Terahertz Band Communications: Applications, …Terahertz Band Communications: Applications,...

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Department of Electronics and Communications Engineering

Terahertz Band Communications: Applications, Research Challenges,

and Standardization Activities

Department of Electronics and Communications Engineering Tampere University of Technology, Tampere, Finland

Vitaly Petrov: vitaly.petrov@tut.fi

Motivation for THz communications (1) Trends in Wireless Networks

* IEEE 802.15.3d Task Group, 2014

Wide Area Paging

First Alphanumeric

GSM (2G)

UMTS (3G)

LTE (4G) LTE-A (4.5G)

Ethernet IEEE 802.3

IEEE 802.3 U IEEE 802.3 Z

IEEE 802.3 AE IEEE 802.3 BA

1 Kbps

1 Mbps

1 Gbps

1 Tbps

1970 1975 1980 1985 1990 1995 2000 2005 2010 2015 2020

Cellular LAN

q Wireless Terabit-per-second (Tbps) links will become a reality within the next 5 years*

q  Spatial loss §  E.g. free-space loss for

omnidirectional antennas q  Shannon Capacity Limit

§  Link-level performance in case of “best” modulation and coding scheme

Path loss and capacity trade offs

LP f ,d( ) = 4π fdc0

C = B log2(1+ SNR)

q  Smaller antenna size

§  λ/2 and λ/4 for 10 MHz = 15 (7.5) m §  λ/2 and λ/4 for 1 GHz = 15 (7.5) cm §  λ/2 and λ/4 for 1 THz = 150 (75) mcm

q  MIMO (!) §  Massive MIMO è Higher capacity §  Adaptive MIMO è Interference cancellation

q  Devices miniaturization §  Micro and Nano Scale networks

Practical benefits of higher frequencies

What is the THz band? Definitions and advantages

0.1–10THz (IEEE: 0.3–3THz)

Advantages of the THz band: q  Very large amount of bandwidth available (~10THz)

o  Enabling Tbit/s links with 0.1bit/sec/Hz -> sounds feasible q  Miniaturized antennas (λ~1mm for 300GHz)

o  Enabling technology for interactions of micro-scale objects (buzzword: “Nanonetworks”)

q  Still penetrate visually non-transparent objects o  Can work in environments, where Visible Light can hardly,

such as box, pocket, device with a plastic cover... [!] Enabler technologies are coming...

q  Equipment is available from late 1990s* 1.  Lasers:

§  Quantum cascade lasers (QCL) §  Far infrared lasers (FIR)

2.  Free electron based: §  Schottky diodes §  Travelling Wave

Tubes (TWT), etc.

Macro generators of the THz radiation

*D. Grischkowsky et al., "Far-Infrared Time-Domain Spectroscopy with TeraHz Beams of Dielectrics and Semiconductors,” The Journal of the Optical Society of America B, October 1990

Poor performance at room temperature

Size and power requirements

q  One atom thick carbon material q  Produced by Andre Geim,

K. Novoselov in 2004 §  Nobel prize 2010

q  Major electrical property: §  Extremely high electrical conductivity

q  Derivatives: §  Carbon Nanotubes (CNT) §  Graphene Nanoribbons (GNR)

Graphene and Carbon Nano Tubes (CNTs)

Feasibility of micro- and nano-scale antennas

q  Significantly decrease the size of THz signal generators and detectors

§  By Rohm, Japan, 2011* §  Frequency: 300 GHz §  Estimated price: 1.3 USD

Proposal 1. Resonant-tunneling diode + voltage oscillator

* Rohm Semiconductor Press-release, November 2011

Achieved rate: 1.5 Gbps Estimated rate: 30 Gbps

Size: 1.5 x 3 cm

q  Significantly decrease the size of THz antennas

§  By Astar, Singapore and Imperial College, London in 2012*

§  Size of few hundreds nanometers

Proposal 2. Optical rectification for continuous-wave terahertz emission

*H. Tanoto et al., “Greatly enhanced continuous-wave terahertz emission by nano-electrodes in a photoconductive photomixer”, Nature Photonics, January 2012

Size: 255 х 341 nm Operational at room temperature*

q  Enhance the performance of THz signal generators and detectors

1.  Increase efficiency

2.  Decrease losses

Proposal 3. SPP waves and plasmonic antennas

* J. M. Jornet and I. F. Akyildiz, "Graphene-based Plasmonic Nano-antenna for Terahertz Band Communication in Nanonetworks," IEEE Journal on Selected Areas in Communications (JSAC), December 2013

In theory, operational at room temperature*

[!] Many decisive applications envisioned

Envisioned application (1) Backhaul for mmWaves cell

q  Backhaul rate should be higher than of the fronthaul o  275-325GHz o  Static link o  Alignment during the installation o  Low interference with mmWaves spectrum

Envisioned Application (2) Terahertz Information Shower

Main features: q  Data rates: up to 100Gbit/s* q  Communication rage: 0.1-5m

One of the potential deployment strategies for

THz access points

Areas to be deployed in: q  Gates with high traffic

§  Metro, highway entrance q  Dense environments

§  Shopping mall, airport *IEEE 802.15.3d “Application Requirements Document”, IEEE 802.15-14/0304r16, May 2015

