IEEE 802.11n
Encyclopedia
IEEE 802.11n-2009 is an amendment to the IEEE 802.11-2007 wireless network
ing standard to improve network throughput over the two previous standards—802.11a and 802.11g—with a significant increase in the maximum net data rate
from 54 Mbit/s to 600 Mbit/s (slightly higher gross bit rate including for example error-correction codes, and slightly lower maximum throughput
) with the use of four spatial streams at a channel width of 40 MHz.
802.11 is a set of IEEE standards that govern wireless networking transmission methods. They are commonly used today in their 802.11a, 802.11b, 802.11g, and 802.11n versions to provide wireless connectivity in homes and businesses. The enhanced security features of 802.11n is deserving of its own section below detailing security improvements over previous standards.
, IEEE 802.11r-2008, IEEE 802.11y-2008, and IEEE 802.11w-2009, and builds on previous 802.11 standards by adding multiple-input multiple-output (MIMO) and 40 MHz channels to the PHY (physical layer)
, and frame aggregation
to the MAC layer.
MIMO is a technology which uses multiple antennas to coherently resolve more information than possible using a single antenna. One way it provides this is through Spatial Division Multiplexing (SDM). SDM spatially multiplexes multiple independent data streams, transferred simultaneously within one spectral channel of bandwidth. MIMO SDM can significantly increase data throughput as the number of resolved spatial data streams is increased. Each spatial stream requires a discrete antenna at both the transmitter and the receiver. In addition, MIMO technology requires a separate radio frequency chain and analog-to-digital converter for each MIMO antenna which translates to higher implementation costs compared to non-MIMO systems.
Channels operating at 40 MHz are another feature incorporated into 802.11n which doubles the channel width from 20 MHz in previous 802.11 PHYs to transmit data. This allows for a doubling of the PHY data rate over a single 20 MHz channel. It can be enabled in the 5 GHz mode, or within the 2.4 GHz if there is knowledge that it will not interfere with any other 802.11 or non-802.11 (such as Bluetooth) system using those same frequencies.
Coupling MIMO architecture with wider bandwidth channels offers increased physical transfer rate over 802.11a (5 GHz) and 802.11g
(2.4 GHz).
and postcoding techniques, respectively, to achieve the capacity of a MIMO link. Precoding includes spatial beamforming
and spatial coding, where spatial beamforming improves the received signal quality at the decoding stage. Spatial coding can increase data throughput via spatial multiplexing
and increase range by exploiting the spatial diversity, through techniques such as Alamouti coding
.
notation helps identify what a given radio is capable of. The first number (
) is the maximum number of transmit antennas or RF chains that can be used by the radio. The second number (
) is the maximum number of receive antennas or RF chains that can be used by the radio. The third number (
) is the maximum number of data spatial streams the radio can use. For example, a radio that can transmit on two antennas and receive on three, but can only send or receive two data streams would be 
.
The 802.11n draft allows up to
. Common configurations of 11n devices are 
, 
, and 
. All three configurations have the same maximum throughputs and features, and differ only in the amount of diversity the antenna systems provide. In addition, a fourth configuration, 
is becoming common, which has a higher throughput, due to the additional data stream.
Frame aggregation
is a process of packing multiple MSDUs or MPDUs together to reduce the overheads and average them over multiple frames, thus increasing the user level data rate. A-MPDU aggregation requires the use of Block Acknowledgement
or BlockAck, which was introduced in 802.11e and has been optimized in 802.11n
, 802.11b
and 802.11a
. There are MAC and PHY level protection mechanisms as listed below:
Even with protection, large discrepancies can exist between the throughput an 802.11n device can achieve in a greenfield network
, compared to a mixed-mode network, when legacy devices are present. This is an extension of the 802.11b/802.11g coexistence problem.
is fairly congested. With 802.11n, there is the option to double the bandwidth per channel to 40 MHz which results in slightly more than double the data rate. However, when in 2.4 GHz enabling this option takes up to 82% of the unlicensed band, which in many areas may prove to be unfeasible.
The specification calls for requiring one primary 20 MHz channel as well as a secondary adjacent channel spaced ±20 MHz away. The primary channel is used for communications with clients incapable of 40 MHz mode. When in 40 MHz mode the center frequency is actually the mean
of the primary and secondary channels.
