High Availability Free Space Optical (FSO) and MM-Wave Hybrid Wireless Networks;

Concept, Architecture, Experimental Verifications and Path Forward

MSU - OCT 3rd, 2005

Hoss IzadpanahCollege of Optics and Photonics

UCF – Orlando Floridahizadpan@creol.ucf.edu

TBTS - 2

Terrestrial Fiber and MM-Waves Wireless Networks Physical Layer Architecture

Terrestrial Fiber NetworksCore communications network through DWDM led to massively increased transmission capacityTerabit, many 1000’s miles with mw power and extreme highest network capacity and lowest transmission BERBackbone, metro, LAN and access to include 40 Gbps research networksBut less than 10% high bandwidth users have access to fiber: Last mile bottleneckCostly and lengthy new fiber wiring

RF and Mm-waves WirelessNew mm-wave bands opportunitiesSpectra limitations & license requirementsP-t-P & P-t-MP up to lower Gbps rates Relative costly & complex technologyPower consumptionLimited “Networked” potentialChannel isolation, xtalk, etc.

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FSO Wireless Technology Its Role In Terrestrial and Space Communications Networks

LaserComIn 60’s and 70’s made its mark on inter-satellite, satellite-ground and satellite-submarine Now is becoming a feature of urban terrestrial communications technologyMany commercial operating units for short distance (100’s meters to few km)

Backbone and interconnectionsLast mile, campus intranet, small communities, airports, etc.

Under fast development/deployment stages, at Gbps data rates:Airborne- (inter-, to and from) ground high speed and high capacityMOBILE links and SPACE GRIDHigh speed inter-planetary Internet connections

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Airborne Gbit Communications GridHigh Compatibility for FSO Link Requirements

Satellite and Airborne FSO LinksLow weight, low complexity and low power

• No nonlinear Up/Down converters, no power hungry DAC or ADC or ADCHigh capacity and high date rates

• Doubled spectral efficiency with dual polarization practiced in FSO and RF system today

WAN

MMW

WAN WAN

RF RFRF

MMWMMW

FSO

FSO FSO

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NASA INTERPLANETARY INTERNET PLAN

IEEESpectrumAUG 2005

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Free Space Optical (FSO) Wireless All Weather Hybrid Optical/MM-Wave Wireless Network Architecture

LaserCom

Hybrid Fail/Safe Rings

ANAN

AlternateProtection SW

Mm-Wave

LaserComAN

Optical and RFWireless Bridge

BackboneWDM

Fiber Network

AN

AN mm-WaveWireless

Access andDistribution

Network

AN

BackboneFiber Network

SW/GW

PCS, MMDS, LMDS Reach Extension

SW/GW

BackboneFiber Network

RegionalNetwork

• PtP links•All-Weather• Rapidly deployable• Gbit capacity• Flexible traffic routing• “SECURE” Channels

SW SW

RF

FSOW

GW GW

Geophysical Diversity“Single Band”

Wireless Access Network& Distribution Topology

MMDS, LMDS, etc.

BuildingDistribution

NeighborhoodDistribution

BackboneFiber Network

LaserCom

LaserCom

SW/GW

• Fiber access to buildings ~ < 5%• FSO feed To remote Pico-cells• Gbit service delivery to remote RF

“Multi-Band”

• Multi-band, multi-service RF remoting

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Broadband Hybrid MMW/FSO Wireless Access and Distribution SystemFunctional Network Segmentation and Topology

Sub network islands of transparency for all optical managed networksSingle RF platform, modular IF stages on HFR and FSOW towards passive AP connectivityA converged and Integrate the wire and wireless infrastructure for an Internet multi-service networkLeave the RF signal where it belongs (to radiate) and relax network operational complexity

Local

Satellite Downlink

NetworkOperation

Center (NOC)

