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Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 : shiv rpi Towards Multi-Hop Free-Space-Optical (FSO) Mesh Networks and MANETs: Low-Cost Building.

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Presentation on theme: "Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 : shiv rpi Towards Multi-Hop Free-Space-Optical (FSO) Mesh Networks and MANETs: Low-Cost Building."— Presentation transcript:

1 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 : shiv rpi Towards Multi-Hop Free-Space-Optical (FSO) Mesh Networks and MANETs: Low-Cost Building Blocks Shiv Kalyanaraman : shiv rpi

2 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 2 : shiv rpi Students and Collaborators q Jayasri Akella (PhD) q Murat Yuksel (post-doc, now at Univ. Nevada, Reno) q Bow-Nan Cheng (PhD) q David Partyka (MS) q Chang Liu (MS) q Prof. Partha Dutta (optoelectronic devices) q Prof. Mona Hella (RF/photonic circuits)

3 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 3 : shiv rpi Scope of Talk q Understanding and overcoming limitations of FSO q Error correction to Improve multi-hop link performance q Use of directionality concept in the network layer: q routing and localization schemes PHY Data-link Line-Of-Node Localization Multiple Element Antennas Geographic RoutingAuto- 3D-LOS Alignment Node Localization 2-D Multiple Element FSO Antennas Error Correction Schemes Orthogonal Rendezvous Routing Network

4 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 4 : shiv rpi Free Space Optical (FSO) Communications q Open spectrum: 2.4GHz, 5.8GHz, 60GHz, > 300 GHz q Lots of open spectrum up in the optical regime! q Data transfer through atmosphere q OOK Modulated light pulses. q Line of sight optical wireless technology. q Visible to near infrared regions. q Currently terrestrial point-to-point links q bridging connectivity gaps q between buildings in a metro area q medical imaging q disaster recovery q DoD use of FSO: q Satellite communications q DARPA ORCL project: air-to- ground, air-to-air, air-to-satellite a/g, e, Cellular (2G/3G)

5 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 5 : shiv rpi FSO vs RF: Directional Antenna Sizes: 2.4 Ghz, 5.8 Ghz Dual Band a/b/g Directional antennas 5.8 Ghz a Directional antennas 2.4 Ghz b Pringles Can antennas

6 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 6 : shiv rpi FSO Trans-receivers: Much Smaller! q Higher frequency: smaller antennas q Small size => Can pack in 2-d array and 3-d structures ! q Increasing use of HBLEDs in solid state lighting: can leverage low cost devices. 2-d Array of LEDs Transreceivers: LED +PD (packed on a 3d sphere)

7 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 7 : shiv rpi Elementary FSO: sending multi-channel music Audio Mixing: Tabletop laboratory systems used for propagating music via multiple channels through free space

8 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 8 : shiv rpi Why Free Space Optical Communication? q FSO potential: q Multi-Gbps System capacity q Spatial re-use/minimal interference q Suitable form factors (power, size and cost) q Quick and easy installation. q If interference-limited, then attractive for the last mile access or home networking where LOS exists. q If power-limited, then attractive for sensor networks: much lower-power vs RF q Challenges: q FSO Needs line-of-sight (LOS) alignment q Poor performance in adverse weather conditions : reliability q How to seamlessly integrate and leverage FSO in the context of multi-hop networks? From LightPointe Optical Wireless Inc.

9 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 9 : shiv rpi Apps: Opportunistic Links & Networks Expensive sat-com links for most urgent data, and delay-tolerant links to offload delay-tolerant data: DARPA ORCL program is already looking at some of this Opportunistic links to cell towers. Flying over oceans… Opportunistic links Air-to-air or air-satellite

10 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 10 : shiv rpi FSO Advantages q High-brightness LEDs (HBLEDs) and VCSELs are very low cost and highly reliable components q cents a piece, and $2-$5 per transceiver package + up to 10 years lifetime q Amenable to high density integration (eg: VCSEL arrays) q Very low power consumption q 4-5 orders of magnitude improvement in energy/bit compared to RF, e.g. 100 microwatts for Mbps. q Huge spatial reuse => multiple parallel channels for huge bandwidth increases due to spectral efficiency q Not interference limited, unlike RF q More Secure: Highly directional + small size & weight => low probability of interception (LPI)

