Physical Layer Security Transmission Research Articles

Encrypting Wireless Communications on the Fly Using One-Time Pad and Key Generation

The one-time pad (OTP) secure transmission relies on the random keys to achieve perfect secrecy, while the unpredictable wireless channel is shown to be a good random source. There is very few work of the joint design of OTP and key generation from wireless channels. This article provides a comprehensive and quantitative investigation on secure transmission achieved by OTP and wireless channel randomness. We propose two OTP secure transmission schemes, i.e., identical key-based physical-layer secure transmission (IK-PST) and un-IK-PST (UK-PST). We quantitatively analyze the performance of both schemes and prove that UK-PST outperforms IK-PST. We extend the pairwise schemes to a group of users in networks with star and chain topologies. We implement prototypes of both schemes and evaluate the proposed schemes through both simulations and experiments. The results verify that UK-PST has a higher effective secret transmission rate than that of IK-PST for scenarios with both pairwise and group users.

Physical layer security transmission algorithm based on cooperative beamforming in SWIPT system

Physical layer security transmission algorithm based on cooperative beamforming in SWIPT system

Secure transmission for heterogeneous cellular network with limited feedback

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.

Cooperative Physical Layer Security Transmission Scheme Based on Energy Harvesting

Energy harvesting (EH) is introduced into the physical layer security transmission of wireless sensor networks. It takes the energy efficiency and security into account simultaneously. To improve the physical layer security of the cooperative wireless sensor network, an EH-based physical layer security transmission scheme called multi-relay time switching (MRTS) is proposed in this paper. In the multi-source single-destination network with eavesdroppers, multiple relay nodes with time switching (TS) protocol convert the received signals into energy and information according to the time slots, and the converted energy is used to amplify and forward the received information. The research shows the optimal time switching ratio, under which the maximum secrecy capacity is achievable with the optimal converted energy. The results prove that under the same conditions, the secure transmission scheme based on MRTS is better than power splitting-based relaying (PSR) scheme when the total power of sources is limited.

Physical Layer Secure MIMO Communications Against Eavesdroppers With Arbitrary Number of Antennas

Recently, MIMO (multiple-input-multiple-output) physical layer secure transmission has attracted great attentions. However, current schemes cannot defend against the passive eavesdroppers with arbitrary number of antennas. To address this problem, in this work, we propose a practical physical layer MIMO secure communication scheme (PLSC) to defend against such an eavesdropper with arbitrary number of antennas. In the proposed scheme, the transmitter first independently generates a random binary sequence as the “key bits (KB)” to “encrypt” (XOR) the confidential information. After that, the transmitter sends the “encrypted information” over the wireless channel, along with mapping key bits to the legitimate receiver simultaneously. The key principle lies in that the KB information is coded in the indexes of the activated/non-activated antennas combination of the legitimate user. Then, the legitimate receiver first observes his/her activated antenna indexes to obtain the corresponding key bits. After that, he/she demodulates the “encrypted information” at the activated antennas, and finally “decrypts” (XOR) the confidential information by using the observed key bits. However, due to the uniqueness and independence of MIMO wireless channel, for any other eavesdroppers who suffer an independent channel from legitimate users, we prove that it cannot observe any information about KB from the received signals, regardless of how many antennas it has used. Consequently, without knowledge of KB, it cannot decrypt any information about the confidential information, too. The reliability and security of PLSC are theoretically demonstrated. The simulation and numerical results fully verified the validity and effectiveness of the proposed scheme.

Cooperative secure transmission against collusive eavesdroppers in Internet of Things

