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Reconfigurable intelligent surface (RIS) has attracted a lot of attention due to its capability to intelligently change the wireless propagation environment. However, the accuracy of direction of arrival (DOA) estimation in strong interference environment will be seriously affected. In this paper, a RIS aided system for DOA estimation is developed and analysed for non-line-of-sight (NLOS) scenarios. Unlike traditional DOA estimation systems, a low-cost system with only one full-functional receiver is given by changing the phases of the reflected signals at the RIS elements to realize the multiple measurements. Moreover, a new method based on the corrected projection jam algorithm is proposed for the DOA estimation by constructing the orthogonal projection matrix of the jamming subspace as a block matrix, so as to constrain the strong interferences. Furthermore, the phase shift matrix design of RIS elements is transformed into a specific objective optimization problem and then solved by fractional programming. Simulation results show that the proposed method achieves computational complexity in the RIS-aided strong interference system with only one receiving channel than various benchmark schemes.

Pilot spoofing attack brings new challenges to physical layer secure transmission. However, this method will not work without any knowledge about the pilot sequence and active eavesdropping can be detected by constructing random pilot sequence. Intelligent reflecting surface (IRS), with the real-time programmable features for wireless channels, provides new possibilities for effective pilot spoofing. In this paper, the IRS is deployed near the legitimate users and the legitimate signal can always be passively reflected. Then the control strategy is embedded into the communication process under time-division duplex mode to assist eavesdroppers to conduct pilot spoofing. By setting different phase shifts at the IRS during the uplink phase and downlink phase, the channel reciprocity disappears, and thus secure beamforming vector is biased towards the eavesdropper. Furthermore, in order to overhear more information, the average secrecy rate minimization problem based on statistical channel state information is established by carefully designing the phase shifts, which is non-trivial to solve. With alternating optimization and Charnes-Cooper transformation technique, the original problem is transformed into convex form and a near optimal solution is achieved. Finally, simulation results show that our proposed scheme can pose serious secure threat without any energy footprint. What's more, if the IRS is not utilized by the internal users properly, it will bring more threat.

Physical layer secret key generation schemes can provide lightweight encryption for resource-constrained Internet of Things (IoT) devices. However, many IoT devices are stationary and the environment is usually static, which leads to ultra-low/zero secret key rates. To circumvent this problem, a novel secret key generation scheme based on Reconfigurable Intelligent Surface (RIS) is proposed for Multiple-Input Single-Output IoT communications. The RIS is introduced into the network, and the phase shifts at RIS are tuned randomly in each frame, which makes time-varying reflection channels superimposed on the original channels. And then, the secret key capacity of all nodes within the cell coverage area can be remarkably improved. Compared with the existing methods, the scheme is loosely coupled with the existing communication system. The closed-form expressions of secret key capacity taking into account eavesdropping are first derived for the case studies of independent and correlated channels. We can conclude that sharing the same phase shifts randomness will not bring key information leakage. Compared with existing user-introduced randomness schemes, the proposed scheme can maintain good performance as the number of eavesdropping nodes increases. Further, the impact of parameters, such as the number of reflecting units, the transmit antennas, and the Rician factor, on secret key performance are analyzed respectively, which can offer guidelines for system design. Finally, simulation results verify the theoretical analysis.

Physical layer secret key generation is a promising candidate to achieve one-time-pad encryption approach for the wireless communication system. However, in a static environment, the secret key rate is low due to the lack of channel time-variation. To solve this problem, this letter proposes a novel secret key generation scheme assisted by an intelligent reflecting surface with discrete phase shifts. In the scheme, legitimate nodes construct the dynamic time-varying channel by rapidly and randomly switching the phase of IRS elements. Then, channel coefficients are used to generate the secret key. Based on the IRS channel model, we derive the probability distribution of the channel coefficient and the expressions of the secret key rate. Furthermore, we optimize the secret key rate by adjusting the switching time of the IRS phase. Monte Carlo simulation and numerical results show that our proposed scheme can update the secret key in a static environment.

