Digital predistorter characterization using extended orthogonal Chebyshev polynomials

Abstract

As communication signals become more dynamic and have wider bandwidth, it is desirable to have a tool that helps to understand digital predistortion (DPD) solution space for a given power amplifier (PA). Two-tone measurements have been used extensively for PA characterization. However, direct application of two-tone measurements to DPD characterization is difficult because of the correlation in conventional polynomial basis functions. In this paper, we establish a technique for characterizing the DPD solution space using 2-carrier narrowband signals by adopting the memory polynomial model and extending the orthogonal Chebyshev polynomials. This approach allows a direct view of different intermodulation products in the DPD solutions for various 2-carrier signals. We performed characterization on a Class AB PA and found interesting characteristics of the solution space. Based on the findings, we propose a new DPD adaptation scheme for frequency hopped 2-carrier GSM signals. The proposed scheme achieves excellent linearization performance for the frequency-hopped GSM signals.