Introduction to 802.11 Wireless LAN (Wlan), Technology, Market, Operation, and Services by Lawrence Harte

Author:Lawrence Harte [Harte, Lawrence]
Language: eng
Format: azw3
Publisher: UNKNOWN
Published: 2017-03-20T04:00:00+00:00

Figure 1.15, 802.11 WLAN Association 1 to release the PDA identification from its memory. When the PDA senses AP 2, it transmits an association request. This example shows that the association of the PDA with AP 2 allows information from a distant computer to reach the PDA.

Industry Standards

The industry standards for Wireless LAN include several variations of

802.11 and HiperLAN. The 802.11 standards include the original 802.11,

802.11a, 802.11b, and 802.11g versions. These standards primarily vary based on frequency bands and data transmission rates. The 802.11 series of industry standards are based on 802.3 Ethernet technologies. This allows the WLAN system to more easily integrate with existing wired Ethernet systems. The 802 family of standards include 802.1 (management), 802.2

(link layer control), and 802.3 (Ethernet technology).

Prior to 802.11 industry standardization, there were many wireless LAN (WLAN) systems in use worldwide and many of these systems use radio communications protocols that are proprietary to the manufacturer of WLAN equipment. This has resulted in incompatibility between products. To overcome this limitation, the Institute of Electrical and Electronic Engineers (IEEE) created an industry standard specification in June 1997 (802.11) that defines a wireless protocol for homogeneous systems. The IEEE 802.11 standard for wireless LANs (WLANs) allows interoperability among products from different vendors.

The 802.11 specifications have three transmission options; one infrared (IR) option and two radio frequency (RF) options: direct sequence spread spectrum (DSSS) and frequency hopping spread spectrum (FHSS).

When choosing a wireless LAN system, customers should consider their future requirements and how the system can be expanded or changed to meet the needs of their future requirements. An Infrared (IR) system provides a basic 1 Mbps data transfer rate with an option for a 2 Mbps system. The Radio Frequency systems can provide data transfer rates from 1 Mbps to 54 Mbps.

802.11 The original 802.11 standard offered WLAN on a frequency band of 2.4 GHz with data transfer rates of 1 or 2 Mbps. The original 802.11 systems could use frequency hopping spread spectrum (FHSS) or direct sequence spread spectrum (DSSS) radio transmission. Optionally, this system could use Infrared (IR) transmission instead of radio transmission.

802.11A 802.11a is a high-speed data version of the 802.11 wireless local area network (WLAN) industry standard. It was developed to operate in the 5.7 GHz spectrum and permits data transmission speeds up to 54 Mbps. The 802.11a system provides for 8 non-overlapping 25 MHz wide channels and up to 64 users per access point (AP).

Figure 1.16 shows the frequency band and radio channel size that is used in the 802.11a system. This example shows that the basic radio channel in the 802.11a system is 25 MHz wide and that the center frequency of the radio channel can be assigned to different points (channels) in the three 100 MHz wide 5.7 GHz industrial, scientific, and medical (ISM) unlicensed frequency bands.

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