Improved data predistortion using intersymbol interpolation

An efficient data predistortion technique is presented to compensate for transmitter high-power amplifier (HPA) nonlinearities in digital microwave radio systems employing quadrature amplitude modulation (QAM) signal formats. The proposed technique makes use of a specific transmitter pulse shaping that leads to discrete signal levels at time instants spaced by half a symbol interval. The predistortion circuit is designed so as to cancel nonlinear distortion at the HPA output at these instants. With respect to conventional data predistortion, which can only compensate for warping of the signal constellation, this technique also compensates for nonlinear intersymbol interference (ISI). It is shown that, using the 64 and 256 QAM signal formats, the presented technique leads to a considerably more efficient utilization of the available HPA power