Artificial noise (AN) can degrade eavesdroppers' signal-to-noise ratio (SNR) in anti-terrorism emergency communications to secure tactical data transmissions. However, system secrecy performance depends on licensed receivers' AN cancellation capabilities. Imperfect channel state information (CSI) will induce residual AN at licensed receivers, thereby degrading system secrecy performance. Unlike the previous methods of simply optimizing power allocation at the transmitter, this study proposes a joint transceiver optimization scheme to mitigate the impact of channel estimation error. Firstly, we present an ANaided anti-terrorism emergency communication model and theoretically derive the statistical properties of the channel estimation error and the closed-form expression of the achievable secrecy rate. Then, a joint optimization scheme for power allocation at the transmitter and cancellation factor at the receiver is presented to maximize the achievable secrecy rate. On this basis, the optimal values of power allocation weight and cancellation factor are derived. The simulation and analysis results prove that the proposed optimization scheme can effectively improve the system security performance in the presence of channel estimation error, and its achievable secrecy rate can be improved by about 16% compared with the power allocation alone.
Artificial noise (AN) can degrade eavesdroppers' signal-to-noise ratio (SNR) in anti-terrorism emergency communications to secure tactical data transmissions. However, system secrecy performance depends on licensed receivers' AN cancellation capabilities. Imperfect channel state information (CSI) will induce residual AN at licensed receivers, thereby degrading system secrecy performance. Unlike the previous methods of simply optimizing power allocation at the transmitter, this study proposes a joint transceiver optimization scheme to mitigate the impact of channel estimation error. Firstly, we present an ANaided anti-terrorism emergency communication model and theoretically derive the statistical properties of the channel estimation error and the closed-form expression of the achievable secrecy rate. Then, a joint optimization scheme for power allocation at the transmitter and cancellation factor at the receiver is presented to maximize the achievable secrecy rate. On this basis, the optimal values of power allocation weight and cancellation factor are derived. The simulation and analysis results prove that the proposed optimization scheme can effectively improve the system security performance in the presence of channel estimation error, and its achievable secrecy rate can be improved by about 16% compared with the power allocation alone.
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.
We consider the problem of secure communication with multiantenna transmission in fading channels. The transmitter simultaneously transmits an information-bearing signal to the intended receiver and artificial noise to the eavesdroppers. We obtain an analytical closed-form expression of an achievable secrecy rate and use it as the objective function to optimize the transmit power allocation between the information signal and the artificial noise. Our analytical and numerical results show that equal power allocation is a simple yet near-optimal strategy for the case of noncolluding eavesdroppers. When the number of colluding eavesdroppers increases, more power should be used to generate the artificial noise. We also provide an upper bound on the SNR, above which, the achievable secrecy rate is positive and shows that the bound is tight at low SNR. Furthermore, we consider the impact of imperfect channel state information (CSI) at both the transmitter and the receiver and find that it is wise to create more artificial noise to confuse the eavesdroppers than to increase the signal strength for the intended receiver if the CSI is not accurately obtained.
Secure communication with noisy feedback is studied in this correspondence. Unlike the majority of previous research efforts where the eavesdropper's channel state information (CSI)-either instantaneous or statistical CSI, is known by the legitimate users, a joint feedback and artificial noise scheme without any eavesdropper's CSI is proposed. The proposed scheme lets the source and the legitimate destination alternatively transmit private messages and degrade the eavesdropper's channel quality in all transmission phases. An insightful discovery is that if the transmit power is lager than a certain threshold, a positive secrecy capacity can be achieved, which overcomes the problem that the secrecy cannot be achieved when the legitimate user's CSI is worse than the eavesdropper's. The secrecy capacity maximization problem is investigated by adaptive power allocation for the private signals and the artificial noise where a near optimal solution of the power of artificial noise is obtained under the high SNR situation. Finally, the numerical results verify the theoretical analysis and illustrate the secrecy performance of the proposed scheme.
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.
Utilizing artificial noise (AN) is a good means to guarantee security against eavesdropping in a multi-input multi-output system, where the AN is designed to lie in the null space of the legitimate receiver's channel direction information (CDI). However, imperfect CDI will lead to noise leakage at the legitimate receiver and cause significant loss in the achievable secrecy rate. In this paper, we consider a delayed feedback system, and investigate the impact of delayed CDI on security by using a transmit beamforming and AN scheme. By exploiting the Gauss-Markov fading spectrum to model the feedback delay, we derive a closed-form expression of the upper bound on the secrecy rate loss, where Nt= 2. For a moderate number of antennas where Nt>; 2, two special cases, based on the first-order statistics of the noise leakage and large number theory, are explored to approximate the respective upper bounds. In addition, to maintain a constant signal-to-interference-plus-noise ratio degradation, we analyze the corresponding delay constraint. Furthermore, based on the obtained closed-form expression of the lower bound on the achievable secrecy rate, we investigate an optimal power allocation strategy between the information signal and the AN. The analytical and numerical results obtained based on first-order statistics can be regarded as a good approximation of the capacity that can be achieved at the legitimate receiver with a certain number of antennas, Nt. In addition, for a given delay, we show that optimal power allocation is not sensitive to the number of antennas in a high signal-to-noise ratio regime. The simulation results further indicate that the achievable secrecy rate with optimal power allocation can be improved significantly as compared to that with fixed power allocation. In addition, as the delay increases, the ratio of power allocated to the AN should be decreased to reduce the secrecy rate degradation.
In this paper, we study the secure multiantenna transmission with artificial noise (AN) under imperfect channel state information (CSI) in the presence of spatially randomly distributed eavesdroppers. We derive the optimal solutions of the power allocation between the information signal and the AN for minimizing the secrecy outage probability (SOP) under a target secrecy rate and for maximizing the secrecy rate under an SOP constraint, respectively. Moreover, we provide an interesting insight that channel estimation error affects the optimal power allocation strategy in opposite ways for the two given objectives. When the estimation error increases, more power should be allocated to the information signal if we aim to decrease the rate-constrained SOP, whereas more power should be allocated to the AN if we aim to increase the SOP-constrained secrecy rate.