Target Secrecy Rate Research Articles

Secrecy Performance Analysis for Fixed-Gain Energy Harvesting in an Internet of Things With Untrusted Relays

In this paper, the radio frequency energy harvesting (EH) and security issues in Internet of Things (IoT) sensor networks with multiple untrusted relays are considered. In particular, the communication protocol is divided into two phases. The first phase is used for EH, in which the IoT sensor nodes (SNs) and relays harvest energy from multiple power transfer stations. The second phase is used for information transmission in two steps: 1) the selected SN uses the harvested energy to broadcast information to the controller and the relays, and 2) the selected relay forwards information to the controller by applying the amplify-and-forward protocol to improve the quality of the communication between the SN and the controller. During information transmission, the controller is at risk of losing information because the relay may act as an eavesdropper (namely, an untrusted relay). Thus, to improve the secrecy performance of the considered system, we propose an optimal scheme, namely, best-sensor-best-untrusted-relay (BSBR) and compare this scheme with random-sensor-random-untrusted-relay and a threshold-based scheme. The closed-form expressions for the secrecy outage probability (SOP) and secrecy throughput (ST) are obtained and verified through Monte Carlo simulations to confirm the superior performance of our approach. EH time optimization and the target secrecy rate optimization algorithms are also proposed. In addition, the impacts of the EH time, the EH efficiency coefficient, the numbers of SNs and untrusted relays, and the target secrecy rate on the SOP and the ST are investigated. The results indicate that the BSBR generally outperforms the two baseline schemes in terms of the SOP and ST.

Secrecy performance of finite-sized cooperative full-duplex relay systems with unreliable backhauls

This paper investigates secrecy performance of finite-sized cooperative full-duplex relay (FDR) systems with unreliable wireless backhaul connections across multiple transmitters under Nakagami- $m$ fading. Closed-form expressions for the secrecy outage probability and probability of nonzero achievable secrecy rate are derived in terms of self-interference (SI), transmitter cooperation, and backhaul reliability. It is shown that transmitter cooperation can effectively enhance the secrecy performance, while the asymptotic limits on the secrecy outage probability and probability of nonzero achievable secrecy rate are exclusively determined by backhaul reliability. With the aid of transmitter cooperation, the burden of SI cancelation can be alleviated for the FDR system in achieving the smallest allowed secrecy outage probability. Compared to that of a half-duplex relay (HDR) system, the FDR system achieves a lower secrecy outage probability with well suppressed SI. The analysis shows that the secrecy outage probability achieved by the FDR system converges to that of the HDR system under perfect backhaul as the target secrecy rate becomes small. The secrecy performance metrics of the considered system are verified by simulations for various backhaul scenarios.

Beamforming and Power Splitting Designs for AN-Aided Secure Multi-User MIMO SWIPT Systems

In this paper, an energy harvesting scheme for a multi-user multiple-input-multiple-output secrecy channel with artificial noise (AN) transmission is investigated. Joint optimization of the transmit beamforming matrix, the AN covariance matrix, and the power splitting ratio is conducted to minimize the transmit power under the target secrecy rate, the total transmit power, and the harvested energy constraints. The original problem is shown to be non-convex, which is tackled by a two-layer decomposition approach. The inner layer problem is solved through semi-definite relaxation, and the outer problem, on the other hand, is shown to be a single-variable optimization that can be solved by 1-D line search. To reduce computational complexity, a sequential parametric convex approximation method is proposed to find a near-optimal solution. This paper is then extended to the imperfect channel state information case with norm-bounded channel errors. Furthermore, tightness of the relaxation for the proposed schemes is validated by showing that the optimal solution of the relaxed problem is rank-one. Simulation results demonstrate that the proposed SPCA method achieves the same performance as the scheme based on 1-D but with much lower complexity.

Joint resource allocation and artificial noise design for multiuser wiretap OFDM channels

PHY-layer security is one of promising techniques for enhanced security and privacy protection in 5G communications. In this paper, the joint resource allocation and artificial noise (AN) design problem of multiuser wiretap orthogonal frequency-division multiplexing (OFDM) systems is investigated to improve the system secrecy rate and power efficiency, which can help to provide waveform design references for secure 5G communications. In such a multiuser wiretap OFDM system, one legitimate transmitter (Alice), multiple legitimate receivers (Bobs), and one eavesdropper (Eve) are simultaneously considered. The time-domain artificial noise is firstly involved to guarantee the target secrecy rates of multiple Bobs. Then a sum secrecy rate maximization problem with nonconvex integer nonlinear programming is formulated to jointly optimize the power, subcarrier allocation and AN design. To solve this tough problem with low computational complexity, a heuristical sub-optimal subcarrier allocation method is proposed, followed by the Lagrange dual method based joint power allocation and AN design scheme. Moreover, considering that sum secrecy rate maximization may result in unfairness for Bobs with bad channel gains, the transmit power minimization problem that ensures a target secrecy rate for each individual Bob is further addressed. An iterative algorithm is proposed to solve this power minimization problem by updating the subcarrier, power allocation and AN design alternatively. Numerical results demonstrate the effectiveness of the proposed algorithms.

