Research On Iterative Demodulating And Decoding Of LDPC-Coded Pulse-position Modulation For Space Optical Communication

Space optical communication has a large channel capacity, and the price of setting upand maintaining is low. For these advantages, space optical communication is widely used inboth defense and civil areas. But space optical communication can be easily influenced by theenvironment, some special weather, like rain, fog and so on, will make a big change of thebackground noise and cause the loss of the channel, and the quality of the communication willbe seriously impacted.Channel coding and modulation technology is one of the key technologies in spaceoptical communication, and this paper mainly studies the influence of PPM modulation andchannel coding techniques on the system performance of space optical communication.Low-density parity-check code is a good code, whose performance can approximate Shannonlimit. Some scholars already studied how to improve the system performance of space opticalcommunication with LDPC code. But the research on iterative demodulating and decoding ofLDPC-Coded Pulse-Position Modulation for space optical communication is a new field. Onthe basis of detailed studying on LDPC code and Pulse-Position Modulation, this paperstudies a new LDPC-Coded Pulse-Position Modulation iterative demodulating and decodingscheme. The following is the main contributions of this paper.Firstly, we have a detailed study on the basic principles of PPM modulation, harddemodulation and soft demodulation, analyze the performance of OOK modulation and PPMmodulation, the performance of hard demodulation and soft demodulation with the method ofcomputer simulation, and draw their performance curve in matlab.Secondly, on the basis of detailed studying on the basic principles of LDPC code, itscoding and decoding, we make a simulation analysis for LDPC code in the opticalcommunication system, and compare LDPC code with RS code with the same length and rate.Based on the results, we give some conclusions.Finally, this paper studies a new LDPC-Coded Pulse-Position Modulation iterativedemodulating and decoding scheme, and analyzes the influence of the new scheme for thesystem performance of space optical communication in Gaussian channel.The conclusions of this paper offer a probability of improving the system performance ofspace optical performance and achieving better wireless transmission.