  In this letter, a novel wireless powered protocol is proposed to maximize the
system throughput of an energy harvesting (EH) based cognitive radio network,
while satisfying a minimum primary user rate requirement. For EH, we exploit
both dedicated wireless power transfer from primary base station as well as
ambient ones available due to wireless information transfer among primary and
secondary users. Specifically, we prove convexity of the optimization problem
and obtain semi-closed-form for globally optimal solution. Numerical results
validate the analysis, and show an average performance improvement of $70\%$
over benchmark scheme for various system parameters.
