Time series analysis and its applications

In this letter, we consider an unmanned aerial vehicle (UAV) relay network, where the UAV works as an amplify-and-forward relay. We optimize the trajectory of UAV, the transmit power of UAV, and the mobile device by minimizing the outage probability of this relay network. The analytical expression of outage probability is derived first. A closed-form low-complexity solution with joint trajectory design and power control is proposed to solve this non-convex problem. Simulation results show that the outage probability of the proposed solution is significantly lower than that of the fixed power relay and circle trajectory for the UAV relay.

Joint Trajectory and Power Optimization for UAV Relay Networks

As a complement to high-layer encryption techniques, physical layer security has been widely recognized as a promising way to enhance wireless security by exploiting the characteristics of wireless channels, including fading, noise, and interference. In order to enhance the received signal power at legitimate receivers and impair the received signal quality at eavesdroppers simultaneously, multiple-antenna techniques have been proposed for physical layer security to improve secrecy performance via exploiting spatial degrees of freedom. This paper provides a comprehensive survey on various multiple-antenna techniques in physical layer security, with an emphasis on transmit beamforming designs for multiple-antenna nodes. Specifically, we provide a detailed investigation on multiple-antenna techniques for guaranteeing secure communications in point-to-point systems, dual-hop relaying systems, multiuser systems, and heterogeneous networks. Finally, future research directions and challenges are identified.

A Survey on Multiple-Antenna Techniques for Physical Layer Security

Physical layer security (PLS) has been extensively explored as an alternative to conventional cryptographic schemes for securing wireless links. Many studies have shown that the cooperation between the legitimate nodes of a network can significantly enhance their secret communications performance, relative to the noncooperative case. Motivated by the importance of this class of PLS systems, this paper provides a comprehensive survey of the recent works on cooperative relaying and jamming techniques for securing wireless transmissions against eavesdropping nodes, which attempt to intercept the transmissions. First, it provides a in-depth overview of various secure relaying strategies and schemes. Next, a review of recently proposed solutions for cooperative jamming techniques is provided with an emphasis on power allocation and beamforming techniques. Then, the latest developments in hybrid techniques, which use both cooperative relaying and jamming, are elaborated. Finally, several key challenges in the domain of cooperative security are presented along with an extensive discussion on the applications of cooperative security in key enablers for 5G communications, such as nonorthogonal multiple access, device-to-device communications, and massive multiple-input multiple-output systems.

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A Comprehensive Survey on Cooperative Relaying and Jamming Strategies for Physical Layer Security

In this two-part paper, we consider the problem of adaptive multidimensional/multichannel signal detection in Gaussian noise with unknown covariance matrix. The test data (primary data) is assumed as a collection of sample vectors, arranged as the columns of a rectangular data array. The rows and columns of the signal matrix are both assumed to lie in known subspaces, but with unknown coordinates. Due to this feature of the signal structure, we name this kind of signal as the double subspace signal. Part I of this paper focuses on the adaptive detection in homogeneous environments, while Part II deals with the adaptive detection in partially homogeneous environments. Precisely, in this part, we derive the generalized likelihood ratio test (GLRT), Rao test, Wald test, as well as their two-step variations, in homogeneous environments. Three types of spectral norm tests (SNTs) are also introduced. All these detectors are shown to possess the constant false alarm rate (CFAR) property. Moreover, we discuss the differences between them and show how they work. Another contribution is that we investigate various special cases of these detectors. Remarkably, some of them are well-known existing detectors, while some others are still new. At the stage of performance evaluation, conducted by Monte Carlo simulations, both matched and mismatched signals are dealt with. For each case, more than one scenario is considered.

Adaptive Double Subspace Signal Detection in Gaussian Background—Part I: Homogeneous Environments

The sine-BOC (binary offset carrier) modulation is used in several signals of the new European Global Navigation Satellite System, Galileo, and modernized GPS. It provides these signals with enhanced robustness against multipath and increases the precision of the range measurement. However, this modulation presents some drawbacks. The most severe is the ambiguity problem in acquisition and tracking, which introduces a large bias in the pseudo-range measurement. In order to solve this problem, an unambiguous tracking technique for sine-BOC signals is proposed. This technique is based on a pseudo correlation function (PCF) which does not have any side peak and thus completely removes all of the false lock points on the discriminator output. Impacts of thermal noise and multipath on the proposed technique are investigated. Theoretical and numerical results obtained with BOC(n,n) and BOC(2n,n) signals show that this technique has a good noise mitigation performance and an average multipath performance.

