Look-up table techniques for adaptive digital predistortion: a development and comparison

Simple techniques are presented for performing digital predistortion by use of look-up tables. Performance is measured by the traditional spectral regrowth analysis which quantifies the out-of-band distortion. Also included in the performance evaluation is constellation distortion which quantifies the in-band distortion which is important for bit error rate (BER) performance. As an added performance measure, predistortion is also analyzed with respect to its effect on amplifier efficiency. A nonuniform spacing technique is described which is simple to implement and has a performance very close to the cited optimum approach. In addition, scaling the gain of these tables provides further improvement in terms of correction and efficiency performance. Finally, adaptive indexing is introduced. These algorithms allow the various techniques to adapt to changing signal and power amplifier characteristics.