IEEE 802.11n-2009

IEEE 802.11n is a proposed amendment to the IEEE 802.11-2007 wireless networking standard to significantly improve network throughput over previous standards, such as 802.11b and 802.11g, with a significant increase in the maximum raw (PHY) data rate from 54 Mbit/s to a maximum of 600 Mbit/s. The current state of the art supports a PHY rate of 450 Mbit/s, with the use of 3 spatial streams at a channel width of 40 MHz. Depending on the environment, this may translate into a user throughput (TCP/IP) of 110 Mbit/s.

802.11n is expected to be approved by IEEE-SA RevCom in Nov 2009, although many "Draft N" products are already available.

Description

IEEE 802.11n builds on previous 802.11 standards by adding multiple-input multiple-output (MIMO) and Channel-bonding/40 MHz operation to the physical (PHY) layer, and frame aggregation to the MAC layer.

MIMO uses multiple transmitter and receiver antennas to improve the system performance. MIMO is a technology which uses multiple antennas to coherently resolve more information than possible using a single antenna. Two important benefits it provides to 802.11n are antenna diversity and spatial multiplexing.

MIMO technology relies on multipath signals. Multipath signals are the reflected signals arriving at the receiver some time after the line of sight (LOS) signal transmission has been received. In a non-MIMO based 802.11a/b/g network, multipath signals were perceived as interference degrading a receiver's ability to recover the message information in the signal. MIMO uses the multipath signal's diversity to increase a receiver's ability to recover the message information from the signal.

Another ability MIMO technology provides is 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.

Channel Bonding, also known as 40 MHz, is a second technology incorporated into 802.11n which can simultaneously use two separate non-overlapping channels to transmit data. Channel bonding increases the amount of data that can be transmitted. 40 MHz mode of operation uses 2 adjacent 20 MHz bands. This allows direct doubling of the PHY data rate from a single 20 MHz channel. (Note however that the MAC and user level throughput will not double.)

Coupling MIMO architecture with wider bandwidth channels offers the opportunity of creating very powerful yet cost-effective approaches for increasing the physical transfer rate.

Data encoding

The transmitter and receiver use precoding 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.

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 $a\times b\colon c$ notation helps identify what a given radio is capable of. The first number ($a$) is the maximum number of transmit antennas or RF chains that can be used by the radio. The second number ($b$) is the maximum number of receive antennas or RF chains that can be used by the radio. The third number ($c$) 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 $2\times 3\colon 2$.

The 802.11n draft allows up to $4\times 4\colon 4$. Common configurations of 11n devices are $2\times 2\colon 2$, $2\times 3\colon 2$, and $3\times 3\colon 2$. 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, $3\times 3\colon 3$ is becoming common, which has a higher throughput, due to the additional data stream.

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:

1. Aggregation of MAC Service Data Units (MSDUs) at the top of the MAC (referred to as MSDU aggregation or A-MSDU)
2. Aggregation of MAC Protocol Data Units (MPDUs) at the bottom of the MAC (referred to as MPDU aggregation or A-MPDU)

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.

Backward compatibility

When 802.11g was released to share the band with existing 802.11b devices, it provided ways of ensuring coexistence between the legacy and the new devices. 802.11n extends the coexistence management to protect its transmissions from legacy devices, which include 802.11g, 802.11b and 802.11a. There are MAC and PHY level protection mechanisms as listed below:

1. 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 CTS protection.
2. PHY level protection: Transmissions using a 40 MHz channel in the presence of 802.11a or 802.11g clients require using CTS protection on both 20 MHz halves of the 40 MHz channel, to prevent interference with legacy devices.
3. PHY 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, 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 throughput 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 the existing computer stock is predominantly 802.11b/g only. Replacement of incompatible WiFi cards or of entire laptop stock is necessary for older computers to operate on the network. 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, it’s generally best 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.