Processing/Switchingand Service Integration

NGIMAN/WAN

Global Network

NGIMAN/WAN

AP

Hybrid mm-wave & Free-Space Optical

Wireless

AP

< 500 m

Access Point and Distribution

Multi-tenant high bandidth users

OW & Hybrid Fiber Radio

AP

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FSO Bandwidth, Capacity and Link Availability

Fiber optics extremely large amount of bandwidth over continental distances not been matched in FSOFSO links present unpredictable channel impairments (attenuation, delay and aberrations)- over times as short as msecDemonstrations of 160 GHz DWDM link BUT commercial FSO links are limited to a few GHz over distances of a few tens of kmMoving beyond these limitations requires

Agility in transmission power, modulation format and rates as well as laser emission wavelength

AtmosphericTurbulenceEffect Close

To Buildings

Like a Phase Mask

LOS

Scattered

Pointing Error

*** Spatial, angular and temporal spread of signal

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High Availability FSO/MM-Wave Combined LinksDesign challenges and potential solutions

Real-time link performance characterization and adaptation for enhanced performance during adverse weather

Dynamic transmitter power control• Large FSO link margin combats many scintillation/turbulence fades• Dynamic FEC & Control

Modulation and data rate control • Format at 64 QAM to 32, …,QPSK & BPSK• Rate reduction from high say OC-48 to 12, or even OC-3)

Hybrid FSO/RF Wireless Network for High AvailabilityRF layer to increase link availability in times of several cloud blockagePath diversity, dynamic load switching and multi-hop routing (mesh network) to maintain the link/network availability and connectivity

Proactive SchemesIdentify & initiate, in a real time, restoration of the FSO link

Channel ConditioningAdaptive and Multiple Antennas, Alignment and Trakting

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Optical & RF Common Link Experiment (ORCLE)DARPA’S THOR (Pure LaserCom) Program Extension

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RF photonic based signal generation, modulation and transport• delivery in the 30-140 GHz spectral region

Combined RF/MMW and FSO diversity solution for DLS and traffic portioning

Millimeter Wave & Optical SpectrumGbit RF/MMW and FSO Hybrid Link

10GHz

100GHz

1THz

10THz

100THz

1000THz

94 GHz *

140 GHz *

220 GHz *

CurrentFrequency RangeMillimeter Wave

Radios

50 GHz x160 Channels

Newly Opened Frequencies

* In Development

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Multi-hop Routing Approach to Enhanced the Link Availability

Objective:To improve FSO link and network availability within the system power budget (excessive attenuation)

Trade-offs:Path Availability: favors short links (=> more hops)Path Delay: favors long links (=> less hops)

Problem Statement:Determine the route from source-to-destination that strikes a balance between availability and delay depending on the source-to-destination distance, traffic type and QoS constraints.

Link Metric:The link atmospheric attenuation should be incorporated along with the classical link delay and link load criteria.

AvailabilityRouting Algorithm

for a Mesh Topology

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Comparing ArchitecturesCourtesy: Carlton O’Neal – Ensemble Comm

Mesh-Point to Pointn Base stations with shared bandwidth

over large area (> 75 sq kms)

n One antenna per customer

n Rapid, planned coverage of an area

n Good for carrier class ntwk/growth

Point to Multipointn Series of radios units connecting

individual buildings (served or not)n Multiple antenna placementsn “Biological” network deployment

using planning/operations softwaren Good for cheap/fast connectivity

Sou

rce:

Rad

iant

Net

wor

ks

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1.E-11

1.E-07

1.E-03

1.E+01

12:00 16:00 20:00 0:00 4:00 8:00 12:00Time (hrs)

Inst

. BER

BER 1BER 10

FSOW at OC-12August 18 and 19, 2001Cascaded Link Length - 940m

1.E-11

1.E-08

1.E-05

1.E-02

12:00 16:00 20:00 0:00 4:00 8:00 12:00

Inst

. BER

BER 1BER 10

FSOW at OC-3August 13 and 14, 2001Cascaded Link Length - 940m

Signal Formats:

