  This paper investigates an orthogonal frequency division multiplexing
(OFDM)-based wireless powered communication system, where one user harvests
energy from an energy access point (EAP) to power its information transmission
to a data access point (DAP). The channels from the EAP to the user, i.e., the
wireless energy transfer (WET) link, and from the user to the DAP, i.e., the
wireless information transfer (WIT) link, vary over both time slots and
sub-channels (SCs) in general. To avoid interference at DAP, WET and WIT are
scheduled over orthogonal SCs at any slot. Our objective is to maximize the
achievable rate at the DAP by jointly optimizing the SC allocation over time
and the power allocation over time and SCs for both WET and WIT links. Assuming
availability of full channel state information (CSI), the structural results
for the optimal SC/power allocation are obtained and an offline algorithm is
proposed to solve the problem. Furthermore, we propose a low-complexity online
algorithm when causal CSI is available.
