Jointing Adaptive Modulation Relay Selection Protocols for Two-Way Opportunistic Relaying Systems with Amplify-and-Forward Policy

Two novel best-relay selection protocols, the jointing adaptive modulation max–min (AM-MM) protocol and the jointing adaptive modulation maximum harmonic mean (AM-MHM) protocol, are proposed for two-way opportunistic relaying systems with amplify-and-forward policy (TWOR-AF). By integrating the adaptive modulation with the conventional max–min (NonAM-MM) and maximum harmonic mean protocols, the effect of the modulation schemes used at both sources is exploited perfectly in the proposed AM-MM and AM-MHM protocols. The analytical expressions to the approximate upper bounds of overall average symbol error probability (SEP) for TWOR-AF systems with these different relay selection protocols are obtained through theoretic analysis. The numerical results demonstrate that the average SEP of TWOR-AF systems can be improved greatly when the proposed jointing adaptive modulation relay selection protocols are performed. Furthermore, in certain channel realizations, the adaptive modulation non-selection protocol outperforms the conventional NonAM-MM protocol in which the adaptive modulation is not integrated.