studies on next generation access technology using radio over free space optic links

Studies on Next Generation Access Technology using Radio over

Free-Space Optic Links

NGMAST 2008

Kamugisha Kazaura1, Pham Dat1, Alam Shah1,Toshiji Suzuki1, Kazuhiko Wakamori1, Mitsuji Matsumoto1,

Takeshi Higashino2, Katsutoshi Tsukamoto2 and Shozo Komaki21Global Information and Telecommunication Institute (GITI),

Waseda University, Saitama, Japan2Graduate School of Engineering, Osaka University, Osaka, Japan

[email protected] September 2008

2

Contents Introduction

Overview of FSO/RoFSO systems

Experiment setup

Results and analysis

Summary

3

Global

Suburban

Macro-Cell

Urban

Micro-Cell

In-Building

Pico-Cell

Home-Cell

Personal-Cell

PAN, WSN …

FSO, Cellular systems, WiMAX …

Satellite systems …

IntroductionWireless communication systems

4

Wireless communication technologies and standards

UWB

Full-opticalFSO system

10 Gbps

MM wave communication

1 Gbps

100 Mbps

10 Mbps

1 Mbps

100 Kbps

1 km100 m

WiMAX

10 m 10 km1 m

Bluetooth

ZigBee

WLANa/b/g

Optical fiber communication

Communication distance

Personal areaCommunication

Optical WLAN

IrDAPAN

Long distance communication

Data

rate

Visible light communications

100 km

FSO communication

100 Gbps

Introduction cont.

5

FSO roadmapIntroduction cont.

Cooperation of fiber comm.

～ 1995 ～ 2000 2001 2002 2003 2004 2005 ～ 2010

100K

10G

1G

100M

10M

1M

1T

100G

FSO 10M

FSO 100M

FSO 1G

FSO 2.5G（ Eye safe ） FSO10G （

WDM)

Indoor FSO （ P-MP ）

Indoor FSO （ P-MP)

ISDN

FTTHFTTH 1G

1G-Ethernet standard

10G-Ether standard

100G-Ether

SONET （ trunk line)

WDM

ADSL1.5M

8M

12M 24M

FWA 1.5M(22 ＆ 26G)

FWA 10M(22 ＆ 26G)

FWA 50M(5GHz)

FWA 46M(26G)

IEEE802.11b

11g11a

Analog FSO systemCATV ， cellular phoneVideo use

Wireless BB environment

Radio on FSO

Data

rate

6

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.

Cosmic radiation T radiation V radiation IR radiation Communications radiation

X ray radiation Microwave, radar TV VHF SW

Frequency (Hz) 1020 1018 1016 1014 1012 1010 108 106

250 THz (1 THz) (1 GHz) (1 MHz)

(1 pm) (1 nm) (1 μm) (1 mm) (1 m) (100 m)

Wavelength (m) 10-12 10-9 10-6 10-3 100 102

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

670 780 850 1300 1550 1625 nm

Visible light

Fiber transmissionwavelength range

λ = wavelengthf = frequency

C0 = 300 000 km/sC = λ x f

Visible light

Electromagnetic spectrum

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)

Overview of FSO/RoFSO systems

7

Mountainous terrain

Backhaul(~5 km)

RoFSO transceiver and

remote BS

Metro network extension

Remote locatedsettlements

RoFSO link Optical fiber link RF based links

RoFSO transceiver

Areas with nofiber connectivity

Internet

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

FSO technology application scenarios

Overview of FSO/RoFSO systems cont.

Space station

Inter-satellite link

Data relay satellite

Ground stationwith adaptive optics

Fiber optic link

Demonstration of 2.5 Gbps link

High-speed (10Gbs) optical feeder link

8

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


Optical fiber

Optical source module

FSO channel

Electrical signal

O/E and E/Oconversion module

FSO antenna

(b) New full-optical FSO system

Direct coupling of free-space beam to optical fiber

WDM FSO channel

Optical fiber

FSOantenna

(a) Conventional FSO system

9

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

(c) Advanced DWDM RoFSO system

Heterogeneous wireless service signals

RoF RoF

DWDM RoFSOchannel

Free-space beam directly coupled to optical fiber

RoFSO antenna

DVB

WiFi

WiMAX

Cellular


10

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.

