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Terahertz (THz) fields are increasingly being used to address the critical challenges associated with achieving high data rates and rapid communication. In this study, a hybrid plasmonic THz waveguide is designed and analysed operating in the 2.5–3.5 THz frequency range. The waveguide is constructed using gallium arsenide as the high-refractive-index core, surrounded by aluminium arsenide and silver placed on a high-density polyethylene (HDPE) substrate. Graphene is strategically positioned between the HDPE layers to enhance light confinement. The mode properties of the proposed waveguide are simulated with Comol Multiphysics using the finite-element method and show unique characteristics. Observation of the simulated results at 2.5–3.5 THz reveals a high effective refractive index of 3.79, a maximum effective mode area of 1.88 mm2, a high birefringence of 0.2, a low dispersion of 0.10 ps THz−1 cm−1, a high mode field diameter of 15.8 mm, a high beat length of 123 mm and a low confinement loss of 1.79 × 10−9 mm−1. These features make the proposed waveguide suitable for applications in photonic integrated circuits for THz communications. [ABSTRACT FROM AUTHOR]

This paper investigates the performance of dual-hop unmanned aerial vehicle (UAV)-assisted communication channels, employing a decode-and-forward (DF) relay architecture. The system leverages terahertz (THz) communication for the primary hop and visible light communication (VLC) for the secondary hop. We conduct an in-depth analysis by deriving closed-form expressions for the end-to-end (E2E) bit error rate (BER). Additionally, we use a Monte Carlo simulation approach to generate best-fitting curves, validating our analytical expressions. A performance evaluation through BER and outage probability metrics demonstrates the effectiveness of the proposed system. Specifically, our results indicate that the proposed system outperforms Free-Space Optics (FSO)-VLC and Radio-Frequency (RF)-VLC at a higher signal-to-noise ratio (SNR). The results of this study provide valuable insights into the feasibility and limitations of UAV-assisted THz-VLC communication systems. [ABSTRACT FROM AUTHOR]

This paper demonstrates a 120 Gbit/s 64-Quadrature Amplitude Modulation (64-QAM) transmission link using all-electronics sub-harmonic mixers for the transmitter and the receiver operating in the 300 GHz band. The wireless signal is propagated through a non-line-of-sight free space link where reflections from 2 mirrors provide a channel length of 3 m over-the-air transmission between the transmitter and the receiver modules. Here, we demonstrate that an accurate correction of different error sources such as channel impairments of the 300 GHz wireless link as well as the combined effects of hardware amplitude and phase impairments can successfully be achieved for the high spectral-efficiency 64-QAM modulation scheme. The measured bit error ratio of the calibrated testbed is under the soft-decision forward error correction (SD-FEC) threshold of $2.7\times 10^{-2}$ up to 120 Gbit/s with 20% overhead giving a net data rate of 100 Gbit/s post-FEC. To the best of our knowledge, this is the highest 64-QAM performance achieved using an electronics-based transmitter in the 300 GHz band.

Terahertz (THz) communication is a highly promising solution for addressing the ultra-high data rate requirements of future sixth-generation (6G) wireless systems. However, the unfavorable frequency-dependent channel characteristics of THz communication pose a significant challenge in realizing this promising technology. In this paper, we present a novel solution to this challenge by proposing a wideband THz system featuring a unique THz-specific digital baseband waveform design tailored to the distinctive channel characteristics of the THz spectrum. To address the frequency-dependent challenges posed by the wideband THz channel and the spectral efficiency loss inherent in conventional orthogonal frequency division multiplexing (OFDM) systems due to cyclic prefix overhead, we propose a THz system with beamforming incorporating a multi-band OFDM (MB-OFDM) based waveform design using a filter-bank based channel model that slices the wideband channel into smaller frequency-independent subbands for ultra-wideband THz communication. Furthermore, this work introduces a novel squint model taking into account the printed-circuit-board (PCB) impairments and circuit imperfections, which have not been considered before. We also propose an all-digital mitigation scheme with this model. We propose a channel estimation algorithm using a three-level adaptive method with an auto-regressive (AR) model for exploiting the frequency dependency among the intra and inter-narrow subbands. Apart from these key contributions, we propose a THz environment-aware precoder to mitigate the wideband effect in the THz channel, specifically the subband-specific path loss and environment-related effect, and balance the overall gains across the band. We have also proposed to optimize the number of subbands and zero-padding in MB-OFDM waveform based on the minimum bit error rate (MBER) criterion. Numerical simulations are carried out to evaluate the performance of the proposed schemes demonstrating their feasibility and effectiveness for wideband THz communication with results showing a lower peak-to-average power ratio (PAPR) for the proposed waveform as compared to conventional OFDM.

