The document provides an overview of studies on next generation access technology using radio over free-space optic links. It discusses: 1) An experiment setup using a RoFSO system between two buildings 1 km apart to transmit a 2.5 Gbps optical signal. 2) Results showing the RoFSO system was able to achieve error-free transmission and the received power and bit error rate were influenced by atmospheric conditions like temperature, visibility and precipitation. 3) Challenges of FSO systems including their high dependence on weather conditions and susceptibility to atmospheric effects like beam broadening and angle fluctuations due to turbulence.

1. 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
Global Information and Telecommunication Institute (GITI),
1
Waseda University, Saitama, Japan
Graduate School of Engineering, Osaka University, Osaka, Japan
2
kazaura@aoni.waseda.jp
17th September 2008
NGMAST 2008

2. Contents
 Introduction
 Overview of FSO/RoFSO systems
 Experiment setup
 Results and analysis
 Summary
2

3. Introduction
Wireless communication systems
Global
Suburban
Urban
In-Building
Macro-Cell
Home-Cell Micro-Cell
Pico-Cell
Personal-Cell
PAN, WSN … Satellite systems …
FSO, Cellular systems, WiMAX …
3

4. Introduction cont.
Wireless communication technologies and standards
Full-optical Optical fiber
100 Gbps communication
FSO system
10 Gbps FSO
communication
Visible light
communications
1 Gbps MM wave
Data rate
communication
UWB
Optical
100 Mbps WLAN
WLAN WiMAX
a/b/g
10 Mbps
IrDA Personal area Long distance
PAN Communication communication
1 Mbps Bluetooth
ZigBee
100 Kbps
1m 10 m 100 m 1 km 10 km 100 km
4 Communication distance

5. Introduction cont.
FSO roadmap
Wireless BB environment
Cooperation of
WDM
1T fiber comm.
100G-Ether
100G
SONET （ trunk
Data rate
10G-Ether standard
10G line) FSO 2.5G
（ Eye safe ） FSO10G
1G-Ethernet standard （ WDM)
FSO 1G FWA 50M
1G (5GHz)
FTTH 1G
FSO 100M FTTH Indoor FSO （ P-MP) FWA 46M
100M (26G)
FWA 10M 11g
Indoor 11a Radio on FSO
FSO 10M (22 ＆ 12M 24M
10M FSO （ P- 26G)
MP ） IEEE802.11b 8M
ADSL
1M 1.5M
FWA 1.5M
(22 ＆
26G) CATV ， cellular phone
100K Video use Analog FSO system
ISDN
～ 1995 ～ 2000 2001 2002 2003 2004 2005 ～ 2010
5

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 Visible light
intercept Cosmic radiation T radiation V radiation IR radiation Communications radiation
 Easy to deploy, avoid huge costs X ray radiation Microwave, radar TV VHF SW
involved in laying cables Frequency (Hz) 1020 1018 1016 1014 1012 1010 108 106
 License free 250 THz (1 THz) (1 GHz) (1 MHz)
 Possible for communication up to (1 pm) (1 nm) (1 μm) (1 mm) (1 m) (100 m)
several kms
Wavelength (m) 10-12 10-9 10-6 10-3 100 102
 Can transmit high data rate
De merits C0 = 300 000 km/s λ = wavelength
f = frequency
C=λxf
 High dependence on weather
condition (rain, snow, fog, dust Visible
light
Fiber transmission
wavelength range
particles etc)
 Can not propagate through obstacles 0.4 0.5 0.6 0.7 0.8 0.9 1.0 1.1 1.2 1.3 1.4 1.5 1.6 μm
 Susceptible to atmospheric effects 670 780 850 1300 1550 1625 nm
(atmospheric fluctuations)
Electromagnetic spectrum
6

7. Overview of FSO/RoFSO systems cont.
FSO technology application scenarios
Internet Mountainous terrain
Terrestrial Metro network
RoFSO transceiver
 Metro network extension extension
and remote BS
 Last mile access Backhaul
(~5 km)
 Enterprise connectivity
Areas with no
 Fiber backup fiber connectivity
RoFSO link
 Transmission of Optical fiber link
RF based links
heterogeneous wireless Remote located
RoFSO transceiver
services settlements
Data relay satellite
Space
 Inter-satellite communication Inter-satellite link
(cross link)
Space station
 Satellite to ground data
transmission (down link) Demonstration of High-speed (10Gbs)
2.5 Gbps link optical feeder link
 Deep space communication
Ground station
7 Fiber optic link
with adaptive optics

