Research On Digital Predistortion Techniques In OFDM Systems

OFDM has been widely used due to its high spectrum efficiency and robustanti- interference ability, but the disadvantage of high PAPR makes OFDM verysensitive to the nonlinearities of amplifier, especially the nonlinearities introduced byHPA (High Power Amplifier) in transmitter. In order to reduce the nonlinear distortionsto OFDM signals, it is necessary to compensate the nonlinearities of amplifier.Consequently,a lot of linearization methods have been researched including back-off,feed-back, feed- forward, LINC and predistortion. Digital predistortion techniques inOFDM systems are mainly discussed in this paper. Firstly, the basic principle of digitalpredistortion techniques is briefly introduced. Then, in the case of memoryless HPA,predistortion methods based on polynomial and LUT (Look-up Table) are separatelyused to compensate the nonlinear distortions of amplifier, and it is shown effectual.Meanwhile,according to Wiener model and its separation principle, a predistortiontechnique for memory HPA, called filter polynomial method, is introduced, andsimulation results show that performances of filter polynomial method are better thanmemory polynomial method which is commonly used in the research of memory HPAat present.