This paper investigates secure communications in fixed gain untrusted relay networks. Unlike the trusted relay, an untrusted relay may be an eavesdropper and also does not have the instantaneous channel state information (CSI) of the main link. We propose a destination aided secure transmission scheme. A closed-form of achievable secrecy rate of the proposed scheme is derived and the optimal power allocation between the information signal and jamming signal is also discussed. Simulations elaborately verify our theoretical results.
This paper investigates secure communications in fixed gain untrusted relay networks. Unlike the trusted relay, an untrusted relay may be an eavesdropper and also does not have the instantaneous channel state information (CSI) of the main link. We propose a destination aided secure transmission scheme. A closed-form of achievable secrecy rate of the proposed scheme is derived and the optimal power allocation between the information signal and jamming signal is also discussed. Simulations elaborately verify our theoretical results.
This paper investigates a secure communication via an untrusted relay with channel estimation error, in which a destination-assisted jamming strategy is adopted to prevent the relay from recovering a source signal. In the presence of channel estimation error in the relay-to-destination link, a destination cannot decode the source signal as well as eliminate a jamming signal perfectly, which causes a serious degradation in secrecy performance. Therefore, it is required to propose an effective strategy to determine jamming power level for maximizing secrecy rate. Under the assumption of high transmit signal-to-noise ratio, we derive the closed-form expression of a suboptimal jamming power ratio and propose an adaptive jamming power allocation which can be operated in practical systems. Numerical results confirm that the proposed scheme outperforms the conventional scheme in terms of secrecy rate.
We investigate the physical layer security in non-regenerative untrusted relay networks, where the relay is a potential eavesdropper despite its cooperatively relaying the information. The current research and development of untrusted relay is often based on the assumption of perfect channel knowledge or the capability of variable-rate transmissions which is decided by instantaneous channel state information (CSI). In this paper, we investigate the secure transmission in a more practical scenario, where the source does not have or trust relay's feedback and uses fixed-rate transmissions. We first calculate the exact connection outage probability (COP) and secrecy outage probability (SOP) to describe the level of reliability and security of the communication system, respectively. Then, the closed-form of reliable-and-secure probability (RSP) is derived to character the trade-off between reliability and security. Finally, Monte-Carlo simulation results are presented to verify the validity of our theoretical analysis.
In this article, a new relay-aided secure communication system is investigated, where a transmitter sends signals to a destination via an amplify-and-forward (AF) relay in the presence of an eavesdropper. We consider a general system configuration, where the source, relay, destination, and eavesdropper are all equipped with multiple antennas. In the practical scenarios of unknown eavesdropper's channel state information (CSI) and uncertainty of the eavesdropper's location, we aim to maximize the expected value of the system secrecy rate over the presumed distribution of the eavesdropper's channels, by exploiting the artificial noise (AN) transmitted by the source and relay nodes. The system design issue is formulated as a nonconvex stochastic optimization problem with a source transmission power constraint and a nonconvex relay transmission power constraint. A novel computational method is proposed to solve this challenging problem. The new method is developed based on an exact penalty function method together with a parallel stochastic decomposition algorithm. Numerical simulations are performed to study the effectiveness of the proposed scheme at various locations of the eavesdropper. Simulation results show that for most cases, secure communication can be achieved without the CSI knowledge of eavesdropper's channels, and the achievable secrecy rate follows the trend of a benchmark system where the eavesdropper's full CSI is available. In particular, the achievable system secrecy rate increases with the number of antennas at the legitimate users. Moreover, the optimal power allocated for the transmission of the AN increases with the system signal-to-noise ratio. The proposed computational method achieves a higher system secrecy rate than a conventional penalty function based approach.
In this paper, we consider secure communication via a wireless-powered untrusted relay with outdated channel state information (CSI). The low security clearance of the relay means that both the source and destination wish to keep information confidential from it. To prevent the relay from decoding the source information, the destination emits a jamming signal to the relay during data transmission by the source. The wireless-powered relay uses both the data and the jamming signals as valuable sources of energy for the amplify-and-forward relaying process. In addition, it can adopt either a power splitting or a time switching policy to determine the proportions of energy harvesting and information processing. However, when the CSI of the relay-to-destination link is outdated, the destination cannot remove the jamming signal completely from the relaying signal due to imperfect channel reciprocity. To evaluate the effect of outdated CSI on the secrecy performance, we derive the analytical expressions of two performance metrics, outage probability (Pout) for delay-limited transmission and ergodic secrecy rate (R̅) for delay-tolerant transmission. The results of the analysis also allow us to find the jamming power level and energy harvesting ratio to optimize Poutand R̅, respectively. Numerical simulations are used to verify the precision of our analysis, and confirm that the proposed secure relaying protocols accomplish near-optimal secrecy performances. Our results indicate that there is a need to reduce the jamming power level to ensure secure communication when the channel is severely outdated, while outdated CSI has a relatively low impact on the energy harvesting ratio.
The inherent broadcast characteristics of wireless medium make wireless data transmission difficult to be shielded from unintended recipients. As such, secure communication over wireless channels becomes a critical issue in the design of wireless networks. In this study, the authors study cooperative jamming and power optimisation in untrusted relay networks to improve physical layer security. By exploiting the direct link, a source‐based jamming (SBJ) scheme is proposed to hinder the untrusted relay from intercepting the confidential message. Considering the total power budget, a power allocation strategy is also proposed to optimally determine the power of source and untrusted relay as well as the power of information and jamming signals. Furthermore, to evaluate the secrecy performance of the proposed SBJ scheme with the power allocation strategy, tight lower bound of ergodic secrecy capacity and asymptotic secrecy outage probability are derived in closed form. Simulation verifies the advantages of the proposed SBJ scheme and the power allocation strategy.
The objective of this paper is to maximize the secrecy rate in an untrusted relay network with imperfect channel state information (CSI). Considering bounded channel estimation error in cooperative jamming network, we optimize the power allocation for confidential and jamming signals to maximize the instantaneous secrecy rate. The upper and lower bounds of achievable secrecy rate are analyzed. The ergodic secrecy rate (ESR) is further derived to evaluate the maximum average secrecy rate. And the optimal power allocation is also studied based on ESR. Numerical results show optimal power allocation can increase both instantaneous secrecy rate and ESR, and at higher SNR, the impact of channel estimation error can be neglected for the maximum ESR, which is asymptotically approaches to the upper bound.