  Integrating power transfer into wireless communications for supporting
simultaneous wireless information and power transfer (SWIPT) is a promising
technique in energy-constrained wireless networks. While most existing work on
SWIPT focuses on capacity-energy characterization, the benefits of cooperative
transmission for SWIPT are much less investigated. In this paper, we consider
SWIPT in an orthogonal frequency-division multiplexing (OFDM) relaying system,
where a source node transfers information and a fraction of power
simultaneously to a relay node, and the relay node uses the harvested power
from the source node to forward the source information to the destination. To
support the simultaneous information and energy cooperation, we first propose a
transmission protocol assuming that the direct link between the source and
destination does not exist, namely power splitting (PS) relaying protocol,
where the relay node splits the received signal power in the first hop into two
separate parts, one for information decoding and the other for energy
harvesting. Then, we consider the case that the direct link between the source
and destination is available, and the transmission mode adaptation (TMA)
protocol is proposed, where the transmission can be completed by cooperative
mode and direct mode simultaneously (over different subcarriers). In direct
mode, when the source transmits signal to the destination, the destination
receives the signal as information and the relay node concurrently receives the
signal for energy harvesting. Joint resource allocation problems are formulated
to maximize the system throughput. By using the Lagrangian dual method, we
develop efficient algorithms to solve the nonconvex optimization problems.
