Joint Radar and Communication Empowered by Digital Programmable Metasurface

With large available continuous bandwidth, millimeter wave (mmWave) bands hold promise as a carrier frequency for fifth generation (5G) wireless communications. Moreover, mmWave bands also play an important role in radar detections. Based on this observation, we propose an mmWave wireless communication and radar detection integrated network architecture for railways, not only to increase the capacity of railway wireless communication systems, but also to realize train operation environment detection to enhance train operation safety. To overcome the aggravated path loss in mmWave bands, directional beamforming is generally used to concentrate signal radiation energy both in wireless communications and radar detections. Nevertheless, for wireless communications, the signaling blind zone of directional beamforming makes it less effective in wireless link establishment and maintenance. Therefore, in this proposed integrated network, two frequency bands are employed, where omnidirectionally radiated licensed lower frequency bands carry critical signaling and data, and mmWave bands are time-division multiplexed to transmit large-volume communication data for trains, or to perform environment detection for enhancing train operation safety. To mitigate handovers and to increase baseband processing resource utilization in railway scenarios, the proposed integrated network is deployed based on the cloud radio access network (C-RAN) architecture, where both licensed lower frequency band radio remote units (RRUs) and mmWave band RRUs are connected to a building baseband unit (BBU) pool through high-speed backhauls. Besides, physical (PHY) frame structures and up/downlink communication signaling procedures are designed for this proposed integrated network. Performance analysis results have demonstrated that the proposed integrated network can highly increase the capacity for railway wireless communication systems and achieve high distance and angular resolution for radar detections.

Anthropogenic electromagnetic fields (EMFs) and corresponding electromagnetic radiation (EMR) exposure has long been a concern for the public, policy makers, and health researchers. Beginning 80with radar during World War II, human exposure to Radio Frequency (RF) radiation, and to modulated RF wireless communication (WC) EMFs/EMR has grown substantially over time. In 2011, a working group of the International Agency for Research on Cancer (IARC) reviewed the published literature and categorized WC EMR, termed as RF radiation, as a “possible” (Group 2B) human carcinogen. A broad range of adverse human health effects associated with WC EMFs/EMR have been reported since the IARC review. In addition, two large-scale carcinogenicity studies in rodents exposed to levels of WC EMR that mimic lifetime human exposures have shown significantly increased rates of Schwannomas and malignant gliomas, as well as chromosomal DNA damage. Of particular concern are the effects of WC EMR exposure on the developing brain in children. Compared with an adult male, a mobile phone held against the head of a child exposes deeper brain structures to greater radiation doses per unit volume, and the young, thin skull's bone marrow absorbs a roughly tenfold higher local dose. Experimental and observational studies also suggest that men who keep mobile phones in their trouser pockets have significantly lower sperm counts and significantly impaired sperm motility and morphology, including mitochondrial DNA damage as well as an increased risk of colon cancer. Pending an updated IARC working group review, current knowledge provides justification for governments, public health authorities, and physicians/allied health professionals to warn the population that having a cell phone next to the body is harmful, and to support measures to reduce all exposures to WC EMFs/EMR to as low as reasonably achievable.

A fundamental problem for signal processing in wireless communications is the separation multiple signals/users from their mixture. The problem would be simpler if they are non-overlapping in either time domain or frequency domain. Two signals may be overlapping in both time and frequency, but they still can be easily separated if they are uncorrelated (orthogonal), like in Code Division Multiple Access system (CDMA). It may be interesting to know that two signals may be overlapping in both the frequency and time domain and also are not orthogonal to each other, but they can still be separated if each autocorrelation function at the receiver is separable in the domain of time-lags. In this paper, we will show how the Noise-Loop (NL) modulation, originally thought to produce security at physical layer, can be used to effectively separate uncoordinated/unorthogonal users sharing the same time and frequency band. In order to show the potential of noise-loop multiple access (NLMA) scheme, the theoretical solution is derived as well as numerical semi-analytical simulations. It can be shown that the NLMA is able to distinguish the bit stream of the users. This feature together with the intrinsic security make the NL an interesting scheme for wireless technology.

As wireless technologies advance and new applications emerge, ensuring secure and resilient networks is increasingly critical. Here, we propose a wireless security mechanism based on a meta-encryptor (ME) with low-complexity architecture leveraging the unique capability of information metasurface. ME controls electromagnetic waves in time, space, and frequency domains, and, combined with encryption strategies, enables elastic, complementary multi-dimensional security. Three advanced security dimensions are demonstrated: (1) directional beam secure transmission that confines transmissions to intended receivers; (2) dual channel direct and hybrid modulations that distribute information while complementing resilient cryptography; and (3) wide range frequency-hopping transmission to effectively mitigate eavesdropping. By unifying multiple security functions on a single platform, a V-band prototype attains 100 Mbps while realizes wireless security, allowing flexible and elastic configuration without using conventional baseband mixing and bulky hardware. ME highlights the potential of information metasurface for next-generation secure wireless networks with low complexity and high efficiency.

