Editing Crest factor (section)

== Crest factor reduction ==

Many modulation techniques have been specifically designed to have [[constant envelope]] modulation, i.e., the minimum possible crest factor of 1:1.

In general, modulation techniques that have smaller crest factors usually transmit more bits per second than modulation techniques that have higher crest factors. This is because:
# any given [[linear amplifier]] has some "peak output power"—some maximum possible instantaneous peak amplitude it can support and still stay in the linear range;
# the average power of the signal is the peak output power divided by the crest factor;
# the number of bits per second transmitted (on average) is proportional to the average power transmitted ([[Shannon–Hartley theorem]]).
[[Orthogonal frequency-division multiplexing]] (OFDM) is a very promising modulation technique; perhaps its biggest problem is its high crest factor.<ref>[http://www.apc.org/en/spectrum/pubs/crest-factor-reduction-ofdmwimax-network "Crest Factor Reduction of an OFDM/WiMAX Network"].
</ref><ref>[http://www.ubicc.org/files/pdf/UBICC_Eltholth_cf_115.pdf "Low Crest Factor Modulation Techniques for Orthogonal Frequency Division Multiplexing (OFDM)"] {{Webarchive|url=https://web.archive.org/web/20170829193818/http://www.ubicc.org/files/pdf/UBICC_Eltholth_cf_115.pdf |date=2017-08-29 }}.</ref> Many crest factor reduction techniques (CFR) have been proposed for OFDM.<ref>R. Neil Braithwaite.
[http://wwwen.zte.com.cn/endata/magazine/ztecommunications/2011Year/no4/articles/201202/t20120202_283037.html "Crest Factor Reduction for OFDM Using Selective Subcarrier Degradation"] {{Webarchive|url=https://web.archive.org/web/20180806221454/http://wwwen.zte.com.cn/endata/magazine/ztecommunications/2011Year/no4/articles/201202/t20120202_283037.html |date=2018-08-06 }}.</ref><ref>K. T. Wong, B. Wang & J.-C. Chen,
[http://www.eie.polyu.edu.hk/~enktwong/ktw/WongKT_EL0111.pdf "OFDM PAPR Reduction by Switching Null Subcarriers & Data-Subcarriers," Electronics Letters, vol. 47, no. 1, pp. 62-63 January, 2011] {{Webarchive|url=https://web.archive.org/web/20150923234513/http://www.eie.polyu.edu.hk/~enktwong/ktw/WongKT_EL0111.pdf |date=2015-09-23 }}.</ref><ref>S.C. Thompson,
[https://web.archive.org/web/20080706134849/http://zeidler.ucsd.edu/students/thesis_sthompson.pdf "Constant Envelope OFDM Phase Modulation," PhD Dissertation, UC San Diego, 2005].
</ref> The reduction in crest factor results in a system that can either transmit more bits per second with the same hardware, or transmit the same bits per second with [[low-power electronics|lower-power]] hardware (and therefore lower electricity costs<ref>Nick Wells.
[http://www.atsc.org/cms/pdf/pt2/Wells_ATSC_paper_on_T2.pdf "DVB-T2 in relation to the DVB-x2 Family of Standards"] {{webarchive|url=https://web.archive.org/web/20130526003113/http://www.atsc.org/cms/pdf/pt2/Wells_ATSC_paper_on_T2.pdf |date=2013-05-26 }}
quote: "techniques which can reduce the PAPR, ... could result in a significant saving in electricity costs."
</ref> and less expensive hardware), or both. 
Over the years, numerous model-driven approaches have been proposed to reduce the PAPR in communication systems. In recent years, there has been a growing interest in exploring data-driven models for PAPR reduction as part of ongoing research in end-to-end communication networks. These data-driven models offer innovative solutions and new avenues of exploration to address the challenges posed by high PAPR effectively. By leveraging data-driven techniques, researchers aim to enhance the performance and efficiency of communication networks by optimizing power utilization.
<ref>{{cite conference |last1=Huleihel |first1=Yara |last2=Ben-Dror|first2=Eilam |last3=Permuter |first3=Haim H. |title=Low PAPR Waveform Design for OFDM Systems Based on Convolutional Autoencoder |conference=2020 IEEE International Conference on Advanced Networks and Telecommunications Systems (ANTS) |date=2020 |pages=1–6.}}</ref>
{{buzzword|date=August 2023}}

===Crest factor reduction methods===
Various methods for crest factor reduction exist, such as peak windowing, [[noise shaping]], pulse injection and peak cancellation.