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<p>xAbstract—In this paper, the physical layer security of a dualhop</p>
<p>underlay uplink cognitive radio network is investigated over</p>
<p>Nakagami-m fading channels. Specifically, multiple secondary</p>
<p>sources are taking turns in accessing the licensed</p>
<p>spectrum of the primary users and communicating with a multiantenna</p>
<p>secondary base station (D) through the aid of a multiantenna</p>
<p>relay R in the presence of M eavesdroppers </p>
<p>that are also equipped with multiple antennas. Among the</p>
<p>remaining nodes, one jammer is randomly selected to transmit</p>
<p>an artificial noise to disrupt all the eavesdroppers that are</p>
<p>attempting to intercept the communication of the legitimate links</p>
<p>i.e., Si -R and R-D. The received signals at each node are combined</p>
<p>using maximum-ratio combining. Secrecy analysis is provided by</p>
<p>deriving closed-form and asymptotic expressions for the secrecy</p>
<p>outage probability. The impact of several key parameters on the</p>
<p>system’s secrecy e.g., transmit power of the sources, number of</p>
<p>eavesdroppers, maximum tolerated interference power, and the</p>
<p>number of diversity branches is investigated. Importantly, by</p>
<p>considering two scenarios, namely (i) absence and (ii) presence</p>
<p>of a friendly jammer, new insights are obtained for the considered</p>
<p>communication system. Especially, we tend to answer to the</p>
<p>following question: Can better secrecy be achieved without</p>
<p>jamming by considering a single antenna at eavesdroppers</p>
<p>and multiple-ones at the legitimate users (i.e., relay and enduser)</p>
<p>rather than sending permanently an artificial noise and</p>
<p>considering that both the relay and the destination are equipped</p>
<p>with a single antenna, while multiple antennas are used by the</p>
<p>eavesdroppers? The obtained results are corroborated through</p>
<p>Monte Carlo simulation and show that the system’s security can</p>
<p>be enhanced by adjusting the aforementioned parameters.</p>
Wireless Covert Communications Aided by Distributed Cooperative Jamming over Slow Fading Channels
