Research On Characteristics Of Wireless Optical Adaptive Subcarrier Modulation System

Wireless optical communication is a wireless broadband communication technology,which uses laser as carrier for information transmission.The transmission of laser signals in the atmospheric space is bound to be affected by the atmospheric turbulence.Atmospheric turbulence will bring great difficulties to the detection of receiver signals,resulting in the reduction of system performance,which will cause system communication interruption.Researching adaptive subcarrier modulation technology and Multiple Input Multiple Output can restrain the influence of channel fading caused by atmospheric turbulence and effectively improve the performance of wireless optical communication system.The main content of this paper includes as follows:1.The influence of atmospheric channel on optical signal transmission was described,including atmospheric absorption,atmospheric scattering,and atmospheric turbulence.The Malaga atmospheric turbulence channel model is studied.The MeijerG function expression of its distribution function is derived according to the probability density function of Malaga atmospheric turbulence intensity fluctuation.The average bit error rate and the channel capacity formulas of non-adaptive subcarrier two kinds of MDPSK and MPSK modulation systems over Malaga turbulence channel are derived,and the system characteristics under the two modulations are compared and analyzed.2.A wireless optical adaptive subcarrier modulation system was established.The working principle of the system was described and the system characteristics were analyzed theoretically.Under the Malaga atmospheric turbulence channel,the asymptotic expression of spectral efficiency,average bit error rate,and outage probability for two kinds of adaptive MDPSK and MPSK modulation systems are derived using the Meijer G function and its properties.The numerical simulation compares and analyzes the performance of the non-adaptive and adaptive subcarrier modulation systems.3.Adaptive subcarrier modulation is applied to wireless optical MIMO systems.Based on equal gain combining techniques at the receiver,the MeijerG function and its properties are used to derive the asymptotic expressions of the spectral efficiency,the average bit error rate and the outage probability of the wireless optical MIMO for two kinds of adaptive MDPSK and MPSK modulation systems over the Malaga channel.At the same time,the average bit error rate of the MIMO non-adaptive modulation system is derived.The performance of the multiple input multiple output system and the single input and single output system are compared and analyzed by numerical simulation.The numerical simulation results show:Wireless optical adaptive subcarrier modulation can effectively suppress channel fading caused by atmospheric turbulence.Compared with non-adaptive modulation system,adaptive modulation system can not only obtain lower average bit error rate under the same electrical signal to noise ratio,but also The spectral efficiency is greatly improved without increasing the additional transmission power or sacrificing the system bit error rate performance.The adaptive subcarrier modulation technology is applied to the MIMO,with the increase of the number of transmitting and receiving ends,the performance of the wireless optical communication system can be improved more effectively.