Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of...

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Terahertz Band The Last Piece of RF SpectrumPuzzle for Communication Systems

Hadeel Elayan Osama Amin Basem Shihada Raed M Shubair and Mohamed-Slim Alouini

AbstractmdashUltra-high bandwidth negligible latency andseamless communication for devices and applications areenvisioned as major milestones that will revolutionize the wayby which societies create distribute and consume informationThe remarkable expansion of wireless data traffic that we arewitnessing recently has advocated the investigation of suitableregimes in the radio spectrum to satisfy usersrsquo escalatingrequirements and allow the development and exploitation ofboth massive capacity and massive connectivity of heterogeneousinfrastructures To this end the Terahertz (THz) frequencyband (01-10 THz) has received noticeable attention in theresearch community as an ideal choice for scenarios involvinghigh-speed transmission Particularly with the evolution oftechnologies and devices advancements in THz communicationis bridging the gap between the millimeter wave (mmW) andoptical frequency ranges Moreover the IEEE 80215 suite ofstandards has been issued to shape regulatory frameworks thatwill enable innovation and provide a complete solution thatcrosses between wired and wireless boundaries at 100 GbpsNonetheless despite the expediting progress witnessed in THzwireless research the THz band is still considered one of theleast probed frequency bands As such in this work we presentan up-to-date review paper to analyze the fundamental elementsand mechanisms associated with the THz system architectureTHz generation methods are first addressed by highlightingthe recent progress in the electronics photonics as well asplasmonics technology To complement the devices we introducethe recent channel models available for indoor outdoor aswell as nanoscale propagation at THz band frequencies Acomprehensive comparison is then presented between the THzwireless communication and its other contenders by treatingin depth the limitations associated with each communicationtechnology In addition several applications of THz wirelesscommunication are discussed taking into account the variouslength scales at which such applications occur Further asstandardization is a fundamental aspect in regulating wirelesscommunication systems we highlight the milestones achievedregarding THz standardization activities Finally a futureoutlook is provided by presenting and envisaging severalpotential use cases and attempts to guide the deployment of theTHz frequency band and mitigate the challenges related to highfrequency transmission

Index TermsmdashTerahertz band Terahertz communication Ter-ahertz transceivers Terahertz channel model high-speed trans-mission Terahertz standardization

H Elayan is with the Department of Electrical and ComputerEngineering University of Toronto ON M5S Canada (e-mailhadeelmohammadmailutorontoca)

O Amin B Shihada and MS Alouini are with CEMSE DivisionKing Abdullah University of Science and Technology (KAUST)Thuwal Makkah Province Saudi Arabia (e-mail osamaaminbasemshihadaslimalouinikaustedusa)

R M Shubair is with the Research Laboratory of Electronics Mas-sachusetts Institute of Technology Cambridge MA 02139 USA (e-mailrshubairmitedu)

Fig 1 Wireless Roadmap Outlook up to the year 2035

I INTRODUCTION

The race towards improving human life via developingdifferent technologies is witnessing a rapid pace in diversefields and at various scales As for the integrated circuit fieldthe race focuses on increasing the number of transistors on thewafer area which is empirically predicted by Moorersquos Law [1]In the case of the telecommunication sector the race is movingtowards boosting the data rate to fulfill different growingservice requirements which is anticipated by Edholmrsquos lawof bandwidth [2] Wireless data traffic has been witnessingunprecedented expansion in the past few years On the onehand mobile data traffic is anticipated to boost sevenfoldbetween 2016 and 2021 On the other hand video traffic isforeseeing a threefold increase during the same time period[3] Actually the traffic of both wireless and mobile devicesis predicted to represent 71 of the total traffic by 2022[4] In fact by 2030 wireless data rates will be sufficientto compete with wired broadband [5] as demonstrated inFig 1 Such significant growth of wireless usage has ledthe research community to explore appropriate regions in theradio spectrum to satisfy the escalating needs of individualsTo this end the Terahertz (THz) frequency band (01-10THz) started to gain noticeable attention within the globalcommunity Seamless data transfer unlimited bandwidth mi-crosecond latency and ultra-fast download are all featuresof the THz technology that is anticipated to revolutionizethe telecommunications landscape and alter the route throughwhich people communicate and access information

The THz term has been first used within the microwave

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society during the 1970s to describe the spectral frequencyof interferometers diode detectors coverage and water laserresonance [6]ndash[8] During the 2000s the THz term wasreferred to as the submillimeter-wave with frequencies rangingbetween 100 GHz up to 10 THz However the boarder linebetween the submillimeter-waves and far infrared at that timewas not clearly identified [9] [10] The concept of utilizingthe THz for ultra-broadband communication using non-lineof sight (NLoS) signal components has been first proposedas a powerful solution for extremely high data rates in [11]Since then THz technology in general and communication inparticular grasped the enthusiasm of the research communityThis interest has been reflected in the increased number ofpublications issued in both IEEE and web of science in recentyears as demonstrated in Fig 2

Fig 2 Terahertz publications issued in both IEEE and web of science inrecent years

The THz frequency band assures extensive throughputwhich theoretically extends up to several THz leading tocapacities in the order of Terabits per second (Tbps) [12] Suchpotential associated with THz technology attracted the broaderresearch community In fact the combined efforts of activeresearch groups is resulting in new designs materials andfabrication methods that demonstrate endless opportunities forTHz development Table I presents examples of various groupsthat conduct THz research which indicated that researchin this area is executed in laboratories across the globeConsequently various funding agencies have been supportingTHz projects and opening up new horizons in communicationsand devices deployed for beyond 5G technology A detailedlist of the most recent THz projects is demonstrated in Table II

Several studies available in the literature reviewed anddiscussed the potential benefits that can be reaped from theTHz band [9] The first THz survey was introduced in 2002 bySiegel and focused on the sources sensors and applications forfrequencies higher than 500 GHz [9] [10] [13] [14] Duringthe same time period another article has been issued in anattempt to demonstrate THz material characterization whichresults in several applications including THz imaging andtomography [10] From a medical and biological perspectiveSiegel reviewed in [13] the developments observed in THzirradiation and sensing In [14] Fitch and Osiander presentedthe first overview of THz technology for various practical de-ployments in communications and sensing including security

TABLE IRESEARCH GROUPS WORKING ON THZ COMMUNICATION RELATED

TOPICS

Research GroupLab Location RampD Activities

Mittleman Lab at BrownUniversity

USA THz PHY layer THz spec-troscopy THz probes

Broadband Wireless Net-working Lab at GeorgiaInstitute of Technology

USA

THz PHY layer THz MAClayer THz Nanocommunica-tion THz devices

NaNoNetworking Centerin Catalunya Spain THz Nanocommunication

Ultra-broadbandNano-CommunicationLaboratory at Universityat Buffalo

USATHz PHY layer THz MAClayer THz Nanocommunica-tion THz devices

Terahertz Electronics Lab-oratory at UCLA USA

THz sources detectorsspectrometers reconfigurablemeta-films imaging andspectroscopy

MIT Terahertz IntegratedElectronics Group USA

Sensing metrology securityand communication at THz fre-quencies

Fraunhofer Institute forApplied Solid StatePhysics IAF

GermanyTHz PHY layer MAC layerand RF electronics

Terahertz Communica-tions Lab Germany

Channel investigation and Ter-ahertz reflectors

Core technology labora-tory group in Nippontelegraph and telephone(NTT) corporation

JapanTerahertz IC and Modulariza-tion Technology

Texas Instrument KilbyLab USA

Ultra-Low Power Sub-THzCMOS Systems

Tonouchi Lab at Osakauniversity Japan

THz Nanoscience THz Bio-science THz-Bio sensing andindustrial applications

THz Electronics SystemsLab at Korea University Korea

THz PHY layer MAC layerand RF electronics

NanocommunicationsCenter at TampereUniversity of Technology

FinlandTHz PHY layer THzNanocommunication

and spectroscopy applications After that the promise broughtby THz frequencies ranging from 100 GHz up to 30 THzhas been demonstrated in [15] where discussions in terms ofgeneration techniques and their correlated output power abili-ties have been presented In [16] Jacob et al provided a briefoverview of the research activities including channel modelingand signal generation in both the millimeter wave (mmW) andTHz bands The first review on THz communication systemswas presented in 2010 where Federici and Moeller presenteda focused discussion on channel model basic considerationsTHz generation methods and implementation issues of THzcommunications [17] In [18] Kleine-Ostmann and TadaoNagatsuma further expanded the discussion on the researchprogress in THz technology In [19] Song and Nagatsumashed the light on some advances of THz communication in-cluding achievable data rates and service distances in additionto highlighting the challenges associated with the 275 GHzup to 3 THz frequency band A similar and brief review has

3

TABLE IIEXAMPLES OF THE RECENT FUNDED THZ PROJECTS

Project Title Funding Agency Start Date End Date Fund Objective

The Research and Development Projectfor Expansion of Radio Spectrum Re-sources

The Ministry of informationand communications in Japanand the ministry of EducationScience Sports and Culture

2008 NA NA Developing technology for efficientfrequency use promoting shared fre-quency use and encouraging a shiftto use of higher frequencies

Wireless Local Area CommunicationSystems at Terahertz Band

Korea Government FundingAgency IITA

2008 2012 25M $ Developing wireless LANPAN sys-tems based on electronic devices

Semiconductor Nanodevices for RoomTemperature THz Emission and Detec-tion (ROOTHz Project)

Framework Programmes forResearch and TechnologicalDevelopment European Union

2010 2013 21 M e Fabricating solid state emitters anddetectors at THz frequencies

TERAPAN Ultra-high Data rate trans-mission with steerable antennas at THzFrequencies

German Federal Ministry ofEducation and Research

2013 2016 15M e Demonstrating adaptive wirelesspoint-to-point THz communicationfor indoor environments at data ratesof up to 100 Gbps

iBROW Innovative ultra-BROadbandubiquitous Wireless communicationsthrough terahertz transceivers

European Unionrsquos Horizon2020 research and innovationprogram

2015 2018 4M e Developing novel low cost energy-efficient and compact ultra-broadbandshort-range wireless communicationtransceiver technology

TERAPOD Terahertz based Ultra HighBandwidth Wireless Access Networks

2017 2020 347M e Demonstrating THz wireless linkwithin a data centre proof of conceptdeployment as well as investigatingother use cases to beyond 5G

ThoR TeraHertz end-to-end wirelesssystems supporting ultra high data Rateapplications

European Unionrsquos Horizon2020 research and innovationprogram and the NationalInstitute of Information andCommunications Technologyin Japan (NICT)

2018 2021 15M e Providing technical solutions for thebackhauling and fronthauling of trafficat the spectrum range near 300 GHzwhich is able to cover data rates re-quired for beyond 5G systems

ULTRAWAVE Ultra capacity wirelesslayer beyond 100 GHz based on mil-limeter wave Traveling Wave Tubes

2017 2020 3M e Developing a high capacity backhaulthat enables 5G cell densification byexploiting bands beyond 100 GHz

TERRANOVA Terabits Wireless Con-nectivity by TeraHertz innovative tech-nologies to deliver Optical NetworkQuality of Experience in Systems be-yond 5G

2017 2019 3M e Providing reliable connectivity of highdata rates and almost zero-latency innetworks beyond 5G and extendingthe fiber optic systems to wireless

EPIC Enabling Practical Wireless TbsCommunications with Next GenerationChannel Coding

2017 2020 3M e Developing new FEC codes to serve asan enabler of practicable beyond 5Gwireless Tbps solutions

DREAM D-Band Radio solution En-abling up to 100 Gbps reconfigurableApproach for Meshed beyond 5G net-works

2017 2020 28M e Enabling wireless links with data rateexceeding current V-band and E-bandbackhaul solutions to bring wirelesssystems to the speed of optical sys-tems

WORTECS Wireless OpticalRadioTErabit Communications

2017 2020 3M e Exploring Tbps capability of above 90GHz spectrum while combining radioand optical wireless technologies

TerraNova An Integrated Testbed forTrue Terahertz Communications

National Science Foundation(NSF)

2017 2019 750K $ Developing the first integrated testbedspecific to ultra-broadband communi-cation networks at THz frequencies

EAGER High-performance Optical-phonon-based Terahertz SourcesOperating at Room Temperature

2017 2018 85K $ Systematically exploring how to real-ize a new type of THz sources basedon fundamentally different device op-eration principles

Novel Terahertz Generators Based onmagnetic Materials

2017 2020 210K $ Creating a new type of THz gener-ators that are compact inexpensiveand operate at room temperature byconverting magnetic oscillations intoTHz waves

4

been introduced by Nagatsuma in [20] which focused ondemonstrations from 100 GHz to 300 GHz In [21] Huanget al provided both an overview of the state-of-the-art in THzwireless communication along with a tutorial for emergingapplications in Terabit radio systems In [22] Nagatsuma et alreviewed the progress in photonics technology in generatingTHz signals ranging from 100 GHz to 300 GHz In [23]Akyildiz et al summarized the THz possible applications inwireless communications and defined the challenges of thispromising band In [24] Kurner and Priebe demonstratedmore applications and reviewed briefly some research in THzcommunication In [25] Hirata and Yaita discussed severalTHz technologies related to devices circuits and antennas inaddition to some recent experimental test-beds In [26] Petrovet al discussed further applications and defined major researchchallenges besides showcasing the progress towards THz stan-dardization In [27] Mumtaz et al overviewed the oppor-tunities and challenges in THz communications for vehicu-lar networks indicating that communication at much higherfrequencies is correlated with considerable potential when itcomes to vehicular networks In [28] Mittleman presented aperspective article where he highlighted several breakthroughsin the THz field which enabled new opportunities for bothfundamental and applied research The author emphasized onhow the achievements of integrated THz sources and systemscontinue to accelerate enabling many new applications In [29]Sengupta et al reviewed the current progress in generatingTHz signals using electronics and hybrid electronics-photonicssystems for communication sensing and imaging applicationsRecently in [30] Chen et al provided a literature review onthe development towards THz communications and presentedkey technical challenges faced in THz wireless communicationsystems In [31] from the Medium Access Protocol (MAC)perspective Ghafoor et al presented an in-depth survey ofTHz MAC protocols highlighting key features which shouldbe considered while designing efficient protocols In [32]Tekbiyik et al addressed the current open issues in the designof THz wireless communication systems in terms of hardwarephysical channel and network Finally in [33] Rappaport etal presented a number of promising approaches and novel ap-proaches that will aid in the development and implementationof the sixth generation (6G) of wireless networks using THzfrequencies The aforementioned review articles are listed inTable III indicating clearly a high activity rate since the earlytime of 2000 as a result of the advances in both electronicand photonic technologies and the demand to fulfill severalapplication requirements To this end there is still a demandto have a comprehensive view on the current progress andrecent advances in this field that would help researchers drawfuturistic steps for several communication systems As suchthis paper aims to serve such an objective by presenting thelatest technologies associated with the THz frequency band

Due to the rise of wireless traffic the interest in higherbandwidth will never seem to descend before the capacity ofthe technology even beyond 5G has attained an upper bound[34] In this paper we shed the light on various opportunitiesassociated with the deployment of the THz frequency bandThese opportunities are demonstrated as applications that will

facilitate a refined wireless experience coping with usersrsquoneeds Therefore the main objective of the presented work isto provide the reader with an in-depth discussion in which theauthors summarize the latest literature findings regarding thefundamental aspects of THz frequency band wireless commu-nication The presented work will help researchers determinethe gaps available in the literature paving the way for theresearch community to further develop research in the fieldThe rest of the paper is organized as follows In Section II wereview the THz frequency band generation techniques avail-able in the literature In Section III the THz channel modelswhich capture the channel characteristics and propagation phe-nomena are presented In Section IV an extensive comparisonis conducted in order to highlight the differences betweenTHz wireless and other existing technologies including mmWinfrared visible light and ultraviolet communication In Sec-tion V diverse applications which tackle nano micro as wellas macro-scale THz scenarios are presented In Section VI thestandardization activities involved in regulating the usage ofTHz communication are extensively discussed In Section VIIa plethora of opportunities brought by the deployment of theTHz frequency band are demonstrated in an aim to effectivelymeet the needs of future networks and face the technicalchallenges associated with implementing THz communicationFinally we conclude the paper in Section VIII

II TERAHERTZ FREQUENCY GENERATION METHODS

In recent years broadband wireless links using the THzfrequency band have been attracting the interests of researchgroups worldwide By utilizing the frequency range above 100GHz the potential to employ extremely large bandwidths andachieve data rates exceeding 100 Gbps for radio communi-cations will eventually be enabled Nevertheless in order tofulfill such aim progress from the devices perspective is anecessity In fact the location of the THz band between themicrowave and infrared frequency ranges imposes difficulty onsignal generation and detection Therefore the frequency rangebetween 01 and 10 THz has been often referred to as the THzGap since the technologies used for generating and detectingsuch radiation is considered less mature On the one handtransistors and other quantum devices which rely on electrontransport are limited to about 300 GHz Devices functioningabove these frequencies tend to be inefficient as semiconductortechnologies fail to effectively convert electrical power intoelectromagnetic radiation at such range [35] Operating athigh frequencies requires rapidly alternating currents thuselectrons will not be capable of travelling far enough to enablea device to work before the polarity of the voltage changesand the electrons change direction On the other hand thewavelength of photonic devices can be extended down toonly 10 microm (about 30 THz) This is due to the fact thatelectrons move vigorously between energy levels resulting ina difficulty to control the small discrete energy jumps neededto release photons with THz frequencies Hence designingoptical systems with dimensions close to THz wavelengthsis a challenge [36] Nonetheless with the development ofnovel techniques often combining electronics and photonics

5

TABLE IIITERAHERTZ TECHNOLOGY SURVEYS IN THE LITERATURE

Survey Title Year Published Survey Content Reference

1 Terahertz Technology 2002 The first review article on the applications sourcesand sensors for the THz technology with the em-phasis on frequencies higher than 500 GHz

[9]

2 Materials for terahertz science and technology 2002 The article presents a review on material researchin developing THz sources and detectors to supportdifferent applications

[10]

3 Technology in Biology and Medicine 2004 The emerging field of THz is surveyed in biologyand medicine in which the irradiation and sensingcapabilities of THz waves are applied for differentapplications

[13]

4 Terahertz waves for communications and sensing 2004 This survey gives an overview of THz technologyin terms of sources detectors and modulatorsneeded for several applications such as security andspectroscopy

[14]

5 Cutting-edge terahertz technology 2007 This review article gives an overview of the THztechnology progress status and expected usages inwireless communication agriculture and medicalapplications

[15]

6 An Overview of Ongoing Activities in the Field ofChannel Modeling Spectrum Allocation and Standard-ization for mm-Wave and THz Indoor Communications

2009 An overview of mm-Wave and THz radio channelmodeling along with some investigation results arepresented The article also discusses the status ofstandardization activities and plans

[16]

7 Review of Terahertz and Subterahertz Wireless Com-munications

2010 The first review article on THz communicationsystems which demonstrates basic channel model-ing generation methods detection antennas anda summary of THz communication link measure-ments

[17]

8 A Review on Terahertz Communications Research 2011 A brief overview of emerging THz technologiesTHz modulators channel modeling and systemresearch that might lead to future communicationsystems

[18]

9 Present and Future of Terahertz Communications 2011 A review on THz communication as an alternativesolution for high data rate future wireless commu-nication systems especially short range networks

[19]

10 Terahertz technologies present and future 2011 This paper overviews the progress in THz tech-nology and applications as well as summarizes therecent demonstrations from 100 GHz to 300 GHz

[20]

11 Terahertz Terabit Wireless Communication 2011 The state-of-the-art in THz wireless communica-tion along with the emerging applications in Terabitradio systems are demonstrated

[21]

12 Terahertz wireless communications based on photonicstechnologies

2013 This paper overviews the recent advances in THzgeneration using phonetics towards achieving up to100 Gbps data rate either on real time or offline

[22]