Electromagnetic waves that have a wavelength of less than one millimeter are referred to as sub millimeter waves. In sub millimeter wave-based devices and systems, antennas are critical components that are vital to their operation. Antennas are used in situations when a transition between a directed wave and a free-space wave is needed. Since, electromagnetic characteristics for receiving and transmission of the nano antenna are mutually invertible, the properties of nano antenna are analyzed in sub millimeter wave frequencies and this overcomes the limitations of conventional antenna design. They are very small in size, provide more efficiency, and do not cause health threat. This paper reviews the applications of nano antenna, which operates at sub-millimeter wave frequency, in the field of energy harvesting, space technology, IoT applications, 5G network, smart clothing, bio sensing, communication, etc? Also, the nano antenna fabricated by 3D printing technology is also reviewed. The world’s ever-increasing energy need necessitates the development of alternate energy sources. There is a lot of research and development going on right now to enhance photovoltaic systems so that they can be more efficient, but the constraint is that they can only collect energy from the visible area of the electromagnetic spectrum. As a result, a novel device known as a Nano antenna has been developed to convert heat energy taken from the infrared spectrum into electricity. In the not-too-distant future, it will have an impact on a wide range of fields, such as mobile communication (5G), radar detection, and higher order frequency applications. Space communication, broadband wireless communications, wireless optical communication, and mobile communication will also benefit from its implementation.

Direct modulation of radio frequency (RF) signals has broad applications in wireless communications, radar detection, and other fields. However, the traditional methods face the limitations of high bandwidth requirements and poor noise resistance in scenarios of high data rates and complex environments, and hence, they are gradually replaced by digital modulation technologies. Recently, metasurface has become a significant innovation in RF direct modulation due to its flexibility and low cost. By controlling the amplitude and phase responses of metasurface units, efficient RF signal modulations have been achieved. However, the current metasurface modulation techniques are mainly focused on harmonic modulations and are difficult to implement the baseband modulation. To address these challenges, A high‐order amplitude‐phase modulated metasurface offers precise amplitude and phase control, enabling a spatial vector‐signal generator for efficient baseband and complex signal generation. This innovative approach enhances flexibility and dynamic adaptability in RF modulation,,demonstrating significant potentialfor high‐speed wireless communication, radar detection, and high‐resolution imaging.

Wideband (approximately 0-2000 MHz) electromagnetic scattering from mines and unexploded ordnance (UXO) is considered using a method of moments (MoM) analysis for general targets in a layered medium, with the lossy, dispersive layers representing the typical layered character of many soils. We examine wave phenomenology to identify target features that may be exploited in target detection algorithms. Accordingly, we examine the target signature in both the frequency and time domain, as well as in the SAR image domain. For this study, we restrict ourselves to a single UXO target, i.e., a 155 mm shell, an arbitrary cylindrical metal mine, and a cylindrical plastic mine (TM- 62P3 anti-tank mine). Results show that for the UXO, a strong correlation exists between the target signature in the frequency domain and the target orientation. For the rotationally symmetric mines, despite their small size, results show that these targets contain isolated scattering centers due to the wide bandwidth of the incident pulse. Further, these scattering centers can be used to deconstruct the backscattered time waveform into closely spaced simple wave objects that leads to an observable interference pattern in the frequency domain. This relatively simple scattering deconstruction lends itself well to target detection and discrimination.

Metasurfaces offer precise control over various degrees of freedom of electromagnetic (EM) waves. However, their capability to manipulate surface and space EM waves simultaneously remains a formidable challenge. Here, this challenge is addressed by integrating metasurfaces with topological photonics, resulting in topological metasurfaces that can control both surface and full‐space waves. The topological metasurface is composed of reusable and modular meta‐atoms, exhibiting programmability, reconfigurability, detachability, and scalability. The low‐cost and low‐power platform has big capability to control both surface and full‐space waves, enabling multiple functions such as focusing, holographic imaging, wireless communication, sensing, and object classification. The efficient manipulations of transmitted and reflected space waves are experimentally demonstrated by encoding the modular meta‐atoms and showcasing the programmable control of surface waves by constructing topologically protected multi‐channel propagation pathways. The topological metasurface redefines the paradigm of EM wave manipulation to provide unprecedented opportunities for holographic imaging, object sensing, and wireless signal enhancement, paving the way for intelligent and multifunctional EM controls for next‐generation sensor and communication systems.

