X-ray Communication Technology And System Implementation Based On Short-Frame Fountain Codes

In recent years,as people's demand for exploring the deeper and farther unknown universe continues to increase,the detection and communication missions carried out by various countries in the space environment have also increased,so there are higher requirements for the transmission performance of wireless communication.At present,microwave communication and laser communication are more commonly used,both of which have played an important role in inter-satellite communication and other fields.However,the transmission performance of the two is limited in the electromagnetic shielding environment and the longer-distance communication.The X-ray photon has a short wavelength and a large usable frequency band.When the energy of the X-ray photon is greater than 5keV,it can achieve lossless transmission in a vacuum environment with a pressure of 10-4Pa or less.Therefore,space communication systems using X-rays as carrier waves have become the focus of research in the aerospace field of various countries.However,the current research on X-ray communication systems at home and abroad mainly lies in the enhancement of the performance of X-ray emission sources,detectors and other devices and the innovation of communication theory.The research on X-ray communication link transmission analysis and channel coding and modulation is still weak.In the intersatellite channel,the X-ray communication uses the IM/DD system to modulate the photons.At this time,the channel is affected by the number of transmitted photons and changes.When photons travel between satellites,they are affected by external factors,causing fluctuations in the flow rate reaching the detector.If the traditional communication system is adopted,the stable transmission of the communication system cannot be guaranteed.Based on the characteristics of the X-ray communication channel,this paper proposes a short-frame fountain code as a channel coding scheme based on the fountain code,which is an uncoded rate coding.At the same time,the modulation method of the communication system was determined and verified on the ground.First,this article analyzes the influence of the parameters loaded on the X-ray source on the number of emitted photons according to the selected emission source,and introduces a focusing and collimating optical system to analyze the gain of photon transmission.Then we explore the influence of the transmission distance of X-ray photons on the inter-satellite link and the deflection angle between satellites on the number of photons arriving at the detector,and finally obtain the changes of X-ray photons when they are transmitted between satellites.The status of the X-ray communication channel is estimated by the number of photons that reach the detector when the X-ray photons travel between stars.Secondly,based on the above-mentioned channel real-time change characteristics,a channel coding scheme for short-frame fountain codes is proposed.Based on the UEP method,a windowed degree distribution function is used to perform hierarchical fountain code coding on the source signal,and then the pseudo-code coding is used to increase the signal antiinterference ability,and then interleaving coding is introduced to utilize the communication time slot of the channel.The influence of this coding method on X-ray communication is analyzed by simulation.Then it introduces the two modulation methods OOK and PPM modulation in I/DD system,and selects PPM as the modulation method in this article through comparison.Finally,based on the FPGA development platform,this article completed the hardware implementation of the hierarchical fountain code encoding and PPM modulation in the Xray communication system,and then built a ground X-ray communication verification system and carried out the corresponding communication experiments.The experimental results show that the communication modulation system proposed in this paper can ensure the reliability of X-ray communication.