13 Terahertz band Next frontier for Wireless Communica-tions

2014 A review of THz applications and challenges ingeneration channel modeling and communicationsystems is presented along with a brief discussionon experimental and simulation testbeds

[23]

14 Towards THz Communications-status in research stan-dardization and regulation

2014 The article provides an overview of THz commu-nications research projects spectrum regulationsand ongoing standardization activities

[24]

15 Ultrafast terahertz wireless communications technolo-gies

2015 The article provides an overview of THz commu-nication research development and implementationtestbeds

[25]

16 Terahertz Band Communications Applications Re-search Challenges and Standardization Activities

2016 The article summarizes the recent achievements byindustry academia and standardization bodies inthe THz field as well as discusses the open researchchallenges

[26]

17 Terahertz Communication for Vehicular Networks 2017 An overview of the opportunities and challengesin THz communications for vehicular networks isprovided

[27]

18 Perspective Terahertz science and technology 2017 The article discusses several breakthroughs in theTHz field which enabled new opportunities for bothfundamental and applied research

[28]

19 Terahertz integrated electronic and hybrid elec-tronicndashphotonic systems

2018 The article reviews the development of THz in-tegrated electronic and hybrid electronicndashphotonicsystems used in several applications

[29]

20 A Survey on Terahertz Communications 2019 The paper provides a literature review on the devel-opment towards THz communications and presentssome key technologies faced in THz wireless com-munication systems

[30]

21 MAC Protocols for Terahertz Communication A Com-prehensive Survey

2019 In this survey detailed work on existing THz MACprotocols with classifications band features designissues and challenges are discussed

[31]

22 Terahertz band communication systems Challengesnovelties and standardization efforts

2019 The paper addresses the current open issues in thedesign of THz wireless communication system interms of hardware physical channel and network

[32]

23 Wireless Communications and Applications Above 100GHz Opportunities and Challenges for 6G and Beyond

2019 The paper presents a number of promising ap-proaches that will aid in the development andimplementation of the 6G wireless networks

[33]

6

approaches THz research is recently being pushed into thecenter stage Fig 3 presents a time-line of the progress inTHz communication technology indicating how THz researchis moving from an emerging to a more established fieldwhere an obvious technological leap has been witnessed withinthe last decade The following subsections discuss the latestTHz advancements achieved focusing mainly on both theelectronics and photonics fields while shedding the light onother techniques used to generate THz waves In particularTable V summarizes the advancements in THz technologyby presenting the progress over the years in THz electronicas well as photonic transceivers achievable data rates andpropagating distances as well as output power

A Solid-State Electronics

Recent advances in the development of semiconductor com-ponents and their manufacturing technology are making THzsystems both feasible and affordable resulting in compactdevices In fact technology limitations have been overcome byarchitectural innovations as well as by new device structures

1) Complementary Metal-Oxide-Semiconductor (CMOS)CMOS-based sources have been developing rapidly in recentyears Such technology possesses the advantages of high levelintegration small form factor and potential low cost The highfrequency operation ability of CMOS offers solutions in thelower band of the THz spectrum This has been achievedby adding either a Voltage Controlled Oscillator (VCO) orinserting an active multiplier chain in the CMOS device [51]Various triplers are used to multiply the frequency from alower band to the THz frequency band by using nanoscaleCMOS technology where the consideration for CMOS THzcircuits is enabled by technology scaling In 2006 the scalingof a 65-nm CMOS process has resulted in a power gainfrequency of 420 GHz in which uni-axial strained silicontransistors with physical gate lengths of 29-nm have been used[52] In 2007 a transistor cutoff frequency of 485 GHz [53]has been achieved while utilizing a 45-nm microprocessortechnology The authors in [54] demonstrated a 553 GHzquadruple-push oscillator using 45-nm CMOS technologywhile in [55] the authors presented a 540 GHz signal generatorfabricated in 40-nm bulk CMOS In addition the authors in[56] presented a 560 GHz frequency synthesizer realized in65-nm CMOS technology The chip configuration constitutedof both a THz VCO along with a phase locked loop circuitAs such it could be noticed that the constructive addition ofharmonic signals allows devices to penetrate into hundredsof GHz range which indicates the impending THz era ofCMOS technology Such results states that the industry hasbeen capable of keeping up with the documents reported bythe International Roadmap for Semiconductors [57] CMOStransmitters have actually achieved up to 105 Gbps data rateusing a 40-nm CMOS process at 300 GHz [58]

2) Monolithic Microwave Integrated Circuits (MMIC)Assimilating a large number of tiny transistors into a smallchip leads to circuits that are orders of magnitude smallercheaper and faster than those built of discrete electroniccomponents Critical for reaching THz operational frequencies

2000

2005

2010

2015

2020

10 Gbps transmission over a dista

nce of 2m using 12

0 GHz band [37]

THz demonstration of audio transmissi

on [38]

Analogue video transmission through 30

0 GHz over 22 m [39]

Transmission tria

l of HDTV using 120 GHz for 1

km [40]

10Gbps transmissi

on over 58

km using 120 GHz band [41]

260 GHz CMOS transceiver for wireless chip-to-chip communication [42]

24Gbps data transmissi

on at 300 GHz [43]

100 Gbps data transmissi

on at 2375

GHz for 20 m [44]

Uncompressed 8 K video signal over a dista

nce 125 km [45]

300 GHz Integ

rated Heterodyne Receiver and Transmitter [46]

First300 GHz compact transceiver [47]

Firstapproved THz standard IEEE Std 802153d 2017 [48]

100 Gbps data transmission at 300 GHz [49]

80 Gbps single-chip QAM-capable CMOS transceiver [50]

Fig 3 Time-line of Progress in Terahertz Communication Technology

for integrated circuits are transistors with sufficiently highmaximum oscillation frequency fmax The main approachesin developing high speed transistors include both transistorgate scaling for parasitic reduction as well as epitaxial materialenhancement for improved electron transport properties Avariety of MMIC compatible processes include HeterojunctionBipolar Transistors (HBTs) and High Electron Mobility Tran-sistors (HEMT) Both transistors use different semiconduc-tor materials for the emitter and base regions creating aheterojunction which limits the injection of holes from thebase into the emitter This allows high doping density to beused in the base which results in reducing the base resis-

7

tance while maintaining gain In comparison to conventionalbipolar transistors HBTs have the advantage of higher cut-off frequency higher voltage handling capability and reducedcapacitive coupling with the substrate [59] Materials usedfor the substrate include silicon gallium arsenide (GaAs)and indium phosphide (InP) Both GaAs and InP HBTs arecompatible for integration with 13-15 microm optoelectronicssuch as lasers and photodetectors In the case of HEMTs themost commonly used material combination in the literatureinvolves GaAs Nonetheless gallium nitride (GaN) HEMTsin recent years have attracted attention due to their high-power performance GaN HEMT technology is promisingfor broadband wireless communication systems because ofits high breakdown electric field and high saturation carriervelocity compared to other competing technologies such asGaAs and InP devices [60] In fact by utilizing a MMIC GaAsHEMT front-end data rates up to 64 Gbps over 850 m [61]and 96 Gbps over 6 m [62] have been attained using a 240GHz carrier frequency In terms of InP-HEMT improvementin electron-beam lithography is witnessing the increase in thespeed of such devices as gate length decreases A significantmilestone was the first InP HEMT with fmax gt 1 THz reportedin 2007 [63] Further milestone achievements in amplificationsat higher frequencies have been demonstrated with subsequentgeneration of transistors and designs at 480 GHz [64] 670GHz [65] and 850 GHz [66] By using 25-nm gate InP HEMTfmax reached 15 THz [67] Several devices with high fmax

that operate around 1 THz are reported in Table IVCompared with CMOS higher frequency sources with

higher output powers have been obtained in the literature usingHBT and HEMT technologies [68] Nonetheless CMOS stillremains an attractive candidate for THz technology due to itslower cost and higher integration densities It is to be noted thatthe development of physical principles of THz-wave amplifi-cation and oscillation is one of problems hindering progressin modern solid state electronics towards high frequenciesTherefore novel perspectives are tied with use of resonanttunneling quantum effects characterized by short transienttimes in comparison to the fast response of superconductingdevices as will be discussed in the subsequent section

TABLE IVPROGRESS OF INP HEMT IN RELATION TO OSCILLATION FREQUENCY

AND GATE LENGTH

Gate Length fmax(THz) Reference

75 nm 091 [69]75 nm 13 [70]50 nm 11 [63]50 nm 106 [71]25 nm 15 [67]

3) Resonant Tunneling Diodes (RTD) A resonant-tunneling diode (RTD) operates according to the tunnelingprinciple in which electrons pass through some resonant statesat certain energy levels RTD has been first demonstrated in1974 where it consists of vertical stacking of nanometricepitaxial layers of semiconductor alloys forming a double

barrier quantum well [72] which allows the RTD to exhibit awideband negative differential conductance [73] Over the last10 years progress has been achieved in increasing the outputpower of RTDs by almost two orders of magnitude and inextending the operation frequencies from earlier 07 THz tovalues near 2 THz [59] Oscillations of RTDs in the microwaverange were demonstrated at low temperature in 1984 [74] andthe frequency was updated many times to several hundred GHz[75] In 2010 a fundamental oscillation above 1 THz [76] havebeen attained The oscillation frequency was further increasedup to 142 THz using thin barriers and quantum wells [77]Further the authors in [78] and [79] indicated that reducingthe length of the antenna integrated with the RTD extendedthe frequency up to 155 THz and 192 THz respectively

RTD oscillators are actually suitable for wireless datatransmission because the output power is easily modulated bythe bias voltage and oscillations can be controlled by eitherelectrical or optical signals Wireless data transmission with adata rate of 34 Gbps has been achieved in [80] Because thesize of RTD oscillators is small it is possible to integrate mul-tiple oscillators into one chip which is convenient for multi-channel transmissions Indeed wireless transmissions usingboth frequency division multiplexing (FDM) and polarizationdivision multiplexing (PDM) have been demonstrated in [81]in which data rates up to 56 Gbps were obtained Yet thedrawback of this technology is that it cannot supply enoughcurrent for high power oscillations

The technological progress that has been witnessed by theTHz electronic devices is illustrated in Fig 4 where the fre-quency of operation for CMOS MMIC and RTD technologiesis displayed versus power It could also be concluded that inthe cases where continued scaling of CMOS or integrationwith other silicon-based devices is inefficient heterogeneousas well as tunneling devices are deployed Nonetheless despitethe various progress that has been witnessed and is stillongoing in the field of solid state electronics the drasticpower decrement associated with this technology is a majorbottleneck Thereby other technologies have been gainingconsiderable attention

B Photonics Technologies

THz devices based on electronic components possess bothhigh resolution and high flexibility Yet for many applicationsTHz measurements for wideband and high speed signals areneeded Such requirement may not be implementable viaelectronic devices due to the limited speed and bandwidthHowever modern photonics which have been widely usedfor wideband and high speed microwave measurements canprovide broader bandwidths [108] [109] In fact the rise ofTHz wireless communication began as early as the year 2000upon the initiation of a 120 GHz wireless link generated byphotonic technologies [110] The 120 GHz signal was thefirst commercial THz communication system with an allocatedbandwidth of 18 GHz A data rate of 10 Gbps has been attainedwith an on-off keying (OOK) modulation and 20 Gbps with aquadrature phase shift keying (QPSK) modulation [83] [84]This achievement attracted broadcasters who aimed to transmit

8

TABLE VPROGRESS IN THZ TECHNOLOGY ACHIEVABLE DATA RATES AND PROPAGATION DISTANCE

Freq Data Rate Spectral Eff Distance Modulation Power Technology Reference Year(GHz) (Gbps) (bpsHz) (m) Scehme (dBm)

100 200 - 05 QPSK -10 Photodiode (PD) [82] 2013subharmonic mixer (SHM)

120 10 059 5800 ASK and FEC 16 InGaAsInP composite [41] 2010channel HEMT MMIC

120 10 - 5800 ASK 16 UTC-PD InP HEMT MMIC [83] 2012

120 20 06 1700 QPSK 7 InP HEMT MMIC [84] 2012

120 4260 492ndash 04 64QAM -10 GaAs HEMT [85] 2016

130 11 - 3 ASK 86 CMOS Transceiver Chipset [86] 2015

140 210 286 1500 16 QAM -5 CMOS SHM [87] 2013realnon-real time Schottky barrier diodes

144 48 - 18 QPSKQAM 4 Direct conversion IQ [88] 2016InP double HBT

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

220 25 074 05 ASK -34ndash14 active MMIC (50-nm mHEMT) [91] 2011

240 30 - 40 QPSK8PSK -36 active MMIC components [92] 2013

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 24 024 05 ASK -7 UTC-PD [93] 2012Schottky diode

300 40 - 10 QPSK - Optical sub-harmonic IQ mixer [94] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

330 50 - 05sim1 ASK - UTC-PD [96] 2015Schottky diode detector

340 3 286 50 16 QAM through 32 -175 CMOS SHM [97] 2014IQ parallel channels Schottky barrier diodes

350-475 120 - 05 QPSK - UTC-PD [98] 2017Schottky mixer

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

450 13 - 38 QPSK -28 photomixerPD [103] 2018

450 18 - 38 PDM-QPSK -28 photomixerPD [104] 2018

450 132 45 18 QAM -28 UTC-PDphotomixer [105] 2019

542 3 - 0001 ASK -67 RTD [106] 2012

625 25 - 3 ASK -14 MultiplierSBD [107] 2011

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

CMOS TechnologyMMIC TechnologyRTD Technology

Fig 4 Solid-state electronics frequency of operation versus power

high-definition TV data [18] and demonstrated how photonictechnologies played a key role in the development of first-age THz communication systems Such achievement actuallytriggered the development of electronic devices and integratedcircuits to strengthen the wireless technology This eventuallyresulted in all electronic MMIC-based systems being success-fully deployed in real-world events around the year 2008 [83]Compared to solid-state electronics photonic technologies notonly improves the data rate but also fuses both fiber-optics andwireless networks These devices have broadband characteris-tics high modulation index as well as high-speed amplitudeandor phase coding introduced from optical coherent networktechnologies [111] The most fundamental and widely useddevices are based on the optical-to-THz or THz-to-opticalconversion using interaction media such as nonlinear opticalmaterials photoconductors and photodiodes High speed THzwireless communication systems in the frequency range of 300GHz-500 GHz at data rates of 60 Gbps 160 Gbps and up to260 Gbps have been demonstrated in the literature indicatingthe potential of this technology [101] [112] [113]

1) Unitravelling Carrier Photodiode (UTC-PD) The evo-lution of photonics technology greatly increased the speed ofsignal processing systems Photodiodes are examples of suchdevices that can provide both high speed and high saturationoutput resulting in the development of large-capacity commu-nication systems The combination of a high saturation powerphotodiode with an optical amplifier eliminates the post-amplification electronics extends the bandwidth and simpli-fies the receiver configuration [114] In particular unitravellingcarrier photodiodes (UTC-PD) [115] have a unique mode ofoperation which makes them promising candidates for suchrequirements These photodiodes have been reported to have a150 GHz bandwidth [116] and a high-saturation output currentdue to the reduced space charge effect in the depletion layerwhich results from the high electron velocity [117] Sincethe time UTC-PDs have been invented in 1997 [115] theyhave been used as photomixer chips The frequency of thephotomixer operation ranged from 75 to 170 GHz Afterwards

the monolithic integration of a UTC-PD with planar antennaswas reported and the operation frequency exceeded 1 THz in2003 [118] Upon antenna integration in UTC photomixersoperation frequencies exceeded 2 THz [117] UTC-PDs alsoenable the use of travelling-wave designs [119] which provideslower frequency response roll-off and are more compatiblewith integration UTC-PDs with output powers of 148 microWat 457 GHz and 24 microW at 914 GHz have been approached[120] In addition a 160 Gbps THz wireless link has beenachieved in the 300-500 GHz band using a single UTC-PDbased transmitter as shown in [112]

2) Quantum Cascade Lasers (QCLs) A revolutionary ad-vancement in THz technology arose in 2002 when successfuloperation of a quantum cascade laser (QCL) at THz fre-quencies has been reported in [121] QCL basically bypassessemiconductor band-gap limitations in photonic devices byusing sophisticated semiconductor heterostructure engineeringand fabrication methods The semiconductor layers are thinthereby very low energy transition happens when electrontunnel from one layer to the other Due to the low energy theemitted radiation occurs in the THz region Since 2002 QCLshave quickly progressed in frequency coverage increasedpower output and increased operating temperature Currentlythey are the only sources capable of generating over 10 mWof coherent average power above 1 THz [122] In order tocharacterize the high modulation speed capability of THzQCLs and build a high speed THz communication link a fastdetector is necessary The authors in [123] demonstrated anall-photonic THz communication link at 38 THz by deployingQCL operating in pulse mode at the transmitter and a quantumwell photodetector at the receiver Later the authors in [124]were capable of increasing the frequency to 41 THz by usinga QCL which operates in continuous wave mode

The progress witnessed in the photonics domain is akey enabler to the deployment of THz wireless links Yetthe challenge remains in integrating these micrometer-scalebulky components of photonics into electronic chips Surfaceplasmon-based circuits which merge electronics and pho-tonics at the nanoscale may offer a solution to this size-compatibility problem [125] In plasmonics waves do notrely on electrons or photons but rather electromagnetic wavesexcite electrons at a surface of a metal and oscillate at opticalfrequencies An advantage of these so-called surface plasmonpolaritons (SPPs) is that they can be confined to an ultra-compact area much smaller than an optical wavelength Inaddition SPPs oscillate at optical frequencies and thus cancarry information at optical bandwidths The efficient wavelocalization up to mid-infrared frequencies led plasmonics tobecome a promising alternative in future applications whereboth speed and size matters [126] In particular due to the twodimensional nature of the collective excitations SPPs excitedin graphene are confined much more strongly than those inconventional noble metals The most important advantage ofgraphene would be the tunability of SPPs since the carrierdensities in graphene can be easily controlled by electricalgating and doping Therefore graphene can be applied asTHz metamaterial and can be tuned conveniently even foran encapsulated device [127] Graphene-based THz compo-

10

Terahertz Propagation Phenomenon

Losses [133] Small-Scale Mobility [134] NLoS Propagation [135]

Spreading Loss

Absorption Loss

micro-dopplereffects Refraction

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

Fig 5 Terahertz Band Propagation Characteristics

nents have actually shown very promising results in terms ofgeneration modulation as well as detection of THz waves[128] [129] [130] Furthermore various unique generationtechniques have been recently proposed for THz waves Forinstance the authors in [131] experimentally demonstrated thegeneration of broadband THz waves from liquid water excitedby femtosecond laser pulses Their measurements showcasedthe significant dependence of the THz field on the relativeposition between the water film and the focal point of thelaser beam Compared with THz radiation generated from theair plasma the THz radiation from liquid water has a distinctresponse to various optical pulse durations and shows linearenergy dependence upon incident laser pulses Such workwill contribute to the exploration of laser-liquid interactionsand their future as THz sources Another example of originalTHz generation techniques involves the work demonstrated in[132] The authors have shown that a dipole emitter can excitethe resonances of a nanofiber and lead to strong electric andormagnetic responses They have experimentally demonstratedthe magnetic dipole radiation enhancement for a structurecontaining a hole in a metallic screen and a dielectric sub-wavelength fiber Their results are considered the first proof ofconcept of radiation enhancement of a magnetic dipole sourcein the vicinity of a subwavelength fiber All these techniqueswill eventually result in breakthrough advancements in thevarious technological realms

