Non-linear Distortion Cancellation and Symbol-based Equalization in Satellite Forward Links

Abstract– In this paper, a low-complexity symbol-based equalizer that performs non-linear distortion cancellation is proposed for application at the user terminal in the DVB-S 2X satellite forward link. The channel is comprehensively modelled, including the non-linear travelling wave tube amplifier (TWTA) characteristics, the input-multiplexing (IMUX) and output-multiplexing (OMUX) filter responses at the satellite transponder, and the phase noise at the user terminal, according to the very-small aperture terminal (VSAT) reference scenario. Two detectors in
the cancellation loop are considered, comparing the packeterror rate (PER) performance of simple maximum likelihood
(ML) demodulation with hard decision to soft information exchange with low-density parity-check (LDPC) decoder, and
showing only marginal improvement with the latter solution. The PER performance is compared against a number of predistortion techniques at the transmitter, such as dynamic data pre-distortion, successive data pre-distortion, and static data predistortion. The novel receiver demonstrates superior performance even with one iteration of distortion cancellation, while the joint application of successive data pre-distortion and iterative symbol-based equalization shows up to 4 . 95-dB energy efficiency gain for 32-level amplitude and phase-shift keying ( 32-APSK). The computational complexity is also evaluated. The improved receiver is particularly suitable for application with higher order modulation, a wide-band carrier, and low roll-off factors.