Study Of Cooperative Schemes And Performance In All-optical Free-space Optical Communication System

Free-space optical(FSO)communication is the product of the combination of microwave communication and optical fiber communication technology.It has many advantages such as high transmission rate of optical fiber communication and flexible access of microwave communication.Although FSO has so many advantages,but when the laser is transmitted through atmosphere,it is affected by a variety of atmospheric effects and pointing errors,which limit the transmission distance.To mitigate these effects,scholars have proposed a variety of fading compensation measures.Spatial diversity technology and cooperative diversity technology,also called as relay-assisted transmission technology,are effective ways to resist atmospheric attenuation.All-optical relaying does not require optical-to-electrical and electrical-to-optical convertors,and the performance is better than the traditional relaying.Therefore,based on the theories of spatial diversity technology,cooperative diversity technology and all-optical network,we present an all-optical relaying FSO communication system,which is combined by spatial diversity technology and all-optical relaying.Then there are two novel cooperative schemes are presented,and the performances of system are analyzed.The main works are as follows:Firstly,based on the theory of laser propagation in the atmosphere,we analyze the cause of some noise and atmospheric effects,such as atmospheric loss,atmospheric turbulence,and pointing errors.Furthermore,the corresponding statistical models are presented.Secondly,based on the theory of spatial diversity technology,the performances of multiple inputs multiple outputs(MIMO)FSO,which considers the atmospheric attenuation and turbulence effects,are studied.The results prove that spatial diversity technology can effectively resist atmospheric effects.From comprehensive consideration,the 2 transmit apertures and 2 receiving apertures are more suitable for FSO.The limitation of spatial diversity technology is also pointed out.Finally,we combine spatial diversity technology with all-optical amplify-and-forward relaying.And the fundamental structure of system under the composite fading channel model is established,and then based on the structure;two novel cooperative schemes and corresponding power allocation are provided.Furthermore,how the performances of single input and single output link and all-optical cooperation FSO system are affected by system parameters are derived and simulated.The simulation results show that the performances of the link which adopts all-optical relaying can be improved,and the performance of the system adopts selective relaying is superior to that of all-active relaying.