Multi-beam Directional Modulation Research Articles

Physical-Layer Security for Multi-User Communications With Frequency Diverse Array-Based Directional Modulation

By resorting to the technology of frequency diverse array (FDA)-based directional modulation (DM), this paper designs the physical-layer security in system uplink and downlink. Specifically, the FDA-based single-beam DM is employed to deliver confidential messages from each legitimate user (LU) to the base station (BS) in the uplink. To eliminate mutual interference caused by the simultaneous arriving signals at BS, we propose the FDA-based multi-carrier allocation scheme together with the receiver structure. On the other side of the coin, the FDA-based multi-beam DM is employed to send secrecy information from BS to LUs in the downlink. Moreover, the maximum signal to leakage and noise ratio (MSLNR) and the maximum eavesdroppers to LUs interference and noise ratio (MELINR) are proposed to design the beamforming matrix and the protection matrix, respectively, to enhance downlink security. Simulation results show that the proposed method has better security performance than the zero-forcing (ZF) and singular value decomposition (SVD) methods in the downlink. Moreover, the proposed FDA method outperforms the conventional phased-array system in both uplink and downlink.

Secure beamforming and power‐efficient artificial‐noise optimization for multibeam directional modulation

AbstractIn this article, an anti‐eavesdropping zero‐forcing plus power‐efficient artificial‐noise optimization method for multibeam directional modulation (DM) synthesis is proposed. It aims to prevent known and unknown eavesdroppers intercepting useful signals as far as possible and achieve a narrower bit error rate (BER) main beamwidth under the premise of limited artificial‐noise (AN) power consumption. Beam pattern nulls are generated in known eavesdroppers directions by utilizing the orthogonality of zero‐forcing beamforming. Low‐sidelobe beamforming is also introduced to DM for the first time to suppress unknown eavesdroppers outside main lobes. The distribution of AN power in all directions is optimized by minimizing the AN transmit power subject to a series of secrecy rate (SR) constraints. Simulation results show that the proposed method outperforms the state‐of‐the‐art DM synthesis methods with regard to power efficiency, SR and BER performance.

Spatial Modulation and MP-WFRFT-Aided Multi-Beam Wireless Communication Scheme Based On Random Frequency Diverse Array.

A security-enhanced, spectral-efficient, and power-efficient multi-beam wireless communication scheme based on random frequency diverse array (RFDA) is proposed in this paper. (AN)-aided directional modulation (DM) schemes. Furthermore, with the aid of spatial modulation (SM) technology and cooperative legitimate users (LUs), we can transmit more information bits by the use of LU number informations than the single modulation symbols. Unlike conventional zero-forcing (ZF) beamforming for multi-beam DM, we design a FDA beamforming vector for each LU based on the minimum transmit power method. Numerical simulations show that (1) the proposed scheme is power-efficient compared to the conventional schemes, (2) the proposed scheme can transmit more information bits than the conventional schemes, and (3) the proposed scheme can ensure communication security when eavesdroppers (Eves) are proximal to LUs or even in same locations.

Artificial-Noise-Aided Energy-Efficient Secure Multibeam Wireless Communication Schemes Based on Frequency Diverse Array

In this paper, we research synthesis scheme for secure wireless communication in multibeam directional modulation (MBDM) system, which consists of multiple legitimate users (LUs) receiving their own individual confidential messages, respectively, and multiple eavesdroppers (Eves) intercepting confidential messages. We propose a new type of array antennas, termed frequency diverse arrays (FDA), to enhance security of confidential messages. Leveraging FDA technology and artificial noise (AN) technology, we aim to address the PHY security problem for MBDM by jointly optimizing the frequency offsets, the precoding matrix and the AN projection matrix. In the first stage, with known locations of Eves, precoding matrix is designed to minimize Eve’s receiving power of confidential message (Min-ERP), while satisfying power requirement of LUs. And then artificial-noise projection matrix (ANPM) is calculated to enhance AN impact on Eves without influencing LUs. Furthermore, we research a more practical scenario, where locations of Eves are unknown. Unlike the scenario of the known locations of Eves, precoding matrix is designed to maximize AN transmit power (Max-ATP), while satisfying each LU’s requirement received power of confidential message. In the second stage, we analyze and further optimize secrecy capacity. The problem is solved by optimizing frequency offsets through modified artificial bee colony (M-ABC) algorithm. Numerical results show that the proposed scheme can achieve a secure transmission in MBDM system.

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.

Symbol-independent weight magnitude design for antenna array based directional modulation

Directional modulation (DM) as a physical layer security technique has been studied from many different aspects. Recently, a constant magnitude constraint for all antennas of an array for a given modulation symbol was proposed. However, the proposed design does not work for multiple beams. In practice, multi-beam DM may often be required. As a compromise, instead of setting the same magnitude for all antennas for a given symbol, in this paper, a symbol independent magnitude constraint for each antenna is proposed for the first time. With the same magnitude for different symbols for each antenna, only phase changes between different symbols are needed, which can form multiple DM beams simultaneously, while still reducing the implementation complexity of the whole system. Design examples are provided to show the effectiveness of the proposed design.

