Research On Transmission Strategy Of Mobile Cooperative Communication Systems Based On UAVs

Relay cooperative communication technology can significantly improve the service quality and coverage of communication networks,which is a research hotspot in the field of wireless communication.Considering the mobility advantage of unmanned aerial vehicles(UAVs)and the characteristics of good line-of-sight(LoS)channels,applying UAVs as mobile relays can further improve the flexibility and coverage performance of the networks.At present,as for UAV-assisted relay systems,scholars mostly conduct research on one-way relay,while the research on two-way relay is relatively scarce.Considering that the two-way relay technology can effectively alleviate the shortage of spectrum resources in the field of wireless communication,this thesis investigates the UAV two-way relay system with physical-layer network coding(PNC).Besides,this thesis also pays attention to the actual communication requirements such as long-distance user communication and information timeliness,and investigates the UAV two-way multi-hop relay system.Based on the above considerations,the research content of this thesis is summarized as the following two points:1.Design of UAV two-way relay system based on PNC.In view of the mobility advantage of UAV and the characteristics of high spectrum efficiency of two-way relay system,the UAV two-way relay system based on PNC is studied by combining the UAV relay system with two-way relay system.Comprehensively consider UAV mobility constraints,propulsion power constraints and transmission power constraints,the time slot resources and transmission power of the system are reasonably allocated,and the flight trajectory of the UAV is optimized.By applying genetic algorithm(GA)to solve the time slot resource pairing,slack variables and successive convex approximation(SCA)technique are introduced to realize power allocation and UAV trajectory optimization.Finally,an alternating iterative optimization algorithm is proposed to jointly optimize time slot pairing,transmission power allocation and UAV trajectory design to maximize system sum-rate.In the simulation results,the proposed design is compared with the UAV one-way relay system,fixed relay system and other benchmark designs.The results show that the proposed UAV two-way relay system achieves good performance gains.2.Design of UAV two-way multi-hop relay system.In view of the fact that the traditional UAV one-way relay systems may face the problems of low timeliness and high energy consumption when dealing with the actual communication requirements such as long-distance user communication.Therefore,this thesis proposes the UAV two-way multi-hop relay system,which utilize good air channel conditions and use multi UAVs to carry out information interaction in the air to improve the efficiency of information transmission.Also,referring to the actual communication scenarios,the probability LoS channels are used for communication between UAVs and ground users,and the LoS channels are used for information interaction between UAVs,while considering the causal constraints of information transmission.Through iterative optimization of system time slot scheduling,power allocation and UAV trajectory design,the local optimal solution of the problem is finally found.In the simulation results,the proposed design is compared with the classic UAV one-way dual-hop relay system.Considering the throughput,information timeliness and propulsion energy consumption of UAVs,the comprehensive performance of the proposed UAV two-way multi-hop relay system is better than that the UAV one-way dual-hop relay system.