Physical-layer key generation technology requires information reconciliation to correct channel estimation errors between two legitimate users. However, sending the reconciliation signals over the public channel increases the communication overhead and the risk of information leakage. Aiming at the problem, integrated secure communication schemes using non-reconciled keys have attracted extensive attention. These schemes exploit channel coding to correct both inconsistent keys and transmission error bits. Meanwhile, more redundant code bits must be added to correct errors, which results in a lower secure transmission rate. To address the problem, we analyze the merit of channel correlation between non-reconciled key generation and secure transmission. Inspired by this, we propose a non-reconciled physical-layer keys-assisted secure communication scheme based on channel correlation. First of all, the signal frame is designed to make use of channel correlation between non-reconciled key generation and secure transmission. Based on the channel correlation, non-reconciled keys are then generated from the wireless channel to encrypt transmitted data. Moreover, an adaptive coding algorithm based on the equivalent channel is presented to encode the data bits before encryption, to guarantee reliable transmission. Finally, theoretical analysis and simulations demonstrate the significant performance of the proposed scheme in terms of low bit error ratio and high secure transmission rate.

This paper proposes a novel physical layer one-time pad (OTP) encryption scheme for modulated signals based on the wireless channel. By imitating the OTP encryption for bit sequence, the sufficient conditions of perfect encryption for modulated signals are provided and proved. Then, we provide a detailed process of the scheme in the wireless system. Since the plaintext is the modulated signal rather than the bit sequence, we use high-level quantized channel estimation samples as secret keys and design encryption functions for QAM and PSK signals. The theoretical proof and Monte Carlo simulation results show that the proposed scheme can achieve perfect secrecy by designing the ciphertext signal independent of the plaintext signal. Furthermore, the simulation shows that the error probability of the proposed scheme is lower than that of the current mainstream physical layer encryption scheme because the quantization level is optimized according to the signal-to noise ratio.

In this paper, we investigate the physical layer key generation scheme in most realistic scenarios where the correlation between the legitimate channel and the eavesdropping channel is considered. To degrade the correlation and improve the key generation capacity, a physical layer key generation scheme through scrambling the correlated eavesdropping channel is proposed. Firstly, the artificial noise is sent superimposed over pilots from the legitimate transmitter to confuse the eavesdropper. The artificial noise precoding matrix is randomly selected from decomposed unitary matrices orthogonal to the legitimate channel resulting in having no effect on legitimate channel. Then, the vector quantization algorithm and the winnow algorithm are respectively applied to quantize the channel characteristic and negotiate the generated random sequences to generate the final key. To further support the performance, we next present a power optimization scheme allocated to sending the artificial noise to maximize the generated key capacity under the total transmission power constraint. Finally, simulation results are presented to validate the effectiveness of our proposed scheme.

In this paper, a novel secret key generation scheme based on Reconfigurable Intelligent Surface (RIS) antenna is firstly proposed.

Most existing secret key generation (SKG) methods are complicated and depend on the security capacity. This study aims to propose a non-agreement SKG method based on spatial symmetric scrambling (SSS) and secure polar coding (SPC), which only consists of secure transmission and privacy amplification. First, SSS provides a channel advantage and high security by replacing traditional Gaussian artificial noise with signal-like noise to ensure the existence of secure capacity. Second, the SPC is designed through Gaussian approximation and generic algorithm based on the acquired channel advantage and desired SKG performance to guarantee the security of transmitted information. Finally, the secret information is safely transmitted through SPC and SSS, and secret keys can be further generated by privacy amplification. The simulated results verify the feasibility of SSS and SPC and further illustrate that the proposed SKG method can meet the designed performance requirement. The National Institute of Standards and Technology test is also conducted and the results show the strong randomness of the generated keys.