Secure Communication via a Wireless Energy Harvesting Untrusted Relay

The broadcast nature of the wireless medium allows unintended users to eavesdrop on confidential information transmission. In this regard, we investigate the problem of secure communication between a source and a destination via a wireless energy harvesting untrusted node that acts as a helper to relay the information; however, the source and destination nodes wish to keep the information confidential from the relay node. To realize the positive secrecy rate, we use destination-assisted jamming. Being an energy-starved node, the untrusted relay harvests energy from the received radio-frequency (RF) signals, which include the source's information signal and the destination's jamming signal. Thus, we utilize the jamming signal efficiently by leveraging it as a useful energy source. At the relay, to enable energy harvesting and information processing, we adopt power splitting (PS) and time switching (TS) policies. To evaluate the secrecy performance of this proposed scenario, we derive analytical expressions for two important metrics, viz., the secrecy outage probability and the ergodic secrecy rate. The numerical analysis reveals design insights into the effects of different system parameters such as PS ratio, energy harvesting time, target secrecy rate, transmit signal-to-noise ratio (SNR), relay location, and energy conversion efficiency factor, on secrecy performance. Specifically, the PS policy achieves better optimal secrecy outage probability and optimal ergodic secrecy rate than that of the TS policy at higher target secrecy rate and transmit SNR, respectively.

Probabilistic Robust Secure Beamforming in MISO Channels With Imperfect LCSI and Statistical ECSI

In this paper, we investigate the robust secure transmit beamformming design for multiple-input single-output wiretap channels overheard by multiple non-collaborating single-antenna eavesdroppers. Assuming that at the transmitter, the instantaneous legitimate receiver’s channel state information (CSI) is imperfect and only the statistical eavesdroppers’ CSI is known, we seek to maximize the target secrecy rate $R$ with the total transmit power constraint and the secrecy outage probability constraint. The resulting outage-constrained secrecy rate maximization (O-SRM) is non-convex and difficult to solve. Thus, we develop an efficient algorithm to solve it and determine the robust secure beamforming design. Specifically speaking, we first prove that the original O-SRM problem can be solved by an equivalent outage-constrained power minimization problem (O-PMP), which is easy to perform semi-definite relaxation (SDR) and can be solved by semi-definite program (SDP) consequently. Second, we transform the non-convex secrecy rate outage constraints into deterministic ones by resorting to Bernstein-type inequality II. Finally, by solving the convex approximation of the O-PMP with different $R\text{s}$ and bisection search over $R$ , we convert the original O-SRM problem into a sequence of solvable SDPs. Simulation results are provided to verify the secrecy-rate performance improvement of the proposed robust beamforming compared with the existing worst-case design proposed by Li and Ma and the simple non-robust maximum-ratio transmission.

Wireless Information-Theoretic Security: Theoretical analysis & experimental measurements with multiple eavesdroppers in an outdoor obstacle-dense MANET

Wireless Information-Theoretic Security (WITS) has been suggested as a robust security scheme, especially for infrastructure-less networks. Based on the physical layer, WITS considers quasi-static Rayleigh fading instead of the classic Gaussian wiretap scenario. In this paper, the key parameters of WITS are investigated by implementing an 802.11n ad-hoc network in an outdoor obstacle-dense topology. Measurements performed throughout the topology allow for a realistic evaluation of a scenario with multiple moving eavesdroppers. Low speed user movement has been considered, so that Doppler spread can be discarded. A set of discrete field test trials have been conducted, based on simulation of human mobility throughout an obstacle-constrained environment. Average Signal-to-Noise Ratio (SNR) values have been measured for all moving nodes, and the Probability of Non-Zero Secrecy Capacity has been calculated for different eavesdropping cooperative schemes (Selection Combining and Maximal-Ratio Combining). In addition, the Outage Probability has been estimated with regard to a non-zero target Secrecy Rate for both techniques. The results have been compared with the respective values of WITS key parameters derived from theoretical analysis.