As Internet of Things (IoT) has boomed in recent years, many security issues have also been exposed. Focusing on physical layer security in wireless Internet of Things network communication, a series of security methods have been widely studied. Nevertheless, cooperative jamming methods in physical layer security to fight against collusive eavesdroppers have not been thoroughly studied yet. In this article, we study a cooperative-jamming-based physical layer secure transmission scheme for Internet of Things wireless networks in the presence of collusive eavesdroppers. We design a cooperative jamming strategy without knowing the channel state information of eavesdroppers. Considering the cooperation of multiple nodes with multiple antennas, this strategy can maximize the signal-to-interference-plus-noise ratio at an actuator (legitimate receiver). Meanwhile, the generated cooperative jamming signals can reduce the signal-to-interference-plus-noise ratio at eavesdroppers. To explore the theoretical security performance of our strategy, we perform a secrecy outage probability analysis and an asymptotic analysis. In the cases of cooperative jamming and without cooperative jamming, the closed-form expressions of the secrecy outage probability are deduced, and the influence of system parameters on the secrecy outage probability becomes more intuitive through a strict mathematical asymptotic behavior analysis. In addition, considering the energy limitation of Internet of Things devices, we propose a power allocation algorithm to minimize the total transmission power given the security requirements. The numerical results show the effectiveness of our schemes and are consistent with the theoretical analysis.

Physical-Layer Security in the Finite Blocklength Regime Over Fading Channels

This paper studies physical-layer secure transmissions from a transmitter to a legitimate receiver against an eavesdropper over slow fading channels, taking into account the impact of finite blocklength secrecy coding. A comprehensive analysis and optimization framework is established to investigate secrecy throughput for both single- and multi-antenna transmitter scenarios. Both adaptive and non-adaptive design schemes are devised, in which the secrecy throughput is maximized by exploiting the instantaneous and statistical channel state information of the legitimate receiver, respectively. Specifically, optimal transmission policy, blocklength, and code rates are jointly designed to maximize the secrecy throughput. Additionally, null-space artificial noise is employed to improve the secrecy throughput for the multi-antenna setup with the optimal power allocation derived. Various important insights are developed. In particular, 1) increasing blocklength benefits both reliability and secrecy under the proposed transmission policy; 2) secrecy throughput monotonically increases with blocklength; 3) secrecy throughput initially increases but then decreases as secrecy rate increases, and the optimal secrecy rate maximizing the secrecy throughput should be carefully chosen in order to strike a good balance between rate and decoding correctness. Numerical results are eventually presented to verify theoretical findings.

SVD-Aided Multi-Beam Directional Modulation Scheme Based on Frequency Diverse Array

With the assistance of singular value decomposition (SVD), a multi-beam directional modulation (DM) scheme based on symmetrical multi-carrier frequency diverse array (FDA) is proposed. The proposed DM scheme is capable of achieving range-angle dependent physical layer secure (PLS) transmissions in free space with much lower complexity than the conventional zero-forcing (ZF) method. Theoretical and simulated results about secrecy rate and complexity verify the improved computational efficiency and considerable memory savings despite a very small penalty of secrecy rate.

Improving Physical Layer Security of Cellular Networks Using Full-Duplex Jamming Relay-Aided D2D Communications

This paper investigates the physical layer security and data transmission in cellular networks with inband underlay Device-to-Device (D2D) communications, where there is no direct link between D2D users. We propose to apply full-duplex (FD) transmission and dual antenna selection at the D2D relay node. The relay node can simultaneously act as a friendly jammer to improve the secrecy performance of the cellular network while enhancing the D2D communication data transmission. This is an appealing and practical scheme where spectrum sharing is beneficial for the D2D and cellular networks in terms of reliability enhancement and security provisioning, respectively. The practical scenario, where the eavesdropper is passive, is considered. The eavesdropper uses either selection combining or maximal ratio combining to combine the wiretapped signals of the cellular network. The secrecy performance of the cellular network is analyzed, and closed-form expressions for the secrecy outage probability and the probability of non-zero secrecy capacity are derived. We show that increasing the number of FD jamming antennas enhances the secrecy performance of the cellular network. A closed-form expression of the D2D outage probability is also provided. Simulation and numerical results are provided to verify the efficiency of the proposed scheme and to validate the accuracy of the derived expressions.