This paper proposes a tractable analysis framework to evaluate the reliability, security and secrecy energy efficiency (SEE) performance in a communication network with mobile sinks via a threshold-based access scheme and multi-antenna technique. Specifically, the mobile sinks, legitimate receivers and eavesdroppers are deployed randomly. To achieve reliable results for general communication scenarios, this paper assumes both line-of-sight and non-line-of-sight paths with Rayleigh fading for air-to-ground channel model. In particular, we first exploit the association probability of a randomly located receiver and the activation probability of mobile sinks. Then, we analyze the security, reliability, and SEE of the networks with mobile sinks. Simulation results are finally provided to show the effect of the predetermined access threshold, the transmitter’s resource block, the height of mobile sinks, the density of legitimate receivers, and the density of eavesdroppers on the reliability as well as security performance, and determine the optimal design parameters for a given network with mobile sinks to maximize the SEE.

Existing handover authentication schemes are implemented in the upper layer through cryptographic techniques with different protocols and parameters involved under different handover scenarios, introducing high latency and complexity especially in the next generation (5G) highly heterogeneous network (HetNet). The authors propose to introduce wireless link signatures decided by users' locations as handover authentication data to achieve unified and fast handover authentication at the physical layer in 5G software defined networking-based HetNet. Specifically, the unique wireless channel characteristics between a user and the serving access point (AP) are extracted as the secure context information (SCI) and transferred to the target AP. The latter determines whether the user is the legitimate one who has already been authenticated according to the received SCI. They then analyse the authentication performance relating to multiple attributes and results demonstrate that the authentication strength can be adaptively adjusted. Furthermore, they find that optimum performance can be achieved by setting a proper decision threshold and derive the sub-optimal performance by iterative search. Lastly, analysis and simulations on latency and overhead compared with existing ones are conducted and results prove the effectiveness of the proposed scheme.

Millimeter wave (mm-wave) communications, especially mm-wave relay systems, have been considered as a key technology for next-generation wireless networks due to the rich spectrum resources. However, the problem of information leakage in mm-wave relay systems has not been well investigated. In this paper, artificial noise (AN) aided two-stage secure hybrid beamforming algorithm is proposed in MIMO mm-wave relay system from the perspective of physical layer security. In each time slot of the relay communications, the RF analog beamforming matrices are designed in the first stage, and baseband digital beamforming matrices are designed in the second stage. Through the proposed algorithm, the joint optimization is avoided and the feedback is reduced, which brings low complexity. Moreover, the AN is applied to fight against the eavesdropper by deteriorating the eavesdropping channel. The simulation results show that the proposed hybrid beamforming algorithm considerably improves the performance and achieves a balance between complexity and performance.

This paper develops a tractable analysis framework to evaluate the reliability and security performance of cooperative non-orthogonal multiple access (co-NOMA) in cognitive networks, where both a primary base station (PBS) and a NOMA-strong primary user (PU) send confidential messages to multiple uniformly distributed PUs in the presence of randomly located external eavesdroppers. For constricting the interference to the PUs imposed by cognitive femto base stations (CFBSs), a mobile association scheme is introduced. Moreover, an eavesdropper-exclusion zone is introduced around the PBS for improving the secrecy performance of the primary networks. To characterize the security-reliability tradeoff of the considered network, we first derive the activation probability of CFBSs and the conditional probability density function associated with the distance between the relay user and other PUs. Then, the connection outage probability (COP) and the secrecy outage probability (SOP) of each PU with NOMA (co-NOMA) or non-cooperative NOMA (nco-NOMA) are separately derived to obtain the overall COP and SOP in the primary networks. Finally, the tradeoff between COP and SOP with co-NOMA (identified as transmission SOP) is investigated for simultaneously reflecting the security and reliability. Numerical results demonstrate the performance improvements of the proposed co-NOMA scheme in comparison to that of the nco-NOMA scheme in terms of different parameters. Furthermore, the security-reliability tradeoff performance of co-NOMA is shown.

Delay and security are both highly concerned in massive internet of things (IoT) which is a promising application scenario in 5G wireless communication system. In this study, the authors develop an integrated framework to study delay performance and secrecy performance in massive IoT. First, stochastic geometry and queuing theory are applied to model the spatially location of IoT devices and the temporal arrival of packets. To enhance the physical layer security of massive IoT with limited overhead increment at IoT devices, a low-complexity noise injection scheme is applied. Then, the packet delay and packet secrecy outage probability are derived to characterise delay performance and secrecy performance. It is demonstrated that the IoT device intensity and power allocation coefficient arouse a tradeoff between the delay and security. Furthermore, optimal power allocation coefficient that maximises secrecy transmission rate can be derived, which can improve the delay-security tradeoff. The analytical and simulation results show the effects of power allocation coefficient and IoT device intensity on the tradeoff between delay performance and secrecy performance.