Local regulations may restrict certain channels from operation. For example, Channels 12 and 13 are normally unavailable for use as either a primary or secondary channel in North America. For further information, see List of WLAN channels.
started certifying products based on IEEE 802.11n draft 2.0. This certification program established a set of features and a level of interoperability across vendors supporting those features, thus providing one definition of 'draft n'. The Baseline certification covers both 20 MHz and 40 MHz wide channels, and up to two spatial streams, for maximum throughputs of 144.4 Mbit/s for 20 MHz and 300 Mbit/s for 40 MHz (with Short Guard interval
). A number of vendors in both the consumer and enterprise spaces have built products that have achieved this certification. The Wi-Fi Alliance certification program subsumed the previous industry consortium efforts to define 802.11n, such as the now dormant Enhanced Wireless Consortium (EWC). The Alliance has upgraded its suite of compatibility tests for some enhancements finalized after draft 2.0. Furthermore, it has affirmed that all draft-n certified products remain compatible with the products conforming to the final standards. The Wi-Fi Alliance is investigating further work on certification of additional features of 802.11n not covered by the Baseline certification, including higher numbers of spatial streams (3 or 4), Greenfield Format, PSMP, Implicit & Explicit Beamforming and Space-Time Block Coding.
September 11, 2002: The first meeting of the High-Throughput Study Group (HTSG) was held. Earlier in the year, in the Wireless Next Generation standing committee (WNG SC), presentations were heard on why they need change and what the target throughput would be required to justify the amendments. Compromise was reached in May 2002 to delay the start of the Study Group until September to allow 11g to complete major work during the July 2002 session.
September 11, 2003: The IEEE-SA New Standards Committee (NesCom) approved the Project Authorization Request (PAR) for the purpose of amending the 802.11-2007 standard. The new 802.11 Task Group (TGn) is to develop a new amendment. The TGn amendment is based on IEEE Std 802.11-2007, as amended by IEEE Std 802.11k-2008, IEEE Std 802.11r-2008, IEEE Std 802.11y-2008 and IEEE P802.11w. TGn will be the 5th amendment to the 802.11-2007 standard. The scope of this project is to define an amendment that shall define standardized modifications to both the 802.11 physical layers (PHY) and the 802.11 Medium Access Control Layer (MAC) so that modes of operation can be enabled that are capable of much higher throughputs, with a maximum throughput of at least 100 Mbit/s, as measured at the MAC data service access point (SAP).
September 15, 2003: The first meeting of the new 802.11 Task Group (TGn).
May 17, 2004: Call for Proposals was issued.
September 13, 2004: 32 first round of proposals were heard.
March 2005: Proposals were downselected to a single proposal, but there is not a 75% consensus on the one proposal. Further efforts were expended over the next 3 sessions without being able to agree on one proposal.
July 2005: Previous competitors TGn Sync, WWiSE, and a third group, MITMOT
, said that they would merge their respective proposals as a draft. The standardization process was expected to be completed by the second quarter of 2009.
January 19, 2006: The IEEE 802.11n Task Group approved the Joint Proposal's specification, enhanced by EWC's draft specification.
March 2006: IEEE 802.11 Working Group sent the 802.11n draft to its first letter ballot, allowing the 500+ 802.11 voters to review the document and suggest bug fixes, changes, and improvements.
May 2, 2006: The IEEE 802.11 Working Group voted not to forward draft 1.0 of the proposed 802.11n standard. Only 46.6% voted to approve the ballot. To proceed to the next step in the IEEE standards process, a majority vote of 75% is required. This letter ballot also generated approximately 12,000 comments—many more than anticipated.
November 2006: TGn voted to accept draft version 1.06, incorporating all accepted technical and editorial comment resolutions prior to this meeting. An additional 800 comment resolutions were approved during the November session which will be incorporated into the next revision of the draft. As of this meeting, three of the 18 comment topic ad hoc groups chartered in May had completed their work, and 88% of the technical comments had been resolved, with approximately 370 remaining.
January 19, 2007: The IEEE 802.11 Working Group unanimously (100 yes, 0 no, 5 abstaining) approved a request by the 802.11n Task Group to issue a new draft 2.0 of the proposed standard. Draft 2.0 was based on the Task Group's working draft version 1.10. Draft 2.0 was at this point in time the cumulative result of thousands of changes to the 11n document as based on all previous comments.
February 7, 2007: The results of Letter Ballot 95, a 15-day Procedural vote, passed with 97.99% approval and 2.01% disapproval. On the same day, 802.11 Working Group announced the opening of Letter Ballot 97. It invited detailed technical comments to closed on 9 March 2007.
March 9, 2007: Letter Ballot 97, the 30-day Technical vote to approve draft 2.0, closed. They were announced by IEEE 802 leadership during the Orlando Plenary on 12 March 2007. The ballot passed with an 83.4% approval, above the 75% minimum approval threshold. There were still approximately 3,076 unique comments, which were to be individually examined for incorporation into the next revision of draft 2.
June 25, 2007: The Wi-Fi Alliance
announced its official certification program for devices based on draft 2.0.
