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This method hard clips the signal to achieve the target PAPR. The following figure shows how the PAPR of a signal can be reduced by using clipping by Target PAPR.
Clipping operation can be expressed as:
X[n] is the signal on which CFR is applied.
Xclipping[n] is the clipped signal.
A is the threshold level determined by target PAPR.
The clipping transfer function is represented by the following figure.
Peak Windowing is a CFR method that scales the peaks in signal using a weighted window function to get smooth peaks and achieve the target PAPR. This technique involves the following steps:
The following figure shows the input signal, the threshold level, and the signal obtained after applying the Peak Windowing method of CFR.
CFR is a non-linear operation that introduces out-of-band distortion in the signal. This distortion can be filtered out after the CFR operation.
CFR with filter can be applied on the waveform by enabling filter. The block diagram below shows one iteration of CFR operation with filtering.
CFR applies filtering per sub Block. The diagram below shows an example of sub block configuration for a signal sampled at S samples per second.
|Clipping|| Faster CFR
Trade-off ACP for EVM
|Peak Windowing||Trade Off between ACP and EVM|
NI recommends the Clipping method of CFR, with filter enabled, to obtain waveform with desired PAPR.
For more concept help refer to Crest Factor Reduction topic in NI-RFmx SpecAn Help.
 Sperlich, Roland, et al. Power amplifier linearization with digital pre-distortion and crest factor reduction. Microwave Symposium Digest, 2004 IEEE MTT-S International. Vol. 2. IEEE, 2004.
 Braithwaite, R. Neil. A combined approach to digital predistortion and crest factor reduction for the linearization of an RF power amplifier. IEEE Transactions on Microwave Theory and Techniques 61.1 (2013): 291-302.
 Armstrong, Jean. Peak-to-average power reduction for OFDM by repeated clipping and frequency domain filtering. Electronics letters 38.5 (2002): 246-247.