4G Wireless Networks4G Wireless NetworksNeed for Improved Loss Tolerance

K. K. RamakrishnanAT&T L b R h NJAT&T Labs Research, NJ

Thanks to:Robert Miller(AT&T), Vijay Subramanian and Shiv Kalyanaraman (RPI)

Adaptive Wireless: Goal is to Make Wireless As Good As Wired

Adaptive modulation and coding exploits previouslyAdaptive modulation and coding exploits previouslyinaccessable capacity enabling higher rates

ShannonLimitMultiple Antennas and

Space Time Coding

4GTechnologies e gAdaptive Modulation

Space-Time Coding Combined with Better

Cell Propagation Predictability Provide

“Wire-Like” Performance

UserRate

Technologies e.g.MIMO, Small-Cells

(802.11n)

Adaptive Modulation and Error Correction

Coding Provide Higher Throughputs if

Propagation Allows

Potential Improvement (3G, 802.16)

2.5G Systems

Signal to Noise RatioFixed modulation and coding provides the

same rate to all users, even if their links could

Users in this region could get some

connectivity rather than no service

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provide higher ratesthan no service

Reach-Data rate Tradeoff

100Higher Rate,

Lower-Speed Mobility

Peak10

4G H/S Wireless LAN2.4 & 5 GHz Unlicensed

ond/

Use

r UWB

1

PeakDataRate

4G Wireless NAN2.4 & 5 GHz

ts p

er S

eco

Wider Area,Higher Speed Mobility

3G/802.16 WirelessVarious Bands

3G/MAN Fixed or Pedestrian

Meg

abit

3G/MAN Mobile1

Bluetooth

PANsZigbee

Higher-Speed Mobility

2.5G Mobile/Pedestrian

.1 2.4GHz and UWB

Zigbee (Europe)

2/2.5G Wireless800 MHz, 2 GHzZigbee (US)

10 feet 100 feet 1 mile 10 milesReach

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Cell Coverage Area Trends

MaritimeMobile

• Increased Bandwidth Demand/User• Battery/Dissipation Device Constraints• Moore’s Law Radios• Increased Edge Intelligence

100 Watts

MobileHF RadioService

(~300 mi)1,000,000

1G

g g• Distributed Control Techniques

10 Watts100,000 2G CellularExpandedS

MacrocellularSystems(~8 mi)

10,000 mi2

700 mi2

Mobile/PortableMaximumPowerOutput

1 Watt10,000CellRadius(Feet)

Service(~4 mi)

MetrolinerTrain

Telephone( 15 mi)

MJ-MKMobile

Telephone(~60 mi) The 2G

“Sweet Spot”The 3G/WiMax “Sweet Spot” Output

100 mW1,000

(Feet)

30 mW.01 mi2

(~15 mi)

PCSMicrocells

( 0 5 2 i)

2.5GMicrocells

(~2 mi)

1950 1960 1970Y

100

1980 1990 2000 2010

(~0.5 -2 mi)WNAN/LAN

Nanocells(~.06 -.2mi)

The 4G “SweetSpot”

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Year

Architecting a 2G-3G-4G Wireless “Network Infrastructure”

AT&T VoIP InfrastructureBE

PSTN

Gateway

AT&T Common BB Backbone

BE BE IS-41TDM

BE

Voice

BB Access Network

CellularNetworkMSC MSC

BS

Home4G

4GHot

ZonesEnterprise

4G

BS BS BS BS BS

MunicipalNetwork

Home4G

4GHot

ZonesEnterprise

4G

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How Might A Wireless Deployment Look?

