Studies on Next Generation Access Technology using Radio over Free-Space Optic Links

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Studies on Next Generation Access Technology
using Radio over Free-Space Optic Links

• Kamugisha Kazaura1, Pham Dat1, Alam Shah1,Toshiji
  Suzuki1, Kazuhiko Wakamori1, Mitsuji
  Matsumoto1,Takeshi Higashino2, Katsutoshi
  Tsukamoto2 and Shozo Komaki2
• 1Global Information and Telecommunication
  Institute (GITI), Waseda University, Saitama,
  Japan
• 2Graduate School of Engineering, Osaka
  University, Osaka, Japankazaura_at_aoni.waseda.jp
• 17th September 2008

NGMAST 2008
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Contents

• Introduction
• Overview of FSO/RoFSO systems
• Experiment setup
• Results and analysis
• Summary

3
Introduction
Wireless communication systems
PAN, WSN
Satellite systems
FSO, Cellular systems, WiMAX
4
Introduction cont.
Wireless communication technologies and standards
5
Introduction cont.
FSO roadmap
6
Overview of FSO/RoFSO systems
FSO is the transmission of modulated visible or
infrared (IR) beams through the atmosphere to
obtain broadband communications.RoFSO contains
optical carriers modulated in an analogue manner
by RF sub-carriers.

• Merits
• Secure wireless system not easy to intercept
• Easy to deploy, avoid huge costs involved in
  laying cables
• License free
• Possible for communication up to several kms
• Can transmit high data rate
• De merits
• High dependence on weather condition (rain, snow,
  fog, dust particles etc)
• Can not propagate through obstacles
• Susceptible to atmospheric effects (atmospheric
  fluctuations)

Electromagnetic spectrum
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FSO technology application scenarios
Overview of FSO/RoFSO systems cont.

• Terrestrial
• Metro network extension
• Last mile access
• Enterprise connectivity
• Fiber backup
• Transmission of heterogeneous wireless services
• Space
• Inter-satellite communication (cross link)
• Satellite to ground data transmission (down link)
• Deep space communication

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Overview of FSO/RoFSO systems cont.

• Conventional FSO system
• Operate near the 800nm wavelength band
• Uses O/E E/O conversion
• Data rates up to 2.5 Gbps
• Bandwidth and power limitations
• Next generation FSO system
• Uses 1550nm wavelength
• Seamless connection of space and optical fiber.
• Multi gigabit per second data rates (using
  optical fiber technology)
• Compatibility with existing fiber infrastructure
• Protocol and data rate independent

(a) Conventional FSO system
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Overview of FSO/RoFSO systems cont.
Free-space beam directly coupled to optical
fiber
RoFSO antenna
RoF
RoF
DWDM RoFSOchannel
Heterogeneous wireless service signals
(c) Advanced DWDM RoFSO system

• Advanced DWDM RoFSO system
• Uses 1550nm wavelength
• Transport multiple RF signals using DWDM FSO
  channels
• Realize heterogeneous wireless services e.g.
  WLAN, Cellular, terrestrial digital TV
  broadcasting etc

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Challenges in design of FSO systems
Overview of FSO/RoFSO systems cont.

• Wide beam FSO systems
• Beam divergence in terms of several milliradians
• Easy to align and maintain tracking
• Less power at the receiver (the wider the beam
  the less power)

• Narrow beam FSO systems
• Beam divergence in terms of several tens of
  microradians
• Difficult to align and maintain tracking
• More optical power delivered at the receiver

