Research On Improved Coding And Decoding Method And Cascade Method Of Spinal Code In Free-space Optical Communication

In recent years,with the rapid development of information technology,traditional wireless communication technology has gradually failed to meet people's needs for real-time and reliable data transmission in daily life and entertainment.Therefore,scholars' attention is focused on free-space optical communication,which is with the advantages of high transmission rate,large bandwidth and strong confidentiality.Although there are many advantages of free-space optical communication,the way of using laser as the information carrier through the atmospheric channel to communicate makes it easy to be influenced by the atmospheric channel environment.Especially the atmospheric turbulence effect in atmospheric channel,which can easily decline the stability and reliability of the system,even affecting the communication effect.Channel coding techniques are often used to reduce the impact of atmospheric channels on communications,the common coding schemes include RS codes,LDPC codes,Turbo codes,and an emerging code-Polar codes.However,these fixed rate codes are prone to face the problem of increasing of bit error rate when encountering sudden situations caused by turbulence.Therefore,in free-space optical communication,a new type of rateless code-Spinal codes has received extensive attention.And it's believed that it has great research value and broad application prospects.Therefore,this paper studies the improved coding and decoding method and concatenation method of Spinal codes in free space optical communication.Firstly this paper introduces the domestic and foreign research status of channel coding in free-space optical communication,and studies the domestic and foreign research progress of Spinal codes.Secondly,the atmospheric channel of free-space optical communication is studied and analyzed.Besides,the influence of atmospheric attenuation effect and atmospheric turbulence effect on optical signal are mainly introduced.The log-normal distribution model and the gamma-gamma model are introduced to simulate atmospheric turbulence and theoretically deduced these models.And the light intensity fluctuations caused by atmospheric turbulence effects and the influence of turbulent channels of different intensities on the optical signal are analyzed.After that,the Hash function,coding steps,decoding algorithm and its characteristics of Spinal codes are studied and analyzed in detail.Based on the study of free-space optical communication and Spinal codes,this paper proposes a symmetric Spinal coding method with partial segmented CRC.This method suppresses the unequal error protection characteristic of Spinal code through two coding processes in reverse order,to reduce the error rate of Spinal code.By adding partial segmented CRC check,the decoding calculation amount of Spinal code is reduced,and the decoding efficiency is improved.And the transfer rate of Spinal code has increased.After that,the simulation is carried out under the weak turbulent channel.The results show that compared with the original Spinal code,the symmetric Spinal code with partial segmented CRC can effectively improve the transmission rate,and the decoding calculation amount is reduced too.It also has a good bit error rate in the weak turbulent channel.In addition,this paper proposes the Polar-UEP Spinal concatenated coding method by combining the construction characteristics of Polar codes and the unequal error protection characteristics of Spinal codes.This method utilizes the unequal error protection characteristic of Spinal code to focus on protection of important message bits and error-prone bits in Polar codes,and the frozen bits which transmit fixed sequence are placed at the error-prone tail of Spinal codes.Such method not only effectively protects the error-prone bits and important message bits,but also avoids the problem that errors are prone to occur at the tail of the Spinal code,which reduces the bit error rate in free-space optical communication.The simulation results show that the Polar-UEP Spinal concatenated coding has good bit error rate performance under different turbulence intensities.