| The satellite communication channel is a very typical nonlinear transmission channel,and the nonlinear channel is mainly due to the nonlinear distortion of high power amplifier in communication system.The nonlinear distortion affects the transmission performance of the satellite communication system.With the increasing of the transmission bandwidth,the channel also shows a serious memory effect,which makes performance of the satellite communication system be worse.Pre-distortion and nonlinear equalization can effectively solve the nonlinear distortion of the communication channel.In this paper,we study the fast compensation technique of nonlinear distortion in the satellite communication channel,aiming at solving the problem that when pre-distortion and nonlinear equalization solve the nonlinear distortion of communication channel,its adaptive algorithm has a slow convergence speed.The main results of this paper are as follows:1.A fast pre-distortion compensation technique is studied for memoryless nonlinear distortion in narrowband satellite communication.When adaptive polynomial LMS pre-distortion compensation algorithm is used to compensate the memoryless nonlinear distortion,there occur the defects of the slow convergence speed and big steady state mean square error.To counteract these disadvantages,an improved variable step size least mean square algorithm(IP-VSSLMS)is proposed.Furthermore,a new stronger variable step size factor is obtained by using the error signal and the average energy of error signal and input signal.The algorithm can effectively enhance the ability of dynamic adjustment for step size factor.The simulation results show that the algorithm not only has best power spectrum density,can improve the convergence speed and the steady-state mean square error of the pre-distortion by 700 times and 3dB.2.A fast pre-distortion compensation technique is studied for memory nonlinear distortion in broadband satellite communication.When adaptive polynomial pre-distortion compensation algorithm is used to compensate the memory nonlinear distortion,there occur the defects of the slow convergence speed and big steady state mean square error.To counteract this problem,a fast shrinkage Recursive Prediction Error Method(SH-RPEM)algorithm is devised for the memory polynomial pre-distortion over nonlinear satellite channel.By using a known Shrinkage method and L1-L2 minimization formulation,the relationship between the noise-free posteriori and priori error signal is obtained.Furthermore,an optimal forgetting is proposed by minimizing the mean square of the noise-free posteriori error signal.The simulation results show that the SH-RPEM algorithm improves the convergence speed of pre-distortion by 800 times without changing other performance.3.A fast Wiener equalization compensation technique for memory nonlinear distortion in broadband satellite communication is studied.When the Wiener equalization compensation algorithm is used to respectively compensate the memory distortion and nonlinear distortion,there occur the defects of the slow convergence speed and bad stability.To solve the problem,a fast nonlinear channel variable forgetting factor nonlinear channel recursive least squares algorithm(VFFNCRLS)was proposed.On the basis of traditional NCRLS algorithm,the relation between forgetting factor and step length factor was established.Furthermore,a new variable forgetting factor was derived.The simulation results show that the VFFNCRLS algorithm improves the convergence rate of the equilibrium by 400 times without changing other performance.4.A fast simplified Volterra equalization compensation technique for memory nonlinear distortion is studied in high speed broadband satellite communication.When the simplified Volterra equalizer is used to compensate the memory distortion and nonlinear distortion at the same time,there occur the defects of the slow convergence speed and bad stability.To counteract this problem,a fast shrinkage least mean square Newton(SHLMS Newton)algorithm is devised for adaptive Volterra equalizer over satellite nonlinear channel.A noise-free posteriori and priori error signal are obtained by using a known Shrinkage method and L1-L2 minimization formulation.Furthermore,by minimizing the energy of the noise-free posteriori error signal,the SHLMS Newton method is able to provide a variable step size to update the weight vector for the adaptive Volterra equalizer,significantly enhancing the convergence speed.The simulation results show that the Newton SHLMS algorithm improves the convergence rate of the equilibrium by 800 times without changing other performance. |
