Design And Research On Transmission Mechanisms Of UAV-aided Multi-user Two-way Relaying Networks

In wireless communication,in order to combat the fading of wireless channel,especially in the long-distance or the edge of cell,it is very effective to expand the coverage of cell,and relay assisted cooperative communication is very effective.In recent years,the research of unmanned aerial vehicle(UAV)in the field of wireless communication has attracted the attention of industry and academia.It combines UAV and wireless relay technology to further improve the performance of wireless communication.UAV has the advantages of maneuverability,flexible configuration and high cost-effectiveness,and can provide or replace communication infrastructure in unexpected or temporary emergency tasks.Compared with the traditional static relay,UAV-aided relay has the advantages of mobility and line of sight(LOS),which can provide effective services in more severe environment.With these unique advantages,UAV-aided relay is regarded as a new relay technology,which is expected to further expand the communication scope and improve the communication quality.Although there are many advantages,UAV-aided relay technology still faces many technical difficulties and challenges.Compared with the unidirectional nature of information in one-way relay network,the source node and the end node of the Two-Way Relaying network can realize the exchange of information,which can cover the application scenarios that can not be applied in one-way relay network and greatly improves communication efficiency and frequency band utilization.Therefore,it is of great practical significance to study the optimal transmission strategy in UAV assisted bidirectional relay wireless communication network.In this paper,a UAV relay based on physical layer network coding protocol is designed.Focusing on total rate and energy efficiency,which are the main performance indicators of UAV-aided communication network,we propose a relay transmission scheme called time-slots pairing.The results show that the proposed time slot pairing relay strategy is suitable for mobile two-way relay network,and can effectively enhance the performance of the whole multi-user UAV assisted two-way relay networks.The innovation and main research contents of this paper are summarized as follows:1.Research on UAV-aided Two-way Relay Network Performance Optimization Transmission Strategy.For a multi-user relay communication network,the problem of maximizing the total rate of the communication network is studied.Multiple user pairs need to communicate with each other,but there is no communication link,which makes it impossible to communicate directly.Therefore,a UAV is used as a mobile relay to provide two-way relaying service for these ground users.Taking into account the practical factors such as the quality of service for each pair of users and the limitation of the energy consumption of drones,the optimization problem of the multi-user mobile relay network based on the physical layer network coding protocol is mathematically formulated combining with the time slots pairing relay scheme.Based on block coordinate descent method and convex optimization technique,an iterative algorithm for block rotation optimization with multiple variables is proposed by jointly optimization of slot pairing,user scheduling,power allocation and UAV trajectory design.The simulation results show that the proposed time slot pairing relay scheme can significantly improve the total network rate under the premise of ensuring the quality of service,and can effectively resist the overall network performance degradation caused by the improvement of user quality of service comparing with the traditional relay strategy.2.Research on Transmission Strategy of UAV-aided Two-way Relay Network Energy Efficiency Optimization.Aiming at the two-way relay network serving network edge users,the problem of maximizing network energy efficiency is studied.The edge users outside the cell coverage can not directly connect with the base station.A UAV is employed as a two-way relay to realize the communication.The energy supply of UAV is limited by battery capacity,so it is worth studying to make the limited energy play the most effect in the process of UAV relay information for users.Firstly,a fixed wing UAV flying in 3D space is considered,and the expressions of its communication capacity and propulsion energy consumption are derived.Then,based on the time slot pairing relay strategy,the two-way relay energy efficiency model is established.Finally,by using branch bound method,convex optimization theory and dinckelbach algorithm,the optimal resource allocation and trajectory planning are obtained,and the purpose of energy efficiency is maximum.The experimental results verify the reliability and effectiveness of the time slot pairing relay strategy in energy efficiency optimization.