Macro-scale THz communications - Tiedekunnatmoltchan/ELT-53407/5_macroTHz.pdf§ Coefficients è from...

Department of Electronics and Communications Engineering

Macro-scale THz communications

Presented by: Vitaly Petrov, Researcher

Laboratory of Electronics and Communications Engineering

Tampere University of Technology

Part 1. THz communications. Pros and cons.

q  Growing interest towards the THz band §  Suitability for bandwidth-oriented applications §  Feasible for micro- and nano-scale devices

Devices miniaturization trend

Far beyond 2020

Main-frames

Carriable electronics

1980 1990 2000 2020

§  Adaptation of communication techniques is required §  Novel research challenges raise

Motivation for THz communications (1) Ubiquitous connectivity

Converged infrastructure for Personal Area Networking

Motivation for THz communications (2) Data rate trends in Wireless Networks

* J. M. Jornet, “THz communications”, TUT, Oct 2015

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*

Motivation for THz communications (3) Why THz for Tbit/s links?

q Limitations of existing and emerging systems: o  2.4 and 5-6GHz spectrum:

Ø Not enough bandwidth o  mmWaves spectrum:

§  One of the most significant advantages in 5G §  ~7-15GHz consecutive bandwidth max §  Tbit/s only with ~100bit/sec/Hz

Ø Not enough bandwidth o  Visible Light Spectrum (VLC), 400-790THz

§  Very large available bandwidth Ø  Inter-working and interference issues

[!] Technology has a room...

Definition of the THz band

Frequency range Wavelengths

Industry, IEEE 802.15.3d 0.3 – 3 THz 1 mm – 100 µm

Academia 0.1 – 10 THz 3 mm – 30 µm

Smart academia 0.06 – 10 THz 5 mm – 30 µm

Current presentation Major focus: 0.1 – 3 THz Primary: 3 mm – 100 µm

Advantages of THz band

q  Very large amount of bandwidth available (~10THz) o  Enabling technology for 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 VLC can hardly,

such as box, pocket, device with a plastic cover... [!] Is THz comm a “silver bullet”? - No

Limitations of THz band (1) “THz gap”

q  No efficient methods to generate powerful signal at ~1THz at room temperature o  Too high for microwave o  Too low for optical

Ø  Limited power results in low communication range

Limitations of THz band (2) Small antenna aperture

q  Inherently smaller antenna’s aperture o  limited communication range without huge

antenna’s gain (e.g. massive antenna arrays)

o  For isotropic radiator

Ø  Limited aperture results in low communication range

AEff =λ 2

Limitations of THz band (3) Molecular absorption

q  Molecular attenuation is much higher than in mmWaves spectrum o  Scattered spectrum

Ø  Losses in environment and hardware result in low communication range

[!] Major consequence – low range

Part 2. THz Channel Properties

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

omnidirectional antennas q  Molecular absorption loss

§  Due to internally vibrating molecules on frequencies similar to signal ones

§  Feature of the THz Band §  Coefficients è from HITRAN database

Propagation and path loss

LP f ,d( ) = 4π fdc0

( )( )df

dfLA ,1,

τ= ( ) ( )dfkdfk IGIGeedf ,,)(, ∑==

−−τ

LT f ,d( ) = LP f ,d( )+ LA f ,d( )

Numerical estimation of losses

0 2 4 6 8 1020

d = 0.01m.

d = 1m.

Path loss, dB

f, frequency, THz0 2 4 6 8 10

100d = 0.01m.

d = 1m.

Absorption loss, dB

f, frequency, THz

0 2 4 6 8

200 d = 0.01m.

d = 0.1m.

d = 1m.

Overall loss, dB

f, frequency, Hz

The most beneficial range is 0.1 – 1 THz

Range of minimal losses

q  Feature of the THz band §  Molecules convert part of the

absorbed energy into kinetic energy

Noise in the THz band (2) Molecular absorption noise

PN f ,d( ) = kBNM f( )= kBT 1−τ f ,d( )"# $%=

= kBT 1− e−k f( )d"

#$%2 4 6 8 10

d = 0.01m.

d = 0.1m.

