Atmospheric turbulence and pointing errors represent substantial hurdles to free-space optical communications (FSOs), impeding their practical design. The reconfigurable intelligent surface (RIS) is an emerging technology that enables reflective radio transmission conditions for next-generation 5G/6G wireless frameworks by intelligently adjusting the beam in the desired direction using low-cost inactive reflecting elements. In this paper, we proposed an RIS-assisted FSO system for mitigating the effects of atmospheric turbulence, pointing errors, and communication system signal blockage. The probability density function and cumulative distribution functions of an FSO system composed of N -RIS elements are evaluated in a free-space environment that contains obstructions. We derived closed-form expressions for the proposed system’s bit error rate (BER), outage probability, and channel capacity. The proposed system’s performance is analyzed in terms of BER, outage probability, and channel capacity under various weather conditions, pointing errors, and signal blockage. The results are plotted as a function of number of RIS elements and average signal-to-noise ratio. The proposed system will be beneficial in smart-city applications since it will provide reliable connectivity in urban environments with a high population density and high-rise buildings.

This paper proposes the idea of a new cooperative communication between the Internet of Things (IoT) and the Internet of Underwater Things (IoUT) using wireless optical connectivity for ocean monitoring applications. We considered IoT communication using a hybrid radio frequency (RF)/free space optical (FSO) link and IoUT using a underwater wireless optical communication (UWOC) link. Channel models for RF, FSO, and UWOC links are considered to be Rayleigh, Malaga with pointing errors, and hyperbolic tangent log-normal distributions, respectively. The outage probability and the bit error rate (BER) expressions for the proposed system are derived over the combined channel model, which includes the effects of attenuation, turbulence, and pointing errors. The BER results are plotted for various binary digital modulation schemes such as on–off keying, binary phase-shift keying, binary frequency-shift keying, and differential phase-shift keying over UWOC, hybrid RF/FSO and RF-UWOC, FSO-UWOC with end-to-end systems. BER results are extended for various turbulence regions and pointing errors of the FSO link. Monte Carlo simulation results authenticate the correctness of the results.

This article presents a compact six-element multiple-input multiple-output (MIMO) antenna for vehicle-to-vehicle (V2V) communications. The proposed structure is planar, having a dimension of $1.28\lambda _{0} \boldsymbol {\times } 2.04\lambda _{0}$ , where $\lambda _{0}$ is the wavelength at 25.5 GHz, resonating in n258 and n260 bands. The antenna is a modified rectangular patch designed to generate TM10 and TM02 modes, resulting in vertical and horizontal polarization at 25.5 GHz and 38 GHz. The measured bandwidth of the MIMO antenna is 800 MHz at the n258 band, i.e., 25.1-25.9 GHz, and 850 MHz at the n260 band, i.e., 37.75-38.6 GHz. The isolation between the elements is improved by incorporating a novel open-ended decoupling structure. It resulted in an isolation that surpass 20 dB at both bands. The antenna has a broadside radiation pattern with a maximum realized gain of 9 dBi and 7.2 dBi at 25.5 and 38 GHz, respectively. The antenna is validated for various diversity parameters such as envelope correlation coefficient, diversity gain, channel capacity loss, and mean effective gain. Also, the performance of the proposed antenna for V2V communication is analyzed for line-of-sight and non-line-of-sight conditions. The estimated channel capacity, path loss, and link budget for the above-said condition suggest that the antenna is suitable for V2V communications.

Broadband antennas with a low-profile generating circular polarization are always in demand for handheld/ portable devices as CP antennas counter multipath and misalignment issues. Therefore, a compact millimeter-wave antenna is proposed in this article. The proposed antenna structure comprises two circular rings and a circular patch at the center. This structure is further embedded with four equilateral triangles at a 90° orientation. The current entering the radiator is divided into left and right circular directions. The equilateral triangles provide the return path for current at the differential phase of ±90°, generating circular polarization. Structural development and analysis were initially performed through the characteristic mode theory. It showed that Modes 1 to 4 generated good impedance matching from 20 to 30 GHz and Modes 1 to 5, from 30 to 40 GHz. It also demonstrated the summation of orthogonal modes leading to circular polarization. The antenna-measured reflection coefficient |S11| > 10 dB was 19 GHz (23–42 GHz), and the axial ratio at −3 dB was 4.2 GHz (36–40.2 GHz). The antenna gain ranged from 4 to 6.2 dBi. The proposed antenna was tested for link margin estimation for IoT indoor conditions with line-of-sight (LOS) and non-line-of-sight (NLOS) conditions. The communication reliability with co- and cross-polarization was also studied under these conditions, and the results proved to be satisfactory.