To solve the problem that key is susceptible to eavesdroppers in the correlated channel scenarios, in this paper, we propose a native security scheme based on physical layer chain keys, which can be used for encryption and authentication. First, the physical layer chain key is generated by performing XOR operation on the updated key and the previous chain key, where the updated key is obtained by the current channel state information. The proposed scheme uses the chain key as the authentication root, and the authentication relationship is continuously transferred as the chain grows. Then, CRC is used to realize identity authentication and message verification simultaneously. Finally, the derivation based on information theory proves the security of chain key for encryption and authentication. The simulation results show that the proposed chain key scheme can leak less information and have a lower probability of successful attack than the traditional physical layer key in the correlated channel scenarios.

We study physical layer secure transmission with limited feedback in heterogeneous cellular networks. A transmission protocol is designed to obtain more secure and accurate channel state information (CSI) for enhancing the secrecy performance. Under the proposed protocol, we derive expressions of coverage probability and secrecy outage probability to analyze the security performance with different system parameters such as feedback CSI length and number of antennas. Furthermore, an iteration algorithm is proposed to balance the tradeoff between the feedback and transmission time, and maximize the average secrecy throughput under coverage and secrecy outage constrains. Numeric results demonstrate the optimal feedback overhead and the maximum average secrecy throughput are influenced by the number of antennas.

Authentication is a critical issue in wireless communication due to the impersonation and substitution attacks from the vulnerable air interface launched by the malicious node. There are currently two kinds of authentication research in wireless communication. One is based on cryptography and relies on computational complexity, the other is based on physical layer fingerprint and can not protect data integrity well. Both of these approaches will become insecure when facing attackers with infinite computing power. In this paper, we develop a wireless unconditional authentication framework based on one-time keys generated from wireless channel. The proposed unconditional authentication framework provides a new perspective to resist infinite computing power attackers. We study the performance of the unconditional authentication framework in this paper. First, a physical layer offered chain key (PHYLOCK) structure is proposed, which can provide one-time keys for unconditional authentication. The physical layer offered chain keys are generated by XORing the physical layer updated keys extracted from the current channel state information (CSI) and the previous chain keys. The security of PHYLOCK is analyzed from the perspective of information theory. Then, the boundary of the deception probability is conducted. It is shown that unconditional authentication can achieve a probability of deception 2−12Hk, where Hk is the entropy of the one-time key used for one message. Finally, the conditions for unconditional authentication are listed. Our analysis shows that the length of the key and the authentication code need to be twice the length of the message and the encoding rules of the authentication code need to satisfy the restrictions we listed.

Co-prime linear arrays (CLAs) provide an additional degree of freedom (DOF) with a limited number of physical sensors, and thus help to improve the resolution of direction of arrival (DOA) estimation algorithms. However, the DOF of traditional CLA is restrained by the structure of the array, which cannot be adjusted after deployment. In this paper, we propose a DOA estimation algorithm for reconfigurable intelligent surface co-prime linear array (RIS CLA) based on the multiple signal classification approach. Specifically, an RIS CLA is first constructed on the ground of RIS antenna, by turning on/off specific elements at different times. Then, the covariance matrix of the received signal is vectorized, so as to construct a virtual difference array, whose aperture is considerably expanded. Finally, a spectral peak search on the noise subspace of the received signal of the difference array is conducted to obtain the DOA estimation result. Simulations verify the improvement of the proposed algorithm in terms of DOF and resolution. To be specific, the DOF provided by RIS CLA outnumbers that of CLA by more than 30%, and the resolution of the proposed DOA estimation algorithm is effectively improved, with its accuracy increased up to 70% under the low signal-noise-ratio (SNR) scenario, compared with existing algorithms.