September 7, 2007: Task Group agreed on all outstanding issues for draft 2.07. Draft 3.0 is authorized, with the expectation that it go to a sponsor ballot in November 2007.
November 2007: Draft 3.0 approved (240 voted affirmative, 43 negative, and 27 abstained). The editor was authorized to produce draft 3.01.
January 2008:Draft 3.02 approved. This version incorporates previously approved technical and editorial comments. There remain 127 unresolved technical comments. It was expected that all remaining comments will be resolved and that TGn and WG11 would subsequently release draft 4.0 for working group recirculation ballot following the March meeting.
May 2008:Draft 4.0 approved.
July 2008:Draft 5.0 approved and anticipated publication timeline modified.
September 2008: Draft 6.0 approved.
November 2008: Draft 7.0 approved.
January 2009:Draft 7.0 forwarded to sponsor ballot; the sponsor ballot was approved (158 for, 45 against, 21 abstaining); 241 comments were received.
March 2009: Draft 8.0 proceeded to sponsor ballot recirculation; the ballot passed by an 80.1% majority (75% required) (228 votes received, 169 approve, 42 not approve); 277 members are in the sponsor ballot pool; The comment resolution committee resolved the 77 comments received, and authorized the editor to create a draft 9.0 for further balloting.
April 4, 2009: Draft 9.0 passed sponsor ballot recirculation; the ballot passed by an 80.7% majority (75% required) (233 votes received, 171 approve, 41 not approve); 277 members are in the sponsor ballot pool; The comment resolution committee is resolving the 23 new comments received, and will authorize the editor to create a new draft for further balloting.
May 15, 2009: Draft 10.0 passed sponsor ballot recirculation
June 23, 2009: Draft 11.0 passed sponsor ballot recirculation
July 17, 2009: Final WG Approval passed with 53 approve, 1 against, 6 abstain. Unanimous approval to send Final WG draft 11.0 to RevCom.
September 11, 2009: RevCom/Standards Board approval.
October 29, 2009: Published.
Wireless network
Wireless network refers to any type of computer network that is not connected by cables of any kind. It is a method by which homes, telecommunications networks and enterprise installations avoid the costly process of introducing cables into a building, or as a connection between various equipment...
ing standard to improve network throughput over the two previous standards—802.11a and 802.11g—with a significant increase in the maximum net data rate
Bit rate
In telecommunications and computing, bit rate is the number of bits that are conveyed or processed per unit of time....
from 54 Mbit/s to 600 Mbit/s (slightly higher gross bit rate including for example error-correction codes, and slightly lower maximum throughput
Throughput
In communication networks, such as Ethernet or packet radio, throughput or network throughput is the average rate of successful message delivery over a communication channel. This data may be delivered over a physical or logical link, or pass through a certain network node...
) with the use of four spatial streams at a channel width of 40 MHz.
802.11 is a set of IEEE standards that govern wireless networking transmission methods. They are commonly used today in their 802.11a, 802.11b, 802.11g, and 802.11n versions to provide wireless connectivity in homes and businesses. The enhanced security features of 802.11n is deserving of its own section below detailing security improvements over previous standards.
Description
IEEE 802.11n is an amendment to IEEE 802.11-2007 as amended by IEEE 802.11k-2008IEEE 802.11k-2008
IEEE 802.11k-2008 is an amendment to IEEE 802.11-2007 standard for radio resource management. It defines and exposes radio and network information to facilitate the management and maintenance of a mobile Wireless LAN.-Radio Resource Management:...
, IEEE 802.11r-2008, IEEE 802.11y-2008, and IEEE 802.11w-2009, and builds on previous 802.11 standards by adding multiple-input multiple-output (MIMO) and 40 MHz channels to the PHY (physical layer)
Physical layer
The physical layer or layer 1 is the first and lowest layer in the seven-layer OSI model of computer networking. The implementation of this layer is often termed PHY....
, and frame aggregation
Frame aggregation
Frame aggregation is a feature of the IEEE 802.11e and 802.11n wireless LAN standards that increases throughput by sending two or more data frames in a single transmission....
to the MAC layer.
MIMO is a technology which uses multiple antennas to coherently resolve more information than possible using a single antenna. One way it provides this is through Spatial Division Multiplexing (SDM). SDM spatially multiplexes multiple independent data streams, transferred simultaneously within one spectral channel of bandwidth. MIMO SDM can significantly increase data throughput as the number of resolved spatial data streams is increased. Each spatial stream requires a discrete antenna at both the transmitter and the receiver. In addition, MIMO technology requires a separate radio frequency chain and analog-to-digital converter for each MIMO antenna which translates to higher implementation costs compared to non-MIMO systems.
