The use of multiple antennas at both the transmitter and receiver aims to improve performance or to increase symbol rate of systems, but it usually requires higher implementation complexity. Multiple Input Multiple Output (MIMO) architectures can be used for combined transmit and receive diversity, for the parallel transmission of data or spatial multiplexing. When used for spatial multiplexing, MIMO technology promises high bit rates in a narrow bandwidth. Therefore, it is of high significance to spectrum users. In this case, MIMO system considers the transmission of different signals from each transmit element so that the receiving antenna array receives a superposition of all transmitted signals. Mobile communication systems must support multiple users achieving at the same time privacy of users contents. Security common solutions are based on encrypted algorithms from higher layers, such as private and public encrypted keys. Other possibility is to implement physical layer security schemes. One advantage of physical layer security relies on their ability to be combined with other security schemes from higher layers. Due to the broadcast nature of MIMO systems, security is a critical issue. However, the constellation shaping on the desired direction introduced by a new proposed transmitter means that we have directivity at the transmitted constellation that can be employed to assure security at physical layer. Privacy is achieved since each user must know the set of coefficients associated to each BPSK component as well as the array configuration; otherwise receives useless data. Therefore, the inherent security lies on the constellation directivity, i.e., the direction in which the constellation is optimized, which can be improved by changes on coefficients’ phases or using constellations that are decomposed with a higher number of BPSK components. The several cases analyzed in this speech show effectiveness of the proposed approach to implement a security scheme at physical layer level.
The use of multiple antennas at both the transmitter and receiver aims to improve performance or to increase symbol rate of systems, but it usually requires higher implementation complexity. Multiple Input Multiple Output (MIMO) architectures can be used for combined transmit and receive diversity, for the parallel transmission of data or spatial multiplexing. When used for spatial multiplexing, MIMO technology promises high bit rates in a narrow bandwidth. Therefore, it is of high significance to spectrum users. In this case, MIMO system considers the transmission of different signals from each transmit element so that the receiving antenna array receives a superposition of all transmitted signals. Mobile communication systems must support multiple users achieving at the same time privacy of users contents. Security common solutions are based on encrypted algorithms from higher layers, such as private and public encrypted keys. Other possibility is to implement physical layer security schemes. One advantage of physical layer security relies on their ability to be combined with other security schemes from higher layers. Due to the broadcast nature of MIMO systems, security is a critical issue. However, the constellation shaping on the desired direction introduced by a new proposed transmitter means that we have directivity at the transmitted constellation that can be employed to assure security at physical layer. Privacy is achieved since each user must know the set of coefficients associated to each BPSK component as well as the array configuration; otherwise receives useless data. Therefore, the inherent security lies on the constellation directivity, i.e., the direction in which the constellation is optimized, which can be improved by changes on coefficients’ phases or using constellations that are decomposed with a higher number of BPSK components. The several cases analyzed in this speech show effectiveness of the proposed approach to implement a security scheme at physical layer level.
Security is a demanding challenge in wireless systems due to the broadcast nature of the channel. One the other hand security at physical layer can increase overall system's security since it can be combined with other security schemes from higher layers. High throughput required by modern wireless networks can be assured by MIMO (Multiple-input multiple-output), but when high spectral e-ciencies are needed multilevel modulations with high peak-to-average power ratios should be used, which may afiect e-ciency of power ampliflcation. This problem can be avoided by the MISO (Multi input Single Output) transmitter considered here, where transmitted multilevel constellations are the result of the combination of several uncorrelated BPSK (Bi-Phase Shift Keying) components, that are amplifled and transmitted independently by an antenna. The constellation shaping done by this transmitter means directivity in the transmitted constellation that can be used to assure security at physical layer. Security as well complexity are assured since any eavesdropper must know the set of coe-cients associated to each BPSK component as well as the antenna array conflguration. It is shown that the inherent security assured by this transmitter allows secrecy at physical layer. Several examples are analyzed and the corresponding results show the efiectiveness of the proposed approach to implement a security scheme at physical layer level.
MIMO is a key enabling technology in the currently emerging 5G systems and future 6G-plus paradigms, such as heterogeneous networks, millimeter-wave networks, vehicular sensor networks, among others. The highly desired properties of MIMO such as its ability to supporting high data rates, improving energy and spectral efficiency, as well as overcoming the effects of shadowing and fading have made it increasingly attractive to the wireless communications industry. Nevertheless, a practical secure MIMO model with the required security levels to guarantee user information protection has still not been realized by the industry. In this work, we analyze and quantify the security performance of hybrid MIMO, which was originally proposed by the preceding work titled “Hybrid MIMO: A New Transmission Method For Simultaneously Achieving Spatial Multiplexing and Diversity Gains in MIMO Systems”. In the proposed method, special signal interference-canceling matrices, which are calculated based on the channel’s variations and randomness between the user and receiver, are superimposed with user data at the physical layer level before being transmitted to the receiver. The conducted performance analysis in this study indicates that the signal interference-canceling matrices provide absolute security (zero information leakage) against both internal and external eavesdroppers. Moreover, the new MIMO technique eliminates the need for any processing at the receiver, where users directly receive their intended signals, consequently lowering complexity and power consumption at the receiver. These are highly desirable properties for the future internet of things (IoT) devices as well as 6G and beyond technologies.