Pseudo-Correlation-Function-Based Unambiguous Tracking Technique for Sine-BOC Signals

Cooperative jamming for multiuser multiple input multiple output (MIMO) broadcast channel is studied to enhance the physical layer security with the help of a friendly jammer. We assume the base station transmits multiple independent data streams to multiple legitimate users. During the transmission, however, there are multiple eavesdroppers with multiple antennas that have interests in the streams from the base station. In order to wiretap the desired streams, the eavesdroppers may collude or not, and maximize the signal-to-interference-plus-noise ratio (SINR) of the desired streams using receive beamforming. The optimal cooperative jammer is designed to keep the achieved SINR at eavesdroppers below a threshold to guarantee that the transmission from the base station to legitimate users is confidential. One main advantage of the proposed cooperative jamming scheme is that no modification is needed for the existing precoding schemes at the base station and decoding schemes at legitimate users. Thus, any existing practical precoding/decoding schemes for multiuser MIMO broadcast channel can be applied directly with the help of a friendly jammer using the proposed cooperative jamming.

Optimal Cooperative Jamming for Multiuser Broadcast Channel with Multiple Eavesdroppers

In this paper, an impedance matching underwater acoustic bend with pentamode microstructure is designed. The proposed bend is assembled by pentamode lattice. The effective density and compressive modulus of each unit cell can be tuned simultaneously, which are modulated to guarantee both the bending effect and high transmission. The standard deviations (SDs) of transmitted phase are calculated to quantitatively evaluate the degree of the distortion of the transmitted wavefront, while the transmission is calculated to appraise the degree of acoustic impedance matching. The low SDs and high transmission indicate that the designed bend has a nice broadband bending effect and is impedance-matched to water. This design has potential applications in underwater communication and underwater detection.

Design of an underwater acoustic bend by pentamode metafluid

This study deals with the problem of detecting distributed targets in the presence of homogeneous and partially homogeneous Gaussian disturbance with unknown covariance matrix. The proposed detectors improve the adaptive beamformer orthogonal rejection test (ABORT) idea to address detection of distributed targets, which makes it possible to decide whether some observations contain a useful target or a signal belonging to the orthogonal complement of the useful subspace. At the design stage, the authors resort to either the plain generalised likelihood ratio test (GLRT) or ad hoc design procedures. Remarkably, the considered criteria lead to receivers ensuring the constant false alarm rate (CFAR) property with respect to the unknown quantities. Moreover, authors’ derivations show that the ad hoc detector for a partially homogeneous environment coincides with the generalised adaptive subspace detector. The performance assessment conducted by Monte Carlo simulation has confirmed the effectiveness of the newly proposed detection algorithms.

Adaptive detection of distributed targets with orthogonal rejection

Underwater acoustic communications have found applications in many fields with great developments. Thus, the demand for security of such communications is rapidly growing. Two parties in the communication, after authentication, generally use a secure symmetric key to encrypt all the data they transmit. Thus, an efficient key generation algorithm is in urgent need to guarding the privacy of the communication data. This paper presents a novel key generation system which is easy to be implemented, efficient in computation and communication, and robust to the spatio-temporal variable ocean environments. Unlike those conventional solutions, by exploiting reciprocity, deep fades, randomness extractor and robust secure fuzzy information reconciliators, which is first introduced by us in this paper, channel characteristics are used to generate the key in our solution.

Jun Yang

Papers

Pseudo-Correlation-Function-Based Unambiguous Tracking Technique for Sine-BOC Signals

Optimal Cooperative Jamming for Multiuser Broadcast Channel with Multiple Eavesdroppers

Design of an underwater acoustic bend by pentamode metafluid

Adaptive detection of distributed targets with orthogonal rejection

Secure underwater acoustic communication based on a robust key generation scheme