Optimizing high-speed satellite communication with high-order modulation via adaptive signal processing at both ends of the link

Interactive multimedia wideband satellite services (especially in the field of digital TV) will require the adoption of (coded) spectrally-efficient high-level modulation techniques in future satellite transmission standards. It is known that such modulations suffer from nonlinear distortion caused by the on board (nonlinear) high-power amplifier, so that countermeasures are to be adopted in this respect. The aim of this paper is to investigate the possibility to adopt a suited mixture of adaptive data predistortion (DP) at the transmitter and adaptive nonlinear equalization (NLE) at the receiver to counteract nonlinear distortion at best. We show first that the sensitivity to nonlinear distortion of (uncoded) 16-QAM and 64-QAM constellations is greatly reduced by clever use of both techniques. We also investigate the performance improvement brought forth by such techniques when using a recently introduced optimized 16-APK constellation, as well as its extended 64-point version. We finally re-evaluate the optimized link performance assuming turbo-coded 16-QAM and 16-APK constellations with iterative SISO (soft input soft output) decoding.