Channels operating at 40 MHz are another feature incorporated into 802.11n which doubles the channel width from 20 MHz in previous 802.11 PHYs to transmit data. This allows for a doubling of the PHY data rate over a single 20 MHz channel. It can be enabled in the 5 GHz mode, or within the 2.4 GHz if there is knowledge that it will not interfere with any other 802.11 or non-802.11 (such as Bluetooth) system using those same frequencies.
Coupling MIMO architecture with wider bandwidth channels offers increased physical transfer rate over 802.11a (5 GHz) and 802.11g
IEEE 802.11g-2003
IEEE 802.11g-2003 or 802.11g is an amendment to the IEEE 802.11 specification that extended throughput to up to 54 Mbit/s using the same 2.4 GHz band as 802.11b. This specification under the marketing name of Wi-Fi has been implemented all over the world...
(2.4 GHz).
Data encoding
The transmitter and receiver use precodingPrecoding
Precoding is a generalization of beamforming to support multi-layer transmission in multi-antenna wireless communications. In conventional single-layer beamforming, the same signal is emitted from each of the transmit antennas with appropriate weighting such that the signal power is maximized at...
and postcoding techniques, respectively, to achieve the capacity of a MIMO link. Precoding includes spatial beamforming
Beamforming
Beamforming is a signal processing technique used in sensor arrays for directional signal transmission or reception. This is achieved by combining elements in the array in a way where signals at particular angles experience constructive interference and while others experience destructive...
and spatial coding, where spatial beamforming improves the received signal quality at the decoding stage. Spatial coding can increase data throughput via spatial multiplexing
Spatial multiplexing
Spatial multiplexing is a transmission technique in MIMO wireless communication to transmit independent and separately encoded data signals, so-called streams, from each of the multiple transmit antennas...
and increase range by exploiting the spatial diversity, through techniques such as Alamouti coding
Space–time block code
Space–time block coding is a technique used in wireless communications to transmit multiple copies of a data stream across a number of antennas and to exploit the various received versions of the data to improve the reliability of data-transfer...
.
Number of antennas
The number of simultaneous data streams is limited by the minimum number of antennas in use on both sides of the link. However, the individual radios often further limit the number of spatial streams that may carry unique data. The notation helps identify what a given radio is capable of. The first number () is the maximum number of transmit antennas or RF chains that can be used by the radio. The second number () is the maximum number of receive antennas or RF chains that can be used by the radio. The third number () is the maximum number of data spatial streams the radio can use. For example, a radio that can transmit on two antennas and receive on three, but can only send or receive two data streams would be .The 802.11n draft allows up to
. Common configurations of 11n devices are , , and . All three configurations have the same maximum throughputs and features, and differ only in the amount of diversity the antenna systems provide. In addition, a fourth configuration, is becoming common, which has a higher throughput, due to the additional data stream.Data rates
Data rates up to 600 Mbit/s are achieved only with the maximum of four spatial streams using a 40 MHz-wide channel. Various modulation schemes and coding rates are defined by the standard and are represented by a Modulation and Coding Scheme (MCS) index value. The table below shows the relationships between the variables that allow for the maximum data rate.| MCS index |
Spatial streams |
Modulation type |
Coding rate Code rate In telecommunication and information theory, the code rate of a forward error correction code is the proportion of the data-stream that is useful... |
Data rate (Mbit/s) | |||
|---|---|---|---|---|---|---|---|
| 20 MHz channel | 40 MHz channel | ||||||
| 800 ns GI Guard interval In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another. These transmissions may belong to different users or to the same user .... |
400 ns GI Guard interval In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another. These transmissions may belong to different users or to the same user .... |