Focusing on the problem of information leakage and communication cost in information reconciliation, this paper introduces a non-reconciliation secret Keys based transmission scheme(NASKT) for machine to machine(M2M) communications in Internet of Things(IoT) networks, which uses polar codes to guarantee no error transmission. First, the improved Kalman filter preprocessing algorithm is used to reduce the quantized bit error rate(QBER). Then, QBER is modeled as the transmission bit error rate of the additional white Gaussian noise (AWGN) channel. Finally, the polar codes are designed based on the equivalent AWGN channel and system performance requirements to guarantee the security of transmitted information. Numerical simulations verify that the secure M2M transmission scheme based on the Non-reconciliation secret Keys using polar codes can realize the One-Time Pad lightweight security.

In a heterogeneous simultaneous wireless information and energy transfer (SWIPT) network, the beamforming scheme for multi-users is significantly influenced by the imperfect channel state information (CSI). A joint beamforming scheme for multiple eavesdroppers in two-layer SWIPT network is proposed, jointly design the information and energy beam in the presence of imperfect CSI to serve the several users in the cell. In the meantime, using the signals between macro and pico base stations as the equivalent artificial noise to protect the security and improve the energy efficiency. To this end, an optimization algorithm is designed to approximate the optimal beamforming matrix for maximizing the overall minimum secure energy efficiency. the successive convex approximation (SCA) and semi-positive definite relaxation (SDR) techniques are used to simplify and solve this non-convex optimization problem. The simulation results verifies the security and effectiveness of the scheme.

Most of the existing works on group secret key (GSK) generation are based on pairwise key which wasting the total time and power of the group users. We present a cooperative GSK generation algorithm via star topology with one central node and one reference node. After channel estimation, secure network coding technique is employed by the central node to help all the group users exploit the randomness of reference channel with nothing about that leaking to the eavesdropper. Then all the group users agree on a secret key from the correlative observations of the reference channel in one information reconciliation phase. In addition, the expression of achievable secret key rate is derived. Theoretical and Monte Carlo simulation results validate the performance of our proposed algorithm.

This paper investigates the physical-layer security of uplink non-orthogonal multiple access (NOMA) in the cellular Internet of Things (IoT) with invoking stochastic geometry. Poisson cluster process-based model is applied to characterize the NOMA uplink transmission scenario, where IoT terminals are located around the serving base station. Considering the severe interference brought by a large number of IoT terminals, inter-cell interference is also taken into account. To enhance the physical-layer security of uplink NOMA transmission with limited overhead increment at IoT terminals, the base stations not only receive the signals from IoT terminals but also keep emitting jamming signals all the time to degrade the performance of any potential eavesdroppers. In order to characterize the physical-layer security performances, we derive expressions of coverage probability and secrecy outage probability. To obtain further insights, network-wide secrecy throughput (NST) and network-wide secrecy energy efficiency (NSEE) are analyzed. It is demonstrated that the security performance can be improved by the proposed full-duplex base station jamming scheme at the cost of reliable performance. The analytical and simulation results show the effects of BS intensity and jamming power on network performances. We also verify that NST and NSEE can be significantly enhanced by our proposed scheme. Using these results, the security of confidential information transmitted by low-complexity IoT terminals can be protected from overhearing.

This paper investigates the physical layer security in heterogeneous networks (HetNets) supported by simultaneous wireless information and power transfer (SWIPT). We first consider a two-tier HetNet composed of a macrocell and several femtocells, where the macrocell base station (BS) serves multiple users in the presence of a malicious eavesdropper, while each femtocell BS serves a couple of Internet-of-Things (IoT) users. With regard to the energy constraint of IoT users, SWIPT is performed at the femtocell BSs, and IoT users accomplish the reception of information and energy in a time-switching manner, where information secrecy is to be protected. To enhance the secrecy performance, we inject artificial noise (AN) into the transmit beam at both macrocell and femtocell BSs, and for the sake of achieving green communications, we formulate the problem of maximizing secrecy energy efficiency while considering the fairness in a cross-tier multi-cell coordinated beamforming (MCBF) design. To handle this resulting nonconvex max-min fractional program problem, we propose an iterative algorithm by applying successive convex approximation method. Then, we further develop a decentralized solution based on alternative direction multiplier method (ADMM), which reduces the overhead of information exchange among coordinated BSs and achieves good approximation performance. Finally, simulation results demonstrate the performance of the proposed AN-aided cross-tier MCBF design and verify the validity of distributed ADMM-based approach.

