Crest Factor Reduction
Crest Factor Reduction (CFR) is a technique used to reduce the PAPR (Peak To Average Power Ratio) of the transmitted signals so that the power amplifier can operate more efficiently with less back-off. This tool include "Clipping and filtering" CFR algorithms on each waveform tabs (PSK & QAM).
Clipping and filtering is an iterative method, doing hard clipping and band-pass filtering sequentially.
As shown in the below figure, clipping can cause sharp corners in a clipped signal, which leads to an unwanted out-of-band emission(increased ACP).
The clipping mathematical equation is as follows:
where x(n) is the input signal, c(n) is the clipping algorithm, and A is the maximum magnitude targeted.
To reduce the unwanted out-of-band emissions, the clipped signal will then go through a band-pass filter to reduce the high frequency signals which correspond to the sharp corners in the clipped signal.
So for clipping and filtering method, the main parameters are target PAPR and the band-pass filter parameters: band pass bandwidth, stop attenuation.
- PAPR target: Set the PAPR value to achieve after CFR.
- Filtering: enable filtering
- Max Iterations: Specify the maximum times of iteration. With the increasing of iteration, the PAPR value should converge to a steady level.
- Attenuation: Set out-band attenuation of band pass filter
- Signal BW: Set the band-pass bandwidth of band pass filter