800 ns GI Guard interval In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another. These transmissions may belong to different users or to the same user .... |
400 ns GI Guard interval In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another. These transmissions may belong to different users or to the same user .... |
||||
| 0 | 1 | BPSK | 1/2 | 6.50 | 7.20 | 13.50 | 15.00 |
| 1 | 1 | QPSK | 1/2 | 13.00 | 14.40 | 27.00 | 30.00 |
| 2 | 1 | QPSK | 3/4 | 19.50 | 21.70 | 40.50 | 45.00 |
| 3 | 1 | 16-QAM | 1/2 | 26.00 | 28.90 | 54.00 | 60.00 |
| 4 | 1 | 16-QAM | 3/4 | 39.00 | 43.30 | 81.00 | 90.00 |
| 5 | 1 | 64-QAM | 2/3 | 52.00 | 57.80 | 108.00 | 120.00 |
| 6 | 1 | 64-QAM | 3/4 | 58.50 | 65.00 | 121.50 | 135.00 |
| 7 | 1 | 64-QAM | 5/6 | 65.00 | 72.20 | 135.00 | 150.00 |
| 8 | 2 | BPSK | 1/2 | 13.00 | 14.40 | 27.00 | 30.00 |
| 9 | 2 | QPSK | 1/2 | 26.00 | 28.90 | 54.00 | 60.00 |
| 10 | 2 | QPSK | 3/4 | 39.00 | 43.30 | 81.00 | 90.00 |
| 11 | 2 | 16-QAM | 1/2 | 52.00 | 57.80 | 108.00 | 120.00 |
| 12 | 2 | 16-QAM | 3/4 | 78.00 | 86.70 | 162.00 | 180.00 |
| 13 | 2 | 64-QAM | 2/3 | 104.00 | 115.60 | 216.00 | 240.00 |
| 14 | 2 | 64-QAM | 3/4 | 117.00 | 130.00 | 243.00 | 270.00 |
| 15 | 2 | 64-QAM | 5/6 | 130.00 | 144.40 | 270.00 | 300.00 |
| 16 | 3 | BPSK | 1/2 | 19.50 | 21.70 | 40.50 | 45.00 |
| 17 | 3 | QPSK | 1/2 | 39.00 | 43.30 | 81.00 | 90.00 |
| 18 | 3 | QPSK | 3/4 | 58.50 | 65.00 | 121.50 | 135.00 |
| 19 | 3 | 16-QAM | 1/2 | 78.00 | 86.70 | 162.00 | 180.00 |
| 20 | 3 | 16-QAM | 3/4 | 117.00 | 130.70 | 243.00 | 270.00 |
| 21 | 3 | 64-QAM | 2/3 | 156.00 | 173.30 | 324.00 | 360.00 |
| 22 | 3 | 64-QAM | 3/4 | 175.50 | 195.00 | 364.50 | 405.00 |
| 23 | 3 | 64-QAM | 5/6 | 195.00 | 216.70 | 405.00 | 450.00 |
| 24 | 4 | BPSK | 1/2 | 26.00 | 28.80 | 54.00 | 60.00 |
| 25 | 4 | QPSK | 1/2 | 52.00 | 57.60 | 108.00 | 120.00 |
| 26 | 4 | QPSK | 3/4 | 78.00 | 86.80 | 162.00 | 180.00 |
| 27 | 4 | 16-QAM | 1/2 | 104.00 | 115.60 | 216.00 | 240.00 |
| 28 | 4 | 16-QAM | 3/4 | 156.00 | 173.20 | 324.00 | 360.00 |
| 29 | 4 | 64-QAM | 2/3 | 208.00 | 231.20 | 432.00 | 480.00 |
| 30 | 4 | 64-QAM | 3/4 | 234.00 | 260.00 | 486.00 | 540.00 |
| 31 | 4 | 64-QAM | 5/6 | 260.00 | 288.80 | 540.00 | 600.00 |
Frame aggregation
PHY level data rate improvements do not increase user level throughput beyond a point because of 802.11 protocol overheads, like the contention process, interframe spacing, PHY level headers (Preamble + PLCP) and acknowledgment frames. The main medium access control (MAC) feature that provides a performance improvement is aggregation. Two types of aggregation are defined:- Aggregation of MAC Service Data UnitService Data UnitIn Open Systems Interconnection terminology, a service data unit is a unit of data that has been passed down from an OSI layer to a lower layer and that has not yet been encapsulated into a protocol data unit by the lower layer...
s (MSDUs) at the top of the MAC (referred to as MSDU aggregation or A-MSDU) - Aggregation of MAC Protocol Data UnitProtocol data unitIn telecommunications, the term protocol data unit has the following meanings:#Information that is delivered as a unit among peer entities of a network and that may contain control information, address information, or data....
s (MPDUs) at the bottom of the MAC (referred to as MPDU aggregation or A-MPDU)
Frame aggregation
Frame aggregation
Frame aggregation is a feature of the IEEE 802.11e and 802.11n wireless LAN standards that increases throughput by sending two or more data frames in a single transmission....
is a process of packing multiple MSDUs or MPDUs together to reduce the overheads and average them over multiple frames, thus increasing the user level data rate. A-MPDU aggregation requires the use of Block Acknowledgement
Block acknowledgement
-Block Acknowledgment:Block Acknowledgment was initially defined in IEEE 802.11e as an optional scheme to improve the MAC efficiency. Recently ratified amendment 802.11n enhances this BA mechanism then made it as mandatory to support by all the HT devices...
or BlockAck, which was introduced in 802.11e and has been optimized in 802.11n
Backward compatibility
When 802.11g was released to share the band with existing 802.11b devices, it provided ways of ensuring coexistence between legacy, and successor devices. 802.11n extends the coexistence management to protect its transmissions from legacy devices, which include 802.11gIEEE 802.11g-2003
IEEE 802.11g-2003 or 802.11g is an amendment to the IEEE 802.11 specification that extended throughput to up to 54 Mbit/s using the same 2.4 GHz band as 802.11b. This specification under the marketing name of Wi-Fi has been implemented all over the world...