Double Pass Repeated 1000 meter FSO LinkCharacterization and Performance Evaluation

Digital Baseband, QPSK and 16Qam SCM on 140 MHz

Channel Rates:

80, 120, 155, 240, and

622 (OC-12) Mbps

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Dynamic Load Switching (DLS)Enhances the Link Availability and Maximizes the Capacity

At t=0: RFSOW = RRMMW = 0

Compute the actual atmospheric attenuation for each link averaged over window of Length W

Compute the permissible atmospheric attenuation for each link

Decide the FSOW and MMW link states

Switch load to enhance link availability

Objective:To detect the dynamic status (Available/outage) of FSO links in order to activate necessary procedures for link restoration (if necessary)

Problem:High rate of change of the measured BER causes

• Intermittent short periods (< pre-specified threshold) of link outage • Unnecessary activation of expensive availability enhancement

algorithms (e.g. DLS)Solution:

Sliding Window averaging to filter out frequent oscillations in the BER data.• Window shape: rectangular.• Window length (W): depends on rate of weather changes and

BER/RSSI models

Demonstrated availability figure better than 99.998%

Four possible cases are considered:Both links are availableFSOW failure and RF availableRF failure and FSOW availableBoth links fail

Attenuation threshold settingsBER/RSSIChannel bit rateDLS algorithm

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Instantaneous Link Availability vs. Window Lengths

Impacts of Different Window LengthsShort (W=1, 5? min): high rate BER changesLarge (W= 100 min): info loss, inaccurate availability figure, and unpractical outageIntermediate (10, 20): provides balance between filtering, data loss and availability

Measured FSOW BER at OC-3 Rate

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Real Time Proactive “Availability/Outage” Link CharacterizationDemonstrated Automated Performance Monitoring

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Measured Hybrid Accumulated PerformanceHeavy Fog Day’s Samples

• Hybrid architecture provides higly reliable broadband wireless connectivity during adverse weather events

10 /25 /01 P e rfo rm a n c e o f U n p ro te c te d a n d P ro te c te d IR L in k s

1 .E -12

1 .E -10

1 .E -08

1 .E -06

1 .E -04

1 .E -02

1.E + 00

1.E + 02

1.E + 04

12 :00 14:00 16:00 18 :00 20 :00 22 :00 0:00 2 :00 4 :00 6:00 8:00 10 :00 12 :00T im e (h rs)

Inst

. BER

W e a t h e r D a t a ( 7 6 1 ) f o r 1 0 / 2 5 / 0 1

5 0

5 5

6 0

6 5

7 0

7 5

8 0

1 2 : 0 0 1 4 : 0 0 1 6 : 0 0 1 8 : 0 0 2 0 : 0 0 2 2 : 0 0 0 : 0 0 2 : 0 0 4 : 0 0 6 : 0 0 8 : 0 0 1 0 : 0 0 1 2 : 0 0T im e

Tem

pera

ture

, F

8 4

8 6

8 8

9 0

9 2

9 4

9 6

9 8

1 0 0

Hum

idity

,%

H i T e m pD e w P t

H u m id it y

Protected

SW Events

Unprotected

• Accomplished 306 Hrs of SW’d link availability figure better than 99.998%

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CONCLUSIONTransparent RF/Optical Network Interface Technology

Hybrid FSO/MM-wave architecture and technology enabling to complement and extend the capabilities of the terrestrial fiber grid for air and space communication networksReactive and proactive dynamic link and network level protection to maintain connectivity with high availability

“Dynamic” link performance managements and data rate control“Real time” network topologies, connectivity, and redundancy managements

• Leveraged dynamic load switching and traffic portioning to overcome traditional free-space optical communications pitfalls

• Multi-hop routingFurther research direction

In the system physical interconnected layers, no RF/Optical data FORMAT transformation/conversion should be required as otherwise is practiced today by the present RF wireless cumbersome modulation schemes