The approximate message passing (AMP)-based data detection is a highly effective solution for terahertz (THz) multiple-input multiple-output (MIMO) communications, enabling reliable data detection at ultra-high data rates. However, in the uplink of THz MIMO systems, high channel correlation leads to performance degradation and computational inefficiencies. To address these challenges, we develop correlated probability estimation (CPE) for the standard AMP iterative data detection algorithm (AMP-IDA), achieving Bayesian-optimal (BO) bit error rate (BER) performance in highly correlated THz channels. To mitigate the significant computational complexity of CPE, we propose an effective signal-to-noise ratio (eSNR)-adjusted channel decorrelation preprocessing (ACDP) method, which leverages whitening transformation and convex optimization, mitigating the impact of row correlation without prior knowledge of correlation indices. By integrating eSNR-ACDP with the low-complexity standard AMP-IDA, we design the ACDP-AMP-IDA, which attains BER close to the BO benchmark with significantly reduced complexity. Compared to orthogonal AMP (OAMP) algorithms, ACDP-AMP-IDA outperforms standard OAMP by up to 8 dB and achieves performance comparable to OAMP with linear minimum mean square error (MMSE) while incurring only 3%–6% of its runtime. Additionally, it surpasses existing AMP-IDA-based and MMSE detectors by over 10 dB and guarantees robust convergence across various transmitter-receiver distances in uplink THz MIMO systems.

We consider robust hybrid beamfocusing schemes against statistical and norm-bounded positioning errors in order to improve a total system data rate in near-field communications. To this end, baseband and analog beamfocusing designs are formulated as an ergodic sum rate maximization, which is solved via deterministic and stochastic optimization. In particular, a closed-form expression of the erdodic sum rate is introduced, which makes the problem tractable by deterministic optimization. In turn, a new stochastic optimization algorithm is proposed for further data rate improvements, which incorporates matrix fractional programming (FP) and element-wise phase derivatives into stochastic learning frameworks by penalize methods. The proposed stochastic algorithm theoretically guarantees convergence to stationary points of the original problem. Numerical results confirm that the proposed approaches achieve higher data rates than non-robust approaches and a singular value decomposition (SVD) beamfocusing with perfect position information.

In this paper, we consider near-field beams that can mitigate signal attenuation and blockage effects using a uniform linear array (ULA). In particular, closed-form expressions for phase distributions in a ULA are derived to generate Bessel beams and curving beams based on the desired propagation directions and trajectories. Based on the phase distributions, the maximum steering angle and propagation distance of Bessel beams with a ULA are revealed. In addition, from the sampling theorem in the spatial domain, the requirements for ULAs to properly generate Bessel beams are clarified. For curving beams, trajectories to reach a user while avoiding one obstacle are designed via the Lagrangian method. Numerical results obtained by electromagnetic wave simulations confirm the effectiveness of the analyses for Bessel beams and the curving beam designs. Furthermore, the characteristics of Gaussian beams, beamfocusing, Bessel beams, and curving beams are summarized in terms of the statistical behavior of their intensity and signal processing.

In this paper, the optimal wavefronts for maximum ratio transmission (MRT) are investigated under path blockage effects in the near-field region. To characterize the behavior of the optimal wavefronts, a new deterministic channel model is proposed in the presence of obstacles, which describes blockage effects by the variation of the electric field based on the uniform theory of diffraction (UTD). With the proposed channel model, the linear precoder designs are formulated as optimization problems to maximize the power density at the desired point under fully digital and analog array assumptions, where the amplitude and phase distributions of the solutions characterize the optimal wavefronts to achieve MRT. The optimal precoders reveal that the proposed channel modeling must be required to optimize near-field communications systems in the presence of obstacles, which, together with electromagnetic wave simulations, confirm that linear precoding with the proposed channel model achieves MRT under any blockage effect, and the optimal wavefront varies for each blockage situation.

Scintillation due to atmospheric turbulence is one of the effects challenging the reuse of extremely wideband and high-rate optical satellite-to-satellite communication systems for satellite-to-Earth and Earth-to-satellite transmissions. In this article, we study the possibility of utilizing links in the terahertz (THz) frequency bands for these uplink and downlink transmissions instead. Built upon the physics-based model, originally developed for optical wave propagation, we present a mathematical framework for the THz signal scintillation to analyze atmospheric turbulence's impact on ground-satellite and airplane-satellite connections. Our results indicate that, while the scintillation still significantly impacts the power of the received THz signal (especially at lower elevation angles and under specific weather conditions), the effect is drastically less profound than the extreme losses the optical link will experience in the same weather conditions. We further explore a notable asymmetry of up to 10 dB between uplink and downlink losses. Finally, we illustrate that, even at relatively low airplane altitudes, the airplane-to-satellite link is much less affected than the Earth-to-satellite link, making THz communications a promising candidate technology for future high-rate airplane connectivity systems as a part of 6G and beyond.

Spatial multiplexing is not always feasible in terahertz and sub-terahertz (THz) MIMO channels due to the primarily line-of-sight propagation, but recent works have explored the possibility of using orbital angular momentum (OAM) to enable multiplexing in line-of-sight scenarios. This paper explores a certain physical-layer security risk and a corresponding mitigation strategy for THz MIMO systems using orbital angular momentum (OAM). A novel successive interference cancellation eavesdropping attack is introduced for OAM-MIMO THz systems, and simulations demonstrate that the security of the link decreases in the far field. A security countermeasure is introduced and proven to be effective in physically protecting the communications link.

We propose a novel framework to analyze the coverage performance of three-dimensional (3D) indoor terahertz (THz) communication systems and examine the impact of the location of a user equipment (UE) on such performance. Specifically, we employ Manhattan line processes to precisely characterize the deployment of wall blockages in the indoor environment. Moreover, we model locations of access points (APs) using a Poisson point process and adopt the nearest line-of-sight AP association strategy. Due to the high penetration loss caused by wall blockages, we consider that a UE, its associated AP, and interfering APs are all in the same rectangular area, i.e., a room. Based on the proposed rectangular area model, we first analyze the impact of the location of a UE on the distance to its associated AP. We then derive a new expression for the coverage probability by adopting the fluctuating two-ray distribution to accurately model the small-scale fading in THz communications. Supported by simulation results, we validate our analysis and demonstrate how the location of the UE affects its coverage probability, offering valuable insights for meeting the coverage requirements of future THz communication system deployments.

In this paper, we develop a tractable analytical framework for a three-dimensional (3D) indoor terahertz (THz) communication system to theoretically assess the impact of the pointing error on its coverage performance. Specifically, we model the locations of access points (APs) using a Poisson point process, human blockages as random cylinder processes, and wall blockages through a Boolean straight line process. A pointing error refers to beamforming gain and direction mismatch between the transmitter and receiver. We characterize it based on the inaccuracy of location estimate. We then analyze the impact of this pointing error on the received signal power and derive a tractable expression for the coverage probability, incorporating the multi-cluster fluctuating two-ray distribution to accurately model small-scale fading in THz communications. Aided by simulation results, we corroborate our analysis and demonstrate that the pointing error has a pronounced impact on the coverage probability. Specifically, we find that merely increasing the antenna array size is insufficient to improve the coverage probability and mitigate the detrimental impact of the pointing error, highlighting the necessity of advanced estimation techniques in THz communication systems.

For decades, the terahertz (THz) frequency band had been primarily explored in the context of radar, imaging, and spectroscopy, where multi-gigahertz (GHz) and even THz-wide channels and the properties of THz photons offered attractive target accuracy, resolution, and classification capabilities. Meanwhile, the exploitation of the THz band for wireless communication had originally been limited due to several reasons:1) no immediate need for such high data rates available via THz bands and 2) challenges in designing sufficiently high-power THz systems at reasonable cost and efficiency, leading to what was often referred to as “the THz gap.” Over the recent decade, advances on many fronts have drastically changed the THz landscape. First, the evolution from 5G-to 6G-grade wireless systems dictates the need to support novel bandwidth-hungry applications and services for both data transfer i.e., eXtended Reality (XR), the Metaverse, and vast modeling needs of artificial intelligence (AI) and machine learning (ML), as well as centimeter-precision sensing and classification (i.e., for standalone position location, vehicle-to-everything (V2X), or unmanned aerial vehicle (UAV) tracking). Second, substantial progress in THz hardware has been achieved, offering promise that the THz technology gap will be closed. Hence, THz-band wireless communication seems inevitably an essential part of the future networking technology landscape in the coming decades. To design efficient THz systems, the peculiarities of THz hardware and THz channels need to be understood and accounted for. This roadmap paper first reviews the evolution of the hardware design approaches for THz systems, including electronic, photonic, and plasmonic approaches, and the understanding of the THz channel itself, in diverse scenarios, ranging from common indoors and outdoors scenarios to intrabody and outer space environments. This article then summarizes the lessons learned during this multidecade process and the cutting-edge state-of-the-art findings, including novel methods to quantify power efficiency, which will become more important in making design choices. Finally, this article presents the authors’ perspective and insights on how the evolution of THz systems design will continue toward enabling efficient THz communications and sensing solutions as an integral part of next-generation wireless systems.

In this paper, the physical layer security of terahertz (THz) band communications in the near field is discussed and evaluated. First, a novel class of design approaches to enhance the security of near-field THz links is proposed. These approaches are referred to as wavefront hopping schemes, as they exploit the properties of different THz wavefronts when propagating beams in the near field (particularly, THz Bessel beams and THz Airy beams). Then, a compound evaluation framework is delivered to assess both the performance and the security level of a given single-beam or multi-beam solution for a near-field THz system. Finally, a performance evaluation is conducted illustrating the performance/secrecy trade-offs associated with the modeled single-beam and multi-beam security schemes for both a single Attacker and a team of cooperating Attackers. Our results indicate that the proposed multi-beam solutions combining THz Airy beam(s) with THz Bessel beam through wavefront hopping lead to a notably decreased probability of message eavesdropping while maintaining nearly identical performance with the single-beam schemes. The contributed security schemes, evaluation methodology, and numerical results facilitate further development in the emerging area of secure near-field THz communications for 6G and beyond wireless networks.

