4G Wireless Networks 4G Wireless Networks Need for Improved Loss Tolerance K. K. Ramakrishnan AT&T L b R AT&T Labs Research, NJ h NJ Thanks to: Robert Miller(AT&T), Vijay Subramanian and Shiv Kalyanaraman (RPI)
Adaptive W ireless: Goal is to Make W ireless As Good As W ired Adaptive modulation and coding exploits previously Adaptive modulation and coding exploits previously inaccessable capacity enabling higher rates Shannon Limit Multiple Antennas and Space-Time Coding Space Time Coding Combined with Better Cell Propagation Predictability Provide “Wire-Like” Performance 4G Adaptive Modulation Adaptive Modulation Technologies e g Technologies e.g. and Error Correction MI MO, Small-Cells User Coding Provide Higher (802.11n) Throughputs if Rate Propagation Allows Potential I mprovement (3G, 802.16) 2.5G Systems Signal to Noise Ratio Fixed modulation and Users in this region coding provides the could get some same rate to all users, connectivity rather even if their links could than no service than no service provide higher rates Page 2
Reach-Data rate Tradeoff Higher Rate, Lower-Speed Mobility 100 UWB 4G H/S Wireless LAN ond/User 2.4 & 5 GHz Unlicensed 10 Peak Peak ts per Seco 4G Wireless NAN Data 2.4 & 5 GHz Rate 1 Megabit 3G/802.16 Wireless 3G/MAN Fixed or Pedestrian Bluetooth Various Bands Zigbee Wider Area, PANs 3G/MAN Mobile Higher-Speed Mobility Higher Speed Mobility .1 1 2.4GHz and UWB 2/2.5G Wireless 2.5G Mobile/Pedestrian 800 MHz, 2 GHz Zigbee (US) Zigbee (Europe) 10 feet 100 feet 1 mile 10 miles Reach Page 3
Cell Coverage Area Trends • Increased Bandwidth Demand/User • Battery/Dissipation Device Constraints • Moore’s Law Radios Maritime • Increased Edge Intelligence g g Mobile Mobile Distributed Control Techniques • HF Radio Service (~300 mi) 1,000,000 100 Watts 1G Macrocellular 10,000 mi 2 Systems (~8 mi) 10 Watts 100,000 2G Cellular Expanded 700 mi 2 S Service Mobile/ (~4 mi) MJ-MK Portable Mobile Cell Metroliner 1 Watt Maximum 10,000 Telephone The 3G/WiMax The 2G Train Radius (~60 mi) Power Telephone “Sweet Spot” “Sweet Spot” (Feet) (Feet) Output Output ( 15 mi) (~15 mi) 2.5G Microcells 100 mW 1,000 (~2 mi) . 01 mi 2 PCS Microcells 30 mW ( 0 5 2 (~0.5 -2 mi) i) The 4G WNAN/LAN “Sweet Nanocells 100 Spot” (~.06 -.2mi) 1950 1960 1970 1980 1990 2000 2010 Y Year Page 4
Architecting a 2G-3G-4G Wireless “Network I nfrastructure” PSTN AT&T VoIP Infrastructure Gateway BE BE AT&T Common BB Backbone BE IS-41 BE TDM Voice BB Access Network Cellular MSC MSC Network 4G Home Enterprise Hot 4G 4G Zones BS BS BS BS BS BS Municipal Network 4G Home Enterprise Hot 4G 4G Zones Page 5
How Might A W ireless Deploym ent Look? Page 6
The Muni Network Concept Gets “Legs” The number of municipalities operating The 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 infrastructure Page 7
Fiber, 4G, and Multi-Tier Wireless: A NanoNet 3G / Metro Area Wireless H b (PTMP Fi Hub (PTMP Fixed Service to Businesses, MDUs, d S i t B i MDU EcoPoles w/ o fiber availability) Fiber Ring Local City Fiber PON Fiber PON PON PON Fiber Fiber Hub Hub Eco- Eco- Pole Pole AP LAN AP NAN Wi d Window I ndoor Cell Bridge Cell EcoPole EcoPole AP Page 8
“NanoNet” I ndoor Coverage Using “Window Bridging” 3G / Metro Area Wireless H b (PTMP Fi Hub (PTMP Fixed Service to Businesses, MDUs, d S i t B i MDU EcoPoles w/ o fiber availability) Fiber Ring Local City Fiber PON Fiber PON PON PON Fiber Fiber Hub Hub Eco- Eco- Pole Pole AP AP LAN NAN Wi d Window I ndoor Cell Bridge Cell Page 9
Solving Outdoor-to-I ndoor Penetration: The Window Bridge Page 10
Motivation for our w ork 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 reliability l b l – Especially as we move to multi-hop wireless environments i t • Divide the burden of reliability between link and transport layers transport layers • Keep Residual Loss Rate low; Delay small; Link and Transport Layer Goodput high and Transport Layer Goodput high Page 11
TCP-SACK Perform ance under Lossy Conditions • Sharp drop-off in performance with PER (degrades beyond an error rate of 5% PER) • Performance is poorer as combination of PER and RTT grows Page 12
Goals for our Enhancem ents to TCP • Dynam ic 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 Mechanism s: – 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 in response to a loss)? FEC i t l )? • Tim eout 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 Enhancem ents to TCP: Loss Tolerant-TCP ( LT-TCP) Page 13
LT-TCP Perform ance • Performance of LT-TCP is much better compared to that of TCP-SACK • LT-TCP degrades gracefully (nearly linear degradation with loss rate) Page 14
Transport layer perform ance w ith 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 LL both LL- -HARQ+LT HARQ+LT- -TCP needed TCP needed to get better performance to get better performance Low Loss Rates: Low Loss Rates: just LL just LL- -HARQ (link) helps HARQ (link) helps to get better performance to get better performance g g p p Page 15
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