Performance Analysis Of Wireless Optical Communication System Over M Fading Channels

Recently,wireless optical communication(WOC)has received considerable attention as a cost-effective and wide-bandwidth technique.However,the adverse weather conditions,atmospheric turbulence and pointing errors all degrade the bit error rate performance of the system,which severely limits the application of WOC technology.Therefore,it is meaningful to study how to overcome these adverse factors and improve the system performance.In this work,based on the M fading channel model,the performances of the spatial diversity,relay-aided and low density parity check(LDPC)coded WOC system with considering the combined effects of path loss and pointing errors are investigated in detail.The main contents are as follows:1.Considering the M fading channels,the average bit error rate(ABER)performances of maximal ratio combining(MRC)and equal gain combining(EGC)WOC systems are studied deeply based on the binary phase shift keying(BPSK)modulation.The probability density functions(PDFs)of the system with independently and identically distributed and independently and non-identically distributed dual branches are obtained firstly by expressing the M distribution with the Meijer-G function.The ABER expressions are then derived and represented with the H-Fox function.Monte Carlo simulation is provided to confirm the validity of the proposed ABER expression.Under different turbulence conditions,the performances of the system with dual branches are compared with those of single-in single-out(SISO)system and the effects on the performance of the MRC and EGC systems are then analyzed.2.With the combined effects of atmospheric turbulence-induced fading modeled by M distribution,pointing errors and path loss taken into consideration,the performance of multi-hop parallel WOC system has been studied in detail.The PDF expression of the aggregated fading channel is derived based on the M distribution by using Meijer-G function.Then,the analytical expressions of ABER and outage probability of BPSK subcarrier intensity modulation are derived on the basis of the best path selection scheme.At last,the influence of different weather conditions,pointing errors,turbulence strengths and structure parameters on the ABER and outage performances have been analyzed systematically.3.The ABER performance of LDPC-coded single input multiple output(SIMO)WOC system has been studied based on the composite fading channel consisting of the path loss,pointing errors,and M-distributed atmosphere turbulence.At receiver side,the signals are decoded using belief propagation algorithm(BP)after collected by EGC method.The ABER performance of LDPC-coded system with different turbulence strengths,weather conditions,pointing errors,code rates and the number of links are investigated systematically.This work is applicable for the system design of WOC system.