Molecular noise, dB

f, frequency, THz

Noise highly fluctuates through the frequencies

Range of minimal noise level

1 104 1 10

3 0.01 0.1

100SNR, dB

d, distance, m.

q  Tx/Rx hardware è SNR threshold q  Application requirements è Capacity th. q  (SNR + Capacity) vs distance è Estimation

of effective communication range

SNR and Capacity

1 104 1 10

3 0.01 0.1

1 1011

1 1012

1 1013

1 1014

C, Capacity, Bits/s.

d, distance, m.

q  Distance vs frequency for §  SNR = 10 dB – good performance of

predicted MCSs (discussed further) §  C = 2 Gpbs – sufficient for target

applications §  300 MHz bandwidth

Effective communication range

0 1 2 3 4 5 6 7 8 9 101 10

1SNR = 10dB (C = 1.99Gbps)

d, distance, m.

f, THz

1.  THz channel is highly-frequency selective

2.  Utilisation of so-called “transparency windows” is proposed

0.1 – 3 THz Best performance

Part 3. Transparency Windows and sub-channels

Frequency-selective channel

Window Frequency range Bandwidth Half pulse duration 1 0.10 – 0.54 THz 440 GHz 1.48 ps 2 0.63 – 0.72 THz 95 GHz 6.53 ps 3 0.76 – 0.98 THz 126 GHz 4.92 ps 4 7.07 – 7.23 THz 160 GHz 2.59 ps 5 7.75 – 7.88 THz 130 GHz 3.88 ps

0 2 4 6 8

200 d = 0.01m.

d = 0.1m.

d = 1m.

Overall loss, dB

f, frequency, Hz

q  First transparency window is the most promising

Study 0.1 – 0.54 THz in-depth

q  ~20dB gain over 0.1 – 3 THz (!) §  (10 times in amplitude, 100 in power) §  Sufficient for decoding with major MCS §  Suggested for transmission over

“longer” distances: ≥1 cm

First transparency window, 0.1 – 0.54 THz

0.2 0.4 0.6 0.820

120d = 0.01m.

d = 0.1m.

d = 1m.

Overall loss, dB

f, frequency, Hz

Range/capacity trade off. Small channels

1 103 0.01 0.1 1

1000.10-0.54Thz

0.44-0.54Thz

0.49-0.54Thz

0.10-0.20Thz

0.10-0.15Thz

SNR, dB

d, distance, m.

0.01 0.11 10

1 1010

1 1011

1 1012

1 1013

0.10-0.54Thz

0.44-0.54Thz

0.49-0.54Thz

0.10-0.20Thz

0.10-0.15Thz

C, capacity, bits/s.

d, distance, m.

q  For 10 cm distance: Frequency range (bandwidth) SNR Capacity

0.1 – 0.54 THz (440 GHz) 20 dB 500 Gbps

0.1 – 0.2 THz (100 GHz) 33 dB 300 Gbps

0.1 – 0.15 THz (50 GHz) 35 dB 200 Gbps

Enabling complex MCSs

Range/capacity trade off. Tiny channels

0.01 0.1 1 10 1001

1001MHz

100MHz

1000MHz

SNR, dB

d, distance, m.0.1 1 10

1 1010

100MHz

1000MHz

C, capacity

d, distance, m.

q  For SNR = 10 dB, Smart metering case Frequency range (bandwidth) Range Capacity (at 1 m)

~0.1 THz (1000 MHz) 2 m 8 Gbps

~0.1 THz (10 MHz) 6 m 0.1 Gbps (100 Mbps)

~0.1 THz (1 MHz) 15 m 0.01 Gbps (10 Mbps)

Applicable for sensing applications

Part 4. Modulation and Coding

q  Limitations of continuous-wave MCS: §  Generating carrier at 1-2THz and higher §  Filtering at higher frequencies §  Energy efficiency Advances in physics are needed

q  On/Off keying q  Transmitting s(t):

§  s(t)=1 è Pulse §  s(t)=0 è Silence

“Low-complex” hardware

On/Off Keying simple modulation

1 1 0 01

tt t t t t

v v v v

q  Asymmetric channel: pE1 ≠ pE0 q  Set of threshold è optimisation problem q  BER can be lower than 0.001

BER and throughput estimation for OOK

FEC codes are applicable

0 0.2 0.4 0.6 0.8 10.16

Throughput, v=0.0ps

Throughput, v=0.4ps

Throughput, v=0.8ps

Throughput, v=1.2ps

T, thoughput, Tbps

TP, relative energy detection threshold0 0.2 0.4 0.6 0.8 1

v=0.0ps

v=0.4ps

v=0.8ps

v=1.2ps

pE, bit error probability

TP, relative energy detection threshold

Part 5. Envisioned applications and roadmap

Envisioned “colonization” of THz spectrum

1.  275-325GHz by IEEE 802.15.3d Task Group o  Lead by T. Kurner, TU Braunschweig, Germany o  High antenna gains (20dBi+)

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**

*J. M. Jornet and I. F. Akyildiz, "Graphene-based Plasmonic Nano-antenna for Terahertz Band Communication in Nanonetworks," IEEE JSAC, December 2013

**Akyildiz, I. F., Jornet, J. M., and Pierobon, M. "Nanonetworks: A New Frontier in Communications," Communications of the ACM, November 2011

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) Access for Beyond-5G networks

q  100Gbit/s data rate with “THz plug” at 275-325GHz

*V. Petrov, et al. “Last Meter Indoor Terahertz Wireless Access: Performance Insights and Implementation Roadmap,” to appear in IEEE Communications Magazine, 2018 (available on arxiv).

