  We propose a new artificial-noise aided hybrid time-switching/power-splitting
scheme for orthogonal frequency-division multiplexing (OFDM) systems to
securely transmit data and transfer energy to a legitimate receiving node. In
our proposed scheme, the cyclic prefix has two more benefits in addition to the
cancellation of the inter-symbol interference between the OFDM blocks. Firstly,
it enables the legitimate transmitter to send artificial-noise (AN) vectors in
a way such that the interference can be canceled at the legitimate receiver
prior to information decoding. Secondly, its power is used to energize the
legitimate receiver. We optimize the cyclic prefix length, the time-switching
and power-splitting parameters, and the power allocation ratio between the data
and AN signals at the legitimate transmitter to maximize the average secrecy
rate subject to a constraint on the average energy transfer rate at the
legitimate receiver. Our numerical results demonstrate that our proposed scheme
can achieve up to 23% average secrecy rate gain relative to a pure
power-splitting scheme.
