An efficient power amplification is critical for wireless communications, especially for broadband communications. However, this is difficult when spectrally efficient modulations based on large constellations are employed since the resulting signals have high envelope fluctuations, which means that linear power amplifiers with high back-off need to be employed. Since spectrally efficient constellations have higher power requirements, it is desirable to have power-efficient transmitters for those constellations.
In this paper we propose a highly power-efficient transmitter structure for spectrally efficient modulations with large constellations. Our structure is based on the decomposition of the intended constellation in the sum of several polar components, each one modulating a different constant-envelope signal. These constant-envelope signals are then separately amplified by, low-cost, power efficient strongly nonlinear amplifiers, and the output of each amplifier is sent to a separate antenna so as to avoid combiner losses and/or linearity requirements.