Multiply-and-forward - A robust transmission scheme for two-way cooperative communication in the presence of nonlinear power amplifier distortion

We propose in this paper the idea of multiply-and-forward (MF) as a mean to overcome nonlinear power amplifier (NLPA) distortion in two-way cooperative communication systems using MPSK modulation. Compared to amplify-and-forward (AF), of which the relay broadcasts a scaled sum of the signals received from individual sources, the relay in the proposed MF system broadcasts a scaled product of the individually received signals instead. Through signal analysis and simulation, we show that the bit error rate (BER) of the MF protocol is unaffected by NLPA distortion and is able to deliver a second order diversity effect. In contrast, AF exhibits a high irreducible error floor in the presence of NLPA distortion. Actually, MF with an NLPA attains the same BER as AF with a linear power amplifier.