11 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 11 : shiv rpi FSO Issues/Disadvantages q Limited range (no waveguide, unlike fiber optics) q Need line-of-sight (LOS) q Any obstruction or poor weather (fog, sandstorms, heavy rain/snow) can increase BER in a bursty manner q Bigger issue: Need tight LOS alignment over long distances: q Directional antenna on steroids! q LOS alignment must be changed/maintained with mobility or sway! ~1km Received power Spatial profile: ~ Gaussian drop off

12 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 12 : shiv rpi Geometric Attenuation due to Beam Spread Divergence of light beam is primary cause for geometric attenuation. When an energy detector is used, only a fraction of transmitted power is received. θ R SA T SA R Source Receiver Laser LED

13 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 13 : shiv rpi Typical FSO Communication System Digital Data ON-OFF Keyed Light Pulses Transmitter (Laser/VCSEL/LED) Receiver (Photo Diode/ Transistor) Light beam is directional (-) Line-of-sight is always needed between the transceivers. (+) Spatial re-use, diversity, and neighbor position estimation.

14 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 14 : shiv rpi Elementary FSO System: Block Diagram 1. LED Module 2. Collimating Lens 3. External Magneto-Optic Modulator 4. Pulsed Light 5. Focusing Lens 6. Detector Unit

15 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 15 : shiv rpi Link Design Issues LEDs Attenuation Photodetector

16 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 16 : shiv rpi LEDs Output Optical Power Output Optical Spectral Width P Output Optical Power wavelength I Input Electrical Current Output Optical Power is dependent upon the choice of wavelength. Longer wavelengths are also more safer to humans, but room- temperature devices dont exist.

17 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 17 : shiv rpi Photodetector Responsivity Responsivity is dependent upon the choice of wavelength

18 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 18 : shiv rpi Atmospheric Windows Optical Loss is dependent upon the choice of wavelength. Future devices 1.55um: todays devices

19 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 19 : shiv rpi Error Probability over Single Hop

20 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 20 : shiv rpi Link Budget P RC = P TX –L lens – L GS – L att P RC Output Optical Power in transmitter P TX Received Optical Power in receiver L lens Optical Loss Due to Lens Used in transmitter and receiver L GS Optical Loss Due to Geometrical Spreading in the propagation distance L att Optical Loss Due to attenuation in atmosphere Bottom Line: Trying to Achieve Greater Distance and Reliability With a Single FSO Hop is Tough! Change the game: Use shorter hops, multi-hops, low-cost BBs, and engineer reliability by using diversity at higher layers

21 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 21 : shiv rpi 3d & 2d Designs: Alignment & Capacity 3-d Spheres: LOS detection through the use of 3-d spherical FSO Antennas LOS Node 1 Node 2 … Node 1 Node 2 Repeater 1 Repeater 2Repeater N-1 D D/N 2d Array: 1cm 2 LED/PIN => 1000 pairs in 1ft x 1ft square structure MultiGbps capacity possible, with different color LEDs (simple static WDM).

22 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 22 : shiv rpi 3-d Spheres for Auto-Alignment Initial 3-d FSO prototypes with auto- alignment circuitry Design of 3-d FSO antennas: Honeycomb (tesselated) arrays of transceivers q Auto-alignment Process: q Step 1: Search Phase (pilot pulses) q Step 2: Data Transfer Phase

23 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 23 : shiv rpi 3d-Sphere Auto-Alignment Circuit (contd) q E.g.: 4-circuit block diagram

24 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 24 : shiv rpi 3d Spheres: Mobility Tests Misaligned Aligned q Prior work obtained mobility in FSO for indoor using diffuse optics technology: [Barry, J.R; Al- Ghamdi, A.G.] q Limited power of a single source that is being diffused into all the directions. q Suitable for small distances (typically 10s of meters), but not suitable for longer distances. q Our approach can scale to longer, outdoor distances and consumes less power.

25 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 25 : shiv rpi 3d Spheres: Mobility Contd Detector Threshold Not aligned Aligned Denser packing will allow fewer interruptions (and smaller buffering), but more handoffs… Even w/ buffering: becomes a disruption-tolerant/lossy networking problem over multiple hops. Received Light Intensity from the moving train.

