Studies on Next Generation Access Technology using Radio over Free-Space Optic Links NGMAST 2008 Kamugisha Kazaura 1, Pham Dat 1, Alam Shah 1,Toshiji Suzuki 1, Kazuhiko Wakamori 1, Mitsuji Matsumoto 1, Takeshi Higashino 2, Katsutoshi Tsukamoto 2 and Shozo Komaki 2 1 Global Information and Telecommunication Institute (GITI), Waseda University, Saitama, Japan 2 Graduate School of Engineering, Osaka University, Osaka, Japan 17 th 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 … Introduction Wireless communication systems

4 Wireless communication technologies and standards UWB Full-optical FSO system 10 Gbps MM wave communication 1 Gbps 100 Mbps 10 Mbps 1 Mbps 100 Kbps 1 km 100 m WiMAX 10 m10 km1 m Bluetooth ZigBee WLAN a/b/g Optical fiber communication Communication distance Personal area Communication Optical WLAN IrDA PAN Long distance communication Data rate Visible light communications 100 km FSO communication 100 Gbps Introduction cont.

5 FSO roadmap Introduction cont. Cooperation of fiber comm. ～ 1995 ～ ～ K 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 FTTH FTTH 1G 1G-Ethernet standard 10G-Ether standard 100G-Ether SONET （ trunk line) WDM ADSL 1.5M 8M 12M24M FWA 1.5M (22 ＆ 26G) FWA 10M (22 ＆ 26G) FWA 50M (5GHz) FWA 46M (26G) IEEE802.11b 11g 11a Analog FSO system CATV ， cellular phone Video 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) THz (1 THz) (1 GHz) (1 MHz) (1 pm) (1 nm) (1 μm) (1 mm) (1 m) (100 m) Wavelength (m) μm nm Visible light Fiber transmission wavelength range λ = wavelength f = frequency C 0 = km/s C = 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 located settlements RoFSO link Optical fiber link RF based links RoFSO transceiver Areas with no fiber 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 station with 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 Overview of FSO/RoFSO systems cont. Optical fiber Optical source module FSO channel Electrical signal O/E and E/O conversion module FSO antenna (b) New full-optical FSO system Direct coupling of free-space beam to optical fiber WDM FSO channel Optical fiber FSO antenna (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 DWDM RoFSO channel Free-space beam directly coupled to optical fiber RoFSO antenna DVB WiFi WiMAX Cellular Overview of FSO/RoFSO systems cont.

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 TransmitterReceiver narrow beam FSO antenna TransmitterReceiver wide beam Beam divergence, θ Overview of FSO/RoFSO systems cont.

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

12 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: db/km Overview of FSO/RoFSO systems cont. 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 Scintillation Time Transmit power Received power Combined effect 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 effects Factors influencing performance of FSO systems Suppression techniques: - Aperture averaging - Adaptive optics - Diversity techniques - Coding techniques

14 Satellite 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 QPD for fine tracking FPM (Fine Pointing Mirror) BS2 collimator SMF Beacon signal transmit 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-MUX Boost EDFA Optical source 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 RoFSO antenna RF-FSO antenna RoFSO antenna Tracking PC 2.5Gbps Opt. Tx RF-FSO link RoFSO link Power meter PC New RoFSO system experiment setup diagram

18 Parameter Specification RF-FSORoFSO Operating wavelength785 nm1550 nm Transmit power14 mW (11.5 dBm) 30 mW (14.8 dBm) Antenna aperture100 mm80 mm Coupling loss3 dB5 dB Beam divergence± 0.5 mrad± 47.3 µrad Frequency range of operation 450 kHz ~ 420 MHz ~ 5 GHz Fiber coupling techniqueOE/EO conversion is necessary Direct coupling using FPM WDMNot possiblePossible (20 dBm/wave) Tracking methodAutomaticAutomatic 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 ACLR WCDMA received signal spectrum Effects of weather condition Results: CNR and ACLR characteristics for RF-FSO cont. WCDMA: Wideband Code Division Multiple Access CNR: Carrier to Noise Ratio ACLR: Adjacent Channel Leakage Ratio (a quality metric parameter for WCDMA signal transmission)

20 RF signal transmission characteristics measured using RF-FSO system Results: CNR and ACLR characteristics for RF-FSO 112 dB 45 dB

21 BER and received power characteristics measured using RoFSO system RoFSO system Results: BER and received power characteristics

22 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 measurement RoFSO system Without EDFA: -15 dBm With EDFA: dBm

24 Error Vector Magnitude (EVM) Results: EVM measurement RoFSO system  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 ) 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 Wireless Services WLAN DWDM RoF FSO Tx,Rx OE/EO OE OE/E O WDM FSO 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 WDM 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