Improving Physical Layer Security in Wireless Communication Using Hybrid Techniques

Physical layer security has gained attention due to the increased usage of wireless communication systems. Our target is to avoid eavesdroppers to receive and decode the transmitted voice signals between the authorized transmitter and the receiver. One of the most fundamental methods of enhancing security in physical layer is artificial noise. Especially the arrival of multiantenna technologies has enabled and accelerated the studies on this field. However, artificial noise based techniques are still in theory only. As a result, practical implementation is a very crucial need for these techniques in order to deploy them in next generation wireless systems. In this study, artificial noise technique is implemented on universal software radio peripheral (USRP) kits, and performance analysis is performed under varying channel conditions and modulation levels. The measurement results are compared with the simulation results. In conclusion, it is shown that the usage of artificial noise can achieve a security level in practice, by decreasing the signal reception quality of eavesdroppers.

In this paper, it is aimed to increase the physical layer security by optimizing the power and time parameters in two-user symbiotic radio networks. In the proposed model, the signal provided by the power station is used for both information transmission with the backscatter principle and energy harvesting. In addition, the secrecy rate of the system is maximized by preventing the eavesdropper (ED) intervention with the artificial noise technique. The system is examined under certain channel gains and artificial noise levels, and the effects of backscatter coefficients on energy harvesting and secrecy performance are analyzed. Numerical results show that channel gains are also of critical importance in addition to appropriate power and time allocation, and artificial noise offers an effective solution in physical layer security.

Orthogonal frequency division multiplexing (OFDM) offers a promising solution for emerging high-data-rate services. Moreover, physical layer security was proposed as an alternative way to provide information security in wireless communications. In this work, we focus on improving physical layer security in OFDM systems. Our approach perturbs the effective channels observed at eavesdroppers by nonlinear distortion, while maintaining the same effective channel experienced at the intended receiver. At the transmitter, the perturbation on eavesdropper's effective channel is random and can be changed on a symbol-by-symbol basis based on the known original channel state information (CSI). At the intended receiver, no additional information or information exchange with the transmitter is required for data detection. We derive the results of the proposed scheme for the multiple-input single-output single-antenna-eavesdropper (MISOSE) wiretap channel. According to simulations, the proposed scheme can severely degrade the receiving performance at eavesdroppers and outperform the artificial-noise-based approaches in the performance measure of BER.

Millimeter-wave (mmWave) wireless communication system allows a compact antenna array with a large number of colocated elements, which enables flexible array design and beampattern synthesis. However, security is also particularly important but challenging for the fifth-generation (5G) wireless communications, as the broadcasting nature allows any receivers to have a copy of the transmitted signals. In this paper, we propose a hybrid multiple-input multiple-output (MIMO) phased-array time-modulated directional modulation (DM) scheme for physical layer security in mmWave wireless communications. The hybrid MIMO phased-array enjoys the advantages of MIMO in spatial diversity without sacrificing the main advantage of phased-array in coherent directional gain. The essence is to divide the transmit array into multiple subarrays. Each subarray can be used to form a directional beam, while all subarrays are jointly combined to work as an MIMO for higher angular resolution capabilities. More importantly, a time-modulated DM scheme is applied for the phased-MIMO to achieve physical layer security for mmWave wireless communications, even without the knowledge of the eavesdropper’s position information. The feasibility of the proposed scheme is verified by numerical results.

