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, Japan
kazaura@aoni.waseda.jp
17th September 2008
NGMAST 2008
Contents
 Introduction
 Overview of FSO/RoFSO systems
 Experiment setup
 Results and analysis
 Summary
2
Introduction
Wireless communication systems
Global
Suburban
Urban
In-Building
Home-Cell
Personal-Cell
Macro-Cell
Pico-Cell
Micro-Cell
PAN, WSN …
Satellite systems …
FSO, Cellular systems, WiMAX …
3
Introduction cont.
Wireless communication technologies and standards
FSO
communication
10 Gbps
Data rate
1 Gbps
100 Mbps
10 Mbps
Optical fiber
communication
Full-optical
FSO system
100 Gbps
Visible light
communications
MM wave
communication
OpticalUWB
WLAN
WiMAX
WLAN
a/b/g
IrDA
PAN
Personal area
Communication
1 Mbps
Long distance
communication
Bluetooth
ZigBee
100 Kbps
1m
10 m
100 m
1 km
4
10 km
100 km
Communication distance
Introduction cont.
FSO roadmap
Wireless BB environment
Cooperation of
fiber comm.
WDM
1T
100G-Ether
Data rate
100G
SONET（trunk line)
10G-Ether standard
10G
1G-Ethernet standard
FWA 50M
(5GHz)
Indoor FSO （P-MP) FWA 46M
(26G)
FTTH
100M
10M
1M
100K
FSO 10M
Indoor FSO
（P-MP）
FWA 1.5M
(22＆26G)
Video use
FWA 10M
(22＆26G)
IEEE802.11b
1.5M
11g
11a
12M
～2000
Radio on FSO
24M
ADSL
CATV，cellular phone
2001
FTTH 1G
8M
ISDN
～1995
FSO10G
（WDM)
FSO 1G
1G
FSO 100M
FSO 2.5G
（Eye safe）
2002
Analog FSO system
5 2003
2004
2005
～2010
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
Cosmic radiation
Easy to deploy, avoid huge costs
involved in laying cables

License free

Possible for communication up to
several kms

Can transmit high data rate
T radiation
V radiation
IR radiation
X ray radiation
Frequency (Hz)
1020
Wavelength (m)
High dependence on weather
condition (rain, snow, fog, dust
particles etc)

Can not propagate through obstacles

Susceptible to atmospheric effects
(atmospheric fluctuations)
Communications radiation
Microwave, radar
1018
1016
1014
250 THz
De merits

Visible light
(1 pm)
(1 nm)
10-12
10-9
1012
0.6
0.7
670
6
106
(1 m)
10-3
100
(1 MHz)
(100 m)
102
λ = wavelength
f = frequency
Visible
light
0.5
108
(1 mm)
10-6
SW
(1 GHz)
C0 = 300 000 km/s
C=λxf
0.4
VHF
1010
(1 THz)
(1 μm)
TV
Fiber transmission
wavelength range
0.8
780 850
0.9
1.0
1.1
1.2
1.3 1.4
1300
Electromagnetic spectrum
1.5
1.6
μm
1550 1625 nm
Overview of FSO/RoFSO systems cont.
FSO technology application scenarios
Internet
Terrestrial