Challenges in design of FSO systems

FSO antenna

Transmitter Receivernarrow beam

FSO antenna

Transmitter Receiverwide beam

Beam divergence, θ


11

FSO Performance

Internal parameters(design of FSO system)

External parameters(non-system specific

parameters)

VisibilityAtmospheric attenuationScintillationDeployment distancePointing loss

Optical powerWavelengthTransmission bandwidthDivergence angleOptical lossesBERReceive lens diameter & FOV

FSO system performance related parameters


12

Clear dayVisibility > 20kmAttenuation: 0.06 ~ 0.19 db/km

Cloudy dayVisibility: ~ 5.36 kmAttenuation: 2.58 db/km

Rain eventVisibility: ~ 1.09 kmAttenuation: 12.65 db/km


Visibility under different weather conditions

Visibility greatly influences the performance of FSO systems e.g. fog, rain, snow etc significantly decrease visibility

Factors influencing performance of FSO systems

13

Reduces the optical beam power at the receiver point and causes burst errors

Beam wander

ScintillationTime

Time

Transmit power

Received power

Combined effect

Time

Time

Time

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

Overview of FSO systems cont.

Atmospheric effectsFactors influencing performance of FSO systems

Suppression techniques:

- Aperture averaging

- Adaptive optics

- Diversity techniques

- Coding techniques

14Satellite view of the test area

Source: Google earth

Experimental field

Bldg. 55 Waseda University Okubo Campus

Bldg. 14 Waseda University Nishi Waseda Campus

1 km

15

RoFSO antenna installed on Bldg 14 rooftop

Beacon signal

Okubo campus Bldg. 55S

Waseda campus Bldg 14 rooftop

IR viewer

New RoFSO system experiment setup cont.

16

BS1

Si PIN QPD for coarse tracking using beacon signal

InGaAs PIN QPDfor fine tracking

FPM(Fine Pointing

Mirror)

BS2

collimator

SMF

Beacon signaltransmit aperture

Main transmit and receive aperture

Beacon Source

Bldg. 55S Okubo campus

Bldg. 14 Nishi Waseda campus

Weather measurement device

RoFSO antenna

Atmospheric effects measurement antenna

RF-FSO antenna

Atmospheric turbulence effects recording PC

RoFSO antenna tracking adjustment and monitoring PC

Bit Error Rate Tester(Advantest D3371)

Optical power meter(Agilent 8163A)

Digital mobile radio transmitter tester(Anritsu MS8609A)

DWDM D-MUXBoostEDFA

Opticalsource

Post EDFA

Main transmit and receive aperture

Rough tracking beacon projection

aperture

17

EDFA

BERT

filter

Opt.circulator

PC

Bldg. 55S Okubo Campus

Bldg. 14 Nishi Waseda Campus

Signal Analyzer

BERT

Clock

Opt. Source

Opt.circulator

Signal Generator

Data

2.5Gbps Opt. Rx

Filter & ATTN

RoFSOantenna

RF-FSOantenna

RF-FSOantenna

RoFSOantenna

TrackingPC

2.5Gbps Opt. Tx

RF-FSO link

RoFSO link

Power meter

PC

New RoFSO system experiment setup diagram

18

ParameterSpecification

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

Characteristics of FSO antennas used in the experiment

New RoFSO system experiment

19

Relationship between CNR and ACLRWCDMA received signal spectrum

Effects of weather conditionResults: CNR and ACLR characteristics for RF-FSO cont.