The next generation network (5G) promises to offer a wide spectrum of advantages like massive user connections and high mobility. Massive user connection is achieved by incorporating Multiple Input Multiple Output (MIMO). Securing 5G wireless networks is of greater concern because they are developed with the intention of providing exponentially increasing wireless services where a trillion of legitimate users will be involved. Data transmission in 5G networks has been exposed to various security threats such as eavesdropping, jamming, Denial of Service (DoS) attack and Man-In-The-Middle (MITM) attack. The above mentioned threats have the ability of affecting the performance of 5G wireless networks since 5G is a major support system for new use cases. Some of the existing mechanisms employed to deal with the security threats are Physical Layer Security (PLS) and cryptography. PLS is preferred since its primary focus is on physical and Media Access Control (MAC) layer where variations in security between wireless and wired networks occur. The existing PLS approach for security against single cell MIMO eavesdropper is Original Symbol Phase Rotated (OSPR) secure transmission scheme where one base station serves the user terminals in a single cell. Our paper implements OSPR for a multi cell MIMO where multiple base stations serve multiple user terminals located in different cells. This architecture will be referred to as Multi cell MIMO Eavesdropping (MME). The efficiency of multi cell OSPR will be compared with Artificial Noise (AN) generation. The extent to which OSPR gives protection against MIMO eavesdropper is measured in terms of Symbol Error Rate (SER). As SER increases, security of data transmission increases. The efficiency of multi cell OSPR over AN is expected to be 8% and it will be verified in simulation using MATLAB.

The high speed railway wireless communication system is quite different from public wireless communication system, because the service is train control message, which are closely related to the safety of train transportation. Thus it has much higher requirements for the safety and reliability. In this paper, secrecy capacity and outage probability at the high speed railway scenario with traditional MIMO and beamforming schemes are analyzed. The analytic results show that MIMO scheme can not meet the safety requirements and the beamforming scheme is also helpless while the eavesdropper is close to eNodeB. In order to guarantee the transmission safety of train control messages, a physical layer secure scheme with artificial noise (AN) is proposed for high speed railway communication system. In this proposed scheme, beamforming and AN transmitting directions are adjusted accordingly with the onboard legitimate receiver's channel state information (CSI) and eavesdropper's partial CSI to degrade the eavesdropper while maximize the system secrecy capacity. Simulation results demonstrate the proposed scheme decreases the outage probability under the secrecy capacity constraint, and can meet the safety communication requirements.

Nowadays, security in wireless communication is in high demand. The communication of messages or data should be secure, and various security technologies are used to achieve this. Although there are many advanced cryptographic approaches for securing confidential information, they have one disadvantage: high complexity and computational requirements. To address this drawback, physical layer security has been introduced into wireless networks. This paper provides a brief analysis of various approaches to security (physical security). Two main factors are identified: secrecy rate and security design through optimization. Security design depends on the selection of antennas and nodes, beamforming, and the distance between the source and destination. Based on these factors, optimization approaches for security design are discussed. Four main types of optimization problems are identified: Maximizing the secrecy rate, Minimizing secrecy outage probability, Reducing power consumption, Maximizing secure energy efficiency. The best method to maximize the secrecy rate is cooperative schemes. In the cooperative approach, a relay node is used to enhance security between the source and destination by introducing a noise signal.

Physical layer security is envisaged to provide secure wireless communications. So far there exist schemes that both achieve physical layer security and maintain a reasonable level of link capacity. However, in all these schemes, capacity of a communication link depends on the channel characteristics of both the communication link and the eavesdropping links. Thus, when packets are scheduled in a wireless network with physical layer security, the most critical task is to select an appropriate link for a new transmission such that the network throughput and quality of services are properly balanced. In this paper, packet scheduling is studied for a wireless network with physical layer security considering beamforming and artificial noise. Particularly, a cross-layer scheduling scheme is developed based on the stochastic optimization theory to maximize the admission rate of all users and guarantee queue stability in each link. The scheme takes into account the constraints of physical layer security in different eavesdropping strategies: colluding and non-colluding. The effectiveness of the scheduling scheme is validated via simulations. The impact of antenna number and eavesdropping strategy to the scheduling scheme is also revealed in the performance results.

