Performance Analysis Of Free Space Optical Communication Systems With Partially Coherent Beams

In recent years,free space optical(FSO)communication has attracted lots of attention because of the important role it plays in the last-mile transmission,military operations,backhaul/fronthaul links of cellular systems,and disaster recovery,which benefits from larger capacity,higher throughput,unlicensed spectrum,cost-effectiveness,faster network building speed,etc.in comparison with traditional radio frequency(RF)communication.However,FSO links would be seriously affected by path loss,atmospheric turbulence and pointing errors.It has been reported that partially coherent beam(PCB)could mitigate the influence of atmosphere turbulence and pointing errors,and improve the performance of FSO communication system.Therefore,it is of great significance to study the performance of FSO system with PCB.In this work,the performance of dual-hop mixed RF/FSO transmission system on the basic of partially coherent beams over F-distribution channel models has been analyzed.Moreover,the performance of FSO system assisted by intelligent reflecting surface(IRS)has been also studied in detail.The specific work of this paper is as follows:1.In this work,the outage probability(OP)and average bit error(ABER)performances of dual-hop mixed RF/FSO communication system with partially coherent beam(PCB)have been investigated on the basis of decode-and-forward(DF)protocol.Specifically,both the RF and FSO channels are assumed to follow F-distribution with proper selection of the parameters.Taking the path loss,F-distribution model and pointing errors into consideration,the expressions for the probability density function(PDF)and cumulative distribution function(CDF)of the received signal-to-noise ratio(SNR)have been derived in terms of hypergeometric function and Meijer-G function in RF and FSO links,respectively.Subsequently,on the basis of DF protocol,the expressions for the OP and ABER have been obtained.Finally,the effects of turbulence strength,shadowing strength,pointing errors and degree of spatial coherence on the performance of dual-hop mixed RF/FSO system have been analyzed and discussed,and our analytical results are supported by Monte-Carlo(MC)simulations to validate the analysis.2.The performance of FSO system assisted by intelligent reflecting surface with PCB has been analyzed.Taking the path loss,F-distribution atmospheric turbulence and pointing errors into consideration,the expressions for PDF and CDF for FSO link have been derived in terms of Meijer-G function.Using these derived statistical results,the OP and ABER expressions for single input single output(SISO)IRS-assisted FSO system have been obtained under intensity modulation / direct detection(IM/DD).Considering on off keying(OOK)modulation scheme,the expressions of ABER of single input multiple output(SIMO)system with maximum ratio combining(MRC)and selection combing(SC)receivers have been derived.Moreover,MC simulations are used to verify the analytical expressions.Finally,the effects of turbulence strength,pointing errors and the parameters of PCB on the performance of IRS-assisted FSO system have been analyzed in detail.This work would benefit the design and development of the FSO systems on the basis of PCB.