Due to its superior performance, Orthogonal Chirp Division Multiplexing (OCDM) has recently gained attention as a potential replacement for Orthogonal Frequency Division Multiplexing (OFDM) in beyond-5G systems. In this paper, we provide an analytical characterization of OCDM signals, elucidating the theoretical principles that enable their numerical generation through the Inverse Discrete Fresnel Transform (IDFnT), despite the presence of severe frequency-domain aliasing that substantially distorts the signal at the transmitter output. Furthermore, in light of the proposed utilization of the THz band in beyond-5G systems, we investigate the performance of OCDM in this frequency range in the presence of thermal, molecular, and phase noise. To model the latter, which is expected to be a significant challenge at THz frequencies, we take as a reference an actual Phase Locked Loop (PLL) oscillator operating at 237.7 GHz. The numerical results reveal the achievable performance of OCDM as a function of several key factors, including the modulation order, the bandwidth, the number of chirps constituting the signal, the oscillator parameters, the channel model, and the use of techniques aimed at mitigating the impact of phase noise. The findings are compared with those of OFDM, which is regarded as a benchmark due to its adoption in 4G and 5G systems, and demonstrate the superior performance of OCDM also in the presence of significant phase noise.

This paper investigates the performance of dual-hop unmanned aerial vehicle (UAV)-assisted communication channels, employing a decode-and-forward (DF) relay architecture. The system leverages terahertz (THz) communication for the primary hop and visible light communication (VLC) for the secondary hop. We conduct an in-depth analysis by deriving closed-form expressions for the end-to-end (E2E) bit error rate (BER). Additionally, we use a Monte Carlo simulation approach to generate best-fitting curves, validating our analytical expressions. A performance evaluation through BER and outage probability metrics demonstrates the effectiveness of the proposed system. Specifically, our results indicate that the proposed system outperforms Free-Space Optics (FSO)-VLC and Radio-Frequency (RF)-VLC at a higher signal-to-noise ratio (SNR). The results of this study provide valuable insights into the feasibility and limitations of UAV-assisted THz-VLC communication systems.

A novel graphene antenna composed of a graphene dipole and four auxiliary graphene sheets oriented at 90 ∘ to each other is proposed and analyzed. The sheets play the role of reflectors. A detailed group-theoretical analysis of symmetry properties of the discussed antennas has been completed. Through electric field control of the chemical potentials of the graphene elements, the antenna can provide a quasi-omnidirectional diagram, a one- or two-directional beam regime, dynamic control of the beam width and, due to the vertical orientation of the dipole with respect to the base substrate, a 360 ∘ beam steering in the azimuth plane. An additional graphene layer on the base permits control of the radiation pattern in the θ -direction. Radiation patterns in different working states of the antenna are considered using symmetry arguments. We discuss the antenna parameters such as input reflection coefficient, total efficiency, front-to-back ratio, and gain. An equivalent circuit of the antenna is suggested. The proposed antenna operates at frequencies between 1.75 THz and 2.03 THz. Depending on the active regime defined by the chemical potentials set on the antenna graphene elements, the maximum gain varies from 0.86 to 1.63. [ABSTRACT FROM AUTHOR]

At the dawn of the next-generation wireless systems and networks, massive multiple-input multiple-output (MIMO) in combination with leading-edge technologies, methodologies, and architectures are poised to be a cornerstone technology. Capitalizing on its successful integration and scalability within 5G and beyond, massive MIMO has proven its merits and adaptability. Notably, a series of evolutionary advancements and revolutionary trends have begun to materialize in recent years, envisioned to redefine the landscape of future 6G wireless systems and networks. In particular, the capabilities and performance of future massive MIMO systems will be amplified through the incorporation of cutting-edge technologies, structures, and strategies. These include intelligent omni-surfaces (IOSs)/intelligent reflecting surfaces (IRSs), artificial intelligence (AI), Terahertz (THz) communications, and cell-free architectures. In addition, an array of diverse applications built on the foundation of massive MIMO will continue to proliferate and thrive. These encompass wireless localization and sensing, vehicular communications, non-terrestrial communications, remote sensing, and inter-planetary communications, among others. [ABSTRACT FROM AUTHOR]

