802.11n: Next-Generation Wireless LAN Technology

802.11n: Next-Generation Wireless LANTechnology

Wireless Technology

Wireless Communication Standards

WPANIEEE 802.15

WLANIEEE 802.11

ESTIHyperLAN

WMANIEEE 802.16

ESTIHyperMAN

WWAN3GPP/4G

IEEE 802.20

Range

0 - 10M 0 - 100M 0 – 10KM

Wireless Communication Standards

Source: International Telecommunications Union and WiMAX Forum

802.20

Fixed(Stationary)

Pedestrian(Nomadic)

Mobile(Vehicular)

2G/2.5GCellular

0.1 1.0 10 100

Peak Data Rate per User (Mbits/second)

Mo

bil

ity

802.16e

Commercial

Proposed

802.16a(WiMAX)

79 x 1 MHz79 x 1 MHzBluetoothBluetooth

> 100> 100UWBUWB

2020802.16802.16

55HSDPAHSDPA

1.251.251xEV-DO, 1xEV-DO, 1xEVDV,1xEVDV,802.20802.20

1.251.252G/2.5G2G/2.5G

BandwidthBandwidth(MHz)(MHz)

Bandwidth Assumptions

WWAN(IMT-2000)

cdma2000® 1xEV-DO,cdma2000® 1xEV-DV

3.1

WCDMA HSDPA

802.15.1(Bluetooth)

802.11(WLAN

)

802.15.3a(UWB)

802.11 WLAN Technology

Current 802.11 Standards (I) 802.11(1997, 1999, 802.11(1997, 1999, 20072007))

System architectureSystem architecture CSMA/CA MAC protocolCSMA/CA MAC protocol 802.11 PHY802.11 PHY

802.11a(1999)802.11a(1999) Spread Spectrum in 5GHz bandSpread Spectrum in 5GHz band

802.11b(1999)802.11b(1999) Spread Spectrum in 2.5GHz bandSpread Spectrum in 2.5GHz band

802.11g(2003)802.11g(2003) To develop a new PHY extension to enhance the performance To develop a new PHY extension to enhance the performance

and the possible applications of the 802.11b compatible for and the possible applications of the 802.11b compatible for improve access the data rate achievable by such device.improve access the data rate achievable by such device.

802.11d(2001)802.11d(2001) Specification for operation in additional regulatory domains.Specification for operation in additional regulatory domains.

Current 802.11 Standards (II) 802.11e(2005)802.11e(2005)

To enhance the 802.11 MAC to improve and manage QoS.To enhance the 802.11 MAC to improve and manage QoS. 802.11F(2003)802.11F(2003)

IAPP (Inter-Access Point Protocol)IAPP (Inter-Access Point Protocol) Recommended practice for multi-vendor access point interoperability Recommended practice for multi-vendor access point interoperability

via an Inter-Access Point Protocol across distribution system via an Inter-Access Point Protocol across distribution system supporting IEEE 802.11 operation.supporting IEEE 802.11 operation.

802.11h802.11h To enhance the current 802.11 MAC and 802.11a PHY with network To enhance the current 802.11 MAC and 802.11a PHY with network

management and control extensions for spectrum and transmit management and control extensions for spectrum and transmit power in 5GHz license.power in 5GHz license.

802.11i(2004)802.11i(2004) To enhance the 802.11 MAC to improve security and authentication To enhance the 802.11 MAC to improve security and authentication

mechanism.mechanism. 802.11j(2004)802.11j(2004)

4.9 GHz-5 GHz Operation in Japan4.9 GHz-5 GHz Operation in Japan

Other 802.11 Unapproved Drafts

802.11n(Feb. 2007)802.11n(Feb. 2007) Draft 2.0Draft 2.0 Enhancements for Higher Throughput (108-320 Mbps)Enhancements for Higher Throughput (108-320 Mbps)

802.11n/D3802.11n/D3 Active unapproved draftActive unapproved draft

802.11r/D7802.11r/D7(July 2007)(July 2007) Archived Unapproved DraftArchived Unapproved Draft Fast BSS TransitionFast BSS Transition

802.11y/D5.0802.11y/D5.0 Active Unapproved DraftActive Unapproved Draft 3650-3700 MHz Operation in USA3650-3700 MHz Operation in USA

802.11n

10 Things You Should Know About 802.11n

Wi-Fi Alliance Wi-Fi Alliance In summer 2007, the Wi-Fi Alliance started certifying In summer 2007, the Wi-Fi Alliance started certifying

devices for compliance with Version 2.0 of the devices for compliance with Version 2.0 of the 802.11n draft specification802.11n draft specification

essentially giving vendors (and customers) the go-ahead to essentially giving vendors (and customers) the go-ahead to start actively selling, or at least investigating, the technology.start actively selling, or at least investigating, the technology.

