wireless mesh networks for residential broadband · wireless mesh networks for residential...
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1 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Wireless Mesh NetworksFor Residential Broadband
Dave Beyer, NokiaNational Wireless Engineering Conference
San Diego, 4 November 2002
2 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Design ConstraintsFor Residential Broadband Wireless
• Total solution cost must enable residential business• Equipment; up-front investment; spectrum; maintenance
• Must provide > 90% coverage in typical residential areas• High-confidence installs; applicable to variety of RF environments
• Equal or better service than competing DSL or cable• Extend broadband to new areas or provide a competitive alternative
• Must be easily scalable to high market penetrations• Without negatively impacting service; no revisits to subscriber homes
3 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Wireless networks that model the Internet• Each subscriber unit is part of the infrastructure• Multi-hop routing enables full coverage• Network self-configures and self-heals
Wireless Mesh NetworksFor Residential Broadband
Single “Airhood”A neighborhood
wireless mesh network
4 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Wireless Mesh NetworksFor Residential Broadband
Multiple Airhoods with 4-channels
Fed by PTP, PMP, or wired backhaul links
5 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Solving Coverage
PMP Approach:Focus is on RF & Deployment
Blast over & through obstacles
Mesh Approach:Focus is on smart software
Skip around obstacles
6 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Solving Coverage Path Loss is Highly Variable
Path loss driven by obstacles rather than distance• Leads to the “Log-Normal” path loss model:
C + 10·n·log10(dist) + Xσrandom variable Xσ with standard deviation σ
In PMP networks, large σ is BAD• Must design for worst-case; e.g., leads to 1/r4 or 1/r5 models
In mesh networks, large σ is GOOD!• Best-case links automatically selected and used.
7 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
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Prob. of a reliable link between any two points (z)
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ew n
ode
PMP
Solving Coverage Simplified Model
Assume obstacles completely dominate coverage• Thus, random term (Xσ ) dominates• Link probability simplifies to a fixed probability: z
8 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
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Prob. of a reliable link between any two points (z)
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ode
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AirHead + 10
AirHead + 50
Meshbenefit
Solving Coverage Simplified Model
m-device mesh coverage probability
= 1 – (1 – z) m
Assume obstacles completely dominate coverage• Thus, random term (Xσ ) dominates• Link probability simplifies to a fixed probability: z
Mesh coverage & robustness improve exponentially
as subscribers are added
9 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Solving Coverage Log-Normal RF Environment
Model Parameters• Path loss exponent n=3; standard deviation σ=10 dB• Subscribers randomly located within 1-mile radius cells• Standard 802.11a PHY
• Number of subscribersvaried from 1 to 40
• Compare coverageprobabilities
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1 mile
10 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Solving Coverage Log-Normal RF Environment
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Number of devices in network
Prob
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PMPMeshMesh + 4 seed nodes
90% coverage after 8 subscribers using only WLAN-type RF
11 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Solving Coverage System Gain Benefit of Mesh
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1 mile
Same model, except:• Fixed, 50-subscriber Airhood
• Radio’s link “system gain”varied from baseline –30 dB to +40 dB
• Compare coverageprobabilities
12 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
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-30 -20 -10 0 10 20 30 40Link Improvement in dB
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PMP + 6dB fade margin
50-device mesh
50-device mesh + 4 seeds
Solving CoverageSystem Gain Benefit of Routed Mesh
~40 dB higher system gain required for PMP at 90%
coverage target
13 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Wireless Mesh NetworksInherent Cost Advantages
• Minimal spectrum costs• Unlicensed bands growing globally
• Minimal infrastructure costs• Incremental deployment reduces upfront
investments
• Low-cost subscriber equipment• Standards-based equipment
• Simple, low-cost installation• Adding subscribers increases coverage &
robustness• Omnidirectional antennas simplify installation,
maintenance and reconfiguration
14 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Wireless Mesh RouterInherently Low-cost Architecture
Standard, low-cost PHYE.g., outdoor-enhanced 802.11x PHY Layer
802.16a Mesh ModeDraft standard MAC Layer
Standard IPw/ wireless-aware extensions Routing Layer
15 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
High-Quality, Broadband Servicewith Wireless Mesh Networks
Common questions:• What happens to user throughput over multiple wireless hops?• How can such a system provide high-quality service?