Future cellular networks are expected to benefit from terahertz (THz) frequency bands, which enable high-speed and low-latency wireless connectivity, but several challenges have arisen in utilizing THz bands. In this paper, we first investigate channel characteristics and their modeling for THz bands, highlighting new opportunities and emerging challenges. In this context, we discuss the channel characteristics that become more prominent at THz frequencies than at lower microwave frequencies, such as atmospheric attenuation, scattering, and frequency selectivity. We also review various path-loss and scattering models for THz communications. We further survey the radio frequency front-end nonlinearities that affect THz communications and their modeling for multiple-input multiple-output (MIMO) systems. We then review massive MIMO and hybrid beamforming techniques, and their applicability for THz communications. We identify the challenges that arise from operating at ultra-high frequencies, such as beam blockage, power consumption of large-scale arrays, and beam squint. Finally, we provide an overview of emerging intelligent reflecting surface (IRS) technologies and their potential for enhancing THz wireless networks. We investigate how IRS and massive MIMO technologies can be integrated into THz wireless networks and discuss possible solutions to overcome the limitations that affect the throughput and efficiency of such systems.

In recent years, terahertz (THz) systems have become an increasingly popular area of research thanks to their unique properties such as extremely high data rates towards Tb/s, submillimeter localization accuracy, high resolution remote sensing of materials, and remarkable advances in photonics and electronics technologies. This article traces the progress of THz measurements, antennas and simulations, from historical milestones to the current state of research and provides an outlook on the remaining challenges.

Future Unmanned Aerial Vehicle (UAV)-assisted wireless communication systems are expected to utilize wide bandwidths available at terahertz (THz) frequencies to enhance system throughput. To compensate for the severe path loss in the THz band, it is essential to have a multitude of antennas in the UAV to generate narrow beams for directional transmission. However, narrow beams severely limit its spatial coverage, which greatly affects the efficiency of large-scale access UAV-assisted THz systems. Moreover, the combination of massive antennas and large bandwidth at THz makes the misalignment of the beams caused by beam squint non-negligible and also high energy consumption. UAV-assisted communication technology can effectively increase spatial coverage and provide reliable LoS communication links. In addition, reducing the number of radio frequency (RF) chains while ensuring the number of transmitted data streams and space division multiplexing capability is also an effective way to reduce energy consumption in the UAV communication. In this paper, a single RF chain uniform planar array (UPA) with true-time-delays (TTDs) is equipped on the UAV to achieve two dimensional (2D) beams and split spatial beams to improve transmission efficiency. We analyze the 2D beam squint of the UPA and design a time-delay phased UPA for UAV-assisted THz communication systems. By introducing TTDs between the single RF chain and phase shifters, the beam squint can be controlled flexibly by introducing the delay between each antenna. When TTDs are arranged in both the horizontal and vertical dimensions, the coverage of the beams becomes more complicated compared to uniform linear arrays (ULA). Simulation results show that the proposed time-delay phased UPA can achieve better performance in both single-beam and multi-beam modes for single user and multi-user scenarios compared with conventional phased UPA, respectively. In addition, we propose frequency division beam multiple access (FDBMA) multi access technology, which achieves more efficient multi access by reusing resources from different frequency beam pairs. Finally, the results also show that the enlargement of the beamwidth through the proposed FDBMA strategy can also increase the performance in multi-user scenarios.

Design and assessment of THz communications systems, which will form an essential part of 6G, require an understanding of the propagation channels the systems will operate in. This paper presents investigations of the channel characteristics in various scenarios at 145 GHz, which is the band currently envisioned for the first round of deployments. In particular, we review several extensive measurement campaigns performed by the University of Southern California in both outdoor and indoor environments. We present the measurement and evaluation methodology and sample results that illustrate the dominant propagation effects in different environments. We then summarize the parameters of the statistical channel models for path loss, delay dispersion, and angular dispersion. Based on these results, we find that even in NLoS (non-line-of-sight) situations, Gbit/s communications can be sustained over a 100 m distance; that (for an antenna gain of 20 dB), there is considerable delay dispersion, requiring tens of equalizer taps, and that angular dispersion is significant in both LoS and NLoS situations. The channel parameters can be thus used as a basis for system design and evaluation under realistic operating conditions.

