The IEEE 802.11 Wireless LAN Standard

Table of Contents

This paper is a general overview of the IEEE 802.11 standard and the working group. The IEEE 802.11 defines physical layer options for wireless transmission and MAC layer protocol.

WLANA Commentary
The IEEE 802.11 represents the first standard for WLAN products from an internationally recognized, independent organization. The IEEE manages most of the standards for wired LANs. It represents an important milestone in WLAN systems since customers can now have multiple sources for the components of their WLAN systems. There are still applications where the existing proprietary data communications are a good fit because they may optimize some aspect of the network performance. However, 802.11 compliant products expand the users' options.

The Economics for Standards Based Solutions The majority of the WLAN products available in the marketplace today are proprietary spread spectrum solutions targeting vertical applications operating in the 900MHz and 2.4GHz ISM frequency bands. These products include wireless adapters and access points in PCMCIA, ISA and custom PC board platforms. Proprietary solutions for some applications are beneficial, especially for those requiring market differentiation or customization of a wireless LAN network. Proprietary solutions are typically customized and constrain the end users into purchasing products from a single equipment supplier. However, as products are introduced compliant to the standard, users can choose from a number of vendors that provide compatible products. This increases competition and provides the potential for lower cost products. Interoperability, low cost and stimulation of market demand are some of the advantages that standards based solutions offers.

How it will be used in End Applications
The IEEE 802.11 standard defines the protocol for two types of networks; Ad-hoc and client/server networks. An Ad-hoc network is a simple network where communications are established between multiple stations in a given coverage area without the use of an access point or server. The standard specifies the etiquette that each station must observe so that they all have fair access to the wireless media. It provides methods for arbitrating requests to use the media to ensure that throughput is maximized for all of the users in the base service set. The client/server network uses an access point that controls the allocation of transmit time for all stations and allows mobile stations to roam from cell to cell as illustrated in the figure below. The access point is used to handle traffic from the mobile radio to the wired or wireless backbone of the client/server network. This arrangement allows for point coordination of all of the stations in the basic service area and ensures proper handling of the data traffic. The access point routes data between the stations and other wireless stations or to and from the network server. Typically WLANs controlled by a central access point will provide better throughput performance.

The Standards Committee
The IEEE 802 standards committee formed the 802.11 Wireless Local Area Networks Standards Working Group in 1990. The 802.11 working group took on the task of developing a global standard for radio equipment and networks operating in the 2.4GHz unlicensed frequency band for data rates of 1 and 2Mbps. The 802.11 working group has recently completed the standard. The standard does not specify technology or implementation but simply specifications for the physical layer and Media Access Control (MAC) layer. The standard allows for manufacturers of wireless LAN radio equipment to build interoperable network equipment.

The membership of the committee consists of individuals from a number of companies and universities, who research, manufacturer, install and use products in wireless LAN network applications. Manufacturers of semiconductors, computers, radio equipment, WLAN systems solution providers, University research labs and end-users make up the core group. The working group is globally represented by companies from the United States, Canada, Europe, Israel and the Pacific Rim.

Physical Layer Implementation Choices
The Physical Layer in any network defines the modulation and signaling characteristics for the transmission of data. At the physical layer, two RF transmission methods and one infrared are defined. Operation of the WLAN in unlicensed RF bands requires the of spread spectrum modulation to meet the requirements for operation in most countries. The RF transmission standards in the standard are Frequency Hopping Spread Spectrum (FHSS) and Direct Sequence Spread Spectrum (DSSS). Both architectures are defined for operation in the 2.4GHz frequency band typically occupying the 83 MHz of bandwidth from 2.400 GHz to 2.483 GHz. Differential BPSK (DBPSK) and DQPSK is the modulation for the direct sequence. Frequency hopping uses 2-4 level Gaussian FSK as the modulation signaling method. The radiated RF power at the antenna is set by the rules governed by FCC part 15 for operation in the United States. Antenna gain is also limited to 6 dBi maximum. The radiated power is limited to 1W for the United States, 10mW per 1Mhz in Europe and 10mW for Japan. There are different frequencies approved for use in Japan, United States and Europe and any WLAN product must meet the requirements for the country where it is sold. See the appendix for details of the different frequency allocations for unlicensed operation in US, Europe and Japan. The physical layer data rate for FHSS system is 1 Mbps. For DSSS both 1 Mbps and 2 Mbps data rates are supported. The choice between FHSS and DSSS will depend on a number of factors related to the users application and the environment that the system will be operating.


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