Research On Fading Characteristic Simulation In Mobile Satellite Channel

With the steady development of global networking and informationization, the subscribers'demands to communicate instantly and reliably at any time and any place can no more be simply satisfied by any single mobile communication approach, especially in the coming era of personal communication. As an important solution to this problem, Air-space-ground integrated information networks contains multiple communication systems, such as land microwave communication, cellular mobile communication, high altitude platform station (HAPS) communication, and heterogeneous combination network of low earth orbit (LEO), medium earth orbit (MEO), and geostaationary earth orbit (GEO) satellites. In the research of Air-space-ground integrated information networks, studies on link characteristics are essential. In order to acquire reliable data transmission, proper communication technologies must be selected accurately to adapt to the channel characteristics in the phase of system designing. On the other hand, the channel modeling can be used to simulate and verify the feasibility and affectivity of relevant technologies. Characterized by large coverage, being flexible in organizing a network and capabilities on global seamless roaming, satellites (mainly referred to mobile satellites) are chosen to play a quite important role in Air-space-ground integrated information networks. Against this background, the paper systematically studies simulations of fading characteristics along the satellite mobile link through analyzing related publications and papers, and has obtained some conclusions. The major work of this paper is organized as follows:First, since single-state narrowband statistical model can only describe single channel environment, while multiple-state model brings more parameters and more complicated simulation work, a wide-area environment two-state channel model including both"ideal state"and"nonideal state"was proposed to solve this problem, according to the principle that model should accurately depict the real transmission characteristics of the channel with relative simplicity and feasibility. Meanwhile, simulation of the model was implemented dynamically with filters mthod and Markov chain. Based on the experimental data of Iridium system measured by Communication Research Center, Harbin Institute of Technology, modeling parameters in three kinds of typical channel environment are fitted by using least squares error criterion and the method of linear least squares, and affectivity of the model is verified too.Second, given that broadband satellite mobile communication system must support multimedia service and broadband Internet access, the channel will be no more flat but frequency selective. Therefore, the influence caused by multipath becomes severer than before. Without enough measured data of channel statistics, studies on broadband satellite mobile channel modeling are still in the phase of exploring both at home and abroad. The paper analyzed the reasons of selective fading along broadband satellite mobile channel in time domain and frequency domain, and created a phase variable simulation model and an amplitude variable simulation model of broadband satellite mobile channel according to the multiple spot scattering principle and tapped delay line method respectively. Verified with measured data from German Aerospace Center (DLR), the models are proved to simulate the real transmission environment well.Third, taking antenna into account during channel research, the space dispersion characteristics of satellite mobile channel are analyzed by integrating radio wave transmission and array antenna characteristics. Considering the channel characteristics when the line-of-sight (LOS) link between satellite and mobile terminal with array antenna is obstructed, a three dimensional channel statistical model based on the geometrical cylinder model was created under the circumstance of heterogeneous direction of arrival (DOA) at mobile terminals, in which the azimuth and elevation angular distribution of DOA was described according to Laplace distribution and modified truncated cosine distribution in Parsons model. Expression equations of correlation functions of received signal are also given in the paper. Simulation model was built with Sum-of-Sinusoidal (SOS) method, and related parameters are determined by modified equal area method (MMEA). The created models are verified with Aulin model, and the results from numerical simulation have shown how the statistics of channel is influenced by antenna and radio wave dispersion.Finally, on the basis of current research on satellite mobile channel emulator, a set of multichannel intermediate-frequency-equivalent L/S band LEO mobile channel emulator with switchable control matrix was created combining both software and hardware. This channel emulator adopts the channel model proposed in Chapter 3 as its theoretical model, and can be used in constellation satellite communication simulation and verification system to simulate real-time channel characteristics along user link between satellite and mobile terminal in various sceneries. Moreover, the 3×6 switchable control (and 6×3 combining control) matrix on the channel emulator can be applied to simulate satellite beam and multipath switch function.