  In this paper, we investigate the secrecy performance of underlay cognitive
small-cell radio network with unreliable backhaul connections. The secondary
cognitive small-cell transmitters are connected to macro base station by
wireless backhaul links. The small-cell network is sharing the same spectrum
with the primary network ensuring that a desired outage probability constraint
in the primary network is always satisfied. We propose an optimal transmitter
selection (OTS) scheme for small-cell network to transfer information to the
destination. The closed-form expression of secrecy outage probability are
derived. Our result shows that increasing the primary transmitter's transmit
power and the number of small-cell transmitter can improve the system
performance. The backhaul reliability of secondary and the desired outage
probability of the primary also have significant impact on the system.