The prospects of utilizing single-carrier (SC) and multi-carrier (MC) waveforms in future terahertz (THz)-band communication systems remain unresolved. On the one hand, the limited multi-path components at high frequencies result in frequency-flat channels that favor low-complexity wideband SC systems. On the other hand, frequency-dependent molecular absorption and transceiver characteristics and the existence of multi-path components in indoor sub-THz systems can still result in frequency-selective channels, favoring off-the-shelf MC schemes such as orthogonal frequency-division multiplexing (OFDM). Variations of SC/MC designs result in different THz spectrum utilization, but spectral efficiency is not the primary concern with substantial available bandwidths; baseband complexity, power efficiency, and hardware impairment constraints are predominant. This paper presents a comprehensive study of SC/MC waveforms for THz communications, utilizing an accurate wideband THz channel model and highlighting the various performance and complexity trade-offs of the candidate schemes. Simulations demonstrate that discrete-Fourier-transform spread orthogonal time-frequency space (DFT-s-OTFS) achieves a lower peakto- average power ratio (PAPR) than OFDM and OTFS and enhances immunity to THz impairments and Doppler spreads, but at an increased complexity cost. Moreover, DFT-s-OFDM is a promising candidate that increases robustness to THz impairments and phase noise (PHN) at a low PAPR and overall complexity.

A novel graphene antenna composed of a graphene dipole and four auxiliary graphene sheets oriented at 90∘ to each other is proposed and analyzed. The sheets play the role of reflectors. A detailed group-theoretical analysis of symmetry properties of the discussed antennas has been completed. Through electric field control of the chemical potentials of the graphene elements, the antenna can provide a quasi-omnidirectional diagram, a one- or two-directional beam regime, dynamic control of the beam width and, due to the vertical orientation of the dipole with respect to the base substrate, a 360∘ beam steering in the azimuth plane. An additional graphene layer on the base permits control of the radiation pattern in the θ-direction. Radiation patterns in different working states of the antenna are considered using symmetry arguments. We discuss the antenna parameters such as input reflection coefficient, total efficiency, front-to-back ratio, and gain. An equivalent circuit of the antenna is suggested. The proposed antenna operates at frequencies between 1.75 THz and 2.03 THz. Depending on the active regime defined by the chemical potentials set on the antenna graphene elements, the maximum gain varies from 0.86 to 1.63.

The terahertz (THz) band is expected to become a key technology to meet the ever-increasing traffic demand for future 6G wireless communications, and a lot of efforts have been paid to develop its capacity. However, few studies have been concerned with the transmission security of such ultra-high-speed THz wireless links. In this paper, we comprehensively investigate the physical layer security (PLS) of a THz communication system in the presence of multiple eavesdroppers and beam scattering. The method of moments (MoM) was adopted so that the eavesdroppers' channel influenced by the PEC can be characterized. To establish a secure link, the traditional beamforming and artificial noise (AN) beamforming were considered as transmission schemes for comparison. For both schemes, we analyzed their secrecy transmission probability (STP) and ergodic secrecy capacity (ESC) in non-colluding and colluding cases, respectively. Numerical results show that eavesdroppers can indeed degrade the secrecy performance by changing the size or the location of the PEC, while the AN beamforming technique can be an effective candidate to counterbalance this adverse effect. [ABSTRACT FROM AUTHOR]

Abstract This paper documents a simple parametric polynomial line-of-sight channel model for 100–450 GHz band. The band comprises two popular beyond fifth generation (B5G) frequency bands, namely, the D band (110–170 GHz) and the low-THz band (around 275–325 GHz). The main focus herein is to derive a simple, compact, and accurate molecular absorption loss model for the 100–450 GHz band. The derived model relies on simple absorption line shape functions that are fitted to the actual response given by complex but exact database approach. The model is also reducible for particular sub-bands within the full range of 100–450 GHz, further simplifying the absorption loss estimate. The proposed model is shown to be very accurate by benchmarking it against the exact response and the similar models given by International Telecommunication Union Radio Communication Sector. The loss is shown to be within ±2 dBs from the exact response for one kilometer link in highly humid environment. Therefore, its accuracy is even much better in the case of usually considered shorter range future B5G wireless systems.

TeraHertz (THz) communications can satisfy the high data rate demand with massive bandwidth. However, severe path attenuation and hardware imperfection greatly alleviate its performance. Therefore, we utilize the reconfigurable intelligent surface (RIS) technology and investigate the RIS-aided THz communications. We first prove that the small-scale amplitude fading of THz signals can be accurately modeled by the fluctuating two-ray distribution based on two THz signal measurement experiments conducted in a variety of different scenarios. To optimize the phase-shifts at the RIS elements, we propose a novel swarm intelligence-based method that does not require full channel estimation. We then derive exact statistical characterizations of end-to-end signal-to-noise plus distortion ratio (SNDR) and signal-to-noise ratio (SNR). Moreover, we present asymptotic analysis to obtain more insights when the SNDR or the number of RIS’s elements is high. Finally, we derive analytical expressions for the outage probability and ergodic capacity. The tight upper bounds of ergodic capacity for both ideal and non-ideal radio frequency chains are obtained. It is interesting to find that increasing the number of RIS’s elements can significantly improve the THz communications system performance. For example, the ergodic capacity can increase up to 25% when the number of elements increases from 40 to 80, which incurs only insignificant costs to the system. [ABSTRACT FROM AUTHOR]