In this paper, we develop a novel analytical framework for a three-dimensional (3D) indoor terahertz (THz) communication system. Our proposed model incorporates more accurate modeling of wall blockages via Manhattan line processes and precise modeling of THz fading channels via a multi-cluster fluctuating two-ray (MFTR) channel model. We also account for traditional unique features of THz, such as molecular absorption loss, user blockages, and 3D directional antenna beams. Moreover, we model locations of access points (APs) using a Poisson point process and adopt the nearest line-of-sight AP association strategy. Due to the high penetration loss caused by wall blockages, we consider that a user equipment (UE) and its associated AP and interfering APs are all in the same rectangular area, i.e., a room. Based on the proposed rectangular area model, we evaluate the impact of the UE’s location on the distance to its associated AP. We then develop a tractable method to derive a new expression for the coverage probability by examining the interference from interfering APs and considering the MFTR fading experienced by THz communications. Aided by simulation results, we validate our analysis and demonstrate that the UE’s location has a pronounced impact on its coverage probability. Additionally, we find that the optimal AP density is determined by both the UE’s location and the room size, which provides valuable insights for meeting the coverage requirements of future THz communication system deployment.

As Fifth generation (5G) cellular systems transition to softwarized, programmable, and intelligent networks, it becomes fundamental to enable public and private 5G deployments that are (i) primarily based on software components while (ii) maintaining or exceeding the performance of traditional monolithic systems and (iii) enabling programmability through bespoke configurations and optimized deployments. This requires hardware acceleration to scale the Physical (PHY) layer performance, programmable elements in the Radio Access Network (RAN) and intelligent controllers at the edge, careful planning of the Radio Frequency (RF) environment, as well as end-to-end integration and testing. In this paper, we describe how we developed the programmable X5G testbed, addressing these challenges through the deployment of the first 8-node network based on the integration of NVIDIA Aerial RAN CoLab Over-the-Air (ARC-OTA), OpenAirInterface (OAI), and a near-real-time RAN Intelligent Controller (RIC). The Aerial Software Development Kit (SDK) provides the PHY layer, accelerated on Graphics Processing Unit (GPU), with the higher layers from the OAI open-source project interfaced with the PHY through the Small Cell Forum (SCF) Functional Application Platform Interface (FAPI). An E2 agent provides connectivity to the O-RAN Software Community (OSC) nearreal-time RIC. We discuss software integration, network infrastructure, and a digital twin framework for RF planning. We then profile the performance with up to 4 Commercial Off-the-Shelf (COTS) smartphones for each base station with iPerf and video streaming applications, as well as up to 25 emulated User Equipments (UEs), measuring a cell rate higher than 1.65 Gbps in downlink and 143 Mbps in uplink.

Biosensors are shaping the future of healthcare through their vital role in disease detection, diagnostics, biomarker detection, and continuous health monitoring. In intra-body wireless nanosensor networks, biosensors are anticipated to incorporate antennas employing high frequencies, including the terahertz frequency band. Terahertz technology facilitates fast communication and the creation of compact designs. However, photothermal effects will be induced due to the absorption of the radiation by the tissue. In this paper, a photothermal model is developed on COMSOL Multiphysics®to explore the impact of the implanted biosensor electromagnetic radiation on the skin. According to the model’s findings, the increase in the skin’s temperature is proportional to the increase in both the transmission power and the number of biosensors in the network. Furthermore, power fluctuations resulting from the presence of multiple biosensors are found to be separate and distinct from temperature variations in the tissue. This indicates that at certain points in the skin, the power level might be moderate, but the temperature is high. Such analysis is beneficial to better understand the photothermal effects of the terahertz radiation from implanted devices and to define safe deployment guidelines.

The beam split effect (BSE) can result in a serious loss in achievable rate in terahertz (THz) transmission. In this work, we propose a new sub-band assignment scheme in a multiuser THz communications system to address the BSE. We consider a base station employs true-time-delay hardware between radio frequency chains and uniform planar arrays (UPAs). The core idea of this hardware is that, rather than fine-tuning the UPA delays to form a single beam from each UPA, we facilitate multi-beam transmission from each UPA. We derive a novel expression for the maximum sub-band bandwidth for UPA, ensuring that the BSE is avoided within each beam. Based on this expression we design sub-band assignment across users and power allocation among sub-bands to maximize the sum-rate, relying on the principles of beam multiplexing and aggregation (BMA). Using numerical results, we demonstrate (i) the merits of our proposed sub-band assignment in contrast to the distance-aware sub-band assignment scheme, (ii) the effectiveness of BMA in comparison with the BSE, and (iii) the improved performance resulting from our proposed optimal power allocation relative to equal power allocation.

Wireless biomonitoring is revolutionizing healthcare by empowering remote real-time patient monitoring, facilitating disease early detection, and improving disease management. This technology has the potential to transform the way various organs are monitored, including the silent sentinel, the liver, which is responsible for processing nutrients, filtering toxins and waste, producing proteins, and regulating blood sugar levels. Incor-porating terahertz technology with wireless biomonitoring will not only enable non-invasive intrabody communication but also empower sensing and detecting variations in tissue properties, enhancing disease early detection. Nevertheless, to utilize this technology, a clear understanding of the photothermal impact of terahertz radiation on the liver tissue is crucial for designing safe and efficient biomonitoring implanted devices/sensors. In this work, a COMSOL ® multiphysics model is developed to study the photothermal dynamics resulting from the terahertz electromagnetic radiation absorbed by the liver tissue. The effect of power, pulse duration, and shape, as well as the fat content in a fatty liver patient, are investigated. Results indicate that utilizing terahertz-based implant devices can have minimal to no thermal impact on the liver when designed with careful control of transmission power and duration tailored to individual patients to ensure liver health and safety.

Terahertz-band (100 GHz-10 THz) communication is a promising radio technology envisioned to enable ultra-high data rate, reliable and low-latency wireless connectivity in next-generation wireless systems. However, the low transmission power of THz transmitters, the need for high gain directional antennas, and the complex interaction of THz radiation with common objects along the propagation path make crucial the understanding of the THz channel. In this paper, we conduct an extensive channel measurement campaign in an indoor setting (i.e., a conference room) through a channel sounder with 0.1 ns time resolution and 20 GHz bandwidth at 140 GHz. Particularly, the impact of different antenna directivities (and, thus, beam widths) on the channel characteristics is extensively studied. The experimentally obtained dataset is processed to develop the path loss model and, subsequently, derive key channel metrics such as the path loss exponent, delay spread, and K-factor. The results highlight the multi-faceted impact of the antenna gain on the channel and, by extension, the wireless system and, thus, show that an antenna-agnostic channel model cannot capture the propagation characteristics of the THz channel.

Wireless backhaul links, already ubiquitous and expanding further with 5G and beyond, are employed for many critical functions, such as financial trading on Wall Street. In this work, we demonstrate for the first time that such links are acutely vulnerable to a new class of aerial metasurface attacks. In particular, we show how an adversary Eve designs and employs MetaFly to covertly manipulate the electromagnetic wavefront of the signals and remotely eavesdrop on highly directional backhaul links. Exploring the foundation of the attack, we demonstrate Eve’s strategy for generating eavesdropping diffraction beams by inducing pre-defined phase profiles at the aerial metasurface interface. We also show how Eve’s flight navigation approach can dynamically shape radiation patterns based on drone mobility via a wavefront-tailored flight refinement principle. We prototype MetaFly and demonstrate Eve’s lightweight, low-cost, transmissive, and power-free aerial metasurface. We implement the attack and perform a suite of over-the-air experiments in both a large indoor atrium and outdoor rooftops in a large metropolitan area. The results reveal that armed with MetaFly, Eve can intercept backhaul transmissions with nearly zero bit error rate while maintaining minimal impact on legitimate communication.

The increasing demand for ultra-high data rates in wireless communications has attracted interest in upper-frequency bands, namely sub-terahertz and terahertz frequencies. However, severe path loss and narrow beamwidth antennas used at these frequencies necessitate precise antenna alignment and realignment algorithms. Existing solutions often rely on constrained simulations or out-of-band techniques that may not capture the unique propagation characteristics of terahertz frequencies. To address this challenge, we introduce THzAlign, an integrated sub-terahertz and terahertz platform that enables rapid prototyping and real-world testing of antenna alignment algorithms. THzAlign combines rotary tables for precise beam steering with a modular software architecture supporting algorithm simulation and over-the-air experiments. To illustrate this platform, we evaluate three reference realignment algorithms in terms of their performance using THzAlign under varying distances, frequencies, and antenna beamwidth conditions. The developed platform with its documented API facilitates real-world hardware validation of forthcoming advanced solutions for beam (re-)alignment as an integral part of intelligent ultra-high-rate communication systems in the (sub-)THz bands toward 6G and beyond.

The Terahertz (THz) band (0.1–10 THz) is projected to enable broadband wireless communications of the future, and many envision deep learning as a solution to improve the performance of THz communication systems and networks. However, there are few available datasets of true THz signals that could enable testing and training of deep learning algorithms for the research community. In this paper, we provide an extensive dataset of 120,000 data frames for the research community. All signals were transmitted at 165 GHz but with varying bandwidths (5 GHz, 10 GHz, and 20 GHz), modulations (4PSK, 8PSK, 16QAM, and 64QAM), and transmit amplitudes (75 mV and 600 mV), resulting in twenty-four distinct bandwidth-modulation-power combinations each with 5,000 unique captures. The signals were captured after down conversion at an intermediate frequency of 10 GHz. This dataset enables the research community to experimentally explore solutions relating to ultrabroadband deep and machine learning applications.

Emerging from the symbiotic combination of nanotechnology and communications, the field of nanonetworking has come a long way since its inception more than fifteen years ago. Significant progress has been achieved in several key communication technologies as enablers of the paradigm, as well as in the multiple application areas that it opens. In this paper, the focus is placed on the electromagnetic nanonetworking paradigm, providing an overview of the advances made in wireless nanocommunication technology from microwave through terahertz to optical bands. The characteristics and potential of the compared technologies are then confronted with the requirements and challenges of the broad set of nanonetworking applications in the Internet of NanoThings (IoNT) and on-chip networks paradigms, including quantum computing applications for the first time. Finally, a selection of cross-cutting issues and possible directions for future work are given, aiming to guide researchers and practitioners towards the next generation of electromagnetic nanonetworks.

Nanotechnology is enabling the development of devices on a scale ranging from one to a few hundred nanometers. At this scale, a nanomachine is defined as the most basic functional unit, integrated by nano-components which can carry out sensing and actuation. Coordination and information communication among several nanomachines expand the potential applications of individual devices both in terms of complexity and range of operation. The resulting nanonetworks can cover wide areas, to reach unprecedented locations in a non-invasive way. Moreover, the integration of nanonetworks with classical networks and ultimately with the Internet results in a new networking paradigm, which is referred to as the Internet of Nano-Things (IoNT) by Akyildiz and Jornet one and a half decades ago.

