The 802.11 standard establishes and defines the mode of channeling the unlicensed radio frequency bands in WLANs. The 2.4 GHz band is broken down into 11 channels for North America and 13 channels for Europe. These channels have a center frequency separation of only 5 MHz and an overall channel bandwidth (or frequency occupation) of 22 MHz.
Generally speaking, IEEE 802.11 standards specify two operating modes:
Infrastructure mode (used to connect computers with wireless network adapters to an existing wired network with the help from wireless router or access point) and
The IEEE 802.11a adopted the OFDM modulation technique and uses the 5 GHz band.
The 802.11a devices operating in the 5 GHz band are less likely to experience interference than devices that operate in the 2.4 GHz band because there are fewer consumer devices that use the 5 GHz band. Also, higher frequencies allow for the use of smaller antennas.
Speed: Uses up to Up to 54 Mbps
a. Has the fastest transmission speed.
b. Allows for more simultaneous users.
c. Uses the 5 GHz frequency, which limits interference from other devices.
a. Higher frequency radio waves are more easily absorbed by obstacles such as walls, making 802.11a susceptible to poor performance due to obstructions.
b. Higher frequency band has slightly poorer range than either 802.11b or 802.11g. Also, some countries, including Russia, do not permit the use of the 5 GHz band, which may continue to curtail its deployment.
c. Is not compatible with 802.11b network adapters, routers, and access points.
This was the first and, until recently, the most common wireless variant used. With transmission speeds of just 11Mbits/sec it is also the slowest. It also used the 40bit Wireless Equivalency Privacy (WEP) security protocol, which was found to have a number of deficiencies. A newer version of this, 802.11b+ maintains speeds to 22Mbits/sec.
Speed: 11megabits per seconds; costs less; has the best signal range.
a. Transmission speed is slow
b. Uses the 2.4 gigahertz (GHz) of frequency the same as some house hold items like cordless, micro waves ovens etc.
c. Provides access to few users simultaneously.
This is the most recent and popular in use now, offering more respectable data transfer speeds of up to 54Mbits/sec, but its speed are much lower. It also uses an upgraded form of Wi-Fi Protected Access (WPA) security protocol.
Speed: Uses Up to 54 Mbps, Has a transmission speed comparable to 802.11a under optimal conditions
a. Allows for more simultaneous users
b. Has the best signal range and is not easily obstructed
c. Is compatible with 802.11b network adapters, routers, and access points
a. Uses the 2.4 GHz frequency so it has the same interference problems as 802.11b
b. Costs more than 802.11b
The 802.11n draft standard is intended to improve wireless data rates and range without requiring additional power or radio frequency band allocation. The 802.11n uses multiple radios and antennae at endpoints, each broadcasting on the same frequency to establish multiple streams. The multiple input/multiple output technology splits a high data-rate stream into multiple lower rate streams and broadcasts, meanwhile over the available radios and antennae. This allows for a speculative maximum data rate of 248 Mb/s using two streams.
Note: If your PC or laptop have more than one wireless network adapter or your adapter uses more than one wireless technology / standard, you are provided with options to specify which adapter or standard to use for each network connection. For example, if you use streaming media, such as videos or music, on your PC or Laptop, choosing 802.11a connection from the options provided would be best for you, because you will get a faster data transfer rate when you watch videos or listen to music.The photo is taken from: http://en.wikipedia.org/wiki/IEEE_802.11#Protocols
Current 802.11ac devices in the market place are based on the first generation 802.11ac chipsets, known as wave-1. These devices currently perform at almost the same bandwidth as 802.11n because of the limitation in wave-1 chipsets. The limitations include: support of three streams maximum (rather than eight), no multi-user MIMO, and no 160 MHz wide channel support.
It’s operating in the 5GHz band. In the US, 5.0 GHz offers 23 non-overlapping channels and has less noise, which means higher bandwidth. However, it also means it has shorter range and does not penetrate solid objects well. This means more APs are needed.
What is New in 802.11ac?
a. Wider channels (80MHz and 160MHz), which means more capacity in the band. (Note: 160 MHz is not supported in wave-1).
b. Denser amplitude modulation with 256 QAM (Quadrature Amplitude Modulation), four times denser than 802.11n, which has 64 QAM.
c. Downlink multi-user MIMO, which allows an AP to transmit to multiple clients simultaneously. (Note: not available in wave-1)
d. Up to eight spatial streams, which doubles the number of spatial streams used in 802.11n (Note: in wave-1, only three spatial streams are supported).
e. Beamforming: detects where devices are and intensifies the signal in their direction(s) to focus RF energy for better signal strength, rather than broadcast wireless signal equally in all directions.
The original material is referred from: www.orbit-computer-solutions.com/Wireless-Standards.php
More tips on Wireless Standards 802.11 at:
details on 802.11 (a to y) at: compnetworking.about.com/cs/wireless80211/a/aa80211standard_2.htm