Statistical channel modeling for short range line-of-sight terahertz communication

Underutilized spectrum constitutes a major concern in wireless communications especially in the presence of legacy systems and the prolific need for high-capacity applications as well as consumer expectations. From this perspective, Terahertz frequencies provide a new paradigm shift in wireless communications since they have been left unexplored until recently. Such a vast frequency spectrum region extending all the way up to visible light and beyond points out significant opportunities from dramatic data rates on the order of tens of Gbps to a variety of inherent security and privacy mechanisms, and techniques that are not available in the traditional systems. Thus, in this paper, we investigate statistical parameters for short-range line- of-sight channels of Terahertz communication. Short-range measurement campaign within the interval of [3cm, 20cm] are carried out between 275GHz to 325GHz range. Path loss model is examined for different frequencies and distances to provide the insight regarding the effect of the operating frequency. Measurement results are provided with relevant discussions and future directions

A Holistic Investigation on Terahertz Propagation and Channel Modeling Toward Vertical Heterogeneous Networks

User-centric and low latency communications can be enabled not only by small cells but also through ubiquitous connectivity. Recently, the vertical heterogeneous network (V-HetNet) architecture is proposed to backhaul/fronthaul a large number of small cells. Like an orchestra, the V-HetNet is a polyphony of different communication ensembles, including geostationary orbit (GEO), and low-earth orbit (LEO) satellites (e.g., CubeSats), and networked flying platforms (NFPs) along with terrestrial communication links. In this study, we propose the Terahertz (THz) communications to enable the elements of V-HetNets to function in harmony. As THz links offer a large bandwidth, leading to ultra-high data rates, it is suitable for backhauling and fronthauling small cells. Furthermore, THz communications can support numerous applications from inter-satellite links to in-vivo nanonetworks. However, to savor this harmony, we need accurate channel models. In this paper, the insights obtained through our measurement campaigns are highlighted, to reveal the true potential of THz communications in V-HetNets.Comment: It has been accepted for the publication in IEEE Communications Magazin

Multiple Antenna Techniques for Terahertz Nano-Bio Communication

Using higher frequency bands becomes an essential demand resulting from the explosive wireless traffic needs and the spectrum shortage of the currently used bands. This paper presents an overview on the terahertz technology and its application in the area of multi-input multi-output antenna system and in-vivo nano-communication. In addition, it presents a preliminary study on applying multiple input-single output (MISO) antenna technique to investigate the signal propagation and antenna diversity techniques inside the human skin tissues, which is represented by three layers: stratum corneum (SC), epidermis, and dermis layers, in the terahertz (THz) frequency range (0.8-1.2) THz. The spatial antenna diversity is investigated in this study to understand MISO system performance for two different in-vivo channels resulting from the signal propagation between two transmitting antennas, located at the dermis layer, and one receiving antenna, located at epidermis layer. Three techniques are investigated: selection combining (SC), equal-gain combing (EGC), and maximum-ratio combining (MRC). The initial study indicates that using multiple antenna technique with THz might be not useful for in-vivo nano-communication

On Channels with Composite Rough Surfaces at Terahertz Frequencies

The paper preliminarily examines the influence of diffuse reflection by composite rough surfaces in ultra-broadband terahertz (THz) communication channels across 300 GHz (0.3 THz) to 310 GHz (0.31 THz) frequency spectrum. At terahertz frequencies, diffuse reflection tends to be higher due to the increased surface roughness and this surface roughness causes an additional attenuation even in a specular direction of reflection (by the amount that is scattered into non-specular directions). Two most famous modeling approaches, Rayleigh-Rice (R-R) and Beckmann-Kirchhoff (B-K) theories are employed to account for the surface scattering and compared by demonstrating the multipath channel transfer function (CTF) dynamics for line-of-sight (LoS) and non-line-of-sight (NLoS) conditions in a simple office environment. The R-R vector perturbation approach predicts diffuse reflection from optically smooth surfaces (σ h /λ≪1), whilst classical B-K theory in addition attempts to predict the angular distribution of the scattered field from very rough surfaces (σ h /λ≪1). The composite rough surfaces considered in this work have a Gaussian probability density of height and a Gaussian correlation function. Based on these results, it is concluded that the rough surface scattering effects are enhanced at terahertz frequencies and the scattering phenomena show a significant impact, especially in NLoS configuration

Modeling and Analysis of sub-Terahertz Communication Channel via Mixture of Gamma Distribution

With the recent developments on opening the terahertz (THz) spectrum for experimental purposes by the Federal Communications Commission, transceivers operating in the range of 0.1THz-10THz, which are known as THz bands, will enable ultra-high throughput wireless communications. However, actual implementation of the high-speed and high-reliability THz band communication systems should start with providing extensive knowledge in regards to the propagation channel characteristics. Considering the huge bandwidth and the rapid changes in the characteristics of THz wireless channels, ray tracing and one-shot statistical modeling are not adequate to define an accurate channel model. In this work, we propose Gamma mixture-based channel modeling for the THz band via the expectation-maximization (EM) algorithm. First, maximum likelihood estimation (MLE) is applied to characterize the Gamma mixture model parameters, and then EM algorithm is used to compute MLEs of the unknown parameters of the measurement data. The accuracy of the proposed model is investigated by using the Weighted relative mean difference (WMRD) error metrics, Kullback-Leibler (KL)-divergence, and Kolmogorov-Smirnov test to show the difference between the proposed model and the actual probability density functions (PDFs) that are obtained via the designed test environment. According to WMRD error metrics, KL-divergence, and KS test results, PDFs generated by the mixture of Gamma distributions fit the actual histogram of the measurement data. It is shown that instead of taking pseudo-average characteristics of sub-bands in the wideband, using the mixture models allows for determining channel parameters more precisely.Comment: This paper has been accepted for publication in IEEE Transactions on Vehicular Technolog