High-rate satellite communications among hundreds and even thousands of satellites deployed at low-Earth orbits (LEO) will be an important element of the forthcoming sixth-generation (6G) of wireless systems beyond 2030. With millimeter wave communications (mmWave, ≈30 GHz–100 GHz) completely integrated into 5G terrestrial networks, exploration of its potential, along with sub-terahertz (sub-THz, 100 GHz–300 GHz), and even THz (300 GHz–3 THz) frequencies, is underway for space-based networks. However, the interference problem between LEO mmWave/THz satellite cross-links in the same or different constellations is undeservedly forgotten. This article presents a comprehensive mathematical framework for modeling directional interference in all key possible scenario geometries. The framework description is followed by an in-depth numerical study on the impact of cross-link interference on various performance indicators, where the delivered analytical results are cross-verified via computer simulations. The study reveals that, while highly directional mmWave and, especially, THz beams minimize interference in many cases, there are numerous practical configurations where the impact of cross-link interference cannot be neglected and must be accounted for.

Future wireless networks and sensing systems will benefit from access to large chunks of spectrum above 100 GHz, to achieve terabit-per-second data rates in 6th Generation (6G) cellular systems and improve accuracy and reach of Earth exploration and sensing and radio astronomy applications. These are extremely sensitive to interference from artificial signals, thus the spectrum above 100 GHz features several bands which are protected from active transmissions under current spectrum regulations. To provide more agile access to the spectrum for both services, active and passive users will have to coexist without harming passive sensing operations. In this paper, we provide the first, fundamental analysis of Radio Frequency Interference (RFI) that large-scale terrestrial deployments introduce in different satellite sensing systems now orbiting the Earth. We develop a geometry-based analysis and extend it into a data-driven model which accounts for realistic propagation, building obstruction, ground reflection, for network topology with up to 105nodes in more than 85 km2. We show that the presence of harmful RFI depends on several factors, including network load, density and topology, satellite orientation, and building density. The results and methodology provide the foundation for the development of coexistence solutions and spectrum policy towards 6G.

Multiple-Input Multiple-Output (MIMO) systems have been presented for Terahertz (THz) communications to combat high path loss and enable Terabit-per-second (Tbps) links. The lack of experimental MIMO channel measurements, however, has restricted the majority of THz MIMO work to the theoretical realm. This paper presents a novel, first-of-its-kind correlation-based MIMO channel sounder with a timing reference for sub-THz communications, which enables broadband, long-range, and time-varying channel characterization of MIMO systems. Preliminary results from a conference room setting show that 28.5% of the tested scenarios can support spatial multiplexing, and even with beamforming, the capacity outperforms the SISO cases substantially.

Near-field mobile terahertz (THz) communications is one of the candidate enablers for high-rate wireless data exchange in sixth-generation (6G) networks. However, operating in the THz near field brings both attractive opportunities and severe challenges. Hence, it becomes of interest to explore if it is possible to design a realistic mobile THz communication system without working in the THz near field. To answer this question, a mathematical framework is presented modeling a mobile THz link that works exclusively in the far field. The study leads to an interesting theoretical conclusion: while the actual frequency is of (almost) no interest, such a system must operate over a limited bandwidth not exceeding a certain threshold. It is then numerically shown that operating only in the far field imposes stringent limitations on mobile THz communications, thus making them less attractive to prospective high-rate services. In contrast, it is shown that a stationary THz link can still be broadband even when staying exclusively in the THz far field. Hence, broadband mobile THz communications MUST be near-field, while broadband stationary THz links do not have to.

Exploring near-field propagation is increasingly relevant for terahertz(THz)-band communications, as very large antenna arrays (VLAA) are required to overcome the large propagation losses. In the near field, the efficiency of conventional far-field beamforming is reduced, while state-of-the-art near-field beamfocusing requires perfect positioning and channel state information to work efficiently. In this paper, first, experimental measurements of wireless data transmission above 100 GHz in indoor scenarios are presented to highlight the need for VLAAs that will likely operate in the near field. Next, diffraction-free Bessel beams are described as a promising near-field contender, with propagation characteristics in the near field similar to those of beamforming in the far field. Numerical results and their interpretations highlight the impact of prospective wideband THz communications during system implementations. It is particularly observed that THz Bessel beams can be optimized for the given environment, potentially improving the performance characteristics of the system.

One of the important questions when discussing next-generation near-Earth mmWave and terahertz (THz) band satellite communications as an integral part of the 5G-Advanced and 6G landscape is the potential interference-related issues when deploying such systems. While the space-to-ground and ground-to-space interference has been explored in multiple works already, the interference at mmWave and THz cross-links, the links between the satellites themselves, have not been extensively studied yet. However, severe cross-link interference may both challenge the reliability of the data exchange within the constellation, as well as compromise the efficient co-existence of multiple satellite constellations (i.e., by different providers) covering the same or neighboring areas. In this paper, both relevant mathematical models and extensive simulation studies are presented for cross-link mmWave and THz satellite communications. Our results indicate that the cross-link interference in the considered setups is a non-negligible factor that must be further explored and accounted for in the design and deployment of next-general mmWave and THz satellite communication systems.

The electromagnetic spectrum plays a fundamental role in the development of the digital society. It enables wireless communications (either between humans or machines) and sensing (for example, for Earth exploration, radio astronomy, imaging, and radars). While each of these uses benefits from a larger bandwidth, the spectrum is a finite resource. This introduces competing interests among the different stakeholders of the spectrum, which have led—so far—to rigid policies and spectrum allocations. Recently, the spectrum crunch in the sub-6-GHz bands has prompted communication technologies to move to higher carrier frequencies, where future sixth-generation (6G) wireless networks can exploit theoretically very large bandwidths. However, the spectrum above 100 GHz features several narrow, yet numerous subbands that are exclusively allocated for passive sensing applications, e.g., for climate and weather monitoring. This prevents the allocation of large contiguous bands to active users of the spectrum, either being communications (which need tens of gigahertz of bandwidth to target terabit-per-second links) or radars. This article explores how spectrum policy and spectrum technologies can evolve to enablesharingamong different stakeholders in the above 100-GHz spectrum, without introducing harmful interference or disrupting either security applications or fundamental science exploration. This portion of the spectrum presents new challenges and opportunities for the design of spectrum sharing schemes, including higher spreading and absorption losses, extremely directional antenna technologies, and ultrahigh data-rate communications, among others. This article provides a tutorial on current regulations above 100 GHz and highlights how sharing is central to allowing each stakeholder to make the most out of this spectrum. It then defines—through detailed simulations based on standard International Telecommunications Union (ITU) channel and antenna models—scenarios in which active users may introduce harmful interference to passive sensing. Based on this evaluation, it reviews a number of promising techniques that can enable active/passive sharing above 100 GHz. The critical review and tutorial on policy and technologies of this article have the potential to kickstart future research and regulations that promote safe coexistence between active and passive users above 100 GHz, further benefiting the development of digital technologies and scientific exploration.

Today’s mmWave WLANs can realize simultaneous multi-user multi-stream transmission solely on the downlink. In this paper, we present Uplink Multi-user Beamforming on single RF chain AP (UMBRA), a novel framework for supporting multi-stream multi-user uplink transmissions via a single RF chain. We design multi-user overlayed constellations and multi-user receiver mechanisms to enable concurrent time-triggered uplink multi-user transmissions received on a single RF chain AP. We devise exemplary beam selection policies to jointly adapt beams at users and the AP for targeting aggregate rate maximization without increasing training requirements compared to single-user systems. We implement the key components of UMBRA using a programmable WLAN testbed using software-defined radios and commercial 60-GHz transceivers and collect over-the-air measurements using phased-array antennas and horn antennas with varying beamwidth. We find that in comparison to single-user transmissions, UMBRA achieves more than$1.45 \times $improvement in aggregate rate regardless of the choice of the user group, geometric separation, receiver beamwidth, and also under LOS blockage.

Terahertz (THz)-band (0.1–10 THz) communication will be key in enabling high speed wireless links due to the wide available bandwidths. At THz frequencies, the path-loss is governed by high spreading loss due to small antenna apertures and by molecular absorption loss due to water vapor. The latter also determines the available transmission bandwidth, which shrinks with distance. Modulations that consider the high propagation loss and the distance-dependent bandwidth are needed to fully exploit the THz channel’s bandwidth. Using a hierarchical constellation to simultaneously service users at symbol rates, Hierarchical Bandwidth Modulation (HBM) leverages molecular absorption to increase aggregate data rates in a broadcast system while offering flexibility to receivers experiencing high path loss. This paper introduces HBM and evaluates its performance. The symbol error rate performance for a 4/M-QAM HBM system is derived and verified using simulations. These results are used to define the design constraints for an HBM system: the HBM functional region and transition region. The functional region is verified using an experimental testbed for ultrabroadband communications. The results show that with proper design HBM successfully achieves its goal to exploit the distance-dependent characteristics of the THz channel, to spatially multiplex users, and to increase the system capacity.

Terahertz (THz) band (0.1 THz to 10 THz) communication is envisioned as a key technology to satisfy the demand for Terabit-per-second (Tbps) links in the sixth generation (6G) wireless systems and beyond. Significant progress within different device technologies is finally closing the so-called THz technology gap. However, there are notable limitations relating to the efficiency and reliability of THz devices. In order to overcome the challenges, innovative ways of digital signal processing, as well as waveform design techniques, need to be considered. In this context, to simultaneously overcome the limitations due to peak to average power ratio (PAPR) and reduce the effective symbol error rate (SER), both while using a high-order modulation scheme for ultrabroadband THz communication, the utilization of m-ary amplitude phase shift keying (M-APSK) is proposed. After optimizing the constellation with the number of rings as a constraint, the performance of the scheme is compared with M-ary quadrature amplitude modulation (M-QAM) and M-ary phase-shift keying (M-PSK) in terms of SER and PAPR. As a proof of concept, experimental results are provided to demonstrate the performance of the proposed scheme in the 120-140 GHz band, achieving bit-rates of up to 50 Gbps on a single-carrier, single-channel tens-of-meters-long link. This constellation will serve as a building block for multi-carrier modulations able to reach the 1 Tbps goal.

