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xAbstract—In this paper, the physical layer security of a dualhop

underlay uplink cognitive radio network is investigated over

Nakagami-m fading channels. Specifically, multiple secondary

sources are taking turns in accessing the licensed

spectrum of the primary users and communicating with a multiantenna

secondary base station (D) through the aid of a multiantenna

relay R in the presence of M eavesdroppers

that are also equipped with multiple antennas. Among the

remaining nodes, one jammer is randomly selected to transmit

an artificial noise to disrupt all the eavesdroppers that are

attempting to intercept the communication of the legitimate links

i.e., Si -R and R-D. The received signals at each node are combined

using maximum-ratio combining. Secrecy analysis is provided by

deriving closed-form and asymptotic expressions for the secrecy

outage probability. The impact of several key parameters on the

system’s secrecy e.g., transmit power of the sources, number of

eavesdroppers, maximum tolerated interference power, and the

number of diversity branches is investigated. Importantly, by

considering two scenarios, namely (i) absence and (ii) presence

of a friendly jammer, new insights are obtained for the considered

communication system. Especially, we tend to answer to the

following question: Can better secrecy be achieved without

jamming by considering a single antenna at eavesdroppers

and multiple-ones at the legitimate users (i.e., relay and enduser)

rather than sending permanently an artificial noise and

considering that both the relay and the destination are equipped

with a single antenna, while multiple antennas are used by the

eavesdroppers? The obtained results are corroborated through

Monte Carlo simulation and show that the system’s security can

be enhanced by adjusting the aforementioned parameters.