As a low-complexity and energy efficient MIMO technique, spatial modulation (SM) can avoid inter-channel interference and inter-antenna synchronization. Combining SM with cooperative relaying, the performance of SM can be effectively improved. Since wireless communication is vulnerable to be eavesdropped, the destination-based-jamming (DBJ) technique is applied to the cooperative SM system for security enhancement. In the DBJ scheme, the jamming signal is sent from the legitimate receiver (Bob) to interfere the eavesdropper (Eve). Based on the amplify-and-forward (AF) relaying, we investigate the secrecy performance of the AF relay assisted cooperative SM system with DBJ over Rayleigh fading channels. The achievable rates by Bob and Eve and the corresponding lower bounds are respectively derived. With these low bounds, the approximated closed-form ergodic rates by Bob and Eve can be obtained, respectively. Using these results, the theoretical closed-form ergodic secrecy rate (ESR) of the system can be further derived. The simulation results are provided to confirm the validity of our theoretical analysis. The derived theoretical expressions are consistent with the corresponding simulations and the DBJ scheme is well capable of enhancing the secrecy performance of the cooperative SM system over Rayleigh fading channels.
As a low-complexity and energy efficient MIMO technique, spatial modulation (SM) can avoid inter-channel interference and inter-antenna synchronization. Combining SM with cooperative relaying, the performance of SM can be effectively improved. Since wireless communication is vulnerable to be eavesdropped, the destination-based-jamming (DBJ) technique is applied to the cooperative SM system for security enhancement. In the DBJ scheme, the jamming signal is sent from the legitimate receiver (Bob) to interfere the eavesdropper (Eve). Based on the amplify-and-forward (AF) relaying, we investigate the secrecy performance of the AF relay assisted cooperative SM system with DBJ over Rayleigh fading channels. The achievable rates by Bob and Eve and the corresponding lower bounds are respectively derived. With these low bounds, the approximated closed-form ergodic rates by Bob and Eve can be obtained, respectively. Using these results, the theoretical closed-form ergodic secrecy rate (ESR) of the system can be further derived. The simulation results are provided to confirm the validity of our theoretical analysis. The derived theoretical expressions are consistent with the corresponding simulations and the DBJ scheme is well capable of enhancing the secrecy performance of the cooperative SM system over Rayleigh fading channels.
This paper investigates the ergodic achievable secrecy rate (EASR) of multiple-antenna amplify-and-forward relay systems, where one eavesdropper can wiretap the relay. To reveal the capability of the multiple-antenna relay in improving the secrecy performance, we derive new tight closed-form expressions of the EASR for three secure transmission schemes: artificial noise aided precoding (ANP), destination based jamming (DBJ) and eigen-beamforming (EB). We also derive the lower bounds of the EASR for ANP and DBJ with a large antenna array at the relay, and investigate their corresponding asymptotic performance in the high SNR and low SNR regimes to show valuable intrinsic insights as well. Based on the asymptotic analysis, we optimally allocate the power to the information signal and the artificial noise. Both the analysis and simulation results indicate that, in the moderate-to-high SNR regime, ANP achieves considerable performance gain over DBJ and EB, while in the low SNR regime, EB outperforms the other two schemes with equal power allocation. As SNR grows large, the EASR of EB approaches a constant independent of the first hop channel. Moreover, in the high SNR regime, it is optimal to allocate around half of total power to artificial noise for ANP and most of the power to artificial noise for DBJ.
Abstract—In this paper, the problem of secure transmission in two-hop amplify-and-forward (AF) systems with an untrusted relay is investigated. To prevent the untrusted relay from intercepting the source message and to achieve positive secrecy rate, the destination-based cooperative jamming (DBCJ) technique is used. In this method the destination sends an intended jamming signal to the relay. This jamming signal helps protecting the source message from being captured reliably at the untrusted relay, while the destination cancels itself intended jamming signal. The optimal power allocation (OPA) technique is considered for the presented system. It is observed that the objective function is a quasiconcave function at high signal-to-noise-ratio (SNR) regimes. Based on this OPA technique, we study the ergodic secrecy rate (ESR) and the secrecy outage probability (SOP) of the system when the source and relay are equipped with a single antenna while the destination is equipped with largescale antenna arrays (LSA). Using the achieved closed-form expressions, one can evaluate the performance of the secure system easily and fast and also, they provide significant insight for system design. Finally, simulation results indicate the accuracy of the derived expressions.