We present a custom-built, multi-physics model to investigate electromagnetic wave propagation in extreme random media such as human tissue and study its subsequent photothermal effects. The proposed finite-element model consists of two segments – the first one estimates the intensity distribution along the beam path, while the second calculates the increase in temperature due to the wave distribution inside the tissue. We determine the intensity variation in the tissue using the radiative transfer equation and compare the results with Monte Carlo analysis and existing analytical models. The intensity information is then utilized to predict the rise in temperature with a bio-heat transfer module, powered by Pennes’ bioheat equation. The model is parametric, and we perform a systematic photothermal analysis to recognize the crucial variables responsible for the temperature growth inside the tissue, particularly for terahertz and near infrared optical frequencies. Our numerical model can serve as a benchmark for intrabody communication studies involving complex heterogeneous media.

We propose a new spectrum allocation strategy for terahertz (THz) band communication (THzCom) systems. Specifically, we design multi-band-based spectrum allocation with adaptive sub-band bandwidth (ASB), by allowing to divide the spectrum of interest into sub-bands with unequal bandwidths. Due to the frequency and distance-dependent nature of the molecular absorption loss, the variation in this loss between the sub-bands would be very high at the THz band when equal sub-band bandwidth (ESB) is considered, as in the literature. The proposed strategy reduces this variation by allowing changes in the sub-band bandwidth, which leads to an overall improvement in the data rate performance. To study the impact of our strategy, we formulate an optimization problem, with the main focus on spectrum allocation, to determine the optimal sub-band bandwidth and transmit power. Thereafter, we propose reasonable approximations and transformations to solve the formulated problem. Aided by numerical results, we show that by enabling and optimizing ASB, a significantly higher data rate can be achieved by our strategy, compared to adopting ESB, and it is more beneficial to adopt ASB when the spectrum with the highest average molecular absorption loss within the THz transmission window is selected during spectrum allocation.

As the interest in the Terahertz (0.1-1THz) band grows with the technological advancements that enable communication at higher data rates, the existing use for THz-based sensing systems motivate exploration of Joint Communication and Sensing systems (JCS). Such systems can be used for the next generation of satellite constellations for the purposes of internet-backhauling, while performing scientific functions such as studying atmospheric gases. The fact that the hardware employed for both applications is highly similar, if not identical, opens the possibility of designing a new waveform that can jointly communicate and sense at the same time. In this paper, we explore Differential Absorption Radars (DAR), traditionally used for weather sensing, as a potential candidate to be operated in combination with a Chirp Spread Spectrum (CSS) modulation. We present a scenario with a satellite at Low Earth Orbit (LEO) where the CSS modulation could outperform traditional PSK modulations while making it possible to retrieve water vapor density profiles of the atmosphere with DAR. Performance of both communication and remote sensing applications are studied through simulation.

The advancement of nano communication has opened the door for the development of intrabody medical application services. Flow-guided nano-communication networks have gained major attraction in recent years as an effective solution for intrabody sensing and actuation. This article builds a three-layer vertical network structure for intrabody nanonetworks, i.e., nano nodes, nano routers, and gateway, where data packets generated by nano nodes are relayed to the gateway through nano routers or other nodes. However, how to guarantee the data transmission through the way of multiple hops in such a scenario is an unsolved challenge. In order to improve the throughput and reduce the energy consumption of intrabody nanonetworks in a single-flow environment where the nano devices are restricted, a flow-guided opportunistic routing (FGOR) protocol is proposed. In FGOR, a relative position (RP) model is proposed to formulate the criterion for candidate relay selection (CRS) and enable the nodes’ direction awareness to the gateway. Moreover, the CRS criterion is redesigned through a mobility gradient (MG) model further derived from the RP model. The candidate nodes are prioritized based on node ID, available energy, and RP information of nodes to perform backoff forwarding for decreasing transmission redundancy. Simulation results show that the RP model improves the throughput and significantly extends the lifecycle of intrabody nanonetwork by reducing the energy consumption. Compared with the RP model, the MG model performs better in terms of delay and successful transmission rate, especially within the circulation environment of intrabody.

With the advances in nanotechnology, novel nanosensing technologies can play a pivotal role in today’s society. Plasmonic sensing has demonstrated unprecedented detection reliability and resolution in a very compact form factor. Traditional plasmonic sensors leverage biofunctionalized metallic grating structures whose frequency response in transmission or reflection changes according to the presence of targeted biomarkers. However, these sensing setups require bulky measurement equipment to couple light to and from sensors for excitation and detection. In parallel, for over a decade, the nanoscale electromagnetic communication community has been leveraging plasmonic structures to transmit information at the nanoscale efficiently. By combining the two realms, this paper proposes the concept of joint nanoscale communication and bio-sensing systems enabled by plasmonic sensing nanoantennas. Sensing nanonodes can communicate from nanonode to nanonode for intra-body networks and from nanonode to a wearable device which, by leveraging the edge, can process and transmit the sensing information to the cloud, resulting in accurate diagnosis and reduced load on the medical testing infrastructure. First, we model the changes in the frequency response of a biofunctionalized plasmonic nanoantenna when exposed to different biomarkers. Then, we propose a chirp-spread spectrum excitation and detection system to enable simultaneous communication and sensing at the nanoscale. We present a data-driven human tissue model for communication through human tissue. We also present numerical results to demonstrate the performance of the proposed system.

Terahertz (THz) band communications are envisioned as a key technology for 6G and Beyond. As a fundamental wireless infrastructure, THz communication can boost abundant promising applications. In 2014, our team published two comprehensive roadmaps for the development and progress of THz communication networks, which helped the research community to start research on this subject afterwards. The topic of THz communications became very important and appealing to the research community due to 6G wireless systems design and development in recent years. Many papers are getting published covering different aspects of wireless systems using the THz band. With this paper, our aim is looking back to the last decade and revisiting the old problems and pointing out what has been achieved in the research community so far. Furthermore, in this paper, open challenges and new research directions still to be investigated for the THz band communication systems are presented, by covering diverse topics ranging from devices, channel behavior, communication and networking, to physical testbeds and demonstration systems. The key aspects presented in this paper will enable THz communications as a pillar of 6G and Beyond wireless systems in the next decade.

We study spectrum allocation for terahertz (THz) band communication (THzCom) systems, while considering the frequency and distance-dependent nature of THz channels. Different from existing studies, we explore multi-band-based spectrum allocation with adaptive sub-band bandwidth (ASB) by allowing the spectrum of interest to be divided into sub-bands with unequal bandwidths. Also, we investigate the impact of sub-band assignment on multi-connectivity (MC) enabled THzCom systems, where users associate and communicate with multiple access points simultaneously. We formulate resource allocation problems, with the primary focus on spectrum allocation, to determine sub-band assignment, sub-band bandwidth, and optimal transmit power. Thereafter, we propose reasonable approximations and transformations, and develop iterative algorithms based on the successive convex approximation technique to analytically solve the formulated problems. Aided by numerical results, we show that by enabling and optimizing ASB, significantly higher throughput can be achieved as compared to adopting equal sub-band bandwidth, and this throughput gain is most profound when the power budget constraint is more stringent. We also show that our sub-band assignment strategy in MC-enabled THzCom systems outperforms the state-of-the-art sub-band assignment strategies and the performance gain is most profound when the spectrum with the lowest average molecular absorption coefficient is selected during spectrum allocation.

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.

Multi-user transmission in 60 GHz Wi-Fi can achieve data rates up to 100 Gbps by multiplexing multiple user data streams. However, a fundamental limit in the approach is that each RF chain is limited to supporting one stream or one user. In this paper, we scale multi-user 60 GHz WLAN data rate by overcoming this limit and propose SIngle RF chain Multi-user BeAmforming (SIMBA), a novel framework for multi-stream multi-user downlink transmission via a single RF chain. We build on single beamformed transmission via overlayed constellations to multiplex multiple users’ modulated symbols such that grouped users at different locations can share the same transmit beam from the AP. For this, we introduce user grouping and beam selection policies that span tradeoffs in data rate, training, and computation overhead. We implement a programmable WLAN testbed using software-defined radios and commercial 60 GHz transceivers and collect over-the-air measurements for different indoor WLAN deployments using a 12-element phased antenna array as well as horn antennas with varying beamwidth. We show that in comparison to single-user transmissions, SIMBA achieves$2\times $improvement in aggregate rate and two-fold delay reduction for simultaneous transmission to four users.

Terahertz (THz) band (0.1-10 THz) communication is envisioned as a key wireless technology to satisfy the need for wireless Terabit-per-second (Tbps) links in 6G systems. The THz band supports very large channel bandwidths with the cost of very high propagation losses. On the one hand, the absorption by water vapor molecules manifests itself in the form of absorption lines that broaden in frequency with distance, resulting into a highly distance-dependent channel bandwidth. On the other hand, the very high spreading or free-space losses require the use of highly directional antennas (DAs) simultaneously in transmission and reception at all times. As with the bandwidth, the beamwidth of such DAs is also related with the transmission distance, and introduces severe synchronization and, correspondingly, delay challenges. These issues become even worse when the system needs to support up to Tbps peak data-rates. The end-to-end (E2E) delay and, correspondingly, effective throughput in multi-hop THz communication networks can drastically suffer if all these peculiarities are not taken into account. In this paper, multi-hop relaying distribution strategies are developed for THz-band communication to minimize the multi-hop E2E delay by considering cross-layer effects between the THz channel, highly DAs, nodes’ buffer and the physical, link and network layers.

Optical signals are commonly used for intrabody applications, such as nano-bio-sensing and imaging and, more recently, nanoscale communication. However, due to the interaction of light with the building blocks of different body tissues, including different types of cells, organelles, and molecular components, the intrabody channel is highly frequency selective, compromising the communication between intrabody nano-devices as well as wearable devices. In this paper, Chirp Spread Spectrum (CSS) modulation is proposed as a way to overcome the frequency selectivity of the optical channel in intrabody applications. More specifically, after reviewing and highlighting the key properties of the intrabody optical channel, the performance of CSS analytically derived. Extensive numerical results are provided both for a generic optical frequency selective channel and for the near-infrared optical in-vivo channel to illustrate the performance of CSS. The obtained results demonstrate how the possibility to detach the symbol duration from the actual signal bandwidth leads to low bit error rates even when operating in very low signal to noise ratio conditions.

