DIGITAL PREDISTORTION TECHNIQUES FOR BEAMFORMING AND INTERMODULATION IMPROVEMENT OF ACTIVE ANTENNAS (ARTES AT 5C.458)

Description

The objective of the activity is to develop and test efficient broadband digital pre-distortion algorithms and architectures for payloads utilising digital processors. The developed concept shall be implemented in a combined RF and digital processor test-bed. Tests in a laboratory environment will be carried out to fully evaluate the performance improvements.Targeted Improvements:- 10-15% improvement of payload capacity/throughput- 30% higher signal C/I- up to 5% DC-to-RF efficiency improvementDescription:Digital pre-distortion techniques are now a reality for on-ground transceivers and digital systems. Digital pre-distortion is employed at the input of the power amplifiers (PAs) to compensate for the non-linearities introduced inherently by the amplification operation. These non-linearities cause clipping and spectral re-growth, which results in modulation distortions and increased out-of-band (OOB) emissions, reducing the maximum throughput delivered by the payload. Currently, in order to minimise the non-linear effects, the PAs are operated in back-off. However, the higher the back-off, the lower is the power-added efficiency (PAE) of the PA. As an example, today a GaN MMIC operating at 4 dB compression at 15dBc noise power ration (NPR) could instead be operated at 1.5 - 2 dB compressionatthe same NPR, whilst maintaining the same PAE when pre-distortion techniques are used. Applying pre-distortion will either increasethe amplifier's useful output power or increase the PAE for the same linearity requirement. Satellite communication systems with digital signal processing and active beamforming capabilities could benefit by employing digital pre-distortion techniques as part ofthe on-board signal processing. A moderate increase in processor power requirement could be traded off against either increased PAE, leading to a reduction of the mass of the thermal management system, or reduced beamforming and intermodulation interference at the same PAE. Intermodulation effects can considerably affect the beamforming quality whenever intermodulation interference signals coherently add in the direction of the beam. This reduces the maximum spectral efficiency available for the end-user, whereas in otherspatial directions, where signals add non-coherently, interference dilution takes place.In this activity benefit will be drawn from ground transceivers and digital systems to develop efficient broadband digital pre-distortion algorithms for communication payloads utilising digital signal processors. This includes the development of a combined RF and digital signal processor architecture. A digital signal processor test-bed will be developed and performance tests will be carried out in a laboratory environment to qualify the performance improvement.

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