| With the development of technology,network and human lives have been inseparable.Radio frequency(RF)communication below 6GHz is the most widely used in wireless communication,and the frequency spectrum used has been divided and used,and it has become an extremely scarce resource.Free-space optical communication(FSO)is an emerging wireless communication method that uses laser and atmosphere as information carriers and transmission media respectively.It has no frequency license,huge bandwidth,high speed,high confidentiality,and low cost.Such advantages have been adopted in more and more wireless communication scenarios,and have good development prospects.However,random factors such as directivity errors and atmospheric turbulence will seriously affect the performance of the FSO system,which greatly shortens the communication distance of the FSO system.Combining RF link and FSO link to form a hybrid communication system can effectively improve the stability of the network,such as hybrid RF/FSO relay system,RF/FSO hybrid backup system,etc.Among them,the hybrid RF/FSO relay system forwards information from the RF link to the FSO link through the relay node,which can extend the transmission distance.Based on the hybrid RF/FSO relay system,this paper conducts research on millimeter wave(mm W)in the RF link.The mm W band is rich in spectrum resources,and the 60 GHz frequency band,which has attracted much attention,does not require spectrum certification,which is very attractive in research work in the field of wireless communications.In the hybrid mm W RF/FSO relay system,mm W RF and FSO can play their respective advantages to extend the communication distance and increase the network capacity.In order to further improve the performance of the hybrid mm W RF/FSO relay system,this paper also applies multiple input multiple output(MIMO)technology in the FSO link,which uses multiple transmit antennas and multiple receive apertures to transmit signals,thereby Reduce the influence of factors such as directivity errors and atmospheric turbulence.The main research contents of this paper are as follows:(1)Modeling and performance analysis of hybrid mm W RF/FSO relay system considering directivity error.The mm W RF link obeys Nakagami-m fading,and FSO is modeled as a joint Gamma-Gamma distribution considering directivity errors.On this basis,the statistical characteristics of the end-to-end signal-to-noise ratio(SNR)of the fixed gain and variable gain are derived respectively.Subsequently,the Meijer-G function is used to calculate the outage probability(OP),the average bit error rate(Average bit error rate,ABER),and the closed-form analytical formula of the traversal capacity.Finally,Monte Carlo(MC)simulation is used to verify the accuracy of the formula,and to compare and analyze the system performance under different conditions.(2)Hybrid mm W RF/MIMO-FSO relay system modeling and performance analysis.MIMO technology is used in the FSO link,the relay adopts fixed gain and variable gain respectively,and the receiving end adopts Equal-gain combining(EGC)method to combine multiple signals.Based on the above conditions,the closed-form expressions of the cumulative distribution function(CDF),OP,ABER and ergodic capacity of the end-to-end SNR of the system are derived,and the accuracy of the derivation of the above formula is verified by MC simulation.Comprehensive analysis of the impact of MIMO technology on the system performance to ensure that the best system performance is achieved at the lowest cost.The simulation experiment in this paper shows that MIMO technology can effectively increase the stability of the system and alleviate the influence of atmospheric turbulence.Amplify-and-forward(AF)relay scheme based on fixed gain can achieve better system performance.The simulation numerical results of the system performance indicators completely match the MC simulation results.The research in this paper can lay the foundation for the research of hybrid RF/FSO relay system in the future. |
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