The narrow transmission of FSO beam of makes
alignment of FSO communication terminals
difficult than wider RF systems.
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Overview of FSO/RoFSO systems cont.
FSO system performance related parameters
Optical powerWavelengthTransmission
bandwidthDivergence angleOptical
lossesBERReceive lens diameter FOV
Internal parameters(design of FSO system)
FSO Performance
VisibilityAtmospheric attenuationScintillationD
eployment distancePointing loss
External parameters(non-system specific
parameters)
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Overview of FSO/RoFSO systems cont.
Factors influencing performance of FSO systems
Visibility under different weather conditions
Visibility greatly influences the performance of
FSO systems e.g. fog, rain, snow etc
significantly decrease visibility
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Overview of FSO systems cont.
Factors influencing performance of FSO systems
Atmospheric effects
Atmospheric turbulence has a significant impact
on the quality of the free-space optical beam
propagating through the atmosphere.
Other effects include - beam broadening and-
angle-of-arrival fluctuations
Suppression techniques - Aperture averaging-
Adaptive optics- Diversity techniques- Coding
techniques
Reduces the optical beam power at the receiver
point and causes burst errors
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Experimental field
Bldg. 14 Waseda University Nishi Waseda Campus
1 km
Bldg. 55 Waseda University Okubo Campus
Satellite view of the test area
Source Google earth
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New RoFSO system experiment setup cont.
RoFSO antenna installed on Bldg 14 rooftop
Okubo campus Bldg. 55S
Beacon signal
IR viewer
Waseda campus Bldg 14 rooftop
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(No Transcript)
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New RoFSO system experiment setup diagram
RF-FSOantenna
RF-FSOantenna
RF-FSO link
RoFSO link
RoFSOantenna
RoFSOantenna
Opt.circulator
Opt.circulator
filter
EDFA
Filter ATTN
TrackingPC
Signal Analyzer
2.5Gbps Opt. Tx
Opt. Source
2.5Gbps Opt. Rx
Power meter
Clock
Data
PC
Signal Generator
BERT
BERT
PC
Bldg. 14 Nishi Waseda Campus
Bldg. 55S Okubo Campus
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New RoFSO system experiment
Characteristics of FSO antennas used in the
experiment
Parameter Specification Specification
Parameter RF-FSO RoFSO
Operating wavelength 785 nm 1550 nm
Transmit power 14 mW (11.5 dBm) 30 mW (14.8 dBm)
Antenna aperture 100 mm 80 mm
Coupling loss 3 dB 5 dB
Beam divergence 0.5 mrad 47.3 µrad
Frequency range of operation 450 kHz 420 MHz 5 GHz
Fiber coupling technique OE/EO conversion is necessary Direct coupling using FPM
WDM Not possible Possible (20 dBm/wave)
Tracking method Automatic Automatic using QPD Rough 850 nm Fine 1550 nm
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Results CNR and ACLR characteristics for RF-FSO
cont.
Effects of weather condition
Relationship between CNR and ACLR
WCDMA received signal spectrum
WCDMA Wideband Code Division Multiple
AccessCNR Carrier to Noise RatioACLR Adjacent
Channel Leakage Ratio (a quality metric parameter
for WCDMA signal transmission)
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Results CNR and ACLR characteristics for RF-FSO
112 dB
45 dB
RF signal transmission characteristics measured
using RF-FSO system
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Results BER and received power characteristics
RoFSO system
BER and received power characteristics measured
using RoFSO system
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Results CNR characteristics
RF-FSO system
CNR characteristics measured using RF-FSO system
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Results ACLR and optical received power
measurement
RoFSO system
Without EDFA -15 dBm
With EDFA -24.5 dBm
Received 3GPP W-CDMA signal ACLR spectrum(3GPP
Test Signal 1 64 DPCH)
Variation of ACLR with the measured received
optical power
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Results EVM measurement
RoFSO system
Error Vector Magnitude (EVM)

• EVM is the ratio in percent of the difference
  between the reference waveform and the measured
  waveform.
• EVM metric is used to measure the modulation
  quality of the transmitter.
• The 3GPP standard requires the EVM not to exceed
  17.5

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Summary

• Presented characteristics of RF signals
  transmission using FSO links under various
  weather conditions reflecting actual deployment
  scenarios.
• Measured, characterized and quantified important
  quality metric parameters e.g. CNR, ACLR, EVM,
  BER, optical received power etc significant for
  evaluation of RF signal transmission using FSO
  links.
• A properly engineered RoFSO link can be used as a
  reliable next generation access technology for
  providing heterogeneous wireless services in the
  absence of severe weather conditions.
• Further work on simultaneous transmission of
  multiple RF signals by DWDM technology using the
  RoFSO system are ongoing.
• The results are significant in design
  optimization, evaluation, prediction and
  comparison of performance as well as
  implementation issues/guidelines of RoFSO systems
  in operational environment.

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This work is supported by a grant from the
National Institute of Information and
Communication (NICT) of Japan

• Thank you for your attention
• Kamugisha KAZAURA (????? ????)
• kazaura_at_aoni.waseda.jp

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Overview of DWDM RoFSO Link research
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Overview of FSO systems cont.
Atmospheric effects suppression techniques

• Aperture averaging
• Reducing scintillation effects by increasing the
  telescope collecting area.
• Adaptive optics
• Measure wavefront errors continuously and correct
  them automatically.
• Diversity techniques
• Spatial diversity (multiple transmitters and/or
  receivers)
• Temporal diversity (signal transmitted twice
  separated by a time delay)
• Wavelength diversity (transmitting data at least
  two distinct wavelengths)
• Coding techniques
• Coding schemes used in RF and wired
  communications systems.