| Along with the increase of wireless users and broadband communications business development, in the modern communication, nonlinear distortions of channel have very strict requirements. Rf power amplifier is the strongest nonlinear source of transmitter system, when a signal through the nonlinear amplifier, can produce distortions within the signal bandwidth and spectral growth beyond the signal bandwidth, causing the bit error rate rise within the signal bandwidth and adjacent channels interference beyond the signal bandwidth, the serious influence communication system performance. Therefore, the study of power amplifier linearization technique is very necessary.This paper studies the nonlinear characteristics of power amplifiers and its impact on the communication system, mainly studies the adaptive pre-distortion technology digital the principle and implementation plan.This paper firstly,discusses power amplifier classification and linearization index, detailed analysis of power amplifier for the nonlinear properties and its influence of communication system, and briefly introduces amplifier linearization commonly used methods and carries on the analysis comparison. Then, detailed analysis of the power amplifier mathematical model and digital pre-distortion method, and introduce a baseband adaptive digital pre-distortion method. Through in-depth study adaptive algorithm, propose a LMS adaptive algorithm with variable step size based on memory-less power amplifier, this algorithm can well solve the basic LMS algorithm can't take into account the convergence speed and steady-state error problem.To the question of amplifiers memory effects which must be considered in the broadband communications systems, we introduce a adaptive digital pre-distortion method based on OFDM systems and present a adaptive algorithm which combined with LMS algorithm, based on the training sequences, and RLS algorithm. The theoretical analysis and simulation results show that the algorithm presented in this paper is simple in structure, and be better to improve the effect of pre-distortion device, so, it can compensate the nonlinear distortion of OFDM amplifier.To meet the demand for digital fiber optic repeater project, this paper studies the digital fiber optic repeater principle then technological indexes, and then combined with WCDMA digital fiber optic repeater power amplifier, this paper presents a rf power amplifier pre-distortion scheme based on the number of fiber optic repeater. Based on look-up table algorithm of the memory polynomial, effectively reduces the complexity of the algorithm, saving hardware resources. The tests show that, adjacent channel interference has been greatly improved. |
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