, 802.11b
IEEE 802.11b-1999
IEEE 802.11b-1999 or 802.11b, is an amendment to the IEEE 802.11 specification that extended throughput up to 11 Mbit/s using the same 2.4 GHz band. This specification under the marketing name of Wi-Fi has been implemented all over the world...
and 802.11a
IEEE 802.11a-1999
IEEE 802.11a-1999 or 802.11a is an amendment to the IEEE 802.11 specification that added a higher data rate of up to 54 Mbit/s using the 5 GHz band. It has seen widespread worldwide implementation, particularly within the corporate workspace...
. There are MAC and PHY level protection mechanisms as listed below:
- PHY level protection: Mixed Mode Format protection (also known as L-SIG TXOP Protection): In mixed mode, each 802.11n transmission is always embedded in an 802.11a or 802.11g transmission. For 20 MHz transmissions, this embedding takes care of the protection with 802.11a and 802.11g. However, 802.11b devices still need CTSIEEE 802.11 RTS/CTSRTS/CTS is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem...
protection. - PHY level protection: Transmissions using a 40 MHz channel in the presence of 802.11a or 802.11g clients require using CTSIEEE 802.11 RTS/CTSRTS/CTS is the optional mechanism used by the 802.11 wireless networking protocol to reduce frame collisions introduced by the hidden node problem...
protection on both 20 MHz halves of the 40 MHz channel, to prevent interference with legacy devices. - MAC level protection: An RTS/CTS frame exchange or CTS frame transmission at legacy rates can be used to protect subsequent 11n transmission.
Even with protection, large discrepancies can exist between the throughput an 802.11n device can achieve in a greenfield network
Greenfield project
In many disciplines a greenfield is a project that lacks any constraints imposed by prior work. The analogy is to that of construction on greenfield land where there is no need to remodel or demolish an existing structure...
, compared to a mixed-mode network, when legacy devices are present. This is an extension of the 802.11b/802.11g coexistence problem.
Deployment strategies
To achieve maximum output a pure 802.11n 5 GHz network is recommended. The 5 GHz band has substantial capacity due to many non-overlapping radio channels and less radio interference as compared to the 2.4 GHz band. An 802.11n-only network may be impractical for many users because they need to support legacy equipment that still is 802.11b/g only. Consequently, it may be more practical in the short term to operate a mixed 802.11b/g/n network until 802.11n hardware becomes more prevalent. In a mixed-mode system, an optimal solution would be to use a dual-radio access point and place the 802.11b/g traffic on the 2.4 GHz radio and the 802.11n traffic on the 5 GHz radio. This setup assumes that all the 802.11n clients are 5 GHz capable, which isn't a requirement of the standard.40 MHz in 2.4 GHz
The 2.4 GHz ISM bandISM band
The industrial, scientific and medical radio bands are radio bands reserved internationally for the use of radio frequency energy for industrial, scientific and medical purposes other than communications....
is fairly congested. With 802.11n, there is the option to double the bandwidth per channel to 40 MHz which results in slightly more than double the data rate. However, when in 2.4 GHz enabling this option takes up to 82% of the unlicensed band, which in many areas may prove to be unfeasible.
The specification calls for requiring one primary 20 MHz channel as well as a secondary adjacent channel spaced ±20 MHz away. The primary channel is used for communications with clients incapable of 40 MHz mode. When in 40 MHz mode the center frequency is actually the mean
Arithmetic mean
In mathematics and statistics, the arithmetic mean, often referred to as simply the mean or average when the context is clear, is a method to derive the central tendency of a sample space...
of the primary and secondary channels.
