US Patent 7970091 Method for reducing spectral regrowth in a spectrally efficient digital modulation scheme

A method that uses time-domain processing on a spectrally efficient digital modulation scheme to reduce the bandwidth expansion in envelope elimination and restoration (EER) amplifiers is disclosed. The method identifies and localizes sections of the signal responsible for the out of band emissions, or spectral regrowth, using a filter. The detected sections are flagged and extended to allow for introduction of a lower frequency transition in place of the extended section, thus reducing spectral regrowth from the output of an EER amplifier. The method is particularly useful for improving the quality of digital AM radio transmission.