Today's mmWave WLANs can realize simultaneous multi-user multi-stream transmission solely on the downlink. In this paper, we present Uplink Multi-user Beamforming on single RF chain AP (UMBRA), a novel framework for supporting multi-stream multi-user uplink transmissions via a single RF chain. We design multi-user overlayed constellations and multi-user receiver mechanisms to enable concurrent time-triggered uplink multi-user transmissions received on a single RF chain AP. We devise exemplary beam selection policies to jointly adapt beams at users and the AP for targeting aggregate rate maximization without increasing training requirements compared to single-user systems. We implement the key components of UMBRA using a programmable WLAN testbed using software-defined radios and commercial 60-GHz transceivers and collect over-the-air measurements using phased-array antennas and horn antennas with varying beamwidth. We find that in comparison to single-user transmissions, UMBRA achieves more than 1.45× improvement in aggregate rate regardless of the choice of the user group, geometric separation, and receiver beamwidth.

With the rise of satellite mega-constellations, high-data-rate and low-latency space-based internet is set to transform the lives of users in remote locations with no access to the fiber-optic infrastructure. While current commercial constellations are relying on microwaves, they are legally and technologically limited to only a few gigahertz of bandwidth, paralyzing the potential for ultra high data rate performance. In this paper, a dual terahertz/Ka-band communication system is proposed and studied as a solution. A space-Earth propagation model based on the International Telecommunication Union most recent recommendations is presented, and a mega-constellation of 8,320 small satellites in low Earth orbit is designed to test the dual-band performance for the uplink, downlink, and crosslink. Extensive simulations are performed using an in-house-developed orbital simulation tool to calculate data rates for each terahertz and Ka band links based on signal-to-noise ratio estimates with dynamic decision making to constantly provide the highest data rate possible. For links between Earth and space, the results show similar performance for terahertz and Ka-band communications, while terahertz significantly outperforms in inter-satellite links. Simulation results show that terahertz communication can be a good candidate for space-Earth and inter-satellite links as both an enhancement to existing microwave technology and as a stand-alone technology with the identified challenges addressed.

In this paper, a link-layer synchronization and medium access control (MAC) protocol for very-high-speed wireless communication networks in the Terahertz (THz) band is presented. The protocol relies on a receiver-initiated handshake to guarantee synchronization between transmitter and receiver. Two scenarios are considered, namely, a macroscale scenario, where nodes utilize rotating directional antennas to periodically sweep the space while overcoming the distance problem at THz frequencies, and a nanoscale scenario, where nano-devices require energy harvesting systems to operate. Both scenarios are implemented on a centralized and an ad-hoc network architecture. A carrier-based physical layer is considered for the macro-scenario, whereas the physical layer for the nano-scenario is based on a femtosecond-long pulse-based modulation scheme with packet interleaving. The performance of the proposed MAC protocol is analytically investigated in terms of delay, throughput and probability of successful packet delivery, and compared to that of an adapted Carrier Sense Multiple Access with Collision Avoidance (CSMA/CA) with and without handshake. The results are validated by means of extensive simulations with ns-3, in which all the necessary THz elements have been implemented. The results show that the proposed protocol can maximize the successful packet delivery probability without compromising the achievable throughput in THz-band communication networks.

Terahertz (THz) band (0.1-10 THz) communication is envisioned as a potential key wireless technology to satisfy the need for much higher wireless data rates. THz-band communication supports a huge bandwidth. However, this advantage comes at the cost of a very high propagation loss. Thus, highly directional antennas (DAs) are simultaneously utilized in both transmission and reception to establish communication links beyond several meters. The application of highly DAs introduces many challenges for multi-hop routing. Among others, the best routing path dynamically changes since the directional communication links are periodically on and off, as determined by the DAs' current directions. Another challenge for routing protocol design comes from the limited memory or buffer size of THz devices, which is filled quickly when concurrent Terabit-per-second (Tbps) transmissions are handled. The buffer will be easily blocked by a locally stored packet that keeps waiting for the availability of the “best” route. This issue becomes even worse in directional networks, where such route may not be available shortly, and severely affects the network performance. In this paper, an adaptive routing protocol for highly dynamic buffer-limited directional THz communication networks is developed. A simulation framework is developed to study the iterations and updates between network performance and the choice made by each node. Extensive simulation results are provided to demonstrate the improvements of our proposed routing protocol.

Multi-user transmission in 60 GHz Wi-Fi can achieve data rates up to 100 Gbps by multiplexing multiple user data streams. However, a fundamental limit in the approach is that each RF chain is limited to supporting one stream or one user. To overcome this limit, we propose SIngle RF chain Multiuser BeAmforming (SIMBA), a novel framework for multi-stream multi-user downlink transmission via a single RF chain. We build on single beamformed transmission via overlayed constellations to multiplex multiple users' modulated symbols such that grouped users at different locations can share the same transmit beam from the AP. For this, we introduce user grouping and beam selection policies that span tradeoffs in data rate, training and computation overhead. We implement a programmable WLAN testbed using software-defined radios and commercial 60-GHz transceivers and collect over-the-air measurements using phased array antennas and horn antennas with varying beamwidth. We find that in comparison to single user transmissions, SIMBA achieves 2× improvement in aggregate rate and two-fold delay reduction for simultaneous transmission to four users.

Terahertz (THz)-band (0.1 THz to 10 THz) communication is envisioned as a key technology to meet the demand for faster, more ubiquitous wireless communication networks. For many years, the lack of compact, fast and efficient ways to generate, modulate, detect and demodulate THz-band signals has limited the feasibility of such communication systems. Recently, major progress within different device technologies is finally closing the so-called THz gap. For the time being, communication testbeds have been developed at sub-THz frequencies, i.e., at or near the boundary with millimeter-wave communication systems. Nonetheless, higher carrier frequencies and their associated bandwidth are needed to meet the demand for much higher data rates. In this paper, the TeraNova platform, i.e., the first integrated testbed for ultra-broadband wireless communications at true THz-band frequencies, is presented. The system consists of a transmitter and a receiver based on Schottky-diode frequency multiplying and mixing chains able to up & down-convert an information-bearing intermediate frequency (IF) signal up to 40 GHz-wide between 1 and 1.05 THz, i.e., the first absorption-defined transmission window above 1 THz. Guided by the experimental characterization of the THz channel in terms of path-loss and noise, tailored framing, time synchronization, channel estimation and single- and multi-carrier modulation techniques are implemented in software and realized by a state-of-the-art arbitrary waveform generator and a digital storage oscilloscope at the transmitter and the receiver, respectively. Experimental results are presented herein to highlight the opportunities and challenges to unleash the potential of the THz band.

Terahertz (THz)-band (0.1 - 10 THz) communication is envisioned as a key wireless technology to satisfy the need for higher wireless data rates in denser networks. Several ongoing approaches are being considered to overcome the grand challenge of the THz band, i.e., the limited communication distance. Among others, the use of new 2D nanomaterials such as graphene to create novel plasmonic devices that operate directly in the THz range and can be densely packed has been proposed. This paper presents a novel THz plasmonic array architecture which leverages the properties of graphene to greatly simplify its design and operation. Each element of the plasmonic array is an independent front-end, consisting of an on-chip plasmonic source, modulator and antenna. The advantages of this array architecture over conventional array architectures are discussed. The trade-offs in the design of the front-end and the array are exhaustively studied in transmission. The ability to perform continuous dynamic beamforming is presented. A new tailored algorithm is developed for beamforming weight selection. Extensive numerical results are provided to demonstrate the functionality of the array for dynamic beamforming and increased power output.

Recent Brain-Machine Interfaces have moved towards miniature devices that can be seamlessly integrated into the cortex. In this paper, we propose communication between miniature devices using light. A number of challenges exist using nanoscale light-based communication and this includes diffraction, scattering, and absorption, where these properties result from the tissue medium as well as the cell's geometry. Under these effects, the paper analyses the propagation path loss and geometrical gain, channel impulse and frequency response through a line of neurons with different shapes. Our study found that the light attenuation depends on the propagation path loss and geometrical gain, while the channel response is highly dependent on the quantity of cells along the path. Additionally, the optical properties of the medium impact the time delay at the receiver and the width and the location of the detectors. Simulations were conducted for cells that are lined horizontally up to a distance of 450 μm using light wavelength of 456 nm and different neuron densities (men's neocortex (25924(±15110) /mm3) and women's (27589(±16854) /mm3)). Based on the simulations, we found that spherical cells attenuate approximately 20% of the transmitted power compared to the fusiform and pyramidal cells (35% and 65%, respectively).

Millimeter-wave (30-300 GHz) and Terahertz-band communications (0.3-10 THz) are envisioned as key wireless technologies to satisfy the demand for Terabit-per-second (Tbps) links in the 5G and beyond eras. The very large available bandwidth in this ultra-broadband frequency range comes at the cost of a very high propagation loss, which combined with the low power of mm-wave and THz-band transceivers limits the communication distance and data-rates. In this paper, the concept of intelligent communication environments enabled by Ultra-Massive MIMO platforms is proposed to increase the communication distance and data-rates at mm-wave and THz-band frequencies. An end-to-end physical model is developed by taking into account the capabilities of novel intelligent plasmonic antenna arrays which can operate in transmission, reception, reflection and waveguiding, as well as the peculiarities of the mm-wave and THz-band multi-path channel. Based on the developed model, extensive quantitative results for different scenarios are provided to illustrate the performance improvements in terms of both achievable distance and data-rate in Ultra-Massive MIMO environments.

Terahertz (THz)-band (0.1-10 THz) communication has been envisioned as a key technology to enable wireless Terabitper-second (Tbps) links. At THz frequencies, the path-loss is governed by the spreading loss and the molecular absorption loss. The latter also determines the available transmission bandwidth, which drastically shrinks with distance. New physical layer solutions that capture this behavior are needed to maximally utilize the THz band. In this paper, the concept of hierarchical bandwidth modulation is introduced for single-transmitter multiple-receiver communication in the THz band. In the proposed modulation scheme, multiple flows of information aimed at users at different distances are transmitted at the same time and over the same frequency, by simultaneously adapting both the modulation order and, more importantly, the symbol time. Details for the modulator and the demodulator implementations are provided. The performance of the proposed modulation is analytically derived, both in terms of the achievable data rate as well as symbol error rate. Extensive numerical results based on analytical channel models that capture the peculiarities of the THz band are provided to illustrate the performance of the proposed scheme. The results show that the proposed modulation scheme can maximize the utilization of the distance-dependent bandwidth of the THz channel, turning molecular absorption into an advantage.

