Performance Analysis Of Multiuser Diversity Free-Space Optical Systems Over Exponentiated Weibull Fading Channels

Wireless optical communication uses laser as the information carrier and atmosphere as transmission medium.It is also known as free space optical communication(FSO).Recently,FSO has drawn considerable attention for its multiple advantages,such as less power,small volume,large bandwidth,excellent security and free license.However,FSO links are always vulnerable to atmosphere turbulence because of its free transmission medium.Accordingly,how to mitigate atmosphere turbulence as well as to some extent transform the unfavorable factor into favorable one is the key to improve the system performance.A lot of research shows that,aperture averaging technique can average the fluctuations of the laser beam to enhance the system performance.Additionally,multiuser diversity can take advantage of the randomness of atmosphere turbulence and the independence of system users to maximize the average capacity.Therefore,a combination of the two techniques can further improve the communication performance.In this work,multiuser diversity is applied to FSO system with several scheduling policies under the consideration of exponentiated Weibull(EW)distribution.The main contents are as follows: 1、The mechanism of N-th best user selection scheme under multiuser diversity scheduling system over EW fading channels has been studied in-deep.The probability density function(PDF)and cumulative distribution function(CDF)of the system model are derived,and then on these basis with the combination of Binary phase shift keying(BPSK)modulation the closed forms of average bit error rate(ABER)and average capacity are achieved.Furthermore,the numerical simulations and Romberg integrations are provided to confirm the validity of the proposed model.Accordingly,the ABER and average capacity performances of FSO-MD systems are investigated with different receiver aperture sizes,turbulence strength values,user numbers K,and orders N.Results show that,a higher capacity can be obtained in the strong turbulence regime,and this phenomenon is more significant with large receiver aperture size.2、The greedy scheduling,selective multiuser diversity scheduling,proportional fair scheduling and selective multiuser diversity scheduling with exponential rule are introduce to FSO-MD systems Firstly,the selection principle of the four different scheduling schemes is introduced comprehensively,and the comparisons of them are made from the point of view of the fairness of users and the received feedback information.Secondly,on the basis of aperture averaging,the derivations or simulations of average capacity and ABER are conducted over EW fading channels with the adoption of binary phase shift keying(BPSK).Finally,the four scheduling schemes are compared with the relative capacity method.Results show that,the greedy scheduling obtains the maximum average capacity at the cost of the fairness of users.The selective multiuser diversity scheduling with exponential rule receives the minimum capacity,but it guarantees the fairness of users.This work provides some reference for design and optimizing of the multiuser FSO systems.