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

Directional modulation (DM), as an emerging promising physical layer security (PLS) technique at the transmitter side with the help of an antenna array, has developed rapidly over decades. In this study, a DM technique using a polarization sensitive array (PSA) to produce the modulation with different polarization states (PSs) at different directions is investigated. A PSA, as a vector sensor, can be employed for more effective DM for an additional degree of freedom (DOF) provided in the polarization domain. The polarization information can be exploited to transmit different data streams simultaneously at the same directions, same frequency, but with different PSs in the desired directions to increase the channel capacity, and with random PSs off the desired directions to enhance PLS. The proposed method has the capability of concurrently projecting independent signals into different specified spatial directions while simultaneously distorting signal constellation in all other directions. The symbol error rate (SER), secrecy rate, and the robustness of the proposed DM scheme are analyzed. Design examples for single- and multi-beam DM systems are also presented. Simulations corroborate that (1) the proposed method is more effective for PLS; (2) the proposed DM scheme is more power-efficient than the traditional artificial noise aided DM schemes; and (3) the channel capacity is significantly improved compared with conventional scalar antenna arrays.

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.

Multi-Beam Directional Modulation Synthesis Scheme Based on Frequency Diverse Array

In this paper, a frequency diverse array-based directional modulation with artificial noise synthesis scheme is proposed to enhance the physical layer security of wireless communications. We aim to optimize the secrecy performance by jointly optimizing the frequency offsets, the beamforming vector, and the artificial-noise projection matrix (ANPM). Specifically, we address the physical layer security problems for known locations of proximal eavesdropper (Eve) and legitimate user (LU). The beamforming vector and frequency offsets are designed to preserve the signal power at LU. The ANPM is calculated to minimize the effect of AN on LU. Furthermore, we extend our approach to the case of multi-LUs with unknown Eve locations. Being different from the case of a single LU, the frequency offsets across array antennas are optimized to equally allocate transmitted power to each LU. The numerical results show that the proposed method can provide a higher secrecy performance than conventional DM methods. In the case of multi-LUs with unknown Eve locations, the proposed method can provide a high secrecy capacity while achieving almost equal achievable capacity to each LU.

Iterative Convex Optimization of Multi-Beam Directional Modulation With Artificial Noise

A joint optimization algorithm for designing multi-beam directional modulation (MBDM) symbols with artificial noise (AN) is proposed for physical layer security in wireless communication systems. The proposed approach guarantees specific minimum error probabilities along the given eavesdropper directions. The algorithm is implemented by iterating between a convex program that optimizes symbols with AN and a convex (linear) program optimizing a set of weight vectors to guarantee specific error probabilities along the eavesdropper directions. The proposed method is compared against several MBDM algorithms, and is found to provide excellent bit error rate performance results. A hardware experimental test bed is described and is used to demonstrate the feasibility of the proposed solution.

Artificial-Noise-Aided Zero-Forcing Synthesis Approach for Secure Multi-Beam Directional Modulation

Great attention has been paid to wireless communication security in recent years. Directional modulation (DM) is one of the promising secure wireless communication techniques. Multi-beam DM has the capability of sending multiple data streams to cooperative users in different desired directions while distorting signal constellations in all other directions. Dynamic multi-beam DM has been proven to be more secure in real communication scenarios. However, previous synthesis approaches for dynamic multi-beam DM are relatively complex and demand a lot of computations. Therefore, an artificial-noise-aided zero-forcing synthesis approach is proposed. The calculation process of the baseband-weighted vector is simplified using the zero-forcing method, which is closely related to the concept of pseudo-inverse. The dynamic property of multi-beam DM is achieved by randomly changing the artificial noise vector. Compared with previous classical dynamic multi-beam DM synthesis approaches, the proposed approach is more efficient and easier to implement in practical systems with tolerable performance loss.

Robust Synthesis Scheme for Secure Multi-Beam Directional Modulation in Broadcasting Systems

Recently, directional modulation has become an active research area in wireless communications due to its security. Unlike existing research work, we consider a multi-beam directional modulation (MBDM) scenario with imperfect desired direction knowledge. In such a setting, a robust synthesis scheme is proposed for MBDM in broadcasting systems. In order to implement the secure transmission of a confidential message, the beamforming vector of the confidential message is designed to preserve its power as possible in the desired directions by minimizing its leakage to the eavesdropper directions while the projection matrix of artificial noise (AN) is to minimize the effect on the desired directions and force AN to the eavesdropper directions by maximizing the average receive signal-to-artificial-noise ratio at desired receivers. Simulation results show that compared with conventional methods, the proposed robust scheme achieves much better bit error rate performance along desired directions for a given signal-to-noise ratio (SNR). From the secrecy-rate aspect, the proposed scheme performs better than conventional methods for almost all SNR regions. In particular, in the medium and high SNR regions, the rate improvement of the proposed scheme over conventional methods is significant.

Orthogonal Vector Approach for Synthesis of Multi-Beam Directional Modulation Transmitters

An orthogonal vector approach is proposed for the synthesis of multi-beam directional modulation (DM) transmitters. These systems have the capability of concurrently projecting independent data streams into different specified spatial directions while simultaneously distorting signal constellations in all other directions. Simulated bit error rate (BER) spatial distributions are presented for various multi-beam system configurations in order to illustrate representative examples of physical layer security performance enhancement that can be achieved.

Directional modulation far‐field pattern separation synthesis approach

In this study, a far-field power pattern separation approach is proposed for the synthesis of directional modulation (DM) transmitter arrays. Separation into information patterns and interference patterns is enabled by far-field pattern null steering. Compared with other DM synthesis methods, for example, bit error rate-driven DM optimisation and orthogonal vector injection, the approach developed in this study facilitates manipulation of artificial interference spatial distributions. With such capability more interference power can be projected into those spatial directions most vulnerable to eavesdropping, that is, the information side lobes. In such a fashion, information leaked through radiation side lobes can be effectively mitigated in a transmitter power efficient manner. Furthermore, for the first time, the authors demonstrate how multi-beam DM transmitters can be synthesised via this approach.