Directional modulation based on chaos scrambling and artificial noise for physical layer security enhancement

Directional modulation (DM), as an emerging promising physical layer security (PLS) transmission technique for wireless communications, has attracted much attention over the past decade. It endows transmitters the ability to directly transmit the confidential messages to legitimate receivers along with pre-specified directions while distorting signal waveform signatures projected along all other spatial directions to guarantee the security of information transmission. Traditional DM designs are based on the assumption that eavesdroppers (Eves) and legitimate users (LUs) are in different directions. Nevertheless, it is not always the scenario in practical applications, as it is possible that Eves and LUs are in the same directions or even at the same positions, which results in that signals received by Eves will be approximately the same as LUs'. To address this problem, the chaos scrambling (CS) technique is employed in this paper. A DM technique based on CS and artificial noise (AN) is proposed for PLS enhancement. The symbol error rate, secrecy rate, and robustness of the proposed CS-AN-aided scheme are analysed and simulated. Simulation results show the effectiveness of the proposed method and the PLS can also be guaranteed even if Eves are aligning with the desired directions or very close to the LUs.

WFRFT-Aided Power-Efficient Multi-Beam Directional Modulation Schemes Based on Frequency Diverse Array

The artificial noise (AN) aided multi-beam directional modulation (DM) technology is capable of wireless physical layer secure (PLS) transmissions for multiple desired receivers in free space. The application of AN, however, makes it less power-efficient for such a DM system. To address this problem, the weighted fractional Fourier transform (WFRFT) technology is employed in this paper to achieve power-efficient multi-beam DM transmissions. Specifically, a power-efficient multi-beam WFRFT-DM scheme with cooperative receivers and a power-efficient multi-beam WFRFT-DM scheme with independent receivers are proposed based on frequency diverse array (FDA), respectively. The bit error rate (BER), secrecy rate, and robustness of the proposed multi-beam WFRFT-DM schemes are analyzed. Simulations demonstrate that 1) the proposed multi-beam WFRFT-DM schemes are more power-efficient than the conventional multi-beam AN-DM scheme; 2) the transmission security can also be guaranteed even if the eavesdroppers are located close to or the same as the desired receivers; and 3) the proposed multi-beam WFRFT-DM schemes are capable of independent transmissions for different desired receivers with different modulations.

Optimal Placement of Low-Altitude Aerial Base Station for Securing Communications

Because of its cost-effective and on-demand deployment, low-altitude aerial base stations (BSs) are capable of providing emergency communication services in many scenarios. This letter investigates the security issue in emergency communications where the aerial BS is deployed optimally to serve ground users in the presence of an eavesdropper. We aim to maximize the probability of non-zero secrecy capacity to improve the possibility of physical-layer security transmission via the optimal placement of the aerial BS. The resulting nonconvex optimization problem will be simplified based on its geometric properties and equivalent transformation. The simplified problem will then be solved by using semidefinite relaxation. Numerical results show that the optimal placement of the aerial BS can significantly improve the probability of non-zero secrecy capacity.

Secrecy Ensured Socially Aware Resource Allocation in Device-to-Device Communications Underlaying HetNet

Device-to-device (D2D) communication standardization is underway and considered as one of the key technologies in the 5G ecosystem. Eavesdropping is a well-known security risk for D2D communications. Thus, ensuring information security for both cellular users (CUs) and D2D pairs in an underlay network is quite challenging. In this paper, we look into the problem of physical-layer secure transmission jointly with resource allocation in D2D communications. Existing research works for D2D underlay networks considered perfect channel state information (CSI), which is usually unrealistic in practical networks due to the wireless channels’ dynamic nature. Hence, unlike the previous works, we are considering imperfect CSI that include estimation errors. We leverage social-domain and frame a coalitional game approach, enabling multiple D2D pairs to share CU spectral resource. We assume heterogeneous cellular network based practical scenario considering multiple eavesdroppers, intra-cell interference, and inter-cell interference to evaluate achievable performances in terms of sum-rate and secrecy capacity for both CUs and D2D pairs. Moreover, we prove our proposed algorithm stability, convergence, and computational complexity. The simulation results establish the effectiveness of our proposed approach that not only maximizes the sum rate (i.e., 10 $ \%$ –60 $ \%$ ) but also improves the secrecy capacity (i.e., 20 $ \%$ –67 $ \%$ ) in comparison to the baseline schemes.

