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Wireless Communications with sub-mm Waves - Specialties of THz Indoor Radio Channels

Sebastian Priebe, Thomas Kürner, 21.06.2012

21.06.2012 | Sebastian Priebe | Wireless Communications with sub-mm Waves | 2/22


1.  Introduction §  Why THz Frequencies for

Communications? §  Feasibility Study §  Towards a Standard for THz

Communications 2.  The THz Indoor Radio Channel 3.  Channel Measurements/Modeling 4.  Summary


§  Common ground with nanonetworks: Terahertz frequencies, i.e. 300 GHz – 3 THz, for data communications

§  What are the drivers? §  Nanonetworks: „Natural“ radiation of THz frequencies with graphene antennas §  Wireless indoor communications: Up to 100 Gbit/s required within a few years from now

Why THz Frequencies for Indoor Communications? (1)


Why THz Frequencies for Indoor Communications? (2) §  Problem: Hardly any unregulated spectrum available below 300 GHz

à Shift to carrier frequencies in the THz range from 300 GHz onwards

3 kHz

300 kHz

3 MHz

30 MHz

300 MHz

3 GHz

30 GHz

300 kHz

3 MHz

30 MHz

300 MHz

3 GHz

30 GHz

300 GHz


§  Aim: Ultra high data rates of 100 Gbit/s and beyond over rather short distances §  Potential scenarios:

à But: Is THz communication feasible?

Why THz Frequencies for Indoor Communications? (3)

(1) WPAN (2) Kiosk downloads

(3) WLAN (4) Video streaming

10...50 Gbit/s

10...20 Gbit/s

10...100 Gbit/s

20...100 Gbit/s


§  Transmission of a DVB-T test signal at 300 GHz:

à  Data rate: 36 Mbit/s with 64 QAM modulation à  Achieved distance: 52 m

à  THz data transmission is technically feasible à  Strong, increasing interest in sub mm-wave communications

Feasibility Study


Feasibility studies

Initiation of the IEEE THz

Interest Group

Propagation investigations •  Channel

measurements

•  Propagation modeling

System simulations

System design

guidelines

IEEE standard for THz WPANs/WLANs ✔ ✔

Towards a Standard for THz Communications

§  On the way to 100 Gbit/s THz WPANs/WLANs: §  An international system standard will be required

§  Accurate propagation modeling is necessary as input

for system simulations à  How does the THz indoor radio channel behave? à  What are arising challenges?

IEEE standard for THz WPANs/

WLANs



1.  Introduction 2.  The THz Indoor Radio Channel

§  Conventional vs. THz Radio Channels

§  Propagation Mechanisms 3.  Channel Measurements/Modeling 4.  Summary


§  Comparison of conventional and THz communication channels:

à  Huge bandwidths à  Very high path losses ⇔ low output powers à  Specific propagation mechanisms?

Conventional vs. THz Radio Channels

2.4 GHz, 5 GHz 60 GHz 300 GHz

Data rates 600 Mbit/s ≈ 4 Gbit/s Up to 100 Gbit/s

Bandwidths 40 MHz ≈ 2 GHz 10...100 GHz

Output powers Limited by regulations ≈ 22 dBm

Limited by technology and regulations; typically ≈ 10 dBm

Currently limited by technology only << 10 dBm

Path loss at 10 m ≈ 60 dB ≈ 88 dB ≈ 101 dB

Antenna gains Low (≈ 3 dBi)

Medium (15...25 dBi)

High (20...40 dBi)


§  Propagation attenuation: §  Total attenuation = free space loss + atmospheric attenuation

à  Challenge: Very high (atmospheric) attenuation à  Solution (1): Line-of-sight connection à  Solution (2): Highly directive antennas à  Solution (3): Transmission in atmospheric windows, e.g. 300 – 320 GHz, 330 – 370 GHz

Propagation Mechanisms (1)

0 20 40 60 80 1000

25

50

75

100

125

d [m]

FS

L [

dB

]

900 MHz (GSM)2.4 GHz (WLAN)60 GHz (WPAN)300 GHz

28 dB

14 dB

8.5 dB

+


Propagation Mechanisms (2) §  Huge occupied bandwidths >> 10 GHz §  Channel frequency dependency: §  Demonstration: Ray tracing in an empty room at 300 – 350 GHz

à Challenge: Significant frequency dispersion è pulse form distortion à Solution: Equalization or pulse pre-distortion

TX

RX

6 m

4 m

300 312.5 325 337.5 350!106

!103.5

!101

!98.5

!96

f [GHz]

PC

IR [

dB

]

Total PowerLOS onlyReflections only

Path

Gai

n [d

B]


§  Typical building materials must be considered as rough at THz frequencies §  Wallpaper §  Plaster

§  Diffuse rough surface scattering occurs

à  Challenge: Multipath propagation and high reflection losses à  Solution: Directive antennas for spatial multipath suppression



