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Transcript of Shivkumar Kalyanaraman Rensselaer Polytechnic Institute 1 : shiv rpi Towards Multi-Hop...
Shivkumar KalyanaramanRensselaer Polytechnic Institute
1 : “shiv rpi”
Towards Multi-Hop Free-Space-Optical (FSO) Mesh Networks and MANETs:
Low-Cost Building Blocks
Shiv [email protected]
: “shiv rpi”
<…or how to communicate w/ your laser pointer …>
Shivkumar KalyanaramanRensselaer Polytechnic Institute
2 : “shiv rpi”
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)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
3 : “shiv rpi”
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
schemesPHY
Data-link
Line-Of-Node Localization
Multiple Element Antennas
Geographic Routing Auto-
3D-LOS Alignment
Node Localization
2-D Multiple ElementFSO Antennas
Error Correction Schemes
Orthogonal Rendezvous Routing
Network
Shivkumar KalyanaramanRensselaer Polytechnic Institute
4 : “shiv rpi”
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
802.11a/g, 802.16e,Cellular (2G/3G)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
5 : “shiv rpi”
FSO vs RF: Directional Antenna Sizes: 2.4 Ghz, 5.8 Ghz
Dual Band 802.11a/b/g Directional antennas
5.8 Ghz 802.11aDirectional antennas
2.4 Ghz 802.11bPringles Can antennas
Shivkumar KalyanaramanRensselaer Polytechnic Institute
6 : “shiv rpi”
FSO Trans-receivers: Much Smaller!
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.
2-d Array of LEDs
Transreceivers: LED +PD(packed on a 3d sphere)
Shivkumar KalyanaramanRensselaer 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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
8 : “shiv rpi”
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?
From LightPointe Optical Wireless Inc.
Shivkumar KalyanaramanRensselaer 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 linksto cell towers.Flying over oceans…
Opportunistic linksAir-to-air or air-satellite
Shivkumar KalyanaramanRensselaer Polytechnic Institute
10 : “shiv rpi”
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 10-100 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)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
11 : “shiv rpi”
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!
~1km
Received powerSpatial profile: ~ Gaussian drop off
Shivkumar KalyanaramanRensselaer Polytechnic Institute
12 : “shiv rpi”
Geometric Attenuation due to Beam Spread
22
)(2
0)( ZY
eIYI
)(cos)( 0 nII
• 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
SourceReceiver
Laser
LED
Shivkumar KalyanaramanRensselaer Polytechnic Institute
13 : “shiv rpi”
Typical FSO Communication System
Digital DataON-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.
Shivkumar KalyanaramanRensselaer 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
2 3 5 61
4
Shivkumar KalyanaramanRensselaer Polytechnic Institute
15 : “shiv rpi”
Link Design Issues
2 3 5 61
4
LEDs Attenuation Photodetector
Shivkumar KalyanaramanRensselaer Polytechnic Institute
16 : “shiv rpi”
LEDs• Output Optical Power
IP24.1
• 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 don’t exist.
Shivkumar KalyanaramanRensselaer Polytechnic Institute
17 : “shiv rpi”
Photodetector Responsivity
Responsivity is dependent upon the choice of wavelength
Shivkumar KalyanaramanRensselaer Polytechnic Institute
18 : “shiv rpi”
Atmospheric Windows
Optical Loss is dependent upon the choice of wavelength.
Future devices
1.55um: today’s devices
Shivkumar KalyanaramanRensselaer Polytechnic Institute
19 : “shiv rpi”
Error Probability over Single Hop
Shivkumar KalyanaramanRensselaer Polytechnic Institute
20 : “shiv rpi”
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 ReliabilityWith 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
Shivkumar KalyanaramanRensselaer 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 2 Repeater N-1
DD/N
2d Array: 1cm2 LED/PIN => 1000 pairs in 1ft x 1ft square structure MultiGbps capacity possible, with different color LEDs (simple static WDM).
Shivkumar KalyanaramanRensselaer Polytechnic Institute
22 : “shiv rpi”
3-d Spheres for Auto-Alignment
LED
PhotoDetector
Micro Mirror
Spherical Antenna
Optical Transmitter/Receiver Unit
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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
23 : “shiv rpi”
3d-Sphere Auto-Alignment Circuit (cont’d)
E.g.: 4-circuit block diagram
Shivkumar KalyanaramanRensselaer Polytechnic Institute
24 : “shiv rpi”
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.
Shivkumar KalyanaramanRensselaer Polytechnic Institute
25 : “shiv rpi”
3d Spheres: Mobility Contd
0
10
20
30
40
50
60
70
0
11
17
23
33
40
.5
51
.5 65
72
79
88
.5
97
.5
10
5
11
2
12
1
12
8
Angular Position of the Train (degree)
Lig
ht
Inte
ns
ity
(lu
x)
DetectorThreshold
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.
Shivkumar KalyanaramanRensselaer Polytechnic Institute
26 : “shiv rpi”
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.
2
2 DtA
Shivkumar KalyanaramanRensselaer Polytechnic Institute
27 : “shiv rpi”
FSO Node Designs 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?
Goal: maximize capacity
Tradeoff: interference vs. angles vs. packaging density
Various factors: Visibility – weather conditions source power and receiver sensitivity angles of devices – small angles are costlier packaging density
Goal: maximize coverage
Tradeoff: interference vs. angles vs. packaging density
Shivkumar KalyanaramanRensselaer Polytechnic Institute
28 : “shiv rpi”
2-D Arrays: Increased Capacity
Consider transmission from transceiver T0 on array A (TA
0) to transceiver T0 on array B (TB0).
The cone not only covers intended receiver TB0 , but also
TB1 , TB
2 , TB4 , TB
7 .
