Joint predistortion and PAPR reduction in multibeam satellite systems

Abstract

Precoding for multibeam satellites with aggressive frequency reuse has attracted interest of late towards enhancing system capacity. Most of the works on precoding mitigate the linear co-channel interference between the beams caused by frequency reuse. However, the high power amplifier (HPA), an integral part of the satellite payload, is inherently non linear. Non-linear amplification combined with the linear co-channel interference introduces nonlinear co-channel distortions at the receiver. Further, signals with very high peak to average power ratios (PAPR), typical of spectrally efficient modulations, are sensitive to the non-linear characteristic of the HPA and necessitate large back-off to have manageable distortion levels. In this work, a novel architecture comprising multistream Crest Factor Reduction (signal pre-clipping) and Signal Predistortion (SPD) in cascade, is devised to counter the nonlinearities and co-channel interference in multibeam satellite systems. An iterative algorithm to optimize the parameters of the signal clipping and predistortion is devised taking recourse to analytical derivations. The proposed joint estimation paradigm is shown to compare favorably with state-of-art and provides a framework to combine predistortion and precoding.

Low complexity transmit processing for multibeam satellite systems with non-linear channels

“…The first of the blocks (C) is a linear combiner matrix that mixes the input streams. This is similar to the precoding matrix in standard linear precoding [18] where the multi-beam nature of the system was inherent to the whole predistorter block, here it is only explicitly addressed in this linear combiner block. The blocks L k are linear filters and are used to counteract the memory mainly caused by the on-board filters .…”

“…In [18], a non-linear processing at the multiuser transmitter that considers amplifier effects in addition to the linear multiuser interference is presented. The processing comprises multichannel PAPR reduction and SPD.…”

“…The processing comprises multichannel PAPR reduction and SPD. However, the multistream SPD architecture in [18] employs a large number of parameters thereby resulting in a complex identification and implementation. In this paper, we propose a non-linear transmission scheme formulated as a cascade of linear multiuser processing, single stream SPD and PAPR reduction blocks.…”

“…This architecture employs lower number of coefficients, thereby enabling reduced complexity estimation and implementation. Further, the PAPR reduction block now appears at the end of the compensation algorithm, unlike in [18]. While this interchange may sound trivial, it impacts the optimization framework devised to obtain the parameters of these blocks.…”

Symbol-level precoding with per-antenna power constraints for the multi-beam satellite downlink

“…A typical solution to this problem in single-user links relies on predistortion techniques [25], [28], [29], but their extension to multi-beam systems relying on precoding is not straightforward, because of the mutual correlation between the data streams induced by the precoding schemes. About this, a joint predistortion algorithm for multi-beam systems is given in [30]. In this framework, the proposed precoding scheme allows to mitigate the signal corruption induced by the non-linear satellite channel.…”