Wireless Mesh Networks for Residential Broadband · Wireless Mesh Networks For Residential Broadband Dave Beyer, Nokia National Wireless Engineering Conference San Diego, ... Wireless

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


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


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


Single “Airhood”A neighborhood

wireless mesh network



Multiple Airhoods with 4-channels

Fed by PTP, PMP, or wired backhaul links


Solving Coverage

PMP Approach:Focus is on RF & Deployment

Blast over & through obstacles

Mesh Approach:Focus is on smart software

Skip around obstacles


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.


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Solving Coverage Simplified Model

Assume obstacles completely dominate coverage• Thus, random term (Xσ ) dominates• Link probability simplifies to a fixed probability: z


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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


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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Solving Coverage Log-Normal RF Environment

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Number of devices in network

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PMPMeshMesh + 4 seed nodes

90% coverage after 8 subscribers using only WLAN-type RF


Solving Coverage System Gain Benefit of Mesh

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Same model, except:• Fixed, 50-subscriber Airhood

• Radio’s link “system gain”varied from baseline –30 dB to +40 dB

• Compare coverageprobabilities


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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


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


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


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?


• 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


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


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


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


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


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


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)

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6-9 Mbps12-18 Mbps24-36 Mbps


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)



• 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

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Wireless Mesh Networks for Residential Broadband · Wireless Mesh Networks For Residential Broadband Dave Beyer, Nokia National Wireless Engineering Conference San Diego, ... Wireless