Fixed WirelessBroadband Access:

Technologies and Standards

Ender Ayanoglu

ISART, Denver, CO9/8/2000

The Broadband Internet Revolution

Video TelephonyVideo Telephony

DataData

TelephonyTelephony

Digital TelevisionDigital Television

GamesGames

DataData

InternetInternetDrivenDriven

EntertainmentEntertainment

What are the BroadbandAccess Choices for the Future?

DSLgood coveragedistance destroys

bandwidthupstream bandwidth

an issueinfrastructure upgrades

Cablecoverage is limited to

residencebuild-out still requiredupstream bandwidth is

limited

Wirelessreachsymmetric bandwidthhigher upstream data

ratesspeed of provisioning

Hub

Broadband WirelessVision Into Reality

PBXEnterpriseCampus

KTSService ProviderFiber Backend

ILEC/CLEC/IXC

Medium Business

Small Business

SOHO/Residential

Enterprise Campus

Point-to-pointWireless Links

Point-to-multi-pointWireless Links

Broadband WirelessAccess Layer System Needs

• 5 Mb/s to 20 Mb/s shared BW for consumers andbusiness

• QoS managed, multiservice, bandwidth-on-demand MAC(Service Level Agreements)

• Standard, proven MAC• High spectral efficiency and frequency re-use capacity• Robust and simple to deploy

• multipath tolerance & automated provisioning

• Low cost• 3-20 mile range• Easily ported to any frequency band

…

…

SubscriberBaseStation

Paths

Multipath Wireless Communication

• Wireless communication involvesmultipath transmission

• Each path has an associated delay whichcauses intersymbol interference (ISI)

• Conventional wireless approaches exhibitdegraded performance

• Other approaches designed to mitigate theeffects of multipath:

– Equalization– Direct sequence spreading– Adaptive space-time coding solutions

Effects of Multipath

• Spatial diversity– Standing-wave pattern

between one transmit-receiveantenna pair

• Time-variation– Motion in environment alters

each standing-wave pattern– Motion in environment

creates time-varyingfrequency response

Broadband WirelessAccess Alternatives

• CDMA (Space-Time CDMA)• SCQAM (ST DFE)• OFDM (MIMO [Vector] OFDM)• Recent Enabling Factors

– Systems on a chip complexity– New practical spatial processing techniques

Broadband WirelessAccess Alternatives

• Not enough BW to offer broadband access withCDMA. High-speed CDMA is inefficient.

• SCQAM is not as robust, has lower spectralefficiency and is more expensive to make work

• Vector OFDM (VOFDM) has a very large linkmargin advantage and can be rigorously shown tobe more cost effective than Space Time DFEs.

OFDM Concept

• OFDM decomposes ISI channel into many ISI-freenarrowband channels for any time-limited channel.

• Exploits frequency diversity rather than inverting channel.• BER performance improves with channel ISI (delay

spread).

Sub

chan

nel A

mpl

itude

s

Subchannel Frequency Index

OFDM Channel Decomposition

OFDM

• OFDM is composed of cyclic prefix and FFT operations• Data at one frequency received independent of other data

ChannelRemoveCyclicPrefix

FFTAdd

CyclicPrefix

IFFT

Upstream 64-QAM CER1/2 µs Rayleigh Channel

18 20 22 24 26 28 30 32 34 3610

-4

10-3

10-2

10-1

100 64QAM Rayleigh Channel Performance

CE

R

SNR(dB)

QAM CER QAM Dual CER OFDM CER OFDM Dual CER

Downstream 64-QAM CERRicean Channel

20 22 24 26 28 30 32 34 36 38 4010 -4

10 -3

10 -2

10 -1

100

SNR (dB)

CE

RDownstream, 6MHz, 64 QAM, Rin=2/3, Channel: AT&T Time Var Fading, M

r=1

QAM, 0 Hz

QAM, 2 Hz

OFDM, 0 Hz OFDM, 2 Hz

14

Better Performance withLower Complexity

• For high sampling rates, computational complexity is lower thanconventional space-time equalization structures

• Above example assumes: 2 µs delay spread, 16QAM, 20 µs OFDM burstlength

0 5 10 15 20 25 30 35 400

200

400

600

800

1000

1200

1400

1600Computational Complexity (CMAC per second) versus data rate

Data rate (Mbits/sec)M

ega-

CM

AC

per

sec

ond

DFEOFDM

0 5 10 15 20 25 30 35 400

20

40

60

80

100

120

140

160Computational Complexity (CMAC per symbol) versus data rate

Data rate (Mbits/sec)

