Research On Combined PAPR Reduction And Predistortion Technique For OFDM System

Orthogonal frequency division multiplex(OFDM)is a multicarrier modulation technology with high data transmission rate.OFDM has high frequency efficiency,robust to multipath fading and narrowband interference.Based on these advantages,OFDM has become one of the core technologies in the next generation communication.However,OFDM has sensitive to non-linear and has a peak-to-average power ratio(PAPR),which restricts the practical application of OFDM.Therefore,reducing the PAPR for OFDM systems and compensating system's nonlinear distortion have an important theoretical significance and practical value.Based on the weakness of high PAPR and slow convergence for large-scale power amplifier device,the paper proposes a method combined clipping and filtering and lookup table predistortion technique.Firstly,the input signal is filtered by clipping and filtering in order to reduce the PAPR.Then the signal is processed by the clipping and filtering before getting into the lookup table predistorter and the power amplifier.The amplifier output signal is fed back to the look-up table by the adaptive algorithm in order to update the look-up table parameters accordingly.The above process is repeated until parameter estimation algorithm converges.Matlab simulation results show that the combined method improves the convergence speed of the system and reduce the PAPR of the system.Based on the weakness of high bit error rate(BER)and power amplifier's nonlinear distortion for portable devices and other handset,the paper proposes method combined clipping and filtering and polynomial predistortion.Firstly,by limiting the source signal with filter module we reduce the outer band distortion and spectral spreading,and the predistortion filters nonlinear distortion not compensated by voltage portion,then using limiting the filtered signal into the polynomial predistorter,the parameter can be adjusted by the adaptive algorithm.The final nonlinear distortion by the amplifier is compensated by the above signal processing.Matlab simulation results using parameters that indicate the performance of the system show that the combined method improves the performance of system's BER,compensates nonlinear distortions.