Standard Technology - Wireless 802.11 Technologies

The future of computing is in wireless technology

The IEEE 802.11a, 802.11b, 802.11g and 802.11n wireless standards are collectively known as Wi-Fi technologies. Many products like wireless routers and smartphones use 802.11 technologies, and they are the standards for implementing fast to ultra-fast wireless local area networks (WLAN) today.

Early wireless standards

Released in 1999 - 802.11b

Release Date	Op. Frequency	Data Rate (Typ)	Data Rate (Max)
1999	2.4 GHz	6.5 Mbps*	11 Mbps*

Maximum raw data rate - 11 Mbps / 2.4 GHz

The 802.11b standard has a maximum raw data rate of 11 Mbps. It uses the same CSMA/CA media access method defined in the original standard. Hence, chipsets and products were easily upgraded to support the 802.11b enhancements.

The dramatic increase in throughput of 802.11b (compared to the original standard) along with substantial price reductions led to the rapid acceptance of 802.11b as the definitive wireless LAN technology.

Lowest raw data rate - 1 Mbps / 2.4 GHz

802.11b cards can operate at 11 Mbps, but will scale back to 5.5, then 2 and then, 1 Mbps (also known as Adaptive Rate Selection), if signal quality becomes an issue. Since the lower data rates use less complex and more redundant methods of encoding the data, they are less susceptible to corruption due to interference and signal attenuation.

Released in 1999 - 802.11a

Release Date	Op. Frequency	Data Rate (Typ)	Data Rate (Max)
1999	5 GHz	25 Mbps*	54 Mbps*

Maximum raw data rate – 54 Mbps / 5 GHz

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 Mbps. This yields realistic net achievable throughput in the mid-20 Mbps. The data rate is reduced to 48, 36, 24, 18, 12, 9 and then, 6 Mbps if required.

802.11a has 12 non-overlapping channels, 8 dedicated to indoor, and 4 to point to point. It is not interoperable with 802.11b/g, except if using equipment that implements both standards.

Less interference on higher band frequency

Since the 2.4 GHz band is heavily used, using the 5 GHz band gives 802.11a the advantage of less interference. However, this high carrier frequency also brings disadvantages.

It restricts the use of 802.11a to almost line of sight, necessitating the use of more access points.

It also means that 802.11a cannot penetrate as far as 802.11b/g since it is absorbed more readily, other things (such as power) being equal.

There are dual-band, dual-mode or tri-mode cards that can automatically handle 802.11a and b, or a, b and g, as available. Similarly, there are mobile adapters and access points which can support all these standards simultaneously.

Recent wireless standards

Released in 2003 - 802.11g

Release Date	Op. Frequency	Data Rate (Typ)	Data Rate (Max)
2003 June	2.4 GHz	25 Mbps*	54 Mbps*

Maximum raw data rate - 54 Mbps / 2.4 GHz

In June 2003, a third modulation standard was ratified: 802.11g. This standard works in the 2.4 GHz band (like 802.11b), but operates at a maximum raw data rate of 54 Mbps or about 24.7 Mbps net throughput like 802.11a.

Backwards compatible with 802.11b

The 802.11g hardware will work with 802.11b hardware. Details of making b and g work well together occupied much of the lingering technical process.

In older networks however, the presence of an 802.11b participant significantly reduces the speed of an 802.11g network. The modulation scheme used in 802.11g is orthogonal frequency-division multiplexing (OFDM) for the data rates of 6, 9, 12, 18, 24, 36, 48 and 54 Mbps.

Warm reception to 802.11g standard

The 802.11g standard swept the consumer world of early adopters starting in January 2003, well before ratification. The corporate users held back and Cisco and other big equipment makers waited until ratification. By summer 2003, announcements were flourishing. Most of the dual-band 802.11a/b products became dual-band/tri-mode, supporting a, b, and g in a single mobile adaptor card or access point.

Signal interference issue at 2.4 GHz

Despite its major acceptance, 802.11g suffers from the same interference as 802.11b in the already crowded 2.4 GHz range. Devices operating in this range include microwave ovens, Bluetooth devices, and cordless telephones.

Released in 2007 - 802.11n

Release Date	Op. Frequency	Data Rate (Typ)	Data Rate (Max)
2007	2.4 GHz	200 Mbps*	54 Mbps*

Maximum raw data rate – 540 Mbps / 2.4 GHz

In January 2004, IEEE announced that it had formed a new 802.11 Task Group (TGn) to develop a new amendment to the 802.11 standard for wireless local area networks – 802.11n. The bit rates of 802.11n promised to be significantly higher than older 802.11 b/g and a.

Higher performance, better range

The 802.11n’s real data throughput or data transfer speed is estimated to reach a theoretical 540 Mbps (which may require an even higher raw data rate at the physical layer). This is up to 100 times faster than 802.11b and well over 10 times faster than 802.11a or 802.11g. 802.11n also offers a better operating distance or range than current networks.

Improving wireless speed and range with MIMO

The 802.11n builds upon previous 802.11 standards by adding MIMO (multiple-input multiple-output). The MIMO technology uses multiple transmitter and receiver antennas to increase data throughput or data transfer rates through spatial multiplexing. By exploiting spatial diversity, perhaps through coding schemes like Alamouti coding, MIMO also increases a network’s range.

The 802.11n standard receives final approval

On May 2, 2006, the IEEE 802.11 Working Group voted not to forward Draft 1.0 of the proposed 802.11n standard for a sponsor ballot. Only 46.6% voted to accept the proposal. To proceed to the next step in the IEEE process, a majority vote of 75% is required. The letter ballot generated approximately 12,000 comments - much more than anticipated.

Finally, after nearly six years of deliberation and several draft versions, the IEEE finally announced in September 2009, its endorsement of 802.11n as the next wireless LAN standard.

Table 1 Comparing wireless standards

Wireless Standard	Release Date	Op. Frequency	Data Rate (Typ)	Data Rate (Max)
802.11b	1999	2.4 GHz	6.5 Mbps*	11 Mbps*
802.11a	1999	5 GHz	25 Mbps*	54 Mbps*
802.11g	2003	2.4 GHz	25 Mbps*	54 Mbps*
802.11n	2007	2.4 GHz	200 Mbps*	500 Mbps*

To learn more about wireless standards and technologies, go to www.wi-fi.org

*Maximum speed and range is achievable when used with same enhanced mode technology. Actual data rates, features and performance may vary depending on your computer system, the environment and other factors.