g uses overlapping batches of samples to ensure that peaks that occur in batch boundary areas are also detected. The Complementary Cumulative Distribution Function is a representation of the distribu- tion of the instantaneous to average power ratio in a signal interval. Typically, it is repre- sented graphically with the X-axis showing the ratio between instantaneous and average transmit power or PAPR (in dB) and the Y-axis showing the relative frequency of occurrence of that specific ratio (or better). The output of the CFR algorithm should yield a curve that has fewer occurrences of a high PAPR signal. Performance improvements include the option to execute the CFR algorithm multiple times, with incrementally more aggressive detection thresholds. Digital Predistortion DPD is the block which implements a complex nonlinear function that approximates the inverse transfer function G = H of the PA baseband transfer function H. The DPD subsystem is imple- mented through two components that we discussed before and are shown below in Fig. 6-16: 1. The Actuator or Feed-Forward path-this component applies the DPD adaptation weights in the runtime system path of the system and hence performance critical Predistorter Power Amplifier FIGURE 6-16 Feed-forward digital predistorter. Chapter 6 User-plane application components 233 2. The DPD adaptation algorithm-this component calculates the DPD adaptation coefficients or weights and typically runs in a nontime-critical subsystem (for example, on host ARM cores). The job of the feed-forward path is to apply the predistortion. We differentiate between algorithms for feed-forward in a few dimensions. First, consider the difference between the application of a memoryless or a memory model. A memoryless model assumes (as the name says), the PA not to have any memory-the current output signal is by no means impacted by previous signals transmitted by the PA. The output at each time as such depends only on the current input, adjusted for nonlinearity. The nonlinearity itself is char-