Parameters: d: distance between arrays θ: divergence angle ρ: Package density
tandr
Shivkumar KalyanaramanRensselaer 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.
Shivkumar KalyanaramanRensselaer Polytechnic Institute
30 : “shiv rpi”
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).
0
)1(0 )1(
222
pppSep
Sep
Y
r
j
jjYe
0
1
0
1
1-pe
pe
1
X Y
BAC capacity: )().(max 00)(
eexp
pHpppHC
Shivkumar KalyanaramanRensselaer Polytechnic Institute
31 : “shiv rpi”
Uniform Array layout: Uncoded, Per-Channel capacity drops quickly with Package density
Shivkumar KalyanaramanRensselaer Polytechnic Institute
32 : “shiv rpi”
Helical Array layout: Channel capacity drops slowly with Package density
Shivkumar KalyanaramanRensselaer 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.
Shivkumar KalyanaramanRensselaer 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 4Link 3
Shivkumar KalyanaramanRensselaer Polytechnic Institute
35 : “shiv rpi”
Multi-hop Channel Model
For small errors Pe <10e-2 , the channel is approximated as:
N
iieP
1
1 1
0
1
0
N
iieP
1
N
iieP
1
1
N
iieP
1
N
iieP
1
1 1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
1
0
N
iieP
1
N
iieP
1
1
N
iieP
1
Visibility is modeled as a two Gaussians for clear and adverse weather.
Shivkumar KalyanaramanRensselaer Polytechnic Institute
36 : “shiv rpi”
Bit Error Rate versus Number of Hops
Assume fixed e2e rangethat is split up into hops(2.5km)
most gains with a few hops(~500m/hop)
Shivkumar KalyanaramanRensselaer Polytechnic Institute
37 : “shiv rpi”
Multi-Hop Error Distribution: more concentratedB
ER
dis
trib
utio
n
Shivkumar KalyanaramanRensselaer Polytechnic Institute
38 : “shiv rpi”
Multi-Hop Offers Robustness to Weather
Number of Hops
Mean BER Mean BER Variance Variance
1 1.5e-3 0.27 0.02 0.1176
5 9e-27 0.005 8e-50 0.0045
Multi-hop significantly outperforms single hop
Clear WeatherClear Weather Adverse Weather Adverse Weather
Shivkumar KalyanaramanRensselaer Polytechnic Institute
39 : “shiv rpi”
Using Multi-directional Communications @ Layer 3
Multi-directional Antennas
Tessellated FSO Transceivers
Shivkumar KalyanaramanRensselaer 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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
41 : “shiv rpi”
FSO Localization Problem
Before localization After localization
FLA
(0,0)
(x5, y5)
(x6, y6) (x7, y7)
(x2, y2)
(x4, y4)
(x3, y3)
(x9, y9)
(x8,, y8)
(x11, y11)
(x10, y10)
Shivkumar KalyanaramanRensselaer 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.
Shivkumar KalyanaramanRensselaer 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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
44 : “shiv rpi”
Void Navigation & Deviation Correction
Basic ExampleVOID Navigation/Sparse
Networks Example
VoidS R
min(+4 = + m = +3
min(+46 = + 4m = +2
min(+4 = + m = 0
min(+44 = + 4m = +2
min(+44 = + 4m = +3
min(+46 = + 4m = +3
Shivkumar KalyanaramanRensselaer Polytechnic Institute
45 : “shiv rpi”
ORRP: Reachability Analysis
P{unreachable} =
P{intersections not in rectangle}
4 Possible Intersection Points
Shivkumar KalyanaramanRensselaer Polytechnic Institute
46 : “shiv rpi”
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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
47 : “shiv rpi”
State Complexity Analysis
GPSR DSDV XYLS ORRP
Node State O(1) O(n2) O(n3/2) O(n3/2)
Reachability High High 100% High (99%)
Name Resolution O(n log n) O(1) O(1) O(1)
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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
48 : “shiv rpi”
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.
Shivkumar KalyanaramanRensselaer 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
Shivkumar KalyanaramanRensselaer Polytechnic Institute
50 : “shiv rpi”
Reliability through Diversity at Higher Layers
Standard technique: code across diversity modes and use degrees of freedom efficiently
Diversity ModesContinuous: Time, Frequency, Space ... Discrete: Code, Antenna, Paths, Routes …
ChannelPerformance
Shivkumar KalyanaramanRensselaer Polytechnic Institute
51 : “shiv rpi”
Erasure Coding
Data = K
FEC (N-K)
Block Size (N)
RS(N,K) >= K of Nreceived
Lossy Network
Recover K data packets!
Shivkumar KalyanaramanRensselaer Polytechnic Institute
52 : “shiv rpi”
Packets
Fragments
Data fragmentsPer-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-channelmm-wave RF subchannel
Opportunistic mapping
Interleaved RLC Fragments
Lossy, variable bit-ratesub-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
Shivkumar KalyanaramanRensselaer 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 nodesElectronic auto-alignment (auto-configuration)Optical auto-configuration (switching, routing)Low-power and highly secureInterdisciplinary, cross-layer design
Bringing optical communications and RF ad-hoc networking together…
High bandwidthLow powerDirectional – secure,Not i/f limited
Free-Space-Optical Communications
Mobile Ad-Hoc Networking
Hybrid Free-Space-Optical/RF Mobile Ad-Hoc Networks
Mobile communicationAuto-configuration
RF Communications
High reliability
Shivkumar KalyanaramanRensselaer 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
R tanθ
τ
ρ
Transceiver
Maximum possible range
Half lobe area
Interference area
Not covered area
Case 2: Overlap, C=L-I
Shivkumar KalyanaramanRensselaer 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 km2 (adverse)2.10km2 (normal)3.24km2 (clear)
~500mpracticalwith cheapLEDs