Status

Work on the 802.11n standard dates back to 2004. The draft is expected to be published in January 2010, but major manufacturers are now releasing 'pre-N', 'draft n' or 'MIMO-based' products based on early specs,and have been since late 2006. These vendors anticipate the final version will not be significantly different from the draft, and in a bid to get the early mover advantage, are pushing ahead with the technology. Depending on the manufacturer, a firmware update may eventually be able to make current "Draft-N" hardware compatible with the final version.

Wi-Fi Alliance

As of mid-2007, the Wi-Fi Alliance has 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 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

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 the need change and what the target throughput would be required to justify the amendments. Compromise was reached in May of 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) approves 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 100Mbps, 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 is issued.

September, 13, 2004

32 first round of proposals are heard.

March 2005

Proposals are downselected to a single proposal, but there is not a 75% consensus on the one proposal. Further efforts are 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 is expected to be completed by the second quarter of 2009.

19 January 2006

The IEEE 802.11n Task Group approved the Joint Proposal's specification, enhanced by EWC's draft specification.

March 2006

The 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.

2 May 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 have had completed their work and 88% of the technical comments had been resolved with approximately 370 remaining.

19 January 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.

7 February 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.

9 March 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 will be individually examined for incorporation into the next revision of Draft 2.

25 June 2007

The Wi-Fi Alliance announces its official certification program for devices based on Draft 2.0.

7 September 2007

Task Group agrees on all outstanding issues for Draft 2.07. Draft 3.0 is authorized, which possibly may 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 is expected that all remaining comments will be resolved and that TGn and WG11 will 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 a 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.

04 April 2009

Draft 9.0 passed sponsor ballot recirculation; the ballot passed by a 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 futher balloting.

CSIRO Patent Issues

In late November 2007, work on the 802.11n standard slowed due to patent issues. The Australian Commonwealth Scientific and Industrial Research Organisation (CSIRO) holds the patent to a component of the 802.11n standard. This component is also part of 802.11a and 802.11g. The IEEE requested from the CSIRO a Letter of Assurance (LoA) that no lawsuits would be filed for anyone implementing the standard. In Sep 2007, CSIRO responded that they would not be able to comply with this request since litigation was involved.

In April 2009, it was revealed that CSIRO reached a settlement with 14 companies, including Hewlett-Packard, Intel, Dell, Toshiba, ASUS, Microsoft and Nintendo, on the condition that CSIRO did not broadcast the resolution.