Envisioned application (3) Security-sensitive communication

q  Health monitoring, E-payments, etc. q  Similar benefits as for military:

o  Fast signal degradation with distance o  Substantial bandwidth for almost any handshakes

Beneficial to study the suitability of: o  PHY layer security o  ID-based crypto systems

q  Micro-scale communications between everything

Ø  THz and VLC are almost the only solutions, operational at both micro- and macro-scales

Envisioned application (4) Ubiquitous connectivity with micro-world

*I. F. Akyildiz, J. M. Jornet and C. Han, "Terahertz Band: Next Frontier for Wireless Communications," Physical Communication (Elsevier) Journal, September 2014

Envisioned application (5) On-board communications

q  May solve complexity and scalability issues q  Homogeneous system structure q  Capacity of THz channel is sufficient for on-board and

intra-chip communications

*Q. J. Gu, "THz interconnect: the last centimeter communication," in IEEE Comm. Mag. April 2015

Envisioned application (6) Terahertz mobile access

System-level performance analysis is required

Link level characteristics: q  Extensive

bandwidth: 0.1–10 THz q  Theoretical

capacity: Tbits/s q  Effective

communication range: <50m

Truly 5G (Beyond 5G) technology

Illustration from Akyildiz et al. “Terahertz band: Next frontier for wireless communications”, 2014

[!] Is THz comm a “silver bullet”? - No

Major challenges with THz mobile access

q  Design of THz electronics: so-called “THz gap” q  Molecular absorption at THz q  Inherently small antenna size

o  Issues with heat dissipation o  Issues with communication

range (high path loss)

[!] Leading to the fundamental limits

AEff =λ 2

Limit 1: Antenna heat dissipation Approach

We balance the consumed and the dissipated power and apply the Stefan–Boltzmann law:

Ta – antenna temperature, Tr – room temperature, η – antenna efficiency, hair – air heat transfer coefficient, σ – Stefan–Boltzmann const. Antenna size: λ/3/2

Limit 1: Antenna heat dissipation Results

Temperature < 50°C: q  0dBm – till 300GHz q  -10dBm – till 1THz q  -20dBm – till 3THz Higher in either frequency or power? §  Other radiation

principles §  Larger number of

elements

[!] Massive antenna arrays are needed

Limit 2: Path loss at THz frequencies Approach

We compare two cases: 1)  Directional + Omni (MxM + 1) 2)  Directional + Directional (MxM + MxM)

Let us write a path loss equation (S – target SNR): For the free-space path loss, range can be expressed as

Limit 2: Path loss at THz frequencies Results

Parameters: q  PTx = 0dBm q  Target SNR = 5dB q  10GHz bandwidth Effective communication range: §  Dir + Omni: <2m §  Dir. + Dir.: <50m

[!] Both Tx and Rx antennas have to be directional to get reasonable range

Limit 3: Efficiency of distributed MAC Approach

For the sake of example, we assume legacy IEEE 802.11 distributed coordination function (DCF) and OFDM. Then, spectral efficiency is limited to: Finally, if NFFT is the number of OFDM symbols and SIFS consists of 4 symbols, maximal spectral efficiency is

Limit 3: Efficiency of distributed MAC Results

Parameters: q  aka. IEEE 802.11

signaling assumed q  SIFS = 4 OFDM

frames q  NFFT = 512

Effective range (for 10 users): §  10ms TXOP: 50m [5G]: 1ms TXOP: 15m §  0.1ms TXOP: 5m

[!] Latency-bounded applications have to either work over short links or apply centralized MAC

Conclusions: practical limitations of THz mobile access

Envisioned “colonization” of the THz spectrum: 1.  275-325GHz by IEEE 802.15.3d Task Group

o  High antenna gains (20dBi+) o  [!] Sketch is to be ready by mid-2017

2.  Around 1THz and 1-1.5THz by leading academic units o  Graphene/CNT/plasmonic nano-antennas/etc. o  Extreme antenna gains (50dBi+)

3.  Micro-scale communications with individual (~omnidirectional) antennas at 1THz+ by academia

Outcomes: 1.  Massive antenna arrays MUST be used 2.  Antennas MUST be directional AT BOTH Tx and Rx 3.  Intelligent MAC MUST be used for delay-critical apps

Summary: Open R&D challenges

Ø  THz band is, most probably, a next frontier for wireless communications, immediately after mmWaves

q  Major advantage: o  Potentially Tbit/s wireless links few meters long

q  Major issues: o  Hardware / electronics o  Propagation: Absorption and small antenna area

q  Major unsolved communication challenges: q  PHY: Reliable P2P interaction over the THz band

§  LoS blockage, massive scattering, high pathloss q  Link: Channel access with dynamic beam steering q  Network: Nodes discovery and addressing

[!] Huge room for further R&D

Terahertz Band Communications: Applications, …Terahertz Band Communications: Applications,...

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