A transparentOptical-subTHz-Optical link providing record-high single line rates of 240 Gbit/s and 192 Gbit/s on a single optical carrier over distances from 5 to 115 m is demonstrated. Besides a direct mapping of the optical to a 230 GHz subTHz-carrier frequency by means of a uni-traveling carrier (UTC) photodiode, we demonstrate direct conversion of data from the subTHz domain back to the optical domain by a plasmonic modulator. It is shown that the subTHz-to-optical upconversion can even be performed at good quality without any electrical amplifiers. Finally, at the receiver, the local oscillator is employed to directly map the optical signal back to the electrical baseband within a coherent receiver. [ABSTRACT FROM AUTHOR]

The problem of efficient ultra-massive multiple-input multiple-output (UM-MIMO) data detection in terahertz (THz)-band non-orthogonal multiple access (NOMA) systems is considered. We argue that the most common THz NOMA configuration is power-domain superposition coding over quasi-optical doubly-massive MIMO channels. We propose spatial tuning techniques that modify antenna subarray arrangements to enhance channel conditions. Towards recovering the superposed data at the receiver side, we propose a family of data detectors based on low-complexity channel matrix puncturing, in which higher-order detectors are dynamically formed from lower-order component detectors. The proposed solutions are first detailed for the case of superposition coding of multiple streams in point-to-point THz MIMO links. Then, the study is extended to multi-user NOMA, in which randomly distributed users get grouped into narrow cell sectors and are allocated different power levels depending on their proximity to the base station. Successive interference cancelation is shown to be carried with minimal performance and complexity costs under spatial tuning. Approximate bit error rate (BER) equations are derived, and an architectural design is proposed to illustrate complexity reductions. Under typical THz conditions, channel puncturing introduces more than an order of magnitude reduction in BER at high signal-to-noise ratios while reducing complexity by approximately 90%.

Future wireless networks designed to operate in the millimeter-wave and terahertz bands are expected to be highly assisted by Reconfigurable Intelligent Surfaces (RIS). The role of the RIS will be to mediate possible non-line-of-sight link by redirecting the incident beam from the transmitter to the receiver and possibly modifying its characteristics, in order to optimize the beamforming efficiency and to maximize the signal power at the receiver. Therefore, it is crucial to understand what are the bounds imposed on the received power and how these bounds depend on the system design parameters. In this paper we show that, contrary to typical line-of-sight links, the increase of the transmitter gain does not always guarantee power increase at the receiver, even for an infinitely large RIS, and we explain how the RIS size can further affect the received power. We present an analytical model that captures the performance of the RIS-aided link in the limit of very large RIS, and we demonstrate numerical examples that provide insight on the interplay between the RIS size and the properties of the transmitter beam.

Nanonetworks are composed of interacting nano-nodes, whose size ranges from several hundred cubic nanometers to several cubic micrometers. The extremely constrained computational resources of nano-nodes, the fluctuations in their energy caused by energy harvesting processes, and their very limited transmission range at Terahertz (THz)-band frequencies (0.1-10 THz), make the design of routing protocols in nanonetworks very challenging. A multi-hop deflection routing algorithm based on reinforcement learning (MDR-RL) is proposed in this paper to dynamically and efficiently explore the routing paths during packet transmissions. First, new routing and deflection tables are implemented in nano-nodes, so that nano-nodes can deflect packets to other neighbors when route entries in the routing table are invalid. Second, one forward updating scheme and two feedback updating schemes based on reinforcement learning are designed to update the tables, namely, on-policy and off-policy updating schemes. Finally, extensive simulations in networks simulator-3 are conducted to analyze the performance of MDR-RL using different updating policies, as well as to compare the performance with other machine learning routing algorithms based on Neural Networks and Decision Tree. The results show that the MDR-RL can increase the packet delivery ratio and number of delivered packets, and can decrease the packet average hop count. [ABSTRACT FROM AUTHOR]