Optimal Power Allocation for Artificial Noise Under Imperfect CSI Against Spatially Random Eavesdroppers

In this correspondence, we study the secure multiantenna transmission with artificial noise (AN) under imperfect channel state information 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 a SOP constraint, respectively. Moreover, we provide an interesting insight that channel estimation error affects the optimal power allocation strategy in opposite ways for the above two 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.

Secure Green Communication via Untrusted Two-Way Relaying: A Physical Layer Approach

In this paper, energy-efficient secure communications via untrusted two-way relaying are investigated considering physical layer security to prevent the relays from intercepting the confidential information of users. The performance metric of secure energy efficiency (EE), defined as the ratio of the secrecy sum rate to the total power consumption, is maximized by jointly optimizing power allocation for all nodes, with the constraints of the maximum allowed power and the minimum target secrecy rate. To deal with this intractable nonconvex optimization problem, some optimization methods termed as fractional programming, alternate optimization, penalty function method, and difference of convex functions programming, are jointly applied to address a solution scheme with comparatively lower complexity. With these above-mentioned optimization methods, the primal problem is transformed into simple subproblems hierarchically so as to adopt the corresponding optimization algorithm. By simulations, the achievable secure EE, the secrecy sum rate and the total transmission power of the proposed scheme are compared with those of secrecy sum rate maximization. It is demonstrated that the proposed scheme can improve secure EE remarkably yet at the cost of secrecy sum rate loss. This fact also reveals the inherent tradeoff between energy and security.

Robust Power Allocation and Outage Analysis for Secrecy in Independent Parallel Gaussian Channels

This letter studies parallel independent Gaussian channels with uncertain eavesdropper channel state information (CSI). Firstly, we evaluate the probability of zero secrecy rate in this system for (i) given instantaneous channel conditions and (ii) a Rayleigh fading scenario. Secondly, when non-zero secrecy is achievable in the low SNR regime, we aim to solve a robust power allocation problem which minimizes the outage probability at a target secrecy rate. We bound the outage probability and obtain a linear fractional program that takes into account the uncertainty in eavesdropper CSI while allocating power on the parallel channels. Problem structure is exploited to solve this optimization problem efficiently. We find the proposed scheme effective for uncertain eavesdropper CSI in comparison with conventional power allocation schemes.

Achieving High Energy Efficiency and Physical-Layer Security in AF Relaying

For transmitting data in a secret and energy-efficient manner in collaborative amplify-and-forward relay networks, the secure energy efficiency (EE) defined as the secret bits transferred with unit energy is maximized to satisfy each node power constraint and target secrecy rate requirement, based on physical security framework. The secure EE is maximized by joint source and relay power allocation, which is a nonconvex optimization problem. To cope with this difficulty, a solution scheme and corresponding algorithms are developed by jointly applying fractional programming, exact penalty, alternate search, and difference of convex functions programming. The key idea of the scheme is to convert the primal problem into simple subproblems step by step, such that related methods are adopted. It is verified that, compared with secrecy rate maximization, the proposed scheme improves the secure EE significantly yet with a certain loss of the secrecy rate due to the tradeoff between secure EE and secrecy rate. Furthermore, the proposed scheme achieves higher secure EE and secrecy rate than total transmission power minimization does, while with a certain increase of power consumption. These results indicate that a reasonable balance among secure EE, secrecy rate, and power consumption can be reached by the proposed scheme.

Maximum Secrecy Throughput of Transmit Antenna Selection with Eavesdropper Outage Constraints

We evaluate the effective secrecy throughput of the multiple-input multiple-output multiple-antenna eavesdropper (MIMOME) wiretap channel with antenna selection at the legitimate transmitter. The optimal target secrecy rate that maximizes the effective secrecy throughput is obtained and confirmed by numerical results. Differently from previous works, we constrain the maximum allowed secrecy outage probability (SOP) and show that, the single-input single-output multi-antenna eavesdropper (SISOME) scheme recently proposed in the literature presents a much lower resilience to the decrease of the maximum allowed SOP than that obtained by MIMOME scheme.

Joint Spectrum and Power Allocation for Green D2D Communication with Physical Layer Security Consideration

In this paper, we consider cooperative D2D communications in cellular networks. More precisely, a cellular user leases part of its spectrum to facilitate the D2D communication with a goal of improving the energy efficiency of a D2D pair. However the D2D pair is untrusted to the cellular user, such resource sharing may result in the information of this cellular user unsecured. In order to motivate the cellular user’s generosity, this D2D pair needs to help the cellular user maintain a target secrecy rate. To address this issue, we formulate a joint spectrum and power allocation problem to maximize the energy efficiency of the D2D communication while guaranteeing the physical layer security of the cellular user. Then, a theorem is proved to indicate the best resource allocation strategy, and accordingly, an algorithm is proposed to find the best solution to this resource allocation problem. Numerical results are finally presented to verify the validity and effectiveness of the proposed algorithm.

