Performance Analysis Of Relay-assisted Wireless Optical Communication System Over Exponentiated Weibull Fading Channels

Wireless optical communication(WOC)uses wireless light as carrier and provides line-of-sight transmission in free space.It is also known as free space optical communication(FSO).Compared with radio-frequency(RF)wireless communication,FSO could provide larger bandwidth with free license.Besides,its links are very secure and could resist electromagnetic interference.However,owing to the inhomogeneities in temperature and pressure of atmosphere,the random changes in the refractive index will lead to optical turbulence.Signal-carrying laser beam would be affected by these turbulence,resulting in random fluctuations of irradiance collected by the receiver.This phenomenon is called scintillation in physical field and also named signal fading in communication.Furthermore,due to the fact that optical equipment is always installed on the high buildings,the installation platforms may appear random vibration caused by human or natural factors,leading to misalignment between the transmitter and receiver.This phenomenon is called pointing errors.Turbulence and pointing errors would deteriorate the performance of FSO system,increase the bit error rate,and even cause communication interruption.Recent years,aperture averaging and relay-assisted techniques arouse wide concern as methods of mitigating those two limitations.In this thesis,the performances of relay-assisted FSO system are studied over exponentiated Weibull(EW)fading channels,which could model the probability density function(PDF)of irradiance in weak-to-strong turbulence regimes with finite receiver aperture adopted(i.e.,under aperture averaging conditions).The main works are shown as follows:(1)With the max-min criterion as the best path selection scheme,the analytical expressions for the end-to-end average bit error rate(ABER)and outage probability(OP)of multihop parallel relaying FSO system with identically and independently distributed links are firstly derived over EW fading channels.The corresponding analytical expression for the end-to-end ABER with non-identically and independently distributed links is further obtained.Those general expressions could be reduced to some special cases when changing the structure parameters.Monte Carlo(MC)simulation is also provided to confirm the correctness of the analytical results.The performance of the considered system are also analyzed in detail under different turbulence conditions,structure parameters and receiver aperture sizes,with specific physical reasons given.(2)The analytical ABER formula of multihop relaying FSO system over composite EW fading channels with nonzero boresight pointing errors considered is firstly achieved.M-ary phase shift keying(MPSK)subcarrier intensity modulation is adopted.Besides,the comparison with MC simulation verifies the validity of the proposed ABER model.The ABER performance is systematically analyzed with different boresight displacements,hop numbers,receiver aperture sizes and under different turbulence conditions.This thesis could provide some theoretical references for designing and realizing relay-assisted FSO system.