Performance Analysis For Wireless Optical Communication System Over Exponentiated Weibull Fading Channels

In recent years,wireless optical communication has gained significant attention because of its license-free frequency spectrum,high security and capacity.However,a signal-carrying laser beam transmitted in changeable atmosphere environment will be affected by atmospheric turbulence,which could result in random fluctuation on the optical power collected by the receiver,and the performance of free space optical communication(FSO)system will be degraded seriously.In addition,misalignment between the transmitter and receiver,also named as pointing error,is another non-negligible limiting factor for FSO system.Therefore,it is significant to explore and study how to mitigate the impact of atmospheric turbulence and pointing errors,and improve the performance of FSO communication system.On the basis of exponentiated Weibull turbulence model and pointing error models,the performances of the relay-assisted,orthogonal frequency division multiplexing(OFDM)and low density parity check(LDPC)coded FSO communication system are studied in detail.The main contents are as follows:(1)Considering the impact of atmospheric turbulence and pointing errors,a multihop parallel relay-assisted FSO communication system with the best path selection scheme is investigated.Firstly,on the basis of exponentiated Weibull turbulence model and two pointing error models,the composite probability density function(PDF)and cumulative distribution function(CDF)of the aggregated fading channel are derived mathematically.Subsequently,with non-identically and independently distributed links,the CDF of the end-to-end SNR for multihop parallel system with a decode-and-forward protocal is obtained.Then the theoretical expressions of end-to-end average bit error rate and outage probability for binary phase shift keying-subcarrier intensity modulated multihop parallel FSO system are also achieved,and Monte Carlo simulation is offered to verify the validity of these results and the proposed models.Subsequently,the influence of structure parameters,turbulence strengths,boresight displacements,jitter variances,receiving aperture sizes on the average bit error rate and outage probability performances is analyzed,in order to explore how to improve the FSO system performance.(2)Based on exponentiated Weibull turbulence model and pointing error model,a LDPC coded OFDM-FSO communication system considering the combined impact of atmospheric turbulence and pointing errors is investigated.On the basis of the PDF and CDF of the composite channel gain,the average bit error rate of this FSO-OFDM system with K-ary phase shift keying,quadrature amplitude modulation and on-off keying modulation schemes are derived by using generalized Gauss-Lagurre quadrature rule.To mitigate the adverse effect of atmospheric turbulence and pointing errors,LDPC codes are applied in the Monte Carlo simulation to improve the average bit error rate performance of this system.Furthermore,the improvement of the system performance provided by LDPC with different turbulence strengths,jitter variances,beamwidths at receiver,and receiving aperture sizes is analyzed in detail.This thesis can provide some references for studying the performance of FSO communication system.