The development of optical nano-bio interfaces is a fundamental step toward connecting biological networks and traditional electronic computing systems. Compared to conventional chemical and electrical nano-bio interfaces, the use of light as a mediator enables new type of interfaces with unprecedented spatial and temporal resolutions. In this paper, the state of the art and future research directions in optogenomic interfaces are discussed. Optogenomic interfaces are light-mediated nano-bio interfaces that allow the control of the genome, i.e., the genes and their interactions in the cell nucleus (and, thus, of all the cell functionalities) with (sub) cellular resolution and high temporal accuracy. Given its fundamental role in the process of cell development, the study is focused on the interactions with the fibroblast growth factor receptor 1 (FGFR1) gene and the integrative nuclear FGFR1 signaling (INFS) module in stem cells and in neuronal cells, whose control opens the door to transformative applications, including reconstructive medicine and cancer therapy. Three stages of optogenomic interfaces are described, ranging from already experimentally validated interfaces activating broad cellular responses and expressing individual genes to more advanced interfaces able to regulate and correct DNA topology, chromatin structure, and cellular development.

The transmission of one-hundred-femtosecond-long pulses by following an ON-OFF keying modulation spread in time has been proposed as a way to enable Terahertz (THz)-band (0.1-10 THz) communications over short distances. Such modulation minimizes the probability of collisions due to the very small time that the channel is occupied by a user. However, given that many of the envisioned applications involve very large node densities, multi-user interference becomes unavoidable. In this paper, a stochastic model of multi-user interference is developed and experimentally validated. The model takes into account the fact that the interference power at the receiver is not a combination of the received powers from the individual nodes, but the power of the combination of the received signal amplitudes. For this, first, a mathematical framework is developed to compute the probability density function (PDF) of the interference generated by one interfering node at the receiver, starting from the PDFs of the pulse received energy and the PDF of the pulse shape. Then, the model is extended to account for multiple nodes which can constructively or destructively interfere. The developed model is experimentally validated by means of an innovative setup and the extensive numerical results are provided to analyze the trends of multi-user interference in pulse-based THz communications.

The millimeter-wave (mmWave) frequency band has been utilized in the IEEE 802.11ad standard to achieve multi-Gbps throughput. Despite the advantages, mmWave links are highly vulnerable to both user and environmental mobility. Since mmWave radios use highly directional antennas, the line-of-sight (LOS) signal can be easily blocked by various obstacles, such as walls, furniture, and humans. In the complicated indoor environment, it is highly possible that the blocked mmWave link cannot be restored no matter how the access point and the mobile user change their antenna directions. To address the problem and enable indoor mobile mmWave networks, in this paper, we introduce the reconfigurable 60 GHz reflect-arrays to establish robust mmWave connections for indoor networks even when the links are blocked by obstructions. First, the reconfigurable 60 GHz reflect-array is designed, implemented, and modeled. Then a three-party beam-searching protocol is designed for reflect-array-assisted 802.11ad networks. Finally, an optimal array deployment strategy is developed to minimize the link outage probability in indoor mobile mmWave networks. The proposed solution is validated and evaluated by both in-lab experiments and computer simulations.

Nanonetworks composed by communicating nano-devices enable new applications in the consumer, biomedical, and environmental fields. Three main characteristics introduce strict requirements for routing protocols design for nanonetworks, namely, short transmission range at Terahertz (THz) frequency (0.1-10 THz), fluctuations in the energy of nano-nodes due to the energy harvesting processes and very limited memory/buffer size of nano-nodes. In this paper, a multi-hop deflection routing algorithm based on Q-learning for energy-harvesting nanonetworks (MDRQEN) is proposed to guarantee the network energy efficiency, while ensuring a low packet loss probability. First, a deflection table is introduced to deflect the packets when the next hop nano-nodes are unavailable due to energy or memory/buffer constraints. Then, a Q-learning scheme is proposed to update the routing table and deflection table by utilizing the reward information contained in the forwarded packet from the previous nano-node. In the Q-learning update scheme, packet deflection ratio, packet loss ratio, packet hop count and node energy status of nano-nodes are taken into consideration. As numerically shown through extensive simulations in Network Simulator 3 (NS-3), the proposed MDRQEN algorithm can achieve a better packet delivery ratio and energy efficiency than random routing algorithm, flooding routing algorithm and the MDRQEN algorithm without the Q-learning update scheme.

Terahertz (THz)-band communication (0.1-10 THz) is envisioned as a key wireless technology to satisfy the in- creasing demand for faster data-rates in beyond 5G systems, thanks to its ultra-broad bandwidth. The very high path loss at THz frequencies and the limited transmission power of THz transceivers impose a major distance limitation for THz wireless communications. To increase the communication distance and the achievable data rates at THz-band frequencies, the concept of Ultra-Massive MIMO (UM-MIMO) has been introduced, which integrates a very large number of nano-antennas (e.g., 1024) in very small footprints (e.g., 1 mm^2). In this paper, an end-to-end model for UM-MIMO communication in the THz band is developed, by accounting for the properties of graphene- based plasmonic nano-antenna arrays and the peculiarities of three- dimensional THz propagation. The developed model is utilized to investigate the performance of the UM- MIMO channel. In particular, the path gain, the array factor and the the wideband capacity for both spatial multiplexing and beamforming regimes are analyzed. The results show that multi-Terabit-per-second links are feasible at distances of up to 20 m when utilizing 1024 × 1024 UM-MIMO systems at 0.3 THz and 1 THz.

Terahertz (THz)-band (0.1-10 THz) communication is envisioned as a potentially key technology to satisfy the need for much higher wireless data rates. The THz-band provides a huge transmission bandwidth, which ranges from hundreds of GHz up to a few THz. Nevertheless, this bandwidth comes at the cost of a very high pass loss, and, as a result, highly directional antennas are needed simultaneously in transmission and reception to establish a communication link beyond a few meters. In directional communication networks, efficient neighbor discovery is needed to overcome the deafness problem. Existing neighbor discovery protocols for lower frequency bands cannot be directly utilized, because they do not capture the peculiarities of the THz band or the need to support multi Giga-bit-per-second and even Tera-bit-per- second links. In this paper, a neighbor discovery protocol for THz- band communication networks that leverages the directional antenna side-lobe information is presented. More specifically, the full antenna radiation pattern is utilized to detect a series of effective signals and map them to a universal detection standard and expedite the neighbor discovery process. A mathematical framework is developed to compare the neighbor discovery protocols with and without the antenna side-lobe information, and numerical results are provided to illustrate the performance of the proposed neighbor discovery protocol in terms of total time needed to complete the discovery process.

In vivo wireless nanosensor networks (iWNSNs) consist of communicating miniature devices with unprecedented sensing and actuation capabilities, which are able to operate inside the human body. iWNSNs are the basis of emerging healthcare applications, such as intrabody health-monitoring and control of biological processes at subcellular level. Major progress in the field of nanoelectronics, nanophotonics, and wireless communication is enabling the interconnection of the nanodevices in iWNSNs. In this paper, the effect of single biological cells and cell assemblies on the propagation of optical wave for intrabody communications of nanosensors is analytically investigated in three distinct ways, namely, geometrical, time-domain, and frequency-domain analyses. The analytical channel model is validated by means of full wave electromagnetic simulations through a case study for red blood cells (RBCs) inside the blood plasma. The results show that RBCs perform as optical microlenses that confine the radiated light on a focal area, which agrees with recent experimental achievements. It is also shown that changes in shape and size of the cells slightly alter the channel impulse response. This study motivates the development of new communication solutions for intrabody nanoscale optical communication networks and new nanobiosensing strategies able to identify diseases which cause cell shape alterations.

In vivo Wireless Nanosensor Networks (iWNSNs) consist of nano-sized communicating devices with unprecedented sensing and actuation capabilities, which are able to operate inside the human body. Major progress in the field of nanoelectronics, nanophotonics and wireless communication is enabling the communication among nanosensors. Among others, plasmonic nanolasers with sub-micrometric footprint, plasmonic nano-antennas able to confine light in nanometric structures, and single-photon detectors with unrivaled sensitivity, enable the communication among implanted nanosensors in the near infrared and optical transmission window. In this paper, a channel model for in vivo optical communication in iWNSNs is developed. By following a geometrical approach to trace and aggregate the path loss and time delay of each of the rays that encounter a biological cell, a closed form channel impulse response is derived. The analytical channel model is validated by means of electromagnetic simulations for a Red Blood Cell (RBC) inside the blood plasma. The results show that RBCs perform as optical micro-lenses in terms of confining the light that is being radiated to them on a focal line right after the cell. This results are in strong agreement with the recent experimental achievements on interactions of light and RBCs.

We introduce X60, the first SDR-based testbed for 60 GHz WLANs, featuring fully programmable MAC/PHY/Network layers, multi-Gbps rates, and a user-configurable 12-element phased antenna array. These features provide us with an unprecedented opportunity to revisit the most important aspects of 60 GHz signal propagation and obtain new insights on performance expected from practical 60 GHz systems. X60's unique capabilities make it an ideal platform for experimentation and prototyping across layers.

Wireless Networks on Chip (WNoC) consist of multiple independent cores interconnected by a smart combination of wired and wireless links. Wired interconnections have progressively moved from electrical tracks to nanophotonic waveguides in order to meet the demand for faster links. However, wireless links still largely rely on radio-frequency, millimeter-wave and, more recently, Terahertz-band communication, which offer a significantly lower bandwidth than their wired counterparts. To overcome this limitation, in light of the state of the art in optical nano-antennas, the use of wireless optical communication on-chip is proposed in this paper for the first time. Wireless optical links across cores can meet the demand for much higher data rates among cores, provide seamless wired and wireless transitions, and support multicast and broadcast transmissions among cores enabled by omnidirectional nano-antennas. To analyze the feasibility of this paradigm, in this paper, a multi-path channel model for on- chip light propagation is developed. More specifically, first, the channel frequency response in the case of line-of-sight propagation is obtained, by capturing the impact of spreading and absorption of light in silicon-based semiconductor materials. Then, the non-line-of-sight paths created by reflection at the material layer interfaces and diffraction at the core edges are modeled. Finally, a multi-path channel model is formulated, validated by means of electromagnetic simulations with COMSOL Multi-physics and utilized to analyze the main properties of on-chip wireless optical communication.

