Energy-aware power allocation for lifetime maximization in single-source relay cooperation

We study the problem of optimal power allocation (PA) among relays for lifetime maximization in a dual-hop cooperative network operated by amplify-and-forward relays with battery limitation. We first formulate the optimization problem for power allocation in a static channel case and present a closed-form solution with the objective of lifetime maximization. This solution simply requires equally distributing energy over time for each participating relay. Based on this, we then develop a perceived lifetime (PLT) PA strategy that can be used in time-varying channel scenarios. We also present a minimum weighted total power (MWTP) strategy that depends only on the current channel condition and residual energy information. PLT and MWTP are compared through analysis and simulations. It is demonstrated that both result in significant lifetime improvement compared to the conventional strategy of minimizing the total power per transmission, especially when the link conditions or initial energy levels are nonuniform among relays.