Artificial noise (AN) is one of physical layer security techniques, which can realize secure communication. AN is a noise signal which is intentionally transmitted from transmitter along with data signals. Since AN is generated to be canceled out at legitimate receivers, it can prevent eavesdroppers from eavesdropping even if transmitters do not know the existence of eavesdroppers. In spite of its usefulness, most of the AN generation techniques cannot be applied to multiple-input multiple-output (MIMO) systems when the number of antennas at the transmitter is less than that at the legitimate receiver. In this paper, we consider time-domain AN generation techniques for MIMO orthogonal frequency division multiplexing (OFDM) systems. A time-domain AN generation technique is originally proposed for single-input single-output (SISO) OFDM systems. Thus, we first consider to apply the conventional time-domain AN generation technique to MIMO-OFDM systems, and show that this technique requires a large number of antennas at the transmitter and/or a longer cyclic prefix (CP). Next, to solve this problem, we propose another time-domain AN generation technique. Our proposed time-domain AN is generated to be canceled out at the legitimate receiver in the frequency domain, while the conventional time-domain AN is canceled out in the time domain. As a result, the proposed time-domain AN generation technique can be applied to MIMO-OFDM systems, irrespective of the number of antennas and the length of CP. Simulation results can show that the proposed AN achieves the same secrecy rate as the conventional time-domain AN. Moreover, the proposed technique achieves a higher secrecy rate when a MIMO-OFDM system is employed with the antenna configuration to which the conventional time-domain AN generation technique is hard to be applied.

The conventional physical-layer (PHY) security approaches, e.g., transmit beamforming and artificial noise (AN)-based design, may fail when the channels of legitimate user (LU) and eavesdropper (Eve) are close correlated. Due to the highly directional transmission feature of millimeter-wave (mmWave), this may occur in mmWave transmissions as the transmitter, Eve and LU are aligned in the same direction exactly. To handle the PHY security problem with directionally-aligned LU and Eve, we propose a novel frequency diverse array (FDA) beamforming approach to differentiating the LU and Eve. By intentionally introducing some frequency offsets across the antennas, the FDA beamforming generates an angle-range dependent beampattern. As a consequence, it can degrade the Eve's reception and thus achieve PHY security. In this paper, we maximize the secrecy rate by jointly optimizing the frequency offsets and the beamformer. This secrecy rate maximization (SRM) problem is hard to solve due to the tightly coupled variables. Nevertheless, we show that it can be reformulated into a form depending only on the frequency offsets. Building upon this reformulation, we identify some cases where the SRM problem can be optimally solved in closed form. Numerical results demonstrate the efficacy of FDA beamforming in achieving PHY security, even for aligned LU and Eve.

Mobile data traffic is growing daily and this presents a significant challenge as the broadcast nature of wireless channels makes it extremely vulnerable to security breaches. A recent report of NSF has estimated 78% of large organisation and 63% of small business are attacked annually, and these figures will continue to increase making the wireless security concerns worldwide. As a consequence, security and privacy is of utmost concern for future wireless technologies. However, securely transferring confidential information over a wireless network in the presence of eavesdroppers that may intercept the information exchange between legitimate terminals, still remains a challenging task. Although security was originally viewed as a high-layer problem to be solved using cryptographic methods, physical layer (PHY) security is now emerging as a promising new (additional) means of defense to realize wireless secrecy in communications. In wireless PHY security, the breakthrough idea is to exploit the characteristics of wireless channels such as fading or noise to transmit a message from the source to the intended receiver while trying to keep this message confidential from both passive and active eavesdroppers. Over the past few years, PHY security has been widely recognized as a key enabling technique for secure wireless communications in future networks because of its potential for addressing security in new networking paradigms, such as the Internet of Things (IoT), for which more traditional methods of security may be impractical. With the fast development of new technologies for wireless communications and networks, i.e., mm-wave communications, massive MIMO, device-to-device communications, energy harvesting communications, 5G networks is expected to be in place in the year 2020. However, these are still challenging demands, particularly in the face of 5G security. These are serious constraints in security which, unresolved, preclude the technological precursors to 5G and, implicitly, challenge the viability of 5G itself. This talk will address this problem, not only for 5G but also the beyond.

