Research On VDES Channel Modeling Technology

Since the beginning of the 21 st century,the ship automatic identification system(AIS)has played an important role in ensuring the safety of maritime transport and maintaining the order of maritime traffic.However,in recent years,with the increasing demand for maritime communications,the ship automatic identification system AIS has been very crowded in the VHF usable frequency band.The data link overload of AIS system leads to information congestion and other problems,which seriously affects the safety of maritime navigation.In this context,IALA puts forward the concept of VDES system.As an upgrade of AIS system,the system has faster and stronger data exchange ability in VHF band.On the basis of guaranteeing the original functions of AIS such as collision avoidance and position recognition,two modules,ASM special application message and VDE broadband VHF data exchange,are added,which greatly improves the coverage of communication.It also provides technical support for e-navigation and GMDSS modernization,and becomes a global data exchange system integrating sea,land and air.Firstly,this paper studies the VDES satellite channel model.The characteristics of satellite mobile channel are analyzed from three aspects: path fading,shadow fading and Doppler frequency shift.The probability distribution commonly used in satellite mobile channel model is introduced theoretically and the corresponding probability density function curve is drawn by MATLAB.Then,the first-order statistical characteristics of the basic C.Loo satellite channel,i.e.probability density function,are theoretically deduced,and the simulation method of satellite channel model is introduced.The Rayleigh distribution,Rice distribution and lognormal distribution are simulated respectively to verify the validity of the basic model.Only the shadow shadowing effects of multipath components and direct components are considered in the traditional C.Loo satellite channel model.On this basis,the Doppler shift of the direct component is considered,and the improved C.Loo channel model is established.The effectiveness of the model is demonstrated by simulation.Secondly,this paper studies the VDES sea surface transmission model.The transmission path of the VDES signal at sea is divided into a direct path,a specular reflection path,and a diffuse reflection path.In addition,the concept of effective diffuse reflectance area is introduced,and the range of effective diffuse reflectance area and the energy of specular reflectance component and diffuse reflectance component under different sea surface environments are simulated and analyzed.On this basis,the small-scale fading of VDES sea channel is simulated by Jakes model.The incident angle and energy of each point in the effective diffuse reflection region to the receiving end are calculated under the preset sea scene.The incident wave is superimposed to form a small-scale fading channel on the sea surface,and the rationality of the channel is obtained by simulation.Then,the transmission loss model of VHF communication at sea is given,and the related physical factors affecting the transmission loss at sea are modeled.The relationship between the related physical factors and transmission loss is analyzed.Finally,the transmission loss model of VDES signal at sea is given and simulated.Finally,this paper studies the OFDM spectrum sensing method and the sea channel performance analysis.With the rapid development of wireless communication technology,the problem of insufficient spectrum resources is becoming more and more serious.In surface communication,especially in some busy ports,VDES system needs to undertake high-capacity and high-speed data communication,which makes the problem of lacking spectrum resources still exist in surface communication.Cognitive radio CR has attracted much attention because it can greatly improve the spectrum efficiency of wireless communication systems.Spectrum sensing is the core technology of cognitive radio.This paper also explores the application of spectrum sensing technology in sea channel.Nowadays,many wireless standards adopt OFDM technology.How to stably perceive the OFDM signal is also very important to provide adequate protection for the primary user.Due to the existence of ISI,the performance of traditional spectrum sensing methods based on CP has dramatically declined.To solve thisproblem,a spectrum sensing method based on CP double correlation coefficient is proposed.In the proposed method,two different correlations of CP were considered and their results were added.By exploiting the correlated and uncorrelated parts in the results,ISI disappeared completely and the total energy of the correlations was found to be just an unbiased estimate of the signal energy which could thus provided an accurate likelihood ratio test(LLRT)statistic for the spectrum sensing.The maritime channel in the preset scenario is established for maritime communication and the relevant spectrum sensing simulation is carried out.The results show that the spectrum sensing method based on CP double correlation coefficient is more performance than the traditional CP-based method in the maritime multipath channel.