Novel multiband linearization technique for closely-spaced dual-band signals of wide bandwidth

In the concurrent dual-band digital predistortion (DPD), it is required that each band of interest be accurately measured, so that the in-band distortion can be modeled and suppressed. However when the two bands are closely spaced, the inter-band modulation by-products overlap with the cross-modulation and the in-band intermodulation, thus leading to linearization performance degradation. On the other hand, by directly applying the single band linearization for closely-spaced dual-band signals, the one-band DPD approach will saturate in performance due to the wide bandwidth as well as the high nonlinear order and memory depth required resulting in an ill-conditioning problem. To resolve the spectral overlaps taking place in closely-spaced dual wide-band system, (1) the in-band intermodulation, (2) the cross-modulation, and (3) the inter-band modulation by-products are jointly extracted in the new proposed dual-band PA characterization scheme to yield an improved frequency/time selective modeling. The signals of interest extracted in each band using the proposed model are then used for dual-band DPD coefficient extraction. Improved modeling and linearization performances by up to 5 dB are verified with experiments performed on two 40-MHz LTE-advanced signals 40 MHz apart.