Modelling And Estimation Of Air-sea Channel For High Sea State UAV Technical Research

The development and construction of marine economy and marine wireless information network all require the deep involvement of maritime UAVs,but there are many problems in establishing effective maritime UAV communication links under high sea state conditions.Correct knowledge of maritime wireless channel characteristics can guarantee the stability of communication under high sea conditions,but the traditional statistical channel modelling method requires multiple devices to conduct surveys,which will consume a huge amount of manpower and material resources.In addition,in order to meet the communication needs of air and sea wireless communication,Orthogonal Frequency Division Multiplexing（OFDM）technology is gaining more and more attention in maritime wireless communication due to its high spectrum utilization and strong resistance to multipath fading,while ensuring high transmission efficiency in the communication process requires high precision channel estimation algorithms are required to ensure high transmission efficiency.Therefore,in this paper,the communication channel characteristics are analyzed by ray tracing method for different sea conditions,and based on this,the maritime wireless channel estimation technique is studied.The work in this thesis is as follows:In this thesis,channel characteristics are first analyzed for different sea conditions.The sea state is an important factor affecting wireless communication in a maritime wireless communication link,and a detailed 3D sea surface model is required to study the channel characteristics under different sea states.Therefore,in this paper,four sea surface models with different wind speeds are established through the JONSWAP wave spectrum.Based on the different sea surface models,a geometric communication scenario of a maritime UAV is built,and the ray tracing（RT）method is used to statistically analyze the path fading,time delay distribution,time delay expansion,angle distribution and multipath number.The simulation results show that this approach provides a more comprehensive picture of the maritime wireless communication characteristics than other conventional maritime communication channel models.A comparison between the basic extension method and the compressed sensing method is then carried out for the dual-selective channel estimation problem in maritime wireless communication.The simulation results show that the NMSE accuracy is less than10^-3when using the base-expansion approach for estimating high sea state wireless channels;since the doubly selective channel can be represented as a sparse signal in the time-delay-doppler domain,the compressive sensing approach can be used for channel estimation,and the maritime wireless channel has cluster sparsity.The block-compressed sensing algorithm GOMP is improved for the structural characteristics of the maritime wireless channel.Compared with other conventional compressive sensing algorithms,the improved algorithm has higher reconstruction accuracy at different doppler frequency shifts and auxiliary guide frequency occupancy.Finally,considering the running time of different algorithms under different sparsity,a strategy for channel estimation under predicted sparsity is proposed,which combines the advantages of ROMP and the improved GOMP algorithm under different sparsity and can ensure high reconstruction efficiency and low time complexity.