Linearity improvement thanks to the association of Active Constellation Extension and digital predistortion for OFDM

Nonlinearity problems for power amplifiers are well known and many linearization techniques have been proposed in the literature, especially digital baseband predistortion. Orthogonal Frequency Division Multiplexing (OFDM) has a very high Peak-to-Average Power Ratio (PAPR), making it very sensitive to non linearities. We have chosen the Active Constellation Extension (ACE) to reduce the crest factor, which is not sufficient. In this paper, we show that the association of ACE with digital predistortion helps to improve the Adjacent Channel Power Ratio (ACPR) and so permits a good linearity improvement. The association is first validated in simulation. In measurements, for 42.5dBm RMS output power, which represents the nominal power, the ACPR is increased from 32dBc to 49dBc. For a given ACPR of 35dBc, the RMS output power is increased from 40.7dBm to 42.7dBm.