Managing Physical Layer Security in Wireless Cellular Networks: A Cyber Insurance Approach

The fifth-generation (5G) wireless networks are expected to provision value-added services with ubiquitous coverage, which makes data security unprecedentedly critical. In this context, physical layer security has emerged as a promising solution to safeguard data transmission by exploiting characteristics of the wireless medium. Despite the recent technological advance in physical layer security and wireless transmission, secrecy outages (i.e., data breaches) and service outages (i.e., connection failures) will inevitably happen and incur financial losses. This economical consequence is a fact that is mostly overlooked by the existing literature. To provide financial protection against secrecy outage and service outage, we introduce a cyber-insurance framework for wireless users in cellular networks, where each user pays a premium to an insurer for a future financial compensation if an outage occurs to him/her. In particular, we derive the network risks of the cellular users in terms of secrecy outage probability and service outage probability as well as the financial risk of the cyber insurer in terms of the ruin probability that indicates the chance that the insurer experiences a deficit in affording the losses of outage users. Through numerical evaluation, we demonstrate the impact of network performance on the financial risk of the insurer. The numerical results also show that the ruin probability of the insurer can be effectively reduced by equipping a larger number of antennas at the base stations or increasing network frequency reuse.

Socially Aware Secrecy-Ensured Resource Allocation in D2D Underlay Communication: An Overlapping Coalitional Game Scheme

With the popularity of proximity-based services, device-to-device (D2D) communication underlaying cellular networks is a promising technology to cope with the growing demands by improving network resource utilization. However, the wireless communication's broadcast nature is vulnerable to eavesdropping, and thus, ensuring a secrecy communication for both cellular user equipments (CUEs) and D2D pairs in an underlay network is a challenging issue. We investigate the problem of physical-layer secure transmission jointly with resource allocation in D2D communications. Different from existing works, we framed overlapping (partial) coalitional game where each D2D pair can access multiple CUEs' spectral resources. Moreover, the multiple D2D pairs can share single CUE subchannel in multiple eavesdroppers scenario to ensure information security for both CUEs and D2D pairs and to maximize system sum rate in a socially aware D2D network. We incorporate the mutual interference and propose different transmission modes for a secrecy-ensured resource allocation-based overlapping coalition formation scheme with transferable utility to obtain a final stable partition. We further prove the proposed algorithm stability, convergence, and computational complexity. Both analytical and numerical results demonstrate the effectiveness of our proposed scheme, which ensures a system-wide security and at the same time improves the performance by maximizing the system sum rate.

Time-Reversal Based Secure Transmission Scheme for 5G Networks over Correlated Wireless Multi-Path Channels

Broadband wireless communication users for 5G networks are primarily implemented in a complicated environment; the complex environment of time-varying multi-path propagation characteristics will seriously affect the performance of communication. One of the core technologies to overcome this problem is to introduce the environment adaptive technique--time reversal in the wireless link. Further, the problem of a Wiretap Channel in physical layer security research has become a popular research topic in recent years. To resolve the physical layer wiretap channel and multi-path fading problems in wireless channels, a novel concept of combining time reversal technology with physical layer security technology is proposed. In this paper, a physical layer secure transmission scheme based on the joint time reversal technique and artificial noise at the sending end is proposed for the wireless multi-path channel. First, in a typical wiretap channel model, the time reversal technique is used to improve the security of the information transmission process by using the properties of spatial and temporal focusing. Second, as the information is easily eavesdropped near the focus point, artificial noise is added to the sending end to disrupt the eavesdropping capability of the eavesdropper. Finally, due to the complexity of the multi-path channels, the influence of the antenna correlation on the system security performance is considered. Compared with the existing physical layer security schemes, theoretical analysis and simulation results show that the proposed scheme has a higher secrecy signal-to-noise ratio, a higher rate of secrecy, and a lower bit error rate of legitimate user.

Multiple Antennas Secure Transmission Under Pilot Spoofing and Jamming Attack

Transmitter-side channel state information of the legitimate destination plays a critical role in physical layer secure transmissions. However, channel training procedure is vulnerable to the pilot spoofing attack (PSA) or pilot jamming attack (PJA) by an active eavesdropper (Eve), which inevitably results in severe private information leakage. In this paper, we propose a random channel training (RCT)-based secure downlink transmission framework for a time division duplex multiple antennas base station. In the proposed RCT scheme, multiple orthogonal pilot sequences (PSs) are simultaneously allocated to the legitimate user (LU), and the LU randomly selects one PS from the assigned PS set to transmit. Under either the PSA or PJA, we provide the detailed steps for the BS to identify the PS transmitted by the LU, and to simultaneously estimate channels of the LU and Eve. The probability that the BS makes an incorrect decision on the PS of the LU is analytically investigated. Finally, closed-form secure beamforming vectors are designed and optimized to enhance the secrecy rates during the downlink transmissions. Numerical results show that the secrecy performance is greatly improved compared to the conventional channel training scheme wherein only one PS is assigned to the LU.

