Performance Analysis Of UAV-assisted Satellite-to-Ground RF/FSO Communication System

As the number of mobile terminals grows rapidly,the traditional satellite-toground communication system with assistance of radio frequency(RF)technology has been difficult to meet the requirements for transmission rate,information security,communication coverage and rapid deployment.Free space optical(FSO)communication has the advantages of huge transmission capacity,high confidentiality,immunity to electromagnetic interference and free license.It can effectively meet the growing requirements for network capacity and alleviate the shortage of spectral resources in wireless communication system.In recent years,the booming unmanned aerial vehicle(UAV)technology has been widely applied in wireless relay communication system as a mobile relay node due to its easy to deploy,high flexibility and low cost.The UAV-assisted satellite-to-ground RF/FSO communication system combines RF and FSO communication technologies by UAV and relay communication technologies,which can break the limit of single communication technology.It can improve the flexibility and coverage of system,and overcome the problem that FSO communication is easily blocked by obstacles.However,the RF link and FSO link are affected by such fading factors as shadow fading,atmospheric turbulence,pointing error,attenuation loss and angle-of-arrival(AOA)fluctuation,which will seriously weaken the performance of communication system.For the influence of the above fading factors on UAV-assisted satellite-to-ground RF/FSO communication system,the paper carries out the research on performance analysis of UAV-assisted satellite-toground RF/FSO communication system,and discusses the influence characteristics of shadow fading,atmospheric turbulence,pointing error,attenuation loss and AOA fluctuation on system performance.The main research contents of the paper include:(1)The UAV-assisted satellite-to-ground RF/FSO communication system is constructed with fixed gain amplify-and-forward relay protocol.The RF link follows the shadowed Rician distribution considering the influence of shadow fading,and the FSO link follows the Málaga distribution considering the combined influence of atmospheric turbulence,attenuation loss and pointing error.The cumulative distribution function(CDF),probability density function(PDF)and moment generating function of end-to-end signal noise ratio are derived.Thereafter,the closed form expressions of system outage probability,average bit error rate(BER)and ergodic channel capacity are derived and analyzed.With the help of Monte Carlo simulation,the paper further proves the accuracy of the expression derivation.(2)The paper proposes a new FSO channel distribution model,considering that the AOA fluctuation caused by UAV hovering and vehicle equipment movement will seriously weaken the performance of FSO link.The distribution model considers the influence of atmospheric turbulence,attenuation loss,pointing error and AOA fluctuation on FSO link.The Málaga distribution is used to describe the fading caused by atmospheric turbulence,which is suitable for three kinds of turbulence including weak,medium and strong turbulence.Thereafter,the closed form expressions of outage probability and average BER for the channel model are derived and analyzed.The research indicates that the system performance improves greatly when the FOV angle increases,and then decreases slowly after the FOV angle exceeds a threshold value.(3)The paper further constructs a UAV-assisted satellite-to-ground RF/FSO communication system under the influence of AOA fluctuation.The RF link follows the shadowed Rician distribution considering the influence of shadow fading,and the FSO link follows the proposed FSO channel distribution model considering the combined influence of atmospheric turbulence,attenuation loss,pointing error,and AOA fluctuation.The closed form expressions of end-to-end outage probability and average BER of RF/FSO communication system are derived and simulated.The correctness of the results is verified by Monte Carlo simulation.