| There are nonlinear effects which affects the transmission signal in digital satellite communication systems, this kind of effect will cause serious signal amplitude distortion and phase rotation at the receiving end, thus affecting the performance of the satellite communication system. This nonlinear effect comes mainly from the non-linear characteristics of internal amplifier of satellite, but studies have shown that group delay distortion effect which caused by various distortions in satellite channel is also an important factor leading to the signal nonlinear distortion. Researches about channel modeling and compensation techniques at home and abroad which do not consider this factor has certain limitations.In this paper, following aspects are studied against defects of the traditional methods of modeling and equalizing nonlinear satellite channel.(1) To solve the problems which caused by traditional Volterra series modeling, In the analysis of the relationship between structural characteristics of Wiener models and nonlinear characteristics of the satellite internal amplifier, the method of using Wiener model to model and combining with Hammerstein model channel to equalize the nonlinear satellite channel is proposed, the modeling effect of Wiener model is studied under different SNR of uplink at the same time. Simulation results show that modeling Traveling Wave Tube Amplifier with Wiener model is reasonable,which can get a better effect combining with Hammerstein equalizer.(2) Uplink channel noise is considered as the α stable distribution noise which is more common in actual channel (Domestic and foreign research generally assumes uplink noise as Gaussian White Noise),and then traveling wave tube amplifier is modeled with Adaptive Neuro-Fuzzy Interference System because of its ability that ANFIS can unlimited approach nonlinear systems. Simulation results show that Wiener model is completely unable to fit the nonlinear properties of Traveling Wave Tube Amplifier, while ANFIS model can achieve good results under a stable distribution noise environment.(3) Researches at home and abroad which do not consider the impact of nonlinear effects produced by the group delay distortion of the signal has certain limitations. In this paper, satellite channel model integrating nonlinear effects of satellite communications systems and group delay of the nonlinear amplifier is constructed by considering these two effects, then, the satellite channel analytic model based on the priori information of satellite channel is constructed by analyzing the priori information of satellite channel. Comparing with Wiener model,the satellite channel analytic model constructed in this way has faster convergence and smaller steady-state error,so it is more practical.(4) To solve the problem that the classic Volterra equalizer has large amount of computation, an improved non-linear adaptive equalizer of the satellite channel is proposed, This new nonlinear adaptive equalizer has less computational complexity than Volterra equalizer. Meanwhile, APSK signal which equalized by improved adaptive equalizer has more compact constellation points. |