To ensure the best levels of compatibility among 802.11n To ensure the best levels of compatibility among 802.11n APs and clients, make sure to upgrade to firmware and APs and clients, make sure to upgrade to firmware and drivers that are Wi-Fi-certified for 802.11 Draft 2.0, if drivers that are Wi-Fi-certified for 802.11 Draft 2.0, if available. available.


MIMOMIMO A key component of 802.11n, MIMO (multiple input, A key component of 802.11n, MIMO (multiple input,

multiple output) uses spatial multiplexing to multiple output) uses spatial multiplexing to simultaneously transmit different chains of information simultaneously transmit different chains of information at the same time on the same channel, leveraging at the same time on the same channel, leveraging multipath reflection to make sure everything gets to its multipath reflection to make sure everything gets to its destination without interference or dropouts.destination without interference or dropouts.

These simultaneous transmissions are the key These simultaneous transmissions are the key ingredient of 802.11n's higher throughput. ingredient of 802.11n's higher throughput.


Antennas Antennas The most common antenna configurations currently The most common antenna configurations currently

are either are either three by threethree by three or or two by threetwo by three transmit/receive chains, but 802.11n will have plenty transmit/receive chains, but 802.11n will have plenty more options over time.more options over time.

Vendors will explore both the Vendors will explore both the low end (single low end (single transmit/dual receive)transmit/dual receive) for the budget-conscious and for the budget-conscious and the the high end (four by four)high end (four by four) for those in need of serious for those in need of serious bandwidth.bandwidth.

The marketing could get pretty confusing here, so The marketing could get pretty confusing here, so buyers should be aware that fewer transmit chains will buyers should be aware that fewer transmit chains will equal less bandwidth – don't expect 100 Mbps from a equal less bandwidth – don't expect 100 Mbps from a device with a single transmitting antenna. device with a single transmitting antenna.


Dual-Band Dual-Band 802.11n can operate in either the 2.4GHz or 802.11n can operate in either the 2.4GHz or

5GHz band5GHz bandconferring more conferring more deployment flexibilitydeployment flexibility by allowing by allowing

implementers to get away from common sources implementers to get away from common sources of interference.of interference.

IT buyers should be aware that almost all 802.11n IT buyers should be aware that almost all 802.11n clients based on CardBus or ExpressCard operate clients based on CardBus or ExpressCard operate only in the 2.4GHz band at this time, but several only in the 2.4GHz band at this time, but several embedded or mini-PCI adapters currently work in embedded or mini-PCI adapters currently work in either band. either band.


40MHz Channels 40MHz Channels 802.11n can operate using the standard 20MHz 802.11n can operate using the standard 20MHz

channels or with wide 40MHz channels that confer channels or with wide 40MHz channels that confer higher top-end throughput.higher top-end throughput.

Draft 2.0 of the specification recommends that 40MHz Draft 2.0 of the specification recommends that 40MHz channels only be used in the 5GHz band – but many channels only be used in the 5GHz band – but many implementations will allow customers to manually implementations will allow customers to manually configure configure 40MHz channels in the 2.4GHz band40MHz channels in the 2.4GHz band as as well. well.


Power over Ethernet Power over Ethernet The current POE standard, 802.3af, may not supply The current POE standard, 802.3af, may not supply

enough juice to power access points with 3x3 or enough juice to power access points with 3x3 or greater antenna configurations.greater antenna configurations.

A new POE standard, A new POE standard, 802.3at802.3at, is in the works, but in , is in the works, but in the meantime administrators may need to get creative the meantime administrators may need to get creative with the number of antennas, the number of devices with the number of antennas, the number of devices per POE switch or some kind of midline, nonstandard per POE switch or some kind of midline, nonstandard injection. injection.


Network Drop Network Drop With possible top-end wireless throughput in excess With possible top-end wireless throughput in excess

of 100M bps, wireless implementers need to look at of 100M bps, wireless implementers need to look at upgrading the access point'supgrading the access point's wired network wired network connection to Gigabit Ethernetconnection to Gigabit Ethernet..