THZ RF measurement techniques

Abstract. In this thesis, literature review on available methods, techniques and procedures for terahertz antenna measurement system and terahertz propagation measurement system are reported. The paper presented the terahertz frequency spectrum allocation by FCC, ITU, ETSI and its application in wireless communication system with advantage in obtaining terabits per second data rates. Terahertz antenna parameters are reported and measurement systems for measurement of these chapters are reviewed. Literature of three papers on terahertz antenna measurement system with their respective measurement setup, calibration techniques and measurement procedures are reviewed. An automated antenna measurement system is reviewed with stochastic and systematic measurements and has achieved terahertz antenna s-parameter measurements in far field region at frequency range of 220 GHz to 330 GHz. Another measurement system with single port short-open-load (SOL) calibration technique is reviewed. In this measurement of s-parameter of terahertz antenna is carried out, using receiver horn placed on 3 D positioner, which records the AUT 3D radiation pattern. The third paper reviewed, is a reconfigurable terahertz antenna measurement system, with capabilities of working on large bandwidths, with small change in work bench instrumentation. This setup contains the multiplexing stages for terahertz frequency generation. Beam pattern measurements are conducted at 1.37 THz supporting the simulations and the system stability for reconfigurations. In the later study, terahertz propagation parameters are studied and presented for review of available terahertz propagation measurement systems. Literature review of three papers describing different setup and procedures for terahertz propagation measurement system are reported. The first system with the setup to record path loss in LOS and NLOS links at 260 GHz to 400 GHz is presented. Propagation parameters containing reflections, shadowing is measured. LOS and NLOS channel capacity models are obtained based on data rates in terabits per second for using above 5G wireless communication systems. Another system with office architecture, indoor LOS link, viable for indoor wireless communication applications is reported. Propagation parameters containing power density profile (PDP) are measured and validated for 140 GHz to 220 GHz. A measurement system which reports effect of atmospheric pressure, temperature and humidity is reported in the last. The setup used short, offset-short, load and thru (SOLT) technique for calibration and PDP propagation parameter is measured for 0.5 THz to 0.75 THz. Terahertz antenna and wave propagation measurement system reviewed in the papers are vital for development of terahertz systems in wireless and mobile communication. Further the study can be extended for measurement of terahertz antennas and wave propagation parameters with models of use in wireless hand-held devices, connected devices, mobile backhaul system and more

306-321 GHz Wideband Channel Measurement and Analysis in an Indoor Lobby

The Terahertz (0.1-10 THz) band has been envisioned as one of the promising spectrum bands to support ultra-broadband sixth-generation (6G) and beyond communications. In this paper, a wideband channel measurement campaign in an indoor lobby at 306-321 GHz is presented. The measurement system consists of a vector network analyzer (VNA)-based channel sounder, and a directional antenna equipped at the receiver to resolve multi-path components (MPCs) in the angular domain. In particular, 21 positions and 3780 channel impulse responses (CIRs) are measured in the lobby, including the line-of-sight (LoS), non-line-of-sight (NLoS) and obstructed-line-of-sight (OLoS) cases. Multi-path propagation is elaborated in terms of clustering results, and the effect of typical scatterers in the indoor lobby scenario in the THz band is explored. Moreover, indoor THz channel characteristics are analyzed in depth. Specifically, best direction and omni-directional path losses are analyzed by invoking close-in and alpha-beta path loss models. The most clusters are observed in the OLoS case, followed by NLoS and then LoS cases. On average, the power dispersion of MPCs is smaller in the LoS case in both temporal and angular domains, compared with the NLoS and OLoS counterparts.Comment: 6 pages, 15 figure

Terahertz Communications and Sensing for 6G and Beyond: A Comprehensive View

The next-generation wireless technologies, commonly referred to as the sixth generation (6G), are envisioned to support extreme communications capacity and in particular disruption in the network sensing capabilities. The terahertz (THz) band is one potential enabler for those due to the enormous unused frequency bands and the high spatial resolution enabled by both short wavelengths and bandwidths. Different from earlier surveys, this paper presents a comprehensive treatment and technology survey on THz communications and sensing in terms of the advantages, applications, propagation characterization, channel modeling, measurement campaigns, antennas, transceiver devices, beamforming, networking, the integration of communications and sensing, and experimental testbeds. Starting from the motivation and use cases, we survey the development and historical perspective of THz communications and sensing with the anticipated 6G requirements. We explore the radio propagation, channel modeling, and measurements for THz band. The transceiver requirements, architectures, technological challenges, and approaches together with means to compensate for the high propagation losses by appropriate antenna and beamforming solutions. We survey also several system technologies required by or beneficial for THz systems. The synergistic design of sensing and communications is explored with depth. Practical trials, demonstrations, and experiments are also summarized. The paper gives a holistic view of the current state of the art and highlights the issues and challenges that are open for further research towards 6G.Comment: 55 pages, 10 figures, 8 tables, submitted to IEEE Communications Surveys & Tutorial