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REFERENCE

TMWi-FiSERIES

802.11n Principles Demystified

Client Shipments Relative Rate and RangeImproved MAC Throughput

802.11a/b/g Interoperability

Data Rates

Standardization Timeline

MIMO Signal Processing

Glossary

Channel Bonding

Spatial Multiplexing

M

Rx 1

Rx 2

Rx M

MTransmitter

Data Stream Data StreamReceiver

Tx 1

Tx 2

Tx N

Spatial Multiplexing transmits completely separate data streams on different antennas (in the same channel) that are recombined to produce new 802.11n data rates. Higher data rates are achieved by splitting the original data stream into separate data streams. Each separate stream is transmitted on a different antenna (in the same channel). MIMO signal processing at the receiver can detect and recover each stream. Streams are then recombined which yielding higher data rates.

Source: Dell’Oro Group 11/06

(Mill

ions

)

2005 2006

100

50

02007 2008 2009

802.11a/b/g802.11a/b/g/n

New Applications

Range

Capa

city

Enabling New Applications

WirelessHDTV

WirelessBackup

CAD, DesignGraphics

ApplicationsOn-Demand

Training

EmployeeVideo

Conferencing

WirelessSDTV

VideoOn Demand Gaming

RemoteLearning

RemoteVideo

Surveillance

InternetAccess E-mail

Voice overWi-Fi

Point of Sale+ Scanners Hot Spots

802.11n

Data

Rat

e

Range

802.11a/g

802.11b

MIMO (Multiple In Multiple Out) Signal Processing uses multiple antennas and takes advantage of multipath reflections to improve signal coherence that greatly increases receiver sensitivity. This extra sensitivity can be used for greater range or highter data rates.

The newly enhanced signal is the processed sum of individual antennas. Signal Processing eliminates nulls and fading that any one antenna would see. MIMO Signal Processing is sophisticated enough to discern multiple spatial streams (see Spatial Multiplexing).

MIMO Digital Signal Processing

Frequency Across Subcarriers

Attenuation

Antenna 1 Signal

MIMO Processed Signal

Antenna 2 Signal

Antenna 3 Signal

Receiver

802.11n—A yet to be released IEEE Standard for wireless networking that has as target of at least 100Mbps of throughput.

Channel Bonding—Using two adjacent channels together asone to increase data rates.

Green Field Mode—Eliminates support for 802.11a/b/g devices when only 802.11n devices are present.

MIMO (Multiple In, Multiple Out)—Signal processing that improves both range and rate by receiving and transmitting signals on multiple antennas.

MIMO Power Save Mode—Conserves power consumption by making use of multiple antennas (and radios) only when needed.

Spatial Multiplexing—Transmitting two or more separate data streams on different antennas at the same time in the same channel to increase data rate, requires 11n adapters on both sides of the link.

Wi-Fi Alliance—Organization that certifies 802.11a/b/g/n products for interoperability.

As of December 2006

Profiles and Final Certification

Initial Draft and Letter

Ballot

20062003 2004 2005 2007 2008

CommentResolution

UnPlug Fests

Baseline Certification

Proposals and

Down Selection

Joint ProposalDraft Spec’s Confirmed

First SponsorBallot

SecondLetterBallot

Final Working Group Approval

RevCom Approval

Q2 Q3Q1Q4Q3Q2Q1Q4Q3Q2Q1

TGnFormed

IEEE Publishes the Final

Specification

Wi-Fi Alliance Estimated Timeline

IEEE Estimated Timeline

Note: Wi-Fi Alliance 802.11n Certification will require devices to support two spatial streams and channel bonding.

N

ACK Frame

N

Data Frame

2

Data Frame

PHY Header

MAC Header

Data Frame Payload

ACK Frame Payload

Frame Aggregation MAC data frames are combined and given a single PHY header Implicit Block ACK acknowledges all data frames within aggregate New 802.11n modes are 40% more efficient than legacy modes.

