The Maryland Optics Group February 17Wireless Communications HYBRID FSO/RF LINKS AND NETWORKS WITH...

February 17 Wireless CommunicationsThe Maryland Optics Group

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


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


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 can’t be connected by wires


Dynamic, Reconfigurable

Hybrid FSO/RF Wireless Networks

Modified from a TeraBeam picture


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


Hybrid FSO/RF Wireless Networks – WHY?• Deal with the non-acceptance of optical wireless

alone• High availability (>99.99%)• 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


0 10 20 30 40 50 60 70 80 90 100

FSO LINK AVAILABILITY (%)

0

1

2

3

AVERAGE DATA RATE (Gb/s)

AVERAGE DATA TRANSFER RATE OF HYBRID FSO/RF LINK

FSO 2.5Gb/s

RF 10Mb/s

A Hybrid FSO/RF Link Handles Weather

A Hybrid FSO/RF Network Involves Disparate Data Rates


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 R&D stage

• High performance PAT must be developed


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


TerrestrialNear-Surface,Surface, and

Subsurface User Systems

Optical Links+

Peer-to-Peerand

Base-Station RF “subnets”

Airborne Free Space Optical

Backbone

Figure 1. Deployable THOR NetworkFigure 1. Deployable THOR Network


DYNAMIC AND VOLATILE ATMOSPHERICAND PLATFORM EFFECTS


OPTICAL WIRELESS TRANSCEIVER


OMNIDIRECTIONAL OPTICAL WIRELESS TRANSCEIVER


Topology Control

in Optical Wireless Networks

Network Layer

Link Layer

Physical Layer

Topology Control•Autonomous Backbone Reconfiguration•Pointing, Acquisition and Tracking


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


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)


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

Bi-Static Transceiver Design


Link Failures between 2 Transceivers

For large application distance

For short application distance


PAT Process

Object disappears

Acquisition Process

Tracking Process

TransceiverAxis

AlignmentStep

Select the desired target from the CCD

image

SystemScanning

Step

Using TCP/IP socket to check link availability

Link TableUpdate

Record the current [θ,φ] into the link table

Object still exists

TrackingProcess

Motion Prediction Analysis(Track beacon)


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


FEATURES OF OUR CURRENT OPTICAL WIRELESS SYSTEMS

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


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 > 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


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


BACKUP SLIDES


TX TX

RXRX

Bistatic optical wireless link


The DARPA ORCLE PROGRAM(formerly THOR Program)

• Long range (up to 100km) high altitude (10km) laser communication links

• Rytov variance is 2

lnI 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

6/116/722ln 23.1 LkCnI =


Many Link Physics and Engineering Issues

• Turbulence– Variations with height

• Obscuration– Optical depth– Spatial distribution

• Aerosols

• Aperture averaging

• Transceiver optimization


1.00e-18 1.00e-17 1.00e-16 1.00e-152 3 4 5 6 2 3 4 5 6 2 3 4 5 6

Cn2 m-2/3

100

101

102

2

3

4567

2

3

4567

2

3

4567

Rytov Variance

RYTOV VARIANCE FOR A 100km LINK

1.3micrometer laser

The Maryland Optics Group February 17Wireless Communications HYBRID FSO/RF LINKS AND NETWORKS WITH...

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