Impact of pulse shaping and analog filtering on the PAPR of a modulated signal
Purola, Juho (2025-06-13)
Purola, Juho
J. Purola
13.06.2025
© 2025 Juho Purola. Ellei toisin mainita, uudelleenkäyttö on sallittu Creative Commons Attribution 4.0 International (CC-BY 4.0) -lisenssillä (https://creativecommons.org/licenses/by/4.0/). Uudelleenkäyttö on sallittua edellyttäen, että lähde mainitaan asianmukaisesti ja mahdolliset muutokset merkitään. Sellaisten osien käyttö tai jäljentäminen, jotka eivät ole tekijän tai tekijöiden omaisuutta, saattaa edellyttää lupaa suoraan asianomaisilta oikeudenhaltijoilta.
Julkaisun pysyvä osoite on
https://urn.fi/URN:NBN:fi:oulu-202506134457
https://urn.fi/URN:NBN:fi:oulu-202506134457
Tiivistelmä
Telecommunications systems aim to improve the speed and reliability of data transmission by various modulation methods, as well as to improve the power consumption of systems and reduce costs by reducing the requirements of components and improving the efficiency of amplifiers. Achieving high spectral efficiency usually requires waveforms with a high peak-to-average power ratio (PAPR). This comes at the cost of reduced transmitter power efficiency, due to the fact that the amplifiers are required to be driven with power backoff from their most efficient operation point. As reducing the PAPR is crucial to improving power efficiency, the effect of filtering and component frequency response must be considered. Both digital and analog filtering methods can cause a non-flat frequency response in the passband due to filter characteristics or digital processing constraints. All components and systems also have their own frequency response that can attenuate certain frequencies of the transmitted signal. Attenuation and ripple at passband frequencies can be caused by parasitic capacitances, imperfect impedance matching, or distortion, leading to unwanted envelope fluctuations, increasing the PAPR.
This work explores how digital filtering and passband frequency response of analog filtering affect the PAPR of single-carrier modulated signals. The effect of filtering is simulated with ready-made blocks in MATLAB-Simulink. The procedure contains modulation of a message signal to symbols followed by oversampling and pulse shaping, and finally by filtering. By modifying the parameters of pulse shaping and the characteristics of the filter response, such as passband ripple, the effect of these parameters on the signal envelopes can be studied. Pulse shaping using a root-raised cosine filter with a roll-off factor of 0.4 resulted in a 3.4 dB increase in PAPR with PSK modulations, while QAM modulations ranged from 5.4 dB using 32-QAM to 7 dB using 1024-QAM. Filtering a pulse-shaped 8-PSK signal using 2nd to 10th order Butterworth filters with a 3 dB passband cutoff point resulted in a 0.25 dB to 0.9 dB additional increase in PAPR. Switching to Chebyshev filters with 3 dB of passband ripple caused an increase from 0.8 dB to 3.4 dB, respectively. Reducing ripple magnitude by 2 dB improved the power ratio by an average of 0.7 dB. Results indicate that in addition to pulse shaping, also analog filter response can have impact on the signal PAPR, especially if the original PAPR of the modulated signal is low.
This work explores how digital filtering and passband frequency response of analog filtering affect the PAPR of single-carrier modulated signals. The effect of filtering is simulated with ready-made blocks in MATLAB-Simulink. The procedure contains modulation of a message signal to symbols followed by oversampling and pulse shaping, and finally by filtering. By modifying the parameters of pulse shaping and the characteristics of the filter response, such as passband ripple, the effect of these parameters on the signal envelopes can be studied. Pulse shaping using a root-raised cosine filter with a roll-off factor of 0.4 resulted in a 3.4 dB increase in PAPR with PSK modulations, while QAM modulations ranged from 5.4 dB using 32-QAM to 7 dB using 1024-QAM. Filtering a pulse-shaped 8-PSK signal using 2nd to 10th order Butterworth filters with a 3 dB passband cutoff point resulted in a 0.25 dB to 0.9 dB additional increase in PAPR. Switching to Chebyshev filters with 3 dB of passband ripple caused an increase from 0.8 dB to 3.4 dB, respectively. Reducing ripple magnitude by 2 dB improved the power ratio by an average of 0.7 dB. Results indicate that in addition to pulse shaping, also analog filter response can have impact on the signal PAPR, especially if the original PAPR of the modulated signal is low.
Kokoelmat
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