As indicated by Table V a tradeoff between power distanceand data rate have to be achieved in order to choose the mostapplicable THz wireless communication scenario based on theuser requirements By varying the modulation schemes fromthe most simple amplitude shift keying (ASK) to PDM-QPSKas well as experimenting with different configurations of THz-fiber integration all electronics or all photonics systems newopportunities are continuously developing for feasible THz

wireless communication scenarios

III CHANNEL MODELING IN THE THZ FREQUENCY BAND

In order to realize an efficient wireless communicationchannel in the THz band it is imperative to consider thevarious peculiarities which distinguishes such frequency rangeIn fact the THz frequency band has high frequency attenuation[133] [136] distinctive reflective [137] [138] and scattering[139]ndash[141] properties as well as specular [142] and non-specular [143] spatial distribution of the propagation pathsMoreover the highly directive antenna radiation pattern usedto overcome high path loss results in frequent misalignmentsof beams due to small scale mobility of user equipments[134] The major propagation characteristics of THz wavesare presented in Fig 5 These effects cannot be neglected inthe modeling process As such the existing channel modelsfor the radio frequency (RF) band cannot be reused for theTHz band as they do not capture various effects including theattenuation and noise introduced by molecular absorption thescattering from particles which are comparable in size to thevery small wavelength of THz waves or the scintillation ofTHz radiation Such features motivate the exploration of newmodels that efficiently characterize the THz spectrum In ourdiscussion of channel modeling in the THz frequency bandwe will follow the classification illustrated in Fig 6

A Outdoor Channel Models

Models that emulate THz channels in outdoor environmentsare scarce focusing only on point to point links The first 120GHz experimental radio station license has been provided bythe Ministry of Internal Affairs and Communications of Japanin 2004 where the first outdoor transmission experimentsover a distance of 170 m have been conducted [144] These

11

Terahertz Channel Model

Outdoor Channel Model[41] [83] [84] [144] [145] Indoor Channel Model

Nanoscale ChannelModel [133] [146]ndash[149]

Point-to-PointLinks

DeterministicModels [135][150]ndash[154]

Stochastic Models[155]ndash[165]

Fig 6 Terahertz Channel Model Classification

experiments relied on utilizing mmW amplifiers along withhigh-gain antennas such as the Gaussian optic lens antennasor the Cassegrain antennas leading to a successful outdoortransmission experiment Starting from 2007 onward the 120GHz wireless signals were generated using InP HEMT MMICtechnologies accounting on the electronic systems advantagesof compactness and low cost [145] Upon the introduction offorward error correction (FEC) technologies a 58 km 10 Gbpsdata transmission was achieved by increasing both the outputpower as well as antenna gain [41] [83] The transmissiondata rate has been further increased to 222 Gbps by using theQPSK modulation scheme as shown in [84]

The current outdoor channel models tackle only point topoint cases This is because few cases exist in the litera-ture where experimental measurements have been reportedIn specific for outdoor measurements the interference fromunintentional NLoS paths can limit the bit error rate (BER)performance [166] For long distance wireless communica-tions THz links can suffer significant signal loss due toatmospheric weather effects as illustrated in Fig 7 Yet acloser look indicates that despite the existence of absorptionpeaks centered at specific frequencies the availability oftransmission windows allows establishing viable communica-tion at the THz frequency band Thus it will be importantto estimate the weather impact on high capacity data linksand compare the performance degradation of THz links incomparison to other competing wireless approaches [167] Asthe THz band channel is considered highly frequency selectivethe transmission distance is limited by attenuation and theappropriate carrier frequency is determined according to theapplication To be capable of developing THz outdoor channelmodels the evaluation of link performance using realistic datastreams is needed In our opinion a complete outdoor channelmodel could be attained by further exploring geometry-basedvisibility-region based as well as map-based models whichinclude parameterization from measurement campaign resultsIt must be emphasized that in order to operate in outdoorenvironments certain measures have to be considered to avoidinterference of passive services operating in the same bandSuitable frequency ranges are reported in Table VI based onstudies conducted in [168] [169]

Fig 7 The attenuation impact of different environmental effects at variousfrequencies [170]

TABLE VITHZ FREQUENCY RANGES FOR FIXED SERVICES [169]

Frequency Range(GHz)

Contiguous Band-width (GHz)

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

B Indoor Channel Models

Unlike outdoor channel models several indoor channelmodels are available in the literature Indoor channel modelscan be categorized into either analytical or stochastic modelsIn terms of deterministic channels the ray-tracing model isusually applied [135] [150]ndash[154] This technique is site-specific abiding with propagation theories and capturing thephenomenon of wave transmission with precision as it is basedon geometrical optics in which it is used for analyzing boththe line of sight (LoS) and NLoS THz wave propagation paths

12

Yet the accuracy of the ray-tracing models depends heavily onthe complete knowledge of material properties This requirescontinuously adapting the model to a new environment whichcan limit its time efficiency From the communications per-spective it is fundamental to understand the large and small-scale statistics of the channel including path loss shadowingand multipath propagation [155] Hence statistical methodsarise as suitable options to model THz propagation based onempirical channel measurements The first statistical modelfor THz channels spanning the range between 275 and 325GHz has been provided in [156] The given model depends onextensive ray-tracing simulations to realize the channel statis-tical parameters Yet the information concerning the channelstatistics such as the correlation function and power-delayprofile cannot be captured easily To tackle such concernsthe authors in [157] [158] presented a geometrical statisticalmodel for device-to-device (D2D) scatter channels at the sub-THz band These models mimic the scattering and reflectionpatterns in a sub-THz D2D environment It is important tonote that since the reflecting and scattering properties arefrequency-dependent in the THz band statistical distributionsand parameters for intra-cluster and inter-cluster need to bemodeled properly Therefore a number of papers consideredthe characteristics of scattered multipath clusters includingboth angle and time of arrival for THz indoor channel mod-eling [159]ndash[161] In addition by investigating the blockingprobability in order to describe the blocking effects of thepropagation signals the authors in [162] provided a modifiedTHz channel model and proposed a path selection algorithmfor finding the dominant signal Similarly in [171] the authorsstudied mean interference power and probability of outagein the THz band using stochastic geometry analysis Furtherthe authors in [172] presented a time-domain channel modelin the THz band where the coherence bandwidth has beencomputed for both the entire THz band and its sub-bandsThe demonstrated numerical evaluation along with the pro-vided experimental results indicate that the obtained impulseresponse satisfies causality and show that knowledge of thevariations in the coherence bandwidth allows the selection ofthe proper center frequency for wireless communications in theTHz band Unlike traditional channel measurements scenario-specific models are also available in the literature The authorsin [163] presented a stochastic model for kiosk applicationsin the THz band specifically between 220 and 340 GHz A3D ray-tracing simulator has been utilized to extract channelcharacteristics of three different kiosk application scenariosFurther a stochastic channel model for future wireless THzdata centers has been presented in [164] The presentedstochastic channel model accounts for the temporal and spatialdispersion of the propagation paths and enables fast generationof channel realizations Both the RMS delay and angularspreads are employed as a validation of the model In [165]another study on the statistical channel characterization of aTHz scenario has been presented This study deals with thefrequency range between 240 and 300 GHz and is consideredone of the first to provide single-sweep THz measurementresults The measured data enables finer temporal details tobe attained aiding the design of reliable transceiver systems

including antenna misalignment problemsTo achieve a balance between accuracy and efficiency

the authors in [173] suggested a hybrid channel model thatcombines both deterministic and statistical methods In theirdiscussion the authors noted that a stochastic scatterer place-ment and ray-tracing hybrid approach could be developedScatterers in this case are stochastically placed whereasthe multipath propagation is traced and modeled based onray-tracing techniques in a deterministic fashion As suchgeometry-based stochastic channel models are establishedThe advantage of following such mechanism includes thehigh modeling accuracy and the low complexity On theone hand the very rich multipath effects are included usingstatistical modeling On the other hand the critical multipathcomponents are computed deterministically

Furthermore the authors in [174] provided an assessmentfor the communication system design requirements at higherfrequencies In fact channel measurement results for 650GHz carrier frequencies in comparison with 350 GHz carrierfrequencies are given for a typical indoor environment Theauthors presented an extensive multipath channel model whichdescribes the spatial distribution of all available paths withtheir respective power levels Thereby a more establishedperception is provided for THz wave propagation at differentwavelength ranges

C Nanoscale Channel Models

In the past few years advancements in the field of nan-otechnology have paved the way towards the development ofminiaturized sensing devices which capitalize on the propertiesof novel nanomaterials Such devices denoted as nanodevicescan perform simple tasks including computing data storingsensing and actuation As such the formulation of nanonet-works will allow various applications in the biomedical in-dustrial and military fields [175] Based on radiative transfertheory and in light of molecular absorption a physical channelmodel for wireless communication among nanodevices in theTHz band is presented in [133] The provided model considersthe contribution from the different types and concentrations ofmolecules where the HITRAN database is used in order tocompute the attenuation that a wave suffers from The Beer-Lambert law was used to compute the transmittance of themedium which relies on the medium absorption coefficientThe model provided in [133] was also utilized to computethe channel capacity of nanonetworks operating in the THzband in which the authors deployed different power allocationschemes The authors recommended using the lower end of theTHz band which has lower absorption coefficients in orderto ensure a strong received signal Moreover the sky noisemodel is the basis of the existing absorption noise models Theauthors in [146] elaborated on this topic by presenting differentperspectives on how to model the molecular absorption noiseHowever there is no real experiments conducted in orderto validate the proposed models Not only absorption butalso scattering of molecules and small particles affects thepropagation of electromagnetic waves Hence a widebandmultiple scattering channel model for THz frequencies has

13

TABLE VIIWIRELESS COMMUNICATION CANDIDATES

Technology Millimeter Wave Terahertz Infrared Visible Light Ultra-Violet

Data Rate Up to 10 Gbps Up to 100 Gbps Up to 10 Gbps Up to 10 Gbps Few Gbps

Range Short range Short range minusMedium range

Short range minus long range Short range Short range

Power Consumption Medium Medium Relatively low Relatively low Expected to be low

Network Topology Point to Multi-point Point to Multi-point Point to Point Point to Point Point to Multi-point

Noise Source Thermal noise Thermal noise Sun Light + Ambient Light Sun Light + Ambient Light Sun Light + Ambient Light

Weather Conditions Robust Robust Sensitive minus Sensitive

Security Medium High High High To be determined

been demonstrated in [147] Further the authors in [148]presented an analytical model based on stochastic geometryfor interference from omnidirectional nanosensors Howeverin their model they disregarded interference arising due to theexistence of base stations The authors in [149] tackled thisissue where they studied interference from beamforming basestations As such it has been concluded that having a highdensity of base stations using beamforming with small beam-width antennas and deploying a low density of nanosensors isrecommended to improve the coverage probability

IV WILL THE TERAHERTZ BAND SURPASS ITS RIVALS Carrier frequencies utilized for wireless communications

have been increasing over the past years in an attempt to satisfybandwidth requirements While some of the interest of theresearch community is steered towards the mmW frequenciesin an attempt to fulfill the demands of next generation wirelessnetworks another direction involves moving towards opticalwireless communication to allow higher data rates improvephysical security and avoid electromagnetic interference Theoptical wireless connectivity is permitted using infrared vis-ible or ultraviolet sub-bands offering a wide range perfor-mance of coverage and data rate [176] To highlight thenecessity of utilizing the THz frequency band and showcase itscapability in comparison to other envisioned enablers of futurewireless communication we present through the followingsubsections a comprehensive study of the features of thedifferent technologies as summarized in Table VII

A Millimeter Wave versus Terahertz

Millimetre-wave frequencies of 28 60 as well 73 GHzcan enable myriad applications to existing and emergingwireless networking deployments Recent researches intro-duced mmW as a new frontier for wireless communicationsupporting multiple Gbps within a coverage of few metersThe mmW frequency range has been adopted by the FederalCommunications Commission as the operational frequencyof 5G technology By designating more bandwidth fasterhigher-quality video and multimedia content and services willcontinue to be delivered [177]

Despite the growing interest that arouse in mmW systemsthe allocated bandwidth in such systems ranges from 7-9

GHz This will eventually limit the total throughput of thechannel to an insufficient level due to consumersrsquo increasingdemand Moreover to reach the envisioned data rate of 100Gbps transmission schemes must have a challenging spectralefficiency of 14 bpsHz [24] In addition the capacity of thefronthaulbackhaul link needed to achieve few Gbps shouldbe several times higher than the user data rate to guaran-tee reliable and timely data delivery from multiple usersNonetheless as the frequency increases up to the THz bandTbps links could be attained with moderate realistic spectralefficiencies of few bits per second per Hz Operating at theTHz frequency band also allows a higher link directionalityin comparison to mmW at the same transmitter aperture sinceTHz waves have less free-space diffraction due to its shorterwavelength compared to the mmW Therefore using smallantennas with good directivity in THz communications reducesboth the transmitted power and the signal interference betweendifferent antennas [178] Another interesting feature is thelower eavesdropping chances in the THz band compared withthe mmW This is due to the high directionality of THz beamswhich entail that unauthorized user(s) must be on the samenarrow beamwidth to intercept messages

B Infrared versus Terahertz

One of the attractive well-developed alternatives of radiofrequency spectrum for wireless communication is the uti-lization of infrared radiation The infrared technology useslaser transmitters with a wavelength span of 750-1600 nmthat offer a cost-effective link with high data rates that couldreach 10 Gbps As such it can provide a potential solutionfor the backhaul bottleneck [179] The infrared transmissionsalso do not penetrate through walls or other opaque barrierswhere they are confined to the room in which they originateSuch a feature secures the signal transmission against eaves-dropping and precludes interference between links operatingin different rooms Nevertheless as infrared radiation cannotpenetrate walls the installation of infrared access points thatare interconnected via a wired backbone is required [180]

As part of the optical spectrum infrared communicationfaces similar challenges that degrade its performance in differ-ent environments For indoor environments the ambient lightsignal sources such as fluorescent lighting induces noises at

14

the receiver side As for outdoor environments in addition tomoonsun light noise level atmospheric turbulence can limitthe communication link availability and reliability thus it isone of the main clogging factors of infrared communicationdeployment The performance of optical links can be degradedeven in clear weather as a result of scintillation and temporaryspatial variation of light intensity Another major problem isthe necessity of developing pointing acquisition and tracking(PAT) techniques which are essential for operation due to theunguided narrow beam propagation through the free space Asa result optical transceivers must be simultaneously pointed ateach other for communication to take place in which precisealignment should be maintained [181]

THz frequency band is a good candidate to replace the in-frared communication under inconvenient weather conditionssuch as fog dust and turbulence Fig 7 indicates that the THzband suffers lower attenuation due to fog compared to theinfrared band Recent experimental results showed that theatmospheric turbulence has a severe effect on the infrared sig-nal while it does not almost affect the THz signal Moreoverthe attenuation under the presence of cloud dust degrades theinfrared channel but exhibits almost no measurable impact onthe THz signal As for the noise THz systems are not affectedby ambient optical signal sources Due to the low level ofphoton energies at THz frequencies the contribution to thetotal noise arises from the thermal one [170]

C Visible Light versus Terahertz

Communication through visible light is a promising energy-aware technology that has attracted people from both indus-try and academy to investigate its potential applications indifferent fields Visible light communication (VLC) carriesinformation by modulating light in the visible spectrum (390-750 nm) [182] Recent advancements in lighting through lightemitting diodes (LEDs) have enabled unprecedented energyefficiency and luminaire life span since LEDs can be pulsedat very high speeds without noticeable effect on the lightingoutput and human eye LEDs also possess several attractivefeatures including their low power consumption small sizelong life low cost and low heat radiation Therefore VLCcan support a lot of vital services and application such asindoor localization human-computer interaction device-to-device communication vehicular networks traffic lights andadvertisement displays [176]

Despite the advantages associated with the deploymentof VLC communication several challenges exist that couldhamper the effectiveness of the wireless communication linkIn order to achieve high data rates in VLC links a LoSchannel should be primarily assumed in which both thetransmitter and the receiver ought to have aligned field ofviews (FOV) to maximize the channel gain Neverthelessdue to the receiver movement and continuous changes inorientation the receiversrsquo FOV cannot be always aligned withthe transmitter Such misalignment results in a significant dropin the received optical power [183] In occasions where anobject or a human blocks the LoS a noticeable degradationof the optical power is witnessed resulting in severe data

rate reduction Similar to infrared waves interference fromambient light can significantly reduce the received signal tooise ratio (SNR) degrading the communication quality [182]Current research in visible light networking also sheds thelight on downlink traffic without taking into consideration howthe uplink can operate Since a directional beam towards thereceiver should be maintained in VLC uplink communicationsignificant throughput reductions when the mobile device isconstantly movingrotating may occur Thus other wirelesstechnology should be used for transmitting uplink data [176]

Contrary to VLC systems the THz frequency band permitsNLoS propagation which acts as a supplement when LoS isunavailable [23] In such scenarios NLoS propagation can bedesigned by strategically placing mounted dielectric mirrorsto reflect the beam to the receiver The resulting path loss isadequate due to the low reflection loss on dielectric mirrorsIn fact for distances up to 1 meter and a transmit power of 1Watt the capacity of only the NLoS component of a THz linkis around 100 Gbps [152] Furthermore the THz frequencyband is considered a candidate for uplink communication acapability which VLC communication lacks Another specificapplication where THz becomes a valuable solution is whenthere is a need to switch the lights off while looking fornetwork service Due to the restriction of positive and realsignals VLC systems will suffer from spectral efficiencyloss Indeed utilizing unipolar OFDM system by imposingHermitian symmetry characteristic leads to 3 dB performanceloss in comparison to traditional bipolar systems that can beused in THz communication [184]

D Ultra-Violet versus Terahertz

To relax the restrictions enforced by the PAT requirementsof optical wireless communication researchers investigatedthe optical wireless communication with NLoS capabilitiesThe deep ultra-violet (UV) band (200-280 nm) proves to be anatural candidate for short range NLoS communication whichis known also as optical scattering communication In factsince solar radiation is negligible at the ground level theeffect of background noise is insignificant allowing the use ofreceivers with wide FOV Thus NLoS-UV can be used as analternative to outdoor infrared or VLC links or in combinationwith existing optical and RF links as it is relatively robust tometeorological conditions [179]

Although UV communication possesses favorable featuresit suffers from a number of shortcomings For LoS links anddespite the deployment of moderate FOV receivers achievableranges are still limited due to absorption by the ambient ozoneWhen operating under NLoS conditions for long rangesthe detrimental effects of fully coupled scattering as wellas turbulence deteriorate the communication link The effectof fading further impacts the received signal resulting in adistorted wave-front and fluctuating intensity Therefore datarates are limited to few Gbps and distances are restricted toshort ranges [185]

Compared to UV links the THz frequency band is consid-ered a suitable contender Unlike UV communication whichimposes health restrictions and safety limits on both the eye

15

Fig 8 Different ranges of Terahertz related applications

and skin an important point to emphasize is that the THzband is a non-ionization band therefore no health risks areassociated with such frequencies [186] From a communicationperspective this indicates that the THz data rates will not bevulnerable to any constraints The fact that developing a UVsystem model suitable for practical application scenarios isstill a demanding issue indicates that THz can compete UVcommunication in its anticipated applications

V TERAHERTZ APPLICATIONS

The THz band is envisioned as a potential candidate for aplethora of applications which exist within the nano micro aswell as macro scales as illustrated in Fig 8 Tbps data ratesreliable transmission and minimal latency [187] are amongthe multiple features that allow such band to support severalscenarios in diverse domains

