4G Wireless Networks - SIGCOMM · 4G H/S Wireless LAN 2.4 & 5 GHz Unlicensed o nd/User UWB 1 Data...
Transcript of 4G Wireless Networks - SIGCOMM · 4G H/S Wireless LAN 2.4 & 5 GHz Unlicensed o nd/User UWB 1 Data...
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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