Research On Power Amplifier Linearization In Wireless Communication System

Power amplifier(PA)is essential to wireless communication system,but most PAs are nonlinear.This feature will reduce quality of communication and effect other devices.To solve this problem,linearization methods are required.In the first part of this paper,the digital-predistortion(DPD)method is introduced.Testing and modeling a nonlinear PA,this paper simulated the DPD structure with the nonlinear model of PA.All works were done in MATLAB.Besides,a new DPD structure is proposed which contains parameters-selecting part.With this method,the precision of linearization can be improved.This paper divided the PA model into several parts according to input power,and set several groups of parameters to fit different parts of PA model.By recognizing the input signal,predistortion parts selects proper parameters for polynomials.With this method,precision of predistortion gets four times higher,and the(ACPR)adjacent channel power ratio of OFDM signal is reduced about 21 dB,better than traditional method with 7dB.Then,to realize the DPD method with FPGA,structure-design of DPD is proposed with Verilog programming.This section contains a new polynomial structure,a parallel structure with several polynomial cores and some additional models.The parallel structure can realize faster predistortion,and its RTL simulation is down with altera model-sim.The last part of this paper introduced the harmonic-probing model in frequency domain,this model can describe the nonlinearity of PA without considering the memory effect.With this model,the output wave can be predicted according to input signal power.This paper combined the model with feed-forward method,and proposed a digital feed-forward method.In this method,the generating loop of feed-forward signal with replaced by a digital signal generator with harmonic probing,this design avoids the matching of feedforward signal and main signal,the harmonics are restrained with 20 dB in average.