Terahertz (THz) band (0.1-10 THz) communication, which is envisioned as one of the key wireless communication technologies of the next decade, exhibits an extremely large bandwidth at the cost of an extremely high path loss. The unique distance-dependent behavior on the available bandwidth in THz communication interrelates all THz properties, and affects the design and performances within and across the physical, link and network layers. More specifically, the limited transmission power, combined with the high path loss, requires the use of directional antennas (DAs). High DAs have a clear impact at the link layer as well as the network layer, where relaying becomes a requirement. In this paper, optimal relaying strategies for THz-band communication networks are investigated. More specifically, a mathematical framework is formulated and used to study the optimal relaying distance that maximizes the network throughput by taking into account the cross-layer effects between the channel, the antenna, and the physical, link and network layers. Numerical results are provided to illustrate the importance of accurate cross-layer design strategies for THz networks.

The fifth generation wireless systems are expected to rely on a large number of small cells to massively offload traffic from the cellular and even from the wireless local area networks. To enable this functionality, mm-wave (EHF) and Terahertz (THF) bands are being actively explored. These bands are characterized by unique propagation properties compared with microwave systems. As a result, the interference structure in these systems could be principally different to what we observed so far at lower frequencies. In this paper, using the tools of stochastic geometry, we study the systems operating in the EHF/THF bands by explicitly capturing three phenomena inherent for these frequencies: (1) high directivity of the transmit and receive antennas;( 2) molecular absorption; and (3) blocking of high-frequency radiation. We also define and compare two different antenna radiation pattern models. The metrics of interest are the mean interference and the signal-to-interference-plus-noise (SINR) ratio at the receiver. Our results reveal that: (1) for the same total emitted energy by a Poisson field of interferers, both the interference and SINR significantly increase when simultaneously both transmit and receive antennas are directive and (2) blocking has a profound impact on the interference and SINR creating much more favorable conditions for communications compared with no blocking case.

The fifth generation wireless systems are expected to rely on a large number of wideband small cells to offload traffic from the cellular and wireless local area networks. To create such small cells, EHF and THF bands are actively explored. These frequencies are characterized by fundamentally different propagation characteristics resulting in different interference structure at the receiver compared to, e.g., microwave systems. In this paper, we study the interference structure for systems operating in EHF/THF bands by explicitly capturing three major phenomena: (i) extreme directivity of the transmit and/or receive antennas, (ii) pass loss component caused by molecular absorption and (iii) blocking of high-frequency radiation. The metric of interest is the mean interference at the receiver. Our results reveal that (i) for the same emitted energy in a Poisson field of interferers, the interference increases with the directivity of the transmit or receive antennas, (ii) blocking has a profound impact on the interference creating much more favorable conditions for communications compared to lower frequencies and (iii) the choice of the antenna model is of crucial importance for accurate performance assessment.

In recent years, numerous research efforts have been dedicated towards developing efficient implantable devices for Deep Brain Stimulation (DBS). However, there are limitations and challenges with the current technologies. Firstly, the stimulation of neurons currently is only possible through implantable electrodes which target a population of neurons. This results in challenges in the event that stimulation at the single neuron level is required. Secondly, a major hurdle still lies in developing miniature devices that can last for a lifetime in the patient's brain. Recently, the concept of neural dust has been introduced as a way to achieve single neuron monitoring and potentially actuation. In parallel to this, the field of optogenetics has emerged where the aim is to stimulate neurons using light, usually by means of optical fibers inserted through the skull. Obviously, this introduces many challenges in terms of user friendliness and biocompatibility. We address this shortcoming by proposing the wireless optogenetic neural dust (wi-opt neural dust). The wiopt neural dust is equipped with a miniature LED that is able to stimulate the genetically engineered neurons, and at the same time harvest energy from ultrasonic vibrations. The simulation results presented in the paper investigates the behaviour of the light propagation in the brain tissue, as well as the performance of designed circuitry for the energy harvesting process. The results demonstrates the feasibility of utilizing wi-opt neural dust for long term implantation in the brain, and a new direction towards precise stimulation of neurons in the cortex.

Wireless Nanosensor Networks (WNSNs), i.e., networks of miniaturized devices with unprecedented sensing capabilities, are at the basis of transformative applications in the biomedical, environmental and industrial fields. Recent developments in plasmonic nano-antennas point to the Terahertz (THz) band (0.1-10 THz) as the frequency range of communication among nanosensors. While this potentially enables extremely high data rates in WNSNs, the very high path-loss at such frequencies and the limited power of energy-harvesting nano-devices limit the achievable throughput. In this paper, the link throughput maximization problem in WNSNs is addressed by taking into account the device and communication interdependencies in WNSNs. The optimal data packet size which maximizes the link efficiency is derived by capturing the device, channel, physical and link layer peculiarities of WNSNs. The energy harvesting limits and the successful packet transmission time are defined as the optimization problem constraints, and the optimal solution is derived by using a bisection method. Numerical results are provided to analyze the impact of the packet size for different error control strategies. The results show that the optimal packet size quickly decreases with the transmission distance, approaching several hundreds bits for distances beyond a few millimeters.

The radio frequency (RF) spectrum becomes overly crowded in some indoor environments due to the high density of users and bandwidth demands. To accommodate the tremendous wireless data demands, efficient spectrum-sharing approaches are highly desired. To this end, this paper introduces a new spectrum sharing solution for indoor environments based on the usage of a reconfigurable reflect-array in the middle of the wireless channel. By optimally controlling the phase shift of each element on the reflect-array, the useful signals for each transmission pair can be enhanced while the interferences can be canceled. As a result, multiple wireless users in the same room can access the same spectrum band at the same time without interfering each other. Hence, the network capacity can be dramatically increased. To prove the feasibility of the proposed solution, an experimental testbed is first developed and evaluated. Then, the effects of the reflect-array on transport capacity of the indoor wireless networks are investigated. Through experiments, theoretical deduction, and simulations, this paper demonstrates that significantly higher spectrum-spatial efficiency can be achieved by using the smart reflect-array without any modification of the hardware and software in the users' devices.

Nanotechnology is enabling the development of miniature devices able to perform simple tasks at the nanoscale. The interconnection of such nano-devices with traditional wireless networks and ultimately the Internet enables a new networking paradigm known as the Internet of Nano-Things (IoNT). Despite their promising applications, nano-devices have constrained power, energy, and computation capabilities along with very limited memory on board, which may only be able to hold one packet at once and, thus, requires packets to be delivered before certain hard deadlines. Toward this goal, a fully-distributed computation-light provably-correct scheduling/MAC protocol is introduced for bufferless nano-devices, which can maximize the network throughput, while achieving perpetual operation. More specifically, the proposed scheduling algorithm allows every nano-device to make optimal transmission decisions locally based on its incoming traffic rate, virtual debts, and channel sensing results. It is proven that the proposed algorithm is timely throughput optimal in the sense that it can guarantee reliable data delivery before deadlines as long as the incoming traffic rates are within the derived maximum network capacity region. This feature not only can lead to high network throughput for the IoNT, but also guarantees that the memory of each device is empty before the next packet arrives, thus addressing the fundamental challenge imposed by the extremely limited memory of nano-devices. In addition, the optimal deadline is derived, which guarantees that all the nano-devices can achieve perpetual communications by jointly considering the energy consumption of communications over the terahertz channel and energy harvesting based on piezoelectric nano-generators.

The six papers in this special section focus on the Internet of nanotechnology things. While researchers are currently investigating these challenges to develop fully functional nano communication systems, a question remains as to whether they can represent an extended communication network that is part of the broader Internet. These papers address new solutions for the Internet of Nano Things. The Internet of Things paradigm has transformed the way we operate our personal and professional lives, it is driving our economy and will continue to enable many new opportunities in broad research areas. As this pervasive and ubiquitous interconnection of our everyday life appliances continues into the future, new types of devices enabled by nano and biotechnology promise to push engineering to previously unexplored application domains, where the exchange of information and access from/to the broader Internet for their monitoring and control are even more essential. The research on nanoscale communication and networks aims to develop systems for interconnecting these novel devices at the nanoscale, i.e., the Internet of Nano Things.

Ongoing research in graphene-based nano-transceivers and nano-antennas points to the Terahertz (THz) band (0.1-10 THz) as the communication frequency range for nano-devices. Femtosecond-long pulse-based modulation schemes have been proposed to enable ultra-broadband communication among nano-devices. One of the main challenges with ultra-high-speed pulse-based communications is the need for tight symbol synchronization between transmitter and receiver. In this paper, a synchronization scheme for pulse-based THz-band communications is designed and analyzed. The proposed scheme is aimed at iteratively estimating the symbol start time and reducing the observation window length for the symbol detector. The proposed scheme is fully analog and can be implemented with a combination of voltage-controlled delay (VCD) lines and Continuous-Time Moving-Average (CTMA) symbol detectors. Closed form expressions are obtained for the number of preamble symbols needed to achieve synchronization as well as the maximum number of bits that can be transmitted before requiring re-synchronization in the presence of clock skew. Similarly, the symbol error rate of the CTMA receiver is analytically modeled as a function of the resulting observation window length. Finally, the synchronization and symbol detection impact on the achievable throughput is studied. The developed scheme is experimentally tested with measured THz pulses and its performance is numerically investigated. The results show how the proposed scheme can successfully estimate the symbol start time and minimize the symbol error rate with less than ten synchronization preamble bits.

In this paper, a link-layer synchronization and medium access control (MAC) protocol for very-high-speed wireless communication networks in the THz band is presented. The protocol relies on a receiver-initiated handshake as a way to guarantee synchronization between transmitter and receiver. In addition, it incorporates a sliding window flow control mechanism, which combined with the one-way handshake, maximizes the channel utilization. Two different application scenarios are considered, namely, a macroscale scenario, in which nodes utilize turning directional antennas to periodically sweep the space while overcoming the distance problem at THz frequencies, and a nanoscale scenario, in which nano-nodes require energy harvesting systems to operate. A carrier-based physical layer is considered for the macro-scenario, whereas the physical layer for the nano-scenario is based on a femtosecond- long pulse-based modulation scheme with frame interleaving. The performance of the proposed MAC protocol is analytically investigated in terms of delay, throughput and successful packet transmission probability, and compared to that of an adapted Carrier Sense Multiple Access with Collision Avoidance with and without handshake. The results are validated by means of extensive simulations with ns-3, in which all the necessary THz elements have been implemented. The results show that the proposed protocol can maximize the successful packet delivery probability without compromising the achievable throughput in THz-band communication networks.

