This material is based upon work supported by the National Science Foundation under Grant No. 1349828.

Disclaimer: Any opinions, findings, and conclusions or recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National Science Foundation.

TeraNets: Ultra-broadband Communication Networks in the Terahertz Band

Project Description

Applications of Terahertz Band Communication

Over the last few years, wireless data traffic has drastically grown due to a change in the way today's society creates, shares and consumes information. This change has been accompanied by an increasing demand for higher speed wireless communication anywhere, anytime. In particular, wireless data-rates have doubled every eighteen months over the last three decades and are quickly approaching the capacity of wired communication systems. Following this trend, wireless Terabit-per-second (Tbps) links are expected to become a reality in the next five to ten years. Terahertz Band (0.1-10 THz) communication provides a very large bandwidth to satisfy the increasing demand for higher speed wireless links, and opens the door to a plethora of novel applications in classical networking scenarios as well as in new nanoscale communication paradigms.

At the macroscale:

  • Ultra-high-speed Cellular Networks: Terahertz Band communication can be used to provide Terabit-per-second (Tbps) links in next generation small cells, i.e., as a part of hierarchical cellular networks or heterogeneous networks (Figure 1). Some specific applications are ultra-high-definition multimedia content streaming to smartphones, or high-definition two-way video conferencing. In addition, highly directional links in the Terahertz Band can be used to provide a wireless backhaul to current small cells.
  • Wireless Short Range Interconnection Among Devices: Tbps links among devices in close proximity are possible with Terahertz Band communication. Specific applications include multimedia kiosks and ultra-highspeed data transfer between personal devices. For example, to transfer the equivalent content of a blueray disk to a tablet-like device or through Terahertz Band links could take less than 1 second with a 1 Tbps link.
  • Secure Wireless Communication for Military and Defense Applications: The Terahertz Band can also enable ultrabroadband secure communication links in the military and defense fields. The very high atmospheric attenuation at Terahertz Band frequencies and the use of very large antenna arrays to overcome the limited communication distance result in very narrow or almost razorsharp beams, which drastically limit the eavesdropping probability.
Figure 1 - Ultra-high-speed Cellular Networks.

At the nanoscale:

  • Health Monitoring Systems: The nanoscale is the natural domain of molecules, proteins, DNA, organelles and the major components of cells. For example, nanomaterial-based biological nanosensors can be deployed over (e.g., tattoo-like) or even inside the human body (e.g., a pill or intramuscular injection) to monitor glucose, sodium, and cholesterol, to detect the presence of infectious agents, or to identify specific types of cancer. A wireless interface between these nano-devices and a micro-device, such as a cellphone or medical equipment, could be used to collect data and to forward it to a healthcare provider (Figure 2).
  • Ultra-high-speed On-chip Communication: The Terahertz Band can provide ultra-high-speed, efficient and scalable means of intercore communication in wireless on-chip networks, by using planar nano-antennas. This novel approach will expectedly fulfill the stringent requirements of the area-constraint and communication-intensive on-chip scenario by virtue of both its high bandwidth and extremely low area overhead. This makes Terahertz Band communication a promising technology to enable next-generation massive multicore architectures.
  • The Internet of Nano-things: The integration of nano-devices with communication capabilities in every single object will allow the interconnection of almost everything in our daily life, from cooking utensils to every element in our working place or also the components of every device with existing communication networks and ultimately Internet defines a truly cyber-physical system which we further refer to as the Internet of Nano-Things.
Figure 2 - Health Monitoring Systems.
[Back to top]

Graphene-based Transceivers and Antennas for Terahertz Band Communication

One of the most promising technology to enable Terahertz Band communication is the use of graphene, i.e., a one-atom-thick nanomaterial which was experimentally obtained for the first time in 2004, to develop novel transceivers and antennas. Graphene has outstanding physical, electrical and optical properties, and it is often termed as "the wonder material" of the 21st century. Graphene and its derivatives, namely, carbon nanotubes (CNTs) and graphene nanoribbons (GNRs), have been used to fabricate optical detectors for visible and infrared radiation which exhibit very fast response. However, emission and detection in the Terahertz Band by using graphene for communication is a emerging field of research for the time being.

In this project, we will develop a novel graphene-based plasmonic transceiver for Terahertz Band communication. Contrary to existing Terahertz Band signal emitters and detectors, our proposed transceivers are expected to be able to operate at room temperature without an external optical source for electron pumping and will be able to provide a high modulation bandwidth thanks to the unique behavior of electrons in graphene.

In addition to the transceiver, ultra-broadband antennas are needed to support ultra-high-speed communication at Terahertz Band frequencies. However, the efficiency of classical ultra-broadband antennas when operating at these high frequencies remains unknown. It is also not clear how these classical antennas could be integrated with the proposed graphene-based plasmonic transceivers, since the expectedly very high interconnection loss between a plasmonic transceiver and the antenna would drastically limit the feasibility of this approach.

In this project, contrary to traditional antenna designs, we will explore novel graphene-based antennas for THz Band communication. As we have recently shown, graphene can be used to build novel plasmonic nano-antennas (see Figure 3), which exploit the behavior of Surface Plasmon Polariton (SPP) waves in GNRs to efficiently radiate in the Terahertz Band. However, there are many challenges in the realization of such antennas. Amongst others, optimal antenna designs with maximal efficiency need to be investigated. In addition, antenna feeding mechanisms suited for graphene need to be designed. Ultimately, the join performance of the transceiver and the antenna will be analyzed.

