  Wireless energy harvesting is regarded as a promising energy supply
alternative for energy-constrained wireless networks. In this paper, a new
wireless energy harvesting protocol is proposed for an underlay cognitive relay
network with multiple primary user (PU) transceivers. In this protocol, the
secondary nodes can harvest energy from the primary network (PN) while sharing
the licensed spectrum of the PN. In order to assess the impact of different
system parameters on the proposed network, we first derive an exact expression
for the outage probability for the secondary network (SN) subject to three
important power constraints: 1) the maximum transmit power at the secondary
source (SS) and at the secondary relay (SR), 2) the peak interference power
permitted at each PU receiver, and 3) the interference power from each PU
transmitter to the SR and to the secondary destination (SD). To obtain
practical design insights into the impact of different parameters on successful
data transmission of the SN, we derive throughput expressions for both the
delay-sensitive and the delay-tolerant transmission modes. We also derive
asymptotic closed-form expressions for the outage probability and the
delay-sensitive throughput and an asymptotic analytical expression for the
delay-tolerant throughput as the number of PU transceivers goes to infinity.
The results show that the outage probability improves when PU transmitters are
located near SS and sufficiently far from SR and SD. Our results also show that
when the number of PU transmitters is large, the detrimental effect of
interference from PU transmitters outweighs the benefits of energy harvested
from the PU transmitters.
