The artificial noise shielded frequency-hopping (AN-FH) architecture can secure wireless communications against interference and eavesdropping. However, the AN suppression performance is highly sensitive to the radio frequency (RF) impairments, and the transceiver in-phase and quadrature (IQ) imbalances and phase noise in FH systems are more severe for the wide FH bandwidth. In this study, the AN-FH transceivers under RF impairments are mathematically modeled. Subsequently, distortions for transceiver phase noise are represented by the common phase error, distortions for transceiver IQ imbalances are represented by the mirror image component, and closed-form expressions for their respective power are derived and compared with the thermal noise power. Finally, the AN suppression capability is evaluated via the AN suppression ratio (ANSR), defined as the ratio of the AN-plus-noise power before and after suppression. It is found that when only phase noise exists, shortening the channel compensation cycle can enhance ANSR and reduce ANSR degradation; when the distortions’ power is smaller than the thermal noise power, it is also recommended to enhance the transmitting power and the power ratio of AN to information signals. When only IQ imbalances exist, increasing the power ratio of AN to information signals is suggested; when the distortions’ power is smaller than the thermal noise power, enhancing the transmitting power is also suggested.
The artificial noise shielded frequency-hopping (AN-FH) architecture can secure wireless communications against interference and eavesdropping. However, the AN suppression performance is highly sensitive to the radio frequency (RF) impairments, and the transceiver in-phase and quadrature (IQ) imbalances and phase noise in FH systems are more severe for the wide FH bandwidth. In this study, the AN-FH transceivers under RF impairments are mathematically modeled. Subsequently, distortions for transceiver phase noise are represented by the common phase error, distortions for transceiver IQ imbalances are represented by the mirror image component, and closed-form expressions for their respective power are derived and compared with the thermal noise power. Finally, the AN suppression capability is evaluated via the AN suppression ratio (ANSR), defined as the ratio of the AN-plus-noise power before and after suppression. It is found that when only phase noise exists, shortening the channel compensation cycle can enhance ANSR and reduce ANSR degradation; when the distortions’ power is smaller than the thermal noise power, it is also recommended to enhance the transmitting power and the power ratio of AN to information signals. When only IQ imbalances exist, increasing the power ratio of AN to information signals is suggested; when the distortions’ power is smaller than the thermal noise power, enhancing the transmitting power is also suggested.
The artificial noise (AN) shielded frequency-hopping (FH) architecture can effectively resist wiretapping and electromagnetic interference, but its wide hopping bandwidth will raise a non-negligible in-phase and quadrature (IQ) imbalance at transceiver oscillators, yielding significant signal distortions during IQ mixing. Considering this, first, signal distortions raised by transceiver IQ imbalances are modelled in this study, and their characteristics are mathematically investigated as well. Next, the signal to distortion-plus-noise ratio (SDNR) is extracted to measure the quality of the obtained signal after AN cancellation, and the secrecy capacity is subsequently derived to evaluate system secrecy under multiple wiretappers. Then, based on the performance evaluations, the transmitting power ratio of AN to information signals is optimized to counteract the secrecy degradation raised by transceiver IQ imbalances. Simulations show that both the AN cancellation and system secrecy performance will decline sharply as the amplitude or phase imbalance deteriorates. Besides, compared with the case where the power ratio of AN to information signals is 2, the average secrecy enhancements of an equal power scheme, a power scheme ignoring IQ imbalances, and our proposed power scheme approximate 8.4%, 9.66%, and 11.05% for a fixed phase imbalance, and approximate 10.88%, 12.61%, and 14.26% for a fixed amplitude imbalance, respectively.
This paper adopts an artificial noise (AN) shielded frequency hopping (FH) architecture to counteract both wire-tapping and hostile attack, but the inevitable phase noise will degrade both the AN cancellation and secrecy performance. Considering this, first, the AN cancellation performance is analyzed by separating the received AN into the cancellable common phase component (CPC) and non-cancellable inter-carrier interference (ICI). On top of this, the system secrecy is analyzed via secrecy capacity, and the secrecy degradation for phase noise is extracted in terms of 3 dB coherence bandwidth of the adopted oscillators, transmitting power ratio of AN to expected signal (ES), propagation channel quality, and parameter estimation period. Numerical and simulation results show that phase noise will degrade both the AN cancellation and secrecy performance, and this degradation can be diminished by shortening the parameter estimation period, optimizing the power ratio of AN to ES, and improving the propagation channel quality.
Artificial noise (AN) is an effective physical security measure against eavesdropping in wireless communication. In previous literatures, AN is generally analyzed in multiple transmit antenna systems and is suppressed by zero-forcing algorithm, which is implemented by using the spatial degrees of freedom. In this paper, an AN suppression model under single-input multi-output (SIMO) systems is presented, and the impact of imperfect frequency synchronization on the AN suppressed performance is analyzed. Specifically, we first analyze the AN suppression performance of single branch with imperfect frequency synchronization. Then the output signal to interference plus noise ratio (SINR) after multi-branch merging is derived. Finally, the secrecy capacity of AN based on SIMO systems is extracted on the basis of the obtained SINR. Theoretical and simulation results show that imperfect frequency synchronization reduces the SINR of each branch, and thus degrades both the output SINR and secrecy capacity in SIMO systems. Moreover, when the residual AN power is greater than noise power, no diversity gain will be achieved by multi-branch merging.
This study investigates covert communication in the presence of a half-duplex amplify-and-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.
Transmitting the information-bearing signal simultaneously with artificial noise (AN) can guarantee secure data exchange on the open wireless channel. One of the key technologies is AN reconstruction and cancellation at the legitimate receiver, but its performance will be deteriorated by the ineluctable clock jitter at the analog-to-digital converter (ADC). In this paper, first, the received signal distorted by clock jitter is mathe-matically modelled. Then, the closed-form expression of signal to interference-plus-noise ratio (SINR) after AN cancellation is deduced, and the secrecy capacity is derived to evaluate the system security. Furthermore, to alleviate the effect of clock jitter, the optimized transmitting power allocation scheme for AN and information signal is provided. Theoretical and simulation results demonstrate that the secrecy performance is limited by the 3 dB coherence bandwidth of the phase noise caused by clock jitter, time synchronization period, and transmitting power allocation factor. With the optimized power scheme, the secrecy capacity can be increased by up to 11 % in comparison to the equal power allocation, and the optimal power allocation factor equals one when there is no clock jitter.
Impairments baseband model in-phase and quadrature-phase Imbalance (IQI) and Residual hardware impairments (RHI) are two key factors degrading the performance of wireless communication systems (WCS). In this paper, the joint effect of both IQI and RHI on the secrecy outage probability (SOP) of a WCS subject to Fox’s H-fading channel is investigated. Such a fading model generalizes most, if not all, of well-known fading and turbulence models. To this end, novel generalized closed-form expression is derived for the secrecy outage probability for all possible scenarios namely (i) Transmitter (Tx) only impaired, (ii) Receiver (Rx) only impaired, and (iii) both Tx and Rx are impaired. α−µ has been considered as a particular case of Fox’s H-fading distribution. The analytical derivations, revealed by simulation results, demonstrate that the RF impairments’ effects should be seriously taken into account in the design of secure next-generation wireless technologies. On the other hand, the numerical results show that the parameters of fading channels can be used as a key to mitigating the effects of RF impairments on the secrecy performance.