Legacy Operation

High Throughput Operation

Data Frame

• • •

• • • • • •

1

Data Frame Block ACK Frame

1 12 2N N

ACK Frame

1 2

ACK Frame

N N

Data Frame

SIFS

SIFS

SIFS

RIFS RIFS

Legacy Operation

High Throughput Operation

Data Frame ACK Frame

• • •

• • •• • •

1

1 2

Data Frame Data Frame Data Frame

Block ACKRequestFrame

Block ACKResponse

Frame

1 2 N

1 2 2

2

Data Frame ACK Frame

N

ACK Frame

RIFS Usage (Reduced Inter-Frame Spacing)

Legacy Only

High Throughput withLegacy Protection

Derive CCADuration fromLength & Rate

Derive CCADuration fromLength & Rate

CCA Duration = (Legacy Length/Legacy Rate)

Legacy Training Fields Legacy Signal Field HT Signal Field HT Training Fields HT PSDU

Legacy Training Fields Legacy Signal Field Legacy PSDU

When an HT frame is transmitted in Mixed Mode, the L-SIG field provides rate and length values for the transmitted packet.The L-SIG rate and length values are used by a legacy STA Station to set the CCA.The L-SIG rate is set to 6Mbps and the length is spoofed to cover the remainder of the packet.

The L-SIG field (Legacy Signal Field) sets the Clear Channel Assessment (CCA) on legacy devices so they do not attempt to transmit during a HT (High Throughput) frame transmission.

PHY Level Spoofing (Protects Legacy Devices)

CCA Duration = (Legacy Length/Legacy Rate)

Ch# Ch# 40MHz Channel AllocationExample Channels that can be Bonded

FrequencyChannel 1 Channel 2 f, (MHz) U.S. EU

36 40 5190 X

44 48 5230 X

52 56 5270 X

60 64 5310 X

100 104 5510 X

108 112 5550 X

116 120 5590 X

124 128 5630 X

132 136 5670 X

149 153 5755 X

157 161 5795 X

40MHz channels are specified by two fields as (Nprimary_ch, Secondary) where the first field represents the primary channel number and the second field indicating whether the secondary channel is above (1) or below (-1) the primary channel. Channel Bonding won’t increase aggregate capacity and can make channel planning more difficult.

40

20 MHz 20 MHz

36

40 MHz

(40, -1)

Standard 802.11 channels are effectively 20MHz wide.

Channel bonding combines two adjacent 20MHz channels into a single 40MHz channel providing increased throughput.

Wi-Fi Certified Data Rates and Channels

802.11b

11Mbps

3 3 312 12

54Mbps 54Mbps 130Mbps 130Mbps

33Mbps 162Mbps 648Mbps 390Mbps 1560Mbps

802.11g 802.11a 802.11n (2.4GHz) 802.11n (5GHz)

Wi-Fi Cert.Data Rates

Channels

CapacityPer Cell

Expected First Generation Device Data Rates Expected Second Generation Device Data Rates

OptionallyMultiply By 2.077

to BondTwo 20MHzChannels

OptionallyMultiply by 1.11 for

Shorter Guard Interval to Increase Symbol Rate

Note: Wi-Fi Alliance 802.11n Certifica-tion will require devices to support two spatial streams and channel bonding.

OptionallyMultiply by 2, 3, 4for the Number of

Additional Spatial Streams

Choose New Base Encoding + Modulation

BPSK (6.5)QPSK (13, 19.5)QAM-16 (26, 39)

QAM-64 (58.5, 65)

New 11nData Rate

Obtaining 802.11n Data Rates

x x x =

Expected 802.11n Data Rates

802.11a 802.11gRates

69

121824364854

11n Mandatory Data Rates

6.513

19.5263952

58.565

With ChannelBonding (40MHz)

13.527

40.55481

108121.5135

With ShortGuard Interval

1530456090

120135150

Two SpatialStreams

1326395278

104117130

With ChannelBonding (40MHz)

275481

108162216243270

With ShortGuard Interval

306090

120180240270300

Three SpatialStreams

19.539

58.578

117156

175.5195

With ChannelBonding (40MHz)

40.581

121.5162243324

364.5405

With ShortGuard Interval

4590

135180270360405450

Four SpatialStreams

265278

104156208234260

With ChannelBonding (40MHz)

54108162216324432486540

With ShortGuard Interval

60120180240360480540600

One Spatial Stream Two Spatial Streams Three Spatial Streams Four Spatial Streams