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Abstract
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This study investigates covert communication in the presence of a half-duplex amplifyand-
forward (AF) relay, while accounting for transceiver hardware impairments. A cooperative jamming
strategy and channel uncertainty are employed to achieve covertness. For a trusted relay, informed jammers
mitigate the effect of artificial noise (AN) at the legitimate receiver and increase the warden’s uncertainty,
thereby enhancing the covert rate. For an untrusted relay, the jammer must emit AN while the data signal
is transmitted toward the untrusted relay to reduce the untrusted relay’s signal-to-interference-plus-noise
ratio (SINR), which poses a challenge for deploying an informed jammer. The results show that, in both
trusted and untrusted relay scenarios, increasing the transmit power yields only marginal performance gains
due to hardware impairments, highlighting the importance of high-quality transceivers and compensation
algorithms. Notably, under specific conditions, impairments in the legitimate receiver’s transmitter can
slightly enhance performance in the trusted relay case, while in untrusted relay scenarios, impairments
in any legitimate node degrade covert communication performance. Differences in hardware equipment
quality between the transmitter (or retransmitter) and its associated jammer also affect the warden’s ability
to detect the transmission.
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