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The Muni Network Concept Gets “Legs”

The number of municipalities operatingThe number of municipalities operating,installing, or planning Wi-Fi networks

is growing rapidly, driven by…

• User acceptance/use of Wi-Fi• User acceptance/use of Wi-Fi

• Large number of devices already equipped (instant customer base)

• Availability of low-cost networking• Availability of low-cost networking systems (including mesh)

• Ability to transport Ethernet-like throughputs

• Desire to project “Cybercity” image

• “Digital Divide” amelioration

• Improvement in public service• Improvement in public service communications capabilities

• Leverage existing municipal infrastructure and fiber

• Revenue opportunities/new business models

• Ability to raise bond capital for

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infrastructure

3G / Metro Area WirelessH b (PTMP Fi d S i t B i MDU

Fiber, 4G, and Multi-Tier Wireless: A NanoNet

Hub (PTMP Fixed Service to Businesses, MDUs, EcoPoles w/o fiber availability)

FiberRing

CityFiber

LocalPONFiber PON

Eco-PoleAPLAN

Wi d

FiberHub

PONHub

Fiber PON

NAN

Eco-PoleAP

IndoorCell

WindowBridge

EcoPole

Cell

EcoPoleAP

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“NanoNet” Indoor Coverage Using “Window Bridging”

3G / Metro Area WirelessH b (PTMP Fi d S i t B i MDUHub (PTMP Fixed Service to Businesses, MDUs,

EcoPoles w/o fiber availability)

FiberRing

CityFiber

LocalPONFiber PON Fiber

HubPONHub

NAN

Eco-PoleAP

Fiber PON

Eco-PoleAP

Wi dLAN

Cell WindowBridge

IndoorCell

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Solving Outdoor-to-Indoor Penetration: The Window Bridge

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Motivation for our work on LT-TCP

• Dense wireless deployments in urban areas/ high rises will cause disruptions/ burst errors due to interference

• Protocols need to be loss tolerant and provide l b lreliability

– Especially as we move to multi-hop wireless i tenvironments

• Divide the burden of reliability between link and transport layerstransport layers

• Keep Residual Loss Rate low; Delay small; Link and Transport Layer Goodput highand Transport Layer Goodput high

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TCP-SACK Performance under Lossy Conditions

• Sharp drop-off in performance with PER (degrades beyond an error rate of 5% PER)

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• Performance is poorer as combination of PER and RTT grows

Goals for our Enhancements to TCP• Dynamic Range: y a c a ge

– Can we extend the dynamic range of TCP into high loss regimes?– Can TCP perform close to the theoretical capacity achievable under

high loss rates?• Congestion Response:

– How should TCP respond to notifications due to congestion.. – … but not respond to packet erasures that do not signal

congestion?congestion?• Mix of Reliability Mechanisms:

– What mechanisms should be used to extend the operating point of TCP into loss rates from 0% - 50 % packet loss rate? TCP into loss rates from 0% 50 % packet loss rate?

– How can Forward Error Correction (FEC) help? – How should the FEC be split between sending it proactively

(insuring the data in anticipation of loss) and reactively (sending FEC i t l )?FEC in response to a loss)?

• Timeout Avoidance: – Timeouts: Useful as a fall-back mechanism but wasteful otherwise

especially under high loss rates especially under high loss rates. – How can we add mechanisms to minimize timeouts?

• Our Enhancements to TCP: Loss Tolerant-TCP (LT-TCP)

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LT-TCP Performance

• Performance of LT-TCP is much better compared to that of TCP-SACK

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• LT-TCP degrades gracefully (nearly linear degradation with loss rate)

Transport layer performance with loss tolerance across layers• Combining Loss Tolerance at the Transport layer with Link layer enhancements allows us to strike a balance in providing the appropriate loss tolerance over a wide range of losses• Limiting ARQ at link layer to manage latency• Manageable link level residual loss rate• Reasonable Goodput even under extreme conditions

High Loss Rates:High Loss Rates:both LLboth LL--HARQ+LTHARQ+LT--TCP neededTCP needed

to get better performanceto get better performance

Low Loss Rates:Low Loss Rates:just LLjust LL--HARQ (link) helpsHARQ (link) helpsto get better performanceto get better performance

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