Study On The Propagation Characteristics Of Radio Waves In Heated Ionosphere Based On Software Defined Radio

Due to the existence of the ionosphere,propagation characteristics of radio waves in the ionosphere would be affected,which makes the study about the radio waves propagating in space plasma very meaningful.This thesis studies from the theory of ohmic heating and wave propagation theory in random media,in which the transmission characteristics of the waves in artificial space plasma are investigated.The main work of this paper is as follows:Firstly,the structural characteristics of the ionosphere is introduced briefly,which includes the layered structure of the ionosphere,the formation mechanism,as well as a variety of common changes and phenomena in the ionosphere.Then the A-H dispersion formula is given to describe anisotropic plasma medium and the Shkarofsky power spectrum is given to describe the irregular body,the expression of the two-dimensional horizontal correlation function based on the Shkarofsky power spectrum is given.Secondly,starting from the ohmic heating model on ionosphere of a high-power and high-frequency heating source,the alternating direction implicit method is applied to the momentum equation and the energy equation to perform numerical discretization in this thesis.With the help of computer programming,the influence of different parameters on the heating result is simulated.According to the simulation results,it can be found that the electrons are heated under the action of electromagnetic waves.The closer the distance to the reflection height,the more the electron temperature increases.However,the electron density has a maximum point and a minimum point at the height of the reflection,respectively.As the heating power and heating time increase,the heating effect of the ionosphere will be saturated.Thirdly,using the Haselgrove equation in spherical coordinates,the propagation path in the space plasma is simulated by numerical simulation.According to the simulation results,that the higher the elevation angle and the emission frequency is,the higher the reflection height of electromagnetic wave in the ionosphere is concluded.But electromagnetic waves may travel through the ionosphere if the frequency is too high.And the existence of the heating ionosphere will make the Short-Wave's propagation path deflect high or low.Fourthly,this thesis divides the ionospheric into conventional ionospheric and electron density uneven body which includes gaussian random fluctuation and the electron density changes in the process of heating ionosphere.According to the formula of Doppler frequency shift caused by the interaction between high frequency electromagnetic wave and the ionosphere,the simulation result and analysis result is given.According to the simulation result,that the Doppler effect is mainly caused by the motion of the ionosphere and the inhomogeneity of the electron density is concluded.Fifthly,according to the higher order symmetric moment equation,a general analytical solution for the general strong fluctuation is presented,which includes the Gauss solution and the non-Gauss correction term,and the concrete expressions of the second moment and the fourth moment under the plane wave incidence present are given.Finally,the ionospheric scintillation index and correlation function are simulated.According to the simulation result,there is a positive correlation between the ionospheric scintillation and the parameters such as the spectral index,the internal and external scales and the mean square fluctuations of the electron density etc.But the scintillation index of high frequency is lower than that of low frequency.Sixthly,the theoretical basis of software radio is briefly introduced in this thesis,including signal sampling theorem,multi-rate signal processing and digital quadrature modulation.Then the open source software radio system composed of GNU Radio and USRP is introduced.Besides the propagation characteristics of electromagnetic wave signal,including ASK signal and DPSK signal,in the wireless channel are simulated based on the system.According to the simulation results,it can be seen that the existence of heating ionosphere will decrease the quality of electromagnetic wave transmission.