| Researching Purpose of the dissertation: Satellite mobile communication as one of the main role in the future personal communication is widely applied recently by the unique merit on covering area and movement. Satellite communication system is a both power and bandwidth limited system. In land mobile satellite communication, for the difference elevations corresponding to difference satellites and movement of the mobile terminal, the received signals are affected by the multipath fading and shadow effect. Thereby the communication links between satellite and mobile terminal constrain the performance of the whole system. So the channel model of land mobile satellite communication is the researching focus in the field of satellite communication from beginning to now. Different models can be constructed according to different elevation, different geographical environment and different measuring methods. Based on the situation that the LOS between the satellite and mobile terminal is resisted, there are following kinds of channel model: urban environment (the LOS is resisted completely) in which the major received signals is multipath signals; suburb environment (partial LOS is resisted) in which the received signals are consisted of LOS affected by shadow fading and multipath components; open area (the LOS is not resisted completely) in which the major received signals is LOS. According to the different degree of received signals be affected by shadow fading, there are following two kinds of channel models: partial shadow model and full shadow model. For former the shadow fading only affected the LOS; for latter the shadow fading affected not only the LOS but also the multipath components. Up to now there are typical models as following: C.loo's suburb environment model; Suzuki's urban environment model; Corazza's low orbit channel model; Lutz's two-states model. The aforementioned models have following shortages: the limited applicable environment; the implicit physical meanings; lack of researching on high order statistic character. There have been many new progresses in researches of channel model from 90's. P?tzold proposed improved Suzuki model. And Y. J. Xie proposed universal model. Entering the 21st century , in order to meet the requirements for speed and quality of transmission, wide-band satellite communication becomes the focus of be discussed more and more. The research for channel model of wide-band satellite communication is developed, the properties of wide-band satellite communication channels are focused on frequency-selected multipath fading. In this paper, we studied five aspects as followed: 1. Discussing the survey of satellite communication. Satellite communicat-ion presents many predominant characteristics: constructing terminal convenient-ly; covering area widely; the expenses have no relation to the distance; overcoming the geographical obstructions such as sea,desert and mountains etc; terminal can run in outlying regions or country independently and technologies are ripe. With the development of satellite communication and improvement of requirement for multimedia communication, the concept of wide-band satellite communication was given. It is used for multi-channel broadcasting, and long-distance transmission of internet and intranet. As access of land multimedia communication system, wide-band satellite communication become necessary means of realizing global personal communication and internet aerial high-speed communication. 2. Introducing several kinds of multiple accesses in satellite communication system. They are FDMA, TDMA and CDMA. FDMA distinguishes different consumer based on frequency, TDMA based on slot, CDMA based on code. Each multiple access has different characteristics but CDMA becomes main technology in 3G Mobile Communication System because it's unique merit. 3. Modeling flat fading channel of satellite mobile communicate-on. The model contains two types, one is that assuming the received signals isn't affected by shadow fading, the analysis is easier; the other is that considering the effect of shadow fading, and the effect acts on not only LOS but also multipath components. The amplitude of LOS affected by shadow fading is lognormal distribution, so the analysis of signal is more complex, but the model conforms to the real transmission environments of electromagnetic wave better. The probability density function (pdf) and autocorrelation function (acf) of the envelope of received signal are given as well as two high-order statistics, and the... |
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