The use of physical layer methods for improving the security of wireless links has recently become the focus of a considerable research effort. Such methods can be used in combination with cryptography to enhance the exchange of confidential messages over a wireless medium in the presence of unauthorized eavesdroppers, or they can be used to enable secrecy in the absence of shared secret keys through the use of coding strategies, jamming or beamforming. Indeed, one of the driving forces behind the recent emergence of physical layer techniques for security is the push toward adding extra degrees of freedom in the form of multiple antennas at the transmitter and receiver of the link. Multiple-input multiple-output (MIMO) wireless systems have been extensively studied during the past two decades, and their potential gains in throughput, diversity, and range have been well quantified. MIMO approaches are now an integral part of the WiFi and 4G standards in use today. It is not surprising that MIMO architectures are useful in improving wireless security as well, since they can provide focused transmit selectivity of both information and noise toward desired and undesired receivers. In this chapter, we discuss a number of different ways that physical layer security can be achieved in wireless networks with MIMO links. We will focus primarily on signal processing related issues (e.g., beamforming, power control, resource allocation) that enable reliable reception at intended recipients and minimize data leakage to eavesdroppers, and we will consider a variety of different MIMO settings including point-to-point, broadcast, interference, and multi-hop networks. We cannot offer an exhaustive survey of such methods in just a single chapter; instead, we present a few representative approaches that illustrate ✐ ✐ — — ✐ ✐ ✐ ✐ ✐ ✐ Physical Layer Security in Wireless the gains that multiple antennas provide. Additional and more complete treatments of the physical layer security problem can be found in [1-4] as well as other chapters in this book.
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.
Wireless broadcast allows widespread and easy information transfer. However, it may expose the information to unintended receivers, which could include eavesdroppers. As a solution, cryptography at the higher network levels has been used to encrypt and protect data. Cryptography relies on the fact that the computational power of the adversary is not enough to break the encryption. However, due to increasing computing power, the adversary power also increases. To further strengthen the security and complement the encryption, the concept of physical layer security has been introduced and surged an enormous amount of research. Widely speaking, the research in physical layer security can be divided into two directions: the information-theoretic and signal processing paradigms. This thesis starts with an overview of the physical layer security literature and continues with the contributions which are divided into the two following parts. In the first part, we investigate the information-theoretic secrecy rate. In the first scenario, we study the confidentiality of a bidirectional satellite network consisting of two mobile users who exchange two messages via a multibeam satellite using the XOR network coding protocol. We maximize the sum secrecy rate by designing the optimal beamforming vector along with optimizing the return and forward link time allocation. In the second scenario, we study the effect of interference on the secrecy rate. We investigate the secrecy rate in a two-user interference network where one of the users, namely user 1, requires to establish a confidential connection. User 1 wants to prevent an unintended user of the network to decode its transmission. User 1 has to adjust its transmission power such that its secrecy rate is maximized while the quality of service at the destination of the other user, user 2, is satisfied. We obtain closed-form solutions for optimal joint power control. In the third scenario, we study secrecy rate over power ratio, namely ``secrecy energy efficiency''. We design the optimal beamformer for a multiple-input single-output system with and without considering the minimum required secrecy rate at the destination. In the second part, we follow the signal processing paradigm to improve the security. We employ the directional modulation concept to enhance the security of a multi-user multiple-input multiple-output communication system in the presence of a multi-antenna eavesdropper. Enhancing the security is accomplished by increasing the symbol error rate at the eavesdropper without the eavesdropper's CSI. We show that when the eavesdropper has less antennas than the users, regardless of the received signal SNR, it cannot recover any useful information; in addition, it has to go through extra noise enhancing processes to estimate the symbols when it has more antennas than the users. Finally, we summarize the conclusions and discuss the promising research directions in the physical layer security.
Emerging from the information-theoretic characterization of secrecy, physical-layer security exploits the physical properties of the wireless channel for security purpose. In recent years, a great deal of attention has been paid to investigating the physical-layer security issues in multiple-input multiple-output (MIMO) wireless communications. This paper analyzes the secrecy performance of transmit-receive diversity system and spatial multiplexing systems with zero-forcing equalization and minimum mean-square-error equalization. Specifically, exact and asymptotic closed-form expressions are derived for the secrecy outage probability of such MIMO systems in a Rayleigh fading environment, and the corresponding secrecy diversity orders and secrecy array gains are determined. Numerical results are presented to corroborate the analytical results and to examine the impact of various system parameters, including the numbers of antennas at the transmitter, the legitimate receiver, and the eavesdropper. These contributions bring about valuable insights into the physical-layer security in MIMO wireless systems.