| Primary channel |
20 MHz | 40 MHz above | 40 MHz below | ||||
|---|---|---|---|---|---|---|---|
| Blocks | 2nd ch. | Center | Blocks | 2nd ch. | Center | Blocks | |
| 1 | 1-3 | 5 | 3 | 1-7 | Not Available | ||
| 2 | 1-4 | 6 | 4 | 1-8 | Not Available | ||
| 3 | 1-5 | 7 | 5 | 1-9 | Not Available | ||
| 4 | 2-6 | 8 | 6 | 2-10 | Not Available | ||
| 5 | 3-7 | 9 | 7 | 3-11 | 1 | 3 | 1-7 |
| 6 | 4-8 | 10 | 8 | 4-12 | 2 | 4 | 1-8 |
| 7 | 5-9 | 11 | 9 | 5-13 | 3 | 5 | 1-9 |
| 8 | 6-10 | 12 | 10 | 6-13 | 4 | 6 | 2-10 |
| 9 | 7-11 | 13 | 11 | 7-13 | 5 | 7 | 3-11 |
| 10 | 8-12 | Not Available | 6 | 8 | 4-12 | ||
| 11 | 9-13 | Not Available | 7 | 9 | 5-13 | ||
| 12 | 10-13 | Not Available | 8 | 10 | 6-13 | ||
| 13 | 11-13 | Not Available | 9 | 11 | 7-13 | ||
Local regulations may restrict certain channels from operation. For example, Channels 12 and 13 are normally unavailable for use as either a primary or secondary channel in North America. For further information, see List of WLAN channels.
Wi-Fi Alliance
As of mid-2007, the Wi-Fi AllianceWi-Fi Alliance
The Wi-Fi Alliance is a trade association that promotes Wireless LAN technology and certifies products if they conform to certain standards of interoperability. Not every IEEE 802.11-compliant device is submitted for certification to the Wi-Fi Alliance, sometimes because of costs associated with...
started certifying products based on IEEE 802.11n draft 2.0. This certification program established a set of features and a level of interoperability across vendors supporting those features, thus providing one definition of 'draft n'. The Baseline certification covers both 20 MHz and 40 MHz wide channels, and up to two spatial streams, for maximum throughputs of 144.4 Mbit/s for 20 MHz and 300 Mbit/s for 40 MHz (with Short Guard interval
Guard interval
In telecommunications, guard intervals are used to ensure that distinct transmissions do not interfere with one another. These transmissions may belong to different users or to the same user ....
). A number of vendors in both the consumer and enterprise spaces have built products that have achieved this certification. The Wi-Fi Alliance certification program subsumed the previous industry consortium efforts to define 802.11n, such as the now dormant Enhanced Wireless Consortium (EWC). The Alliance has upgraded its suite of compatibility tests for some enhancements finalized after draft 2.0. Furthermore, it has affirmed that all draft-n certified products remain compatible with the products conforming to the final standards. The Wi-Fi Alliance is investigating further work on certification of additional features of 802.11n not covered by the Baseline certification, including higher numbers of spatial streams (3 or 4), Greenfield Format, PSMP, Implicit & Explicit Beamforming and Space-Time Block Coding.
Timeline
The following are milestones in the development of 802.11n:September 11, 2002: The first meeting of the High-Throughput Study Group (HTSG) was held. Earlier in the year, in the Wireless Next Generation standing committee (WNG SC), presentations were heard on why they need change and what the target throughput would be required to justify the amendments. Compromise was reached in May 2002 to delay the start of the Study Group until September to allow 11g to complete major work during the July 2002 session.
September 11, 2003: The IEEE-SA New Standards Committee (NesCom) approved the Project Authorization Request (PAR) for the purpose of amending the 802.11-2007 standard. The new 802.11 Task Group (TGn) is to develop a new amendment. The TGn amendment is based on IEEE Std 802.11-2007, as amended by IEEE Std 802.11k-2008, IEEE Std 802.11r-2008, IEEE Std 802.11y-2008 and IEEE P802.11w. TGn will be the 5th amendment to the 802.11-2007 standard. The scope of this project is to define an amendment that shall define standardized modifications to both the 802.11 physical layers (PHY) and the 802.11 Medium Access Control Layer (MAC) so that modes of operation can be enabled that are capable of much higher throughputs, with a maximum throughput of at least 100 Mbit/s, as measured at the MAC data service access point (SAP).
September 15, 2003: The first meeting of the new 802.11 Task Group (TGn).
May 17, 2004: Call for Proposals was issued.
September 13, 2004: 32 first round of proposals were heard.
March 2005: Proposals were downselected to a single proposal, but there is not a 75% consensus on the one proposal. Further efforts were expended over the next 3 sessions without being able to agree on one proposal.
July 2005: Previous competitors TGn Sync, WWiSE, and a third group, MITMOT
MITMOT
MITMOT proposal for IEEE 802.11n, the high throughput Wi-Fi MIMO standard has been initiated jointly by Motorola and Mitsubishi in order to propose a new PHY and MAC layer specification competing with WWiSE and TGnSync proposals addressing the need for integration of Wi-Fi chipsets into mobile...
, said that they would merge their respective proposals as a draft. The standardization process was expected to be completed by the second quarter of 2009.