8. Overview of FSO/RoFSO systems cont.
Optical source FSO
antenna
Conventional FSO system
module
 Operate near the 800nm
wavelength band
 Uses O/E & E/O conversion
Optical fiber FSO channel  Data rates up to 2.5 Gbps
Electrical O/E and E/O  Bandwidth and power limitations
signal conversion module
(a) Conventional FSO system
Next generation FSO system
 Uses 1550nm wavelength
Direct coupling of free-space
beam to optical fiber FSO  Seamless connection of space and
antenna
optical fiber.
 Multi gigabit per second data rates
(using optical fiber technology)
Optical fiber  Compatibility with existing fiber
WDM FSO
channel infrastructure
(b) New full-optical FSO system
 Protocol and data rate independent
8

9. Overview of FSO/RoFSO systems cont.
Free-space beam directly
coupled to optical fiber
Cellular
RoFSO
antenna
DVB
WiFi
RoF RoF
WiMAX
DWDM RoFSO
Heterogeneous wireless channel
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
9

10. Overview of FSO/RoFSO systems cont.
Challenges in design of FSO systems
Beam divergence, θ
FSO antenna FSO antenna
Transmitter Receiver Transmitter Receiver
wide beam narrow beam
Wide beam FSO systems Narrow beam FSO systems
 Beam divergence in terms of several  Beam divergence in terms of several
milliradians tens of microradians
 Easy to align and maintain tracking  Difficult to align and maintain tracking
 Less power at the receiver (the wider  More optical power delivered at the
the beam the less power) receiver
The narrow transmission of FSO beam of makes alignment of FSO
communication terminals difficult than wider RF systems.
10

11. Overview of FSO/RoFSO systems cont.
FSO system performance related parameters
Optical power
Wavelength
Transmission bandwidth
Internal parameters Divergence angle
(design of FSO system) Optical losses
BER
Receive lens diameter & FOV
FSO
Performance
Visibility
External parameters Atmospheric attenuation
(non-system specific Scintillation
parameters) Deployment distance
Pointing loss
11

12. Overview of FSO/RoFSO systems cont.
Factors influencing performance of FSO systems
Visibility under different weather conditions
Clear day Cloudy day Rain event
Visibility > 20km Visibility: ~ 5.36 km Visibility: ~ 1.09 km
Attenuation: 0.06 ~ 0.19 db/km Attenuation: 2.58 db/km Attenuation: 12.65 db/km
Visibility greatly influences the performance of FSO systems e.g.
fog, rain, snow etc significantly decrease visibility
12

13. 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.
Transmit Received
power power Other effects include:
- beam broadening and
Beam wander - angle-of-arrival fluctuations
Time Time
Suppression techniques:
- Aperture averaging
Time Time
Scintillation
- Adaptive optics
Reduces the optical beam - Diversity techniques
power at the receiver point Combined - Coding techniques
effect
and causes burst errors
Time
13

14. 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
14

15. New RoFSO system experiment setup cont.
RoFSO antenna installed
on Bldg 14 rooftop
Okubo campus
Beacon Bldg. 55S
signal
IR viewer 15 Waseda campus
Bldg 14 rooftop

16. Main transmit and
receive aperture Si PIN QPD for coarse tracking
using beacon signal
BS1
Main transmit and
receive aperture SMF
BS2
collimator
FPM
(Fine Pointing
Mirror)
Beacon signal Beacon InGaAs PIN QPD
Rough tracking
beacon projection transmit aperture Source for fine tracking
aperture
Post EDFA Digital mobile radio transmitter tester
(Anritsu MS8609A)
Bldg. 14 Nishi
Waseda campus
RoFSO antenna tracking
adjustment and monitoring PC Optical
source
Boost
Weather measurement EDFA DWDM D-MUX
device
RF-FSO
antenna
Atmospheric effects
measurement antenna
RoFSO
Bldg. 55S antenna
Okubo campus
16
Atmospheric turbulence
effects recording PC
Bit Error Rate Tester
(Advantest D3371)
Optical power meter
(Agilent 8163A)

17. New RoFSO system experiment setup diagram
RF-FSO RF-FSO
antenna antenna
RF-FSO link
RoFSO link
RoFSO RoFSO
antenna antenna
Opt.
circulator Opt.
circulator
filter
EDFA Filter &
ATTN
Tracking
PC
Signal 2.5Gbps Power 2.5Gbps Opt.
Analyzer Opt. Tx meter Opt. Rx Source
Clock Data
PC
Signal
PC BERT BERT Generator
Bldg. 55S Okubo Bldg. 14 Nishi Waseda
Campus
Campus 17

