It is part of the mission of the IEEE to develop standards for wireless LAN operation within the framework of the FCC rules and regulations. Following are the four main IEEE standards for wireless LANs that are either in use or in draft form:
- 802.11
- 802.11b
- 802.11a
- 802.11g
IEEE 802.11
The 802.11 standard was the first standard describing the operation of wireless LANs. This standard contained all of the available transmission technologies including Direct Sequence Spread Spectrum (DSSS), Frequency Hopping Spread Spectrum (FHSS), and infrared.
The IEEE 802.11 standard describes DSSS systems that operate at 1 Mbps and 2 Mbps only. If a DSSS system operates at other data rates as well, such as 1 Mbps, 2 Mbps, and 11 Mbps, then it can still be an 802.11-compliant system. If, however, the system is operating at any rate other than 1 or 2 Mbps, then, even though the system is 802.11- compliant because of its ability to work at 1 & 2 Mbps, it is not operating in an 802.11- compliant mode and cannot be expected to communicate with other 802.11-compliant devices.
IEEE 802.11 is one of two standards that describe the operation of frequency hopping wireless LAN systems. If a wireless LAN administrator encounters a frequency hopping system, then it is likely to be either an 802.11-compliant or OpenAir compliant system (discussed below). The 802.11 standard describes use of FHSS systems at 1 and 2 Mbps. There are many FHSS systems on the market that extend this functionality by offering proprietary modes that operate at 3-10 Mbps, but just as with DSSS, if the system is operating at speeds other than 1 & 2 Mbps, it cannot be expected to automatically communicate with other 802.11-compliant devices.
802.11 compliant products operate strictly in the 2.4 GHz ISM band between 2.4000 and 2.4835 GHz. Infrared, also covered by 802.11, is light-based technology and does not fall into the 2.4 GHz ISM band.
IEEE 802.11b
Though the 802.11 standard was successful in allowing DSSS as well as FHSS systems to interoperate, the technology has outgrown the standard. Soon after the approval and implementation of 802.11, DSSS wireless LANs were exchanging data at up to 11 Mbps. But, without a standard to guide the operation of such devices, there came to be problems with interoperability and implementation. The manufacturers ironed out most of the implementation problems, so the job of IEEE was relatively easy: create a standard that complied with the general operation of wireless LANs then on the market. It is not uncommon for the standards to follow the technology in this way, particularly when the technology evolves quickly.
IEEE 802.11b, referred to as "High-Rate" and Wi-Fi™, specifies direct sequencing (DSSS) systems that operate at 1, 2, 5.5 and 11 Mbps. The 802.11b standard does not describe any FHSS systems, and 802.11b-compliant devices are also 802.11-compliant by default, meaning they are backward compatible and support both 2 and 1 Mbps data rates. Backward compatibility is very important because it allows a wireless LAN to be upgraded without the cost of replacing the core hardware. This low-cost feature, together with the high data rate, has made the 802.11b-compliant hardware very popular.
The high data rate of 802.11b-compliant devices is the result of using a different coding technique. Though the system is still a direct sequencing system, the way the chips are coded (CCK rather than Barker Code) along with the way the information is modulated (QPSK at 2, 5.5, & 11 Mbps and BPSK at 1 Mbps) allows for a greater amount of data to be transferred in the same time frame. 802.11b compliant products operate only in the 2.4 GHz ISM band between 2.4000 and 2.4835 GHz.
IEEE 802.11a
The IEEE 802.11a standard describes wireless LAN device operation in the 5 GHz UNII bands. Operation in the UNII bands automatically makes 802.11a devices incompatible with all other devices complying with the other 802.11 series of standards. The reason for this incompatibility is simple: systems using 5 GHz frequencies will not communicate with systems using 2.4 GHz frequencies.
Using the UNII bands, most devices are able to achieve data rates of 6, 9, 12, 18, 24, 36, 48, and 54 Mbps. Some of the devices employing the UNII bands have achieved data rates of 108 Mbps by using proprietary technology, such as rate doubling. The highest rates of some of these devices are the result of newer technologies not specified by the 802.11a standard. IEEE 802.11a specifies data rates of only 6, 12, and 24 Mbps. A wireless LAN device must support at least these data rates in the UNII bands in order to be 802.11a-compliant. The maximum data rate specified by the 802.11a standard is 54 Mbps.
IEEE 802.11g
802.11g provides the same maximum speed of 802.11a, coupled with backwards compatibility for 802.11b devices. This backwards compatibility will make upgrading wireless LANs simple and inexpensive. Since 802.11g technology is new, 802.11g devices are not yet available as of this writing.
IEEE 802.11g specifies operation in the 2.4 GHz ISM band. To achieve the higher data rates found in 802.11a, 802.11g compliant devices utilize Orthogonal Frequency Division Multiplexing (OFDM) modulation technology. These devices can automatically switch to QPSK modulation in order to communicate with the slower 802.11b- and 802.11- compatable devices. With all of the apparent advantages, 802.11g’s use of the crowded 2.4 GHz band could prove to be a disadvantage.
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