Implementation Challenges in Implementation Challenges in Real-Time Middleware forReal-Time Middleware forDistributed Autonomous Distributed Autonomous

SystemsSystems

Prof. Vincenzo LiberatoreProf. Vincenzo Liberatore

Research supported in part by NSF CCR-0329910, Department of CommerceTOP 39-60-04003, NASA NNC04AA12A, a Lockheed grant, an ABB contract, and an OhioICE training grant.

MotivationMotivation

Sustainable presence on planetary surfaceSustainable presence on planetary surface Human-robotic missionsHuman-robotic missions E.g., construction, maintenanceE.g., construction, maintenance

ConsequencesConsequences Higher performanceHigher performance

Earth tele-operation inappropriate for constructionEarth tele-operation inappropriate for construction Multiple assetsMultiple assets

Communication and coordination Communication and coordination

Autonomous Distributed SystemAutonomous Distributed System

Potential Scenario (Teleops)Potential Scenario (Teleops)

Tele-operationsTele-operations Robots, roversRobots, rovers Pressurized vehiclesPressurized vehicles

RequirementsRequirements Single- or multi-hopSingle- or multi-hop End-point adaptation End-point adaptation

to network non-to network non-determinismdeterminism

Quality-of-ServiceQuality-of-Service System and control System and control

metricsmetrics

Lander (Later Habitat)

Surface Terminal

4-6 Humans on EVA

AutonomousRobot

LunarRelay

TeleoperatedRobot

PressurizedVehicle

Repeater

Talk OverviewTalk Overview

Bandwidth allocationBandwidth allocation

Play-back bufferPlay-back buffer

Quality-of-Service (QoS)Quality-of-Service (QoS)

DRE implementationDRE implementation

ConclusionsConclusions

Bandwidth AllocationBandwidth Allocation

Objectives:Objectives: Stability of control systemsStability of control systems Efficiency & fairnessEfficiency & fairness Fully distributed, asynchronous, & scalableFully distributed, asynchronous, & scalable Dynamic & self reconfigurableDynamic & self reconfigurable

Problem FormulationProblem Formulation

Define a utility fn Define a utility fn UU((rr) ) that isthat is Monotonically increasingMonotonically increasing Strictly concaveStrictly concave Defined for Defined for rr ≥ ≥ rrminmin

Optimization formulationOptimization formulation

( )

min,

max ( )

s.t. , 1,...,

and

i ii

i li l

i i

U r

r C l L

r r

S

Distributed ImplementationDistributed Implementation

Two independent algorithmsTwo independent algorithms End-systems (plants) algorithm End-systems (plants) algorithm Router algorithm (later on)Router algorithm (later on)

NCS Plant NCS ControllerRouter

max

min

1( ) 1 ' ( )r

rt tp pr h U

p p

p

Determination ofDetermination of k kpp andand k kii

Stability region in the Stability region in the kkii–k–kp p planeplane Stabilizes the NCS-AQM closed-loop system for Stabilizes the NCS-AQM closed-loop system for

delays less or equal delays less or equal dd

Analysis of quasi-polynomials, Analysis of quasi-polynomials, f(s,ef(s,ess))

Simulations & ResultsSimulations & Results

50 NCS Plants:

( ) ( )dx

ax t bu tdt

/ ( ) a ra bKU r e

a

min ln

ar

bK abK a

()

((

))j

ju

tK

Rx

t

[Branicky et al. 2002]

[Zhang et al. 2001]

Simulations & Results (cont.)Simulations & Results (cont.)

PI¤

P¤

Talk OverviewTalk Overview

Bandwidth allocationBandwidth allocation

Play-back bufferPlay-back buffer

Quality-of-Service (QoS)Quality-of-Service (QoS)

DRE implementationDRE implementation

ConclusionsConclusions

Information FlowInformation Flow

FlowFlow Sensor dataSensor data Remote controllerRemote controller Control packetsControl packets

Timely deliveryTimely delivery StabilityStability SafetySafety PerformancePerformance

Main IdeasMain Ideas

Predictable application timePredictable application time If control applied early, plant is not in the state If control applied early, plant is not in the state

for which the control was meant for which the control was meant If control applied for too long, plant no longer If control applied for too long, plant no longer

in desired statein desired state

Keep plant simpleKeep plant simple Low space requirementsLow space requirements

Integrate Playback, Sampling, and ControlIntegrate Playback, Sampling, and Control

