Research On Frameless Random Access Methods In UAV Networks

With the enormous development potential of unmanned aerial vehicle(UAV)in multiple industries,UAV networks have gradually become a research hotspot.However,these networks have problems such as severe inter-node interference and poor transmission efficiency.Multiple access technologies can reduce inter-node interference and improve transmission efficiency,which are crucial for UAV networks.As a new type of multiple access technology,frameless random access technologies have the characteristics of no pre-dividing resource and unfixed frame structure.The high flexibility of frameless random access technologies can well match the dynamic of UAV networks.The main research contents and contributions are summarized below.Firstly,for dynamic UAV network scenarios,this thesis proposes a frameless random access performance analysis method based on the degree distribution evolution.To begin with,the frameless access is modeled by Luby Transform(LT)codes,and the matrix based LT codes representation method is proposed to achieve more direct degree distribution representation.Then,the degree distribution evolution algorithm is proposed.Based on the above representation method,the change of degree distribution in the decoding process is derived,and the success probability and degree distribution of each decoding step are obtained.Finally,the prediction results of access performance are derived according to the results of degree distribution evolution.The simulation results show that the proposed scheme is more accurate and less complex than the benchmark schemes.Secondly,for distributed dynamic UAV networks,based on the above works,this thesis designs a novel frameless access method.First,the access process for the access system is designed,that is,each UAV segments and preencodes the collected data,and then uploads the processed data to the leader UAV.The leader UAV uses the Successive Interference Cancellation(SIC)and precoding decoding algorithm to recover the data.Based on the above access process,this thesis proposes the node number estimation method,the access probability calculation method,and the adaptive slot number adjustment method for the distributed and highly dynamic UAV networks.Finally,simulation results show that the proposed access method has a certain performance improvement compared to the benchmark methods,and can maintain efficient and stable data transmission in dynamic scenarios.