Presentation is loading. Please wait.

Presentation is loading. Please wait.

<…or how to communicate w/ your laser pointer …>

Similar presentations

Presentation on theme: "<…or how to communicate w/ your laser pointer …>"— Presentation transcript:

1 Towards Multi-Hop Free-Space-Optical (FSO) Mesh Networks and MANETs: Low-Cost Building Blocks
<…or how to communicate w/ your laser pointer …> Shiv Kalyanaraman : “shiv rpi”

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

3 Scope of Talk Understanding and overcoming limitations of FSO
Error correction to Improve multi-hop link performance Use of directionality concept in the network layer: routing and localization schemes Orthogonal Rendezvous Routing Network Geographic Routing Node Localization Auto - Data-link Error Correction Schemes 2-D Multiple Element FSO Antennas Node Localization Line - Of - 3D-LOS Alignment FSO and RF technologies complement each other, so a hybrid is a powerful combination Figure: physical layer, data link layer PHY Multiple Element Antennas

4 Free Space Optical (FSO) Communications
Open spectrum: 2.4GHz, 5.8GHz, 60GHz, > 300 GHz Lots of open spectrum up in the optical regime! Data transfer through atmosphere OOK Modulated light pulses. Line of sight “optical wireless” technology. Visible to near infrared regions. Currently terrestrial point-to-point links bridging connectivity gaps between buildings in a metro area medical imaging disaster recovery DoD use of FSO: Satellite communications DARPA ORCL project: air-to-ground, air-to-air, air-to-satellite High speed physical layer technology Point-to-point, Disaster recovery, considered for mobile base station backhaul 802.11a/g, 802.16e, Cellular (2G/3G)

5 FSO vs RF: Directional Antenna Sizes: 2.4 Ghz, 5.8 Ghz
2.4 Ghz b Pringles Can antennas Dual Band a/b/g Directional antennas 5.8 Ghz a Directional antennas

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

7 Elementary FSO: sending multi-channel music
Audio Mixing: Tabletop laboratory systems used for propagating music via multiple channels through free space

8 Why Free Space Optical Communication?
FSO potential: Multi-Gbps System capacity Spatial re-use/minimal interference Suitable form factors (power, size and cost) Quick and easy installation. If interference-limited, then attractive for the last mile access or home networking where LOS exists. If power-limited, then attractive for sensor networks: much lower-power vs RF Challenges: FSO Needs line-of-sight (LOS) alignment Poor performance in adverse weather conditions: reliability How to seamlessly integrate and leverage FSO in the context of multi-hop networks? No or minimum interference, Cost, power, size form factors -- suitable for sensor networks. From LightPointe Optical Wireless Inc.

9 Apps: Opportunistic Links & Networks
Air-to-air or air-satellite Opportunistic links to cell towers. Flying over oceans… 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

10 FSO Advantages High-brightness LEDs (HBLEDs) and VCSELs are very low cost and highly reliable components 35-65 cents a piece, and $2-$5 per transceiver package + up to 10 years lifetime Amenable to high density integration (eg: VCSEL arrays) Very low power consumption 4-5 orders of magnitude improvement in energy/bit compared to RF, e.g. 100 microwatts for Mbps. Huge spatial reuse => multiple parallel channels for huge bandwidth increases due to spectral efficiency Not interference limited, unlike RF More Secure: Highly directional + small size & weight => low probability of interception (LPI)

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

12 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 SAT SAR Source Receiver Laser Figure font too small Aperture spelling LED

13 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. Explain diversity

14 Elementary FSO System: Block Diagram
2 3 5 6 1 4 LED Module Collimating Lens External Magneto-Optic Modulator Pulsed Light Focusing Lens Detector Unit

15 Link Design Issues 2 3 5 6 1 4 LEDs Attenuation Photodetector

16 Output Optical Power is dependent upon the choice of wavelength.
LEDs Output Optical Power 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 don’t exist. Output Optical Spectral Width

17 Photodetector Responsivity
Responsivity is dependent upon the choice of wavelength

18 Atmospheric Windows Future devices 1.55um: today’s devices
Optical Loss is dependent upon the choice of wavelength.

19 Error Probability over Single Hop

20 Link Budget PRC = PTX –Llens– LGS – Latt
PRC — Output Optical Power in transmitter PTX — Received Optical Power in receiver Llens — Optical Loss Due to Lens Used in transmitter and receiver LGS — Optical Loss Due to Geometrical Spreading in the propagation distance Latt — 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 3d & 2d Designs: Alignment & Capacity
LOS 3-d Spheres: LOS detection through the use of 3-d spherical FSO Antennas Node 1 Node 2 Repeater 1 Repeater 2 Repeater N-1 D D/N 2d Array: 1cm2 LED/PIN => 1000 pairs in 1ft x 1ft square structure MultiGbps capacity possible, with different color LEDs (simple static WDM).

22 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 Auto-alignment Process: Step 1: Search Phase (pilot pulses) Step 2: Data Transfer Phase

23 3d-Sphere Auto-Alignment Circuit (cont’d)
E.g.: 4-circuit block diagram

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

25 3d Spheres: Mobility Contd
Received Light Intensity from the moving train. 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.

26 Toy Train Experiment Contd.
tA : Time duration of alignment θ: Divergence angle of LED. D: Circuit delay Ω: Train's angular speed φ: Angular separation between transceivers on sphere.