In this article, the physical layer security (PLS) is investigated for reconfigurable intelligent surface (RIS)-aided wireless communication systems, where one RIS is deployed to assist the communications between a pair of transmitter (Alice) and receiver (Bob), under a passive eavesdropper (Eve) attack. For the Eve, different from the bounded channel state information uncertainty model, the distribution of the Eve's location is introduced into the wiretap link. In the proposed system, considering that the Eve can overhear signals transmitted from Alice or reflected by the RIS, two scenarios are studied for RIS-aided secure communication systems: one is that the Eve distributes close to Alice without the RIS orientation, and the other is that the Eve locates close to Bob and in the presence of the RIS. After investigating the probability distribution functions of the Eve's location and the wiretap link, the novel cumulative density functions (CDFs) of the received signal-to-noise ratios (SNRs) at the Eves are, respectively, derived for the two considered scenarios, taking into account the effects of RIS reflection coefficients, pathloss, and Eve's location distribution. The closed-form expressions for the probability of the nonzero secrecy capacity and the ergodic secrecy capacity are obtained, providing insights into the impact of the Eve's location uncertainty and the RIS design on the secrecy performance. Moreover, based on the derived CDFs for received SNRs at Eves, the secrecy outage probabilities are, respectively, analyzed. Specifically, under the constraint of the secrecy outage probability, the closed forms of the minimum required SNRs at Bob and the number of RIS elements are also obtained. Simulation and analytical results corroborate the derived expressions and reveal the tradeoff between the system's energy efficiency and the number of RIS elements.

Secure wireless communication has always been a hot research topic due to the vulnerabilities associated with wireless channel. Physical layer aspects to secure wireless communication, based on the information-theoretic security and signal processing methods have gained much recognition over the last decade. Specifically, artificial noise (AN) methods are assumed to be good means for providing security against potential eavesdroppers in multi-input multi-output (MIMO) systems and/or relay systems. However, there are still a large number of nodes which do not have multi-antennas or support sophisticated protocols in wireless networks. In this paper, a novel AN-aided method is proposed to secure wireless communications between the legitimate users (not equipped with multiple antennas) in the presence of an eavesdropper. In this proposed method frequency selective property of wireless channel is exploited. The basic principle is same in which transmitter generate random AN signal utilizing some of the transmission power to confuse eavesdropper. However artificial noise is generated in such a way that it appears to be zero at the sampling time, only for the legitimate receiver while degrading eavesdropper's channel. Artificial noise is specified using the channel state information (CSI) of the legitimate users' link. However, the secrecy of proposed scheme doesn't depend on the secrecy of CSI. Extensive simulation suggests that the proposed scheme can effectively utilized for securing wireless transmissions.

Physical layer security (PLS) in wireless communication systems has attracted extensive research attentions in recent years. Unlike cryptography-based methods applied in upper-layer in network, PLS methods are applied in physical layers and can provide information-theoretic security by utilizing the randomness of signals and wireless channels. In this survey, we provide a comprehensive review in the domain of physical layer authentication (PLA) in wireless communication systems, including the concepts, several key techniques of typical PLA architectures as well as future challenges and research trends in more sophisticated communication systems. The survey begins with an overview of the background and basic concepts of PLA, such as the general model of wireless security communication system, typical frameworks of key-based/less PLA systems, and the common attack models. We then discuss the major concerns and key techniques that are applied in PLA systems, where three types of authentication schemes are considered, i.e., the authentication based on channel information, radio-frequency and identity watermarks. Basic models and representative research results about key approaches and techniques applied to the authentication systems above are subsequently covered. Finally, the associated challenges and potential research trends of PLA in future communication systems are presented at the end of the survey paper.

Power efficient ultra-wideband based wireless communication for wireless body area network applications