1 Survey on Terahertz Nanocommunication and Networking: A Top-Down Perspective Filip Lemic∗, Sergi Abadaly, Wouter Tavernierz, Pieter Stroobantz, Didier Collez, Eduard Alarcon´ y, Johann Marquez-Barja∗, Jeroen Famaey∗ ∗Internet Technology and Data Science Lab (IDLab), Universiteit Antwerpen - imec, Belgium yNaNoNetworking Center in Catalunya (N3Cat), Universitat Politecnica` de Catalunya, Spain zInternet Technology and Data Science Lab (IDLab), Ghent University - imec, Belgium Email: fi[email protected] Abstract—Recent developments in nanotechnology herald Communication and coordination among the nanodevices, nanometer-sized devices expected to bring light to a number of as well as between them and the macro-scale world, will groundbreaking applications. Communication with and among be required to achieve the full promise of such applications. nanodevices will be needed for unlocking the full potential of such applications. As the traditional communication approaches Thus, several alternative nanocommunication paradigms have cannot be directly applied in nanocommunication, several alter- emerged in the recent years, the most promising ones being native paradigms have emerged. Among them, electromagnetic electromagnetic, acoustic, mechanical, and molecular commu- nanocommunication in the terahertz (THz) frequency band is nication [2]. particularly promising, mainly due to the breakthrough of novel In molecular nanocommunication, a transmitting device materials such as graphene. For this reason, numerous research efforts are nowadays targeting THz band nanocommunication releases molecules into a propagation medium, with the and consequently nanonetworking. As it is expected that these molecules being used as the information carriers [3]. Acoustic trends will continue in the future, we see it beneficial to nanocommunication utilizes pressure variations in the (fluid summarize the current status in these research domains. In this or solid) medium to carry information between the transmit- survey, we therefore aim to provide an overview of the current ter and receiver. In mechanical (i.e., touch-based) nanocom- THz nanocommunication and nanonetworking research. Specif- ically, we discuss the applications envisioned to be supported munication, nanorobots are used as carriers for information by nanonetworks operating in the THz band, together with exchange [4]. Finally, electromagnetic nanocommunication the requirements that such applications pose on the underlying uses the properties of electromagnetic waves (e.g., amplitude, nanonetworks. Subsequently, we provide an overview of the phase, delay) as the information carriers [5]. Among the above current contributions on the different layers of the protocol stack, paradigms, molecular and electromagnetic nanocommunica- as well as the available channel models and experimentation tools. As the final contribution, we identify a number of open tion show the greatest promise for enabling communication be- research challenges and outline several potential future research tween nanodevices [6]. This work focuses on electromagnetic directions. nanocommunication. This is due to the fact that it is among the Index Terms—Nanotechnology, electromagnetic, terahertz, two most promising nanocommunication paradigms, as well as nanocommunication, nanonetworking, protocols, channel models, due to its suitability to different propagation mediums (e.g., experimentation tools. in-body, free space, on-chip) and potential for meeting the applications’ requirements (more details in Section III). I. INTRODUCTION Classical electromagnetic communication and networking “There’s Plenty of Room at the Bottom: An Invitation paradigms are not directly applicable to the majority of arXiv:1909.05703v3 [cs.NI] 5 Feb 2021 to Enter a New Field of Physics” [1] was the title of a nanoscale communication and networking scenarios, predom- visionary lecture given by the Nobel Prize recipient Prof. inantly due to the small sizes and limited capabilities of nan- Richard Feynman at the annual American Physical Society odevices [7], [8]. That it to say, microwave or even millimeter- meeting at the California Institute of Technology (Caltech) wave (mmWave) frequencies impose relatively large antennas in December 1959. Prof. Feynman discussed the possibility (i.e., mm-scale and larger) that do not fit into nanodevices. of directly manipulating materials on an atomic scale - and To meet the size requirements of nanodevices, a classical he surely wasn’t joking. The concepts originally outlined by metallic antenna would be required to use very high radiation Prof. Feynman later became circumscribed under the term frequencies. For example, a one-micrometer-long dipole an- “nanotechnology”, first introduced by Prof. Norio