  In this paper, we analyze the throughput performance of incremental relaying
using energy harvesting (EH) decode-and-forward (DF) relays in underlay
cognitive radio networks (CRNs). The destination combines the direct and
relayed signals when the direct link is in outage. From the derived closed-form
expressions, we present an expression for the power-splitting parameter of the
EH relay that optimizes the throughput performance. We demonstrate that
relaying using EH DF relays results in better performance than direct
signalling without a relay only when the destination combines the direct signal
from the source with the relayed signal. Computer simulations demonstrate
accuracy of the derived expressions.