Although this is probably not necessary immediately, Although this is probably not necessary immediately, growing usage of the wireless network will demand growing usage of the wireless network will demand this step over time to minimize traffic bottlenecks. this step over time to minimize traffic bottlenecks.


Network Aggregation Network Aggregation With each access point's wireless link capable of With each access point's wireless link capable of

pushing over 100 Mbps and a new Gigabit Ethernet pushing over 100 Mbps and a new Gigabit Ethernet infrastructure, the traffic bottleneck may move to the infrastructure, the traffic bottleneck may move to the wireless controllerwireless controller..

Wireless switches that perform traffic decryption or Wireless switches that perform traffic decryption or are otherwise in the middle of the data plane may not are otherwise in the middle of the data plane may not be able to handle as many access points as before. be able to handle as many access points as before.


Backward-Compatibility Backward-Compatibility 802.11n is designed to be 802.11n is designed to be backward-compatiblebackward-compatible with with

both 802.11b/g in the 2.4GHz band and 802.11a in both 802.11b/g in the 2.4GHz band and 802.11a in the 5GHz band.the 5GHz band.

For a long time to come, the majority of wireless For a long time to come, the majority of wireless clients on an 802.11n network will be legacy devices, clients on an 802.11n network will be legacy devices, so administrators must continue to plan WLAN so administrators must continue to plan WLAN

deployment to support these devices.deployment to support these devices.


Wi-Fi Cell ShapeWi-Fi Cell Shape While the traditional wireless LAN cell shape is While the traditional wireless LAN cell shape is

roughly spherical (sans obstructions), MIMO and roughly spherical (sans obstructions), MIMO and spatial multiplexing will make 802.11n "cells" spiky spatial multiplexing will make 802.11n "cells" spiky and less predictable depending on environmental and less predictable depending on environmental factors. factors. This may render traditional site survey This may render traditional site survey planning tools obsoleteplanning tools obsolete – or at least less effective. – or at least less effective.

Key Features

Primary IEEE 802.11 Specifications

Major Components of Draft 802.11n (I)

FeatureFeature DefinitionDefinition Specification StatusSpecification Status

Better OFDMBetter OFDM Supports wider bandwidth & higher Supports wider bandwidth & higher code rate to bring maximum data rate code rate to bring maximum data rate to 65 Mbpsto 65 Mbps

MandatoryMandatory

Space-Division Space-Division MultiplexingMultiplexing

Improves performance by parsing Improves performance by parsing data into multiple streams transmitted data into multiple streams transmitted through multiple antennasthrough multiple antennas

Optional for up to four Optional for up to four spatial streamsspatial streams

DiversityDiversity Exploits the existence of multiple Exploits the existence of multiple antennas to improve range and antennas to improve range and reliability. Typically employed when reliability. Typically employed when the number of antennas on the the number of antennas on the receiving end is higher than the receiving end is higher than the number of streams being transmitted.number of streams being transmitted.

Optional for up to four Optional for up to four antennasantennas

MIMO Power MIMO Power SaveSave

Limits power consumption penalty of Limits power consumption penalty of MIMO by utilizing multiple antennas MIMO by utilizing multiple antennas only on as-needed basisonly on as-needed basis

RequiredRequired

Major Components of Draft 802.11n (II)

FeatureFeature DefinitionDefinition Specification StatusSpecification Status

40 MHz 40 MHz ChannelsChannels

Effectively doubles data rates by Effectively doubles data rates by doubling channel width from 20 MHz doubling channel width from 20 MHz to 40 MHzto 40 MHz

OptionalOptional

AggregationAggregation Improves efficiency by allowing Improves efficiency by allowing transmission bursts of multiple data transmission bursts of multiple data packets between overhead packets between overhead communicationcommunication

RequiredRequired

Reduced Inter-Reduced Inter-frame Spacing frame Spacing (RIFS)(RIFS)

One of several draft-n features One of several draft-n features designed to improve efficiency. designed to improve efficiency. Provides a shorter delay between Provides a shorter delay between OFDM transmissions than in 802.11a OFDM transmissions than in 802.11a or g.or g.

