Performance Analysis Of UAV Cooperative Multi-relay Communication System

Unmanned aerial vehicles(UAV)is a significant complement to conventional communications because of its convenience,flexible deployment,low cost and wide coverage.With the rapid development of science and technology,UAV has been widely used in public and civil fields.As UAV technology matures,people combining the technology and modern communication technology,which not only solve the problem of inadequate coverage of existing communication networks in some remote areas,but also relieves the pressure of ground communication facilities in the event of natural disasters or large-scale sports events.It can realize rapid deployment and restore communication even under adverse conditions.UAV can also be used as an auxiliary device to assist the traditional communication network,to communicate and to improve the network performance.As the first year of the development of 5G(The 5th Generation Mobile Networks),how to further improve the communication quality and emergency communication performance under special circumstances has also attracted people's great attention in 2020.On the one hand,affected by various factors such as signal refraction and reflection,multipath fading occurs in the transmission process of wireless communication,the quality of transmission is seriously affected and the capacity of the system is greatly limited.On the other hand,due to its natural characteristics of openness,wireless communication makes it easy for eavesdroppers to receive illegally through wireless channels,which results in security threats and serious challenges to the security of wireless communication.This thesis is to study the multi-relay cooperative communication system based on UAV,and to propose different relay selection strategies to select the best relay to participate in the communication and to analyze the performance of the communication system.Firstly,we use the Max-min Relay Selection(MMRS)strategy to select the best relay under the system model of this paper,and then analyzes the outage performance of the communication system,and through approximation,the asymptotic outage performance has also been analyzed,and finally the diversity gain of the system is studied through the analysis results.In this paper,we establish a two-dimensional mathematical model analysis chart,and considering various random parameters,by referring to the cumulative distribution function known in the literature and introducing the first-order Marcum Q function approximation,the performance indicators such as the outage probability and asymptotic outage probability of the entire system are calculated in closedform expression.This paper also takes into account the convenient characteristics of UAV deployment.By considering the path loss and the coverage area encountered by the UAV during the information transmission process,the optimal flying height of the UAV is derived.Subsequently,we studies the physical layer security performance of the system model,uses the maximum secrecy capacity as the selection mechanism for relay selection,and add an eavesdropper to the channel between the selected best relay drone and the user.In this paper,the probability density function of the system is derived from the known cumulative distribution function,the secrecy outage probability(SOP)of the system is theoretically analyzed and its closed-form expressions are deduced.Under different condition of parameters,computer simulation is used for simulation analysis and verification.