Although Polarization Modulation offers a high spectral efficiency, it has been not exploited much in modern communication systems because of the involvement of high switching speeds and complexity of associated hardware. We propose a dynamically controllable graphene metasurface capable to switch the polarization state of incident THz waves in real-time. The metasurface is designed by patterning two-dimensional graphene sheets with Fano-resonant chiral unit cells. Since the reflectance spectrum is characterized with co and cross polarized fields that bear asymmetric Fano line-shapes, several combinations of linear and elliptical polarization states are observed in a narrowband spectrum. At a fixed frequency, the electrostatic tunability property of graphene allows to switch between different polarization states by varying the chemical potential between 500 and 700 meV. The polarization state modulation with the proposed chiral graphene based metasurface is applied to implement a quaternary modulated digital communication system. Full-wave simulation results show the strong possibility of polarization modulation in THz communication systems. Graphene metasurfaces on account of the high electron mobility and discrete Fermi levels offer high switching speeds and seamless integration with digital systems. [ABSTRACT FROM AUTHOR]

Following recent advances in terahertz (THz) technology, there is a consensus on the crucial role of THz communications in the next generation of wireless systems. Aiming at catalyzing THz communications research, we propose TeraMIMO, an accurate stochastic MATLAB simulator of statistical THz channels. We simulate ultra-massive multiple-input multiple-output antenna configurations as critical infrastructure enablers that overcome the limitation in THz communications distances. We consider both line-of-sight and multipath components and propose frequency- and delay-domain implementations for single- and multi-carrier paradigms in both time-invariant and time-variant scenarios. We implement exhaustive molecular absorption computations based on radiative transfer theory alongside alternative sub-THz approximations. We further model THz-specific constraints, including wideband beam split effects, spherical wave propagation, and misalignment fading. We verify TeraMIMO by analogy with measurement-based channel models in the literature and ergodic capacity analysis. We introduce a graphical user interface and a guide for using TeraMIMO in THz channel generation and analyses. [ABSTRACT FROM AUTHOR]

The authors introduce four kinds of terahertz photonics components based on photonic integrated circuits (PICs). A PIC‐based integrated optoelectronic synthesiser for THz communications is described, which can be tuned continuously over the range 0.254–2.723 THz using photomixing. A laterally‐coupled dual‐grating distributed feedback laser (DFB) diode integrated with an electroabsorption modulator is used to generate an 820 GHz beat signal. THz signal production is reported using a dual‐wavelength DFB diode laser with a two‐section phase‐shifted sampled Bragg grating. Finally, a THz source at 640 GHz, based on a sampled grating distributed Bragg reflector semiconductor mode‐locked laser diode, is reported offering superior reproducibility, controllability, and a wider operation range than other reported mode‐locked THz laser diodes. Each of these sources is a monolithic construction emitting light at 1.5 µm. The light can be amplified in an erbium‐doped fibre amplifier, delivered over silica optical fibre and used to generate THz radiation via a photodiode antenna or photoconductive antenna in a remote location.

The Internet of Everything (IoE) is a recently introduced information and communication technology (ICT) framework promising for extending the human connectivity to the entire universe, which itself can be regarded as a natural IoE, an interconnected network of everything we perceive. The countless number of opportunities that can be enabled by IoE through a blend of heterogeneous ICT technologies across different scales and environments and a seamless interface with the natural IoE impose several fundamental challenges, such as interoperability, ubiquitous connectivity, energy efficiency, and miniaturization. The key to address these challenges is to advance our communication technology to match the multi-scale, multi-modal, and dynamic features of the natural IoE. To this end, we introduce a new communication device concept, namely the universal IoE transceiver, that encompasses transceiver architectures that are characterized by multi-modality in communication (with modalities such as molecular, RF/THz, optical and acoustic) and in energy harvesting (with modalities such as mechanical, solar, biochemical), modularity, tunability, and scalability. Focusing on these fundamental traits, we provide an overview of the opportunities that can be opened up by micro/nanoscale universal transceiver architectures towards realizing the IoE applications. We also discuss the most pressing challenges in implementing such transceivers and briefly review the open research directions. Our discussion is particularly focused on the opportunities and challenges pertaining to the IoE physical layer, which can enable the efficient and effective design of higher-level techniques. We believe that such universal transceivers can pave the way for seamless connection and communication with the universe at a deeper level and pioneer the construction of the forthcoming IoE landscape.Index Terms– Internet of Everything, Universal IoE Transceiver, Interoperability, Multi-modality, Hybrid Energy Harvesting, Molecular Communications, THz Communications, Graphene and related nanomaterials.