Energy Efficient Secure Communication Over Decode-and-Forward Relay Channels

In this paper, we raise the concern on energy-efficient secure communication over a decode-and-forward relay network with potential eavesdroppers. Our objective is maximizing the secure energy efficiency (EE), which is defined as the ratio of secrecy rate to total power, subject to the given individual power, relay decoding rate, and target secrecy rate constraints. The problem is formulated as a unified mixed integer nonlinear optimization adapting to different assumptions of channel state information (CSI). To deal with this combinatorial optimization, a suboptimal solution scheme is developed upon some mathematical methods as decoupling of mixed integer programming, fractional programming, dual decomposition, and difference of convex functions programming. The core of the scheme is to transform the primal problem into simple subproblems step by step, and then convex programming can be exploited finally. The proposed scheme for the case with statistical eavesdropper's CSI, may be conditionally extended to the scenario with full CSI in which a local optimal solution may be obtained in certain cases. Finally, the performance and achievable secure EE of the proposed algorithm are demonstrated by simulations where the tradeoff between secure EE and secrecy rate is also revealed.

On Transmission Secrecy Outage of a Multi-Antenna System With Randomly Located Eavesdroppers

This letter studies the physical-layer security of a multi-antenna transmission system in the presence of Poisson distributed eavesdroppers. The transmission secrecy outage probability (TSOP) is adopted to evaluate the security. We derive an accurate integral expression as well as a closed-form upper bound on TSOP for the noncolluding eavesdroppers' case and a closed-form solution for the colluding eavesdroppers' case, respectively. Based on these, we define a novel concept of security region to intuitively illustrate the security from a spatial perspective. We further analyze the impacts of various factors on the security, such as the number of transmit antennas, the node intensity, and the target secrecy rate.

PHY Layer Security Based on Protected Zone and Artificial Noise

We address physical layer security in multiple- input-multiple-output (MISO) communications in the presence of an unknown passive eavesdropper. Beamforming and artificial noise broadcasting are chosen to increase communications security. We first study the effect of a close eavesdropper on security and then we define a “Protected Zone” in the transmitter's vicinity. We present an optimisation strategy that intelligently sets the transmission power and the size of the protected zone to probabilistically achieve secrecy at a specified target secrecy rate. The results show that this strategy can achieve a high probability of secrecy by efficiently prioritising the use of the available resources.

Enhancing Security in Correlated Channel With Maximal Ratio Combining Diversity

In this correspondence, we consider a confidential communication through slow non-selective correlated Rayleigh fading channel, where a single antenna transmitter communicates at a pre-decided constant rate with a legitimate receiver in the presence of an eavesdropper. Both the legitimate receiver and eavesdropper are equipped with multiple antennas and employ maximal ratio combining (MRC) reception scheme. With the presence of channel diversity, we find the closed-form expressions for the probability of non-zero secrecy capacity and the outage probability of secrecy capacity in terms of channel parameters such as correlation coefficient and the ratio of main and eavesdropper channel gains that will be called average channel gain ratio (CGR). The analysis of secure outage performance with the MRC diversity scheme tells how the channel diversity enhances the secrecy capacity. We quantify the effect of antenna correlation on the probability of positive secrecy capacity and the secure outage probability. We also investigate how the target secrecy rate influences the effect of antenna correlation on the secure outage probability. Moreover, as a result of obtaining the closed-form expressions for the probability of positive secrecy capacity and the outage probability, it is insightful to see how the channel parameters affect the secure outage performance of the correlated channels.

A Closed-Form Power Allocation for Minimizing Secrecy Outage Probability for MISO Wiretap Channels via Masked Beamforming

In this letter, we aim to achieve secure communication for a multiple-input single-output (MISO) wiretap channel in the presence of multiple non-colluding eavesdroppers. It is assumed that the eavesdroppers' channels are unavailable to the transmitter, and artificial noise (AN) is used to provide masked beamforming for degrading the eavesdroppers' channels. First, we derive the secrecy rate outage probability for the masked beamforming system and then the optimal power allocation between data and AN is obtained in closed form for minimizing the secrecy rate outage probability under a total power constraint. The effects of the number of transmit antennas, the transmit power, and the target secrecy rate on the optimal power allocation parameter are characterized. Numerical results are presented to show the performance of our proposed power allocation scheme.