Signal Space Diversity based Cognitive Two-Way Relay Network with Underlay Spectrum Sharing

In this paper, signal space diversity (SSD) is introduced in an underlay cognitive two-way relay network where two secondary source terminals communicate with each other directly and via an intermediate secondary relay in the presence of a primary user. SSD is applied at all transmitting nodes in the secondary network to rotate and interleave the signal components before transmission that enables both source terminals and intermediate relay to transmit different symbols. Therefore, SSD enhances the mutual information of the SSD-based underlay cognitive two-way relay network compared to the conventional one. Thus, performance analysis and results of the proposed system are different than that of the conventional system. It is shown that the proposed system improves the outage performance and spectral efficiency of the underlay cognitive two-way relay network. Moreover, the closed-form expression for exact outage probability of the proposed system is derived over Rayleigh fading channels. Monte Carlo simulations are carried out to validate the analytical work. In all analysis, interference power constraints and correlation among signal-to-noise ratios are taken into consideration to provide accurate results. Furthermore, the impact of channel estimation error on the outage probability of the system is investigated and the closed-form expression of the outage probability is derived.