates and analyzes RAM C III and background vehicle plasma sheath's effect satellite navigation receiver performance.In order to utilize beam-forming technology to enhance satellite signal power,weakening the role of the plasma sheath influence,the beam-forming key technologies are studied systematically.Firstly,theoretical analyzing and simulation comparing different beam-forming standards,including minimum mean square error?MMSE?standard,maximum signal to interference-plus-noise ratio?MSINR?standard and minimum variance?MV?standard.On this basis,theoretical analyzed and simulation compared several different digital beam-forming algorithm performance,including least mean square?LMS?algorithm,recursive least squares?RLS?algorithm,linearly constrained minimum variance?LCMV?algorithm and side-lobe canceller?SLC?.Considering the accuracy of direction and other needed factors,the LCMV algorithm is selected as the beam-forming algorithm in plasma sheath.Finally,the antenna array layout of beam-forming technology has been optimized designed.The results show that under same number of array elements,the circular array has the best beam-forming effect.Simulation analyzes the feasibility that the antenna array beam-forming technology restrains plasma sheath.It is suggest a technology combine electromagnetic simulation results of wave propagation and array signal DOA estimation.At the same time,an analysis method is proposed that plasma sheath affect satellite navigation signal propagation direction and multipath effect.With the help of this method,the results show that plasma sheath has little effect on the signal wave direction,while it can cause serious multipath signals in other directions.It also suggests that beam-forming technology can be used to improve the gain of DOA,while suppressing multipath signals in other directions.Using electromagnetic field numerical simulation technology analyzes plasma sheath's influence of array antenna coupling parameters,a method is proposed that plasma sheath effect beam-forming results combination beam-forming technology and electromagnetic field numerical simulation technology.The simulation results show that,when the plasma sheath density is small,the effect on coupling between antennas and beam-forming result is small,but the gain of beam-forming direction will decreases with the electron density increases.However,when the plasma sheath density is reach10^{1 8}m^-3,the array antenna is unable to form a beam in given direction;beam-forming technology is no longer valid.Finally,the experiments about plasma sheath's impact on wave propagation and satellite navi gation's performance are done.The results of plasma's influence of signal propagation character istics show that the attenuation of signal amplitude will increases with the electron density incre ases.The consistent with measured results and theoretical results verifies the correctness of nu merical simulation.The experiment of plasma's influence of satellite navigation receivers'perfo rmance reproduces the“blackout”phenomenon.The results show,with the increases of electron density,the CNR of the receiver falls.It will results the satellite signal loss lock and the receive r cannot properly position,the“blackout”phenomenon appears.