RequiredRequired

Greenfield Greenfield ModeMode

Improves efficiency by eliminating Improves efficiency by eliminating support for 802.11a/b/g devices in an support for 802.11a/b/g devices in an all draft-n networkall draft-n network

Currently optionalCurrently optional

Better OFDM

In the 802.11n draft, the first requirement is to In the 802.11n draft, the first requirement is to support an OFDM implementation that improves support an OFDM implementation that improves upon the one employed in the 802.11a/g upon the one employed in the 802.11a/g standards, using a higher maximum code rate standards, using a higher maximum code rate and slightly wider bandwidth. This change and slightly wider bandwidth. This change improves the highest attainable raw data rate to improves the highest attainable raw data rate to 65 Mbps from 54 Mbps in the existing standards.65 Mbps from 54 Mbps in the existing standards.

MIMO Improves Performance MIMO – Multiple Input Multiple OutputMIMO – Multiple Input Multiple Output

exploits a radio-wave phenomenon called multipath: transmitted exploits a radio-wave phenomenon called multipath: transmitted information bounces off walls, doors, and other objects, reaching information bounces off walls, doors, and other objects, reaching the receiving antenna multiple times via different routes and at the receiving antenna multiple times via different routes and at slightly different times.slightly different times.

Uncontrolled, multipath distorts the original signal, making it Uncontrolled, multipath distorts the original signal, making it more difficult to decipher and degrading Wi-Fi performance.more difficult to decipher and degrading Wi-Fi performance.

MIMO harnesses multipath with a technique known as space-MIMO harnesses multipath with a technique known as space-division multiplexing. The transmitting WLAN device actually division multiplexing. The transmitting WLAN device actually splits a data stream into multiple parts, called spatial streams, splits a data stream into multiple parts, called spatial streams, and transmits each spatial stream through separate antennas to and transmits each spatial stream through separate antennas to corresponding antennas on the receiving end.corresponding antennas on the receiving end.

The current 802.11n draft provides for up to four spatial streams, The current 802.11n draft provides for up to four spatial streams, even though compliant hardware is not required to support that even though compliant hardware is not required to support that many.many.

MIMO Power Save Mode Doubling the number of spatial streams from one Doubling the number of spatial streams from one

to two effectively doubles the raw data rate. to two effectively doubles the raw data rate. There are trade-offs, however, such as There are trade-offs, however, such as

increased power consumption and, to a lesser increased power consumption and, to a lesser extent, cost.extent, cost.

The draft-n specification includes a MIMO The draft-n specification includes a MIMO power-save mode, which mitigates power power-save mode, which mitigates power consumption by using multiple paths only when consumption by using multiple paths only when communication would benefit from the additional communication would benefit from the additional performance.performance.

The MIMO power-save mode is a required The MIMO power-save mode is a required feature in the draft-n specification.feature in the draft-n specification.

MIMO Enhancements There are two features in the draft-n specification that There are two features in the draft-n specification that

focus on improving MIMO performance, called focus on improving MIMO performance, called beam-forming and and diversity..

Beam-formingBeam-forming a technique that focuses radio signals directly on the target a technique that focuses radio signals directly on the target

antenna, thereby improving range and performance by limiting antenna, thereby improving range and performance by limiting interference.interference.

DiversityDiversity exploits multiple antennas by combining the outputs of or exploits multiple antennas by combining the outputs of or

selecting the best subset of a larger number of antennas than selecting the best subset of a larger number of antennas than required to receive a number of spatial streams.required to receive a number of spatial streams.

This is important because the draft-n specification supports up to This is important because the draft-n specification supports up to four antennas, so devices will probably encounter others built four antennas, so devices will probably encounter others built with a different number of antennas.with a different number of antennas.

Diversity With diversity, surplus antennas are put to good use. With diversity, surplus antennas are put to good use.

The device with more antennas uses the extra ones to The device with more antennas uses the extra ones to operate at longer range.operate at longer range. For example, the outputs of two antennas may be combined to For example, the outputs of two antennas may be combined to

receive one spatial stream to achieve a longer link range.receive one spatial stream to achieve a longer link range. The concept may be extended to combine the outputs of three The concept may be extended to combine the outputs of three

antennas to receive two spatial streams for higher data rate and antennas to receive two spatial streams for higher data rate and range and so on.range and so on.

Diversity is not restricted to 802.11n or even WLAN.Diversity is not restricted to 802.11n or even WLAN. It can be used to improve any type of radio communication.It can be used to improve any type of radio communication.

In fact, diversity has typically been implemented in some In fact, diversity has typically been implemented in some existing 802.11a, 802.11b, and 802.11g hardware existing 802.11a, 802.11b, and 802.11g hardware through selection of the best of two antennas.through selection of the best of two antennas.