A Terahertz Nanoscale Applications

On a nanoscale and with the advent of the Internet ofNanoThings (IoNT) the interconnection of various objectssensors as well as devices results in ubiquitous networkstailored not only for device-to-device communication but alsofor extracting data from areas hard to access Based onsuch technological progress the communication architectureof nanonetworks has been established These networks rely onthe THz band to achieve communication between its differententities constituting of nanoscale transistors processors aswell as memories [188] The interconnection of these per-vasively deployed nanodevices with existing communicationnetworks via the Internet creates a cyber physical systemThus nanoscale wireless communication is a key enablerof applications involving operations inside computers anddevices for a typical range of few cm These include chip-to-chip board-to-board and device-to-device communicationsIn addition THz nanocells are envisioned to be part of thehierarchical cellular network for potential mobile users tosupport various indoor as well as outdoor applications [189]Actually almost all modern automation depends on nanoscaledevices that can communicate with each other in order toprovide smarter technical options Hence nanoscale com-munication is suited for applications in multimedia securityand defense environment and industry as well as biomedical

applications [190] For example THz nanosenors detectorsand cameras can support security applications through thecapabilities that THz radiation possess which enables thedetection of weapons explosives as well as chemical andbiological agents [191] From an environmental perspectiveTHz nanosensors allows the detection of pollutants and as suchrenders the technology useful for food preservation and foodprocessing applications In terms of imaging the THz bandspectroscopic characteristics surpasses the currently availablebackscattering techniques and elucidates the dynamics oflarge biomolecules [192] In addition nanoantennas enablewireless interconnection amongst nanosensors deployed insideand over the human body resulting in many bio-nanosensingapplications [193] Several works exist pointing to the THzband as an enabler of in-vivo wireless nanosensor networks(iWNSNs) [194] [195] In particular the authors in [196]presented an attenuation model of intrabody THz propagationto facilitate the accurate design and practical deployment ofiWNSNs In subsequent studies the authors also demonstratedboth the photothermal impact [197] along with the noise effect[198] of THz intrabody communication to further verify thefeasibility and prosperity of such propagation mechanism

B Terahertz Microscale Applications

THz wireless communication promises luring applicationsthat meet consumerrsquos demands of higher data rates especiallyat the micro-scale Wireless local area network (WLAN) andwireless personal area network (WPAN) form the basis of suchapplications which include high-definition television (HDTV)in home distribution wireless displays seamless transfer offiles and THz access points in the areas with human conges-tion The THz band provides small cell communication formobile cellular networks where ultra-high data rate can beprovided to mobile users within transmission range up to 20m As such THz frequencies provides transmission solutionsin adhoc networks and for nomadic users by facilitating con-nection to access points including gates to the metro stationpublic building entrances shopping malls etc In additionmicroscale wireless communication at the THz band involveswireless transmission of uncompressed high definition (HD)videos for education entertainment telemedicine as well assecurity purposes The authors in [199] actually demonstratedthe integration of a 4K camera into a THz communication

16

link and showed the live streaming and recording of theuncompressed HD and 4K videos followed by analysis of thelink quality The BER was measured at several link distanceswhere even at the maximum distance of 175 cm the BERwas below the FEC limit of 10minus3 Not only that NHK (Japanbroadcasting corporation) has already started trial experimentsby telecasting 8K video using proprietary devices for Olympicgames that will be held in 2020 [200] Within the samescope the new vision of modern railways signifies the need tointerconnect infrastructure trains and travelers Therefore torealize a seamless high data rate wireless connectivity hugebandwidth is required Such demand motivates the deploymentof THz communications as they can offer orders of mag-nitude greater bandwidth than current spectrum allocationsand enable very large antenna arrays which in turn providehigh beamforming gains [201] This facilitates relevant sce-narios for railway applications including train to infrastructureinter-wagon and intra-wagon communications Further kioskdownloading is another example of microscale applicationat THz frequencies which offers ultra high downloads ofdigital information to usersrsquo handheld devices For instanceAd posters in metros trains or streets can be the front interfacefor downloading pre-fixed contents such as newly releasedmovie trailers CDs books and magazines [189]

C Terahertz Macroscale ApplicationsOn a macroscale THz wireless communication facilitates

potential outdoor applications which range from few meters upto kilometers For instance wireless backhaulingfronthaulingis one of the envisioned applications for the standard 100 Gbpstransmission solutions [202] In terms of backhauling wirelesspoint-to-point links are widely applied for transmission ofinformation to the base stations of macrocells especially inthose points where optic fiber is not available In terms offronthauling wireless point-to-point links are those betweenthe radio equipment controller of a base station and theremote radio head (radio unit) These systems are normallyoperating within the spectrum of 6 GHz to 80 GHz in whichthey necessitate strict compliance with the LoS conditionsbetween the transceivers of two nodes [203] The increasingnumber of mobile and fixed users in both the private industrialand service sectors will require hundreds of Gbps in thecommunication either to or between cell towers (backhaul)or between cell towers and remote radio heads (fronthaul)In such scenarios apart from the high targeted data-rates (1Tbps) the critical parameter is range which should be inthe order of some kilometers [187] From the point of viewof economic feasibility the principal difference between themicrowave solutions and the solutions for THz waves coversthe price of spectrum equipment costs and the differencein the time spent for assembly and on-site tuning Futureadvancements which include massive deployment of smallcells implementation of cooperative multipoint transmissionand Cloud Radio Access Networks (C-RAN) may increasethe required data rates for either fronthauling or backhaulingor both

Wireless data centers are considered another promisingapplication at the macroscale Actually the increasing call for

cloud applications triggered competition between data centersin an attempt to supply users with an upgraded experienceThis is accomplished by accommodating an extensive numberof servers and providing adequate bandwidths to supportmany applications In fact wireless networking possess severalfeatures including the the adaptability and efficiency neededto provide possible ways to manage traffic bursts and finitenetwork interfaces [204] Nonetheless wireless transmissioncapabilities are limited to short distances and intolerance toblockage leading to a deterioration in the efficiency of datacenters if all wires are substituted A better alternative existsthrough the augmentation of the data center network withwireless flyways rather than exchanging all cables [205] Theauthors in [206] suggested using THz links in data centersas a parallel technology Such deployment in data centersresults in an enhanced performance experience along withimmense savings in cable prices without compromising anythroughput The authors adopted a bandwidth of 120 GHzfor data center applications where atmospheric data has beenutilized to model the THz channel

VI THZ STANDARDIZATION ACTIVITY

The work towards developing a powerful THz standard haslaunched during the last decade when the THz communicationresearch was still in its infancy stage In 2008 the IEEE 80215established the THz Interest Group as a milestone towardsinvestigating the operation in the so called ldquono manrsquos landrdquoand specifically for frequency bands up to 3000 GHz Thenew group conducted a liaison to the International Telecom-munication Union (ITU) and the International Radio AmateurUnion (IARU) regarding the description of the frequencybands higher than 275 GHz Moreover the group launched acall for contribution to cover different topics including possibleTHz applications ways to realize transmitters and receiversexpected ranges and data rates impact on regulations andmarket as well as ongoing research status The journey ofTHz exploration started with studying the link budget for shortdistances considering the atmospheric attenuation for frequen-cies up to 2 THz Despite the uncertainty in determining therealistic transmitted power receiver sensitivity and thermalnoise floor at this band the study concluded the THz potentialto deliver multi Gbps at an early time in 2008 [207] Thenfurther solid analysis were conducted based on Shannon theoryprinciples to prove the THz applicability for future in-homeapplication with a data rate of 100 Gbps [208] In addition theTHz interest group discussed the recent advances in researchand lab measurements that encourage investigating the 300GHz radio channel [209] Specifically detailed discussionsabout the current status of semiconductor technologies andphotons based techniques for generation have been conductedin [210] [211] and [212] [213] respectively Another impor-tant aspect that has been discussed is the desirable performanceto the industry in addition to the cost and safety issues [214][215]

In Nov 2008 a science committee has been formed in orderto bring the THz science communities together as a step toconvert the THz interest group to a study group To that end

17

the committee provided a comprehensive study on channelmodels gave a general overview of technology trends andprovided helpful technical feedback to ITU [216] In March2010 the THz interest group renewed the THz call for contri-butions to discuss the advances since the last call and furtherinvestigate the applicable modulation techniques THz channelmodels THz needed infrastructure and several other points[217] In Nov 2010 the interest group discussed the issuesthat will enable the THz communication deployment in orderto prepare the agenda of the next ITU WRC that would beheld in 2012 [217] The discussion included defining spectrumbands for active services where several bandwidths are definedwith allowable attenuation for short distances Moreover thediscussion showed the necessity to develop a holistic designapproach which includes investigating channel characteristicsby measurements designing antennas to overcome the highattenuation defining suitable communication systems buildingan integrated RF front end and consider the connection tobackbone network In 2011 the THz interest group put moreeffort on investigating the existing THz generation technolo-gies and the potential communication performance in additionto the expected road map in order to be discussed in WRC2012 [218]ndash[220] In March 2012 the interest group reviewedthe results of WRC 2012 and the ITU radio regulations whichallow the coexistence of active services beside passive servicesin the frequency band 275-1000 GHz Specifically the radioastronomy service occupies 275-323 GHz 327-371 GHz and388-424 GHz while the earth exploration-satellite and spaceresearch services operates in 275-277 GHz 294-306 GHz and316-334 GHz bands The main issue in the discussion wasabout the necessary practical steps that should be adoptedto prevent various active services (nomadic links fixed linksairborne systems and multiple interferes) from interfering withthe aforementioned passive services [221] [222] The interestgroup discussed the prerequisites needed to start a study groupwhich included the participation of MAC expertise and peoplefrom industry in addition to the current PHY contributions[223]

Staring from 2013 the interest group added the MAC layerto its discussion sessions in order to investigate the require-ments that should be fulfilled by the MAC protocols to accom-modate for several THz communication applications [224] Alink level study is conducted via a simulation environment forTHz communications using ray-tracing channel model [225]Moreover the data center operation and requirements havebeen discussed as a guide for future THz utilization for datacenter interconnection links [226]ndash[228] Up until this stage oftime the IEEE 80215 THz interest group activities includedintroducing a summary of THz technological developmentschannel modeling and spectrum issues as well as workingto generate a technical expectations document [229] In July2013 the THz interest group proposed starting a study groupto explore the possibility of launching a standard towards100 Gbps over beam switchable wireless point-to-point linkswhich can be used in wireless data center and backchainingThe inauguration of IEEE 80215 study group 100G has beendone in September 2013 [230] The study group working tasksincluded discussing current technologies limits investigating

relevant PHY and MAC protocols defining possible applica-tions and introducing proposals for THz communication onwireless data centers [229]

In 2014 a group called ldquothe task group 3d (TG3d)rdquo hasbeen initiated to adjust the 802153 metrics in an aim toaddress100 Gbps for switched point-to-point links Severalapplications are involved within this category including wire-less data centers backhaulingfronthauling as well as close-proximity communication such as kiosk downloading and D2Dcommunication [231] The first step towards defining bandsfor active services has been done when IEEE contacted theITU to discuss allocating the THz band from 275 GHz to 325GHz for mobile and fixed services The ldquospectrum engineeringtechniquesrdquo ITU group confirmed also the availability of 23GHz in the band 252-275 GHz for mobile and fixed services[169] In addition the WRC 2015 agreed to discuss the land-mobile and fixed active services spectrum allocation in 275-450 GHz while maintaining protection of the passive servicesin the agenda of WRC 2019 [232] To this end the ITU-Ris invited to identify technical and operational characteristicsstudy spectrum needs develop propagation models conductsharing studies witlsquo the passive services and identify candidatefrequency bands Specifically 8 groups namely spectrumengineering techniques propagation fundamentals point-to-area propagation point-to-point and earth space propagationland mobile service fixed services space research earthexploration-satellite service and radio astronomy are involvedin conducting these studies [232] The first standard of THzcommunication came to the scene in 2017 where it focused onpoint-to-point highly-directive links using 8 different channelbandwidths (as multiples of 216 GHz) [48] Within the pasttwo years the interest group discussed several THz researchactivities such as multi-scale channel measurements statisti-cal channel characterization solid state generation methodsantenna array designs THz networks challenges and designinterference studies for THz intra-device communication sys-tems and measurements of research data center

VII FUTURE RESEARCH DIRECTIONS

In this section we shed the light on key enablers that willfacilitate the progress and deployment of THz frequency linksas well as open the door towards numerous applications thatsupport both cellular as well as vehicular networks

A Terahertz Ultra-Massive MIMO

The THz frequency band is considered a key enabler insatisfying the continuously expanding demands of higher datarates Yet despite the huge bandwidth it provides the bandsuffers from high atmospheric losses Therefore high-gaindirectional antennas are utilized in order to invoke commu-nication over distances exceeding a few meters Specificallyin the THz band antennas become smaller and more elementscan be installed in the same footprint As such stemmed fromthe Massive MIMO concept [233] the authors in [234] for-mulated an Ultra-Massive MIMO (UM-MIMO) channel Theconcept of UM-MIMO relies on the adoption of ultra-densefrequency-tunable plasmonic nano-antenna arrays which are

18

TABLE VIIITIMELINE OF THZ STANDARDIZATION

Jan 2008 middot middot middot middot middot middotbull the IEEE 80215 established theldquoTHz Interest Grouprdquo

Mar 2008 middot middot middot middot middot middotbull Call for contribution

Nov 2008 middot middot middot middot middot middotbull Science committee formation

Jul 2009 middot middot middot middot middot middotbull Call for THz application

Nov 2011 middot middot middot middot middot middotbull Call for THz application

2012 middot middot middot middot middot middotbull THz applications and PHY layerissues discussion

Sep 2013 middot middot middot middot middot middotbull Inauguration of IEEE 80215 studygroup 100G

Dec 2013 middot middot middot middot middot middotbull Study group 100G call forapplications

2014 middot middot middot middot middot middotbull Task group 3d (TG3d) formation

2015-2016 middot middot middot middot middot middotbullDiscussion with ITU about THzband allocation for mobile and fixedservices

Sep 2017 middot middot middot middot middot middotbullIEEE Std 802153d-2017 standardis approved as 100 Gbps wirelessswitched point-to-point system

simultaneously utilized in transmission and reception therebyincreasing the communication distance and ultimately theachievable data rates at THz frequencies [235] Actually theradiated signals may be regulated both in the elevation and theazimuth directions when securing two-dimensional or planarantenna arrays rather than one-dimensional or linear arraysThis results in 3D or Full-Dimension MIMO The performanceof UM-MIMO technology depends on two metrics namelythe prospects of the plasmonic nanoantenna as well as thecharacteristics of the THz channel As such a channel modelfor the UM-MIMO systems using the array-of-subarray archi-tecture has been proposed in [236] The results indicate thatwhen using 1024 times 1024 UM-MIMO systems at 03 THz and1 THz multi-Tbps links are achievable at distances of up to 20m Another important aspect is the dynamic resource allocationthat can fully utilize the UM-MIMO system and gain themaximum benefits by adaptive design schemes [237] Furtherspatial modulation techniques that can influence the attributesof densely packed configurable nanoantenna subarrays havebeen studied by the authors in [238] By using such anapproach both the capacity and spectral efficiency of thesystem are improved while maintaining acceptable beamform-ing performance A particular spatial modulation configurationthat establish good channel conditions is suggested based onthe communication distance and the frequency of operation

B Terahertz Virtual Reality Perception via Cellular Networks

In order to attain a high-mobility automotive content stream-ing guarantee and guarantee an ultra reliable low latency

communication it is essential to go well beyond what 5G candeliver Although there are numerous compelling augmentedreality and virtual reality applications video is the mostimportant and unique in its high bandwidth requirements Assuch the THz frequency band is sought as a technology thatwill provide both high capacity and dense coverage to bringthese applications close to the end user THz cellular networkswill enable interactive high dynamic range videos at increasedresolutions and higher framerates which actually necessitate10 times the bit-rate required for 4K videos THz transmissionwill help relieve any interference problem and provide extradata to support various instructions in video transmission Inaddition the THz band will be an enabler of 6 degrees offreedom (6DoF) videos providing users with an ability tomove within and interact with the environment Streaming live6DoF content to deliver a ldquobe thererdquo experience is basicallya forward-looking use case [239] The results presented in[240] show that THz can deliver rates up to 164 Gbps with adelay threshold of 30 ms given that the impact of molecularabsorption on the THz links which considerably limits thecommunication range of the small base station is relievedthrough network densification

C Terahertz Communications for Mobile HetNets

As the demands of communication services are developingin the direction of multiple users large capacity and highspeed mobile heterogeneous networks (HetNets) which com-bine various access network technologies have become animminent trend As such applying the THz technology toHetNets is a promising way to improve the transmission rateas well as the capacity and achieve a throughput at the level ofTbps [241] Despite the high path loss and highly directionalantenna requirements these disadvantages could change intosatisfactory features while operating in the femtocell regimeThe deployment of femtocells reduces the required distancebetween both the active base-station and the user while main-taining high signal to interference and noise ratio (SINR) at thereceiver Through such setup femtocell base-stations improvethe principle of frequency reuse and increase the capacityof the THz band systems These access points are appliedas portals to in-home service and automation metro-stationsshopping malls traffic lights and many other applicationsAs such a novel era of communications via THz signals formobile HetNets will be witnessed through the installation ofthese access points Based on several metrics including theenvironment the quality and type of communication serviceboth picocells and femtocells will be accordingly collocatedwithin the macrocell footprint as illustrated in Fig 9 Infact the authors in [242] note that 6G technology will allowcell-less architectures and compact integration of multiplefrequencies and communication technologies Such vision maybe achieved by deploying multiple connectivity approachesand providing support for diverse and heterogeneous radios inthe devices Both seamless mobility support without overheadfrom handovers and QoS guarantees even in challengingmobility scenarios will be assured via the cell-less networkprocedures In addition since ultra-dense (UD)-HetNets are

19

bound to networks of big data the authors in [243] intro-duced an AI-based network framework for energy-efficientoperations The presented framework supplies the networkwith the abilities of learning and inferring by analyzing thecollected big data and then saving energy from both largescales (base station operation) and small scales (proactivecaching and interference-aware resource allocation) The factthat THz communication is composed of access points inpervasive WiFi networks or base-station clustering in heteroge-nous networks reinforcement learning may be deployed Suchself-organization capability is needed in THz communicationto allow femtocells to autonomously recognize available spec-trum and adjust their parameters subsequently These cells willtherefore operate under restrictions of avoiding intrainter-tierinterference and satisfy QoS requirements [244]

Fig 9 Picocells and femtocells will be collocated within the macrocellfootprint for THz wireless communication

D Terahertz 3D Beamforming Technology

One of the anticipated key enablers of THz wireless sys-tems is 3D MIMO technology In fact real-world channelsemphasize 3D characteristics leaving 2D MIMO techniquessuboptimum [245] 3D beamforming emerges as a solutionto allow the construction of directional beams extend thecommunication range as well as lower the interference levelSuch technology holds a lot of promise to mitigate theunavoidable path loss experienced by the THz channel Inspecific the vertical beam pattern possesses a complete activecorrespondence per resource and per user equipment 3Dbeamforming can also increase the strength of the signal byallowing the vertical main lobe to be located precisely atthe receiver at any position By adopting beam coordinationor MIMO schemes the alteration in vertical dimension hasthe potential to capitalize on additional diversity or spatialseparation This will lead to increasing the quality of the signalor increasing the number of supported users [246] The abilityto control the arrayrsquos radiation pattern in 3D is nonethelesshelpful to manipulate the multipath environment resulting ina constructive addition of the many signal components atthe location of the expected receiver On a similar frontierthe authors in [247] showcase tunable beam steering devicesbased on multilayer graphene-dielectric metamaterials Sincethe effective refractive index of such metamaterials can bealtered by changing the chemical potential of each graphenelayer the spatial distribution of the phase of the transmittedbeam can be tailored This results in establishing mechanisms

for active beam steering resulting tunable transmitterreceivermodules for imaging and sensing at THz frequencies

In addition in order to mitigate the severe Doppler effectin mmWTHz massive MIMO systems the authors in [248]proposed a beam division multiple access technique withper-beam synchronization capability in time and frequencyThe authors verified via simulations the effectiveness of theproposed technique where they showed that both the channeldelay spread and Doppler frequency spread can be decreasedvia per-beam synchronization This results in reducing theoverall system overhead and outperforming conventional tech-niques in typical mobility scenarios

