Performance Analysis Of Mixed RF And MIMO FSO System Based On Amplify And Forward Relay

Free-space optical communication(FSO)system refers to the optical transmission technology using optical carriers to transmit information from the source node to the destination node in free space.In recent years,more attention has been paid to the FSO communication system for its various advantages including high bandwidth,large communication capacity,fast transmission rate,high security,easy installation and deployment,and free spectrum license.However,the performance of FSO system is impaired by the atmospheric attenuation and turbulence effects which also limit the communication span.In this thesis,we propose a mixed radio frequency(RF)/multiple input multiple output(MIMO)FSO system to reduce the atmospheric effects and channel fading combining the advantages of traditional RF communication technology and FSO technology.And in the mixed system,the amplify-and-forward(AF)relay,including the fixed-gain and variablegain relay,is adopted for the RF sub-network to achieve seamless access to the FSO backbone network and improve the reliability of the mixed RF/MIMO FSO system.What's more,in order to further improve the utilization of RF spectrum and communication capacity,we propose a fixed-gain relay-based mixed underlay cognitive radio network(CRN)/MIMO FSO system.And then we analyzed the three types of mixed system performance.The main research works are as follows:Firstly,the principle of the dual-hop relay transmission system is illustrated.And we present the statistical model of the RF link with the CRN technology employed or not according to the transmission characteristics of the RF link.Moreover,we present the statistical model of atmospheric attenuation and turbulence according to the optical transmission characteristics.What' s more,we derive the channel model for MIMO FSO system employing spatial diversity under the influence of atmospheric attenuation and turbulence.Secondly,based on the dual-hop relay transmission system which is adopted for the RF sub-network to achieve seamless access to the FSO backbone network,we investigate a mixed RF/MIMO FSO system with the fixed-gain relay and variable-gain relay,and then we derive the analytical expressions for various performance metrics of the mixed transmission system.Depending on the above expressions,the effect of various system parameters on the mixed system is simulated under atmospheric turbulence.The results show that coherent binary phase shift keying modulation offer superior performance of bit error rate compare with other modulations in the mixed system,and the spatial diversity can effectively improve the system performance.Finally,we propose a fixed-gain relay-based mixed underlay CRN/MIMO FSO system to further improve the utilization rate of RF spectrum and communication capacity.and then we derive the outage probability of the mixed system and simulate the outage performance of the mixed system on the effect of various system parameters under the atmospheric attenuation and turbulence.The results show that the scheme of sharing spectrum by primary users and secondary users in underlay cognitive network and increasing the number of transmitting apertures and receiving apertures can significantly reduce the impairment of atmospheric attenuation and turbulence on the mixed system.What's more,it's more appropriate to select 2 transmitting apertures and 2 receiving apertures with the consideration of maximizing economic benefits and system performance.