B.P.C. College , Piravom
IEEE initiated the IEEE 802.11 project in 1990.
In 1997, IEEE first approved the interoperability standard for WLANs.
In 1999 , IEEE ratified two amendments to the IEEE 802.11 standard-IEEE 802.11a and 802.11b.
In 2003 , IEEE released the IEEE 802.11g amendment.
In 2006 , the first IEEE 802.11n draft was introduced.
What is IEEE 802.11n?
IEEE 802.11n-2009 is an amendment to IEEE 802.11-2007 wireless networking standard to improve network throughput over the two previous standards with a significant increase in the maximum raw data rate from 54 Mbps to 600 Mbps with the use of four spatial streams at a channel width of 40 MHz .
IEEE 802.11n 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.
New components in IEEE 802.11n
PHY Enhancements, applicable to both 2.4GHz and 5GHz
The new PHY supports OFDM modulation with additional coding methods, preambles, multiple streams and beam-forming
Multiple Input Multiple Output (MIMO) Radio Technology With Spatial Multiplexing
High throughput PHY – 40 MHz channels – Two adjacent 20 MHz channels are combined to create a single 40 MHz channel.
Two MAC aggregation methods are supported to efficiently pack smaller packets into a single MPDU
Block Acknowledgement – A performance optimization in which an IEEE 802.11 ACK frame need not follow every unicast frame and combined acknowledgements may be sent at a later point in time.
Compare to traditional Single Input Single Output Radio (with optional receive diversity)
What is MIMO?
Multiple Input Multiple Output (MIMO)
Transmit and Receive with multiple radios simultaneously in same spectrum
Spatial Division Multiplexing
Multiple independent data streams are sent between the transmit and receive antennas to deliver more bits in the specified bandwidth
Cross-paths between antennas are automatically decoded by the receiver, assuming sufficient “richness” in the propagation environment
IEEE 802.11b-1999 or 802.11b, is an amendment to the IEEE 802.11 specification that extended throughput up to 11 Mbps using the same 2.4 GHz band.
It uses CSMA/CA media access method.
Eventhough 802.11b is a direct extension of the DSSS modulation technique defined in the original standard, it uses Complementary code keying(CCK) as its modulation technique.
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 Mbps using the 5 GHz band.
It uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM) with a maximum raw data rate of 54 Mbps , which yields realistic net achievable throughput in the mid-20 Mbps.
IEEE 802.11g-2003 or 802.11g is an amendment to the IEEE 802.11specification that extended throughput to up to 54 Mbps using the same 2.4 GHz band as 802.11b.
802.11g hardware is fully backwards compatible with 802.11b hardware.
The modulation scheme used in 802.11g is orthogonal frequency-division multiplexing.
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.
It provides information to discover the best available access point.
IEEE 802.11r-2008 or fast BSS transition (FT) is an amendment to the IEEE 802.11 standard to permit continuous connectivity aboard wireless devices in motion, with fast and secure handoffs from one base station to another managed in a seamless manner.
IEEE 802.11r specifies fast Basic Service Set(BSS) transitions between access points by redefining the security key negotiation protocol.
IEEE 802.11y-2008 is an amendment to the IEEE 802.11-2007 standard that enables high powered Wi-Fi equipment to operate on a co-primary basis in the 3650 to 3700 MHz band in the United States.
It adds three new concepts to 802.11-2007 Standard:
Contention Based Protocol (CBP) - enhancements have been made to the carrier sensing and energy detection mechanisms of 802.11 in order to meet the FCC's requirements for a contention based protocol.
Extended channel switch announcement(ECSA)-
provides a mechanism for an access point to notify the stations connected to it of its intention to change channels or to change channel bandwidth.
Dependent station enablement(DSE)- is the mechanism by which an operator extends and retracts permission to license exempt devices (referred to as dependent STAs in .11y) to use licensed radio spectrum.
IEEE 802.11w-2009 is an approved amendment to the IEEE 802.11 standard to increase the security of its management frames.
IEEE 802.11w is the Protected Management Frames standard for the IEEE 802.11 family of standards.
Modulation and Coding Schemes
The 802.11n standard defines Modulation and Coding Scheme (MCS) – a simple integer assigned to every permutation of modulation , coding rate, guard interval , channel width, and number of spatial streams.
Modulation and coding rate determines how data is sent over the air.
Guard Interval is the time between transmitted symbols.
Unequal Modulation refers to using a different modulation type and coding rate on each spatial stream.
The main medium access control (MAC) feature that provides a performance improvement is aggregation.
Two types of aggregation are defined:
1.MAC Service Data Unit Aggregation (A-MSDU)
2.MAC Protocol Data Unit Aggregation (A-MPDU)
802.11n systems are fully backward compatible with 802.11a/b/g.
The 802.11 standard defines three different modes of operation that describe backward compatibility of 802.11n networks. These are:
1.High Thoughput , Greenfield Mode
2.High Thoughput , Mixed Mode
802.11n Deployment Challenges
RF Planning & Site Surveying
Troubleshooting and Tuning
1.WLAN analyzers must be able to capture and decode 802.11n traffic.
2.Spectrum analyzers must recognize the spectral usage patterns associated with 802.11n APs – including Greenfield mode.
3.Connection diagnostic tools will require the ability to connect to 802.11n APs using any supported MCS value.
4. WLAN analyzers must help 802.11n users overcome their potentially inability to achieve high throughput, due to presence of legacy devices, implementation of protection mechanisms, etc.
5.WLAN analyzers must help administrators understand the real-world overhead incurred when supporting legacy devices.
6.WIPS alerts and reports must be extended to analyze 802.11n PHY and MAC extensions and their impact on WLAN operation and performance.
7. Integration between WIPS and WLAN management systems can help administrators better understand the long-term impact of real-time dynamic channel adjustments caused by 802.11n APs and controllers.
Network Attached Storage(NAS)
802.11n will substantially increase the performance and ubiquitous wireless access of laptops , desktops , smart phones and entertainment devices over the next several years.
802.11n will first appear in client devices and begin to be pervasively deployed in enterprises , homes and eventually metro networks.