Research On Solar Scintillation And It's Effects On Deep Space Telecommunication

During the initial phase of the human deep space exploration, a reliable communication linkbetween a probe and Earth will be required. Signals fromdeep space probes are usually very weakwith high link error rates and high propagation delays when reach the Earth due to distancecondition. Especially, the deep space telecommunication is easy to be affected by the spaceenvironment, mainly by the solar wind and ionospheres around planets. The solar wind is highdensity and strongly turbulent ionized gases erupted from the Sun. Because of much strongturbulence and irregularities, solar corona and near-Sun solar wind are inhomogeneous plasmamedium. When RF waves pass through it, in addition to the effects in homogeneous plasma (suchas group delay , dispersion, Faraday rotation, absorption and phase advance, etc.), the radio signalscause strong scintillation at their amplitude, frequency and phase, especially in the regions veryclose to the Sun (less than 4 solar radius). These effects called solar scintillation will severelydegrade the telecommunication links and even make it impossible.Based on the theory of wave propagation in random media, describe the solar scintillationdetailed, including intensity scintillation, phase scintillation, and spectral broadening. Theintensity scintillation can be described using an index, m ,which is defined as the rms signalintensity fluctuation relative to the mean intensity, and it characterizes the strength of small-scalecharged particle density fluctuations. Spectral broadening refers to an increase in the bandwidthover which half of the signal power resides, and the broadened bandwidth is defined as B . Phase(or Doppler) scintillation is a type of Doppler noise after excluding the frequency changes due tospacecraft motion. The Doppler scintillation parameter isσ_D,the rms of the Doppler. TheSpectral broadening and phase are dependent on both electron density fluctuations and solar windvelocity. The the expressions ofm , B andσ_D are given by Rytov approximation and a geometricmode. And then observed experimental data form NASA is analyzed to verify theircorrection. Solar scintillation causes degradation in telecommunication link performance. The paperpresent a model to study the weak scintillation effects on deep space telecommunication. Based onthe Born approximation, the statistics of the scintillation intensity are presented Rician distributionand then a Rician channel model is obtained. After building the relationship between scintillationindex and Rician factor, the paper simulate the telecommunication link performance with differentscintillation indices, different RF signals band, and different SEP (Sun-Earth-Probe) angles. Thetelecommunication link BER performance as a function of Eb/N0 under solar scintillation effectsare displayed in figures.Besides telecommunications link degradation, rapid change in the amplitude and phase of aradio signal can result a complete loss of lock. Amplitude scintillation alters the SNR andincreases the thermal noise tracking error and phase scintillation increases the PLL tracking errortoo. The paper adopt total power of the received scintillation signal at the input of the receivercombined with cycle slipping model to get the probability of loss of lock versus scintillationindices.At last, the paper provides recommendations and communications strategies for deep spacetelecommunication link under effects of solar scintillation, such as using the higher frequency,higher efficient codeings chemes and so on.And those are the main purpose of the paper.