Enhancing spectral efficiency in cooperative cognitive two-way amplify-and-forward relaying networks

Abstract

In this work, a new cooperative cognitive two-way amplify-and-forward (AF) relaying scheme is proposed. In this model, a primary user (PU) network consisting of two PU sources communicate with each other via a single AF relay. In addition, a secondary user (SU) source transmits its data to a SU destination via the same PU relay node via decode-and-forward protocol. In order to mitigate SU interference caused to the PU network, the PU network considers the SU network pairs (i.e., source and destination) as two additional relay nodes helping the original PU relay node in improving the PU network performance. As a reward for its cooperation, the PU network allows the SU network to communicate simultaneously via the PU relay node using the decode-and-forward (DF) protocol. Two power allocation optimization problems are formulated; the first problem minimizes the weighted sum of the average symbol error probability (SEP) of both PU and SU systems, whereas the second problem maximizes the total achievable sum rate of the PU and SU networks. Results show that the error performance of the proposed model outperforms the conventional two-way relaying networks with amplify-and-forward protocol. Moreover, the total achievable sum rate of the proposed model is higher than the total achievable rate of the conventional ones.