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.
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.
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.
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.
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.
Cooperative jamming (CJ) can mask signal-of-interest (SOI) by additional jamming signal in the presence of eavesdroppers, and thus improves the security performance from the perspective of physical layer. In exchange, an additional CJ canceller should be designed for the destination node to restore the SOI, whose performance is possibly degraded by the nonideal hardware features. Typically, the inherent nonlinearity of power amplifier is unavoidably distorted the CJ as the transmit power increases, leading to the limit of the CJ cancellation performance. Therefore, nonlinear CJ cancellation is suggested to alleviate the impact of nonlinear CJ components on the SOI. Besides, the short-term instability of the oscillator is characterized by phase noise in the time domain, resulting in a random phase mismatch between the received CJ and the reference signal, which further degrades the nonlinear CJ cancellation performance. Inspired by the above problems, this paper explicitly analyzes the impact of phase noise on nonlinear CJ cancellation, where the expression of CJ cancellation ratio (CJCR) in the presence of phase noise and nonlinear distortion is derived, where the coefficients of the nonlinear canceller are estimated by LS estimator, and the deterioration of the spectral purity of CJ caused by phase noise is modeled as inter frequency interference (IFI) additional noise. Theoretical analyses and simulation results show that the CJCR decreases as the normalized 3 dB coherence bandwidth of phase noise increases.
In this paper, we propose a reference-free artificial noise (AN) waveform design and cancellation scheme for single-input-single-output (SISO) wireless secure transmission. First, a system structure with the aid of AN is presented, where we provide a specific method extracting the sign information of each symbol from the desired signal (DS) to form AN at the transmitter. Then, we notice that the legitimate receiver enable to reconstruct the AN from the received signal by almost the same method as the transmitter without AN reference, which reduces the system complexity in practice. Subsequently, the AN cancellation performance and the secrecy capacity at the receiver are analyzed, and their upper bounds are also derived. Finally, simulation results confirm that the proposed reference-free AN design and cancellation scheme can effectively suppress the AN at legitimate receiver, while degrades the signal to noise ratio (SNR) at eavesdropper seriously, which provides impressive secure performance in terms of secrecy capacity.
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.