  This paper proposes and investigates an overlay spectrum sharing system in
conjunction with the simultaneous wireless information and power transfer
(SWIPT) to enable communications for the Internet of Things (IoT) applications.
Considered is a cooperative cognitive radio network, where two IoT devices
(IoDs) exchange their information and also provide relay assistance to a pair
of primary users (PUs). Different from most existing works, in this paper, both
IoDs can harvest energy from the radio-frequency (RF) signals received from the
PUs. By utilizing the harvested energy, they provide relay cooperation to PUs
and realize their own communications. For harvesting energy, a time-switching
(TS) based approach is adopted at both IoDs. With the proposed scheme, one
round of bidirectional information exchange for both primary and IoT systems is
performed in four phases, i.e., one energy harvesting (EH) phase and three
information processing (IP) phases. Both IoDs rely on the decode-and-forward
operation to facilitate relaying, whereas the PUs employ selection combining
(SC) technique. For investigating the performance of the considered network,
this paper first provides exact expressions of user outage probability (OP) for
the primary and IoT systems under Nakagami-m fading. Then, by utilizing the
expressions of user OP, the system throughput and energy efficiency are
quantified together with the average end-to-end transmission time. Numerical
and simulation results are provided to give useful insights into the system
behavior and to highlight the impact of various system/channel parameters.
