| With the large-scale commercial deployment of the fifth generation(5G)mobile communication system,research on the sixth generation(6G)mobile communication technology has also commenced.The 6G communication system proposes four major paradigm shifts:global coverage,all spectra,full applications,and strong security,and is dedicated to achieving seamless wireless network coverage across all terrains and spaces.As a key scenario in the 6G space-air-ground-sea integrated network,maritime communication has garnered increasing attention.Due to the unique characteristics of the marine environment,the technological development of maritime communications has lagged behind that of terrestrial communications and currently fails to fully meet the demands of the Blue Economy.The characteristics analysis and modeling of maritime channels is the indispensable research foundation for the design,planning,deployment,and optimization of maritime communication systems.However,there is still a lack of channel models that can accurately reflect the characteristics of maritime channels.To solve this problem,a series of channel models suitable for different maritime communication scenarios and antenna configurations are proposed,based on a thorough analysis of maritime channel characteristics.These models provide important theoretical support for the research and development of maritime communication technologies.The main contributions and innovations of this dissertation are as follows:(1)A regular shaped-geometry based stochastic model(RS-GBSM)is proposed based on the uniform linear arrays(ULAs)for ship-to-land scenarios.This model considers the ship-to-land signal propagation environment and utilizes spherical structures and elliptic cylindrical structures to describe the three-dimensional(3D)distribution of scatterers such as the sea surface and buildings in the channel.The delay and angle parameters of multipath are computed based on geometric relationships.The key channel statistical properties,such as space-time correlation function,Doppler power spectral density(PSD),and delay PSD,are derived,simulated,and analyzed.By comparing the simulation results and measurement results,the accuracy of the proposed channel model is verified.(2)An irregular shaped-GBSM(IS-GBSM)is proposed based on the ULAs for ship-to-ship scenarios.The channel components in the model vary with the communication distance,thus supporting the characterization of the location-dependent property.In the proposed model,the influence of sea wave fluctuations on antenna trajectories and the trapping effect of the evaporation duct on multipath components are considered.To address the environmental dynamics and the application of massive multiple-input multiple-output(MIMO)antenna arrays,a space-time joint birth-death and evolution mechanism is adopted to describe the non-stationarity of scattering clusters in the time and array domains.The model obtains large-scale channel parameters with spatial consistency using spatial filtering algorithm,and supports large bandwidth and high delay resolution.Based on the proposed channel model,the statistical properties of the channel are derived and simulated,including time/angle/Doppler PSD,stationary interval,space-time correlation function,and root-mean-square(RMS)delay/Doppler spread.The simulation results show that the channel components vary as the antenna position changes,reveal the impact of communication distance on the channel statistical characteristics,and demonstrate that the proposed model can accurately capture the non-stationary property of the channel.Through comparative analysis with the measured data,the accuracy of the model was proved.(3)A 3D non-stationary general GBSM applicable to various maritime communication scenarios such as ship-to-ship,ship-to-land,unmanned aerial vehicle(UAV)-to-ship,and UAV-to-land scenarios is proposed.By adjusting the channel parameters to characterize different scatterers in various scenarios,the proposed channel model can uniformly model the channel characteristics of different maritime communication scenarios.The sea spectrum is used to model the wave height in 3D space,then the distribution of sea surface scattering clusters,the probability of the line-of-sight(LoS)path being blocked by waves,and the rotation of the shipboard antenna array caused by fluctuating sea waves are taken into account.This enables the model to accurately reflect the influence of the sea surface on the channel.The effects of antenna height and building distribution on the link state probability are fully considered to calculate the LoS probability in hybrid land-sea communication links.Additionally,the model considers the effects of UAV rotation and evaporation duct transmission on the channel.The impacts of various channel parameters on the channel characteristics and system performance are investigated by deriving and simulating the channel statistical properties such as space-time-frequency correlation function,angular PSD,RMS delay spread and stationary distance,as well as the channel capacity.The accuracy of the model is validated by comparing the measured results with the simulation results.(4)A 3D non-stationary GBSM and the corresponding beam domain channel model(BDCM)are proposed based on the uniform circular arrays(UCAs)for maritime communication scenarios.Considering the 3D spatial resolution of the UCA,an adapted beamforming matrix is provided,and the invertibility of this matrix is derived to establish the interconversion relationship between the array domain and beam domain channel models.To account for the spatial non-stationarity exhibited by the channels with massive MIMO arrays,the concept of visibility region is employed to model the birth-death behavior of multipath components along the array axis.The large-scale UCA is divided into multiple sub-arrays to reflect the offset of multipath parameters on different antennas.The key statistical properties of the BDCM,including channel power,power leakage,space-time-frequency correlation function,and RMS Doppler/beam spread,are derived and simulated to investigate the necessity of considering array non-stationarity.Some of the statistical properties of the BDCM are compared with those of the GBSM,revealing the sparsity of the beam domain channel matrix and the insensitivity of the BDCM to Doppler shifts.In summary,the research conducted in this dissertation has focused on channel characteristics analysis and channel modeling for 6G-oriented maritime communications.Different channel modeling methods have been employed to mimic several typical maritime communication environments,resulting in the proposal of channel models with scenario adaptability.These research efforts could provide support for the design,evaluation,and testing of 6G maritime communication systems under diverse frequency bands,scenarios,and array deployment conditions,and contribute to the advancement of 6G maritime communication technologies. |
