Advanced transmitters with combined crest factor reduction and digital predistortion techniques

This paper analyses the benefits of combining crest factor reduction (CFR) technique and digital predistortion (DPD). DPD and CFR have been mainly investigated separately, and this is the contribution to the state of the art given here. The combination is attractive in modern wireless transmission systems due to the high peak-to-average-power-ratio (PAPR) of the signals employed. In these cases, the compression of the signal peaks performed by the amplifier in strong saturation region causes uncontrolled in-band and out-of-band distortion that degrades ACLR and EVM of the output signal. The joint architecture can take advantage from the improved linear output power given by DPD together with a controlled reduction of the peaks performed by CFR. The PA can in this way deliver a higher linear output power having at the same time a predictable linearity of the output RF signal. The concept has been implemented and tested on a commercial GaAs PA, obtaining an increased linear output power of 1.9 dB compared to the standalone PA when a WCDMA signal with PAPR of 3.47 dB is employed.