Adaptive baseband predistortion techniques for amplifier linearization

Abstract

Techniques are presented for performing digital predistortion with non-uniformly spaced look-up tables which compensate for amplifier nonlinearities. Performance measures include spectral re-growth analysis, which quantifies the out-of-band distortion, and constellation distortion, which quantifies the in-band distortion. This linearization technique is also analyzed with respect to its effect on amplifier efficiency. To further improve efficiency and performance, the look-up tables are normalized at the operating point instead of the linear gain point. Finally, adaptive algorithms are detailed. It is shown that with a changing signal or amplifier characteristic, adaptive indexing needs to be implemented. This is done efficiently with linked lists.