26 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 26 : shiv rpi Toy Train Experiment Contd. q t A : Time duration of alignment q θ: Divergence angle of LED. q D: Circuit delay q Ω: Train's angular speed q φ: Angular separation between transceivers on sphere.

27 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 27 : shiv rpi FSO Node Designs q Important node design questions: q How good the node can be in terms of coverage or range? q How many transceivers can/should be placed on the nodes? q Do the placement patterns of transceivers matter? Goal: maximize capacity Tradeoff: interference vs. angles vs. packaging density q Various factors: q Visibility – weather conditions q source power and receiver sensitivity q angles of devices – small angles are costlier q packaging density Goal: maximize coverage Tradeoff: interference vs. angles vs. packaging density

28 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 28 : shiv rpi 2-D Arrays: Increased Capacity q Consider transmission from transceiver T 0 on array A (T A 0 ) to transceiver T 0 on array B (T B 0 ). q The cone not only covers intended receiver T B 0, but also T B 1, T B 2, T B 4, T B 7. q Parameters: q d: distance between arrays q θ: divergence angle q ρ: Package density

29 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 29 : shiv rpi Array Designs : Helical Vs Uniform Transceiver Placement Helical array design gives more capacity for a given range and transceiver parameters due to reduced inter-channel interference.

30 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 30 : shiv rpi Inter-channel Interference & Capacity w/ OOK q Interference occurs when a subset of these potential interferers transmit when T A 0 is transmitting. q Probability that such an event occurs gives error probability due to crosstalk. where p 0 is probability(ZERO transmitted) p e pepe 1 X Y BAC capacity:

31 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 31 : shiv rpi Uniform Array layout: Uncoded, Per-Channel capacity drops quickly with Package density

32 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 32 : shiv rpi Helical Array layout: Channel capacity drops slowly with Package density

33 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 33 : shiv rpi OOC (Optical Orthogonal Codes) can further improve the capacity between arrays. Two OOCs with weight 4 and length 32. Each transceiver uses a unique code similar to CDMA wireless users in a cell.

34 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 34 : shiv rpi FSO Arrays and Space-Time Diversity Per-Link: Code over Time and Across Multiple Spatial Channels Per-Hop Per-Path Across a network: Build a virtual link composed of several FSO hops, and possibly perform FEC coding and mapping across multiple routed-paths. Link 1 Link 2 Link 4 Link 3

35 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 35 : shiv rpi Multi-hop Channel Model For small errors P e <10e-2, the channel is approximated as: Visibility is modeled as a two Gaussians for clear and adverse weather.

36 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 36 : shiv rpi Bit Error Rate versus Number of Hops Assume fixed e2e range that is split up into hops (2.5km) most gains with a few hops (~500m/hop)

37 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 37 : shiv rpi Multi-Hop Error Distribution: more concentrated BER distribution

38 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 38 : shiv rpi Multi-Hop Offers Robustness to Weather Number of Hops Mean BER Variance 11.5e e e Multi-hop significantly outperforms single hop Clear Weather Adverse Weather

39 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 39 : shiv rpi Using Multi-directional Layer 3 Multi-directional Antennas Tessellated FSO Transceivers

40 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 40 : shiv rpi FSO-Meshes: Localization FSO-based localization system with granular tessellation of transceivers Granular tessellation allows accurate detection of angle of arrival. RF triangulation: needs THREE neighbors FSO localization: needs ONE neighbor

41 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 41 : shiv rpi FSO Localization Problem Before localization After localization FLA (0,0) (x 5, y 5 ) (x 6, y6) (x 7, y 7 ) (x 2, y2) (x 4, y4) (x 3, y3) (x 9, y 9 ) (x 8,, y 8 ) (x 11, y 11 ) (x 10, y 10 )

42 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 42 : shiv rpi FSO-Meshes: Orthogonal Rendezvous Routing Orthogonal/Directional Routing using FSO nodes The source and destination sends probe packets at North-South and East-West directions based on their local sense of direction. Rendezvous point Essentially choosing random orthogonal directions in the plane for dissemination and discovery.

