Energy Harvesting Cooperative Communication: A Three-Node Decode-and-Forward System with Signal Space Diversity

A three-node cooperative communication system with one-way transmission and a decode-and-forward relaying scheme is considered. The outage probability of the system is analyzed under the assumption that both the source and relay are energy harvesting nodes, and signal space diversity is employed to enhance transmission reliability. Exact closed-form and asymptotic expressions for the outage probability are derived. An optimization problem is also formulated to minimize the outage probability with respect to the transmission powers of the source and relay. Our analysis shows that the outage probability is a convex function of the transmit powers, with a unique global minimum. Monte Carlo simulations are conducted to validate the exact closed-from expression of the outage probability and the optimal transmit powers. In contrast to traditional battery-powered systems, the results show that increasing the transmit power in energy harvesting cooperative communication systems may result in a higher outage probability. The results also show that, at high SNRs, the optimal transmit power of a node is the power that balances its energy harvesting and depletion rates, leading to the best energy utilization.