E Terahertz Communication for Urban EnvironmentsIn 2016 Facebook launched a new project called ldquoTerra-

graphrdquo to provide crowded urban areas with a high-speedinternet service [249] Terragraph adopted the mmW bandspecifically the 60 GHz frequency range and utilized dis-tributed access points over the existing city infrastructure toallow quick easy low cost and tractable installation Themultiple access points communicate with each other creatingmesh network over the city instead of lying down opticalfiber that is unfeasible in the high-density urban environmentsThe Terragraph introduced a powerful solution that uses 7-14GHz bandwidth which is considered the largest commercialradio band ever used till now Moreover it is a licensed freespectrum until this moment which further decreases the meshnetwork deployment cost Therefore the Terragraph networkintroduced a good network connectivity solution to connect theservice provider with end users via Gbps links using existingurban physical assets such as traffic light poles and lampsposts

Despite the advantages mentioned above of the wirelessmesh network solution several obstacles can limit its per-formance and affect using it for similar scenarios in thefuture First the mmW frequency bands for the InternationalMobile Communications (IMT) 2020 are still under studywhere the decision is expected to be taken in the World RadioConference (WRC) 2019 that will be held on Nov 2019 [250]Second the mmW band is expected to become crowded inthe next decade Thus it will not be possible to accommodatemore users and satisfy the exponential increase in populationand data communications services Finally the mmW signalattenuates in the rain environment thus the mesh network canbe down under such circumstances In other words althoughthe Terragraph project proposed rerouting techniques to avoidthe scenario of link outage rain can put most of the network ina blackout As such the THz frequency band provide a reliablewireless network access alternative with multiple backup linksto avoid outages especially that it can work under differentweather conditions The THz band shall accommodate futurepopulation increase urban environment rapid changes and newhungry rate services An illustration of THz communicationfor urban environment is demonstrated in Fig 10

F Terahertz Automotive Applications1) Vehicle to Infrastructure Communication The progress

witnessed in the vehicle to infrastructure communication is

20

Fig 10 THz wireless links as candidates for establishing communication inan urban environment

considered a major milestone in the automotive industryThe initiation of a communication link that connects wire-less between vehicles and the road-side infrastructures pavesthe way towards the the deployment of fully autonomousand smart transportation systems According to the literature[251] the Long Term Evolution (LTE) has been the standardwireless interface which supports communications in vehicularenvironments However due to the stringent requirements ofthe users and the demands of the market in terms of higherdata rates and lower latency to mobile users new solutionsmust arise to fulfill the needs of next-generation networksAs such the authors in [252] discussed the feasibility ofestablishing vehicle to infrastructure communications usinghigher frequencies namely the mmW to support automotiveapplications Despite the anticipated benefits associated withmmW technology in both metropolitan and mobile highwayscenarios a number of challenges still arise These includepath-loss shadowing high directionality of beams as wellas high sensitivity to blockage Thereby the THz frequencyband seems to be a better alternative especially due to itscapability of supporting the required estimated throughput ofterabyte per driving hour [252]ndash[254] A schematic diagrammimicking V2I communication using THz links is providedin Fig 11 As such the high data rate communication high-resolution radar sensing capabilities as well as the directionalbeam alignment capability of the THz transmitter and receiverresult in such technology being a stronger candidate for smartvehicular communication scenarios

Not only vehicle to infrastructure communication technol-ogy is evolving but also train to infrastructure (T2I) communi-cation is developing towards smart rail mobility Indeed sincehigh-data rate wireless connectivity with bandwidth beyondGHz is needed in order to establish T2I and interwagonscenarios the authors in [255] demonstrated a complete studyconcerning measurement simulation and characterization ofthe T2I channel using the THz frequency band Despite thehigh path loss of THz signals as well as the high mobilityexperienced by such high speed trains the authors note thata robust THz link between the access points of the network

can still be achieved This is due to the fact that the userrsquosdesired content may be distributed into several segments thatare delivered individually to broadcast points based on thetrainrsquos schedule Such procedure is facilitated by utilizinga proactive content caching scheme [256] paving the waytowards seamless data transmission

Fig 11 Envisioned V2I future communication scenarios utilizing the THzfrequency band

2) Unmanned autonomous vehicles (UAVs) Unmanned au-tonomous vehicles (UAVs) have recently become accessible tothe public This resulted in several applications targeting bothcivilian and commercial domains Typical examples involveweather monitoring forest fire detection traffic control cargotransport emergency search and rescue as well as commu-nication relaying [257] To deploy these applications UAVsneed to have a reliable communication link accessible at alltimes For heights above 16 km the effect of moisture istrivial thus THz attenuation is negligible As such THz canbecome a strong candidate to initiate reliable communicationsfor varying UAV application scenarios

In comparison to free space optical the THz frequencyband is a sufficient technology since it will not only enablehigh-capacity UAV-UAV wireless backhaul but also allow abetter substitute in alleviating the high mobility environmentof UAVs In fact as a result of mobility communicationlinks which suffer from the Doppler effect are minimized ascarrier frequencies increase Therefore THz communicationcan establish high-speed communication links between twopotentially dynamic locations [258] UAVs also need short-distance secure links to receive instructions or transmit data be-fore dispersing to fulfill their remote controlled or autonomousmissions THz links are thereby considered a reliable venue forexchanging safety-critical information between UAVs as wellas between the UAV and ground control stations The largechannel bandwidth of THz systems allows for specific protec-tion measures against various standoff attacks like jammingand have the ability to completely hide information exchangeFurthermore THz links could be also utilized between UAVsand airplanes in order to support internet for flights instead ofusing the satellite service In this way the UAV will act asa switchboard in the sky serving as an intermediary betweenthe ground station and the airplane

21

G Terahertz Security Measures

Despite the prevailing expectation of enhanced security forwireless data links operating at high-frequencies the authorsin [259] show that an eavesdropper can intercept signals inLoS transmissions even when transmission occurs at high fre-quencies with narrow beams The techniques the eavesdropperuses at high frequencies varies in comparison to those usedfor lower frequency transmissions For high frequencies anobject is placed in the path of the transmission to scatterradiation towards the eavesdropper Hence the authors presenta technique to mitigate such eavesdropping approach whichsuggests characterizing the backscatter of the channel If thesignals incoming towards the transmitter can be measuredand differentiated from the variable backscattered off mobileobjects or the environment then a sign of a probable attackwould be through noticing any change either an increase or adecrease in the signal Such technique provides an extra levelof security especially when added to conventional counter-measures Thus to embed security into a directional wirelesslink systems will necessitate original physical layer compo-nents and protocols for channel estimation The presentedwork implies the significance of physical layer security inTHz wireless networks and the urge for transceiver designsthat include new counter-measures

VIII CONCLUSION

To satisfy the demands for higher data rates and supportservices of various traffic patterns novel and efficient wirelesstechnologies for a range of transmission links ought to bedeveloped As 5G networks are being deployed in variousparts across the globe utilizing the mmW frequencies theresearch community is exploring the THz frequency bandas a revolutionary solution to support beyond 5G networksand enable applications that couldnt be deployed through 5Gdue to unforeseen difficulties In this paper a comprehensivesurvey has been presented for THz wireless communicationin an attempt to review the devices channel models aswell as applications associated with the development of THzsystem architectures As such the THz frequency generationtechniques have been extensively reviewed where the progressin electronics photonics as well as plasmonics techniques hasbeen highlighted Moreover the THz channel models whichcapture the channel characteristics and propagation phenom-ena have been presented for different use-case scenarios Anextensive comparison was further conducted to point the dif-ferences between THz wireless and other existing technologiesincluding mmW infrared visible light and ultraviolet commu-nication indicating the foreseen potential upon the deploymentof the THz band In addition a plethora of applications whichtackle nano micro as well as macro-scale THz scenarioshave been demonstrated Further the standardization activitiesas well as the investigation efforts of frequency bands upto 3000 GHz are demonstrated indicating the collaborativeefforts bringing THz science communities together Finally anumber of promising techniques and deployment opportunitiesare presented in an attempt to efficiently satisfy the needs offuture networks and face the technical challenges associated

with implementing THz communication Actually with thecontinuous progress in THz devices new foundations for rapiddevelopment of practical systems will be established Withthe emergence of THz communication systems societies willbe expecting near-instant unlimited wireless connectivity withcapabilities extending beyond the 5G networks Virtual realityHD streaming as well as automation for the internet of thingsare amongst the many promising applications that shall bebrought through the THz frequency band

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[2] S Cherry ldquoEdholmrsquos law of bandwidthrdquo IEEE Spectr vol 41 no 7pp 58ndash60 July 2004

[3] C V N Index ldquoCisco visual networking index Forecast and method-ology 2015-2020rdquo White paper CISCO 2015

[4] V Cisco ldquoCisco visual networking index Forecast and trends 2017ndash2022rdquo White Paper 2018

[5] R Li ldquoTowards a new internet for the year 2030 and beyondrdquo 2018[6] A J Kerecman ldquoThe Tungsten-P type Silicon point contact dioderdquo in

MTT-S Int Microwave Symp Dig IEEE 1973 pp 30ndash34[7] J R Ashley and F Palka ldquoTransmission cavity and injection stabi-

lization of an X-band transferred electron oscillatorrdquo in MTT-S IntMicrowave Symp Dig IEEE 1973 pp 181ndash182

[8] J W Fleming ldquoHigh-resolution submillimeter-wave Fourier-transformspectrometry of gasesrdquo IEEE Trans Microw Theory Tech vol 22no 12 pp 1023ndash1025 Dec 1974

[9] P H Siegel ldquoTerahertz technologyrdquo IEEE Trans Microw TheoryTech vol 50 no 3 pp 910ndash928 Mar 2002

[10] B Ferguson and X-C Zhang ldquoMaterials for terahertz science andtechnologyrdquo Nature materials vol 1 no 1 p 26 Sep 2002

[11] R Piesiewicz T Kleine-Ostmann N Krumbholz D MittlemanM Koch J Schoebei and T Kurner ldquoShort-range ultra-broadbandterahertz communications Concepts and perspectivesrdquo IEEE AntennasPropag Mag vol 49 no 6 pp 24ndash39 Dec 2007

[12] I F Akyildiz J M Jornet and C Han ldquoTeraNets ultra-broadbandcommunication networks in the terahertz bandrdquo IEEE Commun Magvol 21 no 4 pp 130ndash135 Aug 2014

[13] P H Siegel ldquoTerahertz technology in biology and medicinerdquo IEEETrans Microw Theory Tech vol 52 no 10 pp 2438ndash2447 Oct2004

[14] M J Fitch and R Osiander ldquoTerahertz waves for communicationsand sensingrdquo Johns Hopkins APL technical digest vol 25 no 4 pp348ndash355 2004

[15] M Tonouchi ldquoCutting-edge terahertz technologyrdquo Nature photonvol 1 no 2 p 97 2007

[16] M Jacob S Priebe T Kurner C Jastrow T Kleine-Ostmann andT Schrader ldquoAn overview of ongoing activities in the field of chan-nel modeling spectrum allocation and standardization for mm-Waveand THz indoor communicationsrdquo in IEEE GLOBECOM WorkshopsIEEE 2009 pp 1ndash6

[17] J Federici and L Moeller ldquoReview of terahertz and subterahertzwireless communicationsrdquo J Appl Phys vol 107 no 11 p 6 2010

[18] T Kleine-Ostmann and T Nagatsuma ldquoA review on terahertz commu-nications researchrdquo J Infrared Millim Terahertz Waves vol 32 no 2pp 143ndash171 2011

[19] H-J Song and T Nagatsuma ldquoPresent and future of terahertz commu-nicationsrdquo IEEE Trans THz Sci Technol vol 1 no 1 pp 256ndash263Sep 2011

[20] T Nagatsuma ldquoTerahertz technologies present and futurerdquo IEICEElectron Exp vol 8 no 14 pp 1127ndash1142 July 2011

[21] K-C Huang and Z Wang ldquoTerahertz terabit wireless communicationrdquoIEEE Microwave Magazine vol 12 no 4 pp 108ndash116 2011

[22] T Nagatsuma S Horiguchi Y Minamikata Y Yoshimizu S HisatakeS Kuwano N Yoshimoto J Terada and H Takahashi ldquoTerahertzwireless communications based on photonics technologiesrdquo Opticsexpress vol 21 no 20 pp 23 736ndash23 747 2013

[23] I F Akyildiz J M Jornet and C Han ldquoTerahertz band Next frontierfor wireless communicationsrdquo Physical Commun vol 12 pp 16ndash32Sep 2014

22

[24] T Kurner and S Priebe ldquoTowards THz communications - Statusin Research Standardization and Regulationrdquo J Infrared Millim THzWaves vol 35 no 1 pp 53ndash62 Aug 2014

[25] A Hirata and M Yaita ldquoUltrafast terahertz wireless communicationstechnologiesrdquo IEEE Trans THz Sci Technol vol 5 no 6 pp 1128ndash1132 Nov 2015

[26] V Petrov A Pyattaev D Moltchanov and Y Koucheryavy ldquoTer-ahertz band communications Applications research challenges andstandardization activitiesrdquo in Proc 8th Intern Congress Ultra ModernTelecommun and Control Sys and Workshops (ICUMT) LisbonPortugal 2016 pp 18ndash20

[27] S Mumtaz J Miquel Jornet J Aulin W H Gerstacker X Dongand B Ai ldquoTerahertz communication for vehicular networksrdquo IEEETransactions on Vehicular Technology vol 66 no 7 pp 5617ndash5625July 2017

[28] D M Mittleman ldquoPerspective Terahertz science and technologyrdquoJournal of Applied Physics vol 122 no 23 p 230901 2017

[29] K Sengupta T Nagatsuma and D M Mittleman ldquoTerahertz integratedelectronic and hybrid electronicndashphotonic systemsrdquo Nature Electronicsvol 1 no 12 p 622 2018

[30] Z Chen X Ma B Zhang Y Zhang Z Niu N Kuang W ChenL Li and S Li ldquoA survey on terahertz communicationsrdquo ChinaCommunications vol 16 no 2 pp 1ndash35 2019

[31] S Ghafoor N Boujnah M H Rehmani and A Davy ldquoMac protocolsfor terahertz communication A comprehensive surveyrdquo arXiv preprintarXiv190411441 2019

[32] K Tekbıyık A R Ekti G K Kurt and A Gorcin ldquoTerahertz bandcommunication systems Challenges novelties and standardization ef-fortsrdquo Physical Communication 2019

[33] T S Rappaport Y Xing O Kanhere S Ju A MadanayakeS Mandal A Alkhateeb and G C Trichopoulos ldquoWirelesscommunications and applications above 100 GHz Opportunities andchallenges for 6g and beyondrdquo IEEE Access pp 1ndash1 2019 [Online]Available httpsdoiorg101109access20192921522

[34] H Elayan O Amin R M Shubair and M-S Alouini ldquoTerahertzcommunication The opportunities of wireless technology beyond 5Grdquoin International Conf on Advanced Communication Technologies andNetworking (CommNet) IEEE 2018 pp 1ndash5

[35] Y Zhu and S Zhuang ldquoUltrafast electromagnetic waves emitted fromsemiconductorrdquo in Behaviour of Electromagnetic Waves in DifferentMedia and Structures IntechOpen 2011

[36] M Lee and M C Wanke ldquoSearching for a solid-state terahertztechnologyrdquo Science vol 316 no 5821 pp 64ndash65 2007

[37] T Minotani A Hirata and T Nagatsuma ldquoA broadband 120-GHzSchottky-diode receiver for 10-Gbits wireless linksrdquo in presented atthe Asia Pacific Microw Conf 2002 Paper WE1A-5

[38] T Kleine-Ostmann K Pierz G Hein P Dawson and M KochldquoAudio signal transmission over THz communication channel usingsemiconductor modulatorrdquo Electron Lett vol 40 no 2 pp 124ndash126Jan 2004

[39] C Jastrow K Mu R Piesiewicz T Ku M Koch T Kleine-Ostmannet al ldquo300 GHz transmission systemrdquo Electron Lett vol 44 no 3pp 213ndash214 Jan 2008

[40] A Hirata ldquoTransmission trial of television broadcast materials using120-GHz-band wireless linkrdquo NTT Tech Rev vol 7 no 3 Mar 2009

[41] A Hirata T Kosugi H Takahashi J Takeuchi K Murata N KukutsuY Kado S Okabe T Ikeda F Suginosita et al ldquo58-km 10-Gbpsdata transmission over a 120-GHz-band wireless linkrdquo in InternationalConf on Wireless Information Technology and Systems (ICWITS)IEEE 2010 pp 1ndash4

[42] J-D Park S Kang S V Thyagarajan E Alon and A M NiknejadldquoA 260 GHz fully integrated cmos transceiver for wireless chip-to-chipcommunicationrdquo in Symposium on VLSI Circuits (VLSIC) IEEE2012 pp 48ndash49

[43] H-J Song K Ajito Y Muramoto A Wakatsuki T Nagatsuma andN Kukutsu ldquo24 Gbits data transmission in 300 GHz band for futureTerahertz communicationsrdquo Electron Lett vol 48 no 15 pp 953ndash954 2012

[44] S Koenig D Lopez-Diaz J Antes F Boes R HennebergerA Leuther A Tessmann R Schmogrow D Hillerkuss R Palmeret al ldquoWireless sub-THz communication system with high data raterdquoNature Photon vol 7 no 12 p 977 2013

[45] ldquo125-km-long transmission experiment over 120-GHz-band FPU forSHV signal transmission author=J Tsumochi and F Suginoshitaand S Okabe and H Takeuchi and H Takahashi and A Hiratabooktitle=presented at the IEICE General Conf year=2014 Paper C-2-111rdquo

[46] S Kim J Yun D Yoon M Kim J-S Rieh M Urteaga and S Jeonldquo300 GHz integrated heterodyne receiver and transmitter with on-chipfundamental local oscillator and mixersrdquo IEEE TransTHz Sci andTechnol vol 5 no 1 pp 92ndash101 2014

[47] N T T Corporation ldquoThe worldrsquos-first compact transceiver forTerahertz wireless communication using the 300-GHz band withtransmission rate of several-dozen Gigabits per second-was developedand experimentally demonstrated high-speed data transmissionrdquoNational Institute of Information and Communications TechnologyMay 26 2016 [Online] Available httpwwwnictgojpenpress20160526-1html

[48] T Kurner ldquoTHz communications-An overview and options forIEEE 802 standardizationrdquo IEEE 80215-18-0516-02-0thz Nov2018 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[49] H Hamada T Fujimura I Abdo K Okada H-J Song H SugiyamaH Matsuzaki and H Nosaka ldquo300-GHz 100-Gbs InP-HEMT wire-less transceiver using a 300-GHz fundamental mixerrdquo in Proc IEEEMTT-S Intern Microwave Symp (IMS) IEEE 2018 pp 1480ndash1483

[50] S Lee R Dong T Yoshida S Amakawa S Hara A KasamatsuJ Sato and M Fujishima ldquo95 an 80Gbs 300GHz-band single-chipcmos transceiverrdquo in International Solid-State Circuits Conf-(ISSCC)IEEE 2019 pp 170ndash172

[51] S Jameson and E Socher ldquoA 03 THz radiating active times27 frequencymultiplier chain with 1 mw radiated power in CMOS 65-nmrdquo IEEETransTHz Sci and Technol vol 5 no 4 pp 645ndash648 July 2015

[52] I Post M Akbar G Curello S Gannavaram W Hafez U JalanK Komeyli J Lin N Lindert J Park et al ldquoA 65nm CMOS SOCtechnology featuring strained silicon transistors for RF applicationsrdquoin Electron Devices Meeting 2006 IEDMrsquo06 International IEEE2006 pp 1ndash3

[53] S Lee B Jagannathan S Narasimha A Chou N Zamdmer J John-son R Williams L Wagner J Kim J-O Plouchart et al ldquoRecord RFperformance of 45-nm SOI CMOS technologyrdquo in Electron DevicesMeeting 2007 IEDM 2007 IEEE International IEEE 2007 pp255ndash258