43 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 43 : shiv rpi ORRP vs Geo-Routing L3: Geographic Routing using Node IDs (eg. GPSR, TBF etc.) L2: ID to Location Mapping (eg. HDT, GLS etc.) L1: Node Localization ORRP N/A Classification of Research Issues in Position-based Schemes

44 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 44 : shiv rpi Void Navigation & Deviation Correction Basic Example VOID Navigation/Sparse Networks Example Void S R min(+4 = + m = +3 min(+4 6 = + 4 m = +2 min(+4 = + m = 0 min(+4 4 = + 4 m = +2 min(+4 4 = + 4 m = +3 min(+4 6 = + 4 m = +3

45 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 45 : shiv rpi ORRP: Reachability Analysis P{unreachable} = P{intersections not in rectangle} 4 Possible Intersection Points

46 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 46 : shiv rpi Path Stretch Analysis Average Stretch for various topologies Square Topology – Circular Topology – X 4 Rectangular – 3.24 Expected Stretch – 1.125

47 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 47 : shiv rpi State Complexity Analysis GPSRDSDVXYLSORRP Node StateO(1)O(n 2 )O(n 3/2 ) ReachabilityHigh 100%High (99%) Name ResolutionO(n log n)O(1) InvariantsGeographyNoneGlobal Comp.Local Comp. Notes: ORRP scales with Order N 3/2 ORRP states are fairly evenly distributed – no single pt of failure

48 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 48 : shiv rpi Summary q FSO has interesting/complementary properties w.r.t. RF wireless q Single Hop Issues: LEDs, PDs, Transmittance Windows q Building Blocks: q 3-d Sphere: LOS Auto-alignment, Coverage q 2-d Array: Capacity, Co-channel interference due to geometric spread q Helical Designs and Orthogonal Coding mitigates interference q Low-cost Multi-hop FSO Networks: q Simple OEO Repeaters, Error correction at electronic hops q Use of directional PHY property at higher layers: q Localization q Routing: orthogonal rendezvous routing q Low stretch, high connectivity, O(N 1.5 ) state complexity q Future work on multi-path routing, Wifi backup, coded-multiple parallel channels, WDM for capacity etc q Dual-mode systems for opportunistic V2V links (vehicular ad-hoc) q Extensions of our PHY and L3 mechanisms for higher mobility.

49 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 49 : shiv rpi Thanks ! : shiv rpi Papers, PPTs, Audio talks: Ps: downloadable VIDEOS of all my networking courses available freely at the above web site

50 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 50 : shiv rpi Reliability through Diversity at Higher Layers q Standard technique: code across diversity modes and use degrees of freedom efficiently Diversity Modes Continuous: Time, Frequency, Space... Discrete: Code, Antenna, Paths, Routes … Channel Performance

51 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 51 : shiv rpi Erasure Coding Data = K FEC (N-K) Block Size (N) RS(N,K) >= K of N received Lossy Network Recover K data packets!

52 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 52 : shiv rpi

53 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 53 : shiv rpi Hybrid FSO/RF-Mesh and MANETS Vision Legacy RF MANETS 802.1x with omni-directional RF antennas High-power, Interference limited Low bandwidth – typically the bottleneck link on a path Error-prone, Disruptions Less secure – very vulnerable to interception Spatial reuse and angular diversity in nodes Electronic auto-alignment (auto-configuration) Optical auto-configuration (switching, routing) Low-power and highly secure Interdisciplinary, cross-layer design Bringing optical communications and RF ad- hoc networking together… High bandwidth Low power Directional – secure, Not i/f limited Free-Space-Optical Communications Mobile Ad-Hoc Networking Hybrid Free-Space- Optical/RF Mobile Ad-Hoc Networks Mobile communication Auto-configuration RF Communications High reliability

54 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 54 : shiv rpi 3-d Sphere Node Design Parameters Case 1: No overlap, C=L θ θ R r R φ R tanθ τ ρ Transceiver Maximum possible range Half lobe area Interference area Not covered area Case 2: Overlap, C=L-I

55 Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 55 : shiv rpi Sphere: Analysis Figures Max communication range (m) for optimal node designs given P = 32mWatts, = 170.1mRad. Lollipop design! On top of towers.. Installed to ceilings, may be as lamps.. Reasonable coverage possible: For P=32mWatts, coverage as high as: 0.7 km 2 (adverse) 2.10km 2 (normal) 3.24km 2 (clear) ~500m practical with cheap LEDs


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