Information Engineer

IEEE 802.11 is a set of standards carrying out wireless local area network (WLAN) computer communication and provides 1 or 2 Mbps transmission in the 2.4 GHz in the 2.4, 3.6 and 5 GHz frequency bands using either frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS). They are created and maintained by the IEEE LAN/MAN Standards Committee (IEEE 802).

The original version of 802.11 was released in 1997 and clarified in 1999, but is today obsolete. It specified three alternative physical layer technologies: diffuse infrared operating at 1 Mbit/s; frequency-hopping spread spectrum operating at 1 Mbit/s or 2 Mbit/s; and direct-sequence spread spectrum operating at 1 Mbit/s or 2 Mbit/s. The latter two radio technologies used microwave transmission over the Industrial Scientific Medical frequency band at 2.4 GHz. Some earlier WLAN technologies used lower frequencies, such as the U.S. 900 MHz ISM band.

The 802.11 family includes over-the-air modulation techniques that use the same basic protocol in all its versions. Security was originally purposefully weak due to export requirements of some governments, and was later enhanced via the 802.11i amendment after governmental and legislative changes. 802.11n is a new multi-streaming modulation technique. Other standards in the family (c–f, h, j) are service amendments and extensions or corrections to previous specifications.

Legacy 802.11 with direct-sequence spread spectrum was rapidly supplanted and popularized by 802.11b which became the standard wireless Ethernet networking technology for both business and home. The WiFI organization was created to ensure interoperability between 802.11b products. With a realistic throughput of 2.5-4Mbps, it is fast enough for most network applications and tolerable for file transfers.

IEEE created a second extension to the original 802.11 standard called 802.11a. Due to its higher cost, 802.11a is usually found on business networks whereas 802.11b better serves the home market. 802.11a supports bandwidth up to 54 Mbps and signals in a regulated frequency spectrum around 5 GHz. This higher frequency compared to 802.11b shortens the range of 802.11a networks. The higher frequency also means 802.11a signals have more difficulty penetrating walls and other obstructions.

In 2002 and 2003, WLAN products supporting a newer standard called 802.11g it combine the best of both 802.11a and 802.11b and supports bandwidth up to 54 Mbps, and it uses the 2.4 Ghz frequency for greater range.

The newest IEEE standard in the Wi-Fi category is 802.11n. It was designed to improve on 802.11g in the amount of bandwidth supported by utilizing multiple wireless signals and antennas (called MIMO technology) instead of one. It support data rates of over 100 Mbps. 802.11n also offers somewhat better range over earlier Wi-Fi standards due to its increased signal intensity.

Both 802.11 and Bluetooth control their interference and susceptibility to interference by using spread spectrum modulation. Bluetooth uses a frequency hopping spread spectrum signaling method (FHSS), while 802.11b and 802.11g use the direct sequence spread spectrum signaling (DSSS) and orthogonal frequency division multiplexing (OFDM) methods, respectively. Better or worse performance with higher or lower frequencies (channels) may be realized, depending on the environment. The segment of the radio frequency spectrum used varies between countries.

802.11 divide each of frequency bands into channels, analogously to how radio and TV broadcast bands are sub-divided but with greater channel width and overlap. For example the 2.4000–2.4835 GHz band is divided into 13 channels each of width 22 MHz but spaced only 5 MHz apart, with channel 1 centered on 2.412 GHz and 13 on 2.472 GHz to which Japan adds a 14th channel 12 MHz above channel 13.

Availability of channels is regulated by country, constrained in part by how each country allocates radio spectrum to various services. Besides specifying the centre frequency of each channel, 802.11 also specify (in Clause 17) a spectral mask defining the permitted distribution of power across each channel. The mask requires that the signal be attenuated by at least 30 dB from its peak energy at ±11 MHz from the centre frequency, the sense in which channels are effectively 22 MHz wide.

With the proliferation of cable modems and DSL, there is an ever-increasing market of people who wish to establish small networks in their homes to share their broadband Internet connection. Current 802.11 standards define “frame” types for use in transmission of data as well as management and control of wireless links.

Frames are divided into very specific and standardized sections. Each frame has a MAC header, payload and FCS. Some frames may not have payload portion. First 2 bytes of MAC header is a frame control field that provides detailed information about the frame. The next two bytes are reserved for the Duration ID field. This field can take one of three forms: Duration, contention-free period (CFP), and Association ID (AID).

An 802.11 frame can have up to four address fields. Each field can carry a MAC address. Address 1 is the receiver, Address 2 is the transmitter, Address 3 is used for filtering purposes by the receiver.

Management Frames allow for the maintenance of communication. Some common 802.11 subtypes include: Authentication frame, Association request frame, Association response frame, Beacon frame, Deauthentication frame, Disassociation frame, Probe request frame, Probe response frame, Reassociation request frame, and Reassociation response frame.

Control frames facilitate in the exchange of data frames between stations. Some common 802.11 control frames include: Acknowledgement (ACK) frame, Request to Send (RTS) frame, and Clear to Send (CTS) frame. Data frames carry packets from web pages, files, etc. within the body.

Many hotspot or free networks frequently allow anyone within range, including passersby outside, to connect to the Internet. There are also efforts by volunteer groups to establish wireless community networks to provide free wireless connectivity to the public.