802.11n Wireless Standard

Overview

IEEE 802.11n is a proposed amendment to the wireless networking IEEE standard 802.11-2007 for improving system performance. The standard 802.11 also referred as Wi-Fi, offers wireless LAN for devices such as laptop computers and cellular phones at home, office, and commercial establishments.

The existing standard, 802.11g ratified in 2003 is inadequate due to the complexity of applications and the requirement of more bandwidth. IEEE 802.11n assures higher speed and range. Despite this standard is still in draft stage, it is being implemented by many hardware vendors as "pre-N" or "Draft-N" hardware. As the final version is expected to be similar to the draft version, vendors are pushing this technology ahead to get the early mover advantage.

Features

OFDM - 802.11n draft supports an OFDM implementation that increases the highest raw data rate to 248 Mbps.


MIMO - 802.11n draft supports Multiple Input Multiple Output (MIMO) that uses a multi-path radio-wave phenomenon known as space-division multiplexing. With this feature, the transmitting WLAN device splits the data stream into multiple spatial streams and transmits each of these streams through separate antennas to the corresponding antennas on the receiving end. As a result Wi-Fi performance increases without any distortion of signals.

Beam forming technique focuses radio signals to target directly to antenna to improve range, signal quality, and efficiency.
Diversity allows multiple antennas to combine the outputs or receive a number of spatial streams. The specification supports up to four antennas.


Data Encoding - Pre-coding and post-coding techniques are used by the transmitter and receiver to increase the capacity of a MIMO link. Pre-coding uses spatial beam forming and spatial coding. At decoding stage, beam forming improves signal quality and spatial coding increases data throughput and range.


Higher Data Rates - It is an optional mode for doubling data rates through increasing the width of WLAN communication channel from 20 MHz to 40 MHz. There are around 576 possible data rate configurations in the current 802.11n draft.


Higher Throughput - it is an optional mode to extend the network's range


Short Guard Interval - It improves the efficiency by limiting overhead.


Aggregation - it is the main medium access controller (MAC) feature that provides a performance improvement. There are two types of aggregation.

Aggregation of MAC service data units (MSDUs) at the top of the MAC
Aggregation of MAC protocol data units (MPDUs or frames) at the bottom of the MAC


Backwards Compatibility - 802.11n has an extended coexistence management for 802.11g, 802.11b and 802.11a. It is based on the type of devices and an AP determines what kind of protection must be used for transmission sequence.


IEEE 802.1n Comparison with Other Standards

The current IEEE 802.11n specification varies from its predecessors in that it provides a variety of optional modes and configurations for different maximum data rates.



IEEE 802.1n Benefits


Greater speed

Significantly higher range

Solves the throughput problem of business users

Opens a way for more and more applications

Fewer dead spots in homes served by a single Wi-Fi router

Supports high bandwidth applications like wireless voice over IP, videoconferencing etc.

Higher reliability

Used by multiple users for doing multiple things over a network



IEEE 802.1n Benefits


January 2004 - A new 802.11 Task Group (TGn) was formed by IEEE to develop a new amendment to the 802.11 standard for wireless local-area networks. The expectations were that the real data throughput should reach a theoretical 270 Mbit/s for the required dual stream MIMO device and should be up to 20 times faster than 802.11b, up to 3 times faster than 802.11a, and up to 4 times faster than 802.11g.


July 2005 - The competitors like TGn Sync, WWiSE, and a third group, MITMOT, announced the merging of their respective proposals as a draft.


January 2006 - the Joint Proposal's specification based on EWC's draft specification was approved by the IEEE 802.11n Task Group.


March 2006 - The 802.11n Draft was sent to its first letter ballot, by the IEEE 802.11 Working Group for 500+ voters to review the document for suggesting bug fixes, changes, and improvements.


May 2006 - The proposed 802.11n draft received only 46.6% approved votes, but to proceed further, the required majority vote was 75%. So the Draft 1.0 was not forwarded.


November 2006 - The next draft version 1.06 with all incorporated accepted technical and editorial comment resolutions was accepted with an additional 800 comment resolutions.


January 2007 - The request by the 802.11n Task Group to issue a new Draft 2.0 of the proposed standard was unanimously approved by the IEEE 802.11 Working Group. The draft 2.0 was based on the Task Group's working draft version 1.10.

February 2007 - The Letter Ballot 95 had 97.99% approval and 2.01% disapproval. 802.11 Working opened Letter Ballot 97 inviting detailed technical comments.


March 2007 -Letter Ballot 97 was closed and had received an 83.4% approval, above the 75% minimum approval threshold. There were around 3,076 unique comments to be addressed in the next revision of Draft 2.


September 2007 - All outstanding issues for Draft 2.07 was agreed by the Task Group. Draft 3.0 was authorized.
November 2007 - Draft 3.0 was approved and draft 3.01was authorized.


Future - The final draft is expected to be ready by November 2008 with its publication in July 2009.