Improved Throughput and Higher Data Rates (I)

Another optional mode in the 802.11n draft effectively Another optional mode in the 802.11n draft effectively doubles data rates by doubling the width of a WLAN doubles data rates by doubling the width of a WLAN communications channel from 20 MHz to 40 MHz.communications channel from 20 MHz to 40 MHz.

The primary trade-off here is fewer channels available The primary trade-off here is fewer channels available for other devices.for other devices. In the case of the 2.4-GHz band, there is enough room for three In the case of the 2.4-GHz band, there is enough room for three

non-overlapping 20-MHz channels.non-overlapping 20-MHz channels. Needless to say, a 40-MHz channel does not leave much room Needless to say, a 40-MHz channel does not leave much room

for other devices to join the network or transmit in the same for other devices to join the network or transmit in the same airspace.airspace.

This means intelligent, dynamic management is critical to This means intelligent, dynamic management is critical to ensuring that the 40-MHz channel option improves ensuring that the 40-MHz channel option improves overall WLAN performance by balancing the high-overall WLAN performance by balancing the high-bandwidth demands of some clients with the needs of bandwidth demands of some clients with the needs of other clients to remain connected to the network.other clients to remain connected to the network.

Improved Throughput and Higher Data Rates (II)

Other optional features that draft-n hardware may Other optional features that draft-n hardware may support, for example, include:support, for example, include: high throughput duplicate modehigh throughput duplicate mode

which helps extend the network's range.which helps extend the network's range. short guard intervalshort guard interval

which improves efficiency by further limiting overhead.which improves efficiency by further limiting overhead. With all the optional modes and back-off alternatives, the With all the optional modes and back-off alternatives, the

array of possible combinations of features and array of possible combinations of features and corresponding data rates can be overwhelming.corresponding data rates can be overwhelming. To be precise, the current 802.11n draft provides for 576 To be precise, the current 802.11n draft provides for 576

possible data rate configurations.possible data rate configurations.

Aggregation (I)

One of the most important features in the draft-n One of the most important features in the draft-n specification to improve mixed-mode specification to improve mixed-mode performance is aggregation.performance is aggregation. Rather than sending a single data frame, the Rather than sending a single data frame, the

transmitting client bundles several frames together.transmitting client bundles several frames together. Rather than sending a single data frame, the Rather than sending a single data frame, the

transmitting client bundles several frames together.transmitting client bundles several frames together. Thus, aggregation improves efficiency by restoring Thus, aggregation improves efficiency by restoring

the percentage of time that data is being transmitted the percentage of time that data is being transmitted over the network.over the network.

Aggregation (II)

RIFS It is much easier for draft-n devices to coexist with It is much easier for draft-n devices to coexist with

802.11g and 802.11a hardware because they all use 802.11g and 802.11a hardware because they all use OFDM.OFDM.

Even so, there are features in the specification that Even so, there are features in the specification that increase efficiency in OFDM-only networks. One such increase efficiency in OFDM-only networks. One such feature is Reduced Inter- Frame Spacing, or RIFS, which feature is Reduced Inter- Frame Spacing, or RIFS, which shortens the delay between transmissions.shortens the delay between transmissions.

Greenfield mode

For the best possible performance, the draft-n For the best possible performance, the draft-n specification provides for what is called greenfield mode, specification provides for what is called greenfield mode, in which the network can be set to ignore all earlier in which the network can be set to ignore all earlier standards.standards. It is not clear at this stage whether greenfield mode will be a It is not clear at this stage whether greenfield mode will be a

mandatory or an optional feature in the final 802.11n draft, but it mandatory or an optional feature in the final 802.11n draft, but it is likely to be an option.is likely to be an option.

Power Save

Battery-powered WLAN hardware will continue to be built Battery-powered WLAN hardware will continue to be built around 802.11g and even 802.11b for some time.around 802.11g and even 802.11b for some time.

Despite the improved efficiency built into the draft-n Despite the improved efficiency built into the draft-n specification, however, it is difficult to eliminate all of the specification, however, it is difficult to eliminate all of the obstacles of 802.11b. This means that consumers obstacles of 802.11b. This means that consumers looking for the best possible network performance may looking for the best possible network performance may want to consider replacing 802.11b WLAN hardware on want to consider replacing 802.11b WLAN hardware on their networks.their networks.

Time (Best Case) to Transfer 30-Minute HD Video

Considerations for Choosing Draft-n WLAN Hardware

Documents

802.11n: Next-Generation Wireless LAN Technology