Spectral efficiency (SE) and energy efficiency (EE) in secure communications is of primary importance due to the fact that 5G wireless networks aim to achieve high throughput, low power consumption and high level of security. Nevertheless, maximizing SE and EE are not achievable simultaneously. In this paper, we investigate the SE and EE tradeoff for secure transmission in cognitive relay networks where all nodes are randomly distributed. We first introduce the opportunistic relay selection policy, where each primary transmitter communicates with the primary receiver with the help of a secondary user as a relay. Then, we evaluate the secure SE and secure EE of the primary network based on the outage probabilities analysis. Thirdly, by applying a unified SE-EE tradeoff metric, the secure SE and EE tradeoff problem is formulated as the joint secure SE and EE maximization problem. Considering the non-concave feature of the objective function, an iterative algorithm is proposed to improve secure SE and EE tradeoff. Numerical results show that the opportunistic relay selection policy is always superior to random relay selection policy. Furthermore, the opportunistic relay selection policy outperforms conventional direct transmission policy when faced with small security threat (i.e., for smaller eavesdropper density).

This paper studies a simultaneous wireless information and power transfer system with multiple external eavesdroppers and internal curious users. We model the random network by Poisson cluster process in consideration of the case where eavesdroppers hide around certain targets. Focusing on the users that work in harvesting-transmitting mode with time switching receivers, we establish communication model via time division multiple access. On this basis, we propose a lightweight secure transmission scheme based on dual-thresholds for physical-layer security enhancement, which consists of two protocols applied to the downlink (DL) and uplink (UL) transmission respectively. In the DL, we design a dynamic information-power switching transmission protocol based on signal-to-noise ratio threshold, which provides an opportunistic approach to reform the fixed period allocation of information and power transfer; in the UL, an energy threshold is proposed for users to control the transmission, which is called a user-led on-off transmission protocol. Furthermore, we give a comprehensive performance analysis for the proposed scheme in terms of delay, reliability, security and secrecy throughput. Based on the analysis results, we optimize the two thresholds and the DL-UL allocation coefficient to maximize the secrecy throughput. Simulation results show the proposed scheme can bring about a substantial secrecy gain.

The ever increasing wireless data services, such as imaging, video, audio, multimedia, etc., have demands for the very high speed wireless communications and network, which are unfortunately a bottleneck when combining with the wireline core network. Users' are now expecting high quality of experience with low-cost devices, ubiquitous connectivity, energy efficiency, high reliability, or even ultra-low latency if a vehicle terminal is applied.

Key generation technique generates symmetric keys based on the temporal variation, reciprocity and spatial decorrelation of the wireless channel. Most key generation schemes, however, assume that the eavesdropping channels are independent of the main channel and neglect the influence of the eavesdroppers. In this paper, we analyze the secret key capacity taking into account the information leaked to eavesdroppers, and the security analysis shows the eavesdropping channel correlation will reduce the secret key capacity. Then we propose a security channel estimating (SCE) scheme to resist eavesdroppers and the scheme is shown to be efficient. Finally, we use the Monte Carlo simulation verifies the theoretical analysis results.

In order to deal with the performance degradation caused by resource contention due to the sharing of physical resources between VNFs in the network slicing, we proposed a network slicing deployment method for guaranteeing service performance. Firstly, estimate the basic performance level of VNF from the perspective of resource supply and demand. Then select the candidate deployment servers for VNF, the candidate servers can guarantee the basic performance level of both new incoming and already deployed VNFs. Finally, to reduce deployment costs, our approach uses the candidate server on the shortest path as the final deployment server. The simulation results show that this method not only can reduce performance degradation on physical servers, but also can reduce operating costs.