Intelligent Reflecting Surface Assisted Anti-Jamming Communications Based on Reinforcement Learning

Malicious jamming launched by smart jammer, which attacks legitimate transmissions has been regarded as one of the critical security challenges in wireless communications. Thus, this paper exploits intelligent reflecting surface (IRS) to enhance anti-jamming communication performance and mitigate jamming interference by adjusting the surface reflecting elements at the IRS. Aiming to enhance the communication performance against smart jammer, an optimization problem for jointly optimizing power allocation at the base station (BS) and reflecting beamforming at the IRS is formulated. As the jamming model and jamming behavior are dynamic and unknown, a win or learn fast policy hill-climbing (WoLF-PHC) learning approach is proposed to jointly optimize the anti-jamming power allocation and reflecting beamforming strategy without the knowledge of the jamming model. Simulation results demonstrate that the proposed anti-jamming based-learning approach can efficiently improve both the IRS-assisted system rate and transmission protection level compared with existing solutions.Comment: This paper appears in the Proceedings of IEEE Global Communications Conference (GLOBECOM) 2020. A full version appears in IEEE Transactions on Wireless Communications. arXiv:2004.1253

Energy harvesting towards self-powered iot devices

The internet of things (IoT) manages a large infrastructure of web-enabled smart devices, small devices that use embedded systems, such as processors, sensors, and communication hardware to collect, send, and elaborate on data acquired from their environment. Thus, from a practical point of view, such devices are composed of power-efficient storage, scalable, and lightweight nodes needing power and batteries to operate. From the above reason, it appears clear that energy harvesting plays an important role in increasing the efficiency and lifetime of IoT devices. Moreover, from acquiring energy by the surrounding operational environment, energy harvesting is important to make the IoT device network more sustainable from the environmental point of view. Different state-of-the-art energy harvesters based on mechanical, aeroelastic, wind, solar, radiofrequency, and pyroelectric mechanisms are discussed in this review article. To reduce the power consumption of the batteries, a vital role is played by power management integrated circuits (PMICs), which help to enhance the system's life span. Moreover, PMICs from different manufacturers that provide power management to IoT devices have been discussed in this paper. Furthermore, the energy harvesting networks can expose themselves to prominent security issues putting the secrecy of the system to risk. These possible attacks are also discussed in this review article

RIS-Assisted Robust Hybrid Beamforming AgainstSimultaneous Jamming and Eavesdropping Attacks

Wireless communications are increasingly vulnera-ble to simultaneous jamming and eavesdropping attacks due tothe inherent broadcast nature of wireless channels. With thisfocus, due to the potential of reconfigurable intelligent surface(RIS) in substantially saving power consumption and boostinginformation security, this paper is the first work to investigate theeffect of the RIS-assisted wireless transmitter in improving boththe spectrum efficiency and the security of multi-user cellularnetwork. Specifically, with the imperfect angular channel stateinformation (CSI), we aim to address the worst-case sum ratemaximization problem by jointly designing the receive decoder atthe users, both the digital precoder and the artificial noise (AN)at the base station (BS), and the analog precoder at the RIS, whilemeeting the minimum achievable rate constraint, the maximumwiretap rate requirement, and the maximum power constraint.To address the non-convexity of the formulated problem, we firstpropose an alternative optimization (AO) method to obtain anefficient solution. In particular, a heuristic scheme is proposedto convert the imperfect angular CSI into a robust one andfacilitate the developing a closed-form solution to the receivedecoder. Then, after reformulating the original problem into atractable one by exploiting the majorization-minimization (MM)method, the digital precoder and AN can be addressed by thequadratically constrained quadratic programming (QCQP), andthe RIS-aided analog precoder is solved by the proposed pricemechanism-based Riemannian manifold optimization (RMO).To further reduce the computational complexity of the pro-posed AO method and gain more insights, we develop a low-complexity monotonic optimization algorithm combined with thedual method (MO-dual) to identify the closed-form solution.Numerical simulations using realistic RIS and communicationmodels demonstrate the superiority and validity of our proposedschemes over the existing benchmark schemes

ORBITAL ANGULAR MOMENTUM ORTHOGONALITY-BASED CROSSTALK REDUCTION: THEORY AND EXPERIMENT

Full duplex communication systems allow a single channel to be used for simultaneous two-way communication, increasing spectral efficiency. However, full duplex communication systems suffer from the issue of self-interference between local transmitter and receiver antennas. Analog subtraction and signal processing methods have previously been used to reduce this problem. This dissertation proposes the use of waves carrying orbital angular momentum (OAM) to mitigate the problem of self-interference by offering a means of additional isolation between local antennas. Orbital angular momentum has been widely studied both in the photonics and radio domain. The theoretically infinite orthogonal states of an OAM signal make it highly desirable in the field of communication. The application of OAM in a full duplex system, may be the answer to the problem of self-interference. This dissertation shows how the use of OAM waves may create an additional isolation between local antennas in a full duplex system. Motivated by the promise that OAM orthogonality holds, this dissertation explores the crosstalk reduction achieved through OAM. One of the main contributions of this dissertation is to provide insight into the nature of the effect. It motivates OAM orthogonality as a direction of research for use in future full duplex systems. The effect of OAM on crosstalk must be studied experimentally and theoretically. To this effect, a patch array antenna was designed using the High Frequency Simulation Software (HFSS), to generate OAM beams. The designed antennas are fabricated and characterized. This dissertation discusses the experiments carried out to determine the amount of crosstalk reduction achieved due to the OAM nature of the signal transmitted. The impact of the change in distance between the local transmitter and receiver antennas on crosstalk is also studied. The results obtained are verified through theoretical analysis using simulations in HFSS. This dissertation reports a maximum theoretical crosstalk reduction of 3.6dB, and a crosstalk reduction of 2.6 dB realized experimentally. Building on these results, a compact, more practical antenna configuration was designed. This nested design yields more than 60dB crosstalk reduction and provides for a more elegant system realization. The dissertation includes the design of a parabolic dish antenna to build a complete system, which is also studied in this dissertation. The symmetry of the nested antenna configuration allows for analytic theoretical study which is included herein. The study mathematically proves the orthogonality of OAM modes, and the isolation between two antennas with different OAM modes. A similar study is simulated in HFSS using coaxial based loop antennas, and the crosstalk in the nested design is investigated. The design offers a crosstalk isolation of more than 90dB, and further affirms the mathematical analysis. This dissertation provides a detailed analysis of the isolation offered by OAM orthogonality in local antennas which can be useful in a full duplex system. The work consists of practical, simulated, and mathematical investigation, and considers various antenna configurations and designs. Additionally, it presents and analyses a design for a full duplex system