Research On CoMP And NOMA-based Cellular-Connected UAV Communications Technology

Relying on the wide coverage and low cost characteristics of ground mobile communication system,cellular-connected UAV communication technology has become an international and domestic research hotspot with high attention.However,existing cellular networks are designed and optimized only for the communication needs of ground users,which cannot meet the highly reliable and high-capacity communication needs of UAV users,and cannot realize the harmonious coexistence of air and ground users.The main manifestations are: 1)the base station antenna is tilted downward,and the main lobe signal in vertical direction is directed to the ground users in the coverage cell,resulting in the UAV users can only obtain service through the sidelobe signal,leading to intermittent connectivity in the air-ground link and ping-pong handover of the UAV; 2)the air-ground/ground-air link has a high probability of line-of-sight propagation,and the UAV user will detect a larger number of interfering signal strengths comparable to the useful signal strengths in a larger area; 3)the introduction of UAV users will generate resource competition for ground users,leading to degradation of ground users communication quality.To address the above problems,this paper will carry out research on cellular-connected UAV communication technology based on the combination of Coordinated Multi-Point(CoMP)and Non-orthogonal Multiple Access(NOMA),and the specific research contents and innovative works are as follows:(1)The two base stations and three users CoMP-NOMA cellular-connected UAV communication system is studied.Firstly,the network scene of air-ground user coexistence,airground channel model and air-ground user transmission are modeled.Then,the performance analysis of the CoMP-NOMA scheme is carried out in the two-base stations scene to derive the successful transmission probability and average achievable rate of UAV user and ground user.Finally,the feasibility of the CoMP-NOMA scheme in the air-ground user coexistence scene is verified through experiments,and the experimental results show that the proposed CoMP-NOMA scheme can improve the reliability of UAV communication and the average ergodic rate of the system while guaranteeing the communication quality of ground users.(2)The scheme of research content(1)is extended to multi-cell network scene to study the transmission strategy of cellular-connected UAV users in a multi-cell scene.Firstly,considering the spatial random distribution characteristics of base stations,UAV and ground users,the random fading characteristics of air-ground channels,the poisson point process is used to model the network scene systematically; secondly,considering the strongest average received signal strength association strategy,the classification criterion of UAV users and the construction strategy of CoMP-NOMA clusters are designed; further,the association probabilities of different types of UAV users with the serving base station(collaborative base station set)are derived.(3)Based on the classification criterion of UAV users and the construction strategy of CoMP-NOMA clusters designed in research content(2),the performance analysis framework of CoMP-NOMA cellular-connected UAV communication networks in multi-cell scenes is studied.First,a NOMA transmission model for UAV users and ground users is constructed to derive the distance distribution of communication links between UAV users and service base stations(collaborative base station set)and ground users and service base stations; second,the successful transmission probability,average achievable rate of the user,and the average ergodic rate of the system are derived.Further,Monte Carlo simulations are performed with the help of MATLAB to verify the correctness of the theoretical analysis and reveal the superiority of the CoMP-NOMA scheme in the above performance metrics by comparing with three benchmark schemes,and further quantify the impact of key system parameters on the network.