Figure 3 - A graphene-based plasmonic nano-antenna for Terahertz Band communication.

Moreover, in order to overcome the small gain and effective area of individual Terahertz Band antennas, we will investigate the performance of novel very large antenna arrays. Indeed, the very small size of a THz Band antenna allows for the integration of a very large number of antennas with very small footprint. As part of the project, we will model the interaction and coupling effects among nearby antennas. Moreover, by taking advantage of the possibility to tune each individual antenna response by means of electrostatic material doping, we will investigate radically new approaches for antenna arrays pattern synthesis.

[Back to top]

Terahertz Band Channel Modeling

Existing channel models for lower frequency bands cannot be used in the Terahertz Band, because they do not capture the peculiarities of this spectrum band, e.g., the very high molecular absorption loss or the very high reflection loss. The few Terahertz channel models existing to date are aimed at characterizing the communication in the absorption-defined window at 0.3 THz, due to the very high attenuation created by molecular absorption (hundreds of dB/m). However, a higher-frequency transmission window, or even more than one window at the same time over the entire Terahertz Band, will be needed to provide stable Tbps links.

In this project, we will develop a complete multi-path channel model accounting for the statistical varying envirionment model for Terahertz Band communications. In particular, we will use radiative transfer theory to analyze the several phenomena affecting the line-of-sight propagation of EM waves in the Terahertz Band. Additionally, we will study the characteristics of non-line-of-sight propagation, by computing the reflection coefficent as a function of the material, the shape and the roughness of the surface on which EM waves have been reflected. Stemming from our preliminary results, we will obtain formulations for the following aspects.

First, because the study of the channel model in terms of individual arrival signal suffers from high computational complexity and, moreover, requires prior knowledge of the scenario, such as geometry, and the exact location of the scatters, there is a need to develop a statistical model to characterize the multi-path channel efficiently. As a result, the path loss can be obtained from this channel model, as a function of the frequency, communication distance and the associated random variables. Furthermore, the use of antenna directivity in the Terahertz Band to increase communication ranges is highly advocated. Thus, the impact of antenna directivity on the multi-path channel modeling and the path loss will be investigated. The model will be validated by simulation with COMSOL.

Second, the ambient noise in the Terahertz channel is mainly contributed by the molecular absorption noise. The absorption from molecules does not only attenuate the transmitted signal, but it also introduces noise. The equivalent noise temperature at the receiver is determined by the number and the particular mixture of molecules found along the path. Besides the ambient noise originated in the channel, a major noise sources comes from the receiver. The receiver noise, which is commonly characterized by the noise figure, depends on the device technology in use, e.g., graphene.

Multi-path fading and molecular absorption effects determine the usable bandwidth of the Terahertz channel, ranging from hundreds of GHz to a few THz wide. As a result, the channel capacity of the Terahertz Band is promisingly very large, up to the order of a few terabits per second. This very large capacity enables both, the transmission at very high bit-rates, and the development of novel communication schemes suited for emerging Terahertz Band communication networks. Ultimately, to obtain realistic numbers for the achievable transmission rates, we need to account for the power allocation strategy, the transmitter and the receiver antenna directivity as well as for the gain and noise factor of the receiver.

[Back to top]

Communication Mechanisms and Protocols in the Terahertz Band

The channel peculiarities and novel graphene devices require the development of novel physical layer solutions as well as protocols for Terahertz Band communication networks.

First, classical modulation schemes can be used at Terahertz Band frequencies, but they cannot fully benefit from the properties of the Terahertz Band. New modulations need to exploit the huge distance-dependent bandwidth provided by the channel, while still remain feasible for the hardware limitations. Furthermore, we will investigate and develop advanced modulations enabled by the novel transceiver device technologies. For example, the modulation of a carrier signal by changing the electrostatic doping of graphene-based devices has been recently proposed. By changing the number of available holes and electrons in the material, the response of a graphene-based signal generator, mixer or amplifier, drastically changes. Starting from this result, we will investigate new ultra-broadband modulations suitable for Terahertz Band communication.

Second, we advocate for the use of Massive MIMO techniques to overcome the very high path loss and increase the communication distance in Terahertz Band networks. The wavelength of the EM wave in the Terahertz Band is extremely short, which enables the deployment of a very large amount of uncorrelated antennas in a limited space to form a large antenna array. Massive MIMO can offer antenna directivity and effectively reduce multi-user interference. In particular, rather than using massive MIMO to increase the capacity (which is already really large due to the ultra-broadband transmission windows in this spectrum band), massive MIMO should be optimized to increase the transmission distance in Terahertz Band communication. Therefore, we will investigate the opportunities of diversity gains provided by Massive MIMO, at the expense of increased implememtation complexity.

Third, novel MAC protocols are required for Terahertz Band communication networks due to the following reasons. First, contrary to classical wireless networks, there are multiple transmission windows which are several tens of Gigahertz wide each and which support the transmission at very high bit-rates (up to a few Tbps). Second, the bandwidth is not a fixed value, but there is a unique dependence between the transmission distance, the 3dB bandwidth of each transmission window and the achievable bit rate. Third, very high directivity antennas are needed to overcome the very high path-loss of the Terahertz Band. In this project, we will design MAC protocols specifically suited for ultra-broadband Terahertz Band communication networks, by taking into account the channel peculiarities and novel device technologies.

[Back to top]

You are visitor:

Visit Counter

since 08/01/2013.