Study On Linearization Of Shortwave Power Amplifiers Using A Digital Predistorter

To enhance spectrum efficiency, linear modulation and multicarrier techniques are widely adopted in modem wireless communication systems, these signals be required to amplify linearly. However, in order to increase power efficiency, PAs are often driven into the saturation region, where nonlinear distortion is severe. Shortwave power amplifiers'nonlinearity produces harmonic distortion, cross modulation distortion. Linearization techniques play a key role to resolve the conflict between spectrum efficiency and power efficiency.In broadband communication systems, the memory effects can no longer be ignored, the performance of traditional memoryless modeling and predistortion method is seriously degraded.In this paper, methodologies of nonlinear systems are applied to model and predistort PAs with memory effects in broadband communication systems. The contents of the paper are as follows:(1)At first, we put up an testing platform to get the nonlinearities and memory character of different shortwave power amplifiers. Nonlinear characteristics of power amplifiers and memory effects of power amplifiers and the basic modeling theory are described. According to the measured results, we chose the appropriate behavioral model for each of them.(2)The principles of predistortion techniques are described. The look-up-table based and workfunctinn based predistorter are discussed and compared in detail.(3)A predistortion method is adopted for the linearization of PAs. The predistorter is constructed based on memory polynomial. The direct and indirect learning architectures are adopted to design the predistortion system. Simulation results show that the proposed method can effectively compensate the nonlinear distortion and memory effects of PAs.