HYBRID FSO/RF LINKS AND NETWORKS WITH DIVERSITY CONTROL

1. 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 Wireless Communications

2. 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 Wireless Communications

3. 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 Wireless Communications

4. Modified from a TeraBeam picture Dynamic, Reconfigurable Hybrid FSO/RF Wireless Networks Wireless Communications

5. 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 Wireless Communications

6. 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 Wireless Communications

7. A Hybrid FSO/RF Link Handles Weather A Hybrid FSO/RF Network Involves Disparate Data Rates Wireless Communications

8. 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 Wireless Communications

9. 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 Wireless Communications

10. Wireless Communications

11. DYNAMIC AND VOLATILE ATMOSPHERICAND PLATFORM EFFECTS Wireless Communications

12. OPTICAL WIRELESS TRANSCEIVER Wireless Communications

13. OMNIDIRECTIONAL OPTICAL WIRELESS TRANSCEIVER Wireless Communications

14. Network Layer • Topology Control • Autonomous Backbone • Reconfiguration • Pointing, Acquisition and • Tracking Link Layer Physical Layer Topology Control in Optical Wireless Networks Wireless Communications

15. 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 Wireless Communications

16. 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) Wireless Communications

17. 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 Wireless Communications

18. Link Failures between 2 Transceivers For large application distance For short application distance Wireless Communications

19. Transceiver Axis Alignment Step Select the desired target from the CCD image Acquisition Process System Scanning Step Using TCP/IP socket to check link availability Link Table Update Record the current [θ,φ] into the link table Object still exists Tracking Process Tracking Process Motion Prediction Analysis (Track beacon) Object disappears PAT Process Wireless Communications

20. Experimental 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 Wireless Communications

21. 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 Wireless Communications

22. 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 Wireless Communications

23. 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 Wireless Communications

24. BACKUP SLIDES Wireless Communications

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26. The DARPA ORCLE PROGRAM(formerly THOR Program) • Long range (up to 100km) high altitude (10km) laser communication links • Rytov variance is • 2lnIRanges 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 Wireless Communications

27. Many Link Physics and Engineering Issues • Turbulence • Variations with height • Obscuration • Optical depth • Spatial distribution • Aerosols • Aperture averaging • Transceiver optimization Wireless Communications

28. Wireless Communications