Performance Reseaerch Of Short-length Raptor Codes In FSO/RF Channel

With the continuous rise of communication industry,there is an increasing demand for transmission rates and transmission quality.Under the limit of limited spectrum resources and traditional wireless communication technology(RF)transmission capacity,free space optical(FSO)technology will undoubtedly become an effective solution to large-capacity data transmission.But FSO communication is very susceptible to atmospheric fluctuations and bad weather conditions,so FSO / RF hybrid communication technology has become a new solution to a combination of FSO and RF advantages.In order to make full use of FSO link and RF link,you can use FSO / RF hybrid communication link with soft switching mechanism,the encoded data at the same time transmitted on both links;to ensure the quality of FSO communication,and to avoid the traditional retransmission technology,this paper studies a practical code-Raptor code,which is one of fountain codes and is used as the channel coding of FSO / RF system,and we will carry out an improvement to carry out simulation verification research.Since FSO / RF systems have shorter communication distances(less than 2 km),only atmospheric attenuation is considered when modeling RF channels,and FSO channel modeling needs to consider the effects of atmospheric attenuation,atmospheric turbulence,and geometric attenuation.The FSO atmospheric attenuation model is an empirical model obtained by the researchers through measurement data.The FSO geometric attenuation model is a fixed value for the fixed point of the point-to-point connection.Therefore,according to the specific application scenario,this paper will select the appropriate FSO atmospheric attenuation and geometric attenuation coefficient;In the FSO atmospheric turbulence model,the Gamma-Gamma distribution is suitable for almost all turbulence situations and will be used in the system simulation in this paper.The transmission rate of the FSO channel is very high.For the Raptor code with longer code length,the complexity and the processing time of the decoder at the receiving end are bound to increase,which is very unfavorable to the full use of the FSO channel transmission.Therefore,this paper will construct Raptor short codes,which uses the optimal degree distribution function and average degree algorithm to improve the performance of Raptor short codes at the transmitting end.And at the same time,a low complexity decoding algorithm is proposed to further reduce the system complexity.That is,the Raptor code uses an improved min-Sum algorithm at the receiver end.In this paper,a hybrid soft-switching FSO / RF communication system is set up based on Simulink simulation platform.The parameters of the channel model used in the simulation are obtained through the research conclusions of other literatures.Through the simulation of MATLAB platform,the results show that the proposed encode scheme can improve the performance of Raptor short codes.