Method and apparatus for crest factor reduction
An apparatus and method for performing crest factor reduction (CFR). A peak detection circuit detects peaks from input signal samples based on a first threshold. The first threshold is higher than a second threshold that is determined based on a target peak-to-average power ratio (PAPR). A gain computation circuit determines a gain factor for at least one detected peak. A scaled cancellation pulse generation circuit generates a scaled cancellation pulse for the at least one detected peak based on the gain factor. A combiner circuit combines the scaled cancellation pulse with the input signal samples to generate an output signal. A hard clipping circuit may compress the output signal based on the second threshold. The first threshold is set slightly higher than the second threshold.
1 . An apparatus for performing crest factor reduction (CFR), comprising:
a peak detection circuit configured to detect peaks from input signal samples based on a first threshold, wherein the first threshold is higher than a second threshold that is determined based on a target peak-to-average power ratio (PAPR);
a gain computation circuit configured to determine a gain factor for at least one detected peak;
a scaled cancellation pulse generation circuit configured to generate a scaled cancellation pulse for the at least one detected peak based on the gain factor; and
a combiner circuit configured to combine the scaled cancellation pulse with the input signal samples to generate an output signal.
2 . The apparatus of claim 1 , further comprising:
a hard clipping circuit configured to compress the output signal based on the second threshold.
3 . The apparatus of claim 1 , wherein the peak detection circuit is configured to group detected peaks into a plurality of clusters and select a cluster peak from each cluster, the gain computation circuit is configured to determine the gain factor for each cluster peak, and the scaled cancellation pulse generation circuit is configured to generate the scaled cancellation pulse for each cluster peak.
4 . The apparatus of claim 1 , further comprising:
a memory for storing cancellation pulses,
wherein the scaled cancellation pulse generation circuit is configured to obtain a cancellation pulse from the memory based on parameters of the input signal samples and generate the scaled cancellation pulse by multiplying the gain factor for the at least one detected peak with the cancellation pulse obtained from the memory.
5 . The apparatus of claim 4 , wherein the pre-stored cancellation pulse is generated based on a transmission scheme of the input signal samples.
6 . The apparatus of claim 1 , wherein the scaled cancellation pulse is generated and combined with the input signal samples in one iteration.
7 . The apparatus of claim 1 , wherein the first threshold is 2-3% higher than the second threshold.
8 . The apparatus of claim 1 , further comprising an up-sampling circuit configured to up-sample the input signal samples, and the peak detection circuit is configured to detect the peaks from the up-sampled input signal samples based on the first threshold.
9 . The apparatus of claim 1 , further comprising:
a digital-to-analog converter configured to convert the output signal to an analog signal; and
a power amplifier configured to amplify the analog signal.
10 . A method for crest factor reduction (CFR), comprising:
detecting peaks from input signal samples based on a first threshold, wherein the first threshold is higher than a second threshold that is determined based on a target peak-to-average power ratio (PAPR);
determining a gain factor for at least one detected peak;
generating a scaled cancellation pulse for the at least one detected peak based on the gain factor; and
combining the scaled cancellation pulse with the input signal samples to generate an output signal.
11 . The method of claim 10 , further comprising:
compressing the output signal based on the second threshold.
12 . The method of claim 10 , wherein the detected peaks are grouped into a plurality of clusters and a cluster peak is selected from each cluster, the gain factor is determined for each cluster peak, and the scaled cancellation pulse is generated for each cluster peak.
13 . The method of claim 10 , further comprising obtaining a pre-stored cancellation pulse from a memory based on parameters of the input signal samples, wherein the scaled cancellation pulse is generated by multiplying the gain factor for the at least one detected peak with the pre-stored cancellation pulse obtained from the memory.
14 . The method of claim 13 , wherein the pre-stored cancellation pulse is generated based on a transmission scheme of the input signal samples.
15 . The method of claim 10 , wherein the scaled cancellation pulse is generated and combined with the input signal samples in one iteration.
16 . The method of claim 10 , wherein the first threshold is 2-3% higher than the second threshold.
17 . The method of claim 10 , further comprising up-sampling the input signal samples, wherein the peaks are detected from the up-sampled input signal samples based on the first threshold.
18 . A non-transitory computer-readable medium having instructions stored thereon that, when executed by processing circuitry, cause the processing circuitry to perform the method of claim 10 .