  In this paper, we focus on a typical cooperative communication system with
one pair of source and destination, where a unmanned aerial vehicle (UAV)
flying from a start location to an end location serves as a mobile relay. To
efficiently utilize energy in ambient environment, the UAV's transmission
capability is powered exclusively by radio signal transmitted from the source
via the power-splitting mechanism. In such a cooperative communication system,
we study the end-to-end cooperative throughput maximization problem by
optimizing the UAV's power profile, power-splitting ratio profile and
trajectory for both amplify-and-forward (AF) and decode-and-forward (DF)
protocols. The problem is decomposed into two subproblems: profile optimization
given trajectory and trajectory optimization given profile. The former one is
solved via the dual decomposition with in-depth analysis and the latter one is
solved via successive convex optimization, by which a lower bound is
iteratively maximized. Then the end-to-end cooperative throughput maximization
problem is solved by alternately solving the two subproblems. The numerical
results show that with the proposed optimal solution, choice for the UAV's
power profile and power-splitting ratio profile is more long-sighted than the
greedy strategy from our previous work and the successive optimization is able
to converge in a few rounds of iteration. Moreover, as for the end-to-end
cooperative throughput, the proposed optimal solution outperforms both static
and greedy strategies, especially for the AF protocol.
