A memory polynomial predistorter for compensation of nonlinearity with memory effects in WCDMA transmitters

Power amplifiers (PAs) are inherently nonlinear devices and are used in all transmitters of a communications equipment. To improve the performance of telecommunication channels, digital baseband predistortion is employed to compensate for PA nonlinearities. But most existing architectures base on the memoryless PA model. For wideband signal transmission, PA memory effects can no longer be ignored and memoryless predistortion has poor performance. In this paper, a predistortion scheme based on the indirect learning architecture is proposed and analyzed with application to the wideband wireless transmitter. Then the performance of overall transmitter system is verified by simulation results. The measurement shows that, when inputting a single carrier WCDMA signal with 5 MHz bandwidth, good AM-AM and AM-PM performance and roughly 20 dB improvement of out-of-distortion at an offset frequency of 5 MHz were achieved, after adding the proposed predistortion method.