Envisioned application (3) Immersive Tbit/s wireless links

q  Multi-Tbit/s data rate at 1-1.5THz, enabling

*V. Petrov, et al. “Last Meter Indoor Terahertz Wireless Access: Performance Insights and Implementation Roadmap,” to appear in IEEE Communications Magazine, 2018 (available on rxiv).

o  Tactile Internet o  Holographic Comm

o  Who knows?.. [!] THz vs VLC

Envisioned application (4) Military communications

q  Interest from AirForce, DARPA, and some others o  Eavesdropping is very challenging

*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) 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

Part 5. Challenges and open problems.

Issue 1. Hardware limitations Challenge 1. Need for simple MCS

q  Difficulties for continuous-wave MCS: o  Generating carrier at 1-2THz and higher o  Filtering at higher frequencies o  Energy efficiency Ø  Advances in physics/material science are needed

q  On/Off keying MCS o  Transmitting s(t):

§  s(t)=1 ! Pulse §  s(t)=0 ! Silence

Ø  “Low-complex” hardware Ø  Low utilization of the available time*spectrum resource

1 1 0 01

tt t t t t

v v v v

*P. Boronin, V. Petrov, D. Moltchanov, Y. Koucheryavy, J.M. Jornet, “Capacity and Throughput Analysis of Nanoscale Machine Communication through Transparency Windows in the Terahertz Band,” Elsevier NanoComNet, 2014.

Ø  [Challenge 2.1] Limited applicability of existing system-level models for performance estimation

Issue 2. Molecular component in propagation

Addressing Challenge 2.1 Intra-cell interference modeling in THz networks

q  Random deployment in the cell

q  Poisson process with pin out infinitesimal neighborhood

q  – cell radius (PL) q  – distance between

Tx and Rx q  – distances from

interferers, q  – nodes density q  – minimum distance

between nodes

~x2λ nodes

i ∈ 1:N[ ]

*V. Petrov, et al., “Interference and SINR in Dense Terahertz Networks,” IEEE VTC2015-Fall, Boston, MA, USA, September 2015.

Addressing Challenge 2.1 Intra-cell interference modeling in THz networks

q  Transmit power –10dBm

q  Close to normal distribution of interference (lognormal in dB scale)

q  Perfect match with simulation results

q  Interference level grows with the nodes density Ø  Interference still plays a substantial role in

dense deployments

Challenge 2.2 Need for frequency-specific sub-channeling and distance-aware MCS

q  Sub-channels utilization with power limit is a trade off: o  Rate vs Received power

q  Core idea: o  Occupy more band

for shorter distances o  Occupy less for longer

distance transmissions Ø Not that trivial

to implement

*C. Han, A. O. Bicen, and I. F. Akyildiz, "Multi-Wideband Waveform Design for Distance-adaptive Wireless Communications in the Terahertz Band," IEEE Trans on Signal Proccessing, 2016

Issue 3. Specific transmission/encoding energy consumption relations

q  [Challenge 3] At Tbit/s rates the Tx energy/bit is significantly lower than encoding/decoding energy o  “Wasting” a lot of energy on encoding/decoding

q  Core idea:

o  Transmitting almost raw data without encoding o  Rebranding of the old concept of

cross-layer optimization Ø  Finally got an application..

Issue 4. Energy harvesting as the only solution for micro-scale devices

q  [Challenge 4] Sometimes when packet arrives, node does not have energy to transmit or receive it o  Protocols should be aware of this feature

q  Core idea: o  Initiate a transmission only when both sides have

enough energy to handle it o  Problem: How to know if the receiver has enough

energy without spending energy? o  Solution: Receiver-initiated protocol. Rx sends a

“Ready-to-Receive” packet to mention it is ready

*J. M. Jornet and I. F. Akyildiz, "Joint Energy Harvesting and Communication Analysis for Perpetual Wireless NanoSensor Networks in the Terahertz Band," IEEE Trans Nanotech, May 2012

[!] Issue 5. Highly-directional antennas

q  Almost the only feasible solution to compensate high pathloss at THz o  Directivity at both sides is required for reliable

communication at distances higher than few meters Ø  [!!!] [Challenge 5.1] Medium Access Control for THz

o  Let us assume, nodes know each other’s locations §  Partial solution: Receiver-initiated protocol. §  Rx sends a “Clear-to-Receive” packet to

mention it is ready Ø  Performance issues Ø  Not realistic in dynamic environments

*Q. Xia, et al., "A Link-layer Synchronization and Medium Access Control Protocol for Terahertz-band Communication Networks,” IEEE GLOBECOM, 2015.

