This paper considers a point-to-point communication system which is protected by a cooperative jammer from being eavesdropped. Previous works in this field always assume that the cooperative jamming is cancelled perfectly at the receiver, without considering any imperfections in the jamming cancellation of practical systems. In this paper, by taking into account the residual jamming caused by frequency offset at the receiver, a power allocation scheme is proposed to maximize the secrecy capacity over the additive white Gaussian noise (AWGN) channel, which is derived as an exact closed-form solution. In addition, the relationship between the optimal jamming power and the relative channel quality is analyzed under imperfect jamming cancellation. Simulation results confirm that the proposed power allocation scheme outperforms the power allocation scheme without considering any imperfections in the jamming cancellation, and illustrate that the frequency offset significantly degrade the security performance. Specially, for small frequency offset, the total power consumption increases with the frequency offset, which means the frequency offset consumes extra power to achieve the secrecy capacity target. However, for large frequency offset, the secrecy capacity may fail to meet its preset goal no matter how sufficient the power budget is. More seriously, when the frequency offset is remarkable, the secrecy capacity may drop to 0, which implies that the eavesdropper can always overhear the confidential information.
This paper considers a point-to-point communication system which is protected by a cooperative jammer from being eavesdropped. Previous works in this field always assume that the cooperative jamming is cancelled perfectly at the receiver, without considering any imperfections in the jamming cancellation of practical systems. In this paper, by taking into account the residual jamming caused by frequency offset at the receiver, a power allocation scheme is proposed to maximize the secrecy capacity over the additive white Gaussian noise (AWGN) channel, which is derived as an exact closed-form solution. In addition, the relationship between the optimal jamming power and the relative channel quality is analyzed under imperfect jamming cancellation. Simulation results confirm that the proposed power allocation scheme outperforms the power allocation scheme without considering any imperfections in the jamming cancellation, and illustrate that the frequency offset significantly degrade the security performance. Specially, for small frequency offset, the total power consumption increases with the frequency offset, which means the frequency offset consumes extra power to achieve the secrecy capacity target. However, for large frequency offset, the secrecy capacity may fail to meet its preset goal no matter how sufficient the power budget is. More seriously, when the frequency offset is remarkable, the secrecy capacity may drop to 0, which implies that the eavesdropper can always overhear the confidential information.
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.
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.
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.
Security has become an increasingly important issue in wireless communications for the IoT (Internet of Things) environments, to which physical layer approaches can contribute by differentiating desired transceiver and wiretap channels for security of confidential data. In this paper, we propose an optimal power allocation strategy for practical physical-layer security, based on friendly jamming with cancellation for anti-eavesdropping. In particular, secrecy outage probability is evaluated in scenarios involving a pair of transmitter-receiver and a passive eavesdropper near the receiver. We derive the optimal power allocation strategy and the required cancellation capability to enhance secrecy performance. Numerical results verify the tradeoff between jamming power ratio and cancellation capability. Furthermore, our proposed scheme can achieve the improved secrecy rate regardless of availability of eavesdropper channel information.
This paper studies a robust resource allocation framework to enhance physical layer security where it is assumed that the system is equipped with a full-duplex (FD) receiver in contrast to conventional frameworks where a half-duplex (HD) receiver is at hand. Conventionally, relays are used as jammer to reduce the signal quality received by the eavesdroppers so as to increase the secrecy transmission rate between the legitimate transmitter and receiver. This is referred to as cooperative jamming (CJ). In a system equipped with a FD receiver, we propose to use the FD receiver as the jammer, i.e., the FD receiver simultaneously transmits jamming signals toward the eavesdropper while receiving data from the transmitter. The proposed scheme eliminates the need for external helpers, i.e., jamming relays which is welcome from practical point of view. We consider different scenarios to compare the proposed scheme against the CJ scheme in which, under a legitimate transmitter power constraint, optimal power allocation is obtained for each scenario to maximize the secrecy rate. To take into account the impact of imperfect state information of the channels between the eavesdropper and other nodes on the network, worst-case optimization approaches are considered. Simulation results demonstrate that for certain positions of the jamming relay and eavesdropper, the proposed system can outperform the conventional CJ schemes.
This paper studies the secrecy communication in an orthogonal frequency division multiplexing system, where a source sends confidential information to a destination in the presence of a potential eavesdropper. We employ wireless powered cooperative jamming to improve the secrecy rate of this system with the assistance of a cooperative jammer, which works in the harvest-then-jam protocol over two time slots. In the first slot, the source sends dedicated energy signals to power the jammer; in the second slot, the jammer uses the harvested energy to jam the eavesdropper, in order to protect the simultaneous secrecy communication from the source to the destination. In particular, we consider two types of receivers at the destination, namely Type-I and Type-II receivers, which do not have and have the capability of canceling the (a priori known) jamming signals, respectively. For both types of receivers, we maximize the secrecy rate at the destination by jointly optimizing the transmit power allocation at the source and the jammer over sub-carriers, as well as the time allocation between the two time slots. First, we present the globally optimal solution to this problem via the Lagrange dual method, which, however, is of high implementation complexity. Next, to balance the tradeoff between the algorithm complexity and performance, we propose alternative low-complexity solutions based on the minorization maximization and heuristic successive optimization, respectively. Simulation results show that the proposed approaches significantly improve the secrecy rate, as compared to benchmark schemes without joint power and time allocation.