Multi-Carrier TWTA Characterisation for DVB-S2 Operation
Aloisio, Marinella; Angeletti, P; Casini, E; Colzi, E; D'Addio, S; Oliva Balague, R
ESA

The use of advanced coded and modulation transmission schemes devised by DVB-S2 standard calls for a detailed assessment of the non-linearity effects of the high power amplifiers (namely Traveling-wave Tube Amplifiers-TWTA) in the payload output section.

In DVB-S2, a wide range of bandwidth efficiencies are achieved by a mix of different coding rates combined with different modulation schemes (i.e.: QPSK, 8-PSK, 16-APSK and 32-APSK). In particular the APSK constellations were chosen due to their optimality with respect to non-linearity effects.

In the near term, the bandwidth availability of Ka frequencies, joined with multibeam system architectures, pushes toward multicarrier operation of the payload TWTAs in order to reduce the number of on-board amplifiers while preserving an overall high throughput. In addition, future communications satellite payloads are expected to relay on complex RF front-ends based on distributed amplification (e.g. Multi-Port Amplifiers, Active antennas, etc.) to offer power and bandwidth reconfigurability in accordance to traffic request variations. In these scenarios, TWTAs saturation power and relevant operating points (i.e., the back-off) must be optimized according to the actual, operational multicarrier scenario.

For this purpose a simulator tool was developed to analyse the impact of payload non-idealities on the end-to-end link performance. The impairments introduced by the payload in the reference signal are estimated by the Carrier-to-Interference ratio obtained by means of cross-correlation techniques.

The paper will present the modelling methodology and will report the results of the TWTA characterisation and optimization with respect to multicarrier DVB-S2 operation.