§  Dynamic ray shadowing by person movement:

à  Challenge: Blockage of line-of-sight path with high additional attenuation à  Solution: - Dynamic antenna redirection to a different indirect transmission path

- Electrically steerable antennas



§  Ray shadowing by objects:

à  Challenge: No line-of-sight available, very high transmission attenuation à  Solution: Use of directed non-line-of-sight path with steerable antennas


TX

RX

Office room in top view

Non-line-of-sight area

Screen causing shadowing

TX

RX

Direction of antenna beam



1.  Introduction 2.  The THz Indoor Radio Channel 3.  Channel Measurements/Modeling 4.  Summary


§  Measurement campaign: §  Channel transfer functions in typical

indoor scenarios §  Channel sounding in frequency domain

with vector network analyzer §  Ultra broadband at 275 – 325 GHz §  Spatially resolved §  MIMO antenna configurations

§  Aims: 1. Experimental investigation and

understanding of THz radio channels 2. Validation of ray tracing propagation

modeling 3. Calibration of the ray tracing tool 4. Development of a THz channel model

Channel Measurements/Modeling (1)

VNA

Test Head

Lens

Automatic Rotation Unit

Vector Network Analyzer

Frequency sweep: 275 – 325 GHz

Indoor Channel


§  Methodology: 1.) Measurements in an actual office scenario 2.) Digital 3D model of the scenario 3.) Ray tracing simulations 4.) Comparison of measurements and simulations à Validation of ray tracing modeling


VNA

Test Head

Lens

Automatic Rotation Unit

Door

Wardrobes

RX

TX1Tables

Windows3.59 m

4.52

mTX2

TX3

Ray 1

z

yx

LOS Ray

Ray 2

Ray 4

Ray 3

MIMO Shift


§  Considered scenarios: §  Different offices §  Hallway

§  Exemplary evaluations: §  Angular power spectrum §  Angular power delay

profile

à Comparison with ray tracing propagation simulations


Door

Wardrobes

RX

TX1Tables

Windows3.59 m

4.52

m

TX2

TX3

Ray 1

z

yx

LOS Ray

Ray 2

Ray 4

Ray 3

MIMO Shift

AoA [°]

Ao

D [

°]

Path Loss [dB]

22

3

43

32

33

2

2

44 3

43

2

32

3

3

4

0 90 180 270 3600

90

180

270

360 85

100

115

130

>145

Ray 1

Ray 3

Ray 4

LOS Ray

Ray 2

Reflection atLens Mount

0120

240360 0

2040

!145

!125

!105

!85

! [ns]

Relative Received Power [dB]

AoA [°]

!145

!125

!105

!85

60


§  In-house development of a ray tracing tool §  Verification of ray tracing simulations with channel measurements at 300 GHz:

à  Very good agreement between simulations and measurements is achieved à  Ray tracing proves well-suited to model THz propagation channels


5 10 15 20−190

−175

−160

−145

−130

−115

−100

−85

t [ns]R

elat

ive

rece

ived

pow

er [d

B]

Simulations, x = 40 lcorrMeasurements

c

5 10 15 20−190

−175

−160

−145

−130

−115

−100

−85

t [ns]R

elat

ive

rece

ived

pow

er [d

B]

Simulations, x = 40 lcorrMeasurements

c

RX

TX

Small office scenario Power delay profile


§  Current status: Accurate propagation model available

§  Future steps:

à  System simulations based on the propagation model à  Development of an appropriate system design

Feasibility studies

Initiation of the IEEE THz

Interest Group

Propagation investigations •  Channel

measurements

•  Propagation modeling

System simulations

System design

guidelines

IEEE standard for THz WPANs/WLANs


✔✔ ✔

IEEE standard for THz WPANs/

WLANs



1.  Introduction 2.  The THz Indoor Radio Channel 3.  Channel Measurements/Modeling 4.  Summary


§  THz communications... §  ...opens up huge unregulated bandwidths > 100 GHz §  ...allows for wireless data rates of 100 Gbit/s and more §  ...has plenty potential applications

§  THz radio channels impose the challenges of... §  ...very high free space losses §  ...additional atmospheric attenuation §  ...significant frequency dispersion §  ...rough surface scattering §  ...ray shadowing by objects or persons

§  Solutions are... §  ...high antenna gains §  ...transmission in atmospheric windows §  ...pulse form equalization §  ...beam switching/beam steering

Summary

0 20 40 60 80 1000

25

50

75

100

125

d [m]

FS

L [

dB

]

900 MHz (GSM)2.4 GHz (WLAN)60 GHz (WPAN)300 GHz

28 dB

14 dB

8.5 dB

Can be modeled with ray tracing


Thank you for paying attention.

Dipl.-Ing. Sebastian Priebe [email protected]

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