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.
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.
While 6G provides communication services for massive wireless devices, it faces huge security risks due to its open feature. Cooperative jamming techniques in physical layer security provide a viable way to ensure 6G security. By actively transmitting jamming signals to deteriorate the eavesdropping channel, while authorized receivers implement cooperative jamming cancellation (CJC) using the prior knowledge of cooperative jamming, thus securing the communication at the physical layer. In practice, incomplete matching of oscillator device characteristics will lead to the in-phase and quadrature (IQ) imbalance problem, where the quadrature branches of the up and down converted carrier signals are not perfectly orthogonal to the in-phase branches, which may degrade the CJC performance. For this reason, this paper specifically analyzes the impact of the IQ imbalance problem on the CJC performance, where a closed-form expression of the jamming cancellation ratio (JCR) with respect to amplitude imbalance and phase imbalance is derived. The simulation results show that when jamming-to-noise ratio (JNR) is 35 dB, the system can tolerate up to 1% amplitude imbalance and 1° phase imbalance with 3 dB JCR degradation. Moreover, the IQ imbalance has a noticeable effect on the reachable security rate of the communication system.
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 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.
In the Internet of Things (IoT), distributed idle devices can transmit cooperative jamming to confuse eaves-dropping devices, while authorized receivers utilize distributed cooperative jamming (DCJ) cancellation techniques to achieve signal-to-noise ratio gain, thereby enabling physical layer secure connectivity. However, constrained by the cost and size of IoT terminals, the crystal oscillators they employ typically exhibit low frequency stability, leading to challenges in achieving precise time-frequency alignment during DCJ cancellation. This significantly degrades the DCJ cancellation capability. To address this, the effect of time-frequency mismatch on DCJ cancellation and system sensitivity loss are analysed, and a closed-form expression for the jamming cancellation ratio with respect to the normalized time-frequency error is derived. Simulation results confirm the theoretical analysis that time-frequency mismatch causes a dramatic degradation in the performance of DCJ cancellation and results in a significant increase in the system sensitivity loss, particularly under scenarios involving large-scale jamming nodes.
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 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).