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structure and the ability to effectively compensate for rain attenuation and the Doppler shift.The non-geostationary satellite channel for high speed communications cannot be considered an additive white Gaussian noise (AWGN) channel because of signal fading due to rain and the Doppler shift on the channel. For these reasons, we developed our own rain attenuation model with which we can synthesize the dynamic characteristics of rain attenuation. Carrier offset induced by the Doppler shift is also modeled by the orbit constellation parameters of a non-geostationary orbit satellite system.A simple and efficient estimation and prediction algorithm for channel conditions was required for allocating suitable transmission schemes at each sampling time. We developed various control algorithms and estimated their performance using the rain attenuation model. This paper proposes an efficient transmission system which can be adaptively applied in rain attenuation situations. Our system uses a block turbo code with an M-ary phase shift keying (PSK) strategy and for Doppler shift compensation, a 2-dimensional search algorithm which uses fast Fourier transform (FFT). Because of the successful development of code division multiple access (CDMA) technology for terrestrial mobile communications [3], application of CDMA to satellite communication is now being attempted. We developed a CDMA-based Doppler shift compensation technique to conform to this technological trend.In section II, we briefly present a simulation modeling technique for rain attenuation and the Doppler shift on the satellite communication channel. Section III describes the adaptive transmission scheme and the Doppler shift compensation method, and demonstrates simulation results using our own developed simulation software (S/W) packages. Section IV introduces a hardware (H/W) emulation board with an adaptive rain attenuation compensation algorithm. Finally, conclusions are drawn in section V. II. CHANNEL MODEL 1. Rain Attenuation ModelWe previously developed a rain attenuation model with which we can synthesize time-varying rain attenuation for any given time interval at Ku and Ka frequency bands [4]. This was necessary so that we could estimate the performance of the proposed adaptive compensation algorithm.Several papers have presented techniques on dynamic rain attenuation modeling [5]- [7]. Because Korea experiences heavy rain during a short period, it was difficult to synthesize rain attenuation. Therefore, we believed it necessary to develop a rain attenuation model which could synthesize typical Korean rain attenuation dynamics. The rain attenuation model we developed used measured attenuation data from the 12.25 GHz beacon signal of Koreasat 2 for two years; an example is shown in Fig. 1. Motivated by the fact that rain attenuation is a Markov process, a Markov chain [8] was used to model the rain attenuation process. We assumed that a rain event could be characterized by a 4-state Markov-chain. That is, a rain event consists of a beginning, a fading, ...

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In this paper, we introduce an adaptive radio resource allocation for IP‐based mobile satellite services. We also present a synchronous multibeam CDMA satellite system using an orthogonal resource sharing mechanism among downlink beams for the adaptive packet transmission. The simulation results, using a Ka‐band mobile satellite channel and various packet scheduling schemes, show that the proposed system and resource allocation scheme improves the beam throughput by more than two times over conventional systems. The simulation results also show that, in multibeam satellite systems, a system‐level adaptation to a user's channel and interference conditions according to user locations and current packet traffic is more efficient in terms of throughput improvement than a user‐level adaptation.