Directional Modulation Technique Using a Polarization Sensitive Array for Physical Layer Security Enhancement.

Radio frequency identification (RFID) systems are gaining more attention in new frontiers of applications due to their simplicity, low size factor and low cost of deployment. One of the emerging frontiers of applications of RFID is the healthcare system. In this paper, we propose a novel physical layer security technique (PLS) to secure radio frequency identification (RFID) tags used in healthcare systems. To achieve secure communications for RFID systems, directional modulation (DM) scheme is exploited at the reader side. The proposed system maintains the simple circuity and processing nature of passive tags. The results obtained demonstrate that DM techniques can achieve physical layer security for RFID systems.

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.

In this paper, directional modulation (DM) is investigated to enhance physical layer security. Practical transmitter designs are exploited under imperfect channel state information (CSI) and hardware constraints, such as finite-resolution phase shifters (PSs) and per-antenna power budget. Tailored for the practical issues in realizing DM, a series of practical scenarios are investigated. Starting from the scenario where eavesdroppers (Eve)s' information is completely unknown, corresponding designs are proposed to optimize legitimate users (LU)s' receiving performance while randomizing the Eves' received signal. When the Eves' CSI is imperfectly known, in the second scenario, the Eves' receiving performance is further deteriorated by imposing destructive interference to the Eves. For each scenario, three algorithms are proposed under hardware constraints and imperfect CSI, i.e., one direct-mapping algorithm suitable for high/moderate number of bits in PSs, one heuristic algorithm with improved receiving performance at the cost of complexity, and one iterative-closed-form algorithm with enhanced practicality of symbol-level based DM. Simulation demonstrates that the algorithms achieve lower symbol error rate (SER) at the LUs while significantly deteriorating the Eves' SER, leading to an improved secrecy throughput over the benchmarks.

A two-ray multipath model for frequency diverse array (FDA)-based directional modulation (DM) is proposed in multi-input single-output multi-eavesdropper (MISOME) wiretap channels for the first time. The excitation factors of the FDA and the weighting coefficients of the inserted artificial noise (AN) are jointly designed in a way which imposes no impact on the desired receiver while simultaneously distorting the received signals of eavesdroppers. Secrecy rate is analyzed for the proposed two-ray multipath FDA-based DM model. Numerical simulations verify the capability of physical layer secure (PLS) transmissions of the proposed FDA-DM model in two-ray multipath MISOME wiretap channels.

AI-assisted secure data transmission techniques for next-generation HetNets: A review

With the uninterrupted revolution of communications technologies and the great-leap-forward development of emerging applications, the ubiquitous deployment of Internet of Things (IoT) is imperative to accommodate constantly growing user demands and market scales. Communication security is critically important for the operations of IoT. Among the communication security provisioning techniques, physical layer security (PLS), which can provide unbreakable, provable, and quantifiable secrecy from an information-theoretical point of view, has drawn considerable attention from both the academia and the industries. However, the unique features of IoT, such as low-cost, wide-range coverage, massive connection, and diversified services, impose great challenges for the PLS protocol design in IoT. In this article, we present a comprehensive review of the PLS techniques toward IoT applications. The basic principle of PLS is first briefly introduced, followed by the survey of the existing PLS techniques. Afterwards, the characteristics of IoT are identified, based on which the challenges faced by PLS protocol design are summarized. Then, three newly-proposed PLS solutions are highlighted, which match the features of IoT well and are expected to be applied in the near future. Finally, we conclude the paper and point out some further research directions.

Radio over is an attractive solution for broadband wireless access. In this paper, the performance of externally and direct intensity modulated RoF links is analyzed in the presence of the group velocity dispersion and third-order dispersion of the optical fiber. An external modulation system with dual electrode lithium niobate Mach–Zehnder modulator (DE-MZM) and direct modulation system with vertical-cavity surface-emitting laser (VCSEL) are considered. Both modulation schemes are tested using Gaussian optical pulses. Simulations are performed with the same values for common global parameters for both schemes. Although external modulation is a generally considered more advanced, our simulations show that the direct modulation technique with VCSEL shows a more robust performance. The performances are compared using performance parameters like Q factor, eye diagram, BER and RF signal amplitude.