January 19, 2006: The IEEE 802.11n Task Group approved the Joint Proposal's specification, enhanced by EWC's draft specification.
March 2006: IEEE 802.11 Working Group sent the 802.11n draft to its first letter ballot, allowing the 500+ 802.11 voters to review the document and suggest bug fixes, changes, and improvements.
May 2, 2006: The IEEE 802.11 Working Group voted not to forward draft 1.0 of the proposed 802.11n standard. Only 46.6% voted to approve the ballot. To proceed to the next step in the IEEE standards process, a majority vote of 75% is required. This letter ballot also generated approximately 12,000 comments—many more than anticipated.
November 2006: TGn voted to accept draft version 1.06, incorporating all accepted technical and editorial comment resolutions prior to this meeting. An additional 800 comment resolutions were approved during the November session which will be incorporated into the next revision of the draft. As of this meeting, three of the 18 comment topic ad hoc groups chartered in May had completed their work, and 88% of the technical comments had been resolved, with approximately 370 remaining.
January 19, 2007: The IEEE 802.11 Working Group unanimously (100 yes, 0 no, 5 abstaining) approved a request by the 802.11n Task Group to issue a new draft 2.0 of the proposed standard. Draft 2.0 was based on the Task Group's working draft version 1.10. Draft 2.0 was at this point in time the cumulative result of thousands of changes to the 11n document as based on all previous comments.
February 7, 2007: The results of Letter Ballot 95, a 15-day Procedural vote, passed with 97.99% approval and 2.01% disapproval. On the same day, 802.11 Working Group announced the opening of Letter Ballot 97. It invited detailed technical comments to closed on 9 March 2007.
March 9, 2007: Letter Ballot 97, the 30-day Technical vote to approve draft 2.0, closed. They were announced by IEEE 802 leadership during the Orlando Plenary on 12 March 2007. The ballot passed with an 83.4% approval, above the 75% minimum approval threshold. There were still approximately 3,076 unique comments, which were to be individually examined for incorporation into the next revision of draft 2.
June 25, 2007: The Wi-Fi Alliance
Wi-Fi Alliance
The Wi-Fi Alliance is a trade association that promotes Wireless LAN technology and certifies products if they conform to certain standards of interoperability. Not every IEEE 802.11-compliant device is submitted for certification to the Wi-Fi Alliance, sometimes because of costs associated with...
announced its official certification program for devices based on draft 2.0.
September 7, 2007: Task Group agreed on all outstanding issues for draft 2.07. Draft 3.0 is authorized, with the expectation that it go to a sponsor ballot in November 2007.
November 2007: Draft 3.0 approved (240 voted affirmative, 43 negative, and 27 abstained). The editor was authorized to produce draft 3.01.
January 2008:Draft 3.02 approved. This version incorporates previously approved technical and editorial comments. There remain 127 unresolved technical comments. It was expected that all remaining comments will be resolved and that TGn and WG11 would subsequently release draft 4.0 for working group recirculation ballot following the March meeting.
May 2008:Draft 4.0 approved.
July 2008:Draft 5.0 approved and anticipated publication timeline modified.
September 2008: Draft 6.0 approved.
November 2008: Draft 7.0 approved.
January 2009:Draft 7.0 forwarded to sponsor ballot; the sponsor ballot was approved (158 for, 45 against, 21 abstaining); 241 comments were received.
March 2009: Draft 8.0 proceeded to sponsor ballot recirculation; the ballot passed by an 80.1% majority (75% required) (228 votes received, 169 approve, 42 not approve); 277 members are in the sponsor ballot pool; The comment resolution committee resolved the 77 comments received, and authorized the editor to create a draft 9.0 for further balloting.
April 4, 2009: Draft 9.0 passed sponsor ballot recirculation; the ballot passed by an 80.7% majority (75% required) (233 votes received, 171 approve, 41 not approve); 277 members are in the sponsor ballot pool; The comment resolution committee is resolving the 23 new comments received, and will authorize the editor to create a new draft for further balloting.
May 15, 2009: Draft 10.0 passed sponsor ballot recirculation
June 23, 2009: Draft 11.0 passed sponsor ballot recirculation
July 17, 2009: Final WG Approval passed with 53 approve, 1 against, 6 abstain. Unanimous approval to send Final WG draft 11.0 to RevCom.
September 11, 2009: RevCom/Standards Board approval.
October 29, 2009: Published.
See also
- Spectral efficiency comparison table
- WiMAX MIMOWiMAX MIMOWiMAX MIMO refers to the use of Multiple-input multiple-output communications technology on WiMAX, which is the technology brand name for the implementation of the standard IEEE 802.16.-WiMAX:...
- List of WLAN channels