The Research On Digital Adaptive Predistorter In OFDM Systems

In wireless communication field, OFDM has been widely used due to its robustanti-interference ability and high spectrum efficiency, but the disadvantage of highPAPR makes OFDM very sensitive to the nonlinearities of amplifier, and requires thePA to have a great linear range. In fact, the majority of PA is non-linear. Innarrowband communication systems, the non-linearity is memoryless; and inbroadband ones, the non-linearity is memory. The both non-linearity affect theperformance of communication systems seriously. In order to reduce and eliminatethe nonlinear distortions to OFDM signals, it is necessary to compensate thenonlinearities of amplifier. Many linearization methods have been proposed,including back-off, feed-back, feed-forward, LINC and pre-distortion. The object ofthis study is the method of digital pre-distortion which is the most promising.Firstly, the basic principle of OFDM and DPD techniques is introduced in detail.Then, the four performance of OFDM signal influenced by HPA is researched. Then,four kinds of DPD implementation methods are discussed in the paper and simulatedon MATLAB, including memoryless polynomial, memory polynomial, memorylessLUTs and memory LUTs, the emulational results show that the DPD technologieshave compensated the non-linear of PA. At last, The paper proposes a newpre-distorter structure basing on LUT aiming at the special type of power amplifier，such as SSPA, The results of the simulation show that this technology hascompensated nonlinear distortion of PA, and hardware storage resources and runningspeed are effectively saved.