Taniguchi tenna would resonate at approximately 150 terahertz (THz) [9]. from Tokyo University of Science in 1974. Due to substantial Although the communication bandwidth increases with the in- research efforts in recent years, nanotechnology is today crease in the antenna’s resonance frequency, the same happens paving the way toward sub-µm scale devices (i.e., from one with the propagation loss. Due to the highly constrained power to a few hundred nanometers). Controlling materials on such of nanodevices [10], the feasibility of nanonetworks would be a scale is expected to give rise to integrated nanodevices with compromised if this approach would be adopted. In addition, simple sensing, actuation, data processing and storage, and nanoscale material properties of common metals are unknown, communication capabilities, opening the horizon to a large hence the common assumptions from antenna theory might variety of novel, even groundbreaking applications. not be correct [11]. Finally, it is currently also technologically 2 infeasible to develop miniature transceiver that could operate research, as well at as to identify the “missing pieces” in the at such high frequencies [9]. current results and suggest potential future research directions. As an alternative approach, graphene has attracted sub- stantial research attention, mainly due to its unique electrical A. Methodology and optical properties [12]. The interaction of electromagnetic radiation with graphene and its derivatives (i.e., carbon nan- This survey has been developed following the Systematic otubes (CNT) [13] - rolled graphene and graphene nanoribbons Literature Review (SLR) methodology [24], [25]. We aimed (GNRs) - thin strips of graphene), differs from that of the to select all the relevant works in the context of THz nanocom- conventional metals. Specifically, it has been demonstrated that munication and nanonetworking, in turn resulting in the de- graphene supports the propagation of Surface Plasmon Polari- tection of the open challenges and missing “pieces” in the ton (SPP) waves in the THz frequency band [14]–[16]. Due existing research literature. We have considered the following to that, graphene-enabled electromagnetic nanocommunication inclusion criteria: i) an article proposes a full novel solution in the THz frequencies is able to deliver miniaturization [17], rather than conceptual, informative, or ongoing efforts (i.e., [18], i.e., a prerequisite for nanocommunication. In addition, position, poster, demo, and Work-in-Progress (WiP) articles the possibility to operate at lower frequencies relaxes the were not considered), ii) an article went through a peer-review energy and power requirements for the nanodevices [9], [17]. process and is either publicly available (e.g., in ArXiv) or Moreover, graphene shows unique tunability properties, which included in the Web of Science (WoS), Scopus, IEEEXplore, allow to steer the beam or tune the resonance frequency by ACM, and/or Springer databases, and iii) an article is written just changing a bias voltage [18], [19]. For these reasons in English. In terms of the step-by-step methodology, we have and given its experimentally demonstrated compatibility with used the Google Scholar database in the initial review phase, CMOS manufacturing processes [20]–[22], graphene allows during which the articles were included or excluded based on versatile antennas to be directly integrated in nanocommuni- their titles and abstracts. In the consequent step, the full texts cation devices as envisaged in multiple works [5], [19], [23]. were assessed along the above-mentioned inclusion criteria. Consequently, graphene-enabled THz nanocommunication at- As a commonly accepted practice, we have placed extra tracted substantial attention from a broad scientific community. emphasis on articles published since 2015, highly cited ones, As the efforts targeting THz band nanocommunication and the ones published in the most important venues, e.g., yielded highly encouraging results, the research focus soon IEEE Transactions on Nanotechnology, ELSEVIER’s Nano spread from the communication to the networking community, Communication Networks, IEEE Nanotechnology Magazine, giving birth to nanonetworking in the THz band. Suffice to and ACM International Conference on Nanoscale Computing say, the results of these efforts are equally encouraging and and Communication (ACM NANOCOM). promising, at this point arguably also abundant. Hence, we believe a summary of the research efforts and current State- B. Structure of-the-Art (SotA) on THz nanocommunication and nanonet- working would be beneficial to the community, which provides The rest of this paper is structured as follows. In Section II, the main motivation for this survey. we provide