Link Design And Algorithm Research Based On Digital Predistortion

New technologies of wireless communication improve spectral efficiency, with also increasing the peak-to-average power ratio(PAPR) of the transmitted signals. Without backing off the efficiency of RF power amplifiers(PAs), wideband signals with high PAPR through PAs are more likely to generate nonlinear distortion, increasing bit error rate of communication system. The contradiction between efficiency and linearity challenges the PA linearization techniques. Due to striking a balance between PA efficiency and linearity, digital predistortion(DPD) technique with the advantages of simplicity, flexibility and adaption, has become one of the most potential linearization techniques.In this paper, the key technologies of DPD are analyzed and the digital predistortion link is designed according to the relevant communication industry standards. Then an improved look-up-table(LUT) DPD algorithm based on the existing literatures is proposed to linearize PA. The main contributions of this paper are as follows.First, the general scheme and requirements analysis of the DPD link are established. On this basis, the design and verification of the link are completed and the influencing factors(i.e., delay estimation and compensation and amplitude gain adjustment) on the link are discussed and solved.Second, considering the low-precision and more resources consumption of the previous LUT DPD algorithms, a new LUT DPD algorithm is proposed to achieve PA linearization. And a new pre-adjustment values acquisition strategy based on Aitken iteration and a new LUT resources allocation strategy are described detailed. For digital PA, by the application of the new algorithm whose size is 30 and iteration time is one, simulation results show that the adjacent channel power ratio(ACPR), error vector magnitude(EVM) and normalized mean squared error(NMSE) are 79.04 d Bc/73.17 d Bc、0.0002%、-113.4549 d B, respectively.Third, to validate variety DPD algorithms performances based on the DPD link, some measurements(i.e., input-output characteristics curves, power spectral density and nonlinear distortion indices) are made. Results indicate that the new method can effectively achieve PA linearization. For nonlinear system, by the application of the new algorithm whose size is 30 and iteration time is one, the ACPR, EVM and NMSE are 62.94 d Bc/63.55 d Bc、0.1367%、-57.2709 d B, respectively.