Receiver Originated Physical-Layer Robust Secure Transmissions in Wireless Systems

This letter proposes a receiver-originated physical-layer secure transmissions scheme (ROST) which consists of two-phase communications. In phase 1, the receiver sends a pseudorandom signal (only known by itself) to the transmitter and in phase 2, the transmitter directly sends out the mixture of its confidential message and the received pseudorandom signal. The receiver could estimate the channel with the help of the pseudorandom signal before cancelling it from the received mixed signal, and finally detect the confidential information. By contrast, the eavesdropper can hardly obtain any confidential information because it cannot estimate the channel without any pilot signal in both phases transmissions and is interfered by the pseudorandom signal. Furthermore, we discuss the secrecy capacity of ROST and show that ROST can always keep the security of the confidential message, achieve much higher secrecy capacity than the traditional scheme, even without any channel information at the transmitter.

Secure transmission mechanism based on time reversal over wireless multipath channels

Broadband wireless communication is implemented primarily in a complicated environment. The complex environment with time-varying multi-path propagation characteristics will seriously affect the performance of communication. To solve the problem of insecurity in information transmission in wireless channels, in this paper a system is modeled by using the multi-input single output eavesdropping channel model and the security of information transmission through time reversal technology is ensured. Another problem is that the information focuses on the receiving point. Owing to the temporal and spatial focusing characteristics of the time reversal technology the information near the receiving point can be eavesdropped easily. To solve this problem, a secure transmission scheme based on time reversal technology with artificial noise interference on the transmitter side is proposed. One of the core technologies to solve this problem is to introduce the environment adaptive technique–time reversal in the wireless link. Further, the problem of a wiretap channel in physical layer security research has become a popular research topic in recent years. To solve the problems about the physical layer wiretap channel and multi-path fading in wireless channels, a novel concept combining time reversal technology with physical layer security technology is proposed. In this paper, a physical layer secure transmission scheme based on the joint time reversal technique and artificial noise at the sending end is proposed for the wireless multi-path channel. First, in a typical wiretap channel model the time reversal technique is used to improve the security of the information transmission process by using the properties of spatial and temporal focusing. It refers to the fact that information can be focused at a given moment and in space. Second, as the information is easily eavesdropped near the focus point, artificial noise is added to the sending end to disrupt the ability of the eavesdropper to eavesdrop. The artificial noise has no effect on legitimate user due to the use of null-space artificial noise in legitimate user. Based on this scheme, a closed expression, such as secure signal-to-interference and signal-to-noise ratio, an achievable secrecy rate and bit error rate are obtained, and the influences of the number of antennas, signal-to-noise ratio, and artificial noise are analyzed. The theoretical analysis and simulation results show that the proposed scheme has a higher secrecy signal-to-noise ratio, a higher rate of secrecy, and a lower bit error rate of the legitimate user than the the existing physical layer security schemes.

Hybrid Massive MIMO for Secure Transmissions Against Stealthy Eavesdroppers

Physical-layer secure transmissions require that the legitimate parties Alice and Bob have certain signal advantages over the eavesdropper Eve. Unfortunately, it is still unknown what advantages can be guaranteed realistically in practice. This letter shows that hybrid massive MIMO can be exploited to the advantage of Alice for this purpose. Specifically, it allows Alice to use large antenna arrays that stealthy eavesdroppers cannot afford in many practical situations. To realize this advantage, an efficient transmission scheme is developed with hybrid massive MIMO, random dumb antenna selection, and channel reciprocity-based signal randomization techniques. It can secure the transmission against multiple stealthy eavesdroppers. Transmission security is analyzed assuming eavesdroppers with sufficient side knowledge and channel estimation capabilities. Simulations are conducted to verify the superior performance.