18. 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 450 kHz ~ 420 MHz ~ 5 GHz
operation
Fiber coupling technique OE/EO conversion is Direct coupling using FPM
necessary
WDM Not possible Possible (20 dBm/wave)
Tracking method Automatic Automatic using QPD
Rough: 850 nm
Fine: 1550 nm
18

19. Results: CNR and ACLR characteristics for RF-FSO cont.
Effects of weather condition
55
-10
Clear weather
-20 During rainfall 50
-30 45
Received power [dB]
ACLR: ~ 27 dB
-40
ACLR (dB)
40
-50
35
-60
Attenuation 30
due to rain ACLR: ~ 51 dB
-70
25
-80 Measured data
Fitting line
20
-90 85 90 95 100 105 110 115 120 125
110 115 120 125 130
CNR (dB)
Frequency [MHz]
WCDMA received signal spectrum 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

20. Results: CNR and ACLR characteristics for RF-FSO
150 25
CNRavg
Te m pe ra t ure [οC ]/ Pre c ipit a t ion [m m / h]
120 20
112 dB
C NR [dB] / AC LR [dB]
CNRmin
90 15
ACLR
60 10
45 dB
30 5
Temperature
Precipitation
0 0
Fe b 2 Fe b 3 Fe b 4 Fe b 5
Tim e
RF signal transmission characteristics measured using RF-FSO system
20

21. Results: BER and received power characteristics
RoFSO system
1 00 30
Te mpe ra t ure (οC )/
24 ~ 25 April 2008 BER
Vis ibilit y
Vis ibilit y (km)
1 0- 2 Te mpe ra tu re 25
Re c e ive d Po we r
1 0- 4 20
Bit Erro r Ra t e
1 0- 6 15 - 15
1 0- 8 1 0 - 20
1 0- 1 0 5 - 25
Erro r fre e
1 0- 1 2 0 - 30
21 :00 23:00 01 :00 03:00 05:00 07:00 09:00
Time Re c e ive d po we r (dB)
BER and received power characteristics measured using RoFSO system
21

22. Results: CNR characteristics
RF-FSO system
150 25
24 ~ 25 April 2008
120 20
Te m pe ra t ure (ο C )/ Vis ibilit y (km )
90 15
C NR (dB)
60 10
30 C NRa vg 5
C NRm in
Vis ibilit y
Te m pe ra t ure
0 0
21:00 23:00 01:00 03:00 05:00 07:00 09:00
Tim e
CNR characteristics measured using RF-FSO system
22

23. Results: ACLR and optical received power measurement
RoFSO system With EDFA: Without EDFA:
-24.5 dBm -15 dBm
70
Back-to-back
measurement
60 RoFSO link measurement
with Post EDFA
50
ACLR [dB]
40
RoFSO link
measurement
30 RoFSO Tx 5 MHz
RoFSO Tx 10 MHz
B-to-B Tx 5 MHz
20 B-to-B Tx 10 MHz
with EDFA Tx 5 MHz
with EDFA Tx 10 MHz
10
-35 -30 -25 -20 -15 -10 -5 0
Optical received power [dBm]
Received 3GPP W-CDMA signal
ACLR spectrum Variation of ACLR with the
(3GPP Test Signal 1 64 DPCH) measured received optical power
23

24. Results: EVM measurement
RoFSO system Error Vector Magnitude (EVM)
40
RMS
35 Peak
Error Vector Magnitude [%]
30
25
20
17.5% threshold
15
10
5
0
-35 -30 -25 -20 -15 -10 -5
Optical received power [dBm]
 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

25. 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

26. 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

27. 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
Mobile NW DWDM DWDM Cellular
Cellular
RoF RoFSO
BS Scintillation OE/EO
FSO Digital
FSO
OE, EO
Digital TV OE
WDM
TV
WDM
Tx,Rx Tx,Rx OE/E
WLAN AP O
OE/EO
WLAN
Internet River, New
New
Road, etc Universal Wireless
Wireless
Services Remote BS
Fiber-rich Area Optical Free-Space Rural Area without Broadband Fiber infrastructure
III. Long-term Demonstrative Measurements II. Development of Seamless Connecting
- Pragmatic examination of advanced RoFSO link Equipments between RoF, RoFSO and Wireless
system Systems
- Investigation of scintillation influence on various - Wireless service zone design
types of wireless services transported using the - Total link design through RoF, RoFSO, and Radio
RoFSO system. Links
27

28. 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