Research On Predistortion Techniques And Subsection Linearization In OFDM Systems

This paper mainly deals with predistortion techniques in OFDM (Orthogonal Frequency Division Multiplexing) systems. OFDM as a multicarrier modulation with many outstanding advantages suffers from high peak to average power ratios, which is one of its main disadvantages. As a result, OFDM signal is more sensitive to the nonlinearity of the HPAs (High Power Amplifier) than other signals, and needs wide dynamic range HPAs.In this paper, an improved method of linearization technique called subsection linearization is introduced so that two combined narrow dynamic range HPAs can be used to substitute for one wide dynamic range HPA (the two combined HPAs have the same parameters in this paper).At first, the memory of the HPAs is left out of account. The LUT (Look-up Table) method is discussed and its performance is evaluated according to the simulations. Based on the LUT method, the application of the subsection linearization method on two HPAs without memory is researched. Some simulations have been done, and the results prove that the subsection linearization method can combine two HPAs without memory to substitute for one wide dynamic range HPA without memory and the equivalent HPA's dynamic range is 2 times as wide as one original HPA's. Then, the memory of the HPAs is taken into account. A predistortion method for the HPAs with memory, called SFLUT (Simplified Filter Look-Up Table Method), is introduced. Its performance is also evaluated according to the simulations. The application of the subsection linearization method on two HPAs with memory is discussed. Based on the SFLUT method, some simulations have been done, and the validity of the subsection linearization method on the HPAs with memory is also proved. Finally, an explanation in theory is provided with some formulas for the validity of the subsection linearization method.