An Introduction to  Wi-Fi Technologies

802.11 Operating Modes

Infrastructure Mode is used when there is at least one Wireless Access Point and client. The client connects to the network through the Access Point to gain internet access.

Ad Hoc Mode is used when wireless clients want to directly communicate with each other without going through an Access Point. This is also called peer-to-peer mode.

Note: The vast majority of 802.11 WLANs that you will have encountered will have been operating in Infrastructure Mode.

Further information on application methods for 802.11 Wireless Networks can be found in the Introduction to 2.4GHz Technology and Introduction to 5GHz Technology articles respectively.

Popular 802.11 Standards

802.11a

The 802.11a protocol standard uses the same data link layer protocol and frame format as the original 802.11-1997 standard but instead uses an OFDM air interface for the physical layer. Its operating frequency range is in the 5GHz band and has a maximum bandwidth of 54mbps. Due to the 2.4GHz range becoming overcrowded using the 802.11a standard has a significant advantage. However, the effective range of the 5GHz 802.11a is lower than that of the 802.11b, g and n protocols as, in theory, the signal is more easily absorb by solid objects such as walls due to the smaller wavelength which reduces its penetration. Nevertheless, due to the lack of interference in the 5GHz range, 802.11a often has a similar or even greater range in practice.

802.11b

802.11b was the first widely adopted standard wireless networking products. It has a maximum bandwidth of 11Mbps and uses the same media access method as that of the original 802.11-1997 standard. Working on the 2.4GHz frequency range, 802.11b suffers greatly from interference with other consumer items such as Bluetooth devices, DECT & VoIP Wireless phones, wireless keyboards and mice and also microwave ovens etc.

802.11g

802.11g was the next step on from 802.11b still operating a 2.4GHz but using OFDM based transmission. It has a maximum bandwidth of 54Mbps and is backwards compatible with 802.11b hardware. It was the next industrial standard and was, again, widely adopted for WLAN applications due to the increased data transfer rates. Much similar to 802.11b, 802.11g devices can suffer badly from interference from other 2.4GHz consumer products. OFDM is enabled at speeds above 20Mbps which greatly increases NLOS (Non-Line-of-Sight) capabilities.

802.11n

802.11n is a revision that improves on the previous standards by adding MIMO (Multiple-In-Multiple-Out) capabilities, can operate not just on the 2.4GHz frequency range but also at 5GHz, 40 MHz channels to the physical layer and frame aggregation to the MAC layer. 802.11 is backwards compatible with 802.11a, b and g. OFDM is enabled across the whole speed range which greatly increases NLOS (Non-Line-of-Sight) capabilities.

MIMO uses multiple antennas to intelligently resolve a larger amount of data than possible when using a single antenna. It does this by using SDM (Spatial Division Multiplexing) which uses multiple but independent data streams that are transferred simultaneously inside one channel of bandwidth. This increases the throughput bandwidth as the number of resolved streams is increased.

Doubling the channel size from 20MHz to 40MHz can be enabled on 802.11n compatible equipment which allows for twice the data rate on the physical layer relative to a 20MHz channel.

These two features combined give the 802.11n standard increased bandwidth capabilities when compared to 802.11g at 2.4GHz and 802.11a at 5GHz of up to 600Mbps (in theory) when using 4 spatial streams and a 40MHz channel and an increase in range over previous standards when put in practice. It seems that with 802.11 Wi-Fi chip manufactures applying market pressure to move onto this protocol, 802.11 should become the new standard over the next few years.