85 90 95 100 105 110 115 120 12520

25

30

35

40

45

50

55

CNR (dB)A

CL

R (

dB

)

Measured data Fitting line

WCDMA: Wideband Code Division Multiple AccessCNR: Carrier to Noise RatioACLR: Adjacent Channel Leakage Ratio (a quality metric parameter for WCDMA signal transmission)

110 115 120 125 130-90

-80

-70

-60

-50

-40

-30

-20

-10

Frequency [MHz]

Re

ceiv

ed

po

we

r [d

B]

Clear weatherDuring rainfall

ACLR: ~ 27 dB

ACLR: ~ 51 dB Attenuation due to rain

20

RF signal transmission characteristics measured using RF-FSO system

Results: CNR and ACLR characteristics for RF-FSO

Feb 2 Feb 3 Feb 4 Feb 50

30

60

90

120

150

CNR [dB

] /

AC

LR [dB

]

TimeFeb 2 Feb 3 Feb 4 Feb 5

0

5

10

15

20

25

Tem

pera

ture

[ C

]/ P

reci

pita

tion

[mm

/h]

CNRavg

CNRmin

ACLR

Temperature

Precipitation

112 dB

45 dB

21

21:00 23:00 01:00 03:00 05:00 07:00 09:0010- 12

10- 10

10- 8

10- 6

10- 4

10- 2

100

Bit

Erro

r Rat

e

Time

BERVisibilityTemperatureReceived Power

21:00 23:00 01:00 03:00 05:00 07:00 09:000

5

10

15

20

25

30

Tem

pera

ture

( C)/

Vis

ibilit

y (k

m)

- 15

- 20

- 25

- 30

Received power (dB)

Error free

24 ~ 25 April 2008

BER and received power characteristics measured using RoFSO system

RoFSO system

Results: BER and received power characteristics

22

21:00 23:00 01:00 03:00 05:00 07:00 09:000

30

60

90

120

150

CNR (dB

)

Time

CNRavgCNRminVisibilityTemperature

21:00 23:00 01:00 03:00 05:00 07:00 09:000

5

10

15

20

25

Tem

pera

ture

( C

)/Visib

ility

(km

)

24 ~ 25 April 2008

CNR characteristics measured using RF-FSO system

RF-FSO system

Results: CNR characteristics

23

Received 3GPP W-CDMA signal ACLR spectrum

(3GPP Test Signal 1 64 DPCH)

Variation of ACLR with the measured received optical power

Results: ACLR and optical received power measurementRoFSO system

-35 -30 -25 -20 -15 -10 -5 010

20

30

40

50

60

70

Optical received power [dBm]

AC

LR

[d

B]

RoFSO Tx 5 MHzRoFSO Tx 10 MHzB-to-B Tx 5 MHzB-to-B Tx 10 MHzwith EDFA Tx 5 MHzwith EDFA Tx 10 MHz

Back-to-back measurement

RoFSO link measurement with Post EDFA

RoFSO link measurement

Without EDFA: -15 dBm

With EDFA: -24.5 dBm

24

Error Vector Magnitude (EVM)

Results: EVM measurementRoFSO system

-35 -30 -25 -20 -15 -10 -50

5

10

15

20

25

30

35

40

Optical received power [dBm]

Err

or

Ve

cto

r M

ag

nit

ud

e [

%]

RMSPeak

17.5% threshold

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%

25

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.

Summary

Thank you for your attention

Kamugisha KAZAURA ( カムギシャ　カザウラ )

[email protected]

This work is supported by a grant from the National Institute of Information and

Communication (NICT) of Japan

Supported by

27

DWDM RoFSO

Cellular

River, Road, etc

Digital TV

New Wireless

OE,

EO

Internet

Cellular BS

Digital TV

WLAN AP

New WirelessServices

WLAN

DWDM RoF

FSO

Tx,Rx

OE/EO

OE

OE/EO

OE/EO

WD

MFSO

Tx,Rx

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.

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

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

Fiber-rich Area Optical Free-Space Rural Area without Broadband Fiber infrastructure

WD

M

Scintillation

Universal Remote BS

Mobile NW

Overview of DWDM RoFSO Link research

28

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.

Overview of FSO systems cont.Atmospheric effects suppression techniques