Physical (PHY) layer security approaches for wireless communications can prevent eavesdropping without upper layer data encryption. However, they are hampered by wireless channel conditions: absent feedback, they are typically feasible only when the source-destination channel is better than the source-eavesdropper channel. Node cooperation is a means to overcome this challenge and improve the performance of secure wireless communications. This paper addresses secure communications of one source-destination pair with the help of multiple cooperating relays in the presence of one or more eavesdroppers. Three cooperative schemes are considered: decode-and-forward (DF), amplify-and-forward (AF), and cooperative jamming (CJ). For these schemes, the relays transmit a weighted version of a reencoded noise-free message signal (for DF), a received noisy source signal (for AF), or a common jamming signal (for CJ). Novel system designs are proposed, consisting of the determination of relay weights and the allocation of transmit power, that maximize the achievable secrecy rate subject to a transmit power constraint, or, minimize the transmit power subject to a secrecy rate constraint. For DF in the presence of one eavesdropper, closed-form optimal solutions are derived for the relay weights. For other problems, since the optimal relay weights are difficult to obtain, several criteria are considered leading to suboptimal but simple solutions, i.e., the complete nulling of the message signals at all eavesdroppers (for DF and AF), or the complete nulling of jamming signal at the destination (for CJ). Based on the designed relay weights, for DF in the presence of multiple eavesdroppers, and for CJ in the presence of one eavesdropper, the optimal power allocation is obtained in closed-form; in all other cases the optimal power allocation is obtained via iterative algorithms. Numerical evaluation of the obtained secrecy rate and transmit power results show that the proposed design can significantly improve the performance of secure wireless communications.
This paper investigates cooperative security in wireless networks, where a source (Alice) intends to transmit a confidential message to a legitimate destination (Bob), with the help of a cooperative jammer (Charlie), coexisting with multiple passive eavesdroppers (Eves). In particular, by assuming knowledge of Bob's perfect channel state information (CSI) but only Eves’ statistical CSIs, secrecy beamforming with artificial noise (AN) is utilized for secure transmission, and cooperative jamming (CJ) is explored to further enhance secrecy. We first derive an accurate closed-form expression for the secrecy outage probability (SOP), and establish the condition under which positive secrecy rate is achievable. Then, we provide a secure transmit design for maximizing the SOP constrained secrecy rate. Moreover, based on a strict mathematical analysis, we characterize the impact of the main channel quality and the number of Eves on transmit design and secrecy performance. Specifically, optimal power allocation ratio between the information-bearing signal and the AN signal increases as the main channel quality improves, and decreases with the number of Eves. Numerical results confirm that our design achieves performance improvement in terms of both secrecy rate and secure energy efficiency, as compared to the approach without CJ.
In this paper, we investigate secure two-user AF relaying networks based on a destination assisted cooperative jamming (DACJ). We consider two sources, one destination, one eavesdropper and multiple amplify-and-forwards (AF) relays. In the first time slot, each source broadcasts the information signal to the relays. In order to protect the source message from being eavesdropped, the destination simultaneously transmits a jamming signal to each relay. The selected relay amplifies and forwards the combined signal to the destination and eavesdropper. We introduce reactive relay selection and power allocation to decrease the power consumption. Closed-form expressions for lower bound of ergodic secrecy capacity (ESC) are provided. Numerical results are presented to verify the exactness of the proposed mathematical analysis.
In this paper, we consider a dual-hop amplify-and-forward (AF) multiple-input-multiple-output (MIMO) relay network, where the source, relay, and destination are each equipped with multiple antennas. The relay is untrusted if it is willing to forward the signal to the destination and, at the same time, acts as a potential eavesdropper to interpret the message from the source. Since there exists no direct link between the source and the destination, a positive secrecy rate cannot be obtained. Addressing this issue, we propose a joint destination-aided cooperative jamming and precoding at both the source and the relay scheme: joint source, relay, and destination precoding (JP). We target at maximizing the secrecy rate by jointly designing the source, relay, and destination precoding matrices and propose an alternating iterative optimization algorithm to tackle the nonconvex problem. Then, a comprehensive study on the asymptotic performance is conducted in a high signal-to-noise ratio (SNR) regime. In particular, we present simple closed-form expressions for the two key performance parameters in the asymptotic secrecy rate, i.e., the high-SNR slope and the high-SNR power offset. Finally, numerical results are conducted to demonstrate the validity of the proposed secure scheme and its performance analysis.