Research On Phase Noise Caracteristics And Compensation Technology Of Wireless Optical Subcarrier Modulation

Wireless Optical Commurtication(WOC)is a kind of wirclcss broadband communication technology,which uses laser beam as optical carrier to traiismit information through the atmosphcric space.Subcarricr modulation technique in wireless optical communication can suppress the atmospheric turbulence effectively,but the phasc noisc producedl by electrical demodulation module will due to the degradation of the system performance.By studying the pcrformance affcctcd by the phasc noise over turbulent channel in wireless optical subcanicr multi-phasc shift kcying system can provide a theoretical basis for the phase noise estimation and compensation.The main contents of this ardcle includc:1.Based onthe Tikhonov distribution phase noise model,the probability density function expressed with Fourier seriesof the phase noise is derived by the properties of the first type Bessel function.Under different phase noise deviations,the curves of probability density function are compared between Tikhonov phase noise distribution and Gaussian distribution.2.According to the Boms perturbation theory,the Malaga atmospheric turbulcnce channel is studied.The parameter scUings in the distribution function of Malaga turbulence channelwhich can be expressed as Lognormal distribution.Gamma-Gamma distribution and K distribution channel models are given.The probability density function curves of Malaga atmospheric turbulence channel from K distribution to Gamma-Gamma distribution are simulated.3.The influences of the phase noise under Malaga turbulence on the performance of wireless optical subcarrier modulation system are studied.Combined with Fourier series and Meij erG function properties,the probability density function of the instantaneous signal-to-noise ratio of the Malaga turbulence model is obtained.Under the Malaga turbulence channel,.the Fouricr series of the received signal phase and symbol error rate(SEP)asymptotic expression influenced by the phase noise in MPSK system are derived.The influences of the phase noise on the SEP are analyzed undcr the different modulation orders and the variance of the intensity phase noise on the SEP are analyzed under the different modulation orders and the variance of the intensity fluctuation.The truncation error expression of phase noise Tikhonov distribution is derived and the truncation error expression of the SEP in wireless optical subcarrier MPSK modulation system is also derived.The impacts of the truncated terms on the symbol error rate are analyzed in the wireless optical subcarrier modulation system.4.The phase noise estimation and compensation technique are discussed based Kalman filtering and extended Kalman filtering in wireless optical subcarrier QPSK system.Under the Lognormal atmospheric turbulence channel,the algorithm processes of the phase noise estimation and compensation with Kalman filter and extended Kalman filter are given respectively.The performances of the system are compared and analyzed between two filtering algorithms by simulation.The research results show that the system symbol error rate increases with the light intensity fluctuation variance when the phase noise is lower in wireless optical subcarrier MPSK modulation system affected by phase noise.When the phase noise is larger,the influence of modulation order on the error-rate floor appearing is greater than that of turbulence intensity.With the increasing of modulation order,the corresponding average signal to noise is lower when symbol error rate floor appears.Finally,the phase points in the QPSK constellation can return back to the decision region by using the Kalman and extended Kalman filtering algorithms under turbulence channel,and compensate the impacts of the phase noise.