Generalized Data Predistortion Using Intersymbol Interpolation

Intersymbol-interpolated digital data predistortion is an efficient countermeasure technique against the high-power amplifier non-linearity in digital microwave radio systems employing bandwidth-efficient quadrature amplitude modulation. This concept was recently introduced by the present authors using a specific transmit pulse shaping that leads to discrete signal levels at two or three points per symbol interval. Signal predistortion was then performed so as to cancel non-linear distortion at these equispaced points. In the present paper, we generalize the concept of intersymbol-interpolated data predistortion, and combine it with arbitrary transmit filters. Only a limited number of most significant bits at the transmit filter output are used as inputs to a random-access memory (RAM) which outputs the corresponding predistorted coordinates. The remaining bits are used to make a fine amplitude interpolation between the coarsely quantized RAM output levels. This allows us to define a range of predistorters corresponding to different complexity-performance trade-offs for a given signal constellation, transmit pulse shaping, and receive filtering. It is shown, by means of computer simulations, that this technique is considerably superior to conventional memoryless data predistortion.