Research On Channel Coding And Modulation Technology Of Free Space Optical Communocation

Free space optical communication(FSO) is a technology that uses light as media totransmit information in the space, also it known as the optical wireless communication. FSOcombines the advantages of optical fiber communications and microwave communications,today it has become one of the telecommunications hot technology. But the atmosphericrandom channel will have a very big impact on the laser signal that make the reliability ofcommunication decline, which is a major challenge for FSO. In order to suppress or relieveatmospheric effects, people hace studyed the different aspects of FSO, the main technicalhave light source technology, the adaptive transmission technology, and modulation andcoding technology. This paper will study the Modulation and coding technology.Firstly, this paper reviews the researchdevelopment status of the FSO communicationtechnology, and introduces the advantages of FSO, and analysis and comparison of the keytechnologies of FSO. Then modeling and simulation of atmospheric random channel toprovide a reference for the setting of parameters for channel in the subsequent chapters.Secondly, for ease of hardware implementation, this paper studies FSO communicationsystem of a kind of QC_LDPC code, this QC-LDPC code can take advantage of the checkmatrix to RU coding directly. Under the weak turbulence channel conditions, based onMATLAB simulation software, we made the performance comparesion of QC_LDPC codeand random LDPC code and π-rotation LDPC code, the results show that LDPC codes haveplayed a certain reduction effect to the weak turbulence channel, so it can improve thereliability of communication system. The bit error rate (BER) performance of the QC_LDPCcode is very near to the BER performance of random LDPC code and it is superior to-rotation LDPC code under the circumstances of the weak turbulence channel, butQC_LDPC code and-rotation LDPC code are easier to be implemented by hardware andhave more application value. When the BER is about10-2, SNR about2dB improvement afterthe introduction of this QC_LDPC code FSO communication systems. At the same time, thispaper analyzes the error performance of both the OOK and PPM modulation, and weconbined the PPM modulation with the QC_LDPC code.Finally, in the Quartus ΙΙ simulation platform, selecting Altera’s the Stratix series modelsfor EP1S40F780C7chip, using the verilog hardware language programming and simulate the QC-LDPC code encoder module, and we use the MATLAB software to test the hardwaresimulation results.