  In this paper, we consider a wireless-powered cooperative communication
network, which consists of a hybrid access-point (AP), a hybrid relay, and an
information source. In contrast to the conventional cooperative networks, the
source in the considered network is assumed to have no embedded energy supply.
Thus, it first needs to harvest energy from the signals broadcast by the AP
and/or relay, which have constant power supply, in the downlink (DL) before
transmitting the information to the AP in the uplink (UL). The hybrid relay can
not only help to forward information in the UL but also charge the source with
wireless energy transfer in the DL. Considering different possible operations
of the hybrid relay, we propose two cooperative protocols for the considered
network. We jointly optimize the time and power allocation for DL energy
transfer and UL information transmission to maximize the system throughput of
the proposed protocols. Numerical results are presented to compare the
performance of the proposed protocols and illustrate the impacts of system
parameters.
