Nonlinearity-Aided Hybrid ARQ for Satellite Communications

In satellite communications power consumption and reliability are key concerns. The unreliable nature of the wireless channel can cause erroneous transmissions, which must be compensated using retransmissions, at the expense of more power. This issue is aggravated by the low amplification efficiency of high data rate schemes such as Orthogonal Frequency Division Multiplexing (OFDM). Ideally, retransmissions could be avoided entirely by increasing transmission power, however, this would drastically lower the overall energy efficiency of the system. Sophisticated Hybrid Automatic Repeat Request (HARQ) techniques can simultaneously reduce the need for retransmissions and increase the success likelihood of each retransmission attempt (a critical aspect for delay-constraint services over satellite links), while minimizing average consumed power. In this work, we propose a novel HARQ technique where retransmitted signals are submitted to a soft clipping operation that lowers the Peak-to-Average Power Ratio (PAPR) of the OFDM signal, thereby increasing the amplification efficiency. A Generalized Approximate Message Passing (GAMP) based receiver makes use of the additional distortion in the retransmission to increase the likelihood of a successful decoding. It is shown that this approach can outperform Chase Combining (CC) schemes even for Super Quadrature Amplitude Modulation (Super-QAM), while decreasing the power expended during retransmissions.