AlgorithmAlgorithm

Send regular controlSend regular control Playback timePlayback time

Late playback okayLate playback okay ExpirationExpiration

Piggyback contingency controlPiggyback contingency control

Plant outputPlant output

Open Loop Play-back

Packet lossesPacket losses

Figure 8

Talk OverviewTalk Overview

Bandwidth allocationBandwidth allocation

Play-back bufferPlay-back buffer

Quality-of-Service (QoS)Quality-of-Service (QoS)

DRE implementationDRE implementation

ConclusionsConclusions

Network Quality-of-Service (QoS)Network Quality-of-Service (QoS)

Support real-time distributed applicationsSupport real-time distributed applications Voice, videoVoice, video Networked controlNetworked control

GuaranteesGuarantees Network metricsNetwork metrics

BandwidthBandwidthDelaysDelaysDelay jitterDelay jitterLoss ratesLoss rates

End-point metricsEnd-point metricsTracking in networked controlTracking in networked control

ExampleExample Packet prioritiesPacket priorities

Current support in InternetCurrent support in Internet Significant research and developmentSignificant research and development None of the above: best-effortNone of the above: best-effort

QoS and Space NetworksQoS and Space Networks

ExamplesExamples Human-robotic missions necessitate real-time communicationHuman-robotic missions necessitate real-time communication QoS no longer only for commercial satellite networkQoS no longer only for commercial satellite network

Fully Distributed QoS Fully Distributed QoS [IWQoS 2004][IWQoS 2004] Local mechanisms to protect from global congestion risksLocal mechanisms to protect from global congestion risks Addition to planned QoSAddition to planned QoS Autonomously adaptable to QoS requirements with no human Autonomously adaptable to QoS requirements with no human

supervisionsupervision Protects from error in networks configurationProtects from error in networks configuration Suitable for Distributed Autonomous systemsSuitable for Distributed Autonomous systems Higher performanceHigher performance On the flightOn the flight

The following videos were made possible by NASA funds provided by GRC under Contract NNC05CB20C

Videos:Tele-Operation, Cross-Traffic and

Distributed QoS

Note: video not included in SMC-IT proceedings

Distributed QoSDistributed QoS

DefinitionDefinition Local mechanisms to protect from global riskLocal mechanisms to protect from global risk

Deployment and benefitsDeployment and benefits Addition to planned QoSAddition to planned QoS Autonomously adaptable to QoS requirements with no Autonomously adaptable to QoS requirements with no

human supervisionhuman supervision Protects from error in networks configurationProtects from error in networks configuration Suitable for Distributed Autonomous systemsSuitable for Distributed Autonomous systems Higher performanceHigher performance On the flightOn the flight

Talk OverviewTalk Overview

Bandwidth allocationBandwidth allocation

Play-back bufferPlay-back buffer

Quality-of-Service (QoS)Quality-of-Service (QoS)

DRE implementationDRE implementation

ConclusionsConclusions

Middleware implementationMiddleware implementation

Sophisticated commercial DRESophisticated commercial DREIssuesIssues Embedded devices with limited memory, Embedded devices with limited memory,

computation, powercomputation, power Support for real-time protocolsSupport for real-time protocols Support for network QoSSupport for network QoS Incorporate research contributionsIncorporate research contributions

E.g., bandwidth allocation, buffersE.g., bandwidth allocation, buffers

On-going workOn-going work

Talk OverviewTalk Overview

Bandwidth allocationBandwidth allocation

Play-back bufferPlay-back buffer

Quality-of-Service (QoS)Quality-of-Service (QoS)

DRE implementationDRE implementation

ConclusionsConclusions

ConclusionsConclusions

Sustainable presence on planetary surfaceSustainable presence on planetary surface Human-robotic missionsHuman-robotic missions E.g. construction, maintenanceE.g. construction, maintenance

NeedsNeeds Higher performanceHigher performance Multiple assetsMultiple assets

ImplicationsImplications Network researchNetwork research

Distributed QoSDistributed QoS Middleware researchMiddleware research

Resource allocationResource allocationBuffersBuffersEmbedded implementationEmbedded implementation

Middleware research and development fits between Middleware research and development fits between NetworksNetworks Intelligent systemsIntelligent systems