Simulation and Implementation of Polynomial Predistortion based on Variable-step LMS Algorithm

Aiming at the low convergence speed and the insufficient nonlinearity improvement of traditional constant-step LMS(Least Mean Square) predistortion algorithm,including the high complexity of RLS algorithm predistortion,the polynomial predistortion technology based on variable-step LMS algorithm is studied and researched.Simulation and analysis on algorithm performance indicate that the speed of the algorithm is fairly fast and the nonlinear distortion within frequency band could be improved with no obvious increase of algorithm complexity.A HF(High Frequency) transmitter hardware platform based on DSP and FPGA is built up,thus to testify the algorithm efficiency.The test on dual-tone signal output of PA(Power Amplifier) indicates that IMD3(Third-Order Intermodulation Distortion) decreases by 23.3 dB while IMD5 descends by 15 dB in the algorithm predistortion system,and the efficient improvement of nonlinearity for power amplifier could thus be realized.