Terahertz (THz) communication is a promising technique for chip-to-chip communication and wireless personal area networks. In this paper, we present an experimental study and design to realize such THz communication systems. We develop two different chip sets for on-off-keying (OOK) modulation based THz transceivers which include carrier generators, modulators, THz amplifiers, and baseband amplifiers. Specifically, the first chip set integrates the circuit blocks for the OOK modulation without the THz amplifier for short-range communication. In addition, the second chip set design includes the THz amplifier modules to extend the coverage of transmission. For these two chip sets, we experimentally demonstrate the feasibility of the wireless communication at THz frequency bands and assess performance using the bit error rate (BER) analysis. We estimate the BER by calculating the signal-to-noise ratio (SNR) based on the eye diagram and compare with actual BER measurements and Monte Carlo simulations. We also address the impact of the distance, the transmit power, and the data rate for the proposed THz transceivers based on the link budget analysis, and confirm the accuracy of the derived BER expression. [ABSTRACT FROM AUTHOR]

The terahertz (THz) band is expected to become a key technology to meet the ever-increasing traffic demand for future 6G wireless communications, and a lot of efforts have been paid to develop its capacity. However, few studies have been concerned with the transmission security of such ultra-high-speed THz wireless links. In this paper, we comprehensively investigate the physical layer security (PLS) of a THz communication system in the presence of multiple eavesdroppers and beam scattering. The method of moments (MoM) was adopted so that the eavesdroppers’ channel influenced by the PEC can be characterized. To establish a secure link, the traditional beamforming and artificial noise (AN) beamforming were considered as transmission schemes for comparison. For both schemes, we analyzed their secrecy transmission probability (STP) and ergodic secrecy capacity (ESC) in non-colluding and colluding cases, respectively. Numerical results show that eavesdroppers can indeed degrade the secrecy performance by changing the size or the location of the PEC, while the AN beamforming technique can be an effective candidate to counterbalance this adverse effect.

This paper documents a simple parametric polynomial line-of-sight channel model for 100–450 GHz band. The band comprises two popular beyond fifth generation (B5G) frequency bands, namely, the D band (110–170 GHz) and the low-THz band (around 275–325 GHz). The main focus herein is to derive a simple, compact, and accurate molecular absorption loss model for the 100–450 GHz band. The derived model relies on simple absorption line shape functions that are fitted to the actual response given by complex but exact database approach. The model is also reducible for particular sub-bands within the full range of 100–450 GHz, further simplifying the absorption loss estimate. The proposed model is shown to be very accurate by benchmarking it against the exact response and the similar models given by International Telecommunication Union Radio Communication Sector. The loss is shown to be within ±2 dBs from the exact response for one kilometer link in highly humid environment. Therefore, its accuracy is even much better in the case of usually considered shorter range future B5G wireless systems. [ABSTRACT FROM AUTHOR]

Wireless connectivity in airplanes is becoming more important, demanded, and common. One of the largest bottlenecks with the in-flight Internet is that the airplane is far away from both the satellites and the ground base stations during most of the flight time. Maintaining a reliable and high-rate wireless connection with the airplane over such a long-range link thus becomes a challenge. Microwave frequencies allow for long link distances but lack the data rate to serve up to several hundreds of potential onboard customers. Higher bands in the millimeter-wave spectrum (30 GHz–300 GHz) have, therefore, been utilized to overcome the bandwidth limitations. Still, the per-user throughput with state-of-the-art millimeter-wave systems is an order of magnitude lower than the one available with terrestrial wireless networks. In this paper, we take a step further and study the channel characteristics for the terahertz band (THz, 0.3 THz–10 THz) in order to map the feasibility of this band for aviation. We first propose a detailed channel model for aerial THz communications taking into account both the non-flat Earth geometry and the main features of the frequency-selective THz channel. We then apply this model to estimate the characteristics of aerial THz links in different conditions. We finally determine the altitudes where the use of airplane-to-satellite THz connection becomes preferable over the airplane-to-ground THz link. Our results reveal that the capacity of the airborne THz link may reach speeds ranging from 50–150 Gbps, thus enabling cellular-equivalent data rates to the passengers and staff during the entire flight. [ABSTRACT FROM AUTHOR]

We consider the problem of efficient blind parameter estimation in terahertz (THz)-band ultra-massive multiple-input multiple-output (UM-MIMO) systems. UM-MIMO antenna arrays are crucial to overcoming the distance problem in THz communications. Following recent advancements in THz transceiver design, such arrays are intrinsically compact and reconfigurable. We propose dynamically tuning the modulation types, operating frequencies, and indices of transmitting antenna elements for efficient resource utilization in THz UM-MIMO systems. Furthermore, we propose THz-specific signal processing techniques at the receiver side for blindly detecting the transmission parameters. In particular, we propose a low-complexity antenna index, frequency index, modulation mode, and modulation type detectors, and we study the complexity and performance tradeoffs of the proposed schemes. [ABSTRACT FROM AUTHOR]