[54] D Shim D Koukis D J Arenas D B Tanner and K Kenneth ldquo553-GHz signal generation in CMOS using a quadruple-push oscillatorrdquo inVLSI Circuits (VLSIC) 2011 Symposium on IEEE 2011 pp 154ndash155

[55] W Steyaert and P Reynaert ldquoA 054 THz signal generator in 40 nmbulk CMOS with 22 GHz tuning range and integrated planar antennardquoIEEE J Solid-State Circuits vol 49 no 7 pp 1617ndash1626 July 2014

[56] Y Zhao Z-Z Chen Y Du Y Li R Al Hadi G Virbila Y XuY Kim A Tang T J Reck et al ldquoA 056 THz phase-locked frequencysynthesizer in 65 nm CMOS technologyrdquo IEEE J Solid-State Circuitsvol 51 no 12 pp 3005ndash3019 2016

[57] L Wilson ldquoInternational technology roadmap for semiconductors(itrs)rdquo Semiconductor Industry Association 2011

[58] K Takano S Amakawa K Katayama S Hara R DongA Kasamatsu I Hosako K Mizuno K Takahashi T Yoshida andM Fujishima ldquo179 A 105Gbs 300GHz CMOS transmitterrdquo in 2017IEEE International Solid-State Circuits Conf (ISSCC) Feb 2017 pp308ndash309

[59] P A Houston ldquoHigh-frequency heterojunction bipolar transistor de-vice design and technologyrdquo Electronics Communication EngineeringJournal vol 12 no 5 pp 220ndash228 Oct 2000

[60] S Masuda T Ohki K Makiyama M Kanamura N OkamotoH Shigematsu K Imanishi T Kikkawa K Joshin and N Hara ldquoGaNMMIC amplifiers for W-band transceiversrdquo in Microwave IntegratedCircuits Conf 2009 EuMIC 2009 European IEEE 2009 pp 443ndash446

[61] I Kallfass F Boes T Messinger J Antes A Inam U LewarkA Tessmann and R Henneberger ldquo64 Gbits transmission over 850 mfixed wireless link at 240 GHz carrier frequencyrdquo J Infrared MillimTerahertz Waves vol 36 no 2 pp 221ndash233 2015

[62] F Boes T Messinger J Antes D Meier A Tessmann A Inam andI Kallfass ldquoUltra-broadband MMIC-based wireless link at 240 GHzenabled by 64GSs DACrdquo in 2014 39th International Conf on InfraredMillimeter and Terahertz waves (IRMMW-THz) Sept 2014 pp 1ndash2

[63] R Lai X B Mei W R Deal W Yoshida Y M Kim P H Liu J LeeJ Uyeda V Radisic M Lange T Gaier L Samoska and A FungldquoSub 50 nm InP HEMT device with fmax greater than 1 THzrdquo in 2007IEEE International Electron Devices Meeting Dec 2007 pp 609ndash611

[64] W Deal X Mei V Radisic K Leong S Sarkozy B Gorospe J LeeP Liu W Yoshida J Zhou et al ldquoDemonstration of a 048 THz

23

amplifier module using InP HEMT transistorsrdquo IEEE Microw WirelessCompon Lett vol 20 no 5 pp 289ndash291 2010

[65] W R Deal K Leong V Radisic S Sarkozy B Gorospe J LeeP Liu W Yoshida J Zhou M Lange et al ldquoLow noise amplificationat 067 THz using 30 nm InP HEMTsrdquo IEEE Microw WirelessCompon Lett vol 21 no 7 pp 368ndash370 2011

[66] W Deal K Leong A Zamora V Radisic and X Mei ldquoRecentprogress in scaling InP HEMT TMIC technology to 850 GHzrdquo inMicrowave Symposium (IMS) 2014 IEEE MTT-S International IEEE2014 pp 1ndash3

[67] X Mei W Yoshida M Lange J Lee J Zhou P-H Liu K LeongA Zamora J Padilla S Sarkozy et al ldquoFirst demonstration of am-plification at 1 THz using 25-nm InP high electron mobility transistorprocessrdquo IEEE Electron Device Lett vol 36 no 4 pp 327ndash329 2015

[68] U R ETSI ldquommWave semiconductor industry technologies Statusand evolutionrdquo white paper no 15 2016

[69] T Takahashi Y Kawano K Makiyama S Shiba M Sato Y Nakashaand N Hara ldquoEnhancement of fmax to 910 GHz by adoptingasymmetric gate recess and double-side-doped structure in 75-nm-gateInAlAsInGaAs HEMTsrdquo IEEE Trans on Electron Devices vol 64no 1 pp 89ndash95 Jan 2017

[70] mdashmdash ldquoMaximum frequency of oscillation of 13 THz obtained by usingan extended drain-side recess structure in 75-nm-gate InAlAsInGaAshigh-electron-mobility transistorsrdquo Applied Physics Express vol 10no 2 p 024102 2017

[71] D H Kim J A del Alamo P Chen W Ha M Urteaga and B Brarldquo50-nm E-mode In07Ga03As PHEMTs on 100-mm InP substrate withfmax gt 1 THzrdquo in 2010 International Electron Devices Meeting Dec2010 pp 3061ndash3064

[72] L Esaki and L L Chang ldquoNew transport phenomenon in a semi-conductor ldquosuperlatticerdquordquo Phys Rev Lett vol 33 no 8 p 495 Aug1974

[73] K H Alharbi ldquoHigh performance terahertz resonant tunnelling diodesources and broadband antenna for air-side radiationrdquo PhD disserta-tion University of Glasgow 2016

[74] T Sollner P Tannenwald D Peck and W Goodhue ldquoQuantum welloscillatorsrdquo Applied physics letters vol 45 no 12 pp 1319ndash13211984

[75] A C Beer E R Weber R Willardson R A Kiehl and T G SollnerHigh Speed Heterostructure Devices Academic Press 1994 vol 41

[76] S Suzuki M Asada A Teranishi H Sugiyama and H YokoyamaldquoFundamental oscillation of resonant tunneling diodes above 1 THz atroom temperaturerdquo Applied Physics Letters vol 97 no 24 p 2421022010

[77] H Kanaya R Sogabe T Maekawa S Suzuki and M AsadaldquoFundamental oscillation up to 142 THz in resonant tunneling diodesby optimized collector spacer thicknessrdquo J Infrared Millim TerahertzWaves vol 35 no 5 pp 425ndash431 2014

[78] T Maekawa H Kanaya S Suzuki and M Asada ldquoFrequency increasein terahertz oscillation of resonant tunnelling diode up to 155 THz byreduced slot-antenna lengthrdquo Electronics Letters vol 50 no 17 pp1214ndash1216 2014

[79] mdashmdash ldquoOscillation up to 192 THz in resonant tunneling diode byreduced conduction lossrdquo Applied Physics Express vol 9 no 2 p024101 2016

[80] N Oshima K Hashimoto S Suzuki and M Asada ldquoWirelessdata transmission of 34 Gbits at a 500-GHz range using resonant-tunnelling-diode terahertz oscillatorrdquo Electronics Letters vol 52no 22 pp 1897ndash1898 2016

[81] mdashmdash ldquoTerahertz wireless data transmission with frequency and po-larization division multiplexing using resonant-tunneling-diode oscilla-torsrdquo IEEE TransTHz Sci and Technol vol 7 no 5 pp 593ndash5982017

[82] X Li J Yu J Zhang Z Dong F Li and N Chi ldquoA 400G opticalwireless integration delivery systemrdquo Optics Express vol 21 no 16pp 18 812ndash18 819 2013

[83] A Hirata T Kosugi H Takahashi J Takeuchi H Togo M YaitaN Kukutsu K Aihara K Murata Y Sato et al ldquo120-GHz-bandwireless link technologies for outdoor 10-Gbits data transmissionrdquoIEEE Trans Microw Theory Tech vol 60 no 3 pp 881ndash895 2012

[84] H Takahashi A Hirata J Takeuchi N Kukutsu T Kosugi andK Murata ldquo120-GHz-band 20-Gbits transmitter and receiver MMICsusing quadrature phase shift keyingrdquo in Microwave Integrated CircuitsConf (EuMIC) 2012 7th European IEEE 2012 pp 313ndash316

[85] I Ando M Tanio M Ito T Kuwabara T Marumoto and K KunihiroldquoWireless D-band communication up to 60 Gbits with 64QAM using

GaAs HEMT technologyrdquo in Radio and Wireless Symposium (RWS)2016 IEEE IEEE 2016 pp 193ndash195

[86] M Fujishima S Amakawa K Takano K Katayama and T YoshidaldquoTehrahertz CMOS design for low-power and high-speed wirelesscommunicationrdquo IEICE Trans on Electronics vol 98 no 12 pp1091ndash1104 2015

[87] C Wang C Lin Q Chen B Lu X Deng and J Zhang ldquoA 10-Gbitswireless communication link using 16-QAM modulation in 140-GHzbandrdquo IEEE Trans on Microwave Theory and Techniques vol 61no 7 pp 2737ndash2746 2013

[88] S Carpenter D Nopchinda M Abbasi Z S He M Bao T Erikssonand H Zirath ldquoA d-band 48-Gbits 64-QAMQPSK direct-conversionIQ transceiver chipsetrdquo IEEE Trans on Microwave Theory andTechniques vol 64 no 4 pp 1285ndash1296 2016

[89] H Shams M J Fice K Balakier C C Renaud F van Dijkand A J Seeds ldquoPhotonic generation for multichannel THz wirelesscommunicationrdquo Optics express vol 22 no 19 pp 23 465ndash23 4722014

[90] Z Wang P-Y Chiang P Nazari C-C Wang Z Chen and P HeydarildquoA CMOS 210-GHz fundamental transceiver with OOK modulationrdquoIEEE J Solid-State Circuits vol 49 no 3 pp 564ndash580 2014

[91] I Kallfass J Antes T Schneider F Kurz D Lopez-Diaz S DieboldH Massler A Leuther and A Tessmann ldquoAll active MMIC-basedwireless communication at 220 GHzrdquo IEEE TransTHz Sci and Tech-nol vol 1 no 2 pp 477ndash487 Nov 2011

[92] J Antes S Koenig D Lopez-Diaz F Boes A Tessmann R Hen-neberger O Ambacher T Zwick and I Kallfass ldquoTransmission ofan 8-PSK modulated 30 Gbits signal using an MMIC-based 240GHz wireless linkrdquo in 2013 IEEE MTT-S International MicrowaveSymposium Digest (MTT) June 2013 pp 1ndash3

[93] H J Song K Ajito Y Muramoto A Wakatsuki T Nagatsuma andN Kukutsu ldquo24 Gbits data transmission in 300 GHz band for futureterahertz communicationsrdquo Electronics Letters vol 48 no 15 pp953ndash954 July 2012

[94] A Kanno T Kuri I Morohashi I Hosako T Kawanishi Y Yoshidaand K-i Kitayama ldquoCoherent terahertz wireless signal transmissionusing advanced optical fiber communication technologyrdquo J InfraredMillim Terahertz Waves vol 36 no 2 pp 180ndash197 2015

[95] I Kallfass I Dan S Rey P Harati J Antes A Tessmann S WagnerM Kuri R Weber H Massler et al ldquoTowards MMIC-based 300GHzindoor wireless communication systemsrdquo IEICE Trans on Electronicsvol 98 no 12 pp 1081ndash1090 2015

[96] T Nagatsuma and G Carpintero ldquoRecent progress and future prospectof photonics-enabled terahertz communications researchrdquo IEICE Transon Electronics vol 98 no 12 pp 1060ndash1070 2015

[97] C Wang B Lu C Lin Q Chen L Miao X Deng and J Zhangldquo034-THz wireless link based on high-order modulation for futurewireless local area network applicationsrdquo IEEE TransTHz Sci andTechnol vol 4 no 1 pp 75ndash85 Jan 2014

[98] S Jia X Yu H Hu J Yu T Morioka P U Jepsen and L KOxenloslashwe ldquo120 Gbs multi-channel THz wireless transmission andTHz receiver performance analysisrdquo IEEE Photon Technol Lettvol 29 no 3 pp 310ndash313

[99] G Ducournau K Engenhardt P Szriftgiser D Bacquet M ZaknouneR Kassi E Lecomte and J-F Lampin ldquo32 Gbits QPSK transmissionat 385 GHz using coherent fibre-optic technologies and THz doubleheterodyne detectionrdquo Electronics Letters vol 51 no 12 pp 915ndash9172015

[100] G Ducournau P Szriftgiser A Beck D Bacquet F PavanelloE Peytavit M Zaknoune T Akalin and J-F Lampin ldquoUltrawide-bandwidth single-channel 04-THz wireless link combining broadbandquasi-optic photomixer and coherent detectionrdquo IEEE TransTHz Sciand Technol vol 4 no 3 pp 328ndash337 2014

[101] X Yu R Asif M Piels D Zibar M Galili T Morioka P U Jepsenand L K Oxenloslashwe ldquo60 Gbits 400 GHz wireless transmissionrdquo inPhotonics in Switching (PS) 2015 International Conf on IEEE 2015pp 4ndash6

[102] S Hu Y-Z Xiong B Zhang L Wang T-G Lim M Je andM Madihian ldquoA SiGe BiCMOS transmitterreceiver chipset with on-chip SIW antennas for terahertz applicationsrdquo IEEE J Solid-StateCircuits vol 47 no 11 pp 2654ndash2664 2012

[103] C Wang J Yu X Li P Gou and W Zhou ldquoFiber-THz-fiber link forTHz signal transmissionrdquo IEEE Photonics Journal vol 10 no 2 pp1ndash6 2018

[104] C Wang X Li K Wang W Zhou and J Yu ldquoSeamless integrationof a fiber-THz wireless-fiber 2x2 MIMO broadband networkrdquo in AsiaCommunications and Photonics Conf (ACP) IEEE 2018 pp 1ndash3

24

[105] X Li J Yu L Zhao W Zhou K Wang M Kong G-K ChangY Zhang X Pan and X Xin ldquo132-Gbs photonics-aided single-carrier wireless terahertz-wave signal transmission at 450GHz enabledby 64QAM modulation and probabilistic shapingrdquo in Optical FiberCommunication Conf Optical Society of America 2019 pp M4Fndash4

[106] K Ishigaki M Shiraishi S Suzuki M Asada N Nishiyama andS Arai ldquoDirect intensity modulation and wireless data transmis-sion characteristics of terahertz-oscillating resonant tunnelling diodesrdquoElectronics Letters vol 48 no 10 pp 582ndash583 May 2012

[107] L Moeller J Federici and K Su ldquo25 Gbits duobinary signalling withnarrow bandwidth 0625 terahertz sourcerdquo Electronics Letters vol 47no 15 pp 856ndash858 2011

[108] J Yao ldquoMicrowave photonicsrdquo Journal of Lightwave Technologyvol 27 no 3 pp 314ndash335 2009

[109] R A Minasian E Chan and X Yi ldquoMicrowave photonic signalprocessingrdquo Optics Express vol 21 no 19 pp 22 918ndash22 936 2013

[110] T Nagatsuma A Hirata Y Royter M Shinagawa T FurutaT Ishibashi and H Ito ldquoA 120-GHz integrated photonic transmitterrdquoin Microwave Photonics 2000 MWP 2000 International TopicalMeeting on IEEE 2000 pp 225ndash228

[111] T Nagatsuma G Ducournau and C C Renaud ldquoAdvances in terahertzcommunications accelerated by photonicsrdquo Nature Photonics vol 10no 6 p 371 2016

[112] X Yu S Jia H Hu M Galili T Morioka P U Jepsen and L KOxenloslashwe ldquo160 Gbits photonics wireless transmission in the 300-500GHz bandrdquo Apl Photonics vol 1 no 8 p 081301 2016

[113] X Pang S Jia O Ozolins X Yu H Hu L Marcon P GuanF Da Ros S Popov G Jacobsen et al ldquo260 Gbits photonic-wirelesslink in the THz bandrdquo in Photonics Conf (IPC) 2016 IEEE IEEE2016 pp 1ndash2

[114] Y Miyamoto M Yoneyama K Hagimoto T Ishibashi andN Shimizu ldquo40 Gbits high sensitivity optical receiver with uni-travelling-carrier photodiode acting as decision IC driverrdquo ElectronicsLetters vol 34 no 2 pp 214ndash215 Jan 1998

[115] T Ishibashi N Shimizu S Kodama H Ito T Nagatsuma andT Furuta ldquoUni-traveling-carrier photodiodesrdquo tfilmdash Optoelectronicsp 83 1997

[116] K Sano K Murata T Akeyoshi N Shimizu T Otsuji M Ya-mamoto T Ishibashi and E Sano ldquoUltra-fast optoelectronic circuitusing resonant tunnelling diodes and unitravelling-carrier photodioderdquoElectronics Letters vol 34 no 2 pp 215ndash217 1998

[117] T Ishibashi Y Muramoto T Yoshimatsu and H Ito ldquoUnitraveling-carrier photodiodes for terahertz applicationsrdquo IEEE J Sel TopicsQuantum Electron vol 20 no 6 pp 79ndash88 Nov 2014

[118] H Ito F Nakajima T Furuta K Yoshino Y Hirota and T IshibashildquoPhotonic terahertz-wave generation using antenna-integrated uni-travelling-carrier photodioderdquo Electronics Letters vol 39 no 25 p 12003

[119] K S Giboney J Rodwell and J E Bowers ldquoTraveling-wave pho-todetector theoryrdquo IEEE Trans on microwave theory and techniquesvol 45 no 8 pp 1310ndash1319 1997

[120] C Renaud M Robertson D Rogers R Firth P Cannard R Mooreand A Seeds ldquoA high responsivity broadband waveguide uni-travellingcarrier photodioderdquo in Millimeter-Wave and Terahertz Photonics vol6194 International Society for Optics and Photonics 2006 p 61940C

[121] R Kohler A Tredicucci F Beltram H E Beere E H LinfieldA G Davies D A Ritchie R C Iotti and F Rossi ldquoTerahertzsemiconductor-heterostructure laserrdquo Nature vol 417 no 6885 p156 2002

[122] B S Williams S Kumar Q Hu and J L Reno ldquoHigh-power terahertzquantum-cascade lasersrdquo Electronics letters vol 42 no 2 pp 89ndash912006

[123] P D Grant S R Laframboise R Dudek M Graf A Bezinger andH C Liu ldquoTerahertz free space communications demonstration withquantum cascade laser and quantum well photodetectorrdquo ElectronicsLetters vol 45 no 18 pp 952ndash954 August 2009

[124] Z Chen Z Y Tan Y J Han R Zhang X G Guo H Li J CCao and H C Liu ldquoWireless communication demonstration at 41THz using quantum cascade laser and quantum well photodetectorrdquoElectronics Letters vol 47 no 17 pp 1002ndash1004 August 2011

[125] J Leuthold C Hoessbacher S Muehlbrandt A Melikyan M KohlC Koos W Freude V Dolores-Calzadilla M Smit I Suarez et alldquoPlasmonic communications light on a wirerdquo Optics and PhotonicsNews vol 24 no 5 pp 28ndash35 2013

[126] J Leuthold C Haffner W Heni C Hoessbacher J Niegemann Y Fe-doryshyn A Emboras C Hafner A Melikyan M Kohl D L ElderL R Dalton and I Tomkos ldquoPlasmonic devices for communicationsrdquo

in 17th International Conf on Transparent Optical Networks (ICTON)July 2015 pp 1ndash3

[127] X Luo T Qiu W Lu and Z Ni ldquoPlasmons in graphene recentprogress and applicationsrdquo Materials Science and Engineering RReports vol 74 no 11 pp 351ndash376 2013

[128] M Hasan S Arezoomandan H Condori and B Sensale-RodriguezldquoGraphene terahertz devices for communications applicationsrdquo NanoComm Net vol 10 pp 68ndash78 2016

