28-04-2014, 12:02 PM
Seminar Report 2010-11 802.11n WIRELESS LAN
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INTRODUCTION
In less than a decade, wireless LANs have evolved from an interesting idea to an indispensable technology for millions of businesses and consumers. This technology continues to evolve. The latest generation of high-speed wireless LAN solutions, based on the Institute of Electrical and Electronics Engineers (IEEE) Draft 802.11n standard, are now available.
The 802.11n standard will offer several advantages over previous wireless LAN technologies. The most notable advantages are substantially improved reliability and greater application data throughput. However, before deciding whether to deploy 802.11n wireless solutions, organizations need answers to several questions: What do 802.11n technologies do differently from previous wireless solutions? What is the state of the standardization effort for 802.11n? Will 802.11n be backward-compatible with currently deployed wireless clients and access points? What factors should be considered to determine when it makes sense to deploy 802.11n?
To help you make more informed decisions about 802.11n, this overview provides answers to these and other questions. The overview also provides details on the state of 802.11n technology today, and discusses the reasons why Cisco Systems® is taking an incremental approach to the new standard.
Primary 802.11family Descriptions:
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. The amendment has been incorporated into the published IEEE 802.11-2007 standard.
The 802.11a amendment to the original standard was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band, and uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM) with a maximum raw data rate of 54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s. The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbit/s if required. 802.11a originally had 12/13 non-overlapping channels, 12 that can be used indoor and 4/5 of the 12 that can be used in outdoor point to point configurations. Recently many countries of the world are allowing operation in the 5.47 to 5.725 GHz Band as a secondary user using a sharing method derived in 802.11h. This will add another 12/13 Channels to the overall 5 GHz band enabling significant overall wireless network capacity enabling the possibility of 24+ channels in some countries.
The State of 802.11n Today:
The next-generation of wireless LAN technology is now moving forward, but organizations should recognize that 802.11n is still a draft standard. The final details of 802.11n are still under discussion, and TGn is not expected to ratify the final standard until 2H 2008. The Wi-Fi Alliance is using the interim IEEE 802.11n draft 2.0 as the baseline for the initial round of Wi-Fi certification and compatibility testing that began in June, 2007. Businesses considering 802.11n should weigh the option of whether to deploy today or wait for the standard to be ratified. The 802.11n solutions entering the market now are based on the draft proposal, not on a ratified standard. The industry is working aggressively to try to ensure that existing 802.11n draft 2.0 products will be able to be software upgraded to the final 802.11n standard. However, there is no guarantee that this will be the case.
802.11n Technology
The goal of the work on 802.11n is to dramatically increase the effective throughput of 802.11devices, not to simply build a radio capable of higher bit rates. The difference between these goals is like the difference between the mileage you achieve with your own, personal driving habits and the EPA-rated mileage for your model of car. To increase the effective throughput of an 802.11 device requires more than providing a higher bit rate. There are aspects of the 802.11 standard that are “overhead” for the 802.11 protocol. Many of these overhead aspects can’t be reduced or eliminated. The effect is that, without using other methods, there is an absolute upper bound on the effective throughput. 802.11n is much more than just a new radio for 802.11. In addition to providing higher bit rates (as was done in 802.11a, b, and g), 802.11n makes dramatic changes to the basic frame format that is used by 802.11 devices to communicate with each other. This section will describe the changes incorporated in 802.11n, including MIMO, radio enhancements, and MAC enhancements.
How 802.11n Technology Works
Current wireless solutions operate in the 2.4-GHz radio frequency band (802.11g and 802.11b) or the 5-GHz radio band (802.11a.). Solutions based on the 802.11n standard will operate in the 2.4-GHz, the 5-GHz radio band, or both bands, offering backward compatibility with preexisting 802.11a/b/g deployments. The majority of Wi-Fi devices and access points hitting the market are dual-band – operating in both the 2.4-GHz and 5-GHz frequencies. The net result for business will be a shift to greater utilization of the 5-GHz band with 802.11n given the greater available capacity and cleaner frequency. Wireless solutions based on the 802.11n standard employ several techniques to improve the throughput, reliability, and predictability of wireless LANs. The three primary innovations are:
Multiple Input Multiple Output (MIMO) technology
Packet aggregation
Channel bonding (40MHz Channels)
Together, these techniques allow 802.11n solutions to achieve an approximate fivefold performance increase over current 802.11a/b/g networks.
MIMO Technology
802.11a/b/g wireless access points and clients communicate through a single spatial stream over a single antenna. 802.11n access points and clients transmit two or more spatial streams, and employ multiple receive antennas and advanced signal processing to recover the multiple transmitted data streams. MIMO-enabled access points use spatial multiplexing to transmit different bits of a message over separate antennas, providing much greater data throughput and allowing for more robust, resilient wireless LANs. Whereas previous wireless technologies had problems dealing with signal reflections, MIMO actually uses these reflections to increase the range and reduce “dead spots” in the wireless coverage area.
Ultimately, 802.11n networks that incorporate both MIMO-enabled access points and MIMO enabled wireless clients will deliver dramatic gains in reliability and data throughput. However, even when MIMO is deployed only in wireless access points, the technology still delivers significant performance enhancements (up to 30 percent over conventional 802.11a/b/g networks)—even when communicating only with non-MIMO 802.11a/b/g clients.