Metro network extension
Last mile access
Enterprise connectivity
Fiber backup
Transmission of
heterogeneous wireless
services
Mountainous terrain
Metro network
extension
RoFSO transceiver
and remote BS
Backhaul
(~5 km)
Remote located
settlements
Space
 Inter-satellite communication
(cross link)
 Satellite to ground data
transmission (down link)
 Deep space communication
Areas with no
fiber connectivity
RoFSO link
Optical fiber link
RF based links
RoFSO transceiver
Data relay satellite
Inter-satellite link
Space station
Demonstration of
2.5 Gbps link
7
Fiber optic link
High-speed (10Gbs)
optical feeder link
Ground station
with adaptive optics
Overview of FSO/RoFSO systems cont.
Optical source
module
Optical fiber
Conventional FSO system
FSO
antenna
FSO channel
Electrical
signal
O/E and E/O
conversion module
(a) Conventional FSO system
Direct coupling of free-space
beam to optical fiber
Optical fiber
 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
FSO
antenna
WDM FSO
channel
(b) New full-optical FSO system
8
Overview of FSO/RoFSO systems cont.
Free-space beam directly
coupled to optical fiber
RoFSO
antenna
Cellular
DVB
WiFi
RoF
RoF
Heterogeneous wireless
service signals
DWDM RoFSO
channel
WiMAX
(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
9
Overview of FSO/RoFSO systems cont.
Challenges in design of FSO systems
Beam divergence, θ
FSO antenna
Transmitter
wide beam
FSO antenna
Receiver
Wide beam FSO systems
Transmitter
Receiver
narrow beam
Narrow 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)
 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.
10
Overview of FSO/RoFSO systems cont.
FSO system performance related parameters
Optical power
Wavelength
Transmission bandwidth
Divergence angle
Optical losses
BER
Receive lens diameter & FOV
Internal parameters
(design of FSO system)
FSO
Performance
Visibility
Atmospheric attenuation
Scintillation
Deployment distance
Pointing loss
External parameters
(non-system specific
parameters)
11
Overview of FSO/RoFSO systems cont.
Factors influencing performance of FSO systems
Visibility under different weather conditions
Clear day
Visibility > 20km
Attenuation: 0.06 ~ 0.19 db/km
Cloudy day
Visibility: ~ 5.36 km
Attenuation: 2.58 db/km
Rain event
Visibility: ~ 1.09 km
Attenuation: 12.65 db/km
Visibility greatly influences the performance of FSO systems e.g. fog,
rain, snow etc significantly decrease visibility
12
Overview of FSO systems cont.
Factors influencing performance of FSO systems
Atmospheric effects
Atmospheric turbulence has a significant impact on the quality of the freespace optical beam propagating through the atmosphere.
Transmit
power
Received
power
Other effects include:
- beam broadening and
Time
Beam wander
- angle-of-arrival fluctuations
Time
Suppression techniques:
- Aperture averaging
Time
Scintillation
Reduces the optical beam
power at the receiver point
and causes burst errors
Time
- Adaptive optics
- Diversity techniques
- Coding techniques
Combined
effect
Time
13
Experimental field
Bldg. 14 Waseda University
Nishi Waseda Campus
1 km
Bldg. 55 Waseda University
Okubo Campus
Satellite view of the test area
14
Source: Google earth
New RoFSO system experiment setup cont.
RoFSO antenna installed
on Bldg 14 rooftop
Okubo campus
Bldg. 55S
Beacon
signal
IR viewer
15
Waseda campus
Bldg 14 rooftop
Main transmit and
receive aperture
Si PIN QPD for coarse tracking
using beacon signal
BS1
Main transmit and
receive aperture
BS2
Rough tracking
beacon projection
aperture
FPM
(Fine Pointing
Mirror)
Beacon signal
transmit aperture
Beacon
Source
Post EDFA
Bldg. 14 Nishi
Waseda campus
RoFSO antenna tracking
adjustment and monitoring PC
Weather measurement
device
SMF
collimator
InGaAs PIN QPD
for fine tracking
Digital mobile radio transmitter tester
(Anritsu MS8609A)
Optical
source
Boost
EDFA
DWDM D-MUX
RF-FSO
antenna
Atmospheric effects
measurement antenna
Bldg. 55S
Okubo campus
RoFSO
antenna
16
Atmospheric turbulence
effects recording PC
Bit Error Rate Tester
(Advantest D3371)
Optical power meter
(Agilent 8163A)
New RoFSO system experiment setup diagram
RF-FSO
antenna
RF-FSO
antenna
RF-FSO link
RoFSO link
RoFSO
antenna
RoFSO
antenna
Opt.
circulator
Opt.
circulator
filter
EDFA
Signal
Analyzer
Filter &
ATTN
2.5Gbps
Opt. Tx
2.5Gbps
Opt. Rx
Power
meter
Clock
BERT
BERT
Bldg. 55S Okubo
Campus
17
Opt.
Source
Data
PC
PC
Tracking
PC
Signal
Generator
Bldg. 14 Nishi Waseda
Campus
New RoFSO system experiment
Characteristics of FSO antennas used in the experiment
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
18
Results: CNR and ACLR characteristics for RF-FSO cont.
Effects of weather condition
55
-10
Clear weather
During rainfall
50
-30
45
ACLR: ~ 27 dB
-40
ACLR (dB)
Received power [dB]
-20
-50
40
35
-60
-70
Attenuation
due to rain
30
ACLR: ~ 51 dB
25
Measured data
Fitting line
-80
-90
110
115
120
125
130
20
85
Frequency [MHz]
WCDMA received signal spectrum
90
95
100
105
110
CNR (dB)
115
120
125
Relationship between CNR and ACLR
WCDMA: Wideband Code Division Multiple Access
CNR: Carrier to Noise Ratio
ACLR: Adjacent Channel Leakage Ratio (a quality metric parameter for WCDMA
signal transmission)
19
Results: CNR and ACLR characteristics for RF-FSO
150
25
120
20
CNR [dB] / ACLR [dB]
112 dB
CNRmin
90
15
ACLR
60
10
30
5
45 dB
Temperature
Temperature [C]/ Precipitation [mm/h]
CNRavg
Precipitation
0
Feb 2
Feb 3
Feb 4
0
Feb 5
Time
RF signal transmission characteristics measured using RF-FSO system
20
Results: BER and received power characteristics
100
24 ~ 25 April 2008
Bit Error Rate
10-2
BER
Visibility
Temperature
Received Power
30
25
Temperature (C)/
Visibility (km)
RoFSO system
10-4
20
10-6
15 -15
10-8
10 -20
10-10
Error free
10-12
21:00
5
23:00
01:00
03:00
Time
05:00
-25
0
-30
07:00
09:00
Received power (dB)
BER and received power characteristics measured using RoFSO system
21
Results: CNR characteristics
RF-FSO system
150
25
120
20
90
15
60
10
30
0
21:00
CNRavg
CNRmin
Visibility
Temperature
23:00
01:00
03:00
Time
05:00
07:00
5
0
09:00
CNR characteristics measured using RF-FSO system
22
Temperature (C)/Visibility (km)
CNR (dB)
24 ~ 25 April 2008
Results: ACLR and optical received power measurement
RoFSO system
With EDFA:
-24.5 dBm
70
60
Without EDFA:
-15 dBm
Back-to-back
measurement
RoFSO link measurement
with Post EDFA
ACLR [dB]
50
40
RoFSO link
measurement
30
RoFSO Tx 5 MHz
RoFSO Tx 10 MHz
B-to-B Tx 5 MHz
B-to-B Tx 10 MHz
with EDFA Tx 5 MHz
with EDFA Tx 10 MHz
20
10
-35
Received 3GPP W-CDMA signal
ACLR spectrum
(3GPP Test Signal 1 64 DPCH)
-30
-25
-20
-15
-10
Optical received power [dBm]
-5
Variation of ACLR with the
measured received optical power
23
0
Results: EVM measurement
RoFSO system
Error Vector Magnitude (EVM)
40
RMS
Peak
Error Vector Magnitude [%]
35
30
25
20
17.5% threshold
15
10
5
0
-35