[129] J M Jornet and I F Akyildiz ldquoGraphene-based plasmonic nano-antenna for terahertz band communication in nanonetworksrdquo IEEE JSel Areas Commun vol 31 no 12 pp 685ndash694 2013

[130] H Elayan R M Shubair and A Kiourti ldquoOn graphene-based THzplasmonic nano-antennasrdquo in 16th Mediterranean Microwave Sympo-sium (MMS) Nov 2016 pp 1ndash3

[131] Q Jin Y E K Williams J Dai and X-C Zhang ldquoObservationof broadband terahertz wave generation from liquid waterrdquo AppliedPhysics Letters vol 111 no 7 p 071103 2017

[132] S Atakaramians I V Shadrivov A E Miroshnichenko A StefaniH Ebendorff-Heidepriem T M Monro and S Afshar V ldquoEnhancedterahertz magnetic dipole response by subwavelength fiberrdquo Apl Pho-tonics vol 3 no 5 p 051701 2018

[133] J M Jornet and I F Akyildiz ldquoChannel modeling and capacityanalysis for electromagnetic wireless nanonetworks in the terahertzbandrdquo IEEE Trans Commun vol 10 no 10 pp 3211ndash3221 Oct2011

[134] V Petrov D Moltchanov Y Koucheryavy and J M Jornet ldquoTheeffect of small-scale mobility on terahertz band communicationsrdquoin Proceedings of the 5th ACM International Conf on NanoscaleComputing and Communication ACM 2018 p 40

[135] C Han A O Bicen and I F Akyildiz ldquoMulti-ray channel modelingand wideband characterization for wireless communications in theterahertz bandrdquo IEEE Trans Commun vol 14 no 5 pp 2402ndash2412May 2015

[136] I E Gordon L S Rothman C Hill R V Kochanov Y TanP F Bernath M Birk V Boudon A Campargue K Chance et alldquoThe HITRAN2016 molecular spectroscopic databaserdquo Journal ofQuantitative Spectroscopy and Radiative Transfer vol 203 pp 3ndash692017

[137] S K Nayar K Ikeuchi and T Kanade ldquoSurface reflection physicaland geometrical perspectivesrdquo IEEE Trans on Pattern Analysis ampMachine Intelligence no 7 pp 611ndash634 1991

[138] C Jansen R Piesiewicz D Mittleman T Kurner and M Koch ldquoTheimpact of reflections from stratified building materials on the wavepropagation in future indoor terahertz communication systemsrdquo IEEETrans Antennas Propag vol 56 no 5 pp 1413ndash1419 2008

[139] R Piesiewicz C Jansen D Mittleman T Kleine-Ostmann M Kochand T Kurner ldquoScattering analysis for the modeling of THz commu-nication systemsrdquo IEEE Trans Antennas Propag

[140] mdashmdash ldquoScattering analysis for the modeling of THz communicationsystemsrdquo IEEE Trans Antennas Propag vol 55 no 11 pp 3002ndash3009 Nov 2007

[141] C Jansen S Priebe C Moller M Jacob H Dierke M Koch andT Kurner ldquoDiffuse scattering from rough surfaces in THz communi-cation channelsrdquo IEEE TransTHz Sci and Technol vol 1 no 2 pp462ndash472 2011

[142] H Xu V Kukshya and T S Rappaport ldquoSpatial and temporal char-acteristics of 60-GHz indoor channelsrdquo IEEE J Sel Areas Communvol 20 no 3 pp 620ndash630 2002

[143] S Priebe M Jacob C Jansen and T Kurner ldquoNon-specular scatteringmodeling for THz propagation simulationsrdquo in Proceedings of the 5thEuropean Conf on Antennas and Propagation (EUCAP) IEEE 2011pp 1ndash5

[144] A Hirata T Kosugi N Meisl T Shibata and T Nagatsuma ldquoHigh-directivity photonic emitter using photodiode module integrated withHEMT amplifier for 10-Gbits wireless linkrdquo IEEE Trans MicrowTheory Tech vol 52 no 8 pp 1843ndash1850 2004

[145] A Hirata R Yamaguchi T Kosugi H Takahashi K Murata T Na-gatsuma N Kukutsu Y Kado N Iai S Okabe et al ldquo10-Gbitswireless link using InP HEMT MMICs for generating 120-GHz-bandmillimeter-wave signalrdquo IEEE Trans Microw Theory Tech vol 57no 5 pp 1102ndash1109 2009

[146] J Kokkoniemi J Lehtomaki and M Juntti ldquoA discussion on molec-ular absorption noise in the terahertz bandrdquo Nano CommunicationNetworks vol 8 pp 35ndash45 2016

[147] J Kokkoniemi J Lehtomaki K Umebayashi and M Juntti ldquoFre-quency and time domain channel models for nanonetworks in terahertz

25

bandrdquo IEEE Trans on Antennas and Propagation vol 63 no 2 pp678ndash691 2015

[148] V Petrov D Moltchanov and Y Koucheryavy ldquoInterference and SINRin dense terahertz networksrdquo in 82nd Vehicular Technology Conf (VTCFall) IEEE 2015 pp 1ndash5

[149] C-C Wang X-W Yao C Han and W-L Wang ldquoInterference andcoverage analysis for terahertz band communication in nanonetworksrdquoin Global Communications Conf 2017 IEEE 2017 pp 1ndash6

[150] S Priebe M Jacob and T Kurner ldquoCalibrated broadband ray tracingfor the simulation of wave propagation in mm and sub-mm wave indoorcommunication channelsrdquo in European Wireless 2012 18th EuropeanWireless Conf 2012 VDE 2012 pp 1ndash10

[151] S Priebe M Kannicht M Jacob and T Kurner ldquoUltra broadbandindoor channel measurements and calibrated ray tracing propagationmodeling at THz frequenciesrdquo Journal of Communications and Net-works vol 15 no 6 pp 547ndash558 2013

[152] A Moldovan M A Ruder I F Akyildiz and W H Gerstacker ldquoLOSand NLOS channel modeling for terahertz wireless communicationwith scattered raysrdquo in 2014 IEEE GC Wkshps Dec 2014 pp 388ndash392

[153] F Sheikh N Zarifeh and T Kaiser ldquoTerahertz band Channelmodelling for short-range wireless communications in the spectralwindowsrdquo IET Microwaves Antennas amp Propagation vol 10 no 13pp 1435ndash1444 2016

[154] B Peng S Rey and T Kurner ldquoChannel characteristics study forfuture indoor millimeter and submillimeter wireless communicationsrdquoin 2016 IEEE EuCAP Apr 2016 pp 1ndash5

[155] S Kim ldquoTHz device-to-device communications Channel measure-ments modelling simulation and antenna designrdquo PhD dissertationGeorgia Institute of Technology 2016

[156] S Priebe and T Kurner ldquoStochastic modeling of THz indoor radiochannelsrdquo IEEE Trans Commun vol 12 no 9 pp 4445ndash4455 Sep2013

[157] S Kim and A Zajic ldquoStatistical modeling of THz scatter channelsrdquoin 2015 IEEE EuCAP May 2015 pp 1ndash5

[158] mdashmdash ldquoStatistical modeling and simulation of short-range device-to-device communication channels at sub-THz frequenciesrdquo IEEE TransCommun vol 15 no 9 pp 6423ndash6433 Sep 2016

[159] A A Saleh and R Valenzuela ldquoA statistical model for indoor multipathpropagationrdquo IEEE J Sel Areas Commun vol 5 no 2 pp 128ndash1371987

[160] C-C Chong C-M Tan D I Laurenson S McLaughlin M A Beachand A R Nix ldquoA new statistical wideband spatio-temporal channelmodel for 5-GHz band WLAN systemsrdquo IEEE J Sel Areas Communvol 21 no 2 pp 139ndash150 2003

[161] S Priebe M Jacob and T Kuerner ldquoAoA AoD and ToA characteris-tics of scattered multipath clusters for THz indoor channel modelingrdquoin Wireless Conf 2011-Sustainable Wireless Technologies (EuropeanWireless) 11th European VDE 2011 pp 1ndash9

[162] Y Choi ldquoPerformance analysis of submillimeter-wave indoor com-munications using blocking probabilityrdquo J Infrared Millim TerahertzWaves vol 36 no 11 pp 1123ndash1136 2015

[163] D He K Guan A Fricke B Ai R He Z Zhong A KasamatsuI Hosako and T Kurner ldquoStochastic channel modeling for kioskapplications in the terahertz bandrdquo IEEE Trans THz Sci and Technol2017

[164] B Peng and T Kurner ldquoA stochastic channel model for futurewireless THz data centersrdquo in International Symposium on WirelessCommunication Systems (ISWCS) IEEE 2015 pp 741ndash745

[165] A R Ekti A Boyaci A Alparslan I Unal S Yarkan A GorcinH Arslan and M Uysal ldquoStatistical modeling of propagation channelsfor terahertz bandrdquo in 2017 IEEE CSCN Sep 2017 pp 275ndash280

[166] J Ma R Shrestha L Moeller and D M Mittleman ldquoInvited articleChannel performance for indoor and outdoor terahertz wireless linksrdquoAPL Photonics vol 3 no 5 p 051601 2018

[167] J F Federici J Ma and L Moeller ldquoReview of weather impact onoutdoor terahertz wireless communication linksrdquo Nano CommunicationNetworks vol 10 pp 13ndash26 2016

[168] S Priebe D M Britz M Jacob S Sarkozy K M Leong J ELogan B S Gorospe and T Kurner ldquoInterference investigations ofactive communications and passive earth exploration services in the thzfrequency rangerdquo IEEE TransTHz Sci and Technol vol 2 no 5 pp525ndash537 2012

[169] B Heile ldquoITU-R liaison request RE active services in the bandabove 275 GHzrdquo IEEE 80215-14-439-00-0thz July 2015 [Online]Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[170] A Rogalski and F Sizov ldquoTerahertz detectors and focal plane arraysrdquoOpto-Electron Rev vol 19 no 3 pp 346ndash404 2011

[171] J Kokkoniemi J Lehtomaki and M Juntti ldquoStochastic geometryanalysis for mean interference power and outage probability in THznetworksrdquo IEEE Trans Wireless Commun vol 16 no 5 pp 3017ndash3028 2017

[172] K Tsujimura K Umebayashi J Kokkoniemi J Lehtomaki andY Suzuki ldquoA causal channel model for the terahertz bandrdquo IEEETrans THz Sci and Technol vol 8 no 1 pp 52ndash62 2017

[173] Y Chen and C Han ldquoChannel modeling and analysis for wirelessnetworks-on-chip communications in the millimeter wave and terahertzbandsrdquo in IEEE International Conf on Computer CommunicationsWorkshops (INFOCOM WKSHPS) IEEE 2018

[174] H Zhao L Wei M Jarrahi and G Pottie ldquoExtending spatial andtemporal characterization of indoor wireless channels from 350 GHzto 650 GHzrdquo IEEE Trans THz Sci and Technol 2019

[175] I F Akyildiz and J M Jornet ldquoElectromagnetic wireless nanosensornetworksrdquo Nano Communication Networks vol 1 no 1 pp 3ndash192010

[176] M A Khalighi and M Uysal ldquoSurvey on free space optical communi-cation A communication theory perspectiverdquo IEEE Commun SurveysTuts vol 16 no 4 pp 2231ndash2258 2014

[177] S Rangan T S Rappaport and E Erkip ldquoMillimeter-wave cellularwireless networks Potentials and challengesrdquo Proceedings of the IEEEvol 102 no 3 pp 366ndash385 2014

[178] J Ma ldquoTerahertz wireless communication through atmospheric turbu-lence and rainrdquo PhD dissertation New Jersey Institute of Technology2016

[179] M Uysal and H Nouri ldquoOptical wireless communicationsndash an emerg-ing technologyrdquo in 16th International Conf on Transparent OpticalNetworks (ICTON) IEEE 2014 pp 1ndash7

[180] J M Kahn and J R Barry ldquoWireless infrared communicationsrdquoProceedings of the IEEE vol 85 no 2 pp 265ndash298 1997

[181] J J Fernandes P A Watson and J C Neves ldquoWireless LANsphysical properties of infra-red systems vs mmw systemsrdquo IEEECommun Mag vol 32 no 8 pp 68ndash73 1994

[182] S Arnon Visible light communication Cambridge University Press2015

[183] P H Pathak X Feng P Hu and P Mohapatra ldquoVisible light commu-nication networking and sensing A survey potential and challengesrdquoIEEE Commun Surveys Tuts

[184] Z Wang T Mao and Q Wang ldquoOptical OFDM for visible lightcommunicationsrdquo in 13th International Wireless Communications andMobile Computing Conf (IWCMC) IEEE 2017 pp 1190ndash1194

[185] Z Xu and B M Sadler ldquoUltraviolet communications potential andstate-of-the-artrdquo IEEE Commun Mag vol 46 no 5 2008

[186] E Pickwell and V Wallace ldquoBiomedical applications of terahertztechnologyrdquo Journal of Physics D Applied Physics vol 39 no 17p R301 2006

[187] A-A A Boulogeorgos A Alexiou T Merkle C SchubertR Elschner A Katsiotis P Stavrianos D Kritharidis P-K ChartsiasJ Kokkoniemi et al ldquoTerahertz technologies to deliver optical networkquality of experience in wireless systems beyond 5Grdquo IEEE CommunMag vol 56 no 6 pp 144ndash151 2018

[188] I F Akyildiz and J M Jornet ldquoThe internet of nano-thingsrdquo IEEEWireless Communications vol 17 no 6 2010

[189] T Kurner ldquoWhatrsquos next wireless communication beyond60 GHz (Tutorial IG THz)rdquo IEEE 80215-08-0060-02-0thzJuly 2012 [Online] Available httpsmentorieeeorg80215dcn1215-12-0320-01-0thz-what-s-next-wireless-communication-beyond-60-ghz-tutorial-ig-thzpdf

[190] J M Jornet and I F Akyildiz ldquoThe internet of multimedia nano-thingsrdquo Nano Communication Networks vol 3 no 4 pp 242ndash2512012

[191] J F Federici B Schulkin F Huang D Gary R Barat F Oliveiraand D Zimdars ldquoTHz imaging and sensing for security applications-explosives weapons and drugsrdquo Semiconductor Science and Technol-ogy vol 20 no 7 p S266 2005

[192] D F Plusquellic and E J Heilweil ldquoTerahertz spectroscopy ofbiomoleculesrdquo in Terahertz Spectroscopy CRC Press 2007 pp 293ndash322

[193] K Yang Y Hao A Alomainy Q H Abbasi and K QaraqeldquoChannel modelling of human tissues at terahertz bandrdquo in WirelessCommunications and Networking Conf Workshops (WCNCW) IEEE2016 pp 218ndash221

26

[194] M Nafari and J M Jornet ldquoMetallic plasmonic nano-antenna forwireless optical communication in intra-body nanonetworksrdquo in Pro-ceedings of the 10th EAI International Conf on Body Area Net-works ICST (Institute for Computer Sciences Social-Informaticsand Telecommunications Engineering) 2015 pp 287ndash293

[195] P Biagioni J-S Huang and B Hecht ldquoNanoantennas for visible andinfrared radiationrdquo Reports on Progress in Physics vol 75 no 2 p024402 2012

[196] H Elayan R M Shubair J M Jornet and P Johari ldquoTerahertzchannel model and link budget analysis for intrabody nanoscale com-municationrdquo IEEE Trans Nanobiosci vol 16 no 6 pp 491ndash5032017

[197] H Elayan P Johari R M Shubair and J M Jornet ldquoPhotothermalmodeling and analysis of intrabody terahertz nanoscale communica-tionrdquo IEEE Trans Nanobiosci vol 16 no 8 pp 755ndash763 2017

[198] H Elayan C Stefanini R M Shubair and J M Jornet ldquoEnd-to-endnoise model for intra-body terahertz nanoscale communicationrdquo IEEETrans Nanobiosci vol 17 no 4 pp 464ndash473 2018

[199] K Nallappan H Guerboukha C Nerguizian and M SkorobogatiyldquoLive streaming of uncompressed 4K video using terahertz wirelesslinksrdquo in 2018 IEEE International Conf on Communications (ICC)May 2018 pp 1ndash7

[200] Y Miki T Sakiyama K Ichikawa M Abe S MitsuhashiM Miyazaki A Hanada K Takizawa I Masuhara and K MitanildquoReady for 8K UHDTV broadcasting in Japanrdquo in IBC2015 IET2015

[201] T Kurner G Ke A F Molisch A Bo H Ruisi L Guangkai T LiD Jianwu and Z Zhangdui ldquoMillimeter wave and THz propagationchannel modeling for high-data rate railway connectivity-status andopen challengesrdquo ZTE Commun vol 14 no S1 p 1 2016

[202] T Kurner ldquoRequirements on wireless backhauling andfronthaulingrdquo IEEE 80215-08-0336-00-0thz November2013 [Online] Available httpsmentorieeeorg80215dcn1315-13-0636-01-0thz-requirements-for-wireless-backhauling-fronthaulingpdf

[203] T Narytnyk ldquoPossibilities of using THz-band radio communicationchannels for super high-rate backhaulrdquo Telecommunications and RadioEngineering vol 73 no 15 2014

[204] Y Cui H Wang X Cheng and B Chen ldquoWireless data centernetworkingrdquo IEEE Commun Mag vol 18 no 6 pp 46ndash53 Dec2011

[205] D Halperin S Kandula J Padhye P Bahl and D WetherallldquoAugmenting data center networks with multi-gigabit wireless linksrdquoin ACM SIGCOMM Comput Commun Rev vol 41 no 4 ACM2011 pp 38ndash49

[206] S Mollahasani and E Onur ldquoEvaluation of terahertz channel in datacentersrdquo in 2016 IEEEIFIP NOMS Apr 2016 pp 727ndash730

[207] R Roberts ldquoLink budget exploration for THz communicationsrdquoIEEE 80215-08-0107-00-0thz Mar 2008 [Online] Availablehttpsmentorieeeorg80215documents$amp$is$ $group=0thz

[208] L Razoumov and D Britz ldquoFeasibility of Giga bps datarates at THz frequencies shannon based link budget analysisrdquoIEEE 80215-08-0133-00-0thz Mar 2008 [Online] Availablehttpsmentorieeeorg80215documents$amp$is$ $group=0thz

[209] T Kurner ldquoTerahertz communicationrdquo IEEE 80215-08-0336-00-0thz May 2008 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[210] J-S Rieh ldquoCurrent status of semiconductor technologies andcircuits for THz applicationsrdquo IEEE 80215-08-0437-00-0thz Jul2008 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[211] G T Mearini ldquoHigh power miniature CVD diamond-basedsubmillimeterTerahertz signal sourcesrdquo IEEE 80215-08-0741-00-0thz Oct 2008 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[212] R W Ridgway ldquoMillimeter-wave photonics for high data ratewireless communication systemsrdquo IEEE 80215-08-0433-00-0thz Jul2008 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[213] J Liu ldquoIntegrated photonics for THz applicationsrdquo IEEE 80215-08-0746-01-0thz Nov 2008 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[214] R Roberts ldquoSome thz system issuesrdquo IEEE 80215-08-0410-01-0thz Jul 2008 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[215] mdashmdash ldquoSome THz system issues-part 2-safetyrdquo IEEE 80215-08-0744-00-0thz Nov 2008 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[216] T Kurner ldquoScope and work plan of the science committee on THzcommunicationsrdquo IEEE 80215-09-0229-00-0thz Mar 2009 [Online]Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[217] mdashmdash ldquoTowards wireless 100 Gbs beyond 300 GHzrdquo IEEE80215-10-0847-01-0thz Nov 2010 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[218] mdashmdash ldquoUpdate on the Status of WRC 2012 Preparationrdquo IEEE 80215-11-0462-00-0thz Mar 2011 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[219] I Hosako ldquoThe road map of THz wireless communications systems forJapanrdquo IEEE 80215-11-0491-00-0thz Mar 2011 [Online] Availablehttpsmentorieeeorg80215documents$amp$is$ $group=0thz