CM

AC

per

sym

bol

DFEOFDM

OFDM Advantages• Upstream processing

– Robust burst-mode demodulation possible, even insevere delay spread environments

– Higher spectral efficiency possible– Solves the upstream problem

• Downstream processing– Capable of operating in high delay spread environments– Capable of operating with time-variation– Dual antenna capability at lower complexity

• Interference-limited environments– Very robust to narrow-band interference– Interference cancellation possible with dual antennas

Receiver 1

Receiver 2

Output

Receiver AntennasSpatially Separated

Transmitter

Input

Co

mb

iner

Co

mb

iner

Spatial Diversity

• In the presence of multipath fading, two received signals will haveuncorrelated fading effects due to different path lengths

• Thus, a combined received signal will have a higher SNR that any of theindividual signals

• The greatest processing benefits come from exploitingboth frequency and spatial diversity

Spatial Diversity Advantage

5 10 15 20 25 30 35 40 45

10-3

10-2

10-1

100

SNR

CE

R (

max

sam

ples

: 10

6279

8)

Modem: DS 3MHz, 256/32/180, 16QAM, 2/3 Rate, Flat Fading Ch.

1TX x 1RX2TX x 1RX1TX x 2RX2TX x 2RX

BWIF PHY Standard: Block Diagram

FIR Filtering& Decimation

Synchronization

Cyclic PrefixRemoval and

FFT

ChannelEstimation

AntennaCombining &InterferenceEstimation

SINR MetricCalculation

Decoding &Deinterleaving

RX

• Diversity• Interference cancellation• Soft decoding

• Time synchronization• Frequency locking• Adaptive level control

Encoding &Interleaving

TrainingSymbolInjection

IFFT & CyclicPrefix

FIR Filtering&

Interpolation

TX

BWIF MAC Capabilities

Best effort data

VoIP

IP multicast support

Enhanced security and privacy

QoS guarantees

Virtual Private Networks

DOCSIC 1.1 MAC:

• Fragmentation

• Concatenation

• Payload header suppression

Proven, widely deployed MAC

Service Level Agreements (SLAs):Network and Service Quality Guarantees

Mission Supporting Traffic

Mission Critical Traffic

PublicInternet

Voice TrafficGold Service• Voice• Video-conferencing

Silver Service• ERP Traffic

Bronze Service• Internet Access

Alternative OFDM Technologies

LAN OFDM802.11 & WiLANSimple forms of

OFDMLacks coherent

detectionLacks MIMO

operation andinterferencecancelation

Spectral efficiency islow (PHY & MAC)

Limited MAC & QoS

BWIF OFDMStandards based

productsavailable today

Open standardService being

rolled outSilicon devices

available Jan‘01

Low cost CPEavailable early‘01

WDSL OFDMVery similar to

BWIF OFDMDifferences are

expensive withmarginal benefit

Will be indevelopment for> 2 more years

MIMO OFDMintellectualpropertyproblems

BWIF Members(as of 9/8/2000)

Wireless ReferenceArchitecture

CustomerPremise

Equipment

WirelessModem (WM)

Indoor Unit (IDU)

WM Outdoor Unit (ODU)& Antenna

Wireless AccessTermination System (WATS)

Indoor Unit (IDU)

Operation Support System

Security Server

BackboneNetwork

Wireless Modemto CPE Interface

WM IDU/ODUInterface

Specification

WATS Outdoor Unit (ODU)& Antenna

WATS IDU/ODUInterface

Specification

Wireless AcessTermination

System NetworkSide Interfacee

WAN

Over-The-AirMMDS RF

specification

BWIF Specifications

6

DocumentationOverview

PHY & MACSpecs

WMIDU-ODU

ICD

SubscriberICD

WATSIDU-ODU

ICD

NetworkICD

RadioFrequency

Interface Spec

WM ODUSpec

WATS ODUSpec

OSSI

WM IFModule Spec

WATS IFModule Spec

2

5

7

4

9

8

3

1

11 12 10

SecurityInterfaceControl

DocumentsInteroperability

BWIF Standards Compliant BaseStation and CPE Product Status

Future BWIF Standards EnhancementPossibilities

• More bandwidth (75 Mb/s)• More spectral efficiency modes• Microcell base stations and ultra low cost portable

laptop/PDA implementations• More MIMO transmit and receive diversity options• Narrowband upstream options• Multi-channel MIMO modulation• Layer 1 ARQ• Real-time adaptive modulation and coding• All future enhancements will be customer-driven and

backwards compatible with Revision 1.0 and subsequentspecs