Shown below is a comparison table of the characteristics of the four standards mentioned above:

As explained in the 2.4GHz and 5GHz articles, advertised and theoretical speeds are not representative of actual, real world speeds. Therefore the suggested 'real' speeds of the standards could be said to be as follows (please note that throughput speed will vary for each individual wireless network set up so these figure should only be taken as a rough guide):

Channels

You may have heard the term 'Channels' mentioned in these articles and not been sure exactly what it is referring to. Channels are the sub-division of the main operating frequency range into smaller channels in the exact same way as a television or radio does and ultimately operating on one of these smaller bandwidth channels rather than the whole operating frequency range. For the 2.4GHz range, the band, from 2.4000GHz to 2.4835GHz, is divided into 13 channels each with a bandwidth of 22MHz spaced 5MHz apart. For the 5GHz range, the band, from 5.180GHz to 5.805GHz, is divided into 23 channels each with a bandwidth of 20MHz spaced 20MHz apart. These channels are given numbers for ease of reference and are shown below (only UK legal channels are shown):

Channels 1, 6 and 11 are recommended for 2.4GHz operation to avoid the overlapping of channel usage and all channels for 5GHz operation are non-overlapping. The overlapping of channels on the 2.4GHz frequency range is shown in the diagram below:

Security

802.11 Wireless transmissions can be encrypted to improve the security and confidentiality of the data that is being transferred. WEP (Wired Equivalent Privacy), WPA (Wi-Fi Protected Access) and WPA2 are the three types of security available with WPA2 using AES (Advanced Encryption Standard) technology. The recommended encryption method for modern home and consumer networks is WPA2 (AES Pre-Shared Key) and for the Enterprise level, WPA2 along with a RADIUS authentication server (or another type of authentication server) and a strong authentication method such as EAP-TLS.

802.11 Standards

For further reference, here is a definitive list of all the current and proposed 802.11 standards:

• 802.11 -1997: The WLAN standard was originally 1 Mbps and 2 Mbps, 2.4GHz RF and infrared standard (1997), all the others listed below are amendments to this standard.
• 802.11 a: 54 Mbps, 5GHz standard (1999, shipping products in 2001)
• 802.11 b: Enhancements to 802.11 to support 5.5 and 11 Mbps (1999)
• 802.11 c: Bridge operation procedures; included in the IEEE 802.1D standard (2001)
• 802.11 d: International (country-to-country) roaming extensions (2001)
• 802.11 e: Enhancements: QoS, including packet bursting (2005)
• 802.11 g: 54 Mbps, 2.4GHz standard (backwards compatible with b) (2003)
• 802.11 h: Spectrum Managed 802.11a (5GHz) for European compatibility (2004)
• 802.11 i: Enhanced security (2004)
• 802.11 j: Extensions for Japan (2004)
• 802.11 -2007: A new release of the standard that includes amendments a, b, d, e, g, h, i & j. (July 2007)
• 802.11 k: Radio resource measurement enhancements (2008)
• 802.11 n: Higher throughput improvements using MIMO (multiple input, multiple output antennas) and 5GHz support (September 2009)
• 802.11 p: WAVE-Wireless Access for the Vehicular Environment (such as ambulances and passenger cars) (July 2010)
• 802.11 r: Fast BSS transition (FT) Working "Task Group r" (2008)
• 802.11 s: Mesh Networking, Extended Service Set (ESS) (June 2011)
• 802.11 u: Interworking with non-802 networks (for example, cellular) (Dec 2010)
• 802.11 v: Wireless network management (Dec 2010)
• 802.11 w: Protected Management Frames (September 2009)
• 802.11 y: 3650-3700 MHz Operation in the U.S. (2008)
• 802.11 z: Extensions to Direct Link Setup (DLS) (September 2010)
• 802.11 mb: Maintenance of the standard. Will become 802.11-2011. (Dec 2011)
• 802.11 aa: Robust streaming of Audio Video Transport Streams (Mar 2012)
• 802.11 ac: Very High Throughput <6 GHz; potential improvements over 802.11n: better modulation scheme (expected 10% throughput increase), wider channels (80 or even 160 MHz), multi user MIMO (Dec 2012)
• 802.11 ad: Very High Throughput 60 GHz (Dec 2012)
• 802.11 ae: QoS Management (Dec 2011)
• 802.11 af: TV Whitespace (Mar 2012)
• 802.11 ah: Sub 1Ghz (July 2013)
• 802.11 ai: Fast Initial Link Setup