[attachment=62594]
INTRODUCTION
In less than a decade, wireless LANs have evolved from an interesting idea to an indispensable technology for millions of businesses and consumers. This technology continues to evolve. The latest generation of high-speed wireless LAN solutions, based on the Institute of Electrical and Electronics Engineers (IEEE) Draft 802.11n standard, are now available.
The 802.11n standard will offer several advantages over previous wireless LAN technologies. The most notable advantages are substantially improved reliability and greater application data throughput. However, before deciding whether to deploy 802.11n wireless solutions, organizations need answers to several questions: What do 802.11n technologies do differently from previous wireless solutions? What is the state of the standardization effort for 802.11n? Will 802.11n be backward-compatible with currently deployed wireless clients and access points? What factors should be considered to determine when it makes sense to deploy 802.11n?
To help you make more informed decisions about 802.11n, this overview provides answers to these and other questions. The overview also provides details on the state of 802.11n technology today, and discusses the reasons why Cisco Systems® is taking an incremental approach to the new standard.
Primary 802.11family Descriptions:
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. The amendment has been incorporated into the published IEEE 802.11-2007 standard.
The 802.11a amendment to the original standard was ratified in 1999. The 802.11a standard uses the same core protocol as the original standard, operates in 5 GHz band, and uses a 52-subcarrier orthogonal frequency-division multiplexing (OFDM) with a maximum raw data rate of 54 Mbit/s, which yields realistic net achievable throughput in the mid-20 Mbit/s. The data rate is reduced to 48, 36, 24, 18, 12, 9 then 6 Mbit/s if required. 802.11a originally had 12/13 non-overlapping channels, 12 that can be used indoor and 4/5 of the 12 that can be used in outdoor point to point configurations. Recently many countries of the world are allowing operation in the 5.47 to 5.725 GHz Band as a secondary user using a sharing method derived in 802.11h. This will add another 12/13 Channels to the overall 5 GHz band enabling significant overall wireless network capacity enabling the possibility of 24+ channels in some countries.
The State of 802.11n Today:
The next-generation of wireless LAN technology is now moving forward, but organizations should recognize that 802.11n is still a draft standard. The final details of 802.11n are still under discussion, and TGn is not expected to ratify the final standard until 2H 2008. The Wi-Fi Alliance is using the interim IEEE 802.11n draft 2.0 as the baseline for the initial round of Wi-Fi certification and compatibility testing that began in June, 2007. Businesses considering 802.11n should weigh the option of whether to deploy today or wait for the standard to be ratified. The 802.11n solutions entering the market now are based on the draft proposal, not on a ratified standard. The industry is working aggressively to try to ensure that existing 802.11n draft 2.0 products will be able to be software upgraded to the final 802.11n standard. However, there is no guarantee that this will be the case.
802.11n Technology
The goal of the work on 802.11n is to dramatically increase the effective throughput of 802.11devices, not to simply build a radio capable of higher bit rates. The difference between these goals is like the difference between the mileage you achieve with your own, personal driving habits and the EPA-rated mileage for your model of car. To increase the effective throughput of an 802.11 device requires more than providing a higher bit rate. There are aspects of the 802.11 standard that are “overhead” for the 802.11 protocol. Many of these overhead aspects can’t be reduced or eliminated. The effect is that, without using other methods, there is an absolute upper bound on the effective throughput. 802.11n is much more than just a new radio for 802.11. In addition to providing higher bit rates (as was done in 802.11a, b, and g), 802.11n makes dramatic changes to the basic frame format that is used by 802.11 devices to communicate with each other. This section will describe the changes incorporated in 802.11n, including MIMO, radio enhancements, and MAC enhancements.
How 802.11n Technology Works
Current wireless solutions operate in the 2.4-GHz radio frequency band (802.11g and 802.11b) or the 5-GHz radio band (802.11a.). Solutions based on the 802.11n standard will operate in the 2.4-GHz, the 5-GHz radio band, or both bands, offering backward compatibility with preexisting 802.11a/b/g deployments. The majority of Wi-Fi devices and access points hitting the market are dual-band – operating in both the 2.4-GHz and 5-GHz frequencies. The net result for business will be a shift to greater utilization of the 5-GHz band with 802.11n given the greater available capacity and cleaner frequency. Wireless solutions based on the 802.11n standard employ several techniques to improve the throughput, reliability, and predictability of wireless LANs. The three primary innovations are:
Multiple Input Multiple Output (MIMO) technology
Packet aggregation
Channel bonding (40MHz Channels)
Together, these techniques allow 802.11n solutions to achieve an approximate fivefold performance increase over current 802.11a/b/g networks.
MIMO Technology
802.11a/b/g wireless access points and clients communicate through a single spatial stream over a single antenna. 802.11n access points and clients transmit two or more spatial streams, and employ multiple receive antennas and advanced signal processing to recover the multiple transmitted data streams. MIMO-enabled access points use spatial multiplexing to transmit different bits of a message over separate antennas, providing much greater data throughput and allowing for more robust, resilient wireless LANs. Whereas previous wireless technologies had problems dealing with signal reflections, MIMO actually uses these reflections to increase the range and reduce “dead spots” in the wireless coverage area.
Ultimately, 802.11n networks that incorporate both MIMO-enabled access points and MIMO enabled wireless clients will deliver dramatic gains in reliability and data throughput. However, even when MIMO is deployed only in wireless access points, the technology still delivers significant performance enhancements (up to 30 percent over conventional 802.11a/b/g networks)—even when communicating only with non-MIMO 802.11a/b/g clients.