Graphene is a promising material which has been proposed to build graphene plasmonic miniaturized antennas, or graphennas, which show excellent conditions for the propagation of Surface Plasmon Polariton (SPP) waves in the terahertz band. Due to their small size of just a few micrometers, graphennas allow the implementation of wireless communications among nanosystems, leading to a novel paradigm known as Graphene-enabled Wireless Communications (GWC). In this paper, an analytical framework is developed to evaluate how the channel capacity of a GWC system scales as its dimensions shrink. In particular, we study how the unique propagation of SPP waves in graphennas will impact the channel capacity. Next, we further compare these results with respect to the case when metallic antennas are used, in which these plasmonic effects do not appear. In addition, asymptotic expressions for the channel capacity are derived in the limit when the system dimensions tend to zero. In this scenario, necessary conditions to ensure the feasibility of GWC networks are found. Finally, using these conditions, new guidelines are derived to explore the scalability of various parameters, such as transmission range and transmitted power. These results may be helpful for designers of future GWC systems and networks.

Nanonetworks consist of nano-sized communicating devices which are able to perform simple tasks at the nanoscale. Nanonetworks are the enabling technology of long-awaited applications such as advanced health monitoring systems or high-performance distributed nano-computing architectures. The peculiarities of novel plasmonic nano-transceivers and nano-antennas, which operate in the Terahertz Band (0.1-10 THz), require the development of tailored communication schemes for nanonetworks. In this paper, a modulation and channel access scheme for nanonetworks in the Terahertz Band is developed. The proposed technique is based on the transmission of one-hundred-femtosecond-long pulses by following an asymmetric On-Off Keying modulation Spread in Time (TS-OOK). The performance of TS-OOK is evaluated in terms of the achievable information rate in the single-user and the multi-user cases. An accurate Terahertz Band channel model, validated by COMSOL simulation, is used, and novel stochastic models for the molecular absorption noise in the Terahertz Band and for the multi-user interference in TS-OOK are developed. The results show that the proposed modulation can support a very large number of nano-devices simultaneously transmitting at multiple Gigabits-per-second and up to Terabits-per-second, depending on the modulation parameters and the network conditions.

Nanonetworks, i.e., networks of nano-sized devices, are the enabling technology of long-awaited applications in the biological, industrial and military fields. For the time being, the size and power constraints of nano-devices limit the applicability of classical wireless communication in nanonetworks. Alternatively, nanomaterials can be used to enable electromagnetic (EM) communication among nano-devices. In this paper, a novel graphene-based nano-antenna, which exploits the behavior of Surface Plasmon Polariton (SPP) waves in semi-finite size Graphene Nanoribbons (GNRs), is proposed, modeled and analyzed. First, the conductivity of GNRs is analytically and numerically studied by starting from the Kubo formalism to capture the impact of the electron lateral confinement in GNRs. Second, the propagation of SPP waves in GNRs is analytically and numerically investigated, and the SPP wave vector and propagation length are computed. Finally, the nano-antenna is modeled as a resonant plasmonic cavity, and its frequency response is determined. The results show that, by exploiting the high mode compression factor of SPP waves in GNRs, graphene-based plasmonic nano-antennas are able to operate at much lower frequencies than their metallic counterparts, e.g., the Terahertz Band for a one-micrometer-long ten-nanometers-wide antenna. This result has the potential to enable EM communication in nanonetworks.

Graphene-enabled wireless communications set the Terahertz Band as the frequency band of operation of future nanodevices (0.1-10 THz). Amongst others, femtosecond-long pulse-based modulation schemes have been recently proposed to enable the communication among nanodevices. Within this context, a receiver architecture suitable for nanodevices must be ultra compact, must have high sensitivity and must be ultra-low power. Unfortunately, common receiver architectures used in other communication schemes, such as IR-UWB, show a strong compromise between low complexity and performance. In this paper, a novel receiver architecture for pulse-based communication based on a Continuous-time Moving Average (CTMA) symbol detection scheme is presented. This scheme bases its symbol decision on the received signal power maximum peak after the CTMA, which is implemented with a single low-pass filter. Moreover, an analytical model for the symbol detection is provided and it is quantitatively shown that the proposed CTMA scheme outperforms previous symbol detection schemes for pulse-based modulations in terms of Symbol Error Rate (SER). The low complexity and relaxed synchronization needed for this symbol detector makes this structure specially suited for the development of future transceivers for nano-devices.

Nanotechnology is enabling the development of integrated nano-devices which are able to perform only very simple tasks. Nanonetworks, i.e., networks of nano-devices, will enable advanced applications of nanotechnology in the biomedical, environmental and military fields. One of the major bottlenecks in nanonetworks is posed by the very limited energy that can be stored in a nano-battery in contrast to the energy that is required by a nano-device to operate and, specially, to communicate. Recently, novel energy harvesting mechanisms have been proposed to replenish the energy stored in the nano-batteries. With these mechanisms, nanonetworks can overcome their energy bottleneck and even have infinite lifetime. In this paper, an energy model for self-powered nano-devices is developed that successfully captures the correlation between the energy harvesting and the energy consumption processes. The energy harvesting process is realized by means of a piezoelectric nano-generator, for which a new circuital model is developed which can accurately reproduce existing experimental data. The energy consumption process is due to the communication among nano-devices in the Terahertz Band (0.1-10 THz). A mathematical framework is developed to obtain the probability distribution of the nano-device energy and to investigate the end-to-end successful packet delivery probability, the end-to-end packet delay, and the throughput in nanonetworks. Integrated nano-devices have not been built yet and, thus, the development of an analytical energy model is a fundamental step towards the design of architectures and protocols for nanonetworks.

Nanotechnology is providing the engineering community with a new set of tools to design and manufacture integrated devices just a few hundred nanometers in total size. Communication among these nano-devices will boost the range of applications of nanotechnology in several fields, ranging from biomedical research to military technology or environmental science. Within the different alternatives for communication in the nanoscale, recent developments in nanomaterials point to the Terahertz band (0.1-10 THz) as the frequency range of operation of future electromagnetic nano-transceivers. This frequency band can theoretically support very large bit-rates in the short range, i.e., for distances below one meter. Due to the limited capabilities of individual nano-devices, pulse-based communications have been proposed for electromagnetic nanonetworks in the Terahertz band. However, the expectedly very large number of nano-devices and the unfeasibility to coordinate them, can make interference a major impairment for the system. In this paper, low-weight channel coding is proposed as a novel mechanism to reduce interference in pulse-based nanonetworks. Rather than utilizing channel codes to detect and correct transmission errors, it is shown that by appropriately choosing the weight of a code, interference can be mitigated. The performance of the proposed scheme is analytically and numerically investigated both in terms of overall interference reduction and achievable information rate, by utilizing a new statistical interference model. The results show that this type of network-friendly channel coding schemes can be used to alleviate the interference problem in nanonetworks without compromising the individual user information rate.

Nanotechnology is enabling the development of sensing devices just a few hundreds of nanometers in size, which are able to measure new types of events in the nanoscale by exploiting the properties of novel nanomaterials. Wireless communication among these nanosensors will boost the range of applications of nanotechnology in the biomedical, environmental and military fields, amongst others. Within the different alternatives for communication in the nanoscale, recent advancements in nanomaterials point to the Terahertz band (0.1-10.0 THz) as the frequency range of operation of future electronic nano-devices. This still unlicensed band can theoretically support very large transmission bit-rates in the short range, i.e., for distances below one meter. More importantly, the Terahertz band also enables very simple communication mechanisms suited to the very limited capabilities of nanosensors. In this paper, a new communication paradigm called TS-OOK (Time Spread On-Off Keying) for Electromagnetic Wireless Nanosensor Networks (WNSNs) is presented. This new technique is based on the transmission of femtosecond-long pulses by following an on-off keying modulation spread in time. The performance of this scheme is assessed in terms of information capacity for the single-user case as well as aggregated network capacity for the multiuser case. The results show that by exploiting the peculiarities of the Terahertz band, this scheme provides a very simple but robust communication technique for WNSNs. Moreover, it is shown that, due to the peculiar behavior of the noise in the Terahertz band, the single-user capacity and the aggregated network capacity can exceed those of the AWGN channel classical wireless networks, when the appropriate channel codes are used.

Nanotechnologies promise new solutions for several applications in the biomedical, industrial and military fields. At the nanoscale, a nanomachine is considered as the most basic functional unit which is able to perform very simple tasks. Communication among nanomachines will allow them to accomplish more complex functions in a distributed manner. In this paper, the state of the art in molecular electronics is reviewed to motivate the study of the Terahertz Band (0.1-10.0 THz) for electromagnetic (EM) communication among nano-devices. A new propagation model for EM communications in the Terahertz Band is developed based on radiative transfer theory and in light of molecular absorption. This model accounts for the total path loss and the molecular absorption noise that a wave in the Terahertz Band suffers when propagating over very short distances. Finally, the channel capacity of the Terahertz Band is investigated by using this model for different power allocation schemes, including a scheme based on the transmission of femtosecond-long pulses. The results show that for very short transmission distances, in the order of several tens of millimeters, the Terahertz channel supports very large bit-rates, up to few terabits per second, which enables a radically different communication paradigm for nanonetworks.

Nanotechnology is enabling the development of devices in a scale ranging from one to a few hundred nanometers. Coordination and information sharing among these nano-devices will lead towards the development of future nanonetworks, rising new applications of nanotechnology in the medical, environmental and military fields. Despite the major progress in nano-device design and fabrication, it is still not clear how these atomically precise machines will communicate. The latest advancements in graphene- based electronics have opened the door to electromagnetic communication among nano-devices in the terahertz band (0.1-10 THz). This frequency band can potentially provide very large bandwidths, ranging from the entire band to several gigahertz- wide windows, depending on the transmission distance and the molecular composition of the channel. In this paper, the capacity of the terahertz channel is numerically evaluated by using a new terahertz propagation model, for different channel molecular compositions, and under different power allocation schemes. A novel communication technique based on the transmission of ultra-short pulses, less than one picosecond long, is motivated and quantitatively compared to the capacity- optimal power allocation scheme. The results show that for the very short range, up to a few tens of millimeters, the transmission of short pulses offer a realistic and still efficient way to exploit the terahertz channel.