In recent years, cooperative jamming (CJ) is introduced as a promising method to improve the security performance in the presence of eavesdroppers. By masking the confidential signal with the help of the cooperative jammer, the signal-to-noise ratio of the eavesdropper can be selectively reduced without prior information, whereas the authorized receiver is unaffected since the CJ can be suppressed by some means. Unfortunately, with the impacts of the clock jitter caused by non-ideal crystals, the received CJ may suffer sampling clock offset, carrier frequency offset and phase noise, which deteriorates the performance of the CJ cancellation at the authorized receiver. In this paper, the impacts of clock jitter on CJ cancellation are investigated. First, the deterioration of CJ caused by sampling clock offset is modeled as inter-symbol interference (ISI) in the time domain. Then, the impacts of the sampling clock offset, carrier frequency offset and phase noise on the spectral purity of CJ are modeled as inter-frequency interference (IFI). Furthermore, the expression of the power of residual CJ (PRCJ) is derived to analyze the impacts of clock jitter on CJ cancellation. Finally, numerical results prove the theoretical analysis, indicating that the PRCJ increases as the carrier frequency offset and the 3 dB coherence bandwidth of phase noise increases, and is more sensitive to phase noise.
In recent years, cooperative jamming (CJ) is introduced as a promising method to improve the security performance in the presence of eavesdroppers. By masking the confidential signal with the help of the cooperative jammer, the signal-to-noise ratio of the eavesdropper can be selectively reduced without prior information, whereas the authorized receiver is unaffected since the CJ can be suppressed by some means. Unfortunately, with the impacts of the clock jitter caused by non-ideal crystals, the received CJ may suffer sampling clock offset, carrier frequency offset and phase noise, which deteriorates the performance of the CJ cancellation at the authorized receiver. In this paper, the impacts of clock jitter on CJ cancellation are investigated. First, the deterioration of CJ caused by sampling clock offset is modeled as inter-symbol interference (ISI) in the time domain. Then, the impacts of the sampling clock offset, carrier frequency offset and phase noise on the spectral purity of CJ are modeled as inter-frequency interference (IFI). Furthermore, the expression of the power of residual CJ (PRCJ) is derived to analyze the impacts of clock jitter on CJ cancellation. Finally, numerical results prove the theoretical analysis, indicating that the PRCJ increases as the carrier frequency offset and the 3 dB coherence bandwidth of phase noise increases, and is more sensitive to phase noise.
In the presence of some eavesdroppers, cooperative jamming cancellation (CJC) plays a significant role in physical layer security for wireless communications. The assumption that the cooperative jamming is cancelled ideally with perfect frequency and timing synchronization is commonly used in the past literatures. Due to the instability of crystal oscillators and the relative motion between the cooperative node and the receiving node, residual frequency offset always exists between these two nodes, resulting in performance degradation during CJC. In this paper, a scenario in which all nodes equipped with single antenna is considered. To explicitly analyze the effect of frequency offset on CJC, we model frequency offset as an inter-frequency interference (IFI) in the frequency domain, and evaluate the CJC performance by jamming cancellation ratio (JCR), which is derived as the closed-form expression. Theoretical and simulation results show that, for the additive white Gaussian noise (AWGN) channel, when the ideal received jamming-to-noise ratio (JNR) is 60dB, the jamming bandwidth is 10MHz, and the sampling period of analog-digital converter (ADC) is 100ns, the maximum tolerable frequency offsets that incur 0.1dB, 1dB, and 3dB JCR degradation are 0.82Hz, 2.74Hz, and 5.37Hz, respectively.
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.
Cooperative jamming is one of the promising technologies for securing wireless communications. The cooperative jammer transmits jamming to deteriorate the eavesdropping channel, while the authorized receiver implements cooperative jamming cancellation (CJC) using the pre-stored prior information, thus achieving confidential communication at the physical layer. However, the signal transmission will introduce time delay and frequency offset, as well as zero-intermediate-frequency structures that will cause in-phase and quadrature (IQ) imbalances and local oscillator (LO) leakage, which lead to degradation of the CJC performance. In this paper, we specifically analyze the combined effect of time-frequency mismatch, IQ imbalance and LO leakage on the CJC performance by deducing the closed-form expression for the jamming cancellation ratio. A CJC architecture considering time-frequency mismatch, IQ imbalance and LO leakage is proposed, and the corresponding recursive algorithm for CJC is presented. Simulation results show that the proposed algorithm can effectively improve the CJC performance with the presence of time-frequency mismatch, IQ imbalance and LO leakage, and thus improves the security of the communication system.
This paper considers cooperative jamming (CJ) to ensure secure communication between the transmitter and the legitimate receiver. CJ serves as an effective and promising way to confuse the eavesdropper. However, in the presence of the CJ, the secrecy capacity is obtained at a certain cost of power, which consists of two parts: one part is the extra power consumed by transmitting CJ, and the other part is the signal-to-noise ratio (SNR) loss caused by imperfect CJ cancellation at the authorized receiver, which can be equivalent to the wasted power of the desired signal. In this paper, we both take into account the imperfect CJ cancellation and the extra power penalty to analyze the secrecy capacity, which can be a measurement of system security performance. Numerical simulation is adopted, revealing that the proposed scheme reduces the proportion of power used to transmit jamming signals, and achieves almost the same secrecy capacity as the case which does not take the extra power penalty into consideration. Moreover, the channel capacity of the desired signal is improved.
In physical layer security, imperfect time synchronization results in random mismatch between the received cooperative jamming (CJ) and the reconstructed CJ, leading to performance degradation of CJ cancellation at the authorized receiver. In this letter, the CJ cancellation performance with imperfect time synchronization is analyzed and evaluated by jamming cancellation ratio (JCR). Then, by assuming that the timing error is uniformly distributed within the synchronization accuracy, the expectation and cumulative distribution function (CDF) of JCR are provided. Experimental results confirm the theoretical analysis that imperfect time synchronization causes dramatic performance degradation of CJ cancellation, especially for high jamming-to-noise ratio (JNR).
Cooperative jamming (CJ) can reduce the receiving performance of eavesdroppers and will be reconstructed and canceled at the licensed receiver to ensure reliable communication. However, due to hardware impairments and the limited accuracy of frequency synchronization algorithms, a frequency offset exists between the CJ transmitter and licensed receiver, yielding imperfect jamming cancellation at the licensed receiver. In this letter, assume channel state information of eavesdropper (CSIE) is perfect, a joint transceiver optimization algorithm for CJ cancellation with frequency mismatch is proposed. To maximize the system’s achievable secrecy rate with frequency mismatch, we first derive the closed-form expression of the system’s achievable secrecy rate; then, the security performance of the system is optimized from two aspects: power allocation at the transmitter and jamming cancellation factor optimization at the receiver. Moreover, the feasibility of the proposed optimization scheme under imperfect CSIE is analyzed. Simulations show that the proposed transceiver method significantly improves the system security performance compared with the traditional one.