Research On Improved HARQ Anti-fading Transmission Technology In Optical Communication

With the rapid development of communication technology,laser communication has become a very promising way of communication.However,there are many interference factors in space laser communication,which is easy to cause serious channel fading problems.Therefore,anti-fading transmission technology has become the pivotal technologies and problems in the realization of satellite-to-earth long distance communication.Firstly,the thesis briefly introduces the basic concepts of forward error correction codes,automatic repeat request,hybrid automatic repeat request,adaptive technology,and diversity reception anti-fading transmission technology.Subsequently,the characteristics of fading channels in satellite-to-earth laser communication are analyzed.For the channel fading caused by atmospheric turbulence,the multiple phase screen numerical simulation method is used to perform normalized light intensity simulation.Secondly,in response to the problem of uneven distribution of light intensity at the receiving end caused by atmospheric turbulence,which generates more serial burst errors,The common packet interleaving combined with the traditional HARQ anti-fading scheme does not implement partial retransmission for the error correction frame with a higher error rate,but retransmits the entire error correction frame,resulting in low error correction efficiency and low bandwidth utilization problems,so as to propose an improved HARQ anti-fading scheme based on the strength of optical power.Firstly,after the channel coding at the sending end,the error correction frame data packets form a transmission frame,and the optical power threshold is set.The optical power of the transmission frame is compared with the set optical power threshold,and the error-prone transmission frames below the threshold are re-correct.Subsequently,the bit error rate performance and throughput performance of the improved HARQ scheme are simulated,and the simulation results show that compared with the traditional HARQ scheme,the improved HARQ anti-fading scheme further improves the system bit error rate performance.In addition,CRC check can also be added at the receiving end to further enhance and improve the reliability of the HARQ scheme decoded data.Finally,because it is difficult to determine the power threshold of the HARQ anti-fading scheme based on the strength of the optical power,it may cause a small amount of data to be decoded incorrectly,or unnecessary data frame retransmission occur,wasting system bandwidth resources,and further proposed hierarchical retransmission improvements for the above problems HARQ anti-fading solution.Firstly,the receiver counts and calculates the average optical power of the transmission frame.Below the average optical power threshold,the power threshold is added again,and then the transmission frames below the average optical power threshold are retransmitted hierarchically,In principle,priority is given to the first-level transmission frames with lower optical power.If the decoding still fails,the second-level retransmission is performed again.Finally,the bit error rate and throughput of the HARQ scheme with hierarchical retransmission are simulated.The simulation results show that the hierarchical retransmission scheme compares with the traditional HARQ anti-fading scheme and improves the HARQ anti-fading scheme based on the power threshold,which again improves the system's bit error The rate and throughput performance have certain reference value and significance for improving the anti-fading ability of the satellite-to-earth laser communication system.