-30
-25
-20
-15
Optical received power [dBm]
-10
-5
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%
24
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.
25
Supported by
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
(カムギシャ カザウラ)
kazaura@aoni.waseda.jp
Overview of DWDM RoFSO Link research
I. Development of an Advanced DWDM RoFSO Link System
- Transparent and broadband connection between free-space and optical fiber
- DWDM technologies for multiplexing of various wireless communications and broadcasting
services
WLAN AP
Internet
New
Wireless
Services
Fiber-rich Area
FSO
Tx,Rx
DWDM
RoFSO
Scintillation
Cellular
OE/EO
FSO
Tx,Rx
River,
Road, etc
OE
OE/E
O
OE/EO
Universal
Remote BS
Optical Free-Space
III. Long-term Demonstrative Measurements
- Pragmatic examination of advanced RoFSO link
system
- Investigation of scintillation influence on various
types of wireless services transported using the
RoFSO system.
WDM
Digital TV
OE, EO
Cellular
BS
WDM
DWDM
RoF
Mobile NW
Digital
TV
WLAN
New
Wireless
Rural Area without Broadband Fiber infrastructure
II. Development of Seamless Connecting
Equipments between RoF, RoFSO and Wireless
Systems
- Wireless service zone design
- Total link design through RoF, RoFSO, and Radio
Links
27
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.
28