Intelligent Reflective Surfaces for Wireless Networks: An Overview of Applications, Approached Issues, and Open Problems

Abstract

An intelligent reflective surface (IRS) is a novel and revolutionizing communication technology destined to enable the control of the radio environment. An IRS is a real-time controllable reflectarray with a massive number of low-cost passive elements which introduce a phase shift to the incoming signals from the sources before the propagation towards the destination. This technology introduces the notion of a smart propagation environment with the aim of improving the system performance. In this paper, we provide a comprehensive literature overview on IRS technology, including its basic concepts and reconfiguration, as well as its design aspects and applications for wireless communication systems. We also study the performance metrics and the setups considered in recent publications related to IRS and provide suggestions of future research lines based on still unexplored use cases in the state-of-the-art.

Tracking of Evasive Objects Using Bistatic Doppler Radar Operating in the Millimeter Wave Regime

“…It can be seen that determining transmission frequency sets the barrier in Equation (29). Other than larger scattering strength at high frequency (as mentioned in the introduction), increasing the transmission frequency also lowers the barrier in the proposed scheme and improves the range resolution.…”

“…A fast bullet does not allow long processing times but also does not require it because the high velocity allows less time to be used for processing. Equation (29) demonstrates the relation between the resolution, the velocity, and the processing time. In order to make a comparison between the results of the system and the video recording, it was necessary to perform the measurements on a slow target in relation to the photographic capabilities so that it would be possible to make the comparison.…”

“…From Equation (29), it can be concluded that four main parameters influence the resolution of the proposed scheme. Figure 13 shows how the relationship between the desired range for detection and the size, d, of the system influences the range resolution.…”

“…From Equation (29), it can be concluded that four main parameters influence the resolution of the proposed scheme.…”

“…According to Equation (29), enlarging the distance d between the two transmitters spoils the resolution and raises the barrier from Equation (29) but increases the effective distance for detection, as can be seen in Figure 9, where the ability to separate the different frequencies obtained at the radar output depends on the ratio between the distance of the target and the distance between the two transmitters. It can be seen from Equation ( 11) that a larger alpha angle causes a larger difference between the frequencies.…”