| Inland River means the river flows through one country. Our country is watered by numerous rivers. And the main framework of the inland river network can be seen as a structure called "Four longitudinal and four horizontal", which is composed of Changjiang River, Pearl River, Heilongjiang River and Beijing-Hangzhou Grand Canal. Narrow and curved channels and torrents are the characters of the inland waterway. Due to the limitation of traditional navigator such as radar and GPS, these equipments cannot ensure safety in sailing and avoidance, and they also cannot capture the static information(such as name,depth,destination,arrival time and etc.)and dynamic information(such as position,speed,heading,rotation rate and etc.). So only use these equipments cannot meet the requirements of safety in navigation. Now, Automatic Identification System (AIS) overcome the shortage of traditional navigators, which opens up a new way for safety navigation of inland rivers. AIS is more and more widely applied in the inland navigation of our country. As a kind of Ship Monitoring System, which belongs to wireless mobile communication network, the reliability of communication determines the application of AIS. So the research of reliability of communication of AIS in inland navigation is important for the safety of navigation.The elements which affect the reliability of communication are multiple, and because of special geographical environments, these elements of inland navigation are different from Maritime.The key point of this research is on the communication between the base station and ship berth of AIS. The work principle of base station of AIS is similar to ship berth of AIS. The reliability of wireless communication system is mainly affected by wireless channel. To study and simulate wireless communication system must analyze the characters of channel and use forecast model to study the broadcast discipline of radio firstly. Based on the consideration of factors of application and reliability and so on, this thesis chooses Okumura-Hata model and national standard model.According to the large amount of data tested in japan,Okumura and others have made the curve chart of propagation loss.The feature of the model is that the result of model given by the form of curves is completely based on measured data,it's inconvenient to apply in computer. So, Hata and some other people have analyzed on this basis and summarized a set of empirical formula,that is Okumura-Hata model. Okumura-Hata model is a kind of prediction model widely used in the mobile communication, it is an empirical formula obtained by the statistical analysis of test data, its applicable frequency range is 150～1500MHz, the distance is 1～20km,the effective antenna height of base station is 30～200m,and the mobile station's is 1～10m.Okumura-Hata model is established as the standard by urban propagation loss,the other terrains has made some amendments on this basis.GB/T14617.1-93 model is also a widely used model.In 1994, Okumura-Hata model was brought in the national standard after our country made some modifications, that is the national standard model.It extends the transmission path, leads into the density correction factor of the building and so on, it's a combination of theoretical and empirical models, so it's more suitable for the features of Chinese terrain.In this thesis, these two models are used to study the reliability of AIS communication system, and make some simulation analysis.On the basis of experiment, verifying the accuracy of Okumura-Hata models'application in wuhan, and doing some modifications. |
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