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

28 2-D Arrays: Increased Capacity
Consider transmission from transceiver T0 on array A (TA0) to transceiver T0 on array B (TB0). The cone not only covers intended receiver TB0 , but also TB1 , TB2 , TB4 , TB7 . Parameters: d: distance between arrays θ: divergence angle ρ: Package density Two such identical arrays face each other to facilitate communication between the corresponding optical transceivers on the arrays. each of the transceivers on the array is supposed to communicate only with the corresponding transceiver on the opposite array. But because of the finite transceiver angle, the light signals transmitted will diverge by the time they reach the opposite array and they are not only received by the corresponding transceiver on the opposite array, but also by its neighboring transceivers, causing interference.

29 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 Inter-channel Interference & Capacity w/ OOK
Interference occurs when a subset of these potential interferers transmit when TA0 is transmitting. Probability that such an event occurs gives error probability due to crosstalk. where p0 is probability(ZERO transmitted). BAC capacity: 1 1-pe pe X Y

31 Uniform Array layout: Uncoded, Per-Channel capacity drops
quickly with Package density

32 Helical Array layout: Channel capacity drops slowly with Package density

33 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 FSO Arrays and Space-Time Diversity
Link 1 Link 2 Link 4 Link 3 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.

35 Multi-hop Channel Model
For small errors Pe <10e-2 , the channel is approximated as: Redraw fig 1 Check 10e-2 Visibility is modeled as a two Gaussians for clear and adverse weather.

36 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) Add line

37 Multi-Hop Error Distribution: more concentrated
BER distribution Fix title and info

38 Multi-Hop Offers Robustness to Weather
Multi-hop significantly outperforms single hop Number of Hops Mean BER Variance 1 1.5e-3 0.27 0.02 0.1176 5 9e-27 0.005 8e-50 0.0045 Clear Weather Adverse Weather Clear Weather Adverse Weather Mean error in one box, Variance in one box

39 Using Multi-directional Communications @ Layer 3
Tessellated FSO Transceivers Multi-directional Antennas

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

41 FSO Localization Problem
(0,0) (x5, y5) (x6, y6) (x7, y7) (x2, y2) (x4, y4) (x3, y3) (x9, y9) (x8,, y8) (x11, y11) (x10, y10) FLA FLA is undefined! Before localization After localization

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

43 L3: Geographic Routing using Node IDs L2: ID to Location Mapping
ORRP vs Geo-Routing Classification of Research Issues in Position-based Schemes 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

44 Void Navigation & Deviation Correction
Basic Example VOID Navigation/Sparse Networks Example Void S R = min(+4t, 0) = g + p m = +3 = min(+4t, +6t) = g + p - 4t m = +2 m = 0 = min(+4t, +4t)

45 ORRP: Reachability Analysis
P{unreachable} = P{intersections not in rectangle} 4 Possible Intersection Points

46 Path Stretch Analysis Average Stretch for various topologies
Square Topology – 1.255 Circular Topology – 1.15 25 X 4 Rectangular – 3.24 Expected Stretch – 1.125

47 State Complexity Analysis
GPSR DSDV XYLS ORRP Node State O(1) O(n2) O(n3/2) Reachability High 100% High (99%) Name Resolution O(n log n) Invariants Geography None Global Comp. Local Comp. Notes: ORRP scales with Order N3/2 ORRP states are fairly evenly distributed – no single pt of failure

48 Summary FSO has interesting/complementary properties w.r.t. RF wireless Single Hop Issues: LEDs, PDs, Transmittance Windows Building Blocks: 3-d Sphere: LOS Auto-alignment, Coverage 2-d Array: Capacity, Co-channel interference due to geometric spread Helical Designs and Orthogonal Coding mitigates interference Low-cost Multi-hop FSO Networks: Simple OEO Repeaters, Error correction at electronic hops Use of directional PHY property at higher layers: Localization Routing: orthogonal rendezvous routing Low stretch, high connectivity, O(N1.5) state complexity Future work on multi-path routing, Wifi backup, coded-multiple parallel channels, WDM for capacity etc Dual-mode systems for opportunistic V2V links (vehicular ad-hoc) Extensions of our PHY and L3 mechanisms for higher mobility.

49 Thanks ! : “shiv rpi” Papers, PPTs, Audio talks:
Ps: downloadable VIDEOS of all my networking courses available freely at the above web site

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

51 Erasure Coding RS(N,K) Recover K data packets! >= K of N received
Lossy Network Data = K FEC (N-K) Block Size (N) RS(N,K)

52 HARQ Window (eg: window = 2 original data pkts) Opportunistic mapping
Packets Fragments Data fragments Per-packet FEC fragments Random-linear coded (RLC) FEC Fragments, coded across subsets of data/fec fragments in window HARQ Window (eg: window = 2 original data pkts) FSO sub-channel mm-wave RF subchannel Opportunistic mapping Interleaved RLC Fragments Lossy, variable bit-rate sub-channels Pkt 1 recovered w/o RLC (5 fragments received) Pkt 2 needs RLC (only 4 fragments received). But, 5 RLC fragments, with pkt 1 fragments can recover these 4 missing fragments Fragments suffer bursty loss: data, FEC and RLC fragments lost

53 Hybrid FSO/RF-Mesh and MANETS Vision
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 High reliability 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

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

55 Sphere: Analysis Figures
Lollipop design! Max communication range (m) for optimal node designs given P = 32mWatts,  = 170.1mRad. Reasonable coverage possible: For P=32mWatts, coverage as high as: 0.7 km2 (adverse) 2.10km2 (normal) 3.24km2 (clear) Installed to ceilings, may be as lamps.. Also can be connected to array interference.. Key message is the relationship between interference and coverage, opotimal packaging.. Information retreival problem.. ~500m practical with cheap LEDs On top of towers..

Download ppt "<…or how to communicate w/ your laser pointer …>"

Similar presentations

Ads by Google