[220] R Roberts ldquoSome Expectations for THzrdquo IEEE 80215-11-0498-00-0thz Mar 2011 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[221] T Kurner ldquoReview of the results of WRC 2012rdquo IEEE 80215-11-0498-00-0thz Mar 2012 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[222] S Priebe ldquoWill THz communication interfere with passive remotesensingrdquo IEEE 80215-11-0498-00-0thz Mar 2012 [Online] Avail-able httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[223] T Kurner ldquoOn the future of the IG THzrdquo IEEE 80215-11-0498-00-0thz Mar 2012 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[224] S Priebe ldquoMAC layer concepts for THz communicationsrdquo IEEE80215-15-13-0119-00-0thz Mar 2013 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[225] S Rey ldquoLink level simulations of THz-communicationsrdquo IEEE80215-15-13-406-00-0thz Jul 2013 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[226] T Kurner ldquoLiterature review on requirements for wireless data cen-tersrdquo IEEE 80215-15-13-411-00-0thz Jul 2013 [Online] Availablehttpsmentorieeeorg80215documents$amp$is$ $group=0thz

[227] A Kasamatsu N Sekine H Ogawa N Shibagaki and H HanyuldquoOptical interconnection of data centerrdquo IEEE 80215-15-13-0181-00-0thz Mar 2013 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[228] C Yunlong ldquoTHz bridge for data center rdquo IEEE 80215-15-13-425-00-0thz Jul 20132 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[229] T Kurner ldquoOn the Scope of IEEE 80215 SG 100Grdquo IEEE80215-13-0635-01-0thz Nov 2013 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[230] mdashmdash ldquoInuaguration of IEEE 80215 SG 100Grdquo IEEE 80215-15-13-524-03-0thz Sept 2013 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[231] mdashmdash ldquoTG3d (100G) May 2014 Minutesrdquo IEEE 80215-14-439-00-0thz July 2014 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[232] S Rey ldquoProgress in regulation above 275 GHzrdquo IEEE 80215-14-439-00-0thz July 2016 [Online] Available httpsmentorieeeorg80215documents$amp$is$ $group=0thz

[233] E G Larsson O Edfors F Tufvesson and T L Marzetta ldquoMassiveMIMO for next generation wireless systemsrdquo IEEE Commun Magvol 52 no 2 pp 186ndash195 2014

[234] I F Akyildiz and J M Jornet ldquoRealizing ultra-massive MIMO (1024times1024) communication in the (006ndash10) terahertz bandrdquo Nano CommNet vol 8 pp 46ndash54 2016

[235] L M Zakrajsek D A Pados and J M Jornet ldquoDesign and perfor-mance analysis of ultra-massive multi-carrier multiple input multipleoutput communications in the terahertz bandrdquo in Proc of SPIE ImageSens Technol Materials Devices Systems and Applications IV vol10209 International Society for Optics and Photonics 2017 pp102 090A1ndash102 090A11

[236] C Han J M Jornet and I Akyildiz ldquoUltra-massive mimo channelmodeling for graphene-enabled terahertz-band communicationsrdquo in87th Vehicular Technology Conf (VTC Spring) IEEE 2018 pp 1ndash5

[237] S Rodrigo Munoz ldquoMulti-user ultra-massive MIMO for very highfrequency bands (mmWave and THz) a resource allocation problemrdquoMasterrsquos thesis Universitat Politecnica de Catalunya 2018

[238] ldquoTerahertz-band Ultra-Massive spatial modulation MIMOauthor=Sarieddeen Hadi and Alouini Mohamed-Slim and Al-NaffouriTareq Y journal=arXiv preprint arXiv190504732 year=2019rdquo

27

[239] ABI Research (2017) Augmented and virtual real-ity the first wave of 5G killer apps [On-line] Available httpswwwqualcommcommediadocumentsfilesaugmented-and-virtual-reality-the-first-wave-of-5g-killer-appspdf

[240] C Chaccour R Amer B Zhou and W Saad ldquoOn the reliability ofwireless virtual reality at Terahertz (THz) frequenciesrdquo arXiv preprintarXiv190507656 2019

[241] Z Li L Guan C Li and A Radwan ldquoA secure intelligent spectrumcontrol strategy for future THz mobile heterogeneous networksrdquo IEEECommun Mag vol 56 no 6 pp 116ndash123 2018

[242] M Giordani M Polese M Mezzavilla S Rangan and M ZorzildquoTowards 6G networks Use cases and technologiesrdquo arXiv preprintarXiv190312216 2019

[243] Y Li Y Zhang K Luo T Jiang Z Li and W Peng ldquoUltra-dense HetNets meet big data Green frameworks techniques andapproachesrdquo IEEE Commun Mag vol 56 no 6 pp 56ndash63 2018

[244] G Alnwaimi S Vahid and K Moessner ldquoDynamic heterogeneouslearning games for opportunistic access in LTE-Based macrofemtocelldeploymentsrdquo IEEE Commun Lett vol 14 no 4 pp 2294ndash2308Apr 2015

[245] X Cheng B Yu L Yang J Zhang G Liu Y Wu and L WanldquoCommunicating in the real world 3D MIMOrdquo IEEE Commun Magvol 21 no 4 pp 136ndash144 Aug 2014

[246] H Halbauer S Saur J Koppenborg and C Hoek ldquo3D beamformingPerformance improvement for cellular networksrdquo Bell Labs Tech Jvol 18 no 2 pp 37ndash56 Sep 2013

[247] B Orazbayev M Beruete and I Khromova ldquoTunable beam steeringenabled by graphene metamaterialsrdquo Optics express vol 24 no 8 pp8848ndash8861 2016

[248] L You X Gao G Y Li X-G Xia and N Ma ldquoBDMA formillimeter-waveterahertz massive MIMO transmission with per-beamsynchronizationrdquo IEEE J Sel Areas Commun vol 35 no 7 pp1550ndash1563 2017

[249] N Choubey and A Panah ldquoIntroducing facebookrsquos new terrestrialconnectivity systems-terragraph and project ariesrdquo Facebook Research2016

[250] A J Weissberger (2018) ITU-Rrsquos role in radiofrequency spectrum for 5G networks of the future[Online] Available httpshttpstechblogcomsocorg20181024itu-rs-role-in-radio-frequency-spectrum-for-5g-networks-of-the-future

[251] G Araniti C Campolo M Condoluci A Iera and A Molinaro ldquoLtefor vehicular networking a surveyrdquo IEEE Commun Mag vol 51no 5 pp 148ndash157 2013

[252] M Giordani A Zanella and M Zorzi ldquoLte and millimeter waves forv2i communications an end-to-end performance comparisonrdquo arXivpreprint arXiv190304399 2019

[253] N Lu N Cheng N Zhang X Shen and J W Mark ldquoConnectedvehicles Solutions and challengesrdquo IEEE internet of things journalvol 1 no 4 pp 289ndash299 2014

[254] V Petrov G Fodor J Kokkoniemi D Moltchanov J LehtomakiS Andreev Y Koucheryavy M Juntti and M Valkama ldquoOn unifiedvehicular communications and radar sensing in millimeter-wave andlow terahertz bandsrdquo arXiv preprint arXiv190106980 2019

[255] K Guan B Peng D He J M Eckhardt S Rey B Ai Z Zhong andT Kurner ldquoMeasurement simulation and characterization of train-to-infrastructure inside-station channel at the terahertz bandrdquo IEEE TransTHz Sci and Technol vol 9 no 3 pp 291ndash306 2019

[256] K Kanai T Muto J Katto S Yamamura T Furutono T SaitoH Mikami K Kusachi T Tsuda W Kameyama et al ldquoProactivecontent caching for mobile video utilizing transportation systems andevaluation through field experimentsrdquo IEEE J Sel Areas Communvol 34 no 8 pp 2102ndash2114 2016

[257] Y Zeng R Zhang and T J Lim ldquoWireless communications with un-manned aerial vehicles opportunities and challengesrdquo IEEE CommunMag vol 54 no 5 pp 36ndash42 May 2016

[258] S Mumtaz J M Jornet J Aulin W H Gerstacker X Dong andB Ai ldquoTerahertz communication for vehicular networksrdquo IEEE TransVeh Technol vol 66 no 7 pp 5617ndash5625 2017

[259] J Ma R Shrestha J Adelberg C-Y Yeh Z Hossain E KnightlyJ M Jornet and D M Mittleman ldquoSecurity and eavesdropping interahertz wireless linksrdquo Nature vol 563 no 7729 p 89 2018

I Introduction
II Terahertz Frequency Generation Methods
- II-A Solid-State Electronics
- - II-A1 Complementary Metal-Oxide-Semiconductor (CMOS)
  - II-A2 Monolithic Microwave Integrated Circuits (MMIC)
  - II-A3 Resonant Tunneling Diodes (RTD)
  - - II-B Photonics Technologies
    - - II-B1 Unitravelling Carrier Photodiode (UTC-PD)
      - II-B2 Quantum Cascade Lasers (QCLs)
      - III Channel Modeling in the THz Frequency Band
        
        III-A Outdoor Channel Models
        
        III-B Indoor Channel Models
        
        III-C Nanoscale Channel Models
        
        IV Will the Terahertz Band surpass Its Rivals
        
        IV-A Millimeter Wave versus Terahertz
        
        IV-B Infrared versus Terahertz
        
        IV-C Visible Light versus Terahertz
        
        IV-D Ultra-Violet versus Terahertz
        
        V Terahertz Applications
        
        V-A Terahertz Nanoscale Applications
        
        V-B Terahertz Microscale Applications
        
        V-C Terahertz Macroscale Applications
        
        VI THz Standardization Activity
        
        VII Future Research Directions
        
        VII-A Terahertz Ultra-Massive MIMO
        
        VII-B Terahertz Virtual Reality Perception via Cellular Networks
        
        VII-C Terahertz Communications for Mobile HetNets
        
        VII-D Terahertz 3D Beamforming Technology
        
        VII-E Terahertz Communication for Urban Environments
        
        VII-F Terahertz Automotive Applications
        
        VII-F1 Vehicle to Infrastructure Communication
        
        VII-F2 Unmanned autonomous vehicles (UAVs)
        
        VII-G Terahertz Security Measures
        
        VIII Conclusion
        
        References

Page 2: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

2

society during the 1970s to describe the spectral frequencyof interferometers diode detectors coverage and water laserresonance [6]ndash[8] During the 2000s the THz term wasreferred to as the submillimeter-wave with frequencies rangingbetween 100 GHz up to 10 THz However the boarder linebetween the submillimeter-waves and far infrared at that timewas not clearly identified [9] [10] The concept of utilizingthe THz for ultra-broadband communication using non-lineof sight (NLoS) signal components has been first proposedas a powerful solution for extremely high data rates in [11]Since then THz technology in general and communication inparticular grasped the enthusiasm of the research communityThis interest has been reflected in the increased number ofpublications issued in both IEEE and web of science in recentyears as demonstrated in Fig 2

Fig 2 Terahertz publications issued in both IEEE and web of science inrecent years

The THz frequency band assures extensive throughputwhich theoretically extends up to several THz leading tocapacities in the order of Terabits per second (Tbps) [12] Suchpotential associated with THz technology attracted the broaderresearch community In fact the combined efforts of activeresearch groups is resulting in new designs materials andfabrication methods that demonstrate endless opportunities forTHz development Table I presents examples of various groupsthat conduct THz research which indicated that researchin this area is executed in laboratories across the globeConsequently various funding agencies have been supportingTHz projects and opening up new horizons in communicationsand devices deployed for beyond 5G technology A detailedlist of the most recent THz projects is demonstrated in Table II

Several studies available in the literature reviewed anddiscussed the potential benefits that can be reaped from theTHz band [9] The first THz survey was introduced in 2002 bySiegel and focused on the sources sensors and applications forfrequencies higher than 500 GHz [9] [10] [13] [14] Duringthe same time period another article has been issued in anattempt to demonstrate THz material characterization whichresults in several applications including THz imaging andtomography [10] From a medical and biological perspectiveSiegel reviewed in [13] the developments observed in THzirradiation and sensing In [14] Fitch and Osiander presentedthe first overview of THz technology for various practical de-ployments in communications and sensing including security

TABLE IRESEARCH GROUPS WORKING ON THZ COMMUNICATION RELATED

TOPICS

Research GroupLab Location RampD Activities

Mittleman Lab at BrownUniversity

USA THz PHY layer THz spec-troscopy THz probes

Broadband Wireless Net-working Lab at GeorgiaInstitute of Technology

USA

THz PHY layer THz MAClayer THz Nanocommunica-tion THz devices

NaNoNetworking Centerin Catalunya Spain THz Nanocommunication

Ultra-broadbandNano-CommunicationLaboratory at Universityat Buffalo

USATHz PHY layer THz MAClayer THz Nanocommunica-tion THz devices

Terahertz Electronics Lab-oratory at UCLA USA

THz sources detectorsspectrometers reconfigurablemeta-films imaging andspectroscopy

MIT Terahertz IntegratedElectronics Group USA

Sensing metrology securityand communication at THz fre-quencies

Fraunhofer Institute forApplied Solid StatePhysics IAF

GermanyTHz PHY layer MAC layerand RF electronics

Terahertz Communica-tions Lab Germany

Channel investigation and Ter-ahertz reflectors

Core technology labora-tory group in Nippontelegraph and telephone(NTT) corporation

JapanTerahertz IC and Modulariza-tion Technology

Texas Instrument KilbyLab USA

Ultra-Low Power Sub-THzCMOS Systems

Tonouchi Lab at Osakauniversity Japan

THz Nanoscience THz Bio-science THz-Bio sensing andindustrial applications

THz Electronics SystemsLab at Korea University Korea

THz PHY layer MAC layerand RF electronics

NanocommunicationsCenter at TampereUniversity of Technology

FinlandTHz PHY layer THzNanocommunication

and spectroscopy applications After that the promise broughtby THz frequencies ranging from 100 GHz up to 30 THzhas been demonstrated in [15] where discussions in terms ofgeneration techniques and their correlated output power abili-ties have been presented In [16] Jacob et al provided a briefoverview of the research activities including channel modelingand signal generation in both the millimeter wave (mmW) andTHz bands The first review on THz communication systemswas presented in 2010 where Federici and Moeller presenteda focused discussion on channel model basic considerationsTHz generation methods and implementation issues of THzcommunications [17] In [18] Kleine-Ostmann and TadaoNagatsuma further expanded the discussion on the researchprogress in THz technology In [19] Song and Nagatsumashed the light on some advances of THz communication in-cluding achievable data rates and service distances in additionto highlighting the challenges associated with the 275 GHzup to 3 THz frequency band A similar and brief review has

3

4

5

[9]

[10]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

6

2000

2005

2010

2015

2020

nce of 2m using 12

0 GHz band [37]

on [38]

Transmission tria

km [40]

10Gbps transmissi

on over 58

on at 300 GHz [43]

on at 2375

GHz for 20 m [44]

nce 125 km [45]

300 GHz Integ

7

AND GATE LENGTH

75 nm 091 [69]75 nm 13 [70]50 nm 11 [63]50 nm 106 [71]25 nm 15 [67]

8

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

542 3 - 0001 ASK -67 RTD [106] 2012

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 3: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

3

4

5

[9]

[10]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

6

2000

2005

2010

2015

2020

nce of 2m using 12

0 GHz band [37]

on [38]

Transmission tria

km [40]

10Gbps transmissi

on over 58

on at 300 GHz [43]

on at 2375

GHz for 20 m [44]

nce 125 km [45]

300 GHz Integ

7

AND GATE LENGTH

75 nm 091 [69]75 nm 13 [70]50 nm 11 [63]50 nm 106 [71]25 nm 15 [67]

8

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

542 3 - 0001 ASK -67 RTD [106] 2012

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 4: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

4

5

[9]

[10]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

6

2000

2005

2010

2015

2020

nce of 2m using 12

0 GHz band [37]

on [38]

Transmission tria

km [40]

10Gbps transmissi

on over 58

on at 300 GHz [43]

on at 2375

GHz for 20 m [44]

nce 125 km [45]

300 GHz Integ

7

AND GATE LENGTH

75 nm 091 [69]75 nm 13 [70]50 nm 11 [63]50 nm 106 [71]25 nm 15 [67]

8

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

542 3 - 0001 ASK -67 RTD [106] 2012

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 5: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

5

[9]

[10]

[13]

[14]

[15]

[16]

[17]

[18]

[19]

[20]

[21]

[22]

[23]

[24]

[25]

[26]

[27]

[28]

[29]

[30]

[31]

[32]

[33]

6

2000

2005

2010

2015

2020

nce of 2m using 12

0 GHz band [37]

on [38]

Transmission tria

km [40]

10Gbps transmissi

on over 58

on at 300 GHz [43]

on at 2375

GHz for 20 m [44]

nce 125 km [45]

300 GHz Integ

7

AND GATE LENGTH

75 nm 091 [69]75 nm 13 [70]50 nm 11 [63]50 nm 106 [71]25 nm 15 [67]

8

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

542 3 - 0001 ASK -67 RTD [106] 2012

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 6: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

6

2000

2005

2010

2015

2020

nce of 2m using 12

0 GHz band [37]

on [38]

Transmission tria

km [40]

10Gbps transmissi

on over 58

on at 300 GHz [43]

on at 2375

GHz for 20 m [44]

nce 125 km [45]

300 GHz Integ

7

AND GATE LENGTH

75 nm 091 [69]75 nm 13 [70]50 nm 11 [63]50 nm 106 [71]25 nm 15 [67]

8

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

542 3 - 0001 ASK -67 RTD [106] 2012

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 7: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

7

AND GATE LENGTH

75 nm 091 [69]75 nm 13 [70]50 nm 11 [63]50 nm 106 [71]25 nm 15 [67]

8

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

542 3 - 0001 ASK -67 RTD [106] 2012

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 8: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

8

190 4050 108 002 0006 BPSK -6 130 nm SiGe HBT [88] 2017

200 75 - 0002 QPSK 0 UTC-PD [89] 2014

210 20 024 0035 OOK 46 CMOS [90] 2014

240 6496 115 40 QPSKPSK -36 MMIC [62] 2014

240 64 - 850 QPSK8PSK -36 MMIC [61] 2015

300 64 1 1 QPSK -4 MMIC [95] 2015

385 32 - 05 QPSK -11 UTC-PDSHM [99] 2015

400 46 - 2 ASK -165 UTC-PDSHM [100] 2014

400 60 - 05 QPSK -17 UTC-PDSHM [101] 2015

434 10 - - ASK -185 SiGe BiCMOS [102] 2012

542 3 - 0001 ASK -67 RTD [106] 2012

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 9: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

9

Frequency (GHz)0 200 400 600 800 1000 1200 1400 1600 1800 2000

Pow

er (m

W)

0

5

10

15

20

25

30

35

40

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 10: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

10

Spreading Loss

Absorption Loss

Scattering

Reflection

Multipath

WaterMolecules

Small-ScaleFading

Large-ScaleFading

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 11: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

11

Point-to-PointLinks

Loss (dBkm)

275-320 45 lt 10335-360 25 lt 10275-370 95 lt 100380-445 65 lt 100455-525 70 lt 100625-725 100 lt 100780-910 130 lt 100

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 12: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

12

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 13: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

13

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 14: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

14

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 15: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

15

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 16: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

16

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 17: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

17

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 18: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

18

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 19: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

19

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 20: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

20

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 21: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

21

VIII CONCLUSION

REFERENCES

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 22: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

22

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 23: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

23

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 24: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

24

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 25: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

25

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 26: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

26

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

Page 27: Terahertz Band: The Last Piece of RF Spectrum Puzzle for ... · 1 Terahertz Band: The Last Piece of RF Spectrum Puzzle for Communication Systems Hadeel Elayan, Osama Amin, Basem Shihada,

27

I Introduction
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        
        VIII Conclusion
        
        References

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