Title: HYBRID FSO/RF LINKS AND NETWORKS WITH DIVERSITY CONTROL
1HYBRID 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
2RESOLUTION 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
3WI-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
4Dynamic, Reconfigurable Hybrid FSO/RF Wireless
Networks
Modified from a TeraBeam picture
5Hybrid 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
6Hybrid 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
7A Hybrid FSO/RF Link Handles Weather A Hybrid
FSO/RF Network Involves Disparate Data Rates
8Challenges 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
9Challenges 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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11DYNAMIC AND VOLATILE ATMOSPHERICAND PLATFORM
EFFECTS
12OPTICAL WIRELESS TRANSCEIVER
13OMNIDIRECTIONAL OPTICAL WIRELESS TRANSCEIVER
14Topology Control in Optical Wireless Networks
15Pointing, 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
16Agile 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)
17Bi-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
18Link Failures between 2 Transceivers
For large application distance
For short application distance
19PAT Process
20Experimental Setup
- Study the performance of the link with respect to
link closure latency for different motor
parameters - To investigate the effects of larger FOV of our
system
21FEATURES 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
22OUR 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
23INNOVATION
- 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
24BACKUP SLIDES
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26The 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
27Many Link Physics and Engineering Issues
- Turbulence
- Variations with height
- Obscuration
- Optical depth
- Spatial distribution
- Aerosols
- Aperture averaging
- Transceiver optimization
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