The correct modeling and measurement of ultra-wideband (UWB) radio signal are a critical issue to evaluate the electromagnetic (EM) emission of any communication system based on this technology. In this paper (Part I), UWB radio communication systems based on impulse radio (IR) and multiband orthogonal frequency division multiplex (MB-OFDM) technologies are characterized by simulations and experiments in both frequency and time domains. The EM characteristics of UWB radio are measured by different methods (conducted and radiative) and in different environments (anechoic and reverberation chambers).

Heart period variability has been considered for clinical assessment of autonomic function, determining the presence of haemorrhage or disease states, and for predicting mortality from traumatic injury. However, for heart period variability to be clinically useful, a number of important methodological issues should be addressed, including the minimum number of R-R intervals (RRI) required for accurate derivation, and the reproducibility of these metrics. ECGs were recorded for > or =10 min in 18 resting, supine subjects (12 M/6 F; 19-55 years). Heart period variability analyses included 21 time, frequency and complexity domain metrics. For assessment of minimum RRIs required, measurements were made from ECG recordings of 5 min down to 30 s for time and frequency domain metrics, and from 800 RRIs down to 100 RRIs for complexity metrics, by methodical truncation of the data set. Inter-subject variability was assessed by calculating the range and co-efficient of variation (%CV) across all subjects. Two independent 30 s or 100 RRI ECG segments were used to assess intra-subject variability via calculation of %CV in each subject. Six time and frequency domain metrics were robust down to 30 s of data, while five complexity metrics were robust down to 100 RRIs. All time and frequency domain metrics (except for RRI) exhibited high inter-subject variability (CVs > or = 30.0%), while five of eleven complexity metrics displayed low inter-subject variability (CVs < or = 8.5%). In the assessment of intra-subject variability in metrics valid with 30 s or 100 RRIs of ECG, only one time domain and four complexity metrics had CVs < 10%. Metrics that are highly reproducible and require few RRIs are advantageous for patient monitoring as less time is required to assess physiological status and initiate early interventions. Based on our analyses from healthy, resting humans, we have identified a select cohort of heart period variability metrics that performed well in regards to these two criteria.

With the rapid growth in the number of mobile devices and user connectivity, the demand for higher system capacity and improved quality-of-service is required. As the demand for high-speed wireless communication grows, numerous modulation techniques in the frequency, temporal, and spatial domains, such as orthogonal frequency division multiplexing (OFDM), time division multiple access (TDMA), space division multiple access (SDMA), and multiple-input multiple-output (MIMO), are being developed. Along with those approaches, electromagnetic waves’ orbital angular momentum (OAM) is attracting attention because it has the potential to boost the wireless communication capacity. Antenna electromagnetic radiation can be described by a sum of Eigen functions with unique eigenvalues, as is well known. In order to address such issues, the millimeter-wave (mmWave) communication is proposed which is considered as one of the potential technology for 5G wireless networks. The intrinsic feature of all electromagnetic waves is OAM. The OAM beams’ unique qualities have led to a slew of new uses. Broadband OAM generators, on the other hand, have gotten very little attention, especially in the mmWave frequency band. The use of OAM in conjunction with mmWave can reduce the beam power loss, enhance the received signal quality, and hence increase the system capacity. The transmitter and receiver antennas must be coaxial and parallel to achieve precise mode detection. The proposed mmWave integrated with OAM system model is discussed in this study. The channel model is created using the channel transition characteristics. The simulation results demonstrate that the proposed system model is a good way to boost the system capacity.