Challenge 5.2 [!!!] Nodes discovery. How to find each other with directional antennas?

q  Let’s assume nodes do not know each other’s locations... q  Limitations of existing solutions:

o  Full search beam steering o  O(n2) complexity Ø  Hardly feasible

o  Directional + “omni”, like in 802.11ad: §  O(n) complexity but low SNR at the receiver Ø  Hardly feasible

o  Assistance-oriented schemes (from lower freq.) §  Industry resistance in IEEE, easier with cellular §  Current advantage – to get “there is a neighbor”,

but where to direct the beam? Ø  Partly feasible

Challenge 5.3 Easy LoS blockage

~x2λ nodes

Interferer is blocked

Distance to Tx

Distance to interferer

Interferer is blocked

1.  Deployment a.  Typical uniform

in a circle 2.  [!] Directivity

a.  Tx only b.  Tx+Rx

3.  [!] Blockage a.  Self-blockage

4.  Propagation model a.  [!] With molecular

absorption V. Petrov et al., “Interference and SINR in Millimeter Wave and Terahertz Communication Systems With Blocking and Directional Antennas,” IEEE Transactions on Wireless Communications, 2017.

Addressing Challenge 5.3 Modeling of the self-blockage process

10 20 30 40 50x, m.

pBHxLq Dense

deployment: a.  Human at every

b.  Blockage after ~5m is 80%

q  Ultra-dense deployment a.  Even higher

Ø Blockage significantly limits both useful signal and interference in dense deployments

Addressing Challenge 5.3 NLoS propagation measurements

*J.Kokkoniemi, J.Lehtomäki, V. Petrov, D. Moltchanov, Y. Koucheryavy, M. Juntti, “Wideband Terahertz Band Reflection and Diffuse Scattering Measurements for Beyond 5G Indoor Wireless Networks,” EuWireless, 2016 *J.Kokkoniemi, J.Lehtomäki, V. Petrov, D. Moltchanov, M. Juntti, “Frequency Domain Penetration Loss in the Terahertz Band,” GSMM 2016

q  Measuring 0.1-4THz band (device by TeraView, UK)

Addressing Challenge 5.3 NLoS propagation simulations

*V. Petrov, et al., “Last Meter Indoor Terahertz Wireless Access: Performance Insights and Implementation Roadmap,” submitted for a magazine publication, Spring 2016

Ø  1st reflections doesn’t completely destroy the link

o  Based on ray-tracing with surface tessellation o  Parameterized from field measurements

Issue 6 High nodes mobility and small cell sizes

Ø  [Challenge 6.1] Fast vertical handover o  Continuous coverage with THz cells is impractical o  Reaction time is so low that behavior prediction

pro-active algorithms may help

Ø  How to implement, if different units control different parts of the network?

Long-rangeTHz IS

Mobile User

q Mobile users with opportunistic traffic offloading to ultra-high rate small cells o  Quasi-omnidirectional

antennas (gain) o  Random mobility model

q  Both cellular and THz small cell connectivity

Ø  [Challenge 6.2] Network layer adaptation o  Data pre-caching / TCP upgrade o  Information/data shower concept

Addressing Challenge 6.2 Performance gains estimation

*V. Petrov, et al., “Applicability assessment of terahertz information showers for next-generation wireless networks,” to appear at IEEE ICC, May 2016

q Comprehensive metrics (5G QoE):

o  Continuous time of video playback

o  Required data rate from cellular

Ø  [Challenge 6.3] Real-time monitoring and management o  1 Tbit/s means “If a network switch is down for

0.1sec, you have just lost 100Gb of data” ! o  How to control massive amount of THz APs?

q  Existing solutions: o  “Cellular” protocols stack is too heavy o  SDN is too slow (all the decisions are made on a

remote smart node) q  Two-layer SDN as a potential solution

o  Latency-critical operations – on AP o  Latency-tolerant – on a central node

*G. Bianchi, et al., ”OpenState: programming platform-independent stateful openflow applications inside the switch,” ACM SIGCOMM Computer Communication Review, 2014

Part 6. Summary, open challenges and future research directions

Summary THz commun. as a truly 5G+ technology

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: “THz gap” 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

Macro-scale THz communications - Tiedekunnatmoltchan/ELT-53407/5_macroTHz.pdf§ Coefficients è from...

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