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
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
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
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