In recent years, due to the rapid convergence of multimedia services, Internet and wireless communications, there has been a growing trend of heterogeneity (in terms of channel bandwidths, mobility levels of terminals, end-user quality-of-service (QoS) requirements) for emerging integrated wired/wireless networks. Moreover, in nowadays systems, a multitude of users coexists within the same network, each of them with his own QoS requirement and bandwidth availability. In this framework, embedded source coding allowing partial decoding at various resolution is an appealing technique for multimedia transmissions. This dissertation includes my PhD research, mainly devoted to the study of embedded multimedia bitstreams in heterogenous networks, developed at the University of Bologna, advised by Prof. O. Andrisano and Prof. A. Conti, and at the University of California, San Diego (UCSD), where I spent eighteen months as a visiting scholar, advised by Prof. L. B. Milstein and Prof. P. C. Cosman. In order to improve the multimedia transmission quality over wireless channels, joint source and channel coding optimization is investigated in a 2D time-frequency resource block for an OFDM system. We show that knowing the order of diversity in time and/or frequency domain can assist image (video) coding in selecting optimal channel code rates (source and channel code rates). Then, adaptive modulation techniques, aimed at maximizing the spectral efficiency, are investigated as another possible solution for improving multimedia transmissions. For both slow and fast adaptive modulations, the effects of imperfect channel estimation errors are evaluated, showing that the fast technique, optimal in ideal systems, might be outperformed by the slow adaptive modulation, when a real test case is considered. Finally, the effects of co-channel interference and approximated bit error probability (BEP) are evaluated in adaptive modulation techniques, providing new decision regions concepts, and showing how the widely used BEP approximations lead to a substantial loss in the overall performance.

This letter addresses the application of Linear Dispersion Codes (LDC) in space and frequency domains in Single Carrier-Frequency Domain Equalization (SCFDE) systems. Space-frequency (SF)-LDCs are more suitable than space-time (ST) LDC in high mobility environments. However, the application of LDCs in space and frequency domains in SCFDE systems is not straightforward as in orthogonal frequency division multiplexing (OFDM) systems because in this case there is no direct access to subcarriers at the transmitter. This letter shows that it is possible to induce a target SF symbol dispersion in SCFDE by using a simple linear pre-coder and a conventional LDC that spreads the symbols in time and space domains according to specific ST dispersion matrices. The letter shows how to derive the ST dispersion matrices to be used at the transmitter as a function of the dispersion matrices describing the target SF dispersion. The presented procedure can be applied to both pure transmit diversity and pure multiplexing schemes, which are special cases of LDCs. Therefore, the proposed scheme provides a low complexity implementation of any dispersion in space and frequency over SCFDE systems, which alternatively would require the use of FFT/IFFT also at the transmitter side. The letter also shows a performance comparison of SF-LDCs and ST-LDCs in a typical propagation environment for future radio systems. The comparison confirms the suitability of using the dispersion in frequency rather than time for a wide range of coherence bandwidths.

We describe the main properties of the EQUATOR airborne geophysical system and how the system can be employed to solve some engineering and environmental problems. To date, the EQUATOR system has been used for groundwater search in 2014 and 2015 in Siberia. The name “EQUATOR” originates from the intention to EQUATE, or to balance time and frequency domain approaches in airborne electromagnetics, which is why the system was originally designed. To the best of our knowledge, EQUATOR is the only system to collect electromagnetic data both in time and in frequency domains. We further explain the difference between the two methods on some numerical and field examples. Also we describe some advantages of their coupling. In particular, by virtue of our approach, a numerically more robust solution of the one-dimensional electromagnetic inverse problem may be achieved. The recorded full-time measurements are further converted to in-phase, quadrature and off-time responses, as opposed to standard frequency or time domain solutions, which have been widely adapted within the industry. When inverting the data, our main focus is within the top 100 m of the Earth, which are the most relevant for engineering and environmental studies. We emphasize that a combined use of frequency and time domain data gives more detailed information about geological structures in the near-surface. As an example, we present some case studies obtained over a platform (Siberia) and a crystalline shield (Western Africa) setting. We further suggest using these results in such near-surface studies as sediment thickness estimation, soil state analysis, groundwater search, and geological structural analysis.

Search coil magnetometers are one of the primary tools used to study the magnetic component of low‐frequency electromagnetic waves in space. Their relatively small size, mass, and power consumption, coupled with a good frequency range and sensitivity, make them ideal for spaceflight applications. The basic design of a search coil magnetometer consists of many thousands of turns of wire wound on a high permeability core. When a time‐varying magnetic field passes through the coil, a time‐varying voltage is induced due to Faraday's law of magnetic induction. The output of the coil is usually attached to a preamplifier, which amplifies the induced voltage and conditions the signal for transmission to the main electronics (usually a low‐frequency radio receiver). Search coil magnetometers are usually used in conjunction with electric field antenna to measure electromagnetic plasma waves in the frequency range of a few hertz to a few tens of kilohertzs. Search coil magnetometers are used to determine the properties of waves, such as comparing the relative electric and magnetic field amplitudes of the waves, or to investigate wave propagation parameters, such as Poynting flux and wave normal vectors. On a spinning spacecraft, they are also sometimes used to determine the background magnetic field. This paper presents some of the basic design criteria of search coil magnetometers and discusses design characteristics of sensors flown on a number of spacecraft.