Modulation Diversity in a Two-Way Cooperative System with an Energy Harvesting Relay

This work focuses on two-way cooperation using a decode-and-forward (DF) relay that harvests energy from the environment. We propose to employ modulation diversity (MD) in this conventional two-way system. MD enables the system to transmit each component of a data symbol over a separate fading channel, which makes the proposed system have higher spectral efficiency and higher mutual information, causing the analysis of the proposed system to be more complex, unlike conventional systems. System performance is investigated for outage probability where a closed-form mathematical model is derived taking into account the energy constraint at the relay due to energy harvesting. We also derive an asymptotic expression for the outage probability to explore the system performance for various parameters. Moreover, we study the impact of relay location and energy harvesting on the system performance. All the derived mathematical models are verified by extensive Monte Carlo simulations. Results show that incorporating MD in the conventional energy harvesting two-way system improves the system performance by 5 dB.