Study On Fountain Code Technology In Plasma Channel

When the hypersonic aircraft at high speed enters into the atmosphere, it will generate intense friction, stimulating the air around the aircraft ionizing and dispersing, thus a plasma sheath will be formed. The plasma sheath can absorbe, reflect and scatter the electromagnetic wave signal, causing the communication signal producing the phenomenon of attenuation, phase shift, dispersion and other effects, in severe cases it can interrupt the signal. In response to the "blackout" problem in this communication process. Channel coding is a fundamental technique in modern digital communication systems,it can increase the effectiveness of code. It as an important means of anti-interference technology, is shown more and more important effect in digital communications technology. this paper presents a method for applicating the encoding ideologicalof fountain codes to solve this problem. Bying using the characteristic of no speed rate of fountain codes, that code word can generate and transmit constantly like a fountain until the original data can be recoverd so far. And the forward error correction characteristics of the fountain codes does not require retransmit the data, so achieving effectiveness in exchange for reliability wil be available,and it will be very suitable for complex plasma subchannels.This thesis investigates some aspects of fountain code with emphases on the performance of fountain code on plasma channel and irregular LDPC and encoder of LT codes. The main results and contents as follows:Firstly, this article summarizes and describes the thought of encoding and decoding of the fountain codes systematically, then studies and analyzes the channel model of the plasma, and proposes LT code against the channel for plasma,whose decoding algorithm is soft decision BP algorithm, and makes the corresponding derivation of the algorithm,which makes the the plasma channel be equivalent to the removing channel logically in the application. Through the simulation, the fountain codes with this decoding algorithm has a better error ratio characteristics in the plasma channel at different input data. Then derives the EXIT analysis equation of irregular LDPC codes in plasma channel,simulates and analyzes irregular LDPC codes under different SNR, and get more suitable decoding threshold and channel capacity. Through the simulation and analysis of the irregular UEP-LDPC codes in plasma channel, data shows good unequal error protection performance under plasma channel. Finally, thispaper designs an encoder of LT codes on basis of FPGA against the coding scheme of the fountain code LT codes, and makes the corresponding simulation and test analysis, and the logic function of the encoder is proved correct.The improvement of fountain code algorithm can reduce the plasma channel blackout to some extent, but cannot completely eliminate. How to optimize fountain code for communicate on plasma Channel is a challenge.