Comparison

802.11 network standards
Frequency range, or type	PHY	Protocol	Release date	Freq­uency	Bandwidth	Stream data rate	Max. MIMO streams	Modulation	Approx. range
									In­door	Out­door
				(GHz)	(MHz)	(Mbit/s)
1–7 GHz	DSSS, FHSS	802.11-1997	June 1997	2.4	22	1, 2	—	DSSS, FHSS	20 m (66 ft)	100 m (330 ft)
	HR/DSSS	802.11b	September 1999	2.4	22	1, 2, 5.5, 11	—	CCK, DSSS	35 m (115 ft)	140 m (460 ft)
	OFDM	802.11a	September 1999	5	5, 10, 20	6, 9, 12, 18, 24, 36, 48, 54 (for 20 MHz bandwidth, divide by 2 and 4 for 10 and 5 MHz)	—	OFDM	35 m (115 ft)	120 m (390 ft)
		802.11j	November 2004	4.9, 5.0					?	?
		802.11y	November 2008	3.7					?	5,000 m (16,000 ft)
		802.11p	July 2010	5.9					200 m	1,000 m (3,300 ft)
		802.11bd	December 2022	5.9, 60					500 m	1,000 m (3,300 ft)
	ERP-OFDM	802.11g	June 2003	2.4					38 m (125 ft)	140 m (460 ft)
	HT-OFDM	802.11n (Wi-Fi 4)	October 2009	2.4, 5	20	Up to 288.8	4	MIMO-OFDM (64-QAM)	70 m (230 ft)	250 m (820 ft)
					40	Up to 600
	VHT-OFDM	802.11ac (Wi-Fi 5)	December 2013	5	20	Up to 693	8	DL MU-MIMO OFDM (256-QAM)	35 m (115 ft)	?
					40	Up to 1600
					80	Up to 3467
					160	Up to 6933
	HE-OFDMA	802.11ax (Wi-Fi 6, Wi-Fi 6E)	May 2021	2.4, 5, 6	20	Up to 1147	8	UL/DL MU-MIMO OFDMA (1024-QAM)	30 m (98 ft)	120 m (390 ft)
					40	Up to 2294
					80	Up to 5.5 Gbit/s
					80+80	Up to 11.0 Gbit/s
	EHT-OFDMA	802.11be (Wi-Fi 7)	Sep 2024 (est.)	2.4, 5, 6	80	Up to 11.5 Gbit/s	16	UL/DL MU-MIMO OFDMA (4096-QAM)	30 m (98 ft)	120 m (390 ft)
					160 (80+80)	Up to 23 Gbit/s
					240 (160+80)	Up to 35 Gbit/s
					320 (160+160)	Up to 46.1 Gbit/s
	UHR	802.11bn (Wi-Fi 8)	May 2028 (est.)	2.4, 5, 6, 42, 60, 71	320	Up to 100000 (100 Gbit/s)	16	Multi-link MU-MIMO OFDM (8192-QAM)	?	?
	WUR	802.11ba	October 2021	2.4, 5	4, 20	0.0625, 0.25 (62.5 kbit/s, 250 kbit/s)	—	OOK (multi-carrier OOK)	?	?
mmWave (WiGig)	DMG	802.11ad	December 2012	60	2160 (2.16 GHz)	Up to 8085 (8 Gbit/s)	—	OFDM, single carrier, low-power single carrier	3.3 m (11 ft)	?
		802.11aj	April 2018	60	1080	Up to 3754 (3.75 Gbit/s)	—	single carrier, low-power single carrier	?	?
	CMMG	802.11aj	April 2018	45	540, 1080	Up to 15015 (15 Gbit/s)	4	OFDM, single carrier	?	?
	EDMG	802.11ay	July 2021	60	Up to 8640 (8.64 GHz)	Up to 303336 (303 Gbit/s)	8	OFDM, single carrier	10 m (33 ft)	100 m (328 ft)
Sub 1 GHz (IoT)	TVHT	802.11af	February 2014	0.054– 0.79	6, 7, 8	Up to 568.9	4	MIMO-OFDM	?	?
	S1G	802.11ah	May 2017	0.7, 0.8, 0.9	1–16	Up to 8.67 (@2 MHz)	4		?	?
Light (Li-Fi)	LC (VLC/OWC)	802.11bb	December 2023 (est.)	800–1000 nm	20	Up to 9.6 Gbit/s	—	O-OFDM	?	?
	IR (IrDA)	802.11-1997	June 1997	850–900 nm	?	1, 2	—	PPM	?	?
802.11 Standard rollups
		802.11-2007 (802.11ma)	March 2007	2.4, 5		Up to 54		DSSS, OFDM
		802.11-2012 (802.11mb)	March 2012	2.4, 5		Up to 150		DSSS, OFDM
		802.11-2016 (802.11mc)	December 2016	2.4, 5, 60		Up to 866.7 or 6757		DSSS, OFDM
		802.11-2020 (802.11md)	December 2020	2.4, 5, 60		Up to 866.7 or 6757		DSSS, OFDM
		802.11me	September 2024 (est.)	2.4, 5, 6, 60		Up to 9608 or 303336		DSSS, OFDM

See also

• Spectral efficiency comparison table
• WiMAX MIMO

External links

• Status of the project 802.11n IEEE Task Group TGn
• How does 802.11n get to 600 Mbps?
• 802.11n: Next-Generation Wireless LAN Technology April 2006 Broadcom white paper
• Official homepage of the Wi-Fi Alliance