HYBRID FSO/RF LINKS AND NETWORKS WITH DIVERSITY CONTROL

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HYBRID FSO/RF LINKS AND NETWORKS WITH DIVERSITY
CONTROL

• Christopher C. Davis
• The Maryland Optics Group
• Department of Electrical and Computer Engineering
  
• University of Maryland, College Park, MD 20742

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RESOLUTION IN NEAR-FIELD ACKNOWLEDGEMENTS

• Dr. Stuart D. Milner Department of Civil and
  Environmental Engineering
• Dr. Igor Smolyaninov, Department of Electrical
  and Computer Engineering
• Dr Quirino Balzano, Department of Electrical and
  Computer Engineering
• Professor Kyuman Cho (Sogang University, Seoul,
  KOREA)
• Pam Clark, ITT
• Linda Wasiczko, Sugianto Trisno, Jaime Llorca,
  Tzung-Hsien Ho, Heba El-Erian, Aniket Desai,
  Clint Edwards, (graduate students)
• AFOSR, DARPA,NSA, ARL, Army CECOM

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WI-FI

• The current hot topic
• Its growing popularity will cause its demise
• Spectral overcrowding
• Lack of security
• Interference with other users and equipment
• Remember CB radio?
• But if you are mobile you cant be connected by
  wires

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Dynamic, Reconfigurable Hybrid FSO/RF Wireless
Networks
Modified from a TeraBeam picture
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Hybrid FSO/RF Wireless Networks WHY?

• RF wireless networks
• Broadcast RF networks are not scaleable
• RF cannot provide very high data rates
• RF is not physically secure
• High probability of detection/intercept
• Not badly affected by fog and snow, affected by
  rain
• Optical wireless networks
• Very high data rates
• 2.5Gb/s commercially available
• 1Tb/s demonstrated
• Almost zero probability of detection/intercept
• Affected by fog and snow

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Hybrid FSO/RF Wireless Networks WHY?

• Deal with the non-acceptance of optical wireless
  alone
• High availability (gt99.99)
• Much higher goodput than RF alone
• Last/First Mile Solution
• FSO is not regulated by the FCC
• must be eyesafe
• For greatest flexibility need unlicensed RF band
• Installed optical fiber up to 1M/mile

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A Hybrid FSO/RF Link Handles Weather A Hybrid
FSO/RF Network Involves Disparate Data Rates
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Challenges and Developments

• FSO is available commercially
• has not been widely accepted
• most systems do not do pointing, acquisition, and
  tracking (PAT)
• most systems are not FSO/RF Hybrids
• FSO/RF Hybrid networks are in the RD stage
• High performance PAT must be developed

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Challenges and Developments (2)

• Many applications of FSO/RF networks involve
  dynamic situations
• Reconfigurability (topology control) is required
• Diversity of links (transmitter and receivers)
• Changeover algorithms
• Network optimization
• DoD applications

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DYNAMIC AND VOLATILE ATMOSPHERICAND PLATFORM
EFFECTS
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OPTICAL WIRELESS TRANSCEIVER
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OMNIDIRECTIONAL OPTICAL WIRELESS TRANSCEIVER
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Topology Control in Optical Wireless Networks
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Pointing, Acquisition, and Tracking in Optical
Wireless Networks

• Allows wireless links to be established and
  maintained between moving platforms
• Maintains alignment of optical wireless links
• Required for autonomous reconfiguration and
  topology control in optical wireless networks

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Agile Optical Wireless Transceiver and Motorized
Platform

• Data rate 155Mb/s
• High speed (800K steps per second), resolution
  and pointing accuracy up to 0.00072 per step
• Fish-eye lens (180) used to identify and track
  neighbor nodes (beacons)

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Bi-Static Transceiver Design

• Mono-static
• Advantages Reduces the complexity of PAT process
• Disadvantages Power isolation problem (TX/RX
  feedback)
• Bi-static
• Advantages No power isolation problem
• Disadvantages
• 1. Extra alignment process required to obtain
  parallel axes
• 2. Potential misalignment in short-distance
  application

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Link Failures between 2 Transceivers
For large application distance
For short application distance
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PAT Process
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Experimental Setup

1. Study the performance of the link with respect to
   link closure latency for different motor
   parameters
2. To investigate the effects of larger FOV of our
   system

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FEATURES OF OUR CURRENT OPTICAL WIRELESS SYSTEMS

• Bistatic TX/RX systems
• 1.3?m and 1.55?m transmitters
• CPC and lens based receivers
• Fast aspheric lens receivers
• Cassegrain and Fresnel lens receivers
• Rugged alignment stages
• Topology control

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OUR NEW CONCEPTS AND THEIR IMPACT

• Maximally efficient use of high data rate FSO and
  RF communication modes
• Network and link recovery everywhere through
  communication mode diversity and autonomous
  Physical and logical reconfigurability
• Reduced GTT due to instantaneous network recovery
  
• Physical reconfigurability assures gt 99
  availability
• Higher optical availability increases MDR
• Seamless diversity control between optical and RF
  communication
• Internet-like software fully portable to DoD
  systems
• Network software is independent of terminal
  design specifics

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INNOVATION

• Intelligent Aperture Diversity and Media
  Controller
• Smart identification of RF/FSO availability at
  each RX/TX
• Dynamic allocation of FSO/RF
• Autonomous physical and logical reconfiguration
• Make before break dissemination of topologies
  using high availability RF control channel
• Enhanced TCP/IP protocol suite for Hybrid FSO/RF
  Networks
• Multi-Protocol Label Switching (Traffic
  Engineering) exploits media diversity
• Proxy software provides instantaneous reaction to
  physical change in topology
• Autonomous reconfigurability integrated with
  TCP/IP suite
• Comprehensive network modeling and simulation
• Advanced atmospheric propagation modeling
  (turbulence, aerosols, obscuration)
• Discrete Event Simulation for Hybrid Networks to
  aid implementation planning

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BACKUP SLIDES
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The DARPA ORCLE PROGRAM(formerly THOR Program)

• Long range (up to 100km) high altitude (10km)
  laser communication links
• Rytov variance is
• ?2lnI Ranges from 10 to 100
• Small Cn2, but long range makes this a strong
  turbulence situation
• May be strong boundary layer turbulence at
  transmitter and receivers

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Many Link Physics and Engineering Issues

• Turbulence
• Variations with height
• Obscuration
• Optical depth
• Spatial distribution
• Aerosols
• Aperture averaging
• Transceiver optimization

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