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: [email protected]
Department of Electronics and Communications Engineering
Motivation for THz communications (1) Trends in Wireless Networks
* IEEE 802.15.3d Task Group, 2014
Wide Area Paging
First Alphanumeric
Pager
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*
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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
!
"#
$
%&
2
C = B log2(1+ SNR)
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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
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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...
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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
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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
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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
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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*
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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
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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
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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
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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
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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
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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
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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
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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
4π
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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
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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
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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
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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
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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
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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
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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
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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