As 5G technology is advancing towards its final phase of development and the deployment of 5G networks is underway, academic, development and industrial communities are already moving towards the research and development of 6G wireless networks. While 5G technologies had been hauled as an enabler for Internet of Everything, many limitations of such cellular systems are coming to light as they are being deployed. These drawbacks of 5G networks have motivated worldwide interest on developing the next generation wireless system, 6G, with the capability to fully incorporate wide-ranging applications from virtual reality to autonomous systems. In this paper, an overview of the first five generations of wireless systems has been shown, followed by a survey on 6G wireless network along with a discussion on the possible requirements and challenges of 6G. [ABSTRACT FROM AUTHOR]

The authors introduce four kinds of terahertz photonics components based on photonic integrated circuits (PICs). A PIC‐based integrated optoelectronic synthesiser for THz communications is described, which can be tuned continuously over the range 0.254–2.723 THz using photomixing. A laterally‐coupled dual‐grating distributed feedback laser (DFB) diode integrated with an electroabsorption modulator is used to generate an 820 GHz beat signal. THz signal production is reported using a dual‐wavelength DFB diode laser with a two‐section phase‐shifted sampled Bragg grating. Finally, a THz source at 640 GHz, based on a sampled grating distributed Bragg reflector semiconductor mode‐locked laser diode, is reported offering superior reproducibility, controllability, and a wider operation range than other reported mode‐locked THz laser diodes. Each of these sources is a monolithic construction emitting light at 1.5 µm. The light can be amplified in an erbium‐doped fibre amplifier, delivered over silica optical fibre and used to generate THz radiation via a photodiode antenna or photoconductive antenna in a remote location. [ABSTRACT FROM AUTHOR]

This paper proposes a two dimensional (2-D) statistical channel model for Terahertz (THz) chip-to-chip wireless communication in desktop size metal enclosures. This model differs from traditional statistical channel models as it models both traveling and resonant waves that exist inside metal enclosures. Based on the cavity environment and the statistical properties of the channel inside the metal cavity, the geometrical model which describes propagation in resonant cavity as a superposition of LoS, single bounced (SB), double bounced (DB), and multi-bounced (MB) rays is proposed. Based on the geometrical model, a parametric reference model is proposed. Furthermore, the path loss model that captures signal strength variation in a resonant cavity is proposed. Frequency correlation functions (FCF) and power delay profiles (PDP) for different possible chip-to-chip communication scenarios are derived and compared with the measured ones. The results show a good agreement between the simulated and measured statistics. [ABSTRACT FROM AUTHOR]

The prospect of ultra-massive multiple-input multiple-output (UM-MIMO) technology to combat the distance problem at the Terahertz (THz) band is considered. It is well-known that the very large available bandwidths at THz frequencies come at the cost of severe propagation losses and power limitations, which result in very short communication distances. Recently, graphene-based plasmonic nano-antenna arrays that can accommodate hundreds of antenna elements in a few millimeters have been proposed. While such arrays enable efficient beamforming that can increase the communication range, they fail to provide sufficient spatial degrees of freedom for spatial multiplexing. In this paper, we examine spatial modulation (SM) techniques that can leverage the properties of densely packed configurable arrays of subarrays of nano-antennas, to increase capacity and spectral efficiency, while maintaining acceptable beamforming performance. Depending on the communication distance and the frequency of operation, a specific SM configuration that ensures good channel conditions is recommended. We analyze the performance of the proposed schemes theoretically and numerically in terms of symbol and bit error rates, where significant gains are observed compared to conventional SM. We demonstrate that SM at very high frequencies is a feasible paradigm, and we motivate several extensions that can make THz-band SM a future research trend. [ABSTRACT FROM AUTHOR]

A hollow metallic waveguide‐input resonant tunnelling diode three‐terminal mixer device based on a photonic‐crystal platform for terahertz (THz) communication applications is presented. Coherent detection was successfully demonstrated, with an increase in the sensitivity of >30 dB compared with that of direct detection. Error‐free communications with a data rate >10 Gbit/s at 0.3 THz using the developed device as a coherent THz receiver are achieved. [ABSTRACT FROM AUTHOR]