7.13.7. Digital Predistortion Forward Path
Forward paths compensate for nonlinear power amplifiers by applying the inverse of the distortion that the power amplifier generates, such that the pre-distortion and the distortion of the power amplifier cancel each other out. The power amplifier's non-linearity may change over time, therefore such systems are typically adaptive.
This design example is based on "A robust digital baseband pre-distorter constructed using memory polynomials," L. Ding, G. T. Zhou, D. R. Morgan, et al., IEEE Transactions on Communications, vol. 52, no. 1, pp. 159-165, 2004.
This design example only implements the forward path, which is representative of many systems where you implement the forward path in FPGAs, and the feedback path on external processors. The design example sets the predistortion memory, Q, to 8; the highest nonlinearity order K is 5 in this design example. The file setup_demo_dpd_fwdpath initializes the complex valued coefficients, which are stored in registers. During operation, the external processor continuously improves and adapts these coefficients with a microcontroller interface.
The model file is demo_dpd_fwdpath.mdl.