The Block-Oriented Digital Predistortion Based on the 2-D Complex-Valued Spline Interpolation Lookup Table Method

In this paper, a novel two-dimensional (2-D) complex-valued spline interpolation lookup table (LUT) method is proposed to construct the cascaded digital predistortion (DPD) system. Three schemes, namely the 2-D complex-valued spline interpolation Wiener DPD (2D-CSPW), the 2-D complex-valued spline interpolation Hammerstein DPD (2D-CSPH), and the 2-D complex-valued spline interpolation Wiener-Hammerstein DPD (2D-CSPWH), are given for the DPD model construction, where the different serial orders of linear and nonlinear blocks are considered. The local mapping property achieved by the proposed approach can closely approximate the conventional polynomial model under strong power amplifier (PA) nonlinear conditions, involving only a few free parameters, which is promising for achieving real-time continuous nonlinear learning. The proposed DPD schemes have been extensively validated through different RF measurements, including those for highly nonlinear Doherty PA (DPA) and the load modulation balanced amplifier (LMBA), as well as the commercial PA. The results show that the proposed 2D-CSPWH achieves linear performance that closely approximates the conventional polynomial models, while reducing complexity by 90%, and the other two models also demonstrate optimal trade-offs between complexity and performance.