16 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
• Two-hop path?
Simple example:• Minimally-compliant 802.11a radios• Free-space path loss and common noise environment
Which gives higher user throughput?• Direct path, or
Subscriber ThroughputOver Multiple-hop Paths
AirHeadIntermediateDevice
Subscriber
17 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Subscriber ThroughputOver Multiple-hop Paths
Mesh routers adapt waveform on per-link basis• If direct link supports 6 Mbps waveform, then• Shorter links will use 18 Mbps due to 6 dB less path loss
6 Mbps over direct path; 9 Mbps over two-hop path!• Multihop benefit even greater in non-free-space environments
and/or when routing around obstacles
AirHead SubscriberIntermediateDevice
18 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
High-Quality Service for Multimedia Traffic
Operator provisioning tools & guidelines• Per-class assurance levels consistent with capacity• Symmetric or asymmetric
Differentiated service (DiffServ) support• Packet classification & regulation at ingress points
Efficient MAC with assured per-hop delays• Class- & precedence-aware per-hop packet treatment• Per-hop latencies assured by 802.16a mesh-mode
Like any other multimedia network, QoS requires support throughout system architecture
19 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Scaling Issues for PMP Networks
Inherently difficult signal-to-interference relationship• Base station is exposed to other base stations and all area noise• E.g., ~1/r2 for base station interference versus ~1/r4 for signal
Requires various mechanisms to overcome:FDD or synchronized TDD Directional subscriber antennasMore expensive RF More careful deployment planning
20 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Scaling Advantage for Wireless Mesh
Inherently favorable signal-to-interference relation• Best links actively selected by network; interference blocked by clutter • E.g., ~1/r3 for interference versus ~1/r2.5 for signal
Permits “natural” scaling to large, dense networks• With adaptive power control & neighbor selection• Also enables reliable use of unlicensed frequencies
21 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Scaling Wireless Mesh Networks
Model parameters:• PHY = minimally-compliant 802.11a
Limit to 6 to 36 Mbps rates to maintain required SNR• MAC = Draft 802.16a Mesh Mode
Use 65% subscriber-traffic efficiency• Log-Normal path loss model
Exponent n=3, standard dev. σ=10 dB• 20:1 statistical multiplexing
For provisioned subscriber rates
22 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Data Rates of Active Mesh LinksVersus increasing market penetration
Fixed,100 subscribers per Airhood
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(Region with 500 homes per sq-km)
Dat
a ra
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of a
ctiv
e lin
ks
6-9 Mbps12-18 Mbps24-36 Mbps
23 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Mesh CapacityVersus increasing market penetration
Provisionablesubscriber rate is1-2 Mbps at 10%
penetration(for 100- & 50-sub AirHoods, resp.)
Increasing with subscriber density
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Provisionable Mbps per sub (100-node Airhoods)Provisionable Mbps per sub (50-node Airhoods)Nominal subscriber capacity per sq-km (50-node Airhoods)
24 © NOKIA National Wireless Engineering Conference / Nov 2002 / D.Beyer
Wireless Mesh NetworksFor Residential Broadband
• Low CostMesh routers can combine low-cost radios with smart mesh softwareAllow for incremental deployment & use of unlicensed bands
• Robust Coverage50-device mesh has ~40 dB link gain advantage over PMPAlternate paths ensure robustness, reducing need for high link margins
• Broadband ServiceMultiple mesh hops typically increases effective subscriber capacity802.16a Mesh Mode scheduling ensures per-hop latencies
• Natural ScalingInherently favorable signal-to-interference characteristicsIncreasing subscriber density increases overall network capacity