Two-way relaying using constant envelope modulation and phase-superposition-phase-forward

Abstract

In this article, we propose the idea of phase-superposition-phase-forward (PSPF) relaying for 2-way 3-phase cooperative network involving constant envelope modulation with discriminator detection in a time-selective Rayleigh fading environment. A semi-analytical expression for the bit-error-rate (BER) of this system is derived and the results are verified by simulation. It was found that, compared to one-way relaying, 2-way relaying with PSPF suffers only a moderate loss in energy efficiency (of 1.5 dB). On the other hand, PSPF improves the transmission efficiency by 33%. Furthermore, we believe that the loss in transmission efficiency can be reduced if power is allocated to the different nodes in this cooperative network in an 'optimal' fashion. To further put the performance of the proposed PSPF scheme into perspective, we compare it against a phase-combining phase-forward technique that is based on decode-and-forward (DF) and multi-level CPFSK re-modulation at the relay. It was found that DF has a higher BER than PSPF and requires additional processing at the relay. It can thus be concluded that the proposed PSPF technique is indeed the preferred way to maintain constant envelope signaling throughout the signaling chain in a 2-way 3 phase relaying system.