This paper presents a low power FSK transceiver with ADPLL based on direct modulation and integrated SPDT switch for Bluetooth low energy application. To ensure that the proposed low power transceiver can operate at 1 Mbps data rate, FSK modulation is implemented using an all-digital phase locked-loop with direct modulation technique. The SPDT switch is integrated to share the antenna and matching network between the transmitter and receiver, thus minimizing the system cost by reducing external components. The transceiver is implemented using 1P6M 55-nm CMOS technology. The die area of the transceiver with DC-DC converter is 1.79 mm2. The power consumption of the transmitter and receiver are 6 and 5 mW, respectively, when the output power level of the transmitter is 0 dBm. The noise figure of Rx is up to 6.8 dB with respect to channel frequencies. The phase noise of the ADPLL is −84.7 and −118.9 dBc/Hz at 100 kHz and 1 MHz offset from 2.44 GHz, respectively.

Directional modulation (DM) is a physical layer security technique based on antenna arrays and so far the polarisation information has not been considered in its designs. To increase the channel capacity, we consider exploiting the polarisation information and send two different signals simultaneously at the same direction, same frequency, but with different polarisations. These two signals can also be considered as one composite signal using the four dimensional (4-D) modulation scheme across the two polarisation diversity channels. In this paper, based on cross-dipole arrays, we formulate the design to find a set of common weight coefficients to achieve directional modulation for such a composite signal and examples are provided to verify the effectiveness of the proposed method.

Monopulse based DOA and polarization estimation with polarization sensitive arrays

The physical layer security techniques have made great progress in the past few years. The essential idea of physical layer transmission is to maximize the randomness of undesired channels. The 4-D antenna arrays formed by introducing time as the fourth controlling degree of freedom can be used to regulate the radiated fields in space, time, and frequency domains simultaneously. Thus, 4-D antenna arrays are an effective carrier for achieving physical layer secure transmission. However, the traditional secure transmission approach based on 4-D antenna arrays always inevitably leads to high sidelobe levels (SLLs) of radiated power or less channel randomness. Aimed at this problem, a novel physical layer secure transmission approach based on 4-D antenna arrays is proposed, which combines the advantages of traditional phased arrays and 4-D arrays. The approach can be used to reduce the SLL of radiated power and improve the channel randomness by optimizing the time sequences and static amplitude weighting. Moreover, the signal distortion caused by time modulation can be compensated in the desired direction by premodulating the transmitted signals. Both the numerical and experimental results demonstrate the effectiveness of the proposed approach.

As a physical layer security technique, directional modulation (DM) is normally realized using a fully digital structure due to its easy and flexible hardware design. However, for a large antenna array, such as the case of massive MIMO, to reduce the cost and power consumption, a hybrid digital and analog beamforming structure is widely adopted. In this paper, the DM design problem is studied based on such a hybrid implementation for the first time. As a representative example, the interleaved subarrays are used for the proposed design. Design examples are provided to show the effectiveness of the proposed design.

This paper links the parameter estimation problem of polarization diversity bistatic multiple-input multiple-output (MIMO) radar to propagator method (PM), and proposes an algorithm for joint estimation of direction-of-departure (DOD), direction-of-arrival (DOA) and polarization information for bistatic MIMO radars. PM algorithm is a low complexity algorithm since it requires no eigen-value decomposition (EVD) of the covariance matrix of the received data. The proposed algorithm can estimate the multiple parameter accurately, while achieve paired parameters estimation automatically. Through obtaining polarization information, MIMO radars can further increase the target location and identification accuracy. Simulation results verify the feasibility and effectiveness of the proposed algorithm.

In this paper, a directional polarization modulation method based on a time-modulated vector array is proposed for secure communication. The polarization state of the transmitted signal is used to represent the communication information to realize the directional polarization modulation in the desired direction. The vector antenna is divided into two sub-arrays. Each sub-array is controlled by a different time sequence to turn on the antenna. The correlation between the horizontal and vertical components of the polarization signal is destroyed. The communication direction is not affected, but the desired polarization state cannot be synthesized in the non-communication direction. The simulation results show that the desired polarization state is received in the communication direction, the polarization information of the signal in the non-communication direction is disturbed, and the information leakage from the time-modulated array due to sideband radiation is avoided.

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.