The proliferation of X and Ku band applications in satellite communications, remote sensing, radar systems, and in ever-increasing wireless networks, impels to design of an ultra-wideband reflection-based linear polarization converter. An efficiently designed converter enhances the signal quality in addition to minimizing the interferences in wireless links. Seeing these upcoming myriad number of applications, in this paper, we design and fabricate a lightweight ultra-wideband converter structure by utilizing two 0.15mm thin FR-4 sheets and a Teflon air-spacer having a thickness of 5.25mm. Specifically, the top side of the unit cell consists of a diagonally arranged parallel metallic strip printed on thin FR-4 substrate material which is separated by a Teflon spacer with complete metal on the bottom side. To show the efficacy, numerical simulations are performed and the obtained results are validated by fabricating the device in the lab. The experimental and simulation results show that the proposed structure works as a cross-polarizer with a polarization conversion ratio of more than 90% in the C, X, and Ku bands with an operating range of 6.2-16.6GHz. The measured co-reflection coefficient of the fabricated device completely matched with the simulated reflection coefficient which corroborates with the obtained results. The proposed structure features a sub-wavelength-sized unit cell (0.26?L), which significantly enhances the angular stability of the design. Additionally, it achieves an impressive fractional bandwidth of 91.2% and is characterized by its lightweight structure, making it highly efficient for various applications, such as radiometers and RCS reduction

Device-to-device (D2D) communication that allows direct communication between nearby mobile devices without traversing through the base station is a potential solution to solve the problem of safer and faster data rate communication. This review paper comprehensively explores the security aspects of D2D communication, focusing on the vulnerabilities, threats, and existing security mechanisms. In addition, it provides an in-depth analysis of the security challenges in D2D communication, including eavesdropping, data integrity, authentication, and privacy concerns. Furthermore, it also delves into the potential security risks associated with different D2D communication scenarios, such as public safety, proximity-based services, and ad-hoc networking. Toward the end, this survey discusses the open research challenges and future directions in securing D2D communication, highlighting the need for robust security protocols to mitigate the evolving threats in this dynamic communication paradigm. The findings presented in this survey aim to provide researchers, practitioners, and policymakers with a comprehensive understanding of the security landscape in D2D communication, thereby contributing to the successful deployment of secure and reliable D2D communication systems.

The exponential increase in video data demands over the wireless network has created the interest among the researchers to come up with a potential solution to efficiently distribute the video content over 5G and beyond networks. Therefore, in this paper, an energy-efficient scheme for video content dissemination by utilizing the device-to-device (D2D) communication has been proposed. The work aims to address the twin issues of energy efficiency and distortion minimization simultaneously. In the current cellular networks, every user downloads the video independently which often leads to low quality as the distance between the base station (BS) and mobile device increases. In the proposed scheme, proximate mobile nodes are grouped into clusters and among them a cluster head is chosen which forwards the data to cluster members using D2D communication. To make the system more spectral efficient, performance of the proposed scheme is evaluated in underlay mode where D2D links are sharing the channels with the primary cellular users. To show the efficacy of the proposed scheme, numerical analysis is conducted, and results show that significant energy saving can be achieved with the proposed scheme as compared to the conventional multicasting scheme, and it also provides improved video quality with lesser distortion and delay.

We address the problem of distributed resource allocation for multicast communication in device-to-device (D2D) enabled underlay cellular networks. The optimal resource allocation is crucial for maximizing the performance of such networks, which are limited by the severe co-channel interference between cellular users (CU) and D2D multicast groups. However, finding such optimal allocation for networks with a large number of CUs and D2D users is challenging. Therefore, we propose a pragmatic scheme that allocates resources distributively, reducing signaling overhead and improving network scalability. Numerical simulations establish the efficacy of the proposed solution in improving the overall system throughout, compared to various existing schemes

Seeing the rising applications of metamaterial in sensing and imaging, satellite communications, it becomes evident to design a high-gain microstrip patch antenna. To support these applications, this paper proposes a 7 x 7 array of planar novel metamaterial unit cells used as a superstrate to enhance the gain of microstrip patch antenna operating at 11.2 GHz. This proposed metamaterial structure yields a very low (near zero) value of effective refractive index at 11.2 GHz. Hence, the superstrate behaves as a near zero-indexed-medium (NZIM) around this frequency. NZIM superstrate are very popular because of their ability to focus the radiation and by utilizing this property, a significant gain enhancement has been achieved in the usage of patch antennas. Numerical simulations have been conducted using the CST Microwave studio, and obtained results corroborate that NZIM superstrate when suspended over a microstrip patch antennas significantly improves the gain around the value of 7.5 dB at 11.2 GHz, and efficiency is also improved

Seeing the recent rise in applications of RFID tags in industrial internet of things (IIoT), it become very evident to design an efficient and compact antenna which is able to satisfy the uprising IoT demands. This work presents a new 3D quasi-isotropic electrically small antenna (ESA) for RFID applications in the 2.4 GHz band. The proposed antenna is designed on a single perfect electric conductor (PEC) sheet by loading an inverted L-shaped slot. An opened aperture is excited to realize magnetic dipole characteristics to achieve a quasi-isotropic radiation pattern in 3D spatial coverage. The overall volume of the prototype is O.18Ax0.07Ax0.0096A nm3; here, ? is the free space wavelength that corresponds to operating frequencies. The proposed antenna offers a 30MHz (2.42-2.45 GHz) impedance bandwidth centered at 2.43 GHz. The antenna exhibits a quasi-isotropic radiation pattern with a maximum efficiency of 85%, which makes it suitable for RFID applications.

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This paper considers a device-to-device (D2D) communication-enabled multi-cell massive multi-input multi-output (MIMO) system, where multiple D2D pairs reuse the pilot signal allocated to the cellular users. The closed-form expressions for the spectral efficiency and its lower-bounds are derived using maximal ratio combining. To closely model the channel in the practical environment, a combination of line-of-sight (LoS) path and a stochastic non-line-of-sight (NLoS) component describing a spatially correlated multipath environment is considered. To characterize the achieved spectral efficiency for considered channel modeling, simulations are performed. The obtained results show that the system performance achieved with the Rician correlated fading is higher than the spectral efficiency achieved with Rayleigh-fading.