Nowadays, in order to improve spectral efficiency, modern wireless communication systems use modern modulation and coding scheme techniques that involve multiple subcarriers direct or indirect mapping, such as OFDM (orthogonal frequency division multiplexing), OFDMA (orthogonal frequency division multiple access), SC-FDMA (single-carrier frequency division multiple access), WCDMA (wideband code division multiple access) or multi-carrier GSM (global system for mobile communication). These systems however suffer from high peak to average power ratios (PAPR), which originate from superposing subcarriers or various signals from diverse users. It is known that such kind of high PAPR is undesired because it requires more back-off for the subsequent power amplifier, and thus has a direct consequence on the amplifier's average output power. In order to reduce the dynamics of the incoming composite antenna signal, techniques like Crest Factor Reduction (CFR) are used to improve the PAPR and improve the efficiency of the transmission chain. However such processing algorithms may cause out-of-band spectral regrowth if not designed correctly, leading to non-compliance to regulatory spectral emission masks (SEM).
The noise shaping process is a clipping and filtering crest factor reduction technique which has been proposed to reduce the PAPR. The objective of the noise shaping process is to remove energy from the peaks of a signal and then to add that energy as a noise, inside and outside the signal bandwidth. As a result, the foregoing has the effect of reducing the PAPR as well as introducing in-band distortions which increase the bit-error ratio and also out-of-band degradations which